Reducing Greenhouse Gas Emissions

from Light-Duty Motor Vehicles

Prepared by

NESCCAF

Northeast States Center for a Clean Air Future

September 2004
i

NORTHEAST STATES CENTER FOR A CLEAN AIR FUTURE 

Board of Directors 

Steven P. Suttle, NESCCAF Chair 

Senior Vice President, Corning, Incorporated 

James P. Brooks, Director 

Maine Department of Environmental Protection, Bureau of Air Quality 

Frank Cassidy, President/COO 

PSEG Power, LLC 

Michael Chambrello, President/CEO 

Environmental Systems Products Holdings, Inc. 

Anne Gobin, Acting Director 

Connecticut Department of Environmental Protection, Bureau of Air Management 

Carolyn L. Green, Vice President 

Sunoco, Inc., HES Regulatory Affairs 

Jason Grumet, Executive Director 

National Commission on Energy Policy 

Adele Hurley, Senior Fellow 

University of Toronto, Trinity College 

Barbara Kwetz, Director 

Massachusetts Department of Environmental Protection, Planning & Evaluation 
ii

NORTHEAST STATES CENTER FOR A CLEAN AIR FUTURE 

Board of Directors 

(continued)

Professor Morton Lippmann, Director 

New York University School of Medicine, Human Exposure & Health Effects Program 

Stephen Majkut, Chief 

Rhode Island Department of Environmental Management, Office of Air Resources 

Professor Mario Molina 

Massachusetts Institute of Technology, Department of EAPS 

William O’Sullivan, Director 

New Jersey Department of Environmental Protection, Division of Air Quality 

Dr. Norman Richards, Administrator 

Mohegan Environmental Protection Department 

Robert Scott, Director 

New Hampshire Department of Environmental Services, Air Resources Division 

David Shaw, Director 

New York Department of Environmental Conservation, Division of Air Resources 

Dr. Susan Tierney, Managing Principal 

The Analysis Group 

Richard Valentinetti, Director 

Vermont Department of Environmental Conservation, Air Pollution Control Division 
iii
iv

Reducing Greenhouse Gas

Emissions from

Light-Duty Motor Vehicles

Prepared by

NESCCAF

Northeast States Center for a Clean Air Future

September 2004
v

REDUCING GREENHOUSE GAS EMISSIONS

FROM LIGHT-DUTY MOTOR VEHICLES

Project Director

Coralie Cooper, NESCCAF

Principal Authors

Coralie Cooper, NESCCAF

Dan Meszler, Meszler Engineering Services

Stephen Brueckner, AVL Powertrain Engineering, Inc.

Editors

Arthur Marin, NESCCAF

Marika Tatsutani, NESCCAF

Administrative Support

Wendy Roy, NESCCAF

Emily Savelli, NESCCAF

Principal Contributors

AVL Powertrain Engineering, Inc

Meszler Engineering Services

The Martec Group, Inc.
vi

Acknowledgments

This report was undertaken with generous support from the William and Flora

Hewlett Foundation and we thank the Foundation for making this study possible. We

thank AVL Powertrain Engineering, Inc., Meszler Engineering Services, and The Martec

Group for their contributions to the study. We also thank the following organizations and

groups for technical advice throughout the project: the NESCAUM Mobile Source

Committee, Ricardo Engineering, Inc., Energy and Transportation Technologies, and the

National Renewable Energy Laboratory. In addition, numerous suppliers and original

equipment manufacturers provided information during the course of the study for which

we are grateful. Finally, we thank the many other individuals who made valuable

contributions to this effort. Unless otherwise stated, the opinions presented herein

represent the views NESCCAF. Although the Hewlett Foundation supported the work

leading to this report, any errors contained herein are attributable solely to the authors.
vii

TABLE OF CONTENTS

Executive Summary.......................................................................................................... xii

1. Introduction.............................................................................................................. 1-1

1.1. Purpose of Study.............................................................................................. 1-1

1.2. Basic Science of Global Climate Change........................................................ 1-1

1.3. Environmental Impacts of Climate Change..................................................... 1-3

1.4. Political and Regulatory Context..................................................................... 1-4

1.4.1. International Context ............................................................................... 1-4

1.4.2. California’s Assembly Bill 1493 ............................................................. 1-4

1.4.3. Climate Actions in the Northeast States.................................................. 1-5

1.5. Report Organization......................................................................................... 1-6

2. Overview of Study Method ..................................................................................... 2-1

2.1. Defining Representative Vehicle Classes........................................................ 2-2

2.2. Validating Simulation Modeling Results for Representative Vehicles and

Developing a “Business-As-Usual” Technology Baseline.......................................... 2-3

2.3. Identifying Discrete Vehicle Technology Options for Evaluation.................. 2-8

2.4. Assembling Technology Packages for Model Simulation............................. 2-12

2.5. Assessment of Additional Technologies ....................................................... 2-15

2.5.1. Air Conditioning.................................................................................... 2-16

2.5.2. Methane and Nitrous Oxide Emissions................................................. 2-18

2.5.3. Hybrid Vehicle Assessment................................................................... 2-18

2.6. Cost-Benefit Analysis.................................................................................... 2-22

3. Results of Greenhouse Gas Emission Reduction Analysis ..................................... 3-1

3.1. Overview.......................................................................................................... 3-1

3.2. Emission Reduction Results............................................................................ 3-1

3.2.1. GHG Emission Reduction Potential for Individual Technologies .......... 3-2

3.2.2. Projected Cost of Technologies............................................................... 3-3

3.2.3. GHG Emission Reduction Potential for Technology Combinations....... 3-5

Large Car Results ................................................................................................ 3-6

Small Car Results .............................................................................................. 3-10

Minivan Results................................................................................................. 3-13

Small Truck Results........................................................................................... 3-16

Large Truck Results........................................................................................... 3-19

Methane and Nitrous Oxide Analysis................................................................ 3-22

3.3. Conclusions ................................................................................................... 3-23

Appendix A: Technology Descriptions

Appendix B: AVL Simulation Modeling Description

Appendix C: Vehicle Cost Matrix

Appendix D: Vehicle Air Conditioning

Appendix E: Methane and Nitrous Oxide Emissions
viii

FIGURES

Figure ES-2: Net Vehicle Costs for the Large Car Class Given Two Gasoline Price

Scenarios.................................................................................................... xvii

Figure 2-1: Overview of the Martec Costing Methodology.......................................... 2-11

Figure 3-1: Net Vehicle Costs for the Large Car Class Given Two Gasoline Price

Scenarios........................................................................................................ 3-9

Figure 3-2: Net Vehicle Costs for the Small Car Class Given Two Gasoline Price

Scenarios...................................................................................................... 3-13

Figure 3-3: Net Vehicle Costs for the Minivan Class Given Two Gasoline Price Scenarios

..................................................................................................................... 3-16

Figure 3-4: Net Vehicle Costs for the Small Truck Class Given Two Gasoline Price

Scenarios...................................................................................................... 3-19

Figure 3-5: Net Vehicle Large Truck Costs Given Two Gasoline Price Scenarios Methane

and N2O Analysis ........................................................................................ 3-22

Figure B-1: Layout of the Front Wheel Drive Vehicles (Small Car shown)...................B-3

Figure B-2: Layout of the 4 Wheel Drive Vehicles (Large Truck shown)......................B-3

Figure B-3: Typical characteristics for torque converter in steady state operation.........B-6

Figure B-4: Shift Behavior of AT, and AMT, DCT transmissions...............................B-15

Figure B-5: Layout of an Integrated Starter Generator Hybrid Model..........................B-18

Figure B-6: Single Operating Point Determination.......................................................B-24

Figure B-7: Small Car Combined CO2 Emissions.........................................................B-39

Figure B-8: Small Car Reduction in Combined CO2 Emissions...................................B-39

Figure B-9: Large Car Combined CO2 Emissions.........................................................B-40

Figure B-10: Large Car Reduction in Combined CO2 Emissions.................................B-40

Figure B-11: Minivan Combined CO2 Emissions.........................................................B-41

Figure B-12: Minivan Reduction in Combined CO2 Emissions....................................B-41

Figure B-13: Small Truck Combined CO2 Emissions...................................................B-42

Figure B-14: Small Truck Reduction in Combined CO2 Emissions.............................B-42

Figure B-15: Large Truck Combined CO2 Emissions...................................................B-43

Figure B-16: Large Truck Reduction in Combined CO2 Emissions.............................B-43

Figure D-1: Illustrative Variation in Power Demand for a Pneumatically Controlled

210 cc FDC A/C System [5]....................................................................... D-8

Figure D-2: Variation in Power Demand for Various A/C System Technology

Relative to a 215 cc Pneumatically Controlled FDC System [6] ............ D-14

Figure D-3: Ambient Impacts on Power Demand for an Externally Controlled

VDC System with Enhanced Air Management [5] .................................. D-14

Figure D-4: Power Demand for the Pneumatically Controlled FDC and Externally

Controlled VDC Systems at 1500 rpm Engine Speed.............................. D-15

Figure D-5: A/C System Power Demand Versus Engine Speed .................................. D-25

Figure D-6: CRUISE-Predicted A/C Impacts .............................................................. D-26

Figure E-1: Mileage and Model Year of Vehicles in the ARB VSP Dataset..................E-5

Figure E-2: CH4 Emission Rate Versus THC Emission Rate .........................................E-7

Figure E-3: CH4 Emission Rate Versus NMHC Emission Rate......................................E-8

Figure E-4: N2O Emission Rate Versus NOx Conversion Efficiency [4]......................E-17

Figure E-5: N2O Emission Rate Versus NOx Emission Rate ........................................E-19
ix

FIGURES

(continued)

Figure E-6: N2O Formation Rate Versus Catalyst Temperature [14]............................E-20

Figure E-7: Methane and N2O Emission Rates by Certification Class .........................E-27

Figure E-8: CO2 Equivalent Methane and N2O Emission Rates by Vehicle

Certification Class .....................................................................................E-27
x

TABLES

Table ES-1: Large Car GHG Reduction Results for Combinations of Technologies.......xv

Table 2-1: Characteristics of Evaluated Vehicle Class.................................................... 2-2

Table 2-2: 2002 Class Average Statistics........................................................................ 2-3

Table 2-3: Performance of the 2002 Simulation Models................................................. 2-5

Table 2-4: Dominant Discrete Technologies in 2002 and 2009...................................... 2-6

Table 2-5: Trend-Based Forecast Parameters.................................................................. 2-7

Table 2-6: Vehicle Technologies Evaluated in this Study.............................................. 2-9

Table 2-7: Comparison of Individual versus Combination Benefits............................. 2-14

Table 2-8: Impacts and Costs of Additional CO2 Reduction Technologies.................. 2-17

Table 3-1: Air Conditioning Emissions........................................................................... 3-3

Table 3-2: Comparison of Study RPE with Literature RPE............................................ 3-4

Table 3-3: Estimated Costs of California’s Low Emission Vehicle (LEV) Program...... 3-4

Table 3-4: Large Car GHG Reduction Results for Combinations of Technologies........ 3-7

Table 3-5: Small Car Results......................................................................................... 3-11

Table 3-6: Minivan Results ........................................................................................... 3-15

Table 3-7: Small Truck Results..................................................................................... 3-17

Table 3-8: Large Truck Results..................................................................................... 3-20

Table 3-9: Methane and N2O Emissions ....................................................................... 3-23

Table B-1: Vehicle Component data for all vehicle classes............................................B-4

Table B-2: Engine Parameters.........................................................................................B-5

Table B-3: Gear Ratios and Efficiencies for each of the vehicle classes ........................B-7

Table B-4: Axle Ratios and Efficiencies for each of the baseline vehicles.....................B-7

Table B-5: Gear Ratios and Efficiencies for each of the vehicle classes for the 5AT ..........

.....................................................................................................................B-13

Table B-6: Gear Ratios and Efficiencies for each of the vehicle classes for the 6AT ..........

.....................................................................................................................B-13

Table B-7: Gear Ratios and Efficiencies for each of the vehicle classes for the 5MT..........

.....................................................................................................................B-14

Table B-8: Gear Ratios and Efficiencies for each of the vehicle classes for the 6AMT.......

.....................................................................................................................B-15

Table B-9: 2002 MY Baseline Vehicles........................................................................B-23

Table B-10: Summary of Single Operating Points........................................................B-24

Table B-11: Assessment of Individual Engine Technologies on FTP 75 Cycle ...........B-25

Table B-12: Assessment of Individual Engine Technologies on Highway Cycle ........B-26

Table B-13: Assessment of Individual Engine Technologies on Combined

FTP 75 and Highway Cycles....................................................................B-27

Table B-14: Assessment of Individual Drivetrain Technologies on FTP 75 Cycle ......B-28

Table B-15: Assessment of Individual Drivetrain Technologies on Highway Cycle ...B-28

Table B-16: Assessment of Individual Drivetrain Technologies on Combined

FTP 75 and Highway Cycles....................................................................B-29

Table B-17: Assessment of Individual Other Vehicle Technologies on FTP 75 Cycle ........

..................................................................................................................B-30

Table B-18: Assessment of Individual Other Vehicle Technologies on Highway Cycle .....

..................................................................................................................B-31
xi

TABLES

(continued)

Table B-19: Assessment of Individual Other Vehicle Technologies on Combined

FTP 75 and Highway Cycles....................................................................B-31

Table B-20: Small Car Technology Combination Simulation Results..........................B-34

Table B-21: Large Car Technology Combination Simulation Results..........................B-35

Table B-22: Minivan Technology Combination Simulation Results............................B-36

Table B-23: Small Truck Technology Combination Simulation Results......................B-37

Table B-24: Large Truck Technology Combination Simulation Results......................B-38

Table D-1: Basic Environmental Characteristics of Selected Refrigerants [2,8,14]...... D-5

Table D-2: Frequency of Use and Typical Conditions during A/C System Operation .. D-9

Table D-3: Approximate Enthalpies of Typical A/C System Test Conditions ............ D-11

Table D-4: Estimated A/C System GHG Reductions, Cost, and Cost Effectiveness... D-19

Table E-1: Summary Descriptive Data for Vehicles in the ARB VSP Dataset...............E-6

Table E-2: Regression Statistics for CH4 (g/mi) Versus THC (g/mi) .............................E-7

Table E-3: Regression Statistics for CH4 (g/mi) Versus NMHC (g/mi) .........................E-8

Table E-4: Average Hydrocarbon Emission Rates for Split VSP Database..................E-12

Table E-5: Estimated Methane Emission Rates.............................................................E-13

Table E-6: Cost and Cost Effectiveness of Methane Reductions..................................E-14

Table E-7: Regression Statistics for N2O (g/mi) Versus NOx (g/mi)............................E-19

Table E-8: Average NOx and N2O Emission Rates for Split VSP Database.................E-22

Table E-9: Estimated N2O Emission Rates ...................................................................E-23

Table E-10: Cost and Cost Effectiveness of N2O Reductions.......................................E-24

Table E-11: Estimated Methane and N2O Emission Rates............................................E-26
xii

Executive Summary

ES-1. Overview

This study provides an assessment of the greenhouse gas (GHG) emissions

reductions that could be achieved in new, light-duty motor vehicles through the

application of currently available and advanced motor vehicle technologies in the 2009-

2015 timeframe. Results were obtained from original cost and technology analyses

conducted for this study, together with information obtained from other available reports.

Relative to other sectors of the economy, motor vehicles account for a particularly

large share – 20 to 25 percent – of total anthropogenic GHG emissions in the Northeast.

Because total vehicle miles traveled are predicted to rise steadily in coming decades,

motor vehicles also represent the fastest growing portion of the region’s overall GHG

inventory. As such, the Northeast states – all of which, individually or as a region, are

committed to reducing emissions that contribute to the risk of future climate change –

have a keen interest in addressing the emissions contribution of the light-duty vehicle

fleet. Further impetus for this assessment comes from California’s recent action – as

required by Assembly Bill 1493 – to develop regulations aimed at achieving maximum

feasible and cost-effective reductions in GHG emissions from light-duty vehicles

beginning in model year 2009.

In recent years, numerous technologies that could substantially reduce motor

vehicle GHG emissions have been developed and brought into production. For the most

part, however, recent technology advances have been used to boost vehicle performance

rather than to reduce emissions. With more aggressive deployment of these technologies

and greater emphasis on their application in ways that reduce emissions, this study finds

that average GHG emissions from new vehicles could be substantially reduced over the

next decade.

The report has four sections: Chapter 1 provides background information on the

rationale for reducing passenger car GHG emissions and discusses the regulatory context

for such efforts. Chapter 2 describes the methodology used to assess emissions reduction

potential and cost for various motor vehicle technologies. Chapter 3 presents the results

of this analysis. Finally, several technical appendices attached to this report provide

additional information on the methodology, assumptions, and information sources used in

this study. The following sections provide an overview of each chapter.

ES-2. Methodology

The core of the analysis consisted of a series of modeled simulations to predict the

emissions impacts of incorporating various technology combinations in new vehicles.

Simulations were performed for five classes of vehicles (small car, large car, minivan,

small truck, and large truck) using AVL Powertrain Engineering, Inc.’s CRUISE

software, which provides detailed information on the acceleration, braking, and emissions

performance of different motor vehicle designs, including advanced powertrain designs.

A first step in the analysis was to develop baseline simulation models in each of

the five vehicle classes studied (using average or predominant vehicle characteristics in
xiii

each class), together with a list of GHG-reducing technologies. Based on an initial

estimate of the emissions reduction potential of each individual technology, packages of

technologies were selected for detailed evaluation. Simulation modeling was then

performed to assess the combined emissions impacts of these technology packages. The

only exception to the simulation modeling approach was for hybrid electric vehicles,

which were evaluated using available vehicle certification data. Final steps in the

analysis involved estimating the cost of each package and creating technology cost curves

based on the simulation results. Detailed cost estimates were developed by the Martec

Group, Inc. using industry information gathered from interviews and technical papers.

(Wherever possible, Martec sought to obtain input from two or more automakers and two

or more suppliers for each technology evaluated.) The component costs estimated by

Martec were converted into equivalent retail prices (RPE) using a standard markup

factor. Net cost-effectiveness was evaluated by comparing the estimated retail price

equivalent of the incremental vehicle system and component hardware costs associated

with different technology packages to fuel cost savings over the life of the vehicle.

Finally, separate technology assessments were conducted by Meszler Engineering

Services to assess the GHG-reduction impacts associated with air conditioning systems,

as well as methane and nitrous oxide emissions.

ES-3. Results

Chapter 3 details results for the five classes of vehicles evaluated in this study.

These results indicate that substantial, cost-effective GHG emission reductions are

achievable for light duty vehicles in the 2009 to 2015 timeframe. Specifically, this

analysis showed that emissions in each of the five vehicle classes could generally be

reduced by approximately 14 to 54 percent, relative to 2002 baseline vehicles.

Similar technology packages were evaluated for each of the five classes of

vehicles. The simulation results indicate that each of these packages achieve comparable

CO2 reductions across all vehicle classes analyzed. For example, the technology package

including stoichiometric gasoline direct injection, cam phaser, turbocharging, and

automated manual transmission technology was evaluated for four classes of vehicles. In

each class, estimated emissions reductions achieved by this particular technology

combination were between 27 and 30 percent relative to the baseline vehicle.

1

The

largest number of technology packages was evaluated for the large car category. While

some of these technology combinations were not evaluated for vehicle classes other than

large cars, the consistency of results across vehicle classes suggests that similar CO2

reductions would likely be achieved with the deployment of the same technology

packages in other classes.

Because estimated emissions reductions for all five vehicle classes were

comparable, detailed results are described here only for the large car class. Results for

the other four classes are reviewed briefly after the discussion of large car results;

additional detail concerning the other four categories of vehicles can be found in Chapter

3.

 

1 There are some exceptions to this general finding; these are detailed in Chapter 3.
xiv

ES-3.1. Large Car Results

Table ES-1 presents emission reduction and cost estimates for the 19 technology

packages modeled for the large car class. Column 1 lists the technologies included in

each combination package. Column 2 provides the combined city/highway CO2

emissions rate of the modeled package in grams per mile (g/mi). Column 3 lists the

percent CO2 reduction relative to the 2002 baseline technology package. Column 4 lists

the estimated incremental vehicle cost associated with the addition of these technologies.

Column 5 indicates the net cost of the technology package, defined as incremental

technology cost minus lifetime fuel savings.

2

The net cost analysis assumes a price of

$1.58 per gallon for both gasoline and diesel. Last, Column 6 shows net cost per avoided

ton of CO2 emissions. Note that a negative net cost means that fuel savings more than

offset the incremental cost of the emissions reduction technologies being modeled. In

other words, it equates to projected consumer savings over the lifetime of the vehicle.

As indicated by Table ES-1, estimated emission reductions range from 14-54

percent, relative to the 2002 baseline vehicle, for the 19 large car technology packages

modeled. According to this analysis, combinations of technologies already used in some

production gasoline models can reduce CO2 emissions by approximately 25 percent.

Examples of these technologies include 6-speed automatic transmissions, variable valve

lift and timing, and cylinder deactivation. Reductions beyond this level will require the

introduction of more advanced technologies such as gasoline direct injection, 42-volt

starter generators, and diesel engine technology. For example, the combination of

gasoline direct injection and 42-volt technology, along with turbocharging and advanced

cam and transmission technology, can provide a 37 percent CO2 reduction for an

incremental vehicle cost of $1,700. Even greater CO2 reductions can be achieved using

hybrid-electric designs. It is critical to recognize that while the costs of using advanced

technologies are somewhat greater than the cost of conventional gasoline technologies,

fuel-cost savings over the life of the vehicle far outweigh additional technology costs in

all but the most aggressive technology packages. On a dollar per ton basis, the net cost of

technology packages that produce up to 47 percent CO2 reductions is negative, meaning

that these packages result in net cost savings over the lifetime of the vehicle.

As noted in Table ES-1, the emission reduction packages evaluated in this study

include a wide range of individual technologies. Some of the most cost-effective

packages include automated manual transmissions, turbocharging, stoichiometric

gasoline direct injection, and camless valve actuation technology. Turbocharging,

especially, proves to be a very cost-effective technology in the large car and other vehicle

classes because it enables the manufacturer to downsize the vehicle engine and decrease

engine cylinder count while maintaining equal performance. This study also assessed the

GHG-reducing potential of technologies that are relatively expensive in an effort to

provide a robust overview of the benefits and costs of candidate CO2-reduction

technologies. Given that future technology advances could reduce costs for these

 

2 This analysis assumes the vehicle life to be 12 years and 150,000 miles. More detail on the analysis and

assumptions are provided in Chapter 2 on methods.
xv

Table ES-1: Large Car GHG Reduction Results for Combinations of Technologies

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Dual Cam Phasers, 6-Speed Automatic Transmission 305.4 14.4% 479 Dual Cam Phasers, Continuously Variable Transmission, Electric Power Steering, Improved

Alternator 304.4 14.6% 725 

Discrete Variable Valve Lift, Dual Cam Phasers, 6-Speed Automatic Transmission 300.3 15.8% 640 Continuous Variable Valve Lift, Dual Cam Phasers, 6-Speed Automatic Transmission 291.4 18.3% 864 Dual Cam Phasers, Cylinder Deactivation, 6-Speed Automatic Transmission 288.1 19.2% 640 Dual Cam Phasers, Turbocharging, 6-Speed Automatic Transmission, Electric Power Steering,

Improved Alternator 280.3 21.4% 73 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift, Intake Cam

Phasers, Automated Manual Transmission, Electric Power Steering, Improved Alternator 273.8 23.2% 1,149 

Continuous Variable Valve Lift, Dual Cam Phasers, Automated Manual Transmission, Electric

Power Steering, Improved Alternator 266.3 25.3% 890 

Stoichiometric Gasoline Direct Injection, Cylinder Deactivation, Dual Cam Phasers, Automated

Manual Transmission, Electric Power Steering, Improved Alternator 266.2 25.4% 925 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed Automatic

Transmission, 42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 261.1 26.8% 2,432 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Turbocharging, Automated Manual

Transmission, Electric Power Steering, Improved Alternator 252.5 29.2% 176 

Electrohydraulic Camless Valve Actuation, Automated Manual Transmission, Electric Power

Steering, Improved Alternator 252.0 29.3% 1,219 

Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission, 42 Volt

Integrated Starter/Generator, Electric Power Steering, Electric Accessories 248.6 30.3% 2,780 

Electrohydraulic Camless Valve Actuation, Stoichiometric Gasoline Direct Injection, Automated

Manual Transmission, Electric Power Steering, Improved Alternator 243.4 31.8% 1,478 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift, Intake Cam

Phasers, Automated Manual Transmission, 42 Volt Integrated Starter/Generator, Electric Power

Steering, Electric Accessories

232.8 34.7% 2,745 

Stoichiometric Gasoline Direct Injection, Turbocharging, Dual Cam Phasers, 6-Speed Automatic

Transmission, 42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 225.3 36.8% 1,858 

Motor Assist Gasoline Hybrid 189.9 46.7% 2,797 Fully Integrated Diesel Hybrid 163.0 54.3% 7,543 Fully Integrated Gasoline Hybrid 162.7 54.4% 5,387 
xvi

technologies, the costs presented could be overstated. Consequently, the complete set of

technology packages does not constitute a low-cost solution to any particular CO2-

reduction scenario, but rather presents a host of possible solutions across a range of

reductions and costs.

Figure ES-2 graphically depicts the relative benefits and costs of each of the

evaluated technology packages. As this figure suggests, the technology packages span a

broad range of reduction potentials and costs. For example, packages providing CO2

reductions from 14 to 30 percent (emissions between 300 and 250 g/mi CO2) encompass

a net cost range from approximately negative $1,900 (i.e., net consumer savings) to

positive $500 (i.e., net consumer cost). Clearly, a least-cost solution would favor the

technology packages in the lower end of this cost range. Nevertheless, for purposes of

this study, we have assumed a technology supply curve

3

that includes all of the evaluated

technology packages. This allows for the fact that least-cost technologies may not be

viable for some segments of the market and that vehicle manufacturers may therefore

choose not to implement specific CO2-reduction solutions across the entire vehicle class.

For example, because technologies such as automated manual transmissions and

turbocharging may be limited to a subset of the models in any class of vehicles, a supply

curve constructed solely on the basis of least-cost solutions may understate the actual cost

of a class-wide CO2-reduction solution. Including all of the evaluated technology

packages in the development of the supply curve provides a more robust indication of

likely class-wide impacts.

The solid line in Figure ES-2 represents the CO2-reduction supply curve for the

large car class. As indicated, CO2 reductions of about 45 percent (corresponding to an

emissions rate of 190 g/mi, relative to a 2002 vehicle at about 355 g/mi) are likely to be

obtainable for a net negative cost (i.e. lifetime fuel savings exceed incremental

technology costs). The figure also includes a second supply curve to show the results of

a gasoline price sensitivity analysis in which the assumed prices of gasoline and diesel

fuel are increased from $1.58 per gallon to $2.00 per gallon. At the higher fuel price (the

dashed line in Figure ES-2), all but three of the technology packages reflect negative net

costs, and the costs for two of those three are very nearly at the break-even point. A 42-

volt cylinder deactivation package exhibits a net lifetime cost of $55, while the advanced

gasoline hybrid-electric vehicle exhibits a net lifetime cost of $329. The advanced diesel

hybrid still carries a net lifetime cost of about $2000.

At a gasoline price of $2.00 per gallon, estimated lifetime cost savings range from

$400-$1100 for a vehicle achieving a CO2 emissions rate of approximately 190 g/mi (this

represents about a 45 percent reduction from the 355 g/mi emission rate of the

corresponding baseline 2002 vehicle). Assuming a lower gasoline price of $1.58,

lifetime cost savings are estimated to range from $0 (i.e., no net cost) to $600 for the

same level of emission reduction. While diesel vehicles provide significant CO2

reductions, the higher density of diesel fuel reduces the potential benefit of a given

technology package relative to gasoline vehicles, especially as more aggressive carbon

reduction scenarios are considered. For example, the two diamonds furthest to the right

 

3

For purposes of this study, a supply curve indicates the relationship between CO2 emissions reduction

potential and cost.
xvii

in Figure ES-2 represent the gasoline (lower cost diamond) and diesel (higher cost

diamond) advanced hybrid cases. While the two cases provide very similar CO2

reductions, net costs for the diesel hybrid are about three times those of the gasoline

hybrid (marginal vehicle costs are about 35 percent higher for the diesel vehicle). For

less aggressive CO2 reductions, diesel technology can be cost-effective as the fuel

savings associated with increased diesel engine efficiency are large enough to offset the

additional cost. However, it should be recognized that much of the gasoline engine

technology evaluated here is specifically designed to close the gap between gasoline and

diesel engine efficiency.

Figure ES-2: Net Vehicle Costs for the Large Car Class Given Two Gasoline Price

Scenarios

-2000

-1000

0

1000

2000

3000

4000

350 325 300 275 250 225 200 175 150

CO2(grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per Gallon

Supply Curve @ $2.00 per Gallon

ES-3.2. Small Car Results

Estimated emissions reductions for the 14 technology packages modeled for the

small car class range from 11-56 percent, relative to the corresponding 2002 baseline

vehicle. Some of the most cost effective packages include automated manual

transmissions, turbocharging, and stoichiometric gasoline direct injection. Because this

class of vehicles uses smaller engines, the use of 12-volt idle off technology was explored

as an option. The results suggest that this technology is likely to be very cost-effective

for the small car class. Unlike the other vehicle classes, cylinder deactivation was not

evaluated for the small car class due to the small size of the baseline engine. Compared

to the large car class, the costs for achieving equivalent CO2 reductions are somewhat

higher for certain technologies. There are two reasons for this result. First, technologies

such as turbocharging that allow for engine downsizing provide substantial cost

advantages in the other vehicle classes because they reduce cylinder count. However, at

four cylinders, the base engine in the small car class is at the minimum cylinder count
xviii

considered to have broad market acceptability from a performance and engineering

standpoint. Thus, engine downsizing in the small car class does not generate the same

level of cost savings estimated for engine downsizing in the other vehicle classes.

Second, because the small car class has the lowest baseline CO2 emissions and the lowest

power-to-weight ratio of all the five classes, additional reductions accrue from a more

aggressive baseline and carry somewhat higher costs.

The results for the small car class indicate that emission reductions of about 29

percent (from a baseline CO2 emissions rate of 300 g/mi to about 215 g/mi) are likely to

be obtainable at net negative cost (i.e. with net lifetime savings). The technology supply

curve developed for the small car class suggests that all evaluated technology packages

except the advanced hybrid and 42-volt advanced multi-mode diesel technology packages

produce negative net costs at an assumed fuel price of $2.00 per gallon. Specifically,

estimated lifetime cost savings at this higher fuel price range from $300-$500 for

technology packages that achieve a CO2 emissions rate of approximately 210 g/mi

(equivalent to a 30 percent reduction from the 300 g/mi 2002 baseline). At a lower

gasoline price of $1.58, estimated lifetime cost savings range from $0 (i.e., no net cost) to

$250 for the same level of emission reduction.

ES-3.3. Minivan Results

Estimated emissions reductions (relative to the 2002 baseline vehicle) range from

14-54 percent for the 14 minivan technology packages studied. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 25 percent. Examples of these technologies

include 5 and 6-speed automatic transmissions, variable valve lift and timing, and

cylinder deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, 42-volt starter generators, and

camless valve technology. Even greater CO2 reductions can be achieved using hybridelectric designs. As with the large and small car cases, these advanced technologies are

somewhat more costly than conventional gasoline technologies but fuel cost savings over

the life of the vehicle usually far outweigh the additional cost. On a dollar per ton basis,

the net cost of technologies required to produce CO2 reductions up to 47 percent is

negative, implying net lifetime cost savings.

Some of the most cost-effective packages evaluated for the minivan class include

automated manual transmissions, cylinder deactivation, stoichiometric gasoline direct

injection, turbocharging, and camless valve actuation.

As before, the technology packages evaluated in this class span a broad range of

CO2-reduction potentials and costs. For example, packages that achieve CO2 reductions

of 14-30 percent (i.e. emissions rates between 350 and 285 g/mi) encompass a net cost

range from approximately negative $1,600 to negative $3. Emission reductions

exceeding 29 percent (corresponding to a CO2 emissions rate of 285 g/mi, relative to a

2002 baseline of 410 g/mi) are likely to be obtainable at net negative cost (i.e., achieving

lifetime savings). At a higher fuel price of $2.00 per gallon, all evaluated technology

packages reflect negative net costs except for the advanced gasoline and diesel hybrids.

At this fuel price, estimated lifetime cost savings range from $800-$1,500 for

technologies that reduce CO2 emissions to approximately 220 g/mi (a 47 percent
xix

reduction from baseline 2002 emissions of approximately 410 g/mi). Assuming a lower

gasoline price of $1.58, estimated lifetime cost savings range from $0-1,000 for the same

level of emission reduction.

ES-3.4. Small Truck Results

Estimated emission reductions (relative to the 2002 baseline vehicle) range from

17-53 percent for the 14 small truck technology packages evaluated. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 28 percent. Examples of these technologies

include 6-speed automatic transmissions, variable valve lift and timing, and cylinder

deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, 42-volt starter generators,

camless valve actuation, and diesel engine technology. Some of the most cost-effective

packages include stoichiometric gasoline direct injection, automated manual

transmissions, turbocharging, camless valve actuation, and diesel technology. For

example, a technology package consisting of stoichiometric gasoline direct injection and

camless vale actuation can provide a 32 percent CO2 reduction for an incremental vehicle

cost of about $1,500. Even greater CO2 reductions can be achieved using hybrid-electric

technology. On a dollar per ton basis and taking into account lifetime fuel savings, the

net cost of technologies producing CO2 reductions up to 46 percent is negative, implying

net cost savings over the vehicle life.

Packages that produce CO2 reductions ranging from 17-32 percent (corresponding

to CO2 emission rates between 380 g/mi and 310 g/mi) encompass a net cost range from

approximately negative $2,600 to negative $400. In fact, CO2 reductions exceeding 45

percent are likely to be obtainable for a net negative cost. At a higher fuel price of $2.00

per gallon, all evaluated technology packages achieve negative net costs with the

exception of the advanced diesel hybrid. At this fuel price, average lifetime cost savings

range from $1,600 to $2,200 for CO2 reductions to approximately 250 g/mi (equivalent to

a 46 percent reduction from the 2002 baseline emissions rate of about 460 g/mi).

Significant cost savings can actually be expected for technology packages that reduce

CO2 emissions rates to as little as 215 g/mi, nearly 54 percent below baseline 2002

emissions. At a lower fuel price of $1.58 per gallon, estimated cost savings are

$700-$1,700 over the life of a vehicle, except in the advanced hybrid cases. In sum, the

introduction of CO2-reducing technologies in the small truck category provides high net

savings due to the relatively high baseline CO2 emissions for this class. This results in

proportionately greater fuel savings compared to vehicle classes that start from a lower

baseline CO2 emissions rate.

ES-3.5. Large Truck Results

Emission reduction estimates range from 14-55 percent (relative to the 2002

baseline vehicle) for the 15 large truck technology packages modeled. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 24 percent. Examples of these technologies

include 6-speed automatic transmissions, variable valve lift and timing, and cylinder

deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, camless valve actuation, and
xx

diesel technology, which can provide up to a 30 percent CO2 reduction. Even greater

CO2 reductions can be achieved using hybrid-electric designs. On a dollar per ton basis,

the net cost of technologies producing CO2 reductions of up to 46 percent is negative,

resulting in overall savings over the life of the vehicle.

Some of the most cost-effective packages in this class include automated manual

transmissions, cylinder deactivation, and stoichiometric gasoline direct injection.

Cylinder deactivation was evaluated as a more viable technology for large trucks than

turbocharging and downsizing because of the need to assure adequate durability for

heavily loaded engines operating on work-type duty cycles (e.g., high-load operations

and payload and trailer towing).

The large truck category is the only vehicle class with an eight-cylinder base

engine. Because of this, technology costs in the large truck class are in some cases higher

than in the other vehicle classes due to additional hardware requirements. For example,

eight lost motion devices are required for variable valve lift technology rather than six for

other vehicle classes due to the additional cylinders. Despite these higher costs, fuel

savings more than overcome incremental technology costs for nearly all the large truck

technology packages evaluated.

Packages providing CO2 reductions from 14 to 30 percent (corresponding to CO2

emissions rates between 450 and 370 g/mi) encompass a net cost range from

approximately negative $1,800 to positive $300. Emissions reductions of about 45

percent (corresponding to a CO2 emissions rate of about 285 g/mi compared to a 2002

baseline rate of about 525 g/mi) are likely to be obtainable for a net negative cost (i.e.,

with net lifetime savings). At $2.00 per gallon of gasoline, all evaluated technology

packages reflect negative net costs except the advanced gasoline and diesel hybrid cases.

At this price, net lifetime fuel savings range from $900 to $1,700 for CO2 reductions up

to about 45 percent. At a lower gasoline price of $1.58, average lifetime savings range

from $0 to $1,000 for this same level of CO2 reductions.

ES-4. Conclusions

The results of this analysis suggest that existing and emerging automotive

technologies can achieve substantial and cost-effective reductions in motor vehicle GHG

emissions in the 2009 to 2015 timeframe. Specifically, GHG emissions from light-duty

vehicles can be reduced from 14-55 percent in this timeframe. Assuming a gasoline price

of $1.58 per gallon, this study found that most technology packages capable of achieving

these reductions would result in net cost savings of at least $500, taking into account both

incremental technology costs and fuel savings over the life of the vehicle. At a higher

fuel price of $2.00 per gallon, estimated lifetime net savings are between $300 and

$2,200 per vehicle for a range of CO2 reductions - with the exception of some of the

hybrid vehicles evaluated.
xxi
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-1

1. Introduction

1.1. Purpose of Study

This study provides an assessment of available and emerging technologies that

could be used to reduce greenhouse gas (GHG) emissions from light-duty motor vehicles

in the United States in the 2009-2015 timeframe. Its findings are drawn from the results

of original cost and technology analyses conducted for this study, together with

information obtained from other available reports. This assessment was inspired by the

California legislature’s passage of Assembly Bill 1493 requiring the state Air Resources

Board (ARB) to adopt regulations designed to achieve the maximum feasible and costeffective reductions in GHG emissions from light-duty vehicles beginning in model year

2009. The specific GHGs included in this assessment are carbon dioxide (CO2), methane

(CH4), nitrous oxide (N2O), and hydroflourocarbons (HFCs).

The goal of this assessment is to help define GHG-reducing motor vehicle

technologies that are expected to be feasible, commercially available and cost-effective in

the 2009-2015 timeframe. A wide range of “off-the-shelf” and emerging technologies

were evaluated, both individually and in packages, for their potential to reduce CO2

emissions from light-duty vehicles. The technologies examined fall into six primary

categories: (1) off-the-shelf engine technology; (2) off-the-shelf transmission

technology; (3) emerging engine technology; (4) emerging transmission technology; (5)

other vehicle technologies such as improved aerodynamics; and (6) other emerging

technologies such as improved catalysts and HFC-free air conditioning. The study also

includes an assessment of the potential penetration of these technologies into the fleet by

the projection years of 2009 and 2015.

The results presented in this report have significant implications for states in the

Northeast and elsewhere that share California’s commitment to reducing transportationrelated GHG emissions as part of a broader effort to address the risks posed by global

climate change. In the Northeast, light-duty vehicles account for 20-25 percent of total

emissions of manmade GHGs.

1.2. Basic Science of Global Climate Change

The climatic conditions to which humans and other species have become

accustomed over thousands of years result from a complicated balance between the

amount of solar energy that enters and leaves the atmosphere. In recent decades, a

concern has emerged that human activities are interfering with this balance. Scientists

have postulated that rising concentrations of certain heat-trapping gases in the

atmosphere are enhancing a naturally occurring greenhouse effect which prevents some

of the solar energy re-radiated from the earth’s surface from leaving the atmosphere,

4

producing potentially significant shifts in global climate patterns.

 

4 Without the naturally occurring greenhouse effect, the Earth’s average temperature would be about 16oC

(60

o

F) cooler, and climate conditions on the planet would be much closer to those that prevail on Mars.

The consensus among the scientific community is that human activities are inadvertently enhancing this

effect, with uncertain consequences for global climate conditions.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-2

As noted at the outset, this assessment includes the primary GHGs that are

commonly associated with current concerns about human-induced climate change (i.e.

CO2, CH4, N2O, and HFCs).

5

The heat-trapping properties of each of these gases – and

hence their contribution to overall atmospheric warming – varies. Accordingly, scientists

have developed the concept of “global warming potential” (GWP) under which each gas

is assigned an index number that indicates its relative climate impact, over a specified

period of time, expressed as an equivalent release (by weight) of carbon dioxide. For

example, the current 100-year GWP assigned to methane is 21, which means that one ton

of methane emissions is estimated to have the same global warming impact over 100

years as 21 tons of carbon dioxide emissions. The 100-year GWP values currently used

in national and international GHG reporting for those GHGs included in this study are:

• carbon dioxide (CO2) – 1

• methane (CH4) – 23

• nitrous oxide (N2O) – 296

• hydrofluorocarbons (HFCs) – various (up to 11,700)

6

From the standpoint of anthropogenic emissions generally – and motor vehicle

emissions specifically – the greenhouse gas of greatest concern is CO2. Carbon dioxide

is a natural by-product of the oxidation of carbon in organic matter, through either the

combustion of carbon-based fuels or the decay of biomass; its chief sources globally are

fossil fuel combustion and deforestation. This gas alone presently accounts for over 80

percent of total U.S. anthropogenic GHG emissions. The other gases listed above account

for a much smaller portion of the overall U.S. GHG inventory

7

and also play a smaller

role in terms of vehicle emissions.

Atmospheric measurements and analysis of air trapped in polar ice cores reveal

that atmospheric concentrations of a number of GHGs are increasing. For instance,

measured concentrations of carbon dioxide in the atmosphere have increased from preindustrial levels of 278 parts per million (ppm) to 365 ppm in 1998. Methane has

increased from 0.7 ppm to 1.745 ppm over the same period. Experts widely agree that

human activities are responsible for these increases – most notably, fossil fuel

combustion and tropical deforestation in the case of CO2, and rice cultivation, animal

husbandry, coal mining, natural gas handling, and waste disposal in landfills in the case

of methane.

8

 

5 Other naturally occurring and manmade gases (e.g., water vapor and perfluorocarbons) in the atmosphere

also contribute to the greenhouse effect. Note that in general, all of the chief GHGs – with the exception of

water vapor – are present in the atmosphere in only trace amounts. Nevertheless, they can have profound

impacts on the earth’s climatic balance. The most important GHG overall is water vapor. However, water

vapor is not generated directly by human activities in quantities that are meaningful relative to natural

sources.

6

For motor vehicles HFC-134a constitutes the current HFC of concern and its GWP is 1,300.

7

For example, the next most important manmade GHG after CO2 is methane, which accounted for

approximately 9 percent of the total U.S. inventory in 2000; for the same year the contribution from N2O

was 6 percent and all other gases were under 2 percent.

8 National Research Council, Committee on the Science of Climate Change, Climate Change Science: An

Analysis of Some Key Questions (Washington, DC: National Academy Press, 2001), p. 2.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-3

Scientists have attempted to gauge the impacts of these changes on the global

climate system with sophisticated computer models. The most recent assessment by the

Intergovernmental Panel on Climate Change (IPCC), an international team of

meteorologists and climate scientists convened under the auspices of the United Nations,

found that global average surface temperature had increased by about 0.6 C (1 F) during

the 20th century, and concluded that “In the light of new evidence and taking into

account the remaining uncertainties, most of the observed warming over the last 50 years

is likely to have been due to the increase in greenhouse gas concentrations.” The most

recent projections published by the IPCC project an increase in global average surface

temperatures ranging from 5.8 C (2.5-10.4 F) over the next century, with warming for the

United States as much as 30 percent higher than the global average.

9

1.3. Environmental Impacts of Climate Change

Though climate change predictions remain fraught with uncertainties, even small

changes in mean global temperature could have significant impacts. For example,

average global temperatures during the last major ice age about 11,000 years ago were

only about 3

oC (5.4o

F) lower than at present. Over subsequent millennia, average global

temperatures have varied no more than 1.5

oC (2.7o

F). Moreover, the rate of climate

change, as much as its eventual magnitude, may be critical to the successful adaptation of

human and natural systems. A 2002 report by a special committee of the National

Academy of Sciences warned that the impacts of climate change might not be gradual

and linear: rather, increasing atmospheric GHG concentrations could push the climate

system across thresholds that would trigger abrupt climate changes, such as alterations in

major ocean currents or sudden regional increases in floods, droughts and other extreme

weather events.

10

In terms of the specific risks of climate change for the Northeast states,

projections developed using the Canadian General Circulation Model and the United

Kingdom’s Hadley Climate Model suggest that average temperatures in New England

could increase by 3.1-5.3

oC (about 6-10o

F) by the year 2090. A study funded by the U.S.

Global Change Research Program noted that projected warming at the lower end of this

range would raise average year-round temperature in Boston to a level currently

measured in Richmond, Virginia, while – under the higher estimates – Boston’s climate

would be comparable to that of Atlanta, Georgia.

11 Associated impacts on the region

could include more frequent and intense storms; increased damage in coastal areas from

flooding and erosion associated with sea-level rise; higher numbers of heat-related deaths

during summer heat waves; and a variety of stresses on forests, fishing grounds and

coastal ecosystems which could in turn affect important economic sectors such as

tourism, maple sugaring and skiing.

 

9

Intergovernmental Panel on Climate Change, Working Group I, Climate Change 2001: The Scientific

Basis, Summary for Policymakers, pp. 2, 10, 13 (quote on p. 10).

10 Committee on Abrupt Climate Change, National Research Council, Abrupt Climate Change: Inevitable

Surprises (Washington, DC: National Academy Press, 2002).

11 New England Regional Assessment Group, Preparing for a Changing Climate: The Potential

Consequences of Climate Variability and Change, New England Regional Overview (University of New

Hampshire: U.S. Global Change Research Program, 2001), pp. 6-7.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-4

1.4. Political and Regulatory Context

1.4.1. International Context

As early as 1992, international awareness of the many potential risks associated

with global warming led 160 countries, including the United States, to adopt a

Framework Convention on Climate Change under the stated objective of achieving

“stabilization of greenhouse gas concentrations in the atmosphere at a level that would

prevent dangerous anthropogenic interference with the climate system.”

12

Toward this objective, signatories pledged to work to stabilize greenhouse gas

emissions. A number of industrialized countries, again including the United States,

adopted the specific near-term goal of returning year 2000 greenhouse gas emissions to

1990 levels. It subsequently became evident that most countries, including the United

States, were not on track to meet this objective. In response, parties to the Framework

Convention adopted the Kyoto Protocol in 1997, which included targets and timetables

for reducing GHG emissions to specific levels for each country. As of early 2003, 102

countries had ratified or acceded to the Protocol. However, the United States – citing

concerns about the economic impact of reducing GHG emissions on the time scale

required under the agreement – has not ratified the Kyoto Protocol.

Notwithstanding the federal government’s reluctance to impose mandatory limits

on GHG emissions, many state and local leaders had become sufficiently concerned

about the issue of climate change by the end of the 1990s to adopt a range of measures

aimed at reducing GHG emissions within their jurisdictions. This trend began with a few

leading states in the early 1990s, but has accelerated recently: in 2001 and 2002,

approximately one-third of the states passed new legislation or executive orders

specifically aimed at reducing greenhouse gas emissions.

13

These policies ranged from

comprehensive state action plans with quantitative GHG reduction targets to regulations

or laws limiting emissions from a specific sector such as electric power generation or

transportation.

1.4.2. California’s Assembly Bill 1493

In 2003, the California legislature passed legislation (Assembly Bill 1493) aimed

at reducing GHG emissions from motor vehicles in response to concerns about the

potential impact of global climate change on the state’s economy and on the well-being

of its citizens. The bill, which was signed into law by Governor Davis on July 22, 2002,

requires the state’s Air Resources Board to adopt regulations by 2005 that will achieve

the maximum feasible reductions in GHG emissions from new light-duty vehicles that

can be achieved in a cost-effective manner beginning with the 2009 model year. In

achieving that goal the state is specifically prohibited, under the legislation, from

 

12 United Nations, “Report of the Intergovernmental Negotiating Committee for a Framework Convention

on Climate Change on the Work of the Second Part of Its Fifth Session, Held at New York From 30 April

to 9 May, 1992,” UN Document A/AC.237/18, Part II (May 15, 1992).

13 Additionally, other states adopted measures that were not expressly aimed at climate change but clearly

were driven at least in part by the issue of global warming. Barry G. Rabe, Statehouse and Greenhouse:

The Evolving State Government Role in Climate Change (Arlington, VA: Pew Center on Global Climate

Change, November 2002), p. 7.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-5

adopting any regulatory requirements that would mandate vehicle weight reductions,

restrict sales of any particular vehicle type, or impose fees or taxes on vehicles or vehicle

miles traveled. AB 1493 also provides for a legislative review process.

The standard adopted by ARB is required to account for CO2, CH4, N20 and

refrigerant (HFC) emissions. Particulate matter (PM) emissions may not be included due

to the limited availability of data and the fact that PM emissions are regulated under

California’s low emission vehicle (LEV II) program. In addition, the form of the

standard developed to implement AB 1493 must be carefully designed to provide for

effective and equitable GHG reductions. Options that ARB staff have considered for the

form of the standard include manufacturer-specific standards, a uniform fleet average

standard, an attribute-based approach, a weight-based approach and a weight category

approach.

1.4.3. Climate Actions in the Northeast States

In 2002, the Conference of New England Governors and Eastern Canadian

Premiers (NEG/ECP) adopted a regional climate action plan covering the New England

states and the five eastern Canadian provinces of Quebec, New Brunswick, Nova Scotia,

Newfoundland, and Prince Edward Island. The NEG/ECP climate plan sets overall

regional targets for stabilizing aggregate GHG emissions at 1990 levels by 2010,

followed by a ten percent reduction below 1990 emissions levels in 2020 and substantial

further reductions (by as much as 75 to 80 percent) in subsequent years. In recent years,

other northeastern states – notably New York and New Jersey – have developed or

undertaken their own GHG reduction initiatives, and in some cases have set their own

reduction targets. Given that the transportation sector accounts for a significant portion of

the overall increase in emissions projected for the region in future years, achieving the

region’s climate goals will require effective means to address the motor vehicle

contribution. In that context, Northeast states are closely monitoring the AB1493

rulemaking and some have already expressed an interest in adopting any new California

requirements that are likely to result.

In 2003, for example, a proposal to adopt California’s regulations for the control

of GHG emissions from motor vehicles was included in New York Governor George

Pataki’s State of the State address and was formally introduced in the New York state

legislature.

14 Additionally, the idea was included in policy recommendations submitted

by the New York State Greenhouse Gas Task Force which was created by Governor

Pataki to develop proposals for reducing the state’s GHG emissions. In fact, the

Northeast states have an established track record of adopting California’s more stringent

motor vehicle regulations: several of them have been enforcing California’s Low

Emission Vehicle (LEV) standards in lieu of federal emissions standards for over a

decade.

 

14

Specifically, New York Senate bill S. 4044 (Assembly bill A. 4082) would require the New York State

Department of Environmental Conservation to promulgate California’s regulations for the cost effective

control of GHG emissions from motor vehicles by December 31, 2005 (i.e., one year from the January 1,

2005 deadline for promulgation of California’s rules).
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 1-6

1.5. Report Organization

This report is divided into three sections: Chapter 1, Introduction, describes the

purpose of the report, provides a short summary of the state of the science of climate

change and describes the current political and regulatory context for this assessment.

Chapter 2, Overview of Study Method, describes the computer simulation models used in

this assessment, discusses the selection of potential GHG reduction technologies,

describes the approach used to define vehicles for the baseline assessment, explains the

approach used to assess and package technology options, and describes the methodology

used to project deployment costs for individual technologies and packaged combinations.

Chapter 3, Results, presents the findings of the technical and cost analyses performed for

this study. It also compares the findings of other recent studies with regard to costs.

This report contains results for five classes of vehicles. Technical appendices provide

detailed results of the model simulations, supporting analyses, and cost analyses.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-1

2. Overview of Study Method

This chapter provides an overview of the methodology used to estimate GHG

reductions that could be achieved by introducing advanced technologies into the U.S.

light-duty

15

vehicle fleet in the 2009-2015 timeframe. The core of the analysis consists

of a series of modeled simulations to predict the emissions impacts of incorporating

various technology combinations in new vehicles. A more detailed description of the

specific methods and assumptions used in the analysis is provided in Appendix B.

All simulation modeling for this study was performed using AVL Powertrain

Engineering, Inc.’s CRUISE software, which provides detailed information on the

acceleration, braking, and emissions performance of different motor vehicle designs,

including advanced powertrain designs. The modular structure of CRUISE can

accommodate a variety of vehicle configurations – including cars, motorcycles, trucks,

and buses – and allows for the detailed specification of a wide range of individual vehicle

components. This enables the user to investigate – at the vehicle level of detail – how

modifying or replacing certain components, either individually or in combination, affects

vehicle performance across a number of parameters, including over standardized city and

highway driving cycles; in terms of climbing performance; steady-state and top speed

performance; maximum acceleration and traction force; and braking performance.

16 A

more detailed description of the CRUISE software is included in Appendix B.

Remaining sections of this chapter describe each basic step of the analysis methodology,

In brief, these steps consisted of:

1. Defining five representative vehicle classes (i.e., small car, large car, small truck,

large truck, and minivan).

2. Validating model simulation results against the actual performance of

representative 2002 model year vehicles in each class and developing a “businessas-usual” technology baseline for each class of vehicles in model year 2009.

3. Developing a list of specific technology options and assessing the costs and

potential GHG-reducing benefits of each option in isolation.

4. Constructing various technology combinations or “packages” based on the results

of the above assessment of individual technology options.

5. Performing CRUISE model simulations for each of the vehicle classes and

technology packages selected for analysis.

6. Assessing the emissions reduction benefits of additional technology options such

as low rolling resistance tires, low viscosity lubricating oil, vehicle mass

reduction, air conditioning options, and hybrid vehicle technologies.

7. Assessing the costs and benefits of different technology packages.

 

15 Consistent with the classifications used in most existing state and federal regulations, light-duty vehicles

are defined in this study as vehicles with a Gross Vehicle Weight Rating (GVWR) less than 8,500 lbs.

16 The range of components that can be individually specified in CRUISE includes: vehicle and trailer;

engine (combustion or electric motor); clutches; transmission elements; control elements; shafts (rigid or

torsion-elastic); wheel/tire; electrical components; hybrid components; brakes; and auxiliaries (such as oil

pump, air conditioning or power steering). In addition, the software allows for modification of assumptions

about the driver and about environmental driving conditions (such as wind, road surface, etc.).
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-2

2.1. Defining Representative Vehicle Classes

For purposes of this study, vehicles were first categorized according to major

utility distinctions using 2002 sales and technology data. The objective was to determine

the minimum number of classes that would provide for maximum fleet representation

while maintaining reasonably homogeneous technology composition within classes. A

total of five vehicle classes were selected: large cars, small cars, large trucks, small

trucks, and minivans. The small car class generally includes vehicles defined by the U.S.

Environmental Protection Agency (EPA) as subcompacts and compact cars, while the

large car class includes EPA midsize and large cars. The small and large truck classes

include both pickup trucks and sport utility vehicles (SUVs) and are generally split

according to gross vehicle weight rating (at approximately 6000 pounds). In most cases,

SUVs and pickup trucks share a common platform and utilize similar engine and

driveline technology, so representing them in combination is consistent with current

technology distinctions. Table 2-1 summarizes the chief characteristics of each vehicle

class evaluated in this study and indicates its prevalence in recent (2002) overall lightduty vehicle sales.

Table 2-1: Characteristics of Evaluated Vehicle Class

Vehicle Class Fraction of

Sales in 2002

Dominant Technology Characteristics

Small cars 22% 4-cylinder, naturally aspirated, dual overhead cam

(DOHC), four-speed automatic transmission, front

wheel drive vehicles

Large cars 25% 6-cylinder, naturally aspirated, DOHC, four-speed

automatic transmission, front wheel drive vehicles

Small trucks 23% 6-cylinder, naturally aspirated, DOHC, four-speed

automatic transmission vehicles, with a nearly 50/50

split between two and four wheel drive

Large trucks 21% 8-cylinder, naturally aspirated, overhead valve (OHV),

four-speed automatic transmission vehicles, also with a

nearly 50/50 split between two and four wheel drive

Minivans 7% 6-cylinder, naturally aspirated, OHV, four-speed

automatic transmission, front wheel drive vehicles

For each of these vehicle classes, AVL modeled a production vehicle that best

matched the average characteristics of vehicles in each class. Determining the average

characteristics required specifying both numeric and non-numeric parameters. For

vehicle characteristics that could be specified using continuous numeric parameters —

such as curb weight, engine displacement, peak horsepower, peak torque, etc. — the

value assumed for the model vehicle simply reflected the sales-weighted numeric average

of actual model year 2002 vehicles in each class. For other non-numeric vehicle

characteristics that could not simply be averaged,

17

the model vehicle was assumed to

include whatever discrete technology accounted for the largest share of 2002 class sales.

 

17

For example, a particular class of vehicles might be split evenly between 4-speed and 5-speed automatic

transmission models. However, it is not possible to model a theoretical 4.5-speed “ average” of these two

characteristics.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-3

For example, 31 percent of large cars sold in 2002 had overhead valves, whereas 24

percent had single overhead cam (SOHC) and 45 percent had dual overhead cam

(DOHC) valvetrain technologies. Since DOHC technology has the largest sales share, it

was taken as the class average valvetrain technology for the model large car. Table 2-2

summarizes the specific characteristics assumed for the representative, model vehicle in

each of the five vehicle classes analyzed.

Table 2-2: 2002 Class Average Statistics

Parameter

Large

Truck

Small

Truck

Minivan

Large

Car

Small

Car

Curb Weight (lbs) 4826 3714 3980 3380 2762

GVWR (lbs) 7167 4867 NA NA NA

Displacement (liters) 5.01 3.41 3.42 3.18 2.27

Engine Type V8 V6 V6 V6 L4

Charge Type NA NA NA NA NA

Cam Type OHV DOHC OHV DOHC DOHC

Rated HP 257 195 199 194 148

Peak Torque (lb-ft) 311 218 222 208 152

Driveline 4WD 4WD FWD FWD FWD

Transmission Type Automatic Automatic Automatic Automatic Automatic

Speeds 4 4 4 4 4

CO2 (g/mile - combined) 574 473 436 385 334

HP/Weight Ratio 0.0537 0.0524 0.0498 0.0569 0.0530

Torque/Weight Ratio 0.0649 0.0586 0.0558 0.0610 0.0545

2.2. Validating Simulation Modeling Results for Representative

Vehicles and Developing a “Business-As-Usual” Technology

Baseline

As described in the foregoing section, the specifications used to describe a

representative or “ average” vehicle in each vehicle class for simulation purposes were

based on actual 2002 vehicle characteristics. However, no one, actual vehicle has

characteristics that exactly match the combination of average or representative

specifications developed for each vehicle class. Hence, to validate model simulations of

the average vehicle, it was necessary to identify actual vehicle platforms that were close

to the calculated class averages in terms of technology and performance. To identify

candidate vehicles, a series of parameter-by-parameter closeness statistics was developed

for every actual model year 2002 vehicle in each class to indicate the degree of similarity

with the class average characteristics summarized in Table 2-2

18

The smaller the

 

18

In all, closeness statistics were developed for a total of 14 vehicle parameters. See Appendix C for further

details.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-4

closeness statistic, the closer the particular vehicle is to the theoretical class average

vehicle — with a value of zero being indicative of an exact match. Based on a rank

ordering of the overall closeness statistic for different vehicle platforms, the actual

vehicle selected to validate simulation results for the model or average vehicle in each

class was as follows:

• Small cars: Chevrolet Cavalier 2.2 liter L4

• Large cars: Ford Taurus 3.0 liter V6

• Small trucks: Toyota Tacoma 3.4 liter V6

• Large trucks: GMC Sierra 5.3 liter V8

• Minivans: Chrysler Town & Country 3.3 liter V6

To validate the simulation methodology, model-predicted performance in terms of

CO2 emissions and acceleration (0-60 time) was compared to actual data for each of these

vehicles. The results, which are summarized in Table 2-3, generally suggest that the

model simulations provide good estimates of actual vehicle performance. In terms of CO2

emissions, for example, the simulated values are within one percent of the actual values

for the representative vehicles and within two percent of the class average for all but the

small truck class. Combining the performance of the simulation models for all five

vehicle classes using the appropriate sales weighting (i.e., 0.211 for large trucks, 0.238

for small trucks, 0.067 for minivans, 0.262 for large cars and 0.222 for small cars), yields

a fleetwide CO2 emissions error of 2.0 percent. To the extent that the effect of this error

is the same for both estimated baseline and controlled CO2 emissions, it is unlikely to

affect estimates of the relative difference between them.

Having validated model performance for each of the class-average 2002 vehicles,

the next step was to develop a “ business-as-usual” baseline for technologies likely to be

incorporated in vehicles by model year 2009. Given that vehicle technology will certainly

evolve over the coming years, even absent policy intervention to reduce GHG emissions,

this step was necessary to provide a more realistic baseline against which future

emissions reduction potential and incremental cost could be evaluated. For example, to

the extent that some new technologies are likely to be adopted in response to existing

market forces, they may not be available for additional CO2 reductions in the projection

years. Moreover, to the extent that many of these new technologies are likely to be

applied in ways that improve vehicle performance rather than reduce emissions, some or

all of their associated emissions reduction potential will also not be available. To

estimate the potential impacts of new technology adoption and analyze potential tradeoffs

between improved vehicle performance and emissions reductions, the 2002 models were

adjusted to incorporate new technologies that are expected to enter the fleet between

2002 and 2009.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-5

Table 2-3: Performance of the 2002 Simulation Models

Parameter

Large

Truck

Small

Truck

Minivan

Large

Car

Small

Car

CO2 (grams/mile)

Representative Vehicle 499 427 375 331 276

Model 493 426 376 329 278

Delta -6.5 -1.4 +1.3 -1.3 +1.4

Delta (percent) -1.3 -0.3 +0.3 -0.4 +0.5

Class Average 488 400 371 327 281

Delta +4.8 +25.7 +5.8 +2.5 -3.5

Delta (percent) +1.0 +6.4 +1.6 +0.8 -1.3

0-60 Time (seconds)

Representative Vehicle 9.0 9.7 8.1 8.2

Model 8.9 10.0 10.5 8.1 8.7

Delta -0.14 +0.29 -0.03 +0.54

Delta (percent) -1.6% +3.0% -0.4% +6.6%

To project a “ business-as-usual” evolution in vehicle technology and attributes

over the coming years, Martec conducted detailed market research into Original

Equipment Manufacturer (OEM) product plans and developed a database of estimated

2009 vehicle platforms under baseline conditions. Baseline in this case means that only

currently adopted regulatory requirements were assumed in developing the 2009 vehicles.

The resulting database was used to adjust the 2002 class average vehicle characteristics

that were simulated to reflect expected 2009 baseline technology and performance.

The biggest technology changes anticipated between 2002 and 2009 are:

• Near-universal use of cam phaser (variable valve timing) technology. However,

the sophistication of this technology is likely to vary across models (i.e., intake

valve only, exhaust valve only, both intake and exhaust valves in a coupled or

dual independent configuration, etc.),

• Significant penetration of variable valve lift technology into the fleet,

• Significant penetration of cylinder deactivation technology into the fleet,

• Continued evolution of transmission technology, with six speed automatic

transmissions becoming dominant, and

• Limited growth in the market share of stoichiometric gasoline direct injection

(GDI) and diesel engines as well as turbocharger and hybrid-electric vehicle

technologies.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-6

Existing market forces that are comprehended in the development of the 2009 baseline

fleet characteristics and technology penetration include:

• Light truck CAFE progression from 20.7 mpg to 22.2 mpg in MY2007;

• The California ZEV mandate, also adopted by New York and Massachusetts (at

the time this study was completed);

• Full implementation of Federal Tier 2 emissions standards, which drives a broad

requirement for improved cold-start performance;

• Increased competition in the North American market across all product segments,

which drives OEMs to create differentiation on many vehicle attributes, including

performance;

• Installed powertrain capital base; and

• OEM positioning, sale mix and anticipated attempts to balance market,

regulatory and societal forces.

It is important to note that the 2009 baseline vehicles were not created as a least

cost solution for CO2 reductions. In fact, CO2 reductions were not a consideration in the

2009 baseline vehicle forecast, except to the extent that they were influenced by

responses to the market forces or regulatory requirements described above. The

projections in technology penetrations for 2009 were developed solely in response to the

market forces and trends listed above that will affect manufacturing and design decisions

between now and 2009. For example, the projection of near universal use of cam phasers

in 2009 is based on the need to reduce cold start emissions in order to meet Tier 2

standards. Similarly, the use of six speed automatic transmissions is based on the

forecasted need to provide better acceleration and a smoother ride in order meet expected

consumer demands.

As before, when dealing with discrete vehicle technologies that cannot be

averaged for purposes of the vehicle simulation, it was necessary to predict which

technology would dominate in 2009. Table 2-4 summarizes the predicted dominant

characteristics of class average vehicles in 2009 in comparison to 2002 models. As

indicated by the shaded cells, forecasted changes in dominant technologies are limited to

transmission and valvetrain technologies.

Table 2-4: Dominant Discrete Technologies in 2002 and 2009

Large Truck Small Truck Minivan Large Car Small Car

Parameter

2002 2009 2002 2009 2002 2009 2002 2009 2002 2009

Engine Type V8 V8 V6 V6 V6 V6 V6 V6 L4 L4

Charge Type NA NA NA NA NA NA NA NA NA NA

Cam Type OHV OHV DOHC DOHC OHV OHV DOHC DOHC DOHC DOHC

Driveline 4WD 4WD 4WD 4WD FWD FWD FWD FWD FWD FWD

Transmission A4 A6 A4 A6 A4 A5 A4 A6 A4 A5

Cam Phasing No Coupled No Dual No Coupled No Dual No Dual

Variable Lift No No No Discrete No Discrete No Discrete No Discrete

Cyl. Deact. No No No No No No No No No No
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-7

Under “ business-as-usual” assumptions one would expect changes not only in

vehicle technology, but in vehicle performance and other attributes over the next several

years. To estimate the impacts of these changes, a trend analysis was conducted using

data published by the EPA.

19

Specifically, historical trends in vehicle weight and 0-60

acceleration time for the period 1993-2003 were analyzed and used to project continued

changes to 2009. Table 2-5 summarizes the results of the historical trend analysis for

each of the five vehicle classes considered.

Table 2-5: Trend-Based Forecast Parameters

Parameter

Large

Truck

Small

Truck

Minivan

Large

Car

Small

Car

Inertia Weight (1993-2003)

Change per Year (pounds) 42 25 32 0 22

0-60 Time (1993-2003)

Change per Year (seconds) -0.22 -0.15 -0.19 -0.14 -0.11

As indicated in Table 2-5, all vehicle classes exhibited significant increases in

power (as measured by how quickly they can accelerate from 0-60 mph) and four of the

five classes exhibited significant (and simultaneous) weight increases over the last 10

years (the exception was large cars, which did not get appreciably heavier over this time

period). The trend in improved power (as measured by a decline in 0-60 time) was

assumed to continue without change to 2009 in all classes. However, the trend toward

increased weight was assumed to moderate, largely in response to the small increase in

Corporate Average Fuel Economy (CAFE) requirements anticipated for light trucks over

the next several years.

20 Accordingly, weight was held constant for the truck and

minivan classes, as well as for large cars, leaving only the small car class with an

expected average weight increase of 152 pounds between 2002 and 2009.

21

Once baseline 2002 vehicle characteristics had been updated to 2009 using the

Martec technology database, a validation check was performed to determine whether the

2009 model forecasts were sensitive to possible variations in the penetration of discrete

technologies.

22

This check was performed by identifying the various discrete technology

packages that commanded a five percent or greater share of the 2009 market in each

vehicle class. Discrete CO2 impact estimates developed by AVL were then used to

estimate the overall CO2 impact of each technology package and the results were

 

19U.S. Environmental Protection Agency, Light-Duty Automotive Technology and Fuel Economy Trends:

1975 Through 2003, EPA420-R-03-006, Appendices G and H, April 2003.

20

For light trucks, the CAFE standard will remain at 20.7 mpg for model years 2002-2004, and increase to

21.0 mpg in model year 2005, 21.6 mpg in model year 2006 and 22.2 mpg in 2007.

21 The large car weight was held constant given the lack of weight increase between 1993 and 2003.

22

For example, though the dominant technology characteristics for large trucks include cam phasing

without variable lift, a 6-speed automatic transmission and no cylinder deactivation, the fraction of the

large truck fleet actually represented by this combination of technologies is less than six percent. This is an

artifact of the increasingly diverse set of technologies available to manufacturers, which results in a

situation where technologies that are dominant when viewed in isolation are spread across an otherwise

diverse fleet.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-8

weighted by market penetration to estimate an overall class-specific CO2 impact. Given

that the results of this evaluation showed a maximum CO2 emissions difference of 1.5

percent (6.8 grams per mile), the dominant class-average 2009 technology packages

developed using this methodology are believed to accurately represent likely 2009 fleet

CO2 emissions.

2.3. Identifying Discrete Vehicle Technology Options for Evaluation

Table 2-6 lists the individual vehicle technologies considered in this study for

purposes of evaluating future light-duty vehicle CO2 emissions reduction potential. A

brief description of each of the technologies indicated in Table 2-6, – including an

explanation of how each option might reduce CO2 emissions – is provided in Appendix

A.

As a first step toward identifying individual technology options for further

evaluation, the potential CO2 emissions impact of each of the options listed in Table 2-6

was evaluated in isolation. The purpose of this evaluation was primarily to screen for the

most promising technologies to be included in the more detailed “ package” simulations

conducted later in the analysis. Accordingly, this step was not intended to be precise and

was implemented, to the extent feasible, using simplified approaches. In many cases, for

example, an engine map was selected and the CO2 emissions rate at a specific point on

that map was compared to the corresponding point on the base technology engine map for

each representative vehicle.

23

This comparison was made at the speed/load point that

represented average simulated vehicle CO2 emissions over the highway and city cycles.

For technologies that provided the bulk of their benefits through a shift in speed/load

performance (i.e., primarily transmission technologies), a full CRUISE simulation was

run for the candidate technology and compared to that for the applicable representative

vehicle. Where engine maps were not readily available, impact estimates were developed

through a review of available research papers.

In addition to estimating the emissions reduction potential of each of the

individual technology options listed in Table 2-6, rough cost estimates were developed

for each option to gauge the relative cost-effectiveness of employing one GHG reduction

technology versus another. This task was performed by Martec using available

information on incremental vehicle system and component hardware costs. Incremental

business costs to vehicle manufacturers or impacts on the retail price of vehicles from a

consumer perspective were not evaluated at this stage of the analysis.

24

 

23 An engine map is a graph that provides pollutant or fuel consumed at a corresponding rpm and torque

value over the full operating range of the engine.

24

In order to evaluate possible retail costs and to compare the Martec projections with costs published in

other studies, NESCCAF developed an RPE for each of the Martec costs. The RPE is discussed in section

2.6 of this chapter.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-9

Table 2-6: Vehicle Technologies Evaluated in this Study

Engine Technologies Drivetrain Technologies

Cam Phasing 5-Speed Automatic Transmission

• Single cam phaser 6-Speed Automatic Transmission

• Dual cam phaser Continuously Variable Transmission (CVT)

• Coupled cam phaser Automated Manual Transmission (6 speed)

Variable Valve Lift 42 Volt ISG - Idle Off

• Discrete Valve Events 42 Volt ISG - Launch Assist, Regen, Idle Off

• Continuously Variable Motor Assist Hybrid

Fully Integrated Hybrid

Aggressive Shift Logic

Camless Valve Actuation

• Electromagnetic Actuation

• Electrohydraulic Actuation Early Torque Converter Lock-up

Other Load Reducing Technologies

Advanced Power Steering

Turbocharging

• Variable Geometry

• Electric Assist

• Electrohydraulic

Cylinder Deactivation • Electric

Variable Compression Ratio Electric Oil and Water Pumps

Variable Charge Motion Improved Alternator

Gasoline Direct Injection - Stoichiometric Engine Friction Reduction

Gasoline Direct Injection - Lean Burn

Stratified Charge

Improved Lubricating Oil

Gasoline Homogeneous Charge Compression

Ignition

Air conditioning technologies and refrigerants

Diesel High Speed Direct Injection Vehicle Technologies

Diesel Advanced Multi-Mode Combustion Aerodynamic Drag Reduction

Mass Reduction

Improved Tire Rolling Resistance
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-10

Overall, the study encompassed technologies that are either already in production

for the U.S., European, or Japanese car markets or known to be planned for production in

these markets; technologies identified by AVL or by other members of the NESCCAF

GHG Study Team; and technologies defined in the automotive literature. Through

discussions with AVL and other members of the study team, Martec assembled detailed

functional definitions of each of the GHG reduction technologies as they were modeled

by AVL. This detail was especially important in instances where a technology option

covered a wide variety of functional definitions and mechanizations (e.g., valve train

technologies). Specifically, Martec was provided with:

• A written functional description from which a bill of materials was developed;

• A reference automotive industry technical specification for the technology;

• A reference to an existing vehicle and architecture; or

• A reference to a particular supplier implementation of the technology.

In instances where such sources were not available, Martec gathered industry

information on specific technologies using interviews and technical papers. Field

interviews were conducted with individuals representing all aspects of the automotive

industry, including the management, engineering, purchasing, finance, planning and

product management divisions of both manufacturers and parts suppliers. Wherever

possible, information gleaned from technical papers was verified in interviews. In

general, Martec sought to obtain input from two or more automakers and two or more

suppliers for each technology studied.

Figure 2-1 illustrates the methodology used by Martec to develop technology cost

estimates for this study. Generally speaking, it was not necessary to investigate the

design details of different technologies except in some cases where these details needed

to be understood to reconcile differences in the cost estimates provided by various

sources. Ultimately, all of the costs used in the analysis represent industry-accepted

technology applications that also meet the functional requirements provided by AVL.

The results of Martec’s cost analysis were reported in the form of a matrix which

allows for easy calculation of the net, vehicle-level difference in hardware costs (relative

to a baseline vehicle) for any given package of technologies applied to each of the five

different vehicle types studied for this analysis. The cost matrix is summarized in Chapter

3 which presents the results of this study, and is detailed in Appendix C. Net hardware

costs in this context include system and component costs, as well as applicable credits in

instances where the use of a particular technology would reduce other component or

system costs (for example, some technology packages evaluated eliminate the need for

EGR). Credits were also included for downsizing engines when certain technologies,

such as turbochargers, were applied. Finally, separate cost estimates were developed for

some technology combinations that involved overlapping systems or costs – such as

variable valve lift and cylinder deactivation systems.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-11

Validation &

Analysis



Government 

Academia

Others

• Advanced Engineering

• R&D

• Vehicle platforms

• Finance

• Planning & policy

Vehicle OEMs

• Advanced Engineering

• Product Mgmt.

• Marketing

• Finance

Powertrain Groups

• Engineering

• Product Mgmt.

• Marketing

• Sr. Mgmt.

Tier II Suppliers

• Pre-production

• Contract engineering

Technology

Report Out

Initiation:

• Functional Definition

• Bill-of-Materials

Definition

• Engineering

• Product Mgmt.

• Marketing

• Sr. Mgmt.

Tier I Integrators

Figure 2-1: Overview of the Martec Costing Methodology

As noted at the outset of this section, Martec’s cost estimates do not attempt to

capture all costs to the manufacturer of incorporating new technologies, nor do they

include estimates of cost impact at the consumer level as reflected in the purchase price

of a new vehicle. Additional manufacturer-level costs that were not captured in this

analysis but that could be associated with the use of new technologies include:

• Engineering costs, including advanced R&D, vehicle design and development

engineering for integrating new technologies and software development;

• Warranty and possible recall costs;

• Factory capital costs associated with vehicle-level technology changes;

• Manufacturing costs for powertrain or vehicle assembly.

The costs described by Martec represent an estimate of the cost to the

manufacturer for the hardware needed to incorporate a given GHG-reducing technology

on a high-volume production vehicle. Associated system-level material content such as

wires, control module drivers, etc. are included in these estimates – if purchased from a

supplier, these all represent a variable cost to the automaker. However, the estimates do

not necessarily capture the complete set of variable costs that might be associated with

the introduction of new technologies – for example, applying some technologies might

require body and chassis re-designs that would in turn incur additional costs.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-12

For purposes of estimating net hardware costs, all baseline vehicles are assumed

to use gasoline stoichiometric control systems and exhaust aftertreatment systems. In

addition, all are assumed to be average vehicles using EGR systems. The incremental

cost of exhaust aftertreatment was included when assessing net cost differences for

engine-type technologies. All study vehicles (baseline and future technology packages)

were required to meet the U.S. Tier 2, Bin 5 emissions standards using systems forecast

for usage in the 2009 model year. A consistent scalable model for stoichiometric

aftertreatment systems was applied by Martec for all vehicles. Lean burn (gas and diesel)

aftertreatment systems, based upon designs provided by AVL and NESCCAF from other

industry sources, were also costed by Martec.

All costs are presented in 2003 U.S. dollars and assume that the subject

technologies will be manufactured in a highly competitive environment using flexible

and lean manufacturing methods.

25 Costs are estimated for the year 2009 and beyond

assuming that each manufacturer (automaker or supplier) will produce at least 500,000

units per year, thereby achieving full economies of scale. A flexible and lean

manufacturing environment presumes fast execution of the cost and quality learning

curves for the product design and manufacturing process. It is therefore a key

assumption underlying the cost estimates and was clearly specified in all industry

interviews and analyses concerning the likely costs of different technology advances.

More specifically, Martec assumed that at least three high-volume automakers would use

each technology at volumes of at least 500,000 units per year and that at least three

competing suppliers were available to supply each automaker for each technology. This

would create a highly competitive purchasing environment that would drive prices and

costs to competitive levels. In addition, Martec assumed that the cost of each technology

to the vehicle manufacturer would be the same whether it was provide by an outside

supplier or made by the manufacturer. Generally speaking, the resulting cost estimates

for each technology represent the least costly product option that meets the technology

functional requirements and is recognized as viable in the industry. Importantly, Martec

did not assume future cost reductions due to currently unknown advances in either

technology design or manufacturing - future costs reflect fully learned, high-volume

production of current technology designs. To the extent that basic scientific advances in

design or manufacturing do occur, future costs may be lower than estimated.

2.4. Assembling Technology Packages for Model Simulation

Using the most promising individual technologies that emerged from the initial

screening evaluation described above, in combination with cost estimates for the

individual technologies, a series of technology packages was assembled for each vehicle

class. Generally, these packages were designed to span the full range of CO2 reduction

potential (i.e., from modest to substantial reductions), so they necessarily reflect a range

of impacts (and costs). The specific packages evaluated, along with the model simulation

results for each package are presented in the next chapter (Chapter 3).

A full CRUISE simulation was then performed for each technology package,

using the performance constraints identified for 2009 models. In cases where the

 

25 Lean manufacturing methods involve creating manufacturing modules of modest volumes and

duplicating those modules for additional volume.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-13

technology package being analyzed produced performance benefits over and above the

forecast baseline, the vehicle engine was downsized or the vehicle axle ratio was adjusted

so that estimated emissions benefits reflect constant vehicle performance. As indicated

earlier in this chapter, the CRUISE software is designed to simulate CO2 emissions and

vehicle performance for different combinations of engine and driveline technologies. For

this project, vehicle performance includes full-load acceleration from rest to 60 mph,

from 50 mph to 70 mph in top gear (representing a passing situation), full-load climbing

performance at curb and gross vehicle weights, and the maximum velocity of the vehicle.

Additional detail about the CRUISE simulations is provided in Appendix B.

An important benefit of simulating the performance of technology packages,

rather than individual technologies, is that it eliminates the possibility that CO2

reductions will be “ double counted.” The emissions benefits associated with various

options are not necessarily additive when these improvements are combined in a single

vehicle, particularly to the extent that many technologies target the same sources of

mechanical or thermodynamic inefficiency. The simulation modeling conducted for this

analysis avoids this problem. At the core of each simulation is an engine map that defines

CO2 emissions over a full range of engine speed and load points. Each map reflects the

contribution of all engine technologies incorporated in the vehicle and therefore accounts

for their composite impact on CO2 emissions. Engine maps were completely replaced for

each technology package simulated in this analysis; they were not added or otherwise

manipulated. In the case of technologies that do not directly affect the engine map but

rather the point on the map at which a vehicle is operating (e.g., transmission

technologies), the simulation model ascribes benefits to those technologies (in

combination with all other included technologies) in accordance with their cumulative

effect on engine operation. Thus, at any given point in time, the vehicle is simulated as

operating at one speed/load point as determined by the combination of technologies

present; in turn, the specific CO2 emissions rate for that point in time is simply read from

the underlying engine map.

The following example briefly illustrates how this process works. As described

above, combinations of technologies are modeled as a complete vehicle system. Take,

for example, a technology package consisting of a combination of variable valve timing,

cylinder deactivation, and 6-speed automatic transmission technologies. For a specific

vehicle platform, each technology individually offers a reduction in CO2 emissions as

presented below in Table 2-7 (which, in this case, reflects modeling for the large car

class). However, when modeled in combination, the package provides a reduction that is

somewhat less than the sum of the individual technology benefits. The reason for this is

that each of the three technologies reduces a portion of the throttling loss encountered at

part loads (when the engine is pumping against a partially closed throttle). Once a

portion of the loss has been addressed by one technology, that loss has been eliminated

and cannot be reduced by another technology.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-14

Table 2-7: Comparison of Individual versus Combination Benefits

Technology

Individual

CO2 Emissions

Impact (%)

Dual Cam Phaser -4.3

Cylinder Deactivation -6.2

6-Speed Automatic -2.8

Combination Impacts

Combination Total (Additive) -13.3

Combination Total (Multiplicative) -12.7

Actual Simulated Combination Impact -10.8

Dual cam phasing allows engine load to be reduced by increasing valve overlap

and internal EGR rather than by closing the throttle. As a result, CO2 emissions are

reduced in the partial-load region. At this same speed and load point, a large-car engine

equipped with dual cam phasing emits 4.3 percent less CO2 than an engine not equipped

with the technology.

Cylinder deactivation reduces CO2 emissions by deactivating half of the engine

cylinders at operating points where desired power can be met with a reduced

displacement engine. This forces the cylinders that remain active to operate at higher

load, requiring less throttling (and lower losses). For example, to provide the same

output as the dual cam phaser equipped engine operating at 1914 rpm (revolutions per

minute) and 2.48 BMEP (brake mean effective pressure), the deactivated engine operates

at about 1877 RPM and 3.27 bar BMEP. This higher average operating load results in

about 6 percent less CO2 emitted over the FTP75 cycle.

A 6-speed automatic transmission reduces CO2 emissions by offering more

transmission gear ratios, thereby allowing engine speed and load to be shifted towards

more efficient operating points while maintaining constant power. This is similar to the

benefits for an engine operating with deactivated cylinders, but occurs in all modes of

operation. Compared to the baseline large car, a vehicle equipped with a 6-speed

automatic reduces CO2 emissions by about 3 percent on the FTP75 cycle.

Combined Package Benefits – Since the 6-speed transmission and cylinder

deactivation technologies both shift engine operating points toward higher loads, it is

important to note the effect of the load shift on engine CO2 emissions. At the higher load

condition, the dual cam phaser equipped engine emits about 3 percent less CO2 than the

baseline engine versus 4.3 percent for the cam phaser technology considered alone (as

presented in Table 2-7). This reduction in CO2 emissions impact is due to the fact that at

higher loads, the CO2 emissions difference for the two engines becomes less pronounced.

Furthermore, although the 6-speed automatic and cylinder deactivation technologies both

shift engine operating load higher, the shifts are not additive. This effect, plus the

reduced benefit for the dual cam phaser equipped engine at higher loads, explains the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-15

difference between the sum of the individual technology benefits and the benefits of

those same technologies considered as a package.

2.5. Assessment of Additional Technologies

A number of additional technologies were evaluated using a combination of

CRUISE simulations and available literature data. These include: low rolling resistance

tires, low viscosity lubricating oil, early torque converter lockup, vehicle mass reduction,

engine friction reduction, aerodynamic drag reduction, aggressive shift logic, air

conditioning technology impacts, and hybrid vehicle technology.

For low rolling resistance tires, aerodynamic drag reduction, and vehicle mass

reduction, AVL developed impact estimates (expressed as coefficients defining the

percent CO2 reduced per percent change in the associated force coefficient) through

simulation using CRUISE for the small car and large truck categories.

26 Based on these

coefficients together with estimates of associated reductions in rolling resistance and

aerodynamic drag forces taken from existing technical literature, a conservative estimate

of potential CO2 reductions was developed for each of these technologies. Limited

simulations of these technologies by AVL indicates that when applied in a constant

performance scenario, substantial engine downsizing may be possible, so that the derived

impact coefficients present a very conservative picture of the overall CO2 reductions

possible.

Literature data were used to assess the CO2 reduction potential of early torque

converter lock-up, aggressive shift logic, engine friction reduction, and improved

lubricating oil. In all cases, a small fraction of the maximum potential benefits for each

option was assumed in ascribing CO2 reduction benefits to these technologies. This was

done to avoid ascribing too large a benefit to technologies not fully evaluated through

simulation modeling. In addition, for early torque converter lock-up and aggressive shift

logic, a conservative approach was taken in recognition of the potential driveability

issues associated with early upshifting and associated drivetrain harshness and vibration.

However, it should be recognized that reductions considerably larger than those assumed

in this study may be possible.

Table 2-8 provides a summary of the CO2 emissions reduction estimated for each

of these technologies. For each technology package modeled by AVL, an additional CO2

reduction was assumed for the application of some or all of the technologies described

above. For vehicles with automatic transmissions and automated manual transmissions, a

5 percent reduction was applied. For vehicles with continuously variable transmissions a

4 percent CO2 reduction was applied. Finally, cost estimates for these additional

technologies (as shown in Table 2-8) were developed using the same literature review.

Given that a range of estimates for both CO2 reduction and cost was generally provided in

the literature, a methodology to develop a single CO2 reduction and cost estimate was

required. To resolve these data, the median of the combined estimated cost range for all

technologies was divided by the median of the combined estimated CO2 reduction range

to derive an estimated cost per percent CO2 reduction. This median estimate was

 

26 Average coefficients are as follows: 0.2 percent CO2 reduction per percent aerodynamic drag or rolling

resistance reduction; 0.6 percent CO2 reduction per percent mass reduction.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-16

developed both with and without mass reduction technology to allow for the separate

treatment of mass reduction. Since mass reduction was not investigated as a major CO2

reduction technology in the study, the estimated unit cost without mass reduction was

then multiplied by the assumed CO2 reduction indicated in Table 2-8 to derive the total

estimated marginal price of a combination of these technologies achieving the targeted

CO2 reduction. Actual marginal price could be higher or lower depending on the specific

combination of technology chosen for implementation. This estimated marginal price

was added to the incremental vehicle cost for all scenarios in which these additional

technologies were assumed. As stated, the additional technologies package did not

include weight reduction, although information on weight reduction is included in the

table.

2.5.1. Air Conditioning

An independent evaluation of the impacts of vehicle air conditioning systems on

vehicle CO2 and HFC emissions was conducted by Meszler Engineering Services (MES).

In this evaluation, the results of which are included as Appendix D of this study, MES

evaluated the magnitude of GHG emissions that result from air conditioning systems due

to both the increased load placed on a vehicle engine and refrigerant leakage. To

incorporate the results of this evaluation into the simulation modeling conducted by

AVL, MES developed representative air conditioning load curves for air conditioning

systems typical of current vehicle technology and increased efficiency technology. For

purposes of this analysis, the assumed baseline system is an HFC-134a system utilizing a

pneumatically (freeze point) controlled fixed displacement compressor, while the

increased efficiency system is an HFC-152a system utilizing an externally controlled

variable displacement compressor and forced air recirculation. Both load curves were

developed to be representative of typical ambient conditions experienced during air

conditioning operation in the U.S.

To evaluate the impact of air conditioning use, AVL performed a series of

simulations in which baseline air conditioning loads were added to the normal loads

encountered over the study driving cycles. The additional CO2 emissions that result from

air conditioning use were added to the baseline CO2 emissions predicted by CRUISE

modeling for a corresponding technology scenario without air conditioning. A second

simulation was then conducted with the alternative (i.e., externally controlled variable

displacement) air conditioning system to determine the CO2 reduction impact. It should

be recognized that under either air conditioning scenario, CO2 emissions are greater than

the corresponding scenario without air conditioning, so that the benefits of improved air

conditioning systems cannot be subtracted from a “ no air conditioning” scenario. It

should also be recognized that the effect of refrigerant leakage is independent of vehicle

operation and does not affect the CO2 emissions predicted by CRUISE. As a result,

while benefits associated with reduced leakage have been calculated as described in the

MES report in Appendix D, these benefits do not show up in the simulation modeling.

Reduced leakage benefits are incorporated into the simulation results by adding the

estimated per-mile changes in refrigerant leakage rates, expressed as CO2 equivalent

emissions, to the CRUISE-generated CO2 emission estimates.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 2-8: Impacts and Costs of Additional CO2 Reduction Technologies

Transmission Type Technology Automatic Automated Manual CVT

Impact 10% reduction in rolling resistance = 2% reduction in CO2 Improved Tires Cost $20 to $90 retail price equivalent (RPE)

Engine Friction Reduction or Impact Reduced internal friction/lower viscosity oil, 0.5% CO2 reductio

Improved Lubricating Oil Cost $5 to $15 RPE

Impact 8-10% reduction in drag = 1.5-2% reduction in CO2 Aerodynamic Drag Reduction Cost $0 to $125 RPEImpact 1.5% CO2 reduction 0.5% CO2 reduction Aggressive Shift Logic Cost $0 to $50 RPE $0 to $20 RPE None

Improved Torque Converter or Impact 0.5% CO2 reduction

Early Lockup Cost $0 to $10 RPE None

W Impact 5% reduction in mass = 3% reduction in CO2 eight Reduction Cost $180 to $300 RPETotal Potential Impact 6% to 6.5% CO2 4.5% to 5% CO2 4% to 4.5% CO2(without Weight Reduction) Cost $25 to $290 RPE $25 to $250 RPE $25 to $230 RPETotal Potential Impact 9% to 9.5% CO2 7.5% to 8% CO2 7% to 7.5% CO2(with Weight Reduction) Cost $205 to $590 RPE $205 to $550 RPE $205 to $530 RPE

w/o WR $25 $29 $30 Average RPE per Percent CO2w/ WR $43 $49 $51Impact 5% CO2 reduction 5% CO2 reduction 4% CO2 reduction Assumed Improvement Cost $125 RPE $145 RPE $120 RPE

Notes: (1) Impacts and costs are based on estimates from available data which is summarized in Chapter 3 and detailed in

Appendix B.

(2) Torque converter improvement estimates from Documentation of Technologies Included in the NEMS Fuel

Economy Model for Passenger Cars and Light Trucks, Energy and Environmental Analysis, Inc., 2002.

(3) Simulation modeling by AVL for this study established CO2 percent per percent change coefficients of 0.2 for

rolling resistance and aerodynamic drag reduction and 0.6 for mass reduction.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-18

2.5.2. Methane and Nitrous Oxide Emissions

An independent evaluation of methane and nitrous oxide emissions was also

conducted by MES. In this evaluation, the results of which are included as Appendix E,

MES evaluated the GHG emissions contributions of methane and N2O from both current

and future (i.e., 2009-2015) vehicles. Current emission rates were estimated on the basis

of actual emissions test data; these data were also used to derive relationships between

methane and other organic compound emissions and between N2O and NOx emissions.

Expected future emission rates of methane and N2O were then developed by applying

these relationships to expected future emission rates of organic compounds and NOx.

2.5.3. Hybrid Vehicle Assessment

As described above, the benefits of mild-hybrid (i.e., 42 Volt ISG) technology

were evaluated using the CRUISE simulation code. However, the level of effort required

to construct and validate CRUISE control modules for more advanced, combination

internal combustion engine and motor drive systems was prohibitive. Therefore, the

impacts of what we call "motor assist" and "fully integrated" hybrid technology were

estimated using current vehicle certification data in combination with technology cost

estimates developed for this study. The use of certification data to estimate CO2 impacts

is beneficial in that the derived impacts are based on actual production vehicle data, but

this approach may be conservative in that it assumes no additional technology

improvements between now and 2009-2015.

The impacts of motor assist hybrid vehicle technology are based on the 2004

Honda Civic Hybrid, which employs parallel hybrid technology using a 10 kW

permanent magnet motor. The impacts of the fully integrated hybrid vehicle technology

are based on the 2004 Toyota Prius, which employs combination series/parallel hybrid

technology using a 50 kW permanent magnet motor and a 30 kW generator. Both

vehicles generate the bulk of their CO2 emission reduction impacts through three primary

mechanisms:

• A reduction in internal combustion engine size, allowing a wider range of

operations to be accomplished in regions of high efficiency.

• The capture, storage, and reuse of braking energy.

• The deactivation of the internal combustion engine during periods of vehicle

deceleration and stopping.

However, both the Civic and Prius also incorporate additional technologies that

contribute to CO2 reduction impacts, while adding to incremental costs. Thus, neither

vehicle can be considered in the context of its power electronics alone, since when

viewed as a package (as is the case in this study) both vehicles include non-electronic

technologies not generally found on other conventional vehicles.

The package of technologies that constitute the Civic and Prius can only be

established relative to a specific conventional vehicle. Ideally, the comparative vehicle

will employ technologies consistent with those of the specific vehicle class of which it is
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-19

a component. While there are non-hybrid Civics that could serve as a point of

comparison, conventional Civics generally employ technology that is somewhat more

advanced than average small car technology. Since accounting for the impacts of these

“ non-average” technologies further complicates the comparative process, the

conventional Civic is not used as a comparative basis in this study. The Prius has no

direct conventional counterpart.

In addition to the basic technology consistency criteria, determining the CO2

reduction impacts of hybrids from vehicle certification data also demands a comparative

vehicle that has a 25-50 percent larger engine displacement and performance

characteristics similar to that of the comparative hybrid. The engine displacement offset

is desirable to provide a comparative vehicle that would be similar in displacement to the

hybrid vehicle if the conventional vehicle were converted to hybrid with its

accompanying engine downsizing. The equivalent performance requirement is intended

to ensure that the conventional and hybrid vehicles are approximately equal from a

consumer utility standpoint.

Based on these criteria the conventional vehicle selected for comparison to the

Toyota Prius was the 2004 2.4-liter 4-cylinder automatic transmission Toyota Camry. At

1.5-liters, the engine displacement of the Prius is about 38 percent lower. The Camry

accelerates from 0-60 mph in about 9.2 seconds, while Prius is a bit slower at about 10

seconds. With a difference of less than 10 percent, this is superior to other comparative

alternatives in the large car class. Nevertheless, it should be recognized that there is a

small performance loss associated with the resulting CO2 impact estimates. Compared to

the Camry, the Prius emits about 53 percent less CO2 per mile (approximately 158 grams

per mile compared to 333 grams per mile). Therefore, the CO2 reduction impact of the

fully integrated hybrid is estimated to be 53 percent in this study.

In addition to the introduction of the basic hybrid components (i.e., batteries,

motor, generator, inverter, and control system), the Prius also exhibits the following

technology differences relative to the Camry. It has a drag coefficient that is

approximately 10 percent lower, at 0.26 versus 0.28. It has a curb weight that is

approximately 300 pounds lower, at 2,900 pounds versus 3,200 pounds. This weight

difference is in addition to the estimated 290 pounds required to offset the introduction of

the hybrid electronic system. Thus, a total weight offset of 590 pounds is required to

generate Prius-type CO2 emission improvements relative to the base Camry. In cases

where associated engine downsizing would result in a reduction in cylinder count, there is

an associated weight savings estimated to be approximately 150 pounds. This savings

would accrue for 6 and 8 cylinder vehicles converted to hybrid power, as each is assumed

to drop 2 cylinders in moving to 4 and 6 cylinder internal combustion engines

respectively. Since vehicle and technology weight will vary by vehicle class, the

estimated weight reduction to produce CO2 reductions at the estimated rate (i.e., 53

percent) is best expressed algebraically as:

( )

Downsizing Weight Savings

Electronics/Battery Weight

Base Conventional Weight

Camry Weight

Prius Weight Weight Reduction 1

−

+ 











= −
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-20

Finally, to facilitate the attainment of the estimated 53 percent CO2 reduction rate

across each of the five vehicle classes investigated in the study, the electronics and

batteries employed in the Prius were resized for each vehicle class in accordance with the

ratio of the class average rated horsepower to the rated horsepower of the Camry. This

results in larger electronic systems for the large car, small truck, large truck, and minivan

classes and a smaller system for the small car class. On the basis of these adjustments,

the following weight reduction requirements were estimated for the study classes:

• Small Car ......... 530 pounds

• Large Car ......... 490 pounds

• Small Truck ..... 520 pounds

• Large Truck ..... 690 pounds

• Minivan ............ 590 pounds

It is perhaps important to emphasize three issues related to the estimated weight

reductions. First, a substantial portion of the estimated reduction is associated not with

downsizing, but with offsetting the added weight of the electronic components. A small

(less than 10 percent) weight reduction results from the fact that the estimated CO2

reduction was determined relative to the 2.4-liter Camry, which is heavier than the Prius.

Second, the weight reduction required in the small car class is higher than that for the

large car class because the weight advantage of engine downsizing is essentially

unavailable in the small car class. Finally, even though the Prius is in the large car class

as defined in this study, its CO2 impacts were assessed relative to the 2.4-liter Camry that

is substantially underpowered relative to the large car class average. Thus, the fully

integrated hybrid evaluated for the large car class was upsized relative to the 2004 Prius.

Each of these technology differences is accounted for in the associated cost

estimates for the fully integrated hybrid, using the technology-specific incremental cost

impact described in the previous sections. In addition, the Prius includes an electronic

CVT, but this cost is subsumed in the power electronics cost estimates presented below.

Additional costs are also imposed for an intake cam phaser required to allow internal

combustion to take place over the Atkinson/Miller cycle, as well as for electronic power

steering and electric accessories (which were employed in all hybrid vehicle scenarios in

this study).

The motor assist hybrid impact and cost estimates developed for this study

essentially adhere to an analogous approach conducted for the Honda Civic Hybrid. The

conventional vehicle selected for comparison to the 2004 Civic was the 2004 2.2-liter

4-cylinder automatic transmission Chevrolet Cavalier. At 1.34-liters, the engine

displacement of the Civic Hybrid is about 40 percent lower. The Cavalier accelerates

from 0-60 mph in about 8.2 seconds, while Civic is over 35 percent slower at about 11.3

seconds. Due to this substantial difference, an additional adjustment was employed in the

motor assist hybrid analysis that increased the output (i.e., size) of the Civic electronics in

accordance with the horsepower ratio of the Cavalier to the Civic. This results in a 50

percent upsizing of the Civic electronic system (and adds additional weight that must be

offset to maintain the estimated CO2 reduction), and is expected to bring the acceleration

performance into better agreement with the Cavalier. However, as was the case with the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-21

Prius, it is likely that there is a small performance loss that accompanies the resulting

CO2 impact estimates. Compared to the Cavalier, the Civic emits about 45 percent less

CO2 per mile (approximately 185 grams per mile compared to 334 grams per mile).

Therefore, the CO2 reduction impact of the motor assist hybrid is estimated to be 45

percent in this study.

As was the case with the Prius, the Civic also exhibits non-hybrid technology

differences relative to the Cavalier. It has a drag coefficient that is approximately 20

percent lower, at 0.28 versus 0.36. The curb weights of the two vehicles are

approximately equal, at 2,660 pounds (Civic) versus 2,680 pounds (Cavalier), but weight

reduction is still required to offset the introduction of the hybrid electronic system.

However, relative to weight offsets estimated for the Prius, the required offsets for the

Civic are significantly smaller and in cases where the associated engine downsizing

would result in a reduction in cylinder count, the estimated weight savings of

approximately 150 pounds continues to apply. Since vehicle and technology weight will

vary by vehicle class, the estimated weight reduction to produce CO2 reductions at the

estimated rate (i.e., 45 percent) is best expressed algebraically as:

( )

Downsizing Weight Savings

Electronics/Battery Weight

Base Conventional Weight

Cavalier Weight

Civic Weight Weight Reduction 1

−

+ 











= −

To facilitate the attainment of the estimated 45 percent CO2 reduction rate across

each of the five vehicle classes investigated in the study, the electronics and batteries

employed in the Civic were resized for each vehicle class in accordance with the ratio of

the class average rated horsepower to the rated horsepower of the Cavalier. This results

in larger electronic systems for the large car, small truck, large truck, and minivan

classes. On the basis of these adjustments and the performance adjustment previously

described, the following weight reduction requirements were estimated for the study

classes:

• Small Car ......... 200 pounds

• Large Car ......... 90 pounds

• Small Truck ..... 90 pounds

• Large Truck ..... 140 pounds

• Minivan ............ 90 pounds

Once again, it should be emphasized that the estimated weight reduction is

associated not with downsizing, but with offsetting the added weight of the electronic

components. As with the Prius, the weight reduction required in the small car class is

higher than that for the large car class because the weight advantage of engine

downsizing is unavailable in the small car class. Finally, due to the electronics upsizing

adjustment intended to improve the performance of the Civic relative to the Cavalier,
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 2-22

even the motor assist hybrid system for small car class (of which the Civic is a part) is

upsized relative to the 2004 Civic.

Like the Prius, each of these technology differences is accounted for in the

associated cost estimates for the motor assist hybrid, using the technology-specific

incremental cost impacts described in the previous sections. The Civic Hybrid includes a

CVT, but this cost is included along with the power electronics cost estimates in the

package costs presented below and is, therefore, not costed separately. Additional costs

are, however, incurred for a discrete variable valve lift system with intake cam phasers to

facilitate the lean burn combustion characteristics of the Civic, as well as for electronic

power steering and electric accessories (which were employed in all hybrid vehicle

scenarios in this study).

2.6. Cost-Benefit Analysis

For each of the technology packages described above, an incremental vehicle cost

was determined and is presented in the results section (Chapter 3). Since the Martec

costs were reported as costs to the manufacturer, a conversion of the Martec data to retail

price equivalent was performed. To convert the Martec costs, NESCCAF used a retail

price equivalent mark-up of 40 percent based on the RPE used in the 2002 National

Academy of Sciences study.

27

Using incremental vehicle costs, a cost-benefit analysis was performed for each of

the technology packages. In addition to incremental vehicle cost, this analysis takes into

account the savings realized through reduced fuel-use over the life of the vehicle.

Lifetime cost-savings were estimated using two possible gasoline prices: (1) the 2003

U.S. average gasoline price of $1.58 per gallon available from the Energy Information

Administration

28

and (2) a higher price of $2.00 per gallon. Further assumptions used in

this analysis included:

- vehicle life of 12 years

- 15,600 miles traveled in the first year, declining 4.5% each year thereafter

29

- a 5% discount rate for the net present value (NPV) fuel savings calculation

The next Chapter provides final results for the cost-benefit as well as emissions reduction

portions of the analysis

 

27 National Academy of Sciences, “ Effectiveness and Impact of Corporate Average Fuel Economy (CAFE)

Standards,” National Academy Press, 2002

28 Energy Information Administration

http://www.eia.doe.gov/oil_gas/petroleum/data_publications/wrgp/mogas_history.html

29 U.S. Department of Transportation, 1995 National Personal Transportation Survey (NPTS)

http://nhts.ornl.gov/2001/index.shtml
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-1

3. Results of Greenhouse Gas Emission Reduction Analysis

3.1. Overview

The methodological approaches described in Chapter 2 and detailed in

Appendices A through E were used to predict the CO2 emission impacts and costs

associated with deploying a variety of automotive technologies on future light-duty motor

vehicles. Potential reductions in emissions of methane and nitrous oxide were separately

evaluated to provide for a full accounting of total GHG-reduction potential. In this report,

technical feasibility results and costs are presented for five classes of vehicles: "large

car," “small car,” “ minivan,” “small truck/SUV,” and “ large truck/SUV.”

A total of 35 engine, transmission, and vehicle technologies were evaluated in this

analysis to quantify associated CO2-reduction potential. Currently deployed gasoline

engine technologies such as turbocharging and variable valve lift were evaluated as well

as more advanced technologies such as camless valve actuation, gasoline homogeneous

charge compression ignition, and automated manual transmissions. Hybrid electric

drivetrains and advanced diesel engines were also considered. The emission benefits of

both individual technologies and packages or combinations of these technologies were

analyzed. The study relies on a systems analysis approach that avoids the “ double

counting” that could occur by simply combining the emission reduction benefits of

individual technologies. Examples of the difference between additive benefits and more

sophisticated systems benefits were presented in the method overview to illustrate the

impact of the systems analysis approach on emission benefit projections.

The technologies evaluated in this study are described in Appendix A. This

Chapter first discusses the CO2-reduction potential of individual technologies. The

overall GHG impact and retail price equivalent cost estimates are then presented for each

of the technology packages evaluated. Given the challenges and uncertainties associated

with projecting the costs of future technologies, the cost estimates developed for this

analysis are also compared with those from other recent studies. A range of costs is

provided for individual technologies since there is considerable variation across studies.

3.2. Emission Reduction Results

As described in Chapter 2, the emissions benefit analysis conducted for this study

involved several steps. The first step was a literature survey and engineering assessment

to identify potential GHG-reduction technologies and assess their likely emission

reduction capabilities. Actual vehicle models from the U.S. fleet were selected to

represent each of the five classes of light-duty vehicles evaluated in this study. The study

employed AVL’s CRUISE software program and other approaches to assess the GHG

impacts of individual technologies for each vehicle class. Candidate technologies were

ranked and those suitable for further analysis were identified. These included both standalone technologies and those appropriate for inclusion with other technologies in

combination packages. A systems analysis was subsequently conducted for the selected

technology packages. The results of these analyses are presented in the following

sections.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-2

3.2.1. GHG Emission Reduction Potential for Individual Technologies

Individual technologies were first evaluated to aid in the selection of options for

inclusion in technology packages or combinations which were then subjected to more indepth evaluation using the CRUISE simulation code (as described in detail in the

methodology section). This initial evaluation was designed to provide approximate CO2-

reduction estimates for use solely in the context of selecting technologies for further

investigation. The results of this analysis are presented in Appendix B.

Because this first part of the study served a preliminary screening function, not all

technologies were evaluated using full model simulations. Therefore, in many cases the

full benefits of individual technologies are not captured. For example, the benefits of

technologies that both improve performance and lower GHG emissions may not be fully

characterized since additional benefits available through engine downsizing are not

necessarily reflected. Some technologies were evaluated using full CRUISE simulations,

others using partial CRUISE simulations, and others using data from the published

literature.

30

Individual technologies produced a broad range of projected CO2 reductions. The

analysis indicates that evolutionary engine and drivetrain technologies generally provide

reductions ranging from a few to ten percent. The technologies offering the most

significant GHG reductions (13-27 percent) are diesel advanced multi-mode (partial

HCCI) and direct injection diesel engines and hybrid electric drivetrains (42-53 percent

reductions). Other technologies showing significant reduction potential are 42-volt ISG

(5-10 percent); electrohydraulic camless valve actuation (11-16 percent); 6-speed

automated manual transmissions (5-8 percent); turbocharging (6-8 percent); and variable

valve lift (4-6 percent). The results for all technologies are reasonably consistent across

the five vehicle classes.

Additional GHG-reduction benefits are also achieved through reduced emissions

of methane (CH4) and nitrous oxide (N2O), as well as through reduced CO2 emissions

associated with air conditioner (A/C) operation. AVL conducted simulation modeling of

an alternative A/C system design on the basis of a thorough analysis of the impacts of

A/C system technology as described in Appendix D. Based on that analysis, AVL

modeled the CO2 emissions impacts of an HFC-152a system using an externally

controlled, variable displacement compressor (VDC) and forced air recirculation relative

to the emissions associated with a baseline HFC-134a system using a pneumatically

(freeze point) controlled, fixed displacement compressor (FDC). It should be noted that

CO2 emissions for both systems are greater than emissions under an “ A/C off” scenario,

so that improved efficiency impacts accrue relative to an “ A/C on” situation only.

Because vehicle A/C is not used all the time, the impact estimates that are included in

Tables 3-4 through 3-8 are adjusted to reflect the estimated average percentage of

operation (in miles) that the A/C system is in use (34 percent as described in Appendix

 

30

Single point (i.e., partial simulation) evaluations were conducted on technologies where the engine full

load curve did not dramatically change with the introduction of a technology. This simplified approach

was taken to allow for a greater number of full CRUISE simulations to be run during the technology

package evaluation phase of the project.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-3

D). Table 3-1 presents a summary of both the adjusted and unadjusted A/C system

impacts that are included in the CO2 emission estimates presented in Tables 3-4 through

3-8.

Table 3-1: Air Conditioning Emissions

Emissions Source

Vehicle

Class

Baseline

A/C System

Alternative

A/C System

Emissions

Change

Small Car 49.5 22.7

Large Car 56.1 25.7

Small Truck 69.2 31.8

Large Truck 69.2 31.8

Indirect Efficiency-Based Emissions

(Not Adjusted for A/C “ On” Time)

Minivan 69.2 31.8

Small Car 16.8 7.7

Large Car 19.1 8.7

Small Truck 23.5 10.8

Large Truck 23.5 10.8

Indirect Efficiency-Based Emissions

(Adjusted for A/C “ On” Time)

Minivan 23.5 10.8

-54%

Indirect Mass-Based Emissions All 1.7 1.5 -9%

Direct Leakage Emissions All 8.5 0.4 -95%

Note: Indirect mass-based emissions are not included in Tables 3-4 through 3-8 since vehicle test weights, as

simulated by CRUISE, include the weight of the A/C system.

3.2.2. Projected Cost of Technologies

As discussed in Chapter 2, this study employed a detailed approach to estimating

the costs associated with various GHG-reducing technologies. Much of the cost

information was drawn from inquiries made of automobile manufacturers and component

suppliers. Costs developed using this approach are typically conservative and could

overstate the actual cost that consumers will pay once the technologies are mass

produced, since significant challenges and uncertainties are involved when projecting the

actual cost of future technologies. To provide policymakers with the best available

information, this section presents the RPE cost estimates developed using Martec’s

hardware cost projections for this study along with those of other recent studies. Table

3-2 compares the estimated retail price equivalents developed as part of this study for the

large car class with cost projections from other recent studies. The cost estimates

developed specifically for this study are presented in the column headed “study RPE.” (In

the case of diesel HCCI, a range is presented since the potential cost was subject to a

greater level of uncertainty than typical of other costs.) Cost estimates from other recent

studies are presented in the column headed “ Literature RPE”. In general, the estimates

developed by Martec for this study are within the range of costs predicted by other

studies.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-4

Table 3-2: Comparison of Study RPE with Literature RPE

Technology Study RPE Literature RPE

Single Cam Phaser $98 $18-$70

Couple Cam Phasers $161 $35-$140

Dual Cam Phasers $196 $35-$140

Discrete Variable Valve Lift with Intake Phasers $259 $70-$495

Discrete Variable Valve Lift with Coupled Phasers $322 $70-$495

Discrete Variable Valve Lift with Dual Phasers $357 $70-$495

Continuous Variable Valve Lift with Intake Phasers $483 $70-$495

Continuous Variable Valve Lift with Coupled Phasers $546 $70-$495

Continuous Variable Valve Lift with Dual Phasers $581 $70-$495

Electrohydraulic Camless Valve Actuation $910 $280-$600

Cylinder Deactivation (DeAct) $161 $112-$746

DeAct plus Discrete Variable Valve Lift with Intake Phasers $378 $182-$1241

DeAct plus Discrete Variable Valve Lift with Coupled Phasers $441 $182-$1241

DeAct plus Discrete Variable Valve Lift with Dual Phasers $476 $182-$1241

Stoichiometric Gasoline Direct Injection $259 $450-$750

Gasoline Homogeneous Charge Compression Ignition $581

High Speed Direct Injection Diesel $1225 $1752-$2200

Diesel Homogeneous Charge Compression Ignition $840 to $1050

6-Speed Automatic Transmission $105 $0-$280

Automated Manual Transmission $0 $0-$280

Continuously Variable Transmission $245 $0-$398

42 Volt System (Idle Off, Regen Braking, Launch Assist) $1582 $280-$1400

Motor Assist Gasoline Hybrid Electric Vehicle $2709 $1364-$3036

Fully Integrated Gasoline Hybrid Electric Vehicle $5299 $3184-$5183

Electric Accessories $70 $50

Electric Power Steering $56 $40-$150

Turbocharging $-420 $350-$837

Improved Alternator $56 $15

Table 3-3: Estimated Costs of California’s Low Emission Vehicle (LEV) Program

Vehicle CARB ‘94 CARB ‘96 ACG ‘93 AAMA ‘94 Actual

TLEV $66 $72 $273 $298-487 $35

LEV $120 $120 $788 $911-1343 $83

ULEV $227 $145 $679-1,326 $1,666-4,005 $251

Sources: The CARB and AAMA (American Automobile Manufacturers Association) figures are taken

from Cackette, 1998; the ACG (Automotive Consulting Group) figures are found in ACG, 1993.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-5

As mentioned above, cost almost always represents an area of large uncertainty

and debate because some of the technologies needed to comply with the standards have

not yet been commercialized. Historically, cost estimates are generally more

conservative and higher than actual costs, which usually prove to be lower than first

anticipated.

For example, Table 3-3 compares per-vehicle cost estimates at various points in

time from CARB and various industry sources for California’s different categories of

low-emission vehicles. These projections can be compared against the actual

implementation costs shown in the last column to the right.

As shown in Table 3-3, industry estimates of compliance costs were an order of

magnitude higher than actual costs. Similarly, the cost projections made by CARB also

overstated the actual cost of complying with the LEV standards, although by a much

smaller margin.

3.2.3. GHG Emission Reduction Potential for Technology Combinations

Based on their GHG reduction potential and, in part, on the costs of the

technologies shown above, technology combinations or packages were developed for

each of the five vehicle classes evaluated in this study. The emission impacts of these

technology packages were then evaluated using full CRUISE vehicle simulations.

Ultimately, a total of 75 simulation runs were completed for the five model vehicles

developed to represent each vehicle class.

The emissions reductions attributable to A/C system improvements and a package

of other technologies (including low rolling resistance tires, engine friction reduction, and

other improvements) were incorporated into the reduction estimates for modeled

technology packages. The A/C improvements added a 3-4 percent CO2 reduction benefit,

depending on the CO2 emissions of the vehicle when the A/C was off; the other upgrades

added a 4-5 percent CO2 reduction to non-hybrid technology packages.

While the selection of technology packages was made, in part, from a costeffectiveness standpoint, a broad spectrum of technologies were included in the modeled

packages regardless of cost, to ensure that the full range of potential CO2 reduction

options was evaluated. All of these results (not just the least-cost results) are provided in

the following sections. Tables 3-4 through 3-8 present the combined model simulation,

A/C, and additional technology benefits. The results of the AVL simulation modeling for

each package are provided separately in Appendix B, without the A/C and additional

technology benefit adjustments.

Similar technology packages were evaluated for each of the five categories of

vehicles. The results of the analysis show that deployment of technologies across all five

vehicle classes achieves comparable CO2 reductions. There are, however, some

exceptions; these are detailed in the discussions of the individual vehicle categories

below. To illustrate this point, the technology package including stoichiometric gasoline

direct injection, cam phaser, turbocharging, and automated manual transmission

technology was evaluated in four categories of vehicles— in each, this particular

technology combination provides between a 27 percent and 30 percent CO2 reduction.

Another example: the package including discrete variable valve lift, dual cam phaser, and
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-6

automatic transmission

31

technology was evaluated for all five vehicle classes and was

estimated to provide a 12-18 percent CO2 reduction in each case. The largest number of

technology packages was evaluated for the large car category. While some of these

technology combinations were not evaluated for vehicle classes other than large cars, the

consistency of results across vehicle classes suggests that similar CO2 reductions would

likely be achieved with the deployment of the same technology packages in other classes.

Large Car Results

Table 3-4 presents emission reduction and cost estimates for the 19 technology

packages modeled for the large car class. Column 1 lists the technologies included in

each combination package. Column 2 provides the combined city/highway CO2

emissions rate, in grams per mile (g/mi), of the modeled package. Column 3 lists the

percent CO2 reduction relative to the 2002 baseline technology package. Column 4 lists

the estimated retail incremental vehicle cost associated with the addition of these

technologies. Column 5 indicates the net cost of the technology package, defined as

incremental technology cost minus lifetime fuel savings.

32

The net cost analysis assumes

a price of $1.58 per gallon for both gasoline and diesel. Last, Column 6 shows net cost

per avoided ton of CO2 emissions. Note that a negative net cost means that fuel savings

more than offset the incremental cost of the emissions reduction technologies being

modeled. In other words, it equates to projected consumer savings over the lifetime of the

vehicle.

Emission reduction estimates range from 14-54 percent, relative to the 2002

baseline vehicle, for the 19 large car technology packages modeled. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 25 percent. Examples of these technologies

include 6-speed automatic transmissions, variable valve lift and timing, and cylinder

deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, 42-volt starter generators, and

diesel engine technology. For example, the combination of gasoline direct injection and

42-volt technology, along with turbocharging and advanced cam and transmission

technology, can provide a 37 percent CO2 reduction for an incremental vehicle cost of

$1,700. Even greater CO2 reductions can be achieved using hybrid-electric designs. It is

critical to recognize that while the costs of using advanced technologies are somewhat

greater than the cost of conventional gasoline technologies, fuel-cost savings to the owner

over the life of the vehicle far outweigh the additional cost in all but the most aggressive

technology packages. On a dollar per ton basis, the net cost of technology packages that

produce up to 47 percent CO2 reductions is negative, meaning that these packages result

in net cost savings to the consumer over the lifetime of the vehicle.

 

31

Five or 6-speed automatic transmission was assumed, depending on the vehicle.

32 This analysis assumes the vehicle life to be 12 years and 150,000 miles. More detail on the analysis and

assumptions are provided in Chapter 2 on methods.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 3-4: Large Car GHG Reduction Results for Combinations of Technologies

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Dual Cam Phasers, 6-Speed Automatic Transmission 305.4 14.4% 479 Dual Cam Phasers, Continuously Variable Transmission, Electric Power Steering, Improved

Alternator 304.4 14.6% 725 

Discrete Variable Valve Lift, Dual Cam Phasers, 6-Speed Automatic Transmission 300.3 15.8% 640 Continuous Variable Valve Lift, Dual Cam Phasers, 6-Speed Automatic Transmission 291.4 18.3% 864 Dual Cam Phasers, Cylinder Deactivation, 6-Speed Automatic Transmission 288.1 19.2% 640 Dual Cam Phasers, Turbocharging, 6-Speed Automatic Transmission, Electric Power Steering,

Improved Alternator 280.3 21.4% 73 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift, Intake Cam

Phasers, Automated Manual Transmission, Electric Power Steering, Improved Alternator 273.8 23.2% 1,149 

Continuous Variable Valve Lift, Dual Cam Phasers, Automated Manual Transmission, Electric

Power Steering, Improved Alternator 266.3 25.3% 890 

Stoichiometric Gasoline Direct Injection, Cylinder Deactivation, Dual Cam Phasers, Automated

Manual Transmission, Electric Power Steering, Improved Alternator 266.2 25.4% 925 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed Automatic

Transmission, 42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 261.1 26.8% 2,432 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Turbocharging, Automated Manual

Transmission, Electric Power Steering, Improved Alternator 252.5 29.2% 176 

Electrohydraulic Camless Valve Actuation, Automated Manual Transmission, Electric Power

Steering, Improved Alternator 252.0 29.3% 1,219 

Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission, 42 Volt

Integrated Starter/Generator, Electric Power Steering, Electric Accessories 248.6 30.3% 2,780 

Electrohydraulic Camless Valve Actuation, Stoichiometric Gasoline Direct Injection, Automated

Manual Transmission, Electric Power Steering, Improved Alternator 243.4 31.8% 1,478 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift, Intake Cam

Phasers, Automated Manual Transmission, 42 Volt Integrated Starter/Generator, Electric Power

Steering, Electric Accessories

232.8 34.7% 2,745 

Stoichiometric Gasoline Direct Injection, Turbocharging, Dual Cam Phasers, 6-Speed Automatic

Transmission, 42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 225.3 36.8% 1,858 

Motor Assist Gasoline Hybrid 189.9 46.7% 2,797 Fully Integrated Diesel Hybrid 163.0 54.3% 7,543 Fully Integrated Gasoline Hybrid 162.7 54.4% 5,387 
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-8

As noted in Table 3-4, the emission reduction packages evaluated in this study

include a wide range of individual technologies. Some of the most cost-effective

packages include automated manual transmissions, turbocharging, stoichiometric

gasoline direct injection, and camless valve actuation technology. Turbocharging,

especially, proves to be a very cost-effective technology in the large car and other vehicle

classes because it enables the manufacturer to downsize the vehicle engine and decrease

engine cylinder count while maintaining equal performance. As previously noted, this

study also assessed the GHG-reducing potential of technologies that are relatively

expensive, in an effort to provide a robust overview of the benefits and costs of candidate

CO2 reduction technologies. Given that future technology advances could reduce costs

for these technologies, the costs presented could be overstated. Consequently, the

complete set of technology packages does not constitute a low cost solution to any

particular CO2 reduction scenario, but rather presents a host of possible solutions across a

range of reductions and costs.

Figure 3-1 graphically depicts the relative benefits and costs of each of the

evaluated technology packages. As this figure suggests, the technology packages span a

broad range of reduction potentials and costs. For example, packages providing CO2

reduction from 14 to 30 percent (emissions between 300 and 250 g/mi CO2) encompass a

net cost range from approximately negative $1,900 (i.e., net consumer savings) to

positive $500 (i.e., net consumer cost). Clearly, a least-cost solution would favor the

technology packages in the lower end of this cost range. Nevertheless, for purposes of

this study, we have assumed a technology supply curve

33

that includes all of the

evaluated technology packages. This allows for the fact that least-cost technologies may

not be viable for some segments of the market and that vehicle manufacturers may

therefore choose not to implement specific CO2 reduction solutions across the entire

vehicle class. For example, because technologies such as automated manual

transmissions and turbocharging may be limited to a subset of the models in any class of

vehicles, a supply curve constructed solely on the basis of least-cost solutions may

understate the actual cost of a class-wide CO2 reduction solution. Including all of the

evaluated technology packages in the development of the supply curve provides a more

robust indication of likely class-wide impacts.

The solid line in Figure 3-1 represents the CO2 reduction supply curve for the

large car class. As indicated, CO2 reductions of about 45 percent (190 g/mi, relative to a

2002 vehicle at about 355 g/mi) are likely to be obtainable for a net negative cost (i.e.

lifetime fuel savings exceed incremental technology costs). The figure also includes a

second supply curve to show the results of a gasoline price sensitivity analysis in which

the assumed prices of gasoline and diesel fuel are increased from $1.58 per gallon to

$2.00 per gallon. At the higher fuel price, all but three of the technology packages reflect

negative net costs, and the costs for two of those three are very nearly at the break-even

point. A 42-volt cylinder deactivation package exhibits a net lifetime cost of $55, while

the advanced gasoline hybrid-electric vehicle exhibits a net lifetime cost of $329. The

advanced diesel hybrid still carries a net lifetime cost of about $2000. It is also important

to recognize that the costs used to develop Figure 3-1 are those estimated specifically by

 

33

For purposes of this study, a supply curve indicates the relationship between CO2 emissions reduction

potential and cost.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-9

Martec for this study, as adjusted to reflect estimated retail equivalents. If the generally

lower cost estimates of the other studies listed in Table 3-2 were considered, net costs

would be further shifted to the negative. Nevertheless, as can be seen from the dashed

line corresponding to $2.00 per gallon gasoline, vehicle owners can be expected to save

$400-$1100 over the life of a vehicle achieving a CO2 emissions rate of approximately

190 g/mi (this represents about a 45 percent reduction from an emissions rate of

approximately 355 g/mi for the baseline 2002 vehicle). Assuming a lower gasoline price

of $1.58, vehicle owners are estimated to save from $0 (i.e., no net cost) to $600 over the

life of a vehicle for the same level of emission reduction. While diesel vehicles provide

significant CO2 reductions, the higher density of diesel fuel reduces the potential benefit

of a given technology package relative to gasoline vehicles, especially as more aggressive

carbon reduction scenarios are considered. For example, the two diamonds that are

furthest to the right in Figure 3-1 represent the gasoline (lower cost diamond) and diesel

(higher cost diamond) advanced hybrid cases. While the two cases provide very similar

CO2 reductions, the net costs for the diesel hybrid are about three times those of the

gasoline hybrid (marginal vehicle costs are about 35 percent higher for the diesel

vehicle). For less aggressive CO2 reductions, diesel technology can be cost-effective as

the CO2 reductions associated with increased diesel engine efficiency are large enough to

offset the additional cost. However, it should be recognized that much of the gasoline

engine technology evaluated here is specifically designed to close the gap between

gasoline and diesel engine efficiency.

Figure 3-1: Net Vehicle Costs for the Large Car Class Given Two Gasoline Price

Scenarios

-2000

-1000

0

1000

2000

3000

4000

350 325 300 275 250 225 200 175 150

CO2 (grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per Gallon

Supply Curve @ $2.00 per Gallon
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-10

Small Car Results

Table 3-5 presents emission reduction and cost estimates for the 14 technology

packages modeled for the small car class. Column 1 lists the technologies included in

each combination package. Column 2 provides the CO2 mass emissions rate of the

modeled package. Column 3 lists percent CO2 reductions relative to the 2002 baseline

technology package. Column 4 lists the estimated retail incremental vehicle cost

associated with the addition of these technologies, as estimated from hardware costs

developed by Martec. Column 5 provides the net cost of the technology package, taking

into account associated lifetime fuel savings.

34 As in the large car results discussed

previously, the net cost analysis assumes a price of $1.58 per gallon for both gasoline and

diesel fuel. Lastly, Column 6 displays net costs per ton of avoided CO2 emissions. As

before, a negative net cost figure equates to consumer savings over the lifetime of the

vehicle as a result of fuel savings.

Emission reduction estimates range from 11-56 percent, relative to the 2002

baseline vehicle, for the 14 small car technology packages modeled. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 23 percent. Examples of these technologies

include 5 and 6-speed automatic transmissions and variable valve lift and timing.

Reductions beyond this level will require the introduction of more advanced technologies

such as gasoline direct injection and 12 or 42-volt idle off systems, which can provide a

29 percent CO2 reduction for an incremental vehicle cost of approximately $1,000. Even

greater CO2 reductions can be achieved using advanced hybrid-electric designs. On a

dollar per ton basis, the net cost of technologies producing CO2 reductions of up to 29

percent is negative, indicating net cost savings to the consumer over the life of the

vehicle.

As noted in Table 3-5, the emission reduction packages evaluated in this study

include a wide range of individual technologies. Some of the most cost effective

packages include automated manual transmissions, turbocharging, and stoichiometric

gasoline direct injection. Because this class of vehicles uses smaller engines, the use of

12-volt idle off technology was explored as an option. The results suggest that this

technology is likely to be very cost-effective for the small car class. Unlike the other

vehicle classes, cylinder deactivation was not evaluated for the small car class due to the

small size of the baseline engine. Compared to the large car class, the costs for achieving

equivalent CO2 reductions are somewhat higher for certain technologies. There are two

reasons for this result. First, technologies such as turbocharging that allow for engine

downsizing result in substantial cost reductions in the other vehicle classes as a result of

cylinder count reductions. However, at four cylinders, the base engine in the small car

class is at the minimum cylinder count considered to have broad market acceptability

from a performance and engineering standpoint. Thus, engine downsizing in the small

car class does not generate the same level of cost savings estimated for engine

 

34 This analysis assumes the vehicle life to be 12 years and 150,000 miles. More detail on the analysis and

assumptions are provided in Chapter 2 on methods.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 3-5: Small Car Results

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Dual Cam Phasers, Continuously Variable Transmission, Electric Power Steering,

Improved Alternator 270.9 10.6% 570 

Dual Cam Phasers, Electric Power Steering, Improved Alternator 270.7 10.7% 360 Discrete Variable Valve Lift, Dual Cam Phasers, 5-Speed Automatic Transmission 264.9 12.6% 521 Dual Cam Phasers, 5-Speed Automatic Transmission, Electric Power Steering,

Improved Alternator 261.8 13.6% 494 

Dual Cam Phasers, 6-Speed Automatic Transmission 261.5 13.7% 346 Discrete Variable Valve Lift, Dual Cam Phasers, Automated Manual Transmission,

Electric Power Steering, Improved Alternator 234.9 22.5% 465 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift,

Intake Cam Phasers, Automated Manual Transmission, Electric Power Steering,

Improved Alternator

230.1 24.1% 841 

Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission,

42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 225.3 25.6% 3,643 

Continuous Variable Valve Lift, Dual Cam Phasers, Automated Manual Transmission,

12 Volt Idle Off System, Electric Power Steering 217.9 28.1% 813 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Turbocharging,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 216.1 28.7% 1,128 

Gasoline Homogeneous Charge Compression Ignition, Discrete Variable Valve Lift,

Intake Cam Phasers, Automated Manual Transmission, 42 Volt Integrated

Starter/Generator, Electric Power Steering, Electric Accessories

205.7 32.1% 2,418 

Motor Assist Gasoline Hybrid 160.4 47.1% 3,504 Fully Integrated Gasoline Hybrid 137.7 54.6% 5,639 Fully Integrated Diesel Hybrid 134.9 55.5% 7,690 
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-12

downsizing in the other vehicle classes. Second, because the small car class has the

lowest baseline CO2 emissions and the lowest power to weight ratio of all the five

classes, additional reductions accrue from a more aggressive baseline and carry

somewhat higher costs

Figure 3-2 depicts the relative benefits and costs of each of the evaluated small

car technology packages. As this figure suggests, the technology packages span a broad

range of CO2 reduction potentials and costs.

35

For example, packages providing CO2

reductions from 14-30 percent (CO2 emissions between 260 and 215 g/mi) encompass a

net cost range from approximately negative $800 to positive $1,500. The estimated CO2-

reduction supply curve generated by this study considers this full range of results, rather

than only the least-cost solutions. As noted, this approach is intended to allow for a more

robust consideration of the benefits and costs of a full range of candidate CO2-reduction

technologies.

The solid line in Figure 3-2 represents the CO2-reduction supply curve for the

small car class. As indicated, CO2 reductions of about 29 percent (from an emissions rate

of 300 g/mi for a baseline 2002 vehicle to about 215 g/mi) are likely to be obtainable at

net negative cost (i.e. with net lifetime savings). The figure also includes a second supply

curve that reflects the results of a gasoline price sensitivity analysis in which the assumed

prices of gasoline and diesel fuel are increased from $1.58 to $2.00 per gallon. At the

higher fuel price all evaluated technology packages reflect negative net costs except the

advanced hybrid vehicles and a 42-volt advanced multi-mode diesel technology package.

As can be seen from the dashed line, at $2.00 per gallon of gasoline vehicle owners can

be expected to save an average of about $300-$500 over the life of the vehicle while

achieving a CO2 emissions rate of approximately 210 g/mi (a 30 percent reduction from

the 300 g/mi 2002 baseline). When gasoline prices of $1.58 are evaluated, vehicle

owners will likely save from $0 (i.e., no net cost) to $250 over the life of a vehicle for the

same level of emission reduction. As in the other vehicle classes, diesel vehicles provide

significant CO2 reductions but the higher density of this fuel reduces the potential benefit

of most of the technology options evaluated relative to gasoline vehicles. A modestly

expanded discussion of the cost of diesel CO2 reductions is included in the section on

large car results above.

 

35As stated in the discussion for the large car class, this study intentionally focused on a broad range of

technology packages that provide for an equally broad range of CO2 reduction potentials and costs. Thus,

the study has not attempted to consider only the least-cost solutions, but rather a broader range of

solutions that might better reflect the cost of CO2 reduction across the entire class of vehicles. While

least-cost solutions might be appropriate for some segments of the class, other segments might require a

somewhat more expensive solution to maintain a critical market distinction.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-13

Figure 3-2: Net Vehicle Costs for the Small Car Class Given Two Gasoline Price

Scenarios

Minivan Results

Table 3-6 presents emission reduction and cost estimates for the 14 technology

packages evaluated for the minivan class. As in the previous sections, Column 1 lists the

technologies included in each combination package; Column 2 gives the modeled

combined city/highway CO2 emissions rate; Column 3 shows percent CO2 reductions

relative to the 2002 baseline technology package; Column 4 shows estimated of

incremental retail vehicle cost; Column 5 shows net lifetime costs including fuel savings

at an average price of $1.58 per gallon for both gasoline and diesel;

36

and Column 6

shows net costs per ton of avoided CO2.

Emission reduction estimates relative to the 2002 baseline vehicle range from 14-

54 percent for the 14 minivan technology packages studied. According to this analysis,

combinations of technologies already used in some production gasoline models can

reduce CO2 emissions by approximately 25 percent. Examples of these technologies

include 5 and 6-speed automatic transmissions, variable valve lift and timing, and

cylinder deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, 42-volt starter generators, and

camless valve technology. Even greater CO2 reductions can be achieved using hybrid-

 

36 As with all the vehicle classes analyzed, vehicle life is assumed to be 12 years and 150,000 miles. See

Chapter 2 for more details.

-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

350 325 300 275 250 225 200 175 150 125 100

CO2(grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per Gallon

Supply Curve @ $2.00 per Gallon
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-14

electric designs. As with the large and small car cases, these advanced technologies are

somewhat more costly than conventional gasoline technologies but fuel cost savings to

the owner over the life of the vehicle usually far outweigh the additional cost. On a

dollar per ton basis, the net cost of technologies required to produce CO2 reductions up to

47 percent is negative, implying a net savings to the consumer.

As noted in Table 3-6, the emission reduction packages evaluated in this study

include a wide range of individual technologies. Some of the most cost-effective

packages include automated manual transmissions, cylinder deactivation, stoichiometric

gasoline direct injection, turbocharging, and camless valve actuation. As with the large

car category, turbocharging proves to be a very cost-effective technology because it

enables the manufacturer to downsize the vehicle engine and decrease cylinder count

while maintaining equal performance. Figure 3-3 depicts the relative benefits and costs

of each of the evaluated technology packages. As this figure suggests, the technology

packages span a broad range of CO2-reduction potentials and costs.

37

For example,

packages that achieve CO2 reductions of 14-30 percent (i.e. emissions rates between 350

and 285 g/mi) encompass a net cost range from approximately negative $1,600 to

negative $3. As with the vehicle classes discussed previously, the estimated CO2

reduction supply curve for minivans developed in this study considers this full range of

results, rather than only the least-cost solution, to allow for a more robust consideration

of the benefits and costs of candidate CO2-reduction technologies.

The solid line in Figure 3-3 represents the CO2-reduction supply curve for the

minivan class. As indicated, CO2 reductions exceeding 29 percent (about 285 g/mi CO2,

relative to a 2002 baseline of 410 g/mi) are likely to be obtainable at net negative cost

(i.e., while achieving lifetime savings). The figure also includes a second supply curve

that reflects the results of a gasoline price sensitivity analysis in which the assumed prices

of gasoline and diesel are increased from $1.58 to $2.00 per gallon. At the higher fuel

price, all evaluated technology packages reflect negative net costs except for the

advanced gasoline and diesel hybrids. It is also important to recognize that the costs used

to develop Figure 3-3 are those estimated by Martec specifically for this study and

adjusted to reflect estimated retail equivalents. If the generally lower cost estimates of

the other studies included in Table 3-2 were considered, net costs would be shifted

further to the negative. Nevertheless, even using Martec’s cost estimates, the dashed line

in Figure 3-3 suggests that at a gasoline price of $2 per gallon, vehicle owners can be

expected to save $800-$1,500 over the life of the vehicle with the addition of

technologies that reduce CO2 emissions to approximately 220 g/mi (a 47 percent

reduction from baseline 2002 emissions of approximately 410 g/mi). Assuming a

gasoline price of $1.58, vehicle owners estimated to save $0-1,000 over the life of a

vehicle for the same level of emission reduction.

 

37As stated in the discussion for the large car class, this study intentionally focused on a broad range of

technology packages that provide for an equally broad range of CO2-reduction potential and CO2

reduction cost. See footnote 35.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 3-6: Minivan Results

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Dual Cam Phasers, 6-Speed Automatic Transmission 350.0 14.3% 862 Discrete Variable Valve Lift, Coupled Cam Phasers, 5-Speed Automatic Transmission 344.6 15.6% 528 Stoichiometric Gasoline Direct Injection, Coupled Cam Phasers, Cylinder

Deactivation, Automated Manual Transmission, Electric Power Steering, Improved

Alternator

320.5 21.5% 759 

Discrete Variable Valve Lift, Coupled Cam Phasers, Automated Manual Transmission,

Electric Power Steering, Improved Alternator 317.4 22.3% 494 

Coupled Cam Phasers, Automated Manual Transmission, Turbocharging, Electric

Power Steering, Improved Alternator 317.1 22.3% 322 

Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission,

Electric Power Steering, Improved Alternator 313.3 23.3% 1,526 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 308.8 24.4% 638 

Continuous Variable Valve Lift, Coupled Cam Phasers, Automated Manual

Transmission, Electric Power Steering, Improved Alternator 307.7 24.6% 1,219 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Turbocharging,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 299.2 26.7% 559 

Electrohydraulic Camless Valve Actuation, Stoichiometric Gasoline Direct Injection,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 292.2 28.4% 1,809 

Stoichiometric Gasoline Direct Injection, Coupled Cam Phasers, Automated Manual

Transmission, 42 Volt Integrated Starter/Generator, Cylinder Deactivation, Electric

Power Steering, Electric Accessories

288.8 29.3% 2,374 

Motor Assist Gasoline Hybrid 217.8 46.7% 3,179 Fully Integrated Diesel Hybrid 187.2 54.2% 8,135 Fully Integrated Gasoline Hybrid 186.7 54.3% 5,944 
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-16

Figure 3-3: Net Vehicle Costs for the Minivan Class Given Two Gasoline Price

Scenarios

-2000

-1000

0

1000

2000

3000

4000

400 375 350 325 300 275 250 225 200 175 150

CO2

(grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per Gallon

Supply Curve @ $2.00 per Gallon

Small Truck Results

Table 3-7 presents the emission reduction and cost estimates for the 14

technology packages modeled for the small truck class.

Emission reduction estimates for this class range from 17-53 percent, relative to

the 2002 baseline vehicle, for the 14 small truck technology packages evaluated.

According to this analysis, combinations of technologies already used in some production

gasoline models can reduce CO2 emissions by approximately 28 percent. Examples of

these technologies include 6-speed automatic transmissions, variable valve lift and

timing, and cylinder deactivation. Reductions beyond this level will require the

introduction of more advanced technologies such as gasoline direct injection, 42-volt

starter generators, camless valve actuation, and diesel engine technology. For example, a

technology package consisting of stoichiometric gasoline direct injection and camless

vale actuation can provide a 32 percent CO2 reduction for an incremental vehicle cost of

about $1,500. Even greater CO2 reductions can be achieved using hybrid-electric

technology. As with the other categories of vehicles, fuel cost savings to the owner over

the life of the vehicle generally outweigh the additional technology costs in all but the

most aggressive technology packages. On a dollar per ton basis, the net cost of

technologies producing CO2 reductions up to 46 percent is negative, implying net cost

savings to the consumer.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 3-7: Small Truck Results

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Dual Cam Phasers, 6-Speed Automatic Transmission 381.1 16.7% 479 Discrete Variable Valve Lift, Dual Cam Phasers, 6-Speed Automatic Transmission 377.4 17.5% 640 Dual Cam Phasers, 6-Speed Automatic Transmission, Turbocharging, Electric Power

Steering, Improved Alternator 372.6 18.6% 73 

Dual Cam Phasers, 6-Speed Automatic Transmission, Cylinder Deactivation 368.2 19.5% 634 Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission,

Electric Power Steering, Improved Alternator 342.8 25.1% 1,156 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Cylinder Deactivation,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 335.9 26.6% 906 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 330.2 27.8% 750 

Stoichiometric Gasoline Direct Injection, Dual Cam Phasers, Turbocharging,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 320.3 30.0% 157 

Diesel High Speed Direct Injection, Automated Manual Transmission, Electric Power

Steering, Improved Alternator 318.2 30.5% 1,585 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed

Automatic Transmission, 42 Volt Integrated Starter/Generator, Electric Power

Steering, Electric Accessories

317.6 30.6% 2,451 

Electrohydraulic Camless Valve Actuation, Stoichiometric Gasoline Direct Injection,

Automated Manual Transmission, Electric Power Steering, Improved Alternator 310.9 32.1% 1,459 

Motor Assist Gasoline Hybrid 248.6 45.7% 2,797 Fully Integrated Diesel Hybrid 214.0 53.2% 7,683 Fully Integrated Gasoline Hybrid 213.5 53.3% 5,492 
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-18

As is evident from Table 3-7, the emission reduction packages evaluated in this

study include a wide range of individual technologies. Some of the most cost-effective

packages include stoichiometric gasoline direct injection, automated manual

transmissions, turbocharging, camless valve actuation, and diesel technology. As noted

early in this chapter, not all technology combinations considered for the large car vehicle

class were evaluated for the small truck and other vehicle classes. Had these additional

combinations been evaluated, comparable results would likely have been obtained for the

small truck class. Finally, as with each of the other vehicle classes studied, this

assessment also included options that are relatively expensive in an effort to provide a

robust overview of the benefits and costs of a full range of candidate CO2-reduction

technologies.

Figure 3-4 depicts the relative benefits and costs of each of the evaluated

technology packages. As this figure suggests, the technology packages span a broad

range of CO2 reduction potentials and costs. For example, packages that produce CO2

reductions ranging from 17-32 percent (corresponding to CO2 emission rates between 380

g/mi and 310 g/mi) encompass a net cost range from approximately negative $2,600 to

negative $400. The solid line in Figure 3-4 presents the CO2 reduction supply curve for

the small truck class. As indicated, CO2 reductions exceeding 45 percent are likely to be

obtainable for a net negative cost. The figure also includes a second supply curve that

reflects the results of a gasoline price sensitivity analysis in which the assumed prices of

gasoline and diesel fuel are increased from $1.58 per gallon to $2.00 per gallon. At the

higher fuel price, all evaluated technology packages reflect negative net costs with the

exception of the advanced diesel hybrid. As can be seen from the dashed line ($2.00 per

gallon gasoline), vehicle owners can be expected to save an average of $1,600-$2,200

over the life of a vehicle for CO2 reductions to approximately 250 g/mi, which represent

about a 46 percent reduction from 2002 emissions of about 460 g/mi. Significant savings

can actually be expected for reductions as low as 215 g/mi CO2, a reduction of nearly 54

percent from 2002 emissions. When a gasoline price of $1.58 are evaluated, vehicle

owners can generally be expected to save $700-$1,700 over the life of a vehicle, except

in the advanced hybrid cases. The introduction of CO2 reducing technologies in the small

truck category provides high net savings to consumers due to the relatively high baseline

CO2 emissions for this class, which results in greater fuel savings compared to the lower

CO2 classes evaluated in this study.

The solid line in Figure 3-4 represents the CO2-reduction supply curve for the

small truck class. As indicated, emission reductions exceeding 45 percent are likely to be

obtainable for a net negative cost. As before, the figure includes a second supply curve

that reflects a higher fuel price of $2.00 per gallon. At this price, all evaluated

technology packages except the advanced diesel hybrid achieve negative net costs, with

savings ranging from $1,600-$2,200 over the life of the vehicle for technologies that

achieve a CO2 emissions rate of 250 g/mi (about a 46 percent reduction from the 2002

baseline of 460 g/mi). Significant savings can actually be expected for technology

packages that achieve emission rates as low as 215 g/mi, a reduction of nearly 54 percent

from the 2002 baseline. Assuming a lower gasoline price of $1.58 per gallon, estimated

net lifetime savings range from $700 to $1,700, except in the advanced hybrid cases. The

introduction of CO2-reducing technologies in the small truck category provides

substantial net savings to consumers due to the relatively high baseline CO2 emissions for
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-19

this class. This results in proportionally higher fuel savings compared to vehicle classes

that have lower baseline CO2 emissions.

Figure 3-4: Net Vehicle Costs for the Small Truck Class Given Two Gasoline Price

Scenarios

-3000

-2000

-1000

0

1000

2000

3000

400 375 350 325 300 275 250 225 200

CO2 (grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per Gallon

Supply Curve @ $2.00 per Gallon

Large Truck Results

Table 3-8 presents the emission reduction and cost estimates for the 14

technology packages investigated for the large truck class.

Emission reduction estimates range from 14-55 percent, relative to the 2002

baseline vehicle, for the 15 large truck technology packages modeled. According to this

analysis, combinations of technologies already used in some production gasoline models

can reduce CO2 emissions by approximately 24 percent. Examples of these technologies

include 6-speed automatic transmissions, variable valve lift and timing, and cylinder

deactivation. Reductions beyond this level will require the introduction of more

advanced technologies such as gasoline direct injection, camless valve actuation, and

diesel technology, which can provide up to a 30 percent CO2 reduction. Even greater

CO2 reductions can be achieved using hybrid-electric designs. On a dollar per ton basis,

the net cost of technologies producing CO2 reductions of up to 46 percent is negative,

resulting in overall savings over the life of the vehicle.

As noted in Table 3-8, the emission reduction packages evaluated in this study

include a wide range of individual technologies. Some of the most cost-effective

packages include automated manual transmissions, cylinder deactivation, and

stoichiometric gasoline direct injection. In the large truck class, cylinder deactivation

was evaluated as a more viable technology rather than turbocharging and downsizing in

order to ensure adequate durability for heavily loaded engines operating on work truck

type duty cycles (high-load operations and payload and trailer towing).
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table 3-8: Large Truck Results

(1)

Technology Combinations

(2)

CO2

(g/mi)

(3)

CO2

Change

(percent)

(4)

Marginal

Vehicle

Cost ($)

Coupled Cam Phasers, 6-Speed Automatic Transmission 452.5 13.7% 339 Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed Automatic Transmission 444.2 15.3% 549 Coupled Cam Phasers, Cylinder Deactivation, 6-Speed Automatic Transmission 434.8 17.1% 543 Dual Cam Phasers, Cylinder Deactivation, 6-Speed Automatic Transmission 432.5 17.6% 1,120 Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed

Automatic Transmission, Electrohydraulic Power Steering, Improved Alternator 419.7 20.0% 843 

Coupled Cam Phasers, Cylinder Deactivation, Stoichiometric Gasoline Direct

Injection, Automated Manual Transmission, Electrohydraulic Power Steering,

Improved Alternator

418.3 20.3% 890 

Lean Burn Gasoline Direct Injection, Automated Manual Transmission,

Electrohydraulic Power Steering, Improved Alternator 400.5 23.6% 1,926 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers,

Automated Manual Transmission, Electrohydraulic Power Steering, Improved

Alternator

398.0 24.1% 731 

Electrohydraulic Camless Valve Actuation, Stoichiometric Gasoline Direct Injection,

Automated Manual Transmission, Electrohydraulic Power Steering, Improved

Alternator

383.2 27.0% 2,171 

Cylinder Deactivation, Discrete Variable Valve Lift, Coupled Cam Phasers, 6-Speed

Automatic Transmission, 42 Volt Integrated Starter/Generator, Electric Power

Steering, Electric Accessories

379.6 27.6% 2,430 

Diesel Homogeneous Charge Compression Ignition, Automated Manual Transmission,

42 Volt Integrated Starter/Generator, Electric Power Steering, Electric Accessories 374.8 28.6% 3,535 

Lean Burn Gasoline Direct Injection, Automated Manual Transmission, 42 Volt

Integrated Starter/Generator, Electric Power Steering, Electric Accessories 367.1 30.0% 3,494 

Motor Assist Gasoline Hybrid 285.9 45.5% 3,641 Fully Integrated Gasoline Hybrid 244.9 53.3% 7,540 Fully Integrated Diesel Hybrid 238.7 54.5% 10,592 
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-21

The large truck category is the only vehicle class with an eight-cylinder base

engine. Because of this, technology costs in the large truck class are in some cases higher

than in the other vehicle classes due to additional hardware requirements. For example,

eight lost motion devices are required for variable valve lift technology rather than six for

other vehicle classes due to the additional cylinders. Despite these higher costs, fuel

savings more than overcome incremental technology costs for nearly all the large truck

technology packages evaluated.

Figure 3-5 graphically depicts the relative benefits and costs of each of the

evaluated technology packages. As this figure suggests, the technology packages span a

broad range of CO2 reduction potential and costs.

38

For example, packages providing

CO2 reduction from 14 to 30 percent (emissions between 450 and 370 g/mi CO2)

encompass a net cost range from approximately negative $1,800 to positive $300. The

estimated CO2 reduction supply curve for this study considers this full range of results

rather than only the least cost solutions. As previously noted, this approach is intended to

allow for a more robust consideration of the benefits and costs of candidate CO2

reduction technology.

The solid line in Figure 3-5 presents the CO2 reduction supply curve for the large

truck class. As indicated, CO2 reductions of about 45 percent (about 285 g/mi CO2,

relative to about 525 g/mi for a 2002 vehicle) are likely to be obtainable for a net

negative cost (e.g., a lifetime savings). The figure also includes a second supply curve

that reflects the results of a gasoline price sensitivity analysis in which the assumed prices

of gasoline and diesel fuel are increased from $1.58 per gallon to $2.00 per gallon. At the

higher fuel price, all evaluated technology packages reflect negative net costs except the

advanced gasoline and diesel hybrids. As can be seen from the dashed line ($2.00 per

gallon gasoline), vehicle owners can be expected to save an average of about

$900-$1,700 over the life of a vehicle for a range of CO2 reductions up to about 45

percent. When gasoline prices of $1.58 are evaluated, vehicle owners can be expected to

save an average of $0-$1,000 over the life of a vehicle for this same level of CO2

reductions.

Figure 3-5 depicts the relative benefits and costs of each of the technology

packages considered for large trucks. As with the other vehicle classes, these packages

span a broad range of CO2 reduction potentials and costs. For example, packages that

provide CO2 reductions of 14-30 percent (corresponding to CO2 emission rates between

450 and 370 g/mi) encompass a net cost range from approximately negative $1,800 to

positive $300.

The solid line in Figure 3-5 presents the CO2-reduction supply curve for the large

truck class. As indicated, CO2 reductions of about 45 percent (corresponding to an

emissions rate of about 285 g/mi relative to a 525 g/mi baseline for a 2002 vehicle) are

likely to be obtainable at net negative cost (i.e., lifetime savings). The figure indicates

 

38 As stated in the discussion for the large car class, this study intentionally focused on a broad range of

technology packages that provide for an equally broad range of CO2 reduction potential and CO2

reduction cost. Thus, the study has not attempted to consider only the least cost solutions, but rather a

broader range of solutions that might better reflect the cost of CO2 reduction across the entire class of

vehicles. While least cost solutions might be appropriate for some segments of the class, other segments

might require a somewhat more expensive solution to maintain a critical market distinction.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-22

that at the higher fuel price of $2.00 per gallon, all evaluated technology packages

achieve negative net costs except the advanced gasoline and diesel hybrids. Specifically,

vehicle owners can be expected to save an average of about $900-$1,700 over the life of

a vehicle for a range of CO2 reductions up to about 45 percent. At the lower fuel price of

$1.58 per gallon, vehicle owners can be expected to save an average of $0-$1,000 over

the life of a vehicle for this same level of CO2 reductions.

Figure 3-5: Net Vehicle Large Truck Costs Given Two Gasoline Price Scenarios

Methane and N2O Analysis

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

500 475 450 425 400 375 350 325 300 275 250 225 200

CO2(grams/mile)

Net Cost ($)

Supply Curve @ $1.58 per

Gallon

Supply Curve @ $2.00 per

Gallon

Methane and Nitrous Oxide Analysis

Table 3-9 presents estimates for motor vehicle methane and N2O emissions,

produced according to the methods outlined in Chapter 2 and Appendix E. As indicated,

the GHG impacts of methane and N2O are estimated to be relatively modest compared to

CO2 emissions, which generally range from about 300-525 g/mi in 2002 and approach

150-240 g/mi under the most aggressive CO2 reduction scenarios in 2009-2015. Given

these ranges, methane emissions are generally estimated to represent from 0.04-0.08

percent of 2002 CO2-equivalent emissions and no more than 0.1 percent of 2009-2015

CO2-equivalent emissions under even the most aggressive CO2 reduction scenarios. N2O

emissions are a bit more significant, comprising from 1-2 percent of 2002 CO2-equivalent

emissions and as much as 3 percent of 2009-2015 CO2-equivalent emissions.

Estimated methane and N2O impacts are not included in the overall CO2 impact

estimates presented in Tables 3-4 through 3-8, but are provided here to allow for a full

accounting of all vehicle GHG emissions. To estimate total GHG emissions from a

particular vehicle class and technology combination, the CO2 emission estimates from
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-23

Tables 3-4 through 3-8 would be added to the CO2-equivalent emission estimates for

methane and N2O from Table 3-9.

Table 3-9: Methane and N2O Emissions

Methane Nitrous Oxide

Basic Technology Configuration

2002 2009-2015 2002 2009-2015

Grams per Mile - Expressed as Direct Methane or Nitrous Oxide

Stoichiometric 0.010 0.008 0.021 0.016

Lean Burn 0.005 0.005 0.016 0.016

Grams per Mile - Expressed as CO2-Equivalent

Stoichiometric 0.23 0.18 6.1 4.9

Lean Burn 0.12 0.12 4.9 4.9

3.3. Conclusions

The results of this analysis suggest that existing and emerging automotive

technologies can achieve substantial and cost-effective reductions in motor vehicle GHG

emissions in the 2009 to 2015 timeframe. Specifically, GHG emissions from light-duty

vehicles can be reduced from 12-54 percent in this timeframe. Assuming a gasoline price

of $1.58 per gallon, this study found that—for most technology packages—vehicle

owners will save at least $500 over the life of the vehicle. At a higher fuel price of $2.00

per gallon, vehicle owners will save between $300 and $2,200 over the life of the vehicle

for a range of CO2 reductions up to about 45 percent.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page 3-24
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-1

Appendix A: Technology Descriptions
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-2

Appendix A: Technology Descriptions

A.1. Cam Phasing

Also known as variable valve timing, cam phasing indicates an ability to vary the

point during the combustion cycle at which a valve is opened and closed. Most spark

ignition engines currently use fixed valve timing, where the valve timing does not change

with the speed or load of an engine. This results in higher pumping losses than could be

achieved with optimum valve control. Variable valve timing offers the opportunity to

implement speed and load-dependent (i.e., variable) operating conditions that can reduce

pumping losses while enhancing both low-speed torque and high-speed horsepower.

A.2. Variable Valve Lift

Valve lift is a measure of the height and duration of the valve opening. Most

spark gasoline engines use fixed valve lift, where the valve lift does not change with the

speed and load of an engine. Variable lift allows the period of valve opening to vary

which reduces pumping losses, reduces valve train frictional loss, increases compression

ratio, and reduces idle speed— all of which reduce CO2 emissions.

A.3. Camless Valve Actuation

Camless valve actuation expands upon the concept of variable valve timing and

lift, described above, by completely eliminating the camshaft and mechanical valve

actuation mechanism from the cylinder head. In place of the camshaft mechanism, valve

motion is actuated and controlled through either electrical energy or hydraulic energy,

and this can occur over a wide range of engine operating conditions. This yields greater

CO2 reductions than variable valve lift/timing systems.

A.4. Turbocharging

Internal combustion engines reject 25 to 50 percent of energy into the exhaust. A

turbocharged engine uses a turbine in the exhaust stream to drive a compressor in the

intake manifold, which compresses incoming air to the engine. The higher pressure air in

the intake manifold forces more air into the engine than would otherwise be the case, and

the resulting benefit is an increase in engine power. While the technology doesn't reduce

CO2 emissions directly, the fact that the engine produces greater power allows engines to

be downsized without sacrificing performance, and this downsizing can produce

significant CO2 reductions.

A.5. Cylinder Deactivation

Cylinder deactivation technology allows engines to operate on half their cylinders

during certain operating modes. Generally, such systems “shut down” cylinders during

light load operation so that the engine operates with an efficiency similar to that of a

lower-displacement engine. From an engineering standpoint, the major CO2 reductions

accrue due to a reduction in pumping losses associated with halving the number of

cylinders in operation. The more frequently the deactivation mode occurs, the greater the

CO2 reduction impacts. Therefore, in some cases, the base engine may be upsized to
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-3

allow more frequent operation in deactivation mode, which results in both reduced CO2

and greater maximum power.

A.6. Variable Compression Ratio

Engine efficiency increases with cylinder compression ratio. The greater the

compression, the more work performed for a given air-fuel mixture. In standard

technology engines, the compression ratio is fixed across all operating conditions based

on cylinder geometry. However, the tendency of engines to experience knock varies with

operating conditions. For example, at light loads, higher compression ratios can be

tolerated without knock. However, since the geometry of a standard engine cannot be

varied it is not possible to optimize compression ratios for specific operating conditions.

New engine designs can mechanically vary cylinder geometry. This allows for engines

that operate at a high-compression ratio under part-load conditions and at a lower

compression ratio under high-load conditions. CO2 reductions are achieved through the

use of a smaller engine to achieve identical performance.

A.7. Gasoline Direct Injection

Gasoline direct injection (GDI) technology facilitates lean-burn engine operation.

Lean-burn engines mix more air with the fuel when full power is not needed, resulting in

lower CO2 emissions. Charge “shaping” possible with lean-burn engines facilitates

ignition of the air-fuel mixture at very lean overall air-fuel ratios. Under lean-burn

conditions, highly effective lean NOx aftertreatment will be required for GDI technology

to achieve Tier 2 emission standards, which adds significantly to technology costs.

However, even under stoichiometric conditions, GDI technology can provide significant

CO2 reductions due to its ability to tolerate increased compression ratio and increased

exhaust gas recirculation (EGR). The advanced air and fuel control features of GDI

engines allow them to be operated at either stoichiometric (high-load conditions) or leanburn (light-load conditions) as required.

A.8. Homogeneous Charge Compression Ignition (HCCI)

The design goal of HCCI combustion is the incorporation of the best features of

gasoline/spark-ignition (SI) and diesel/compression-ignition (CI) engines. Like an SI

engine, the intake charge, or fuel/air mixture, is well-mixed (hence the label

“ homogeneous charge”), and like the CI engine the intake charge is compression-ignited

(no spark plug) at high compression ratios, with minimal throttling losses. This leads to

high operating efficiencies, low CO2 emissions, and low NOx and PM emissions. HCCI

is not yet feasible across the full engine operating range, so it is generally employed as a

partial mode system, where HCCI is utilized under light load conditions and more

conventional combustion modes are used at higher speeds and loads. For this study, both

gasoline and diesel HCCI systems were evaluated. The gasoline HCCI system is based

on GDI technology, and the spark ignition features of the GDI engine are retained for

operation in non-HCCI modes. The gasoline HCCI system evaluated was the AVL CSI

(Compression and Spark Ignition) system, a very low NOx and CO2 combustion system

that can operate with a conventional 3-way catalyst. The diesel version of the HCCI

system is denoted as Diesel Advanced Multi-Mode in this study and is essentially a light

load HCCI system that shifts to conventional high-speed direct injection (HSDI) diesel
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-4

operation at high loads and speeds. Advanced common rail injection systems capable of

precisely tailored multiple injections per cycle facilitate the HCCI operations.

A.9. High-Speed Direct Injection Diesel (HSDI)

Heavy-duty diesels have historically been of direct injection (DI) design, where

fuel is directly injected into the engine combustion chamber. Conversely, light-duty

versions – primarily used in Europe and Asia – have historically avoided the vibration

and harshness issues associated with DI designs by using indirect-injection (IDI) designs,

whereby fuel is injected into a pre-chamber and the resulting air-fuel mixture is

subsequently introduced into the main combustion chamber. However, with the advent

of sophisticated, electronically-controlled fuel injection systems, it is possible to

experience the quiet, smooth operation of the IDI, with the low-CO2 emissions

characteristic of DI engines. However, a primary impediment facing HSDI technology in

the U.S. marketplace is stringent NOx and PM emission regulations, which will

necessitate the use of highly effective lean aftertreatment systems.

A.10. 5 and 6 Speed Automatic Transmissions (Increased Step Gear

Ratio Transmissions)

In both automatic and manual transmissions, increasing the number of gears can

provide a wider spread between the lowest (first gear) and highest gear ratios. This

allows the engine to operate closer to its optimum efficiency at a wider variety of speeds

which results in a corresponding decrease in CO2 emissions. Five and six speed

automatic transmissions are now available, both of which provide benefits relative to the

more traditional four-speed transmission.

A.11. Automated Manual Transmissions

An automated manual transmission is similar in design and performance to a

manual transmission, except that shifting and clutch control is performed automatically

outside the control of the driver. These functions instead occur by means of a hydraulic

system or an electric motor, in conjunction with appropriate control electronics. Lower

CO2 emissions result from the elimination of automatic transmission torque converter

losses and the programming of optimum shift points.

A.12. Continuously Variable Transmissions

Current transmissions feature a discrete number of gear ratios (generally four to

six) that determine the relationship between engine speed and vehicle speed. This results

in some compromise in matching engine speed and load-to-vehicle requirements. A

continuously variable transmission (CVT) offers an infinite range of gear ratios between

fixed limits, which allows for the optimization of engine operating conditions and

maximum power transmission efficiency.

A.13. 42 Volt Systems

Forty-two volt systems enable a number of CO2 reducing features, including

engine off at idle, launch assist, regenerative braking, electrical accessory drives, and

electric power steering. While any one of these (except launch assist) can be
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-5

accomplished using current 12-volt automotive systems, the unused power available on

current systems is a major limitation. In contrast to the 3 kW available with current 12-

volt systems, 42-volt systems can provide up to 12 kW maximum power and, thereby,

accommodate significant power-related upgrades. In 42-volt systems, the existing

vehicle starter and alternator are replaced by a combined starter/alternator. The simplest

implementation is a belt-driven starter/alternator, but such systems are limited in their

ability to provide launch assist or regenerative braking benefits. A more complex system

in which the starter/alternator is sandwiched between the engine and transmission allows

substantial launch assist and regenerative braking, as well as other benefits such as a

reduction in required torque converter size and a reduction in engine torque pulsation.

A.14. Hybrid Electric Vehicles (HEVs)

Hybridization involves the interaction, in varying degrees depending on the

design, of a conventional gasoline or diesel-powered powerplant, in conjunction with an

electric motor. Parallel hybrids use the conventional engine coupled directly to the

vehicle’s drivetrain as the prime motive power with varying degrees of electric motor

assist. Series hybrids also employ a conventional engine, but it is physically de-coupled

from the drivetrain, making the electric motor the only motive source. The conventional

engine provides power to operate a generator providing power to a battery pack, which in

turn provides electric power to operate the electric motor. Reduced CO2 emissions are

achieved through a number of mechanisms, including utilization of smaller engines that

operate in a more efficient power band, energy recovery through regenerative braking,

engine shutdown at what would normally be idling conditions, and other strategies.

A.15. 12-Volt Accessory Improvements

Engine-driven accessories account for eight to ten percent of the CO2 emitted over

a typical driving cycle. Such accessories include the alternator, oil pump, water pump,

and power steering pump. A typical vehicle alternator has an efficiency of around 60

percent, as compared with advanced designs that can provide 75-80 percent efficiency.

Similar advances are possible with improved oil and water pump designs. Power steering

pumps are somewhat different in that they operate continuously, but are needed

intermittently. Electrical (instead of hydraulic) systems can significantly reduce CO2

emissions by eliminating this continuous load.

A.16. Lubricating Oil

Lubricating oil serves several functions within an engine, including: friction

reduction, engine cooling, limiting wear on the moving parts of the engine, and protecting

against corrosion. It is primarily the effect of lubricating oil on engine friction that

impacts CO2 emissions. New energy-conserving motor oils reduce engine frictional

forces.

A.17. Drag Reduction

Reductions in vehicle aerodynamic drag have the effect of reducing the load on a

vehicle engine and thereby reducing CO2 emissions. Aerodynamic drag is a resistance

force that acts on the surface of a moving vehicle. The force varies with wind intensity,
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-6

direction, vehicle frontal area, and body shape. Apart from basic vehicle shape changes,

drag reduction is generally achieved by minimizing air friction over vehicle surfaces. For

example, skirts, air dams, and underbody covers can all reduce aerodynamic friction.

The implementation of drag reduction technology generally leads a modest increase in

the weight of the vehicle, but the CO2 emission reductions due to the reduced drag

outweigh the penalties of the increased weight.

A.18. Weight Reduction

Vehicle weight is a principal determinant of vehicle CO2 emissions. Lower

vehicle weight reduces the forces required to accelerate the vehicle and maintain steady

speeds, which in turn reduces CO2 emissions. Generally, weight can be reduced through

the replacement of conventional steel with lighter-weight alternatives, improved

packaging, or downsizing. Modern lightweight materials include high-strength low-alloy

(HSLA) steel, aluminum, magnesium alloys, and plastics. Downsizing also reduces

vehicle weight since it takes less material to make a smaller car.

A.19. Rolling Resistance Reduction

Rolling resistance is a measure of the force required to move the tires of a vehicle

forward. When multiplied by the radius of the tire, this force gives the resistive torque

that must be overcome by the engine when the vehicle is in motion. The rolling

resistance of a tire can be reduced through improved tread and shoulder designs and the

use of improved materials for tire belt and traction surfaces.

A.20. Aggressive Shift Logic

Aggressive shift logic changes the points at which shifting occurs to reduce CO2

emissions. Moving transmission upshift points to lower speeds offers the potential for

reduced CO2 emissions. As upshift speeds are lowered, downshift speeds must be altered

to avoid excessively busy shifting behavior. However, if the downshift speeds are

reduced too much, then the driveability of the vehicle can suffer because it won’t respond

to driver demands for acceleration.

A.21. Early Torque Converter Lock-up

The torque converter, which prevents stalling on automatic transmission vehicles

at rest, is one of the largest sources of inefficiency in the vehicle. The advent of torque

converter lock-up clutches was a major contributor to reducing CO2 emissions. However,

the full potential of this technology is not used because the rigid connection to the engine

transmits vibrations at low engine speeds to the interior of the vehicle.

A.22. Alternative Fuels

Alternative fuels can be used alone or in combination with many of the

technologies described above to reduce GHGs. However, large-volume sales of

alternative fuel vehicles are affected by refueling infrastructure issues that introduce

levels of uncertainty beyond those associated with gasoline and diesel vehicle sales.

Therefore, while alternative fuel vehicles represent a viable and efficient means to

reducing motor vehicle GHG emissions, they were not examined in this study.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-7

Nevertheless, the use of alternative fuels should be considered alongside the technologies

identified in this study in formulating a cost-effective GHG reduction strategy.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page A-8
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-1

Appendix B: AVL Simulation Modeling Description
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-2

Appendix B: AVL Simulation Modeling Description

B.1. Vehicle Simulation

The vehicle simulation software AVL CRUISE was used to evaluate Greenhouse Gas

(GHG) emissions considering combinations of engine and driveline technologies. CRUISE is

used to simulate CO2, criteria exhaust emissions, fuel consumption, and vehicle performance.

Emissions were simulated over three standard test cycles: FTP75, HWFET, and US06. For this

project, vehicle performance includes full load acceleration from rest to 60 MPH, from 50 MPH

to 70 MPH in top gear (representing a passing situation), full load climbing performance at curb

and gross vehicle weights and the maximum velocity of the vehicle. An additional climbing

task, with a 5000lb trailer, was also performed for the truck models.

After the baseline vehicles had been selected (as described in chapter 2 of this report),

data was collected and the models developed. The 2002 model year (MY2002) vehicles are

described in more detail in Section B.2 of this appendix. Section B.3 presents the engine

technology options. Sections B.4 through B.7 describe the modifications required to convert the

MY2002 model from a 4 speed automatic transmission (4AT) to more advanced transmissions

such as a 6 speed automatic transmission (6AT). Section B.8 illustrates the approach used to

model Hybrid drive trains and Section B.9 covers other vehicle technologies that were

considered, such as the effects of additional mass, changes in drag coefficients, air conditioning,

and the electrification of auxiliaries. Section B.10 presents the simulation results from all the

models developed by AVL for the project.

B.2. MY2002 Baseline Models

A review of the vehicles in the current consumer vehicle fleet resulted in a description of

base vehicles that were then modeled in CRUISE. These CRUISE models were calibrated to

provide similar 0-60 MPH times to published data and fuel economy on the emissions test cycles

that matched EPA test car data. These configurations all share similar technology, including

MPFI internal combustion engines and 4 speed automatic transmissions.

Figure B-1 presents the baseline model for a front wheel drive (FWD) vehicle. This

configuration represents the small car (SC), large car (LC), and minivan (MV) models. Figure

B-2 shows a four-wheel drive (4WD) model, which is typical of the small and large truck

vehicles (ST and LT respectively). The primary difference between the models is the addition of

a single ratio transmission and differential representing the rear axle and a clutch between the

front and rear axles. A clutch was included to disengage the power transmission to the front

axle. The small and large trucks were determined to be split nearly 50% between 2WD and

4WD. Since many 4WD vehicles can also be run in a 2WD mode, it was decided to include the

components for the 4WD but to disengage the front axle in order to capture the losses associated

with the non-driven axle. The rest of this section will detail each of the components shown in

Figures B-1 and B-2.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-3

Figure B-1: Layout of the Front Wheel Drive Vehicles (Small Car shown)

Figure B-2: Layout of the 4 Wheel Drive Vehicles (Large Truck shown)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-4

B.2.1. Vehicle Component

The vehicle component contains the general data of the vehicle such as nominal

dimensions and weights. For this project, coefficients defining the resistance of the vehicle were

obtained from data published by the EPA. Additional details, such as the wheelbase, were taken

from OEM data for the particular vehicle. The more important data entered in the vehicle

models are summarized in Table B-1.

Table B-1: Vehicle Component data for all vehicle classes

Parameter Units Small Car Large

Car

Minivan Small

Truck

Large

Truck

Wheelbase mm 2644 2756 3030 3096 3645

Curb weight lbm 2676 3336 4107 3540 4919

Equivalent

Test Weight

lbm 3000 3625 4500 4250* 5500*

Gross Weight lbm 3176 3836 4700 5100 6400

EPA

coefficient A

lbf 27.9 30.19 36.16 47.889 29.8

EPA

coefficient B

lbf/

mph

0.3677 0.6723 0.8909 0.32911 1.9928

EPA

coefficient C

lbf/

mph^2

0.01743 0.01323 01812 0.034627 0.02435

* ETW chosen to coincide with EPA fuel economy test data

B.2.2. Engine Component

The primary source of power for the vehicle is the internal combustion engine. The

engine is modeled by a structure of characteristic curves and maps. The full load and motoring

curves define the high and low torque limits of the engine. During each calculation, the engine

speed and torque are used to interpolate the emissions and fuel consumption from steady state

maps entered in the component. A temperature model is included to consider the influence of

the temperature on the emissions and fuel consumption while the engine is cold.

The thermal model was used to simulate the warm-up for the FTP75 cycle, as well as the

temperature loss during the soak (engine-off) period. Typical times to reach the engine operating

temperature were between 180-300 seconds. For the Highway and US06 cycles, a hot start was

used with transient engine temperature behavior allowed.

Typical engine parameters for the baseline vehicles are presented in Table B-2. Full load

curves from AVL data were adapted to meet the torque and power specifications for the baseline

vehicles. For Task 1 the engine displacement was unchanged for the varying engine

technologies, except for the turbocharged and diesel engine options. For these cases, the engine

displacement was adjusted in order to match 2002 performance levels. In Task 2, the engine was

sized to meet the projected 2009 performance levels for all simulations.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-5

Table B-2: Engine Parameters

Parameter Units Small

Car

Large

Car

Minivan Small

Truck

Large

Truck

Type - Gasoline Gasoline Gasoline Gasoline Gasoline

Turbo - No No No No No

Displacement L 2.2 3.0 3.3 3.4 5.3

# of cylinders - 4 6 6 6 8

Max. speed RPM 6500 6200 5600 5800 6000

Idle speed RPM 850 650 650 650 550

Max torque Nm 202.9 271.0 284.6 298.1 440

Max power kW 104.4 149.1 134.2 141.7 213

B.2.3. Torque Converter

For most light duty vehicles in the U.S., the torque converter is the device used for

decoupling the engine from the drive wheels when the vehicle is at rest and for launching the

vehicle. Torque converters employ the force created by a moving fluid to transmit engine torque

to the gearbox. The torque converter also multiplies torque when there exists a positive speed

difference from the engine side to the transmission side. An impeller (pump) converts the

mechanical energy from the power source into fluid energy. The fluid energy then is converted

back to mechanical energy as a result of fluid pressure on the turbine blades.

Characteristic curves available from published papers were used when possible. In other

cases, curves were estimated based on a combination of published torque ratios at stall, K-factors

at stall, capacity factors at stall, and characteristic curves available in “ Design Practices,

Passenger Car Automatic Transmissions 3

rd

Edition” pages 75-102 published by SAE. Other

sources of information included SAE paper 980821, which contained a chart relating the Kfactor range versus torque converter diameter. The Hydramatic website also provided

information regarding the torque converter diameter in each of GM’s applications. In those

cases where estimation of the performance was necessary, the GM vehicle in that class was used

to provide the size of the converter and as a result a range of nominal K-factors at stall. A

typical torque converter steady state characteristic is shown in Figure B-3.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-6

Figure B-3: Typical characteristics for torque converter in steady state operation

The torque converters were also outfitted with a lock-up clutch. These lock-up clutches

are used to decrease CO2 emissions by making a rigid connection between the incoming and the

outgoing sides of the torque converter when the slip is low. The maximum torque of the lock-up

clutch was set to a level that was greater than the engine torque to guarantee that no slip would

occur when the lock-up clutch was closed (torque transmitted through the clutch).

B.2.4. Torque Converter Lock-up Control Strategy

The clutch control map is used for lock-up clutches of torque converters. The Clutch

Control element controls the opening and closing of this lock-up clutch based on the engine

speed, current gear, and load signal. For the 4AT, lock up was only allowed in 3

rd

and 4

th

gears.

B.2.5. Gear Box

The Gear Box component contains a model for a gear box with different gear steps. As

many gears as required can be defined. For each gear the transmission ratio, the mass moments

of inertia, and efficiency were defined. The gear box component can be used for a manual or

automatic gear box. When used as an automatic gear box, the gear shifting process is controlled

by the Gear Box Control or Gear Box Program. The CRUISE virtual driver will handle this task

when used as a manual gear box.

Relative efficiencies appropriate to the architecture of the gear box and considering the

number of gear sets in mesh and transmitting torque for the particular ratio were established for

each gear. Absolute gear efficiencies (as well as final drive efficiencies) were then set to match
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-7

published performance values for the baseline vehicles. Table B-3 contains the ratios and the

efficiencies for each of the gears in the baseline transmission.

Table B-3: Gear Ratios and Efficiencies for each of the vehicle classes

Small Car Large Car Minivan Small Truck Large Truck

Ratio η Ratio η Ratio η Ratio η Ratio η

Gear 1 2.96 0.94 2.77 0.945 2.84 0.945 2.804 0.95 3.06 0.95

Gear 2 1.63 0.955 1.54 0.96 1.57 0.96 1.531 0.965 1.625 0.965

Gear 3 1.0 0.97 1.0 0.975 1.0 0.975 1.0 0.98 1.0 0.98

Gear 4 0.68 0.955 0.69 0.96 0.69 0.96 0.705 0.965 0.7 0.965

B.2.6. Gear Shift Controls for AT and AMT Transmissions

The shifting of the gear box is controlled by the Gear Box Control or Gear Box Program

components. The Gear Box Control is used during the steady state calculations for the maximum

acceleration in each gear and in the climbing performance tasks. During the elasticity (passing

from 50 MPH to 70 MPH) it is also used to set the initial gear at 50 MPH to the top gear and

hold it so that no shifting would occur.

The Gear Box Program shifts the gears according to specified shift curves. The curves

are given as a function of the load signal and the gear box output speed. The shapes of these

curves constitute a compromise between CO2 emissions, driveability, and performance and are

representative of common industry practice. Once Gear Box efficiencies were obtained (see

above), shift programs were adjusted to match EPA certification data for CO2 emissions on the

study vehicle. The target gear determined by the gear box program is transmitted to the gear box

control which in turn transmitted the desired gear to the gear box. The shift program was used

for all cycle calculation tasks.

B.2.7. Axle

The axle is represented by two components in CRUISE. A Single Ratio Transmission is

used for the transmission ratio and torque losses in the axle. A differential splits the torque

between the two output shafts and was set to be unlocked, i.e. differences in output shaft speeds

were allowed. The axle ratio and efficiency for each of the vehicles are presented in Table B-4.

Table B-4: Axle Ratios and Efficiencies for each of the baseline vehicles

Small Car Large Car Minivan Small

Truck

Large

Truck

Ratio 3.63 3.98 3.62 4.10 3.73

Efficiency 0.97 0.96 0.98 0.94 0.975

B.2.8. Brakes

During a cycle run, the energy for decelerating the vehicle is sometimes greater than what

the engine and driveline can absorb. To make up for the difference, brake elements are included.

The brakes were sized by taking the vehicle model and adjusting the piston size until the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-8

stopping distance of the vehicle was comparable to published data. This sizing was then held

constant through the rest of the analyses.

B.2.9. Wheels

The wheels

and tires link the vehicle to the road. As the rolling resistance is included in the EPA

coefficients, the primary data input for the wheels are the rolling radius and the inertia. The

standard tires specified for the vehicles were used to find the rolling radius on the websites of tire

manufacturers. Appropriate inertia values were used. For the Full Load Accelerations and the

climbing tasks, slip was considered. The longitudinal tire force (circumferential force) results

from the friction coefficient, the wheel load, and the slip factor.

B.2.10. Auxiliaries

The auxiliaries are defined in the Mechanical Consumer elements in the CRUISE models.

For each of the auxiliaries, an engine speed dependent torque loss is defined.

B.2.10.1. Alternator

An electrical load of 300 W was applied to the vehicles during all simulations. An

alternator torque loss was applied at the engine to account for the loss in all non-hybrid cases.

The average alternator efficiency for the MY2002 baseline was approximately 60%. In some

task 2 cases, this efficiency was increased to 80% to represent improvements predicted for the

future. The cases using this higher efficiency alternator are specifically mentioned.

B.2.10.2. Automatic Transmission Oil Pump

The automatic transmission oil pump torque loss varied by vehicle. For the Large Truck,

a variable displacement vane pump was assumed. The other vehicle classes had a torque loss

curve for a fixed displacement pump. The pump losses were taken from “ Design Practices,

Passenger Car Automatic Transmissions 3

rd

Edition” pages 672 and 687 published by SAE. This

pump was deleted on manual, automated manual, and CVT transmissions.

B.2.10.3. Starter

A starter element was added to CRUISE because of the soak (engine off) period in the

FTP75, which requires that the engine be restarted. A Black Box control program was written to

provide a torque signal to restart the engine. A torque of 75 Nm was added through a flange

element until the engine speed reached 200RPM, when the engine received a start signal and

began to power itself.

B.2.11. Anti-Slip Control

The Anti Slip Control element checked the Force Transmission Factor (Ratio between

Force that should be transmitted and maximum transmittable Force) of all connected, driven

wheels. If the torque transmitted to the wheels exceeded the maximum transferable force then

the engine load signal was reduced. The control was used during the full load accelerations and

climbing tasks in order to get a more realistic sense of the performance of the vehicle during

climbing and accelerations. The difference between not considering slip (infinite traction) and

inclusion of slip exceeded 1 second in the 0-60 MPH time.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-9

B.3. Engine Technologies Investigated

Several advanced engine technologies were investigated during the project. Some were

only studied in Task 1 to assess their potential contribution to greenhouse gas reduction. The

more promising concepts also were selected for modeling in combination with other technologies

in Task 2. These engine technologies are described below.

B.3.1. Baseline Multipoint Fuel Injection (MPFI)

The multipoint fuel injection engine was the baseline technology for all vehicles in the

2002 fleet because of its market dominance. In this technology, fuel is metered and injected in

the intake ports of each cylinder. In combination with Exhaust Gas Recirculation (EGR), this

fueling strategy provides a very cost effective and flexible means of engine control with a very

good compromise of CO2 and criteria exhaust emissions, and performance.

B.3.2. Variable Valve Timing / Cam Phasers (ICP, ECP, DCP, CCP)

Variable Valve Timing (VVT) is a very attractive technology that can enhance

performance, while simultaneously reducing all exhaust emissions and fuel consumption.

Engines equipped with an Intake Cam Phaser (ICP) are starting to take a moderate share of the

market but have not reached a point of dominance and this technology was not included in any of

the 2002 baseline vehicles. Intake Cam Phasers allow a better match of the intake valve event to

different speeds and loads providing slightly higher and flatter torque curves and the ability to

reduce throttling losses. Exhaust Cam Phasing (ECP) is being increasingly used as a

performance enhancement technology but more importantly as a means of providing “ Internal”

EGR to reduce the emissions of NOX and CO2 (fuel consumption). Dual Cam Phasing combines

the benefits of ICP and ECP and provides a significant improvement in performance (3-6%).

Dual Cam Phasing also allows very flexible control of valve overlap, which can be used to

aggressively reduce throttling losses, increase EGR, and lower NOX/CO2 emissions and fuel

consumption. The VVT technologies previously described can only be used on engines

equipped with Dual Overhead Camshafts (DOHC) since they control the intake or exhaust valves

independently. On Single Overhead Camshaft (SOHC) or Overhead Valve (OHV) cam in block

engines, independent intake or exhaust control is impossible. However, one Coupled Cam

Phaser (CCP) can be used on these engines to control both intake and exhaust valves equally and

much of the previously mentioned benefits can be obtained. Discrete engine maps were prepared

for each of these four VVT configurations and were used in both Task 1 and Task 2 evaluations

B.3.3. Variable Valve Lift (DVVL, CVVL)

Engines equipped with a single intake cam lobe profile (those technologies described

above) suffer an inherent compromise in that the optimum intake valve event varies with engine

speed and load. At idle, an intake lobe with short duration, low lift, and minimal overlap is

desired for the smoothest operation. At peak power, a cam lobe with high lift, long duration, and

greater valve overlap is beneficial for maximum performance. Intermediate speeds and loads

require values somewhere between these extremes. When an engine is forced to operate with a

single cam lobe, function will be ideal at only one operating point and compromised at all others.

While VVT offers some improvement in the required compromise, it is not as effective as having

different valve lifts. Discrete Variable Valve Lift (DVVL) systems have been produced by

Honda and Porsche and use two different intake cam lobes that are selected depending on engine
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-10

speed and load. This can be used to improve performance or reduce emissions and fuel

consumption. BMW has introduced a mechanical Continuous VVL (CVVL) system into

production, which allows both higher performance and significantly reduced CO2 emissions due

to the reduction or elimination of throttling losses.

B.3.4. Variable Valve Actuation (EVA, EHVA)

Combining VVT and VVL yields the most flexible valve control. The most advanced

versions of these Variable Valve Actuation (VVA) systems are Electromagnetic Valve Actuation

(EVA) and Electro-Hydraulic Valve Actuation (EHVA). EVA is accomplished by using one

electric actuator, like a solenoid or linear motor, per valve to control the valve’s position. The

electric actuator operates the valve, which at rest is positioned at mid-lift by two springs. The

solenoid is excited at the correct frequency and duty cycle to open and close the valves at the

appropriate times. EVA systems are limited to full valve lift but have nearly infinite flexibility

in timing and duration and have faster response than the CVVL systems. These systems tend to

be heavy and noisy and were not considered for inclusion in Task 2 simulations. ElectroHydraulic systems offer the most flexibility of all the VVA systems. Valve timing, duration, lift,

velocity, and acceleration are all controllable by the Electro-Hydraulic control valves and system

pressure regulator. This system is an important enabler for some advanced combustion systems

and was chosen for a number of cases in Task 2.

B.3.5. Turbocharging

Turbocharging uses waste thermal energy from the engine’s exhaust gas stream to drive a

turbine. A compressor mounted on the same shaft as the turbine is used to compress the intake

air allowing a more dense charge to be delivered to the engine cylinder. Engine output can be

increased significantly because of this pressurized intake air and as a result engine downsizing is

possible. Under most operating conditions, the downsized engine operates at higher loads

without boost, thereby reducing throttling losses. When power demand is high, the turbocharger

comes into play to meet the required vehicle performance, effectively providing an engine with

dual displacement. This technology has been used extensively on Diesel engines and high

performance or racing gasoline engines. While turbocharging has not been used widely in the

US passenger vehicle fleet, the potential for downsizing (on the order of 30%) can deliver an

impressive reduction in CO2 emissions and fuel consumption in certain vehicle applications.

B.3.6. Cylinder Deactivation (CYLDCT)

Cylinder Deactivation is another means of obtaining an engine with multiple

displacements. For this technology, a relatively large engine is used at full displacement for high

power demands. When the power demand is lower, a portion of the engine’s cylinders (usually

half) are turned off by disabling the intake and exhaust valves and the fuel injection system for

the deactivated cylinders. In this way, a smaller engine (analogous to the downsized

turbocharged engine) operates at higher load with reduced throttling losses, thereby lowering

CO2 emissions. This is a very cost effective technology for OHV engines and is most

appropriate for vehicles like trucks, which can operate for extended periods of time at high loads

(trailer tow, for example). While this concept can be applied on any engine with an even number

of cylinders (Mitsubishi produced a four cylinder version in the past), it is practically limited to

V8 engines because of vibration. A V6 engine could operate as a three cylinder engine when
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-11

deactivated but customer acceptance is questionable unless extensive attention is paid to

vibration isolation resulting in increased cost.

B.3.6.1. Cylinder Deactivation Control

The decision to enter into deactivation considers the current engine temperature,

transmission ratio, torque, and whether the fuel consumption is less in deactivation or in full

operation. The engine is not allowed to switch into deactivation if the engine temperature is less

than 75°C. The fuel consumption of the full engine is compared to the fuel consumption of the

deactivated engine. Deactivation is allowed in the region where the CO2 emissions of the

deactivated engine are lower than that of the full engine, provided the other criteria are met.

B.3.7. Variable Charge Motion

Variable charge motion uses active components in the intake system or valvetrain to

create differing amounts of in-cylinder charge motion depending on engine speed and load.

High charge motion at low speeds and light loads is beneficial for increasing the rate of

combustion, which gives improved tolerance of lean combustion or high rates of EGR. This

greater dilution tolerance can reduce CO2 emissions because throttling losses can be decreased

but also other emissions can be lowered due to faster exhaust catalyst “ light-off.” While rapid

burn rate is desirable at light loads and could be delivered with non-variable components,

volumetric efficiency at high speeds and loads could be adversely affected and the rate of

cylinder pressure rise might be too high with such a fixed system. Consequently, variable charge

motion systems have been developed to match the degree of charge motion to the engine speed

and load. These dedicated systems are cost effective but most new engine designs can

incorporate this technology in their basic design in combination with other technologies like

VVT or VVL. For this reason, the technology was evaluated in Task 1 but not explicitly

included in Task 2.

B.3.8. Variable Compression Ratio

Variable compression ratio is another technology that reduces CO2 emissions. A high

compression ratio at light loads can improve an engine’s efficiency but would cause knocking

and excessive cylinder pressures at high loads. Variable compression ratio avoids the inherent

compromise of a fixed value and allows both lower CO2 emissions and improved performance.

Several systems have been proposed including complex linkages in the engine’s cranktrain,

variable height pistons, etc. These concepts are generally considered to be too complex and

heavy for mass production and most of the benefits can be obtained with variable “ effective”

compression ratio through the use of cam phasers. For this reason, this technology was not

evaluated in Task 2.

B.3.9. Gasoline Direct Injection (GDIS, GDILBS, GHCCI)

Gasoline Direct Injection (GDI) is a technology that has recently been introduced in mass

production (1996) and has seen moderate market penetration in Japan and Europe. The preferred

embodiment, Lean Burn Stratified Charge GDI (GDILBS), has not seen application in the US

because it requires a Lean NOX Aftertreatment system, the efficiency of which has not been

sufficient to meet the stringent US NOX emissions standards.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-12

The first generation GDILBS systems tended to be “ Wall Guided” designs. In these

systems, the fuel spray was injected on to a “ wall,” a specially shaped surface of the piston, and

then redirected toward the spark plug. This simple design creates a highly stratified mixture,

which allows very lean mixtures to be burned, but suffers from relatively high HC emissions and

the lean NOX aftertreatment challenge described above. Second generation GDILBS systems are

moving toward “ Spray Guided” concepts, which address the HC emissions and further lower

CO2 emissions because of a larger lean operating range but still require lean aftertreatment

systems. Considerable development activity on second generation GDILBS and Lean NOX

aftertreatment systems is ongoing and some applications could be seen in the US in the future.

Stoichiometric GDI systems (GDIS) avoid the aftertreatment difficulty faced by GDILBS

but don’ t offer a large enough reduction in CO2 emissions to justify their cost and have not seen

broad application. However, with Tier 2 and LEV2 standards becoming increasingly more

stringent, the precision cycle by cycle control of fuel delivery of these systems in combination

with other CO2 reduction technologies like Turbocharging or Cylinder Deactivation could make

GDIS attractive.

Gasoline fueled Homogeneous Charge Compression Ignition (GHCCI) is listed as a GDI

technology since the system will probably be built around GDI. HCCI has not yet proven

feasibility across the full operating range of an engine so some alternative method of combustion

(spark ignition, for example) will be required. For this project, AVL modeled the AVL CSI

(Compression and Spark Ignition) engine. To obtain the flexibility in exhaust residual and

cylinder temperature necessary for controlling HCCI combustion, CSI uses a cam phaser and

discrete VVL on the intake and a simplified, limited range EHVA system on the exhaust. Fuel

injection is by GDI and the cylinder head is otherwise a conventional 4-valve pent-roof

combustion chamber with central spark plug for those operating conditions when autoignition is

not possible or desirable. This is a very low NOX and CO2 combustion system that can operate

with conventional 3-way catalyst.

B.3.10. Diesel (HSDI and Advanced Multi-mode)

Diesel combustion systems are very attractive because of their large reduction in CO2

emissions and because of operating cost savings resulting from reduced fuel consumption.

However, conventional high speed direct injection (HSDI) Diesel engines emit NOX and

particulate matter (PM) at rates that are too high for use in the US without aftertreatment. Diesel

particulate filters with the required conversion efficiency have been developed and are in

production but lean NOX aftertreatment for Diesels faces the same challenge as GDILBS

(described above). For this reason, Diesel engines have not seen broad acceptance in the US for

passenger vehicle applications. For this project, AVL used engine maps for an engine equipped

with 1800 bar common rail injection system capable of multiple injections per cycle for

combustion and aftertreatment control. The engine also used a Variable Geometry Turbocharger

(VGT) and cooled EGR and was developed to meet EURO 4/5 standards. Engine-out emissions

levels were predicted and the required aftertreatment conversion efficiencies were used to define

an appropriate aftertreatment system (the cost of which is described in Appendix B).

Homogeneous Charge Compression Ignition (HCCI) represents the ultimate goal for

combustion engineers because there is no flame in HCCI combustion, so NOX emissions are very

low and the homogeneous charge avoids the formation of particulates. Diesel Advanced MultiMode refers to a Diesel-fueled version of HCCI or alternative combustion system. Full range
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-13

operation of HCCI has not proven feasible and conventional HSDI is used at high loads and

speeds and different alternative combustion modes with varying degrees of charge homogeneity

are used at light loads. The alternative combustion processes are enabled by advanced common

rail injection systems capable of precisely tailored multiple injections per cycle. Engine out

emissions of NOX and PM are significantly lower for this technology allowing a lower cost

aftertreatment system. The CO2 emissions reduction of DAMM is not quite as large as HSDI but

still offers an improvement relative to gasoline fueled spark ignition engines.

B.4. Automatic Transmissions – 5, 6 Speeds

Automatic transmissions with more steps were considered as advanced powertrain

systems. The changes from the baseline model included updating the gear box to the new gear

sets and updating the shift and lock-up controls. The ratios for the new gear sets were taken

from current production transmissions. The ratios were chosen based on drive types, FWD drive

ratios for the cars and minivan, and RWD ratios for the trucks.

B.4.1. Changes to the Gear Box

Table B-5: Gear Ratios and Efficiencies for each of the vehicle classes for the 5AT

Small Car Large Car Minivan Small Truck Large Truck

Ratio η Ratio η Ratio η Ratio η Ratio η

Gear 1 3.938 0.955 3.55 0.95 3.938 0.955 3.57 0.945 3.55 0.95

Gear 2 2.194 0.955 2.24 0.95 2.194 0.955 2.20 0.945 2.24 0.95

Gear 3 1.411 0.97 1.54 0.93 1.411 0.965 1.51 0.925 1.54 0.93

Gear 4 0.973 0.97 1.0 0.98 0.973 0.975 1.0 0.975 1.0 0.98

Gear 5 0.703 0.985 0.69 0.965 0.703 0.985 0.80 0.96 0.69 0.965

Table B-6: Gear Ratios and Efficiencies for each of the vehicle classes for the 6AT

Small Car Large Car Minivan Small Truck Large Truck

Ratio η Ratio η Ratio η Ratio η Ratio η

Gear 1 4.044 0.96 4.044 0.96 4.044 0.96 4.171 0.96 4.171 0.96

Gear 2 2.371 0.975 2.371 0.975 2.371 0.975 2.34 0.975 2.34 0.975

Gear 3 1.556 0.96 1.556 0.96 1.556 0.96 1.521 0.96 1.521 0.96

Gear 4 1.159 0.975 1.159 0.975 1.159 0.975 1.143 0.975 1.143 0.975

Gear 5 0.852 0.96 0.852 0.96 0.852 0.96 0.867 0.96 0.867 0.96

Gear 6 0.672 0.975 0.672 0.975 0.672 0.975 0.691 0.975 0.691 0.975

B.4.2. Changes to the Torque Converter Lock-up

For the 5AT, torque converter lock-up was only allowed in 4

th

and 5

th

gears. The lock-up

strategy was nearly identical to that of the 4AT because of the similarity in gear ratios. For the

6AT, lock-up was allowed in 4

th

through 6

th

gears and followed practices designed for the 4AT.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-14

B.5. Manual Transmissions

For manual transmissions the torque converter is replaced by a dry clutch that is

controlled by the driver through a clutch pedal. The clutch capacity was set to allow transmitting

a maximum torque greater than the engine peak torque in order to prevent slipping when the

clutch was engaged. Also, the automatic transmission oil pump was removed from the model.

Table B-7: Gear Ratios and Efficiencies for each of the vehicle classes for the 5MT

Small Car Small Truck

Ratio η Ratio η

Gear 1 3.58 0.96 3.83 0.92

Gear 2 2.02 0.96 2.062 0.92

Gear 3 1.35 0.96 1.436 0.92

Gear 4 0.98 0.965 1.0 0.95

Gear 5 0.69 0.96 0.838 0.92

Shifts during the drive cycles were performed according to U.S. EPA’s standard shift

schedule. The velocity of the vehicle was reviewed to verify that the vehicle stayed within

velocity limitations. If the vehicle could not follow the prescribed velocity profile, a downshift

was added to successfully complete the test.

B.5.1. Driver Shifting Behavior

The gear shifting profile is presented in Figure B-4. The calculations of the acceleration

rates include the temporary loss of drive torque due to the disengagement of the clutch and the

time required to shift the gear. The torque provided during the engagement and release of the

clutch is also included. The overall shift time was 0.5 seconds for a cycle run and 0.4 seconds

during the full load acceleration.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-15

Figure B-4: Shift Behavior of AT, and AMT, DCT transmissions

B.6. Automated Manual Transmissions

The automated manual transmissions were assumed to be 6 speed transmissions. The

ratios also came from current production transmissions. The ratios were chosen based on the

drive type (i.e. FWD 6 AMT ratios were chosen for the SC, LC and MV, and RWD ratios chosen

for the trucks).

B.6.1. Changes to the gear box

Table B-8: Gear Ratios and Efficiencies for each of the vehicle classes for the 6AMT

Small Car Large Car Minivan Small Truck Large Truck

Ratio η Ratio η Ratio η Ratio η Ratio η

Gear 1 3.93 0.97 3.93 0.96 3.93 0.96 4.46 0.95 4.46 0.96

Gear 2 2.48 0.97 2.48 0.96 2.48 0.96 2.61 0.95 2.61 0.96

Gear 3 1.70 0.97 1.70 0.96 1.70 0.96 1.72 0.95 1.72 0.96

Gear 4 1.25 0.97 1.25 0.96 1.25 0.96 1.25 0.95 1.25 0.96

Gear 5 0.98 0.97 0.98 0.96 0.98 0.96 1.0 0.98 1.0 0.99

Gear 6 0.77 0.97 0.77 0.96 0.77 0.96 0.84 0.95 0.84 0.96
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-16

B.6.2. Auxiliary losses

An additional auxiliary was included to model the losses for the shifting mechanism. An

electric shifting mechanism was assumed with average power consumption of 15 W over the

cycle. This consumption was then adjusted by the alternator efficiency (see discussion above) to

determine the torque loss for the mechanical consumer.

B.6.3. Shifting Behavior

Current AMT systems use hydraulic or electrical activation of the main clutch of a

manual transmission so that the decision to shift is no longer controlled by the driver. The shift

behavior of an AMT is similar to that of a manual driver, i.e. loss of torque occurs during the

shift. New technologies are available to reduce the torque loss during the shift of an automated

manual. The most prominent is a Dual Clutch Transmission (DCT). The DCT uses two

clutches, split between the number of gears. When a shift is desired, the desired gear is brought

to speed and the torque is added to the driveline by slipping one of the clutches. During the

engagement of the new gear, the torque transmitted by the current gear is reduced by slipping the

second clutch. In practice there is still a loss of torque during the shift when compared to the

automatic transmission, shown in Figure B-4. As the U.S. market does not like the effect of the

torque loss during the shift on driveability, a DCT is the form of an AMT that would have the

best chance of market penetration. Future versions of the DCT include electric motors to

augment the torque applied to the driveline during shifts. In this form, the shift behavior is more

like that of an automatic transmission. The shift behavior for the AMT in the CRUISE models is

that of an electrically augmented DCT, the loss of torque during the shift is not modeled,

however the additional power requirement for the torque augmentation is not included.

B.7. Continuously Variable Transmission (CVT)

With the CVT gear box included in CRUISE, it is possible to vary the transmission ratio

infinitely between two user defined threshold values. The CVT can convert every point on the

engine’s operating curve to an operating curve of its own, and every engine operating curve into

an operating range within the field of potential driving conditions. The CVT’s advantage over

conventional fixed-ratio transmissions lies in the potential for enhancing performance, reducing

operating cost due to lower fuel usage, and reduced exhaust emissions (by maintaining the

engine at its operating point of maximum efficiency).

B.7.1. CVT Ratio Range

The CVT was only applied to FWD vehicles, i.e. Small Car, Large Car, and Minivan.

The CVT had maximum and minimum ratios of 2.658 and 0.443. The response time required to

shift between the maximum and minimum ratios was chosen to be 2 seconds.

B.7.2. CVT Losses

The CVT losses were obtained from testing done by the Technical University in Graz

Austria under contract by AVL. This data is confidential but covered the transmission ratios

used in the models. From the test data, empirical relations were created to determine the torque

loss as a function of input speed, vehicle velocity, and torque.

Two CVT efficiency maps were prepared for the models, one with a maximum torque

input of 250 Nm (SC) and one with a maximum torque input of 320 Nm (LC, MV). The
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-17

equations for the CVT losses are confidential, but average efficiencies for the smaller capacity

CVT of 80% and for the larger capacity CVT of 75% are typical.

B.7.3. Control of the CVT

The CVT control element in CRUISE uses the vehicle velocity and load signal to

determine what the CVT ratio should be. The generation of this control map was performed

considering the individual vehicle parameters (axle ratio, tire radius), engine efficiency, full load

curve, and the CVT maximum and minimum ratios.

For full throttle operation, the engine’s full load curve was used to calculate the engine

speed at which the most power was transferred to the axle. The CVT ratio was then chosen to

provide that speed.

B.8. Hybrid Vehicles

The hybrid models in CRUISE were used to determine the performance levels of the

vehicle. To predict the cycle CO2 emissions, the electric components were removed and an

offline analysis was performed to subtract the CO2 emitted during idle operation as the engine

would be shut-off during this time or when hybrid control would allow lower CO2 emissions.

The analysis method is described in section B.8.3.

B.8.1. Hybrid Configurations

B.8.1.1. Integrated Starter Generators

The integrated starter generator hybrid contains a 10 kW electric motor placed between

the engine and the torque converter or the clutch. The general layout of this system is seen in

Figure B-5. The ISG hybrids are run on a 42V system and use a lead acid battery for energy

storage. Two ISG control strategies were evaluated: Start Stop (42VSS) and Motor Assist

(42VMA).

The alternator and starter were removed from the baseline model and replaced with an

electrical induction motor and an electrical consumer. The electric motor allows the engine to

shut down at idle, re-starts the engine and assists with the vehicle launch on the motor assist

versions. For this reason, the starter flange, described above, was no longer required. The

electrical load that was applied to the baseline vehicle as a mechanical loss in the alternator is

now applied as an electrical consumer at the nominal 42V of the electrical system. The electrical

consumer element requires that a resistance be defined as a function of voltage. The resistance

was defined for a constant power loss throughout the cycle of 350 W. The electrical power

consumption also includes the electrification of other auxiliary components such as the water

pump and the power steering pump, when so specified. In Task 2, a special case of ISG was run

for the small car. This version used a 4 kW electric motor operated by the accessory drive belt.

This system, referred to as a Belt Alternator Starter (BAS) was designed to run on a lower cost

12 V system and could only function in Start Stop mode. No motor assist was possible in this

configuration.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-18

Figure B-5: Layout of an Integrated Starter Generator Hybrid Model

B.8.1.2. Moderate and Aggressive Hybrid Configurations

The moderate and aggressive hybrid vehicles were not modeled explicitly for this project

because the extreme complexity of their control systems and the effort required for their optimal

calibration was beyond the scope of the project.

B.8.2. Integration with Other Transmissions

The hybridization of a model involved the addition of the electric motor, battery, and

electrical consumer to the baseline transmission model. Any controls required for the base

transmission were maintained. In the case of an AMT, the torque converter was replaced with a

clutch, which was controlled by the normal AMT clutch control.

B.8.3. Post-Processing Analysis to Determine Hybrid Impact on CO2

Emissions

Full modeling and optimization of the various hybrid control strategies were beyond the

scope of the project. Consequently, the theoretical CO2 reduction potential of the different HEV

configurations was evaluated using simulation results from AVL CRUISE and additional

calculations performed in MS EXCEL. The CRUISE model was built with a conventional

drivetrain but with the engine displacement adjusted to match the baseline performance level,

while taking into account the power of the electrical motor. In order to estimate the potential, the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-19

speed and torque requirements of the driveline components throughout each cycle were used to

identify driving modes where fuel consumption could be eliminated or reduced from the time

history trace of the vehicle simulation. For example, during an idle period where the engine

could be shut down, the amount of fuel consumed during that period of time was subtracted from

the total fuel consumption as evaluated in the CRUISE simulation.

The following driving modes are distinguished:

• Vehicle stop: This mode is set when the velocity is zero. This status is used to determine the

effect of a hybrid powertrain with Start/Stop functionality. The fuel consumed during engine

idle periods at zero velocity was subtracted from the overall consumption.

• Vehicle braking event: This mode is identified when the vehicle velocity is above zero and

the brake pedal is actuated (a CRUISE output). The braking event is divided into several

parts (depending on the powertrain topology: Mild or Moderate) and their different possible

braking power levels (10 kW or 30 kW). This event is used to determine the energy saving

potential of regenerative braking. The braking energy recovered could then be used in either

electrical assist or pure electrical driving (Moderate hybrid only).

A fully automated electric braking system was assumed for the hybrid configurations. This

means that the demanded braking energy could be distributed ideally between the electric

motor and the mechanical brake system. The distribution was dependent on the operating

conditions; i.e. low power braking events could be done purely by the electrical motors!

• Powertrain locked: torque or energy transfer through torque converter clutch or friction

clutch - independent of the direction of energy transfer. In this mode, the engine or motor

must provide torque to the driveline (energy consumed by fuel or from the battery).

The topology of the Moderate HEV allows engine shut-off and “simulation” of the fuel

cut off braking torque of the engine using the E-motor to recover electrical energy to the storage

battery. Depending on the vehicle and based on the typical behavior during fuel cut off braking,

a significant amount of energy could be recovered.

After identifying the energy flow within the driveline and the driving modes, the

calculation and integration values (e.g. fuel consumed during start/stop events) are combined and

the CO2 reduction potential (considering the different hybrid topologies) is estimated.

The steps in the analysis for the Start Stop System, the Mild Hybrid, and the Moderate Hybrid

Powertrain are as follows:

1. Calculation of the average powertrain efficiency of the baseline vehicle, without HEV

components and Start Stop operation for the individual cycle.

2. Calculation of the fuel consumption that could be eliminated by using a Start Stop Strategy.

3. Calculate the total driving energy at the wheels over the cycle.

4. Calculate the driving energy that could be recovered (braking and during engine fuel cut-off)

considering the efficiencies of the electric motor and the battery.

5. Reduce total fuel consumption by subtracting the recuperated energy from the total

mechanical driving energy and using the calculated cycle (individual) average powertrain

efficiency.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-20

Remarks:

1. For all calculations, auxiliary losses, electrical and mechanical efficiencies, etc. are

considered. The calculations described above show the method of determining the potential

for reduction of CO2 emissions without specifically describing the losses.

2. The efficiency values for the electric motors and the battery system are from published data.

B.9. Other Technologies

Technologies other than transmission or engine technologies that influence CO2

emissions and performance are included in this category. For the changes in the vehicle

characteristics (mass, drag coefficient, rolling resistance), a physical model was built and

correlated to the baseline data. This was done just for the small car and large truck models. In

these physical calculation models, the EPA coefficients were removed and replaced with an

appropriate aerodynamic drag coefficient, frontal area, and rolling resistance parameters.

B.9.1. Aerodynamic Drag

The effect of aerodynamic drag was determined by reducing the drag coefficient from the

base value in steps of 0.02 until a final value of 0.1 less than the base was reached. The results

were curve fit to determine a percent CO2 reduction per percent change in drag coefficient.

B.9.2. Rolling Resistance

The rolling resistance was also reduced in five steps to 10% less than the baseline value.

Similar to the drag coefficients, a curve fit was then performed to determine a percent CO2

improvement per percent change in rolling resistance value.

B.9.3. Vehicle Mass

The vehicle mass was swept from ETW minus 250 lbm to ETW plus 250 lbm in steps of

50 lbm. The effect of the reduction in load on the rolling resistance was included. The results

from the sweeps were used to create a coefficient for estimating the influence of mass on CO2

emissions. No attempt to resize the engine to maintain baseline performance levels was made so

the coefficients do not include this effect. In Task 2 small car simulations, the EPA coefficients

were adjusted by this mass effect when called for.

B.9.4. Improved Alternator

For the time period investigated, 2009-2015, it was assumed that improvements in

alternator efficiency could be expected. Current alternators operate with an average efficiency of

about 60%. Higher efficiency alternators (approximately 80% average efficiency) are available

currently but have not been implemented broadly because of their cost. Both conventional and

higher efficiency alternators are modeled in CRUISE as engine speed dependent torque loads

driven by the engine. The loads represent the torque required by the alternator to produce 350 W

of electrical power during the test cycles.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-21

B.9.5. Electrified Auxiliaries

With the exception of the alternator, AMT shift mechanism, and transmission oil pump,

all of the auxiliaries are represented as torque losses on the engine motoring curve in the engine

element of the CRUISE model.

B.9.5.1. Power Steering Pump

The torque required to drive the power steering pump with no steering loads applied for a

typical vehicle in each of the classes was included in the base motoring curve. When Electric

Power Steering (EPS) or Electro-Hydraulic Power Steering (EHPS) was specified for a model,

this base torque loss was eliminated from the motoring curve. Since there are no steering inputs

on the chassis dynamometer during an emissions test procedure, no additional losses were

included and this represents a pure load reduction for the engine on the cycle runs.

B.9.5.2. Engine Oil Pump

The load to drive the engine oil pump was also included in the base motoring curve as

described above. Oil pumps are traditionally sized to provide sufficient oil pressure on a high

mileage engine at idle under high ambient temperature conditions. This results in significantly

oversizing the pump causing it to operate in pressure relief under most operating conditions,

thereby wasting energy. The next most severe operating condition for the oil pump is to supply

sufficient oil pressure at full power. Sizing a pump for this condition reduces the pump

displacement by about 30%. An electric oil pump can be used intermittently to handle the gap

between this high power demand and the worn engine, hot idle demand. More aggressive

downsizing of the oil pump requiring more active electric oil pump operation is possible but was

not considered because of engine reliability effects. For this component, the reduction in load

allowed by the 30% downsizing was subtracted from the engine motoring curve.

B.9.5.3. Engine Water Pump

Like the oil pump, engine coolant pumps are traditionally sized very conservatively to

provide the required flow necessary to cool the engine under peak power conditions. At every

other operating condition, the pump is significantly oversized and requires thermostatic control

resulting in relatively high parasitic loads. Additionally, coolant flow could be eliminated or

reduced drastically following an engine cold start allowing much faster warm-up with associated

reduction in CO2 and exhaust emissions. When considering that the water pump shouldn’ t

operate during the first few minutes of a test cycle and then should operate at much lower flow

rates than an engine driven pump, the reduction in power consumed is significant. For simplicity

of modeling, this power was represented as a cycle average value and added to the alternator’s

continuous load.

B.9.6. Air Conditioning

Currently, air conditioning is not operated on the FTP75, Highway or US06 test cycles

(there is a specific test cycle – SC03 to quantify the impact of air conditioning). However, the

air conditioning compressor represents a significant load on the engine and since air conditioning

is becoming nearly standard equipment in the US fleet, it was desired to quantify the air

conditioning effect through simulation. Air conditioning compressor torque curves were

provided by Meszler Engineering Services (MES) for use in these models and are described in
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-22

more detail in Appendix D. Two air conditioning compressor technologies were evaluated: fixed

displacement, and variable displacement with air recirculation. MES developed curves that

represented the loads required to cool vehicles operating at US annual average ambient

temperature and relative humidity conditions for each compressor type using R152a refrigerant.

These loads were modeled as a continuous engine speed dependent torque requirement for the

engine over the cycle and a control was added to drop the air conditioning compressor load if the

driver demanded maximum acceleration.

B.10. Results

The project to assess GHG emissions reduction technologies was divided into several

parts. In the first phase, baseline vehicle models in CRUISE were developed for each of the five

vehicle classes. In the second step, the baseline models were used to evaluate selected individual

engine, drivetrain, or vehicle technologies for their potential to reduce GHG emissions. In the

final task, CRUISE models were created with combinations of promising technologies and the

combined impacts were determined. The results from each of these project segments are

described below.

B.10.1. Development of 2002 Baseline Vehicle Models

The US fleet for the 2002 Model Year (MY) was split into five classes: Small Car, Large

Car, Minivan, Small Truck, and Large Truck. Statistical analyses of each class were performed

and a production vehicle that, on average, represented the characteristics of the “ homogeneous”

class was selected. The following parameters were considered in the selection process: Curb

Weight, Engine Displacement, Power, Power to Weight Ratio, Torque, Torque to Weight Ratio,

City, Highway, and Combined Fuel Economy, etc. The production vehicles selected for each

class and a comparison of the results of the baseline simulations to those vehicles’ published data

are shown in Table B-9. The calibration objective was to duplicate the actual vehicles’ data

within ± 1%.

B.10.2. Task 1 – Assessment of the Greenhouse Gas Reduction Potential of

Individual Technologies

Once the baseline vehicle models were built and calibrated, they were used to evaluate

the GHG reduction potential of several advanced engine, drivetrain, and vehicle technologies.

Depending on the specific technology involved, the assessments were made in one of two ways.

Engine technologies, where possible, were judged by comparing engine brake specific fuel

consumption (BSFC) maps. All other technologies were reviewed by using a full CRUISE

model equipped with the baseline engine.

B.10.2.1. Task 1 - Assessment of the GHG Reduction Potential of Individual

Engine Technologies

Typically, competitive engine technologies are evaluated by comparing BSFC at a

standard speed and load point like 2000 RPM and 2 bar Brake Mean Effective Pressure (BMEP).

While this method provides some insight into the “ average” performance for all vehicles, it

doesn’ t accurately describe the benefits expected for any one vehicle. In order to make the

comparison of different engine maps more realistic, a single engine operating point most

representative of each of the test cycles was determined for every baseline vehicle from the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-23

baseline CRUISE models. The process is shown graphically in Figure B-6. CRUISE determines

a single, CO2 emissions-weighted operating point that best approximates the average operating

condition for the selected vehicle on the appropriate cycle. In the figure, this point is represented

by the yellow diamond, the speed and load coordinates of which are also shown in the plot’s

table.

Table B-9: 2002 MY Baseline Vehicles

FTP Unadjusted MPG

Class

Representative

Vehicle

Published

Vehicle

Data

CRUISE

Model Delta %

Small Car Cavalier 26.5 26.3 -0.8%

Large Car Taurus 22.1 22.3 0.9%

Minivan Town & Country 19.6 19.6 0.0%

Small Truck Tacoma 18.4 18.4 0.0%

Large Truck Sierra 15.2 15.6 2.6%

Highway Unadjusted MPG

Small Car Cavalier 41.5 41.5 0.0%

Large Car Taurus 35.1 34.9 -0.6%

Minivan Town & Country 30.7 30.4 -1.0%

Small Truck Tacoma 24.0 24.2 0.8%

Large Truck Sierra 21.9 21.7 -0.9%

Combined Unadjusted MPG

Small Car Cavalier 31.6 31.5 -0.3%

Large Car Taurus 26.5 26.6 0.4%

Minivan Town & Country 23.4 23.3 -0.4%

Small Truck Tacoma 20.6 20.6 0.0%

Large Truck Sierra 17.6 17.9 1.7%

0-60 Time [s]

Small Car Cavalier 8.2 8.74 6.6%

Large Car Taurus 8.1 8.07 -0.4%

Minivan Town & Country N/A 10.48

Small Truck Tacoma 9.7 9.99 3.0%

Large Truck Sierra 9.0 8.86 -1.6%
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-24

Figure B-6: Single Operating Point Determination

This analysis was conducted for each of the five baseline vehicles for both the FTP 75 (city) and

Highway cycles. A summary of these operating points is shown in Table B-10.

Table B-10: Summary of Single Operating Points

2002 Representative

Vehicle Data

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

FTP 75 Cycle

Engine Speed [1/min] 1995 2038 1864 1950 1483

Engine Load [bar] 2.74 2.13 2.95 2.72 2.74

CO2 [g/mi] 319.9 382.9 426.0 456.0 534.8

Highway Cycle

Engine Speed [1/min] 2188 2179 1837 2325 1526

Engine Load [bar] 3.19 2.63 3.69 3.45 3.70

CO2 [g/mi] 204.4 242.3 276.0 350.9 391.4
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-25

An estimate of the potential reduction in CO2 emissions on the FTP 75 for selected

engine technologies is displayed in Table B-11. For each of these engine technologies, the

BSFC at a vehicle’s appropriate single point was compared to the baseline engine. Please note

that the data in this table represent the improvements obtained at constant engine displacement.

Some of these technologies improve specific output and would allow downsizing for additional

reductions in CO2.

Table B-11: Assessment of Individual Engine Technologies on FTP 75 Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Cam Phaser - Single (Intake) -1% -1% -1% -1% -2%

Cam Phaser - Single (Exhaust) -2% -3% -1% -2% -2%

Cam Phaser – Dual -4% -4% -3% -3% -4%

Cam Phaser – Coupled -3% -4% -2% -3% -4%

Variable Valve Lift – Discrete -4% -5% -4% -4% -4%

Variable Valve Lift – Continuous -5% -7% -4% -5% -6%

Camless Valve Actuation –

Electrohydraulic

-13% -17% -14% -14% -14%

Turbocharging -9% -9% -7% -5%

Cylinder Deactivation -4% -6% -6% -6% -6%

Variable Charge Motion (CBR) -3% -4% -2% -3% -4%

GDI Stoichiometric 1% -1% 1% 1% 0%

GDI Lean Burn Stratified -7% -9% -6% -7% -9%

Gasoline HCCI -5% -7% -4% -5% -6%

Diesel – HSDI -21% -24% -26% -27% -25%

Diesel – Advanced Multi-Mode -16% -18% -21% -22% -20%

For those technologies (Turbocharging, Diesel, Cylinder Deactivation) with radically

different full load curves or operating modes, the single point evaluation method was not

meaningful. In these cases (shaded in the table), the estimates were obtained through full

CRUISE simulations with engine displacements adjusted to maintain vehicle performance at the

baseline level. The Camless Valve Actuation – Electrohydraulic technology included Cylinder

Deactivation and the single point estimates were adjusted based on the results from a single

vehicle simulation. Of additional note, the two Diesel improvement estimates are based on fuel

consumption not CO2 emissions. The true reduction in CO2 emissions would be smaller because

of Diesel fuel’s higher density.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-26

Table B-12: Assessment of Individual Engine Technologies on Highway Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Cam Phaser - Single (Intake) -2% -2% -1% -1% -2%

Cam Phaser - Single (Exhaust) -2% -3% -2% -2% -3%

Cam Phaser – Dual -3% -4% -2% -2% -4%

Cam Phaser – Coupled -3% -4% -2% -2% -4%

Variable Valve Lift – Discrete -4% -4% -3% -3% -4%

Variable Valve Lift – Continuous -4% -6% -3% -4% -4%

Camless Valve Actuation –

Electrohydraulic

-9% -15% -8% -12% -9%

Turbocharging -3% -6% -4% -8%

Cylinder Deactivation -1% -6% -3% -5% -2%

Variable Charge Motion (CBR) -3% -4% -3% -4% -4%

GDI Stoichiometric -1% -1% 1% 1% 0%

GDI Lean Burn Stratified -5% -8% -3% -2% -6%

Gasoline HCCI -3% -6% -2% -2% -4%

Diesel – HSDI -19% -19% -22% -27% -21%

Diesel – Advanced Multi-Mode -11% -11% -15% -21% -13%

Table B-12 and Table B-13 show the improvement potential of the individual engine

technologies on the Highway cycle and Combined City/Highway cycles (weighted 55%/45%)

respectively. The same notes apply to each of these tables.

On a combined city/highway basis, the Cam Phasing and CBR technologies offer

improvements in the 2-4% range. Variable Valve Lift systems show slightly better results.

Turbocharging and Cylinder Deactivation are both variable displacement technologies and offer

reductions approaching 10%. Gasoline Direct Injection (Stratified) exhibits a similar decrease in

CO2. Electrohydraulic Valve Actuation reduces fuel consumption in the range of 15% and

Diesels show the best improvements with 20+%.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-27

Table B-13: Assessment of Individual Engine Technologies on Combined FTP 75 and

Highway Cycles

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Cam Phaser - Single (Intake) -2% -1% -1% -1% -2%

Cam Phaser - Single (Exhaust) -2% -3% -2% -2% -3%

Cam Phaser – Dual -3% -4% -2% -3% -4%

Cam Phaser – Coupled -3% -4% -2% -2% -4%

Variable Valve Lift – Discrete -4% -4% -3% -4% -4%

Variable Valve Lift – Continuous -5% -6% -4% -5% -5%

Camless Valve Actuation –

Electrohydraulic

-11% -16% -11% -13% -12%

Turbocharging -6% -8% -6% -6%

Cylinder Deactivation -3% -6% -5% -6% -4%

Variable Charge Motion (CBR) -3% -4% -2% -3% -4%

GDI Stoichiometric 0% -1% 1% 1% 0%

GDI Lean Burn Stratified -6% -9% -4% -5% -8%

Gasoline HCCI -4% -6% -3% -4% -5%

Diesel – HSDI -20% -22% -24% -27% -23%

Diesel – Advanced Multi-Mode -13% -15% -18% -21% -17%

B.10.2.2. Task 1 – Assessment of the GHG Reduction Potential of Individual

Drivetrain and Other Vehicle Technologies

The influence of advanced transmission or other vehicle technologies on CO2 emissions

is more complicated and could not be assessed using a single point comparison of engine maps.

More specifically, when designed properly, advanced transmissions shift the operating point of

the engine to more efficient areas of the map. For this reason, full CRUISE simulations were

required to determine the improvement potential of these vehicle related technologies. In order

to isolate the effect of individual technologies, the baseline engine was used in each case. No

attempt was made to correct for any improvement or change in vehicle performance compared to

the baseline vehicle.

The CO2 improvement potential of selected drivetrain technologies on the city cycle is

shown in Table B-14. The baseline drivetrain for each vehicle was a 4-speed Automatic

Transmission with lock-up Torque Converter. Engine displacement was held constant as

described above. The 5-speed Manual was shifted according to the US EPA standard shift

schedule. All other Automatics utilized shift curves developed and calibrated on the baseline

vehicle. The reduction in fuel consumption afforded by the hybrid drivetrains was determined

through post-processing of CRUISE results.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-28

Table B-14: Assessment of Individual Drivetrain Technologies on FTP 75 Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

5-Speed Automatic -2% -1% -1% -1% -1%

6-Speed Automatic -3% -4% -5% -4% -2%

6-Speed Automated Manual -12% -10% -11% -10% -9%

5-Speed Manual -4% -1%

CVT Transmission -8% -7% -10%

42-Volt 10 kW ISG (Start Stop) -12% -8% -7% -7% -9%

42-Volt 10 kW ISG (Mot. Assist) -17% -10% -10% -10% -10%

The improvement of these drivetrain technologies on the highway and combined

city/highway cycles are presented in Table B-15 and Table B-16 respectively. As seen in Table

B-15, most of the drivetrain technologies don’ t offer much improvement on the highway because

the torque converter is locked for most of the cycle. Similarly, the lack of transients on this cycle

limits the ability of the hybrids to recover braking energy.

Table B-15: Assessment of Individual Drivetrain Technologies on Highway Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

5-Speed Automatic -1% -1% -1% -1% 0%

6-Speed Automatic -2% -2% -1% -3% -1%

6-Speed Automated Manual -3% -4% -4% -5% -1%

5-Speed Manual -1% -2%

CVT Transmission 2% 1% 3%

42-Volt 10 kW ISG (Start Stop) 0% 0% 0% 0% 0%

42-Volt 10 kW ISG (Mot. Assist) -1% -1% -1% 0% 0%
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-29

Table B-16: Assessment of Individual Drivetrain Technologies on Combined FTP 75 and

Highway Cycles

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

5-Speed Automatic -2% -1% -1% -1% -1%

6-Speed Automatic -3% -3% -3% -3% -2%

6-Speed Automated Manual -8% -7% -8% -8% -5%

5-Speed Manual -2% -1%

CVT Transmission -4% -3% -4%

42-Volt 10 kW ISG (Start Stop) -7% -4% -4% -4% -5%

42-Volt 10 kW ISG (Mot. Assist) -10% -6% -6% -6% -5%

Overall, the trend to greater numbers of speeds in the automatic transmission is

beneficial. The use of 6-speed automatics could improve combined CO2 emissions by about 3%.

Six-speed automated manuals are even better with reductions approaching 8% due to the

elimination of the inefficiency of the torque converter. Conventional manual transmissions can

offer the same improvement if shifted optimally but are not expected to take a major share of the

US market. CVT transmissions offer some benefit but are hampered by losses in the belt drive

system and similar improvements could be obtained less expensively with some of the other

drivetrains. Hybrid drivetrains have an outstanding potential to reduce fuel consumption on the

city cycle due to the ability to recuperate braking energy but much of the advantage is lost on the

highway cycle resulting in combined improvements in the 5-10% range for the hybrid systems

evaluated.

The final part of Task 1 was to investigate the contribution of “ Other Vehicle”

technologies that could not be grouped readily with the engine or drivetrain areas. Some

examples include Air Conditioning, Electric Accessories, Aerodynamic Drag, etc. The CO2

emissions impacts of these technologies on the city cycle are shown in Table B-17.

Please note that the last three technologies, Aerodynamic Drag, Mass, and Tire Rolling

Resistance were modeled physically. Rather than using the published A, B, and C coefficients of

the EPA chassis dynamometer setting to define vehicle resistance, the baseline models were

converted to full physical models capturing drag coefficient, vehicle frontal area, tire rolling

resistance, etc. The variables for these models were adjusted up and down from the baseline case

by 5-10% and impact coefficients were determined through regression for each of these factors.

These coefficients were in the form of % change in CO2 per % change in the parameter. This

would allow continuous variation of these parameters rather than in discrete steps like engine or

drivetrain technologies. All of the other technologies were evaluated only on the small car and

large truck. Since the improvements were quite close for the two extremes of vehicle types, it

was concluded that the estimated improvements of all of the technologies could be applied to any

vehicle.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-30

Table B-17: Assessment of Individual Other Vehicle Technologies on FTP 75 Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Electric Power Steering (EPS) -2% -1%

Higher Efficiency Alternator -1% -1%

Electric Water Pump (EWP) 0% 0%

Electric Oil Pump (EOP) 0% 0%

Electric Accessories -3% -3%

Variable Displacement AC

Compressor (vs. Fixed Displ.)

-12% -10% -8% -11%

Aerodynamic Drag Coefficient (%

CO2 / % Cd)

0.0442 0.0868

Mass Reduction Coefficient

(%CO2 / % Mass Change)

0.4424 0.4992

Tire Rolling Resistance Coefficient

(% CO2 / % TRR)

0.1343 0.1447

The highway cycle and combined cycle effects of the other vehicle technologies are

displayed in Table B-18 and Table B-19 respectively. On a combined basis, the electric

accessory technologies have a fairly small impact (1-2%) but could be applied to all vehicles.

The Variable Displacement Air Conditioning Compressor shows an impressive reduction of

about 10% in CO2 in comparison to the Fixed Displacement Compressor. In current testing

procedures, air conditioning is not used on the FTP 75 or Highway emissions cycles so no

benefit would be obtained on the cycles. However, these benefits could be observed in real

world driving. The impact coefficients for Aerodynamic Drag, Mass Reduction, and Tire

Rolling Resistance agree reasonably well with results published in the literature. For example, a

5% reduction in mass would reduce CO2 emissions by about 3%.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-31

Table B-18: Assessment of Individual Other Vehicle Technologies on Highway Cycle

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Representative Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Electric Power Steering (EPS) -1% -1%

Higher Efficiency Alternator -1% 0%

Electric Water Pump (EWP) 0% 0%

Electric Oil Pump (EOP) 0% 0%

Electric Accessories -2% -2%

Variable Displacement AC

Compressor (vs. Fixed Displ.)

-8% -8% -6% -7%

Aerodynamic Drag Coefficient (%

CO2 / % Cd)

0.3124 0.3200

Mass Reduction Coefficient

(%CO2 / % Mass Change)

0.6302 0.6582

Tire Rolling Resistance Coefficient

(% CO2 / % TRR)

0.2353 0.2755

Table B-19: Assessment of Individual Other Vehicle Technologies on Combined FTP 75

and Highway Cycles

Vehicle Class

Small

Car

Large

Car

Minivan

Small

Truck

Large

Truck

Mule Vehicle Cavalier Taurus

Town &

Country

Tacoma Sierra

Engine 2.2l I4 3.0l V6 3.3l V6 3.4l V6 5.3l V8

Electric Power Steering (EPS) -1% -1%

Higher Efficiency Alternator -1% 0%

Electric Water Pump (EWP) 0% 0%

Electric Oil Pump (EOP) 0% 0%

Electric Accessories -3% -2%

Variable Displacement AC

Compressor (vs. Fixed Displ.)

-10% -9% -7% -9%

Aerodynamic Drag Coefficient (%

CO2 / % Cd)

0.1649 0.1917

Mass Reduction Coefficient

(%CO2 / % Mass Change)

0.5269 0.5708

Tire Rolling Resistance Coefficient

(% CO2 / % TRR)

0.1798 0.2036
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-32

B.10.3. Task 2 – Assessment of the Greenhouse Gas Reduction Potential of

Combinations of Technologies

Upon completion of Task 1, a large number of individual engine, drivetrain, and vehicle

technologies were evaluated and ranked for their potential to reduce GHG emissions. Some

previous studies on the topic of GHG reduction combined separate technologies into “ packages”

and estimated the combined benefit by adding the individual technology improvements together.

It is generally understood that combining improvement estimates in this way results in “ double

counting” or over-prediction of the actual reductions possible. To avoid this source of

inaccuracy, selected technology combination packages were built as full CRUISE vehicle models

and simulated in a more appropriate way. Since the number of possible combinations of all the

technologies evaluated was enormous, the ranking of the Task 1 results together with estimates

of the incremental cost of a technology was used to select reasonable and cost effective packages

to simulate. The results of these technology simulations are described in the next section and the

following tables.

B.10.3.1. Task 2 – Small Car Combinations of Technologies

Table B-20 displays the simulation results of 16 technology combinations compared to

the 2002 MY baseline data. Case 00 represents a quasi-baseline for the 2009 MY. It represents

the combination of technologies projected to take the largest share of the market in the small car

class in 2009. This case was also used to capture projected changes in vehicle mass and

performance in 2009.

The table contains the following information: Case Number, Technologies selected,

adjusted Engine Displacement to match 2009 baseline performance levels, Fuel Economy on the

FTP 75, Highway, and Combined cycles, Tier 2 Bin 5 tailpipe CO2 emissions for the same

cycles, and 0-60 MPH times. The same data is plotted graphically in Figures A-7 and A-8.

Figure B-7 shows the combined cycle tailpipe CO2 emissions, sorted in decreasing order. The

2009 baseline case (00) emits about 270 g/mi. As can be seen, the most effective technologies

(GDI, Diesel, and Hybrids) are clustered near the bottom of the plot. The percentage reduction

in combined CO2 emissions of each package compared to the 2002 MY baseline vehicle is

shown in Figure B-8. Improvements of 15-20% are possible with combinations of currently

available engine and drivetrain technologies. Further reductions (>20%) require the use of

hybrid technologies.

B.10.3.2. Task 2 – Large Car Combinations of Technologies

Table B-21 displays the simulation results of 23 technology combinations compared to

the 2002 MY baseline data. Case 00 again represents a quasi-baseline for the 2009 MY. Figures

A-9 and A-10 plot graphically the tabular values for combined tailpipe CO2 emissions and

percent reduction in combined CO2 emissions. Like the small car class, relatively conventional

technology combinations can yield reductions of 10-20%. Hybrids or advanced technology like

Electro-Hydraulic Valve Actuation must be used to obtain improvements greater than 20%.

B.10.3.3. Task 2 – Minivan Combinations of Technologies

Table B-22 presents the simulation results of 13 technology combinations compared to

the 2002 MY baseline data. Fewer cases were evaluated for the minivan class because the

market share for this class is relatively small. The combined tailpipe CO2 emissions level of the
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-33

2009 MY baseline model is approximately 350 g/mi. The best packages assessed were just

under 300 g/mi for two Gasoline Direct Injection systems. Figures A-11 and A-12 plot

graphically the tabular values for combined tailpipe CO2 emissions and percent reduction in

combined CO2 emissions. Like the previous classes, relatively conventional technology

combinations can yield reductions of 10-20%. Hybrids or advanced technology like EHVA must

be used to obtain improvements greater than 20%. A Mild Hybrid (42VMA) with GDI

demonstrated the largest reduction in CO2 emissions (22%).

B.10.3.4. Task 2 – Small Truck Combinations of Technologies

Table B-23 displays the simulation results of 13 technology combinations compared to

the 2002 MY baseline data. On the combined cycle, the 2009 baseline emits nearly 390 g/mi of

CO2. Fewer cases were modeled on the small truck compared to some of the other classes but

the best case, a Diesel with 6-speed automated manual transmission, delivered a reduction of

about 27%. Figures A-13 and A-14 show the data in graphical format. Readily available

technologies can deliver improvements in the 10-20% range. Larger reductions in CO2 require

hybrid or other advanced technologies.

B.10.3.5. Task 2 – Large Truck Combinations of Technologies

The simulation results of 16 technology packages on the large truck are shown in Table

B-24. The combined CO2 emissions for the 2009 MY baseline were just over 460 g/mi. The

table data is plotted graphically in Figures A-15 and A-16. Combinations of conventional

technologies, including simple mass reduction, could reduce CO2 emissions by 10-20%. More

advanced technologies, like hybrid drivetrain or EHVA, are required to achieve more than 20%

improvement.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table B-20: Small Car Technology Combination Simulation Results

Simulation Technology Displ. [l] FTP HWY Comb. Delta % 

MY 02 B/L MPFI,4AT 2.20 332.6 211.0 277.9 0.0

Case 00 DCP,DVVL,5AT 2.20 316.6 213.9 270.4 -2.7

Case 01 DCP,6AT 2.10 313.1 210.3 266.8 -4.0

Case 02 DCP,4AT,EPS,HIALT 2.30 325.8 216.2 276.5 -0.5Case 03 DCP,5AT,EPS,HIALT 2.20 313.2 210.8 267.1 -3.9Case 04 DCP,CVT,EPS,HIALT 2.40 311.1 228.1 273.8 -1.5

Case 05 DCP,DVVL,6AMT,EPS,HIALT 2.20 269.1 201.7 238.8 -14.1

Case 06 GHCCI,6AMT,EPS,HIALT 2.10 263.7 197.1 233.7 -15.9

Case 07 DCP,TURB,GDIS,6AMT,EPS,HIALT 1.18 239.4 194.1 219.0 -21.2

Case 08 GHCCI,6AMT,42VMA,EPS,EWP,EOP 1.92 222.2 190.8 208.1 -25.1

Case 10 DAMM,6AMT,42VMA,EPS,EWP,EOP 1.72 230.7 208.4 220.7 -20.6

Case 13.1 DCP,TURB,GDIS,6AMT,EPS,HIALT,FIXAC 1.18 306.8 226.4 270.6 -2.6

Case 13.2 DCP,TURB,GDIS,6AMT,EPS,HIALT,VARAC 1.18 270.3 209.3 242.9 -12.6

Case 14 DCP,CVVL,6AMT,12VSS,EPS 2.20 240.4 197.2 221.0 -20.5

Technology Key

DCP Cam Phaser - Dual 6AMT 6-Speed Automated Manual

CCP Cam Phaser - Coupled CVT Continuously Variable Transmission

DVVL Variable Valve Lift - Discrete 12VSS 12-Volt 4 kW ISG (Start Stop)

CVVL Variable Valve Lift - Continuous 42VMA 42-Volt 10 kW ISG (Motor Assist)

EHVA Camless Valve Actuation - Electrohydraulic EPS Electric Power Steering

TURB Turbocharging HIALT Improved Alternator (Higher efficienc

CYLDCT Cylinder Deactivation EWP Electric Water Pump

GDIS GDI Stoichiometric EOP Electric Oil Pump

GDILBS GDI Lean Burn Stratified FIXAC Fixed Displacement AC Compressor

GHCCI Gasoline HCCI VARAC Variable Displacement AC Compress

HSDI Diesel MR Mass Reduction

DAMM Diesel – Advanced Multi-Mode

5AT 5-Speed Automatic

6AT 6-Speed Automatic

Small Car Technology Combination Simulation Results Tier 2 Bin 5 CO2 [g/mi]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table B-21: Large Car Technology Combination Simulation Results

Simulation Technology Displ. [l] FTP HWY Comb. Delta % 

MY 02 B/L MPFI,4AT 3.00 392.7 251.7 329.2 0.0

Case 00 DCP,DVVL,6AT 3.00 362.7 237.9 306.5 -6.9

Case 01 DCP,CYLDCT,6AT 3.00 349.2 225.9 293.7 -10.8

Case 02 DCP,CVVL,6AT 3.00 349.9 232.8 297.2 -9.7

Case 03 DCP,6AT 3.00 370.4 240.5 311.9 -5.3

Case 04 DCP,TURB,6AT,EPS,HIALT 1.67 335.6 224.2 285.5 -13.3

Case 05 DCP,CVVL,6AMT,EPS,HIALT 3.00 311.5 221.1 270.8 -17.7

Case 06 GHCCI,6AMT,EPS,HIALT 3.00 322.4 225.2 278.7 -15.4

Case 07 DCP,TURB,GDIS,6AMT,EPS,HIALT 1.77 287.9 217.6 256.3 -22.2

Case 08 DCP,CVT,EPS,HIALT 3.20 357.1 247.2 307.6 -6.6

Case 09 DCP,TURB,GDIS,6AT,42VMA,EPS,EWP,EOP 1.34 245.6 205.6 227.6 -30.9

Case 10 CCP,DVVL,CYLDCT,6AT,42VMA,EPS,EWP,EOP 2.86 289.8 235.3 265.3 -19.4

Case 11 GHCCI,6AMT,42VMA,EPS,EWP,EOP 2.55 256.8 209.6 235.6 -28.5

Case 12 DAMM,6AMT,42VMA,EPS,EWP,EOP 2.33 260.9 221.5 243.2 -26.1

Case 16.1 DCP,TURB,6AT,EPS,HIALT,FIXAC 1.67 392.2 256.1 331.0 0.5

Case 16.2 DCP,TURB,6AT,EPS,HIALT,VARAC 1.67 364.8 239.7 308.5 -6.3

Case 17 DCP,CYLDCT,GDIS,6AMT,EPS,HIALT 2.70 315.7 215.7 270.7 -17.8

Case 18.1 DCP,CYLDCT,GDIS,6AMT,EPS,HIALT,FIXAC 2.70 380.1 253.7 323.2 -1.8

Case 18.2 DCP,CYLDCT,GDIS,6AMT,EPS,HIALT,VARAC 2.70 342.9 233.1 293.5 -10.9

Case 19 EHVA,6AMT,EPS,HIALT 3.00 296.1 206.4 255.7 -22.3

Case 20 EHVA,GDIS,6AMT,EPS,HIALT 2.70 283.0 202.3 246.7 -25.1

Technology Key

DCP Cam Phaser - Dual 6AMT 6-Speed Automated Manual

CCP Cam Phaser - Coupled CVT Continuously Variable Transmission

DVVL Variable Valve Lift - Discrete 42VSS 42-Volt 10 kW ISG (Start Stop)CVVL Variable Valve Lift - Continuous 42VMA 42-Volt 10 kW ISG (Motor Assist)

EHVA Camless Valve Actuation - Electrohydraulic EPS Electric Power SteeringTURB Turbocharging HIALT Improved Alternator (Higher efficienc

CYLDCT Cylinder Deactivation EWP Electric Water Pump

GDIS GDI Stoichiometric EOP Electric Oil Pump

GDILBS GDI Lean Burn Stratified FIXAC Fixed Displacement AC Compressor

GHCCI Gasoline HCCI VARAC Variable Displacement AC Compress

HSDI Diesel MR Mass Reduction

DAMM Diesel – Advanced Multi-Mode

5AT 5-Speed Automatic

6AT 6-Speed Automatic

Tier 2 Bin 5 CO2 Large Car Technology Combination Simulation Results [g/mi]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table B-22: Minivan Technology Combination Simulation Results

Simulation Technology Displ. [l] FTP HWY Comb. Delta % 

MY 02 B/L MPFI,4AT 3.30 447.8 289.2 376.4 0.0

Case 00 CCP,DVVL,5AT 3.24 413.7 274.4 351.0 -6.7

Case 01 DCP,6AT 3.25 419.6 279.9 356.7 -5.2

Case 02 CCP,DVVL,6AMT,EPS,HIALT 3.06 370.5 263.6 322.4 -14.3

Case 03 CCP,CVVL,6AMT,EPS,HIALT 3.06 356.4 258.1 312.2 -17.1

Case 04 DCP,TURB,GDIS,6AMT,EPS,HIALT 1.85 336.9 262.2 303.3 -19.4

Case 05 CCP,DVVL,CYLDCT,6AMT,EPS,HIALT 3.06 357.9 258.8 313.3 -16.8

Case 06 CCP,CYLDCT,GDIS,6AMT,EPS,HIALT 2.90 376.7 263.4 325.7 -13.5

Case 07 CCP,TURB,6AMT,EPS,HIALT 1.89 364.7 270.1 322.1 -14.4

Case 08 DAMM,6AMT,EPS,HIALT 2.43 336.1 271.1 306.9 -18.5

Case 09.1 CCP,CYLDCT,GDIS,6AMT,EPS,HIALT,FIXAC 2.90 458.5 308.4 391.0 3.9

Case 09.2 CCP,CYLDCT,GDIS,6AMT,EPS,HIALT,VARAC 2.90 411.8 284.2 354.4 -5.9

Case 10 CCP,CYLDCT,GDIS,6AMT,42VMA,EPS,EWP,EOP 2.60 322.6 255.2 292.3 -22.4

Case 11 EHVA,GDIS,6AMT,EPS,HIALT 2.85 336.4 246.3 295.9 -21.4

Technology KeyDCP Cam Phaser - Dual 6AMT 6-Speed Automated Manual

CCP Cam Phaser - Coupled CVT Continuously Variable Transmission

DVVL Variable Valve Lift - Discrete 42VSS 42-Volt 10 kW ISG (Start Stop)

CVVL Variable Valve Lift - Continuous 42VMA 42-Volt 10 kW ISG (Motor Assist)

EHVA Camless Valve Actuation - Electrohydraulic EPS Electric Power Steering

TURB Turbocharging HIALT Improved Alternator (Higher efficienc

CYLDCT Cylinder Deactivation EWP Electric Water Pump

GDIS GDI Stoichiometric EOP Electric Oil Pump

GDILBS GDI Lean Burn Stratified FIXAC Fixed Displacement AC Compressor

GHCCI Gasoline HCCI VARAC Variable Displacement AC Compress

HSDI Diesel MR Mass Reduction

DAMM Diesel – Advanced Multi-Mode

5AT 5-Speed Automatic

6AT 6-Speed Automatic

Tier 2 Bin 5 CO2 Minivan Technology Combination Simulation Results [g/mi]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table B-23: Small Truck Technology Combination Simulation Results

Simulation Technology Displ. [l] FTP HWY Comb. Delta % 

MY 02 B/L MPFI,4AT 3.40 476.5 363.6 425.7 0.0

Case 00 DCP,DVVL,6AT 3.20 429.3 331.9 385.5 -9.4

Case 01 DCP,6AT 3.20 435.6 333.1 389.5 -8.5

Case 02 DCP,TURB,6AT,EPS,HIALT 1.70 428.8 321.3 380.4 -10.6

Case 03 DCP,CYLDCT,6AT 3.20 417.0 325.5 375.8 -11.7Case 04 DCP,TURB,GDIS,6AMT,EPS,HIALT 1.64 344.1 302.8 325.5 -23.5

Case 05 CCP,DVVL,CYLDCT,6AMT,EPS,HIALT 2.96 358.1 308.6 335.8 -21.1

Case 06 CCP,DVVL,CYLDCT,6AT,42VMA,EPS,EWP,EOP 2.91 336.9 305.2 322.6 -24.2

Case 07 DCP,CYLDCT,GDIS,6AMT,EPS,HIALT 2.77 367.4 310.6 341.8 -19.7

Case 08 DAMM,6AMT,EPS,HIALT 2.33 349.2 322.1 337.0 -20.8

Case 09 HSDI,6AMT,EPS,HIALT 2.33 325.2 295.5 311.8 -26.7

Case 10.1 CCP,DVVL,CYLDCT,6AMT,EPS,HIALT,FIXAC 2.96 447.8 356.0 406.5 -4.5

Case 10.2 CCP,DVVL,CYLDCT,6AMT,EPS,HIALT,VARAC 2.96 398.2 331.2 368.1 -13.5

Case 11 EHVA,GDIS,6AMT,EPS,HIALT 2.77 334.8 292.0 315.5 -25.9

Technology Key

DCP Cam Phaser - Dual 6AMT 6-Speed Automated Manual

CCP Cam Phaser - Coupled CVT Continuously Variable Transmission

DVVL Variable Valve Lift - Discrete 42VSS 42-Volt 10 kW ISG (Start Stop)

CVVL Variable Valve Lift - Continuous 42VMA 42-Volt 10 kW ISG (Motor Assist)

EHVA Camless Valve Actuation - Electrohydraulic EPS Electric Power SteeringTURB Turbocharging HIALT Improved Alternator (Higher efficienc

CYLDCT Cylinder Deactivation EWP Electric Water Pump

GDIS GDI Stoichiometric EOP Electric Oil Pump

GDILBS GDI Lean Burn Stratified FIXAC Fixed Displacement AC Compressor

GHCCI Gasoline HCCI VARAC Variable Displacement AC Compress

HSDI Diesel MR Mass Reduction

DAMM Diesel – Advanced Multi-Mode

5AT 5-Speed Automatic

6AT 6-Speed Automatic

Tier 2 Bin 5 CO2 Small Truck Technology Combination Simulation Results [g/mi]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Table B-24: Large Truck Technology Combination Simulation Results

Simulation Technology Displ. [l] FTP HWY Comb. Delta % 

MY 02 B/L MPFI,4AT 5.30 563.3 406.1 492.6 0.0

Case 00 CCP,6AT 5.00 527.1 388.1 464.6 -5.7

Case 01 CCP,DVVL,6AT 4.70 512.6 386.4 455.8 -7.5

Case 02 DCP,CYLDCT,6AT 4.70 494.4 381.2 443.5 -10.0

Case 03 CCP,CYLDCT,6AT 5.00 498.8 381.3 445.9 -9.5

Case 04 CCP,DVVL,CYLDCT,6AT,EPS,HIALT 4.70 475.3 374.6 430.0 -12.7

Case 05 CCP,DVVL,CYLDCT,6AMT,EPS,HIALT 4.80 437.0 370.8 407.2 -17.3

Case 06 GDILBS,6AMT,EPS,HIALT 4.50 427.2 361.5 397.6 -19.3Case 07 CCP,6AT,-15% MR 4.20 451.3 338.6 400.6 -18.7

Case 08 CCP,DVVL,CYLDCT,6AT,EPS,HIALT,-15% MR 3.90 405.3 325.7 369.5 -25.0

Case 09 CCP,DVVL,CYLDCT,6AT,42VMA,EPS,EWP,EOP 4.60 405.3 366.4 387.8 -21.3

Case 10 DAMM,6AMT,42VMA,EPS,EWP,EOP 3.30 369.4 369.9 369.6 -25.0

Case 11 GDILBS,6AMT,42VMA,EPS,EWP,EOP 4.20 372.6 352.3 363.5 -26.2

Case 12 EHVA,GDIS,6AMT,EPS,HIALT 4.50 419.8 357.1 391.6 -20.5

Case 13 CCP,CYLDCT,GDIS,6AMT,EPS,HIALT 4.50 467.9 380.5 428.6 -13.0

Technology Key

DCP Cam Phaser - Dual 6AMT 6-Speed Automated Manual

CCP Cam Phaser - Coupled CVT Continuously Variable Transmission

DVVL Variable Valve Lift - Discrete 42VSS 42-Volt 10 kW ISG (Start Stop)

CVVL Variable Valve Lift - Continuous 42VMA 42-Volt 10 kW ISG (Motor Assist)

EHVA Camless Valve Actuation - Electrohydraulic EPS Electric Power Steering

TURB Turbocharging HIALT Improved Alternator (Higher efficienc

CYLDCT Cylinder Deactivation EWP Electric Water Pump

GDIS GDI Stoichiometric EOP Electric Oil Pump

GDILBS GDI Lean Burn Stratified FIXAC Fixed Displacement AC Compressor

GHCCI Gasoline HCCI VARAC Variable Displacement AC Compress

HSDI Diesel MR Mass Reduction

DAMM Diesel – Advanced Multi-Mode

5AT 5-Speed Automatic

6AT 6-Speed Automatic

Tier 2 Bin 5 CO2 Large Truck Technology Combination Simulation Results [g/mi]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-39

Figure B-7: Small Car Combined CO2 Emissions

Figure B-8: Small Car Reduction in Combined CO2 Emissions

(Compared to 2002 MY Baseline)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-40

Figure B-9: Large Car Combined CO2 Emissions

Figure B-10: Large Car Reduction in Combined CO2 Emissions

(Compared to 2002 MY Baseline)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-41

Figure B-11: Minivan Combined CO2 Emissions

Figure B-12: Minivan Reduction in Combined CO2 Emissions

(Compared to 2002 MY Baseline)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-42

Figure B-13: Small Truck Combined CO2 Emissions

Figure B-14: Small Truck Reduction in Combined CO2 Emissions

(Compared to 2002 MY Baseline)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-43

Figure B-15: Large Truck Combined CO2 Emissions

Figure B-16: Large Truck Reduction in Combined CO2 Emissions

(Compared to 2002 MY Baseline)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page B-44
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page C-1

Appendix C: Vehicle Cost Matrix
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Technology L4 V6 V6 V6 V8 Technology Description - Hardware and 

Engine Technologies

2002 Baseline MPFI Engine 2.2L DOHC 4V 3.0L DOHC 4V 3.4L DOHC 4V 3.3L OHV 2V 5.3L OHV 2V

2002 Baseline Transmission A4 FWD A4 FWD A4 RWD A4 FWD A4 AWD

Cavalier (SC) Taurus (LC) Tacoma (ST) Town & C (MV) Sierra (LT)

DOHC from OHV - - - $500 $600 Substitution of DOHC 4V gas engine for O

cylinder count. Content increase for Vee e

drive, +3 camshafts, +2 valves per cylinde

extra valve seats and valve guides, roller c

heads and Fe block for OHV and Al heads 

External EGR Credit ($25) ($25) ($25) ($25) ($25) External EGR can be deleted if not needed 

exhaust dilution is available.

Variable Cam Phaser

· Single $35 $70 $70 $35 $35 Line DOHC engines -1 phaser on intake

Vee DOHC engines - 2 phasers (1 on eac

Line or Vee OHV - 1 phaser provides coup

· Dual $70 $140 $140 $140 $140 Line DOHC engines - 2 phasers

Vee DOHC engines - 4 phasers

Practical solution for OHV engines undefin

· Coupled $50 $115 $115 $35 $35 Line DOHC engines -1 phaser linked to bo

Vee DOHC engines - 2 phasers (1 linked t

bank)

Line or Vee OHV - 1 phaser provides coup

Variable Valve Lift (VVL) Intake phasing costs must be added to all V

Discrete 2-step VVL (DVVL) - Electromagnetic (EM) $120 4 lost motion devices each operating 1 inta

4 actuators, drivers, harness. Intake valve

valvetrain is separate cam lobe and roller f

each valve of 4V per cylinder. Cylinder hea

cost valve pairing concept.

DVVL - EM $180 $180 6 lost motion devices each operating 1 inta

6 actuators, drivers, harness. Intake valves 

valvetrain cost includes separate cam lobe 

HLA for each valve of 4V per cylinder. Cylin

for low cost valve pairing concept.

DVVL - Electrohydraulic (EH) $75 4 lost motion devices each operating 1 inta

solenoids, drivers, harness. Intake valves o

valvetrain is separate cam lobe and roller f

each valve of 4V per cylinder. Cylinder hea

cost valve pairing concept.

DVVL - EH $115 $115 6 lost motion devices each operating 1 inta

3 solenoids, drivers, harness. Intake valve

valvetrain is separate cam lobe and roller f

each valve of 4V per cylinder. Cylinder hea

cost valve pairing concept.

DVVL - EH $115 6 lost motion devices each operating 1 inta

solenoids, drivers, harness. Intake valves o

cylinder OHV using RHVL lifters.

DVVL - EH $150 8 lost motion devices each operating 1 inta

solenoids, drivers, harness. Intake valves o

cylinder OHV using RHVL lifters.

Continuously Variable Valve Lift (CVVL) $150 $275 $275 $275+DOHC $300+DOHC Ratio linkage including roller element for ea

control shaft positioned by 1 electrohydrau

Forked finger follower operates 1 pair of int

Hydraulic lash adjusters remain. Control of 

engines only. Baseline DOHC valvetrain is 

roller finger follower w/ HLA for each valve 

head redesign required for low cost valve p

2009+ High Volume Variable Hardware Cost Delta Per Vehicle

Vehicle Manufacturer Discrete Hardware Cost Delta

Appendix C: Vehicle Cost Matrix
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Technology L4 V6 V6 V6 V8 Technology Description - Hardware and 

Cylinder Deactivation - Electrohydraulic (EH)

Cylinder Deactivation - EH $115 $115 6 lost motion devices each operating 1 val

drivers, harness. Deactivating all I & E valv

the engine cylinders. Excludes any necess

Baseline DOHC valvetrain is separate cam 

follower w/ HLA for each valve of 4V per cy

redesign required for low cost valve pairing 

Cylinder Deactivation - EH $115 6 lost motion devices each operating 1 valv

harness. Deactivating all I & E valves in ea

engine cylinders. Excludes any necessary 

Baseline cost is 2V per cylinder OHV using 

Cylinder Deactivation - EH $150 8 lost motion devices each operating 1 valv

harness. Deactivating all I & E valves in ea

engine cylinders. Excludes any necessary 

Baseline cost is 2V per cylinder OHV using 

DVVL/Deact Combinations Intake phasing costs must be added to all V

DVVL-EH with Cylinder Deactivation - EH $330 $200 $200 $200 $260 Start with DVVL on intake valves for all cyli

(closed) to intake valves on 1/2 the cylinde

cost solenoids - 1 per deacted cylinder. Ad

for deact on 1/2 the cylinders. Add 2-step s

deact cylinder - no cylinder pairing possible

or Cylinder Deact independently at any tim

does not use DVVL while deactivated.

Camless Valve Actuation (CVA)

· Electromagnetic Actuation $690 $780 $780 $1,100 $1,300 Electromagnetic camless valve actuation. 

cylinder. Includes control electronics. Exp

engine.1 actuator per valve pair. Controller

42V is a requirement - these costs are exc

· Electrohydraulic Actuation $575 $650 $650 $900 $1,100 Electrohydraulic camless valve actuation. 

cylinder. 1 actuator per valve pair. Includes 

electronics. Expressed as net cost per eng

Variable Geometry Turbocharging $400 $400 $400 $400 $400 VGT gasoline turbo, charge air cooler, pisto

steel crankshaft, cooling system upsize, plu

sensor & bearing upgrade. Excludes any n

transmission torque capacity or modificatio

Electric Assist Turbocharging $475 $475 $475 $475 $475 Waste-gate gasoline turbo with 12V EAT fu

consumption. Includes charge air cooler, p

piston cooling, steel crankshaft, cooling sys

gasket upgrade, pressure sensor & bearin

needed increase in transmission torque ca

aftertreatment system.

Gasoline Engine Downsizing Credits These credits apply only when the baseline 

replaced by another gasoline engine of the 

credit. For the study AVL and NESCCAF 

engines at 65%, aggressive hybrids at 63% 

74% so these credits can be applied to tho

Downsizing credit (for both VGT and EAT) na L4 DOHC 4V remains L4 DOHC 4V

Downsizing credit (for both VGT and EAT) ($700) V6 DOHC 4V moves to L4 DOHC 4V

Downsizing credit (for both VGT and EAT) ($550) V6 DOHC 4V moves to L5 DOHC 4VDownsizing credit (for both VGT and EAT) ($700) V6 DOHC 4V moves to L4 DOHC 4V

Downsizing credit (for both VGT and EAT) ($550) V6 DOHC 4V moves to L5 DOHC 4V

Downsizing credit (for both VGT and EAT) ($200) V6 OHV 2V moves to L4 DOHC 4V

Downsizing credit (for both VGT and EAT) ($50) V6 OHV 2V moves to L5 DOHC 4V

Downsizing credit (for both VGT and EAT) ($300) V8 OHV 2V moves to L6 DOHC 4V

Supercharging $435 $435 $435 $435 $435 Advanced supercharger including charge a

upgrade, piston cooling, steel crankshaft, b

gasket upgrade, pressure sensor & bearin

needed increase in transmission torque ca

Variable Charge Motion $30 $50 $50 $50 $60 Active intake port tuning utilizing hydraulica

each port

Direct Injection (DIG) - Stoichiometric $135 $185 $185 $185 $210 Wall-guide DIG 90-100 bar pressures. Exc

base engine

Direct Injection (DIG) - Lean Burn Stratified Charge $135 $185 $185 $185 $210 Wall-guide DIG 90-100 bar pressures. Exc

base engine

Lean Burn DIG Aftertreatment Cost Delta $385 $500 $570 $560 $900 AVL designed 3.0L V6 with 3.73 g/mi engi

includes inactive exhaust cooler. Scaled u

displacements Gasoline HCCI (AVL CSI System) $400 $600 $600 na na AVL CSI System: Wall-guide DIG 90-100 b

cylinder pressure sensing, intake phaser, D

exhaust valve operation for dilution manag

pump and plumbing. Stoichiometric aftertre

2009+ High Volume Variable Hardware Cost Delta Per Vehicle

Vehicle Manufacturer Discrete Hardware Cost Delta
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Technology L4 V6 V6 V6 V8 Technology Description - Hardware and 

Baseline high-speed Diesel Engine Displacement 1.78L L4 2.40L L4 2.28L L4 2.31L L4 3.85L L6 Downsized DOHC 4V turbo diesel engines 

equivalent performance to each baseline g

Baseline high-speed Diesel $1,000 $300 $300 $800 $950 DOHC 4V turbo diesel: Common rail, ~1,8

injectors, VNT, cooled EGR. Includes dow

needed increase in transmission torque ca

Baseline diesel aftertreatment Cost Delta over stoich. $500 $575 $600 $600 $1,000 AVL designed 2-leg system revised to sing

from 2.8L V6 with 0.32 g/mi engine-out NO

Diesel Advanced Multi-Mode $1,000 #REF! #REF! #REF! #REF! DOHC 4V turbo diesel: Common rail, ~1,8

injectors, VNT, cooled EGR. Includes dow

needed increase in transmission torque ca

Diesel Advanced Multi-Mode Aftertreatment Cost Delta $250-350 $300-450 $280-400 $285-400 $500-725 FEV-NREL APBF-DEC light duty advanced 

(DEER 8-2003). Scaled from 1.9L engine 

LNT functionality), 1 underfloor LNT and C

loadings expressed as a range.

Diesel Engine and Aftertreatment downsizing substituion

for Aggressive Hybrid

$900 Per NESCCAF design scaling of hybrid veh

turbo diesel AMM for this large truck vehicl

aggressive hybrid drivetrain. Aftertreatmen

Variable Compression Ratio $320 $380 $380 $380 $440 Hydraulic pump, acutators, tilt design, can 

Drivetrain Technologies

5-Speed Automatic Transmission $100 $100 $100 $100 $100 Conventional step gear

6-Speed Automatic Transmission $50 $75 $75 $75 $80 Lepelletier gear set design

Continuously Variable Transmission (CVT) $150 $175 $175 $175 na Belt CVT. NESCCAF assumptions: Assum

belt technology free of licenses and IP prot

volume and capital infrastructure on par wi

Automated Manual Transmission 6 speed neutral neutral neutral neutral neutral 6-speed, dual wet clutch, fully automated. 

manual transmission capacity does not exi

12V belt starter-alternator (idle off) $200 na na na na 2kW machine. Includes inverter/controller, 

tensioner upgrade. Credit alternator. Start

start. Maximim cylinder displacement ~ .45

Includes 12V Pb acid battery upgrade.

42 Volt BAS - Belt Drive w/ Launch, Regen, Idle Off $450 $450 $450 $450 $500 4kW machine. Includes belt upgrade, pow

converter for split system. Liquid cooled ele

and starter. Maintain starter motor for 5.3L 

battery upgrade.

42 Volt FAS w/ Launch, Regen, Idle Off $800 $800 $800 $800 $800 10kW motor, flywheel integration, power el

split sytem, liquid cooled, credit starter and 

battery upgrade.

42V system lead acid battery for BAS $120 $120 $120 $120 $120 36V 20Ah advanced adsorbent glass mat (

KwHr. Targeted primarily for the BAS syst

42V system lead acid battery set for FAS $330 $330 $330 $330 $330 36V 55Ah advanced adsorbent glass mat 

1.98 KwHr. Targeted primarily for the FAS 

42V system NiMH battery upgrade $400 $400 $400 $400 $400 Full battery pack including 36 cells, 43.2V, 

2117 kJ energy (Ref: SAFT Vh10/42, air co

for BAS or FAS

42V system NiMH battery upgrade $1,090 $1,090 $1,090 $1,090 $1,090 Full battery pack including 36 cells, 43.2V, 

capacity for FAS04 Honda Civic Hybrid architecture scaled 

vehicle class. Net cost includes a conventio

battery pack at 144V, control and power elefor 144V system, 1 permanent magnet mot

for baseline vehicle generator. Excludes c

pack.

$1,650 Battery pack 9.0 Ah, mogen 15 Kw, CVT tr

$2,100 $2,100 Battery pack 12.0 Ah, mogen 20 Kw, CVT 

$2,100 Battery pack 12.0 Ah, mogen 20 Kw, CVT 

may not meet the load carrying and towing 

performance of the baseline vehicle for this 

$2,400 Battery pack 15.0 Ah, mogen 25 Kw, 6 spe

This vehicle may not meet the load carrying 

gradeability performance of the baseline ve

2009+ High Volume Variable Hardware Cost Delta Per Vehicle

Vehicle Manufacturer Discrete Hardware Cost Delta

Moderate Hybrid - Motor Assist
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles 

Technology L4 V6 V6 V6 V8 Technology Description - Hardware and 

04 Toyota Prius hybrid architecture design 

each vehicle class. Net cost includes contin

transmission, NiMH battery pack at 201.6V

electronics including 2 inverters w/ 1 dc:dc 

voltage, 1 permanent magnet generator/en

magnet drive motor. Credit given for baseli

starter motor. Excludes cost of any repla

$2,500 Battery pack 5.9Ah, drive motor 45Kw, gen

$3,100 $3,100 Battery pack 7.8Ah, drive motor 60Kw, gen

$3,100 Battery pack 7.8Ah, drive motor 60Kw, gen

may not meet the load carrying and towing 

performance of the baseline vehicle for this 

$4,000 Battery pack 10.4Ah, drive motor 80Kw, ge

may not meet the load carrying and towing 

performance of the baseline vehicle for this 

Other Load Reducing Technologies

Advanced Power Steering

· Electrohydraulic power steering (EHPS) $60 If 14V electrical system, EHPS required for 

· Electric power steering (EPS) $20 $40 $40 $40 $40 14/42V EPS. 42V is requirement for large 

Electric 42V Demand Water Pump $50 $50 $50 $50 $50 42V requirement for demand water pump.

High Efficiency Generator $40 $40 $40 $40 $40 80% high efficiency Lundell machine

Weight Reduction $3 $3 $3 $3 $3 Aluminum intensive vehicle - body. Cost pe

Important Notes on Technology Cost Matrix

Vehicle manufacturer costs represent variable hardware cost delta over baseline technologies. R&D, capital investment and other costs associated with implementing new technologies are excluded.

Costs are forecast 2009+ at assumed high volume levels. See Methodology Section for full description.

Aggressive Hybrid - Fully Integrated

2009+ High Volume Variable Hardware Cost Delta Per Vehicle

Vehicle Manufacturer Discrete Hardware Cost Delta
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page C-6

References for Appendix C

As mentioned previously in this report, the costs listed in Appendix C were

developed by the Martec Group, Inc. from a literature review and from field interviews

conducted with individuals representing all aspects of the automotive industry, including

the management, engineering, purchasing, finance, planning and product management

divisions of both manufacturers and parts suppliers. Wherever possible, information

gleaned from technical papers was verified in interviews. A partial list of sources used

for the study is presented below.

California Air Resources Board, "Proposed Amendments to the Zero Emission Vehicle

Regulation," April, 2003.

Fuerhapter, A., et al., AVL List GmbH, Austria, "CSI - Controlled Auto Ignition - The

Best Solution for the Fuel Consumption - Versus Emission Trade-Off?," 2003-01-0754,

Society of Automotive Engineers, Inc., 2003.

Gallegos-Lopez, Gabriel, et al., Energenix Center, Delphi Automotive Systems,

"Switched Reluctance Machine Control Strategies for Automotive Applications," 2001-

01-0955, Society of Automotive Engineers, Inc., 2001.

Henry, Rassem, R et al., Delphi Research Labs and Delphi E&C Energenix Center.

"Belt-Driven Starter-Generator for Future 42-Volt Systems," 2001-01-0728, Society of

Automotive Engineers, Inc., 2001.

Honda Motor Company, 2004 Honda Insight Fact Sheet, http://www.honda.com.

Husted, H.L., Dephi Corporation, A Comparative Study of the Production Applications of

Hybrid Electric Powertrains," 2003-01-2307, Society of Automotive Engineers, Inc.,

2003.

Itagaki, K., et al., Toyota Motor Corporation, "Development of the Toyota Mild-Hybrid

System (THS-M)," 2002-01-0990, Society of Automotive Engineers, Inc., 2002.

Johnson, T.V., Corning Incorporated, "Diesel Emission Control Technology - 2003 in

Review," 2004-01-0070, Society of Automotive Engineers, Inc., 2004.

Lambert, Christine et al., Ford Research & Advanced Engineering, "Technical

Advantages of Urea SCR for Light-Duty and Heavy-Duty Diesel Vehicle Applications,"

2004-01-1292, Society of Automotive Engineers, Inc., 2004.

Patton, K.J., et al., General Motors Corporation, "Aggregating Technologies for Reduced

Fuel Consumption: A Review of the Technical Content in the 2002 National Research

Council Report on CAFE," 2002-01-0628, Society of Automotive Engineers, Inc., 2002.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page C-7

Sellnau, M., et al., Delphi Research Labs, "Two-Step Variable Valve Actuation for Fuel

Economy, Emissions, and Performance." 2003-01-0029, Society of Automotive

Engineers, Inc., 2003.

Shahed, S.M., Honewell/Garrett Engine Boosting Systems, "Gasoline Engine

Downsizing and Boosting for CO2 Emission Reduction," California Air Resources Board

Climate Change - International Vehicle Technology Symposium, March, 2003.

Tamia, G., et al., Saturn Powertrain, General Motors Corporation, "Saturn Engine StopStart System with an Automatic Transmission," 2001-01-0326, Society of Automotive

Engineers, Inc., 2001.

Toyota Motor Corporation, "Toyota Hybrid System THS II,"

http://www.toyota.com/index3.html

Turner, J., Lotus Engineering, "Controlled Auto Ignition and Camless Engines,"

presentation March, 2003.

Yamaguchi, J., "Toyota Prius: AEI Best Engineered Vehicle 2004," Automotive

Engineering International, March, 2004.

Yoon, H., et al., Hyundai Motor Company, "An Optimized Control Strategy for Parallel

Hybrid Electric Vehicles," 2003-01-1329, Society of Automotive Engineers, Inc., 2003.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page C-8
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-1

Appendix D: Vehicle Air Conditioning
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-2

Appendix D: Vehicle Air Conditioning

Vehicle air conditioning (A/C) systems impact vehicular GHG emissions through

three distinct mechanisms. Two mechanisms impact vehicle tailpipe emissions of CO2,

while the third mechanism is emissions (refrigerant leakage) from the A/C system itself.

The increased vehicle tailpipe emissions are generally referred to as “ indirect emissions”

since they do not emanate directly from the A/C system. Leakage-related emissions are

generally referred to as “ direct emissions” since they are released directly by the A/C

system.

Indirect emissions result from two influences. First, when operating, A/C systems

place an additional load on the vehicle engine, increasing vehicle CO2 emissions.

Second, regardless of operational status, A/C system mass must be transported whenever

a vehicle is moved, and this also places an additional load on the vehicle engine (relative

to an otherwise identical vehicle without A/C), increasing vehicle CO2 emissions. A

typical A/C system weighs on the order of 30-35 pounds. [1]

A/C systems function by transferring heat through a working fluid, which is

commonly known as the system refrigerant. Current vehicle A/C systems utilize

HFC-134a (1,1,1,2-tetrafluoroethane; C2F4H2) as the working refrigerant. HFC-134a has

a global warming potential (GWP) 1300 times that of CO2. [2] Accordingly, any

refrigerant that leaks from the A/C system represents a potent source of GHG emissions.

This study evaluated all three sources of A/C-related GHG emissions. Both direct

and indirect emissions were assessed through a stand-alone analytical assessment. To

validate the analytical assessment, indirect A/C operational emissions were also assessed

through application of the AVL CRUISE simulation model.

D.1. Stand-Alone Assessment

The stand-alone assessment of vehicle A/C GHG emissions relied on the large

body of A/C system evaluation test data that is currently available in the public domain.

Although a diverse set of resources was utilized in the assessment, primary references are

as follows:

• Direct Emissions:

6FKZDU] : NR-Recherche GmbH, “ Emission of Refrigerant R-134a from Mobile

Air-Conditioning Systems, Annual Rate of Emission from Passenger-Car

Air-Conditioning Systems up to Seven Years Old,” 360 09 006, prepared for the

German Federal Environment Office, September 2001. [3]

6FKZDU] : HW DO NR-Recherche GmbH, “ Establishing the Leakage Rates of

Mobile Air-Conditioners,” B4-3040/2002/337136/MAR/C1, prepared for the

European Commission (DG Environment), April 17, 2003. [4]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-3

• Indirect Emissions:

Forrest, W.O., Delphi, “ Air Conditioning and Gas Guzzler Tax Credits,”

2002-01-1958, Society of Automotive Engineers, Inc., 2002. [5]

Forrest, W.O. and Bhatti, M.S., Delphi Harrison Thermal Systems, “ Energy Efficient

Automotive Air Conditioning System,” 2002-01-0229, Society of Automotive

Engineers, Inc., 2002. [6]

Johnson, V.H., National Renewable Energy Laboratory, “ Fuel Used for Vehicle Air

Conditioning: A State-by-State Thermal Comfort-Based Approach,” 2002-01-1957,

Society of Automotive Engineers, Inc., 2002. [7]

Direct A/C System Emissions: A/C systems are designed to be closed for the

life of a vehicle. Nevertheless, refrigerant emissions (i.e., leakage) can occur through

several mechanisms. Small, but continuous refrigerant emissions occur through

“regular” leakage at component joints and the compressor shaft seal, as well as through

hose permeation. “Irregular” leakage can also occur as the result of system damage

through accidents, etc. The evacuation of refrigerant either during A/C system or other

vehicle service can also lead to significant or minor leakage depending on the use and

efficiency of refrigerant recycling equipment. Finally, evacuation of refrigerant at the

end of vehicle life also results in leakage at a rate that is also dependent on the use and

efficiency of refrigerant recycling equipment.

Estimates of the rate of regular HFC-134a leakage span a relatively wide range of

10-130 grams per year, but most estimates are in the 50-60 gram per year range.

[3,5,8-12] In the most detailed assessment of regular A/C system emissions,

measurements of vehicle A/C system refrigerant mass were taken for 276 light duty

vehicles in the European Union (EU) between November 2002 and January 2003. By

comparing measured charge mass to initial fill specifications, a regular HFC-134a

leakage rate of 52 grams per year was estimated. In recognition of the continuing

primacy of the EU data, the stand-alone assessment assumed a regular leakage rate for

current HFC-134a systems of 50 grams per year.

By definition, precise estimates of the rate of irregular HFC-134a leakage are

difficult to develop. Various researchers have estimated per vehicle-equivalent irregular

emission rates of 7-14 grams per year. [3,10,13] The most robust source of irregular

emission rate data is also an EU-sponsored study that examined vehicle repair records

from nine German service garages. By comparing A/C system losses for vehicles subject

to repair to the number of (A/C equipped) customers at each study service garage, a

nominal irregular emission rate of 14 grams per A/C-equipped vehicle per year was

estimated.

In addition to regular and irregular leakage, refrigerant emissions also occur

during system service due to imperfect recycling techniques. A loss of 4-13 percent of

total system charge is generally estimated as appropriate for current recycling systems

and techniques. [8,10,11,13] Losses for service facilities employing good recycling
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-4

techniques appear to be on the low end of the range, at approximately 6 percent.

Assuming an average initial charge of 750 grams and a normal leakage rate of 50 grams

per year, vehicles will generally require A/C system service twice during their lifetime.

At a 6 percent loss rate, this equates to about 45 grams per service or 90 grams per

lifetime.

Similarly, imperfect recovery at the end of a vehicle’s life also contributes to

refrigerant emissions. A loss of 10-30 percent of remaining charge has been assumed to

be reflective of such emissions, given current recycling systems and techniques.

[10,11,13] Losses given good recycling techniques appear to be on the low end of the

range at approximately 15 percent. Assuming an average initial charge of 750 grams, a

normal leakage rate of 50 grams per year, and two years normal leakage since the last

system service, vehicles will generally have about 650 grams of refrigerant remaining in

the A/C system at the end of their life. At a 15 percent loss rate, this equates to about 98

grams per vehicle per lifetime.

These assumed service and end-of-life loss rates are based on good recycling and

recovery practices. To the extent that actual practice is either non-existent (i.e., direct

atmospheric venting) or poorly performed, refrigerant emissions will be substantially

higher. For example, losses associated with atmospheric venting during two service trips

during a vehicle lifetime and one end-of-life loss might be 2,500 grams of refrigerant or

more. Obviously, this is a significant increase over the 188 grams (90 grams during

service plus 98 grams at end-of-life) assumed in this assessment. Appropriate regulations

(in place) and enforcement are, therefore, required to ensure that actual emissions

approach those assumed.

Direct A/C system GHG emissions can be reduced by minimizing refrigerant

leakage or by utilizing a refrigerant with a lower GWP. The EU has proposed regulations

that require regular emission rates for HFC-134a systems to be controlled to 20-40 grams

per year beginning in 2005, and phase-out the use of refrigerant with a GWP greater than

150 between 2009 and 2018. Since, as described above, HFC-134a has a GWP of 1300,

the EU rules effectively ban the introduction of new HFC-134a A/C systems after 2018.

39

Table D-1 presents a list of alternative refrigerants that are being considered for vehicle

application. As indicated, alternative refrigerants generally span three GWP ranges.

HFC-152a is a hydrofluorocarbon refrigerant with half the fluorine of HFC-134a, and a

GWP that is 91 percent lower. Hydrocarbons such as propane are also effective

refrigerants, and their associated GWP is about 98 percent lower than HFC-134a, and 80

 

39

It is important to recognize that subsequent to the completion of the A/C system assessments described in

this report, the European Parliament substantially amended the proposed EU regulations. While these

amendments are subject to continuing revision during member state negotiations, they significantly alter

the implications of the EU requirements. First, the amendments reduce the allowable GWP of mobile

A/C systems to 50 beginning in 2011 and require the complete elimination of systems with a GWP above

50 by 2014. This would effectively prohibit both HFC-134a and HFC-152a, leaving CO2 and

hydrocarbons as the most likely long term A/C refrigerants in the EU. Second, the amendments eliminate

the specified maximum A/C system refrigerant leakage rates of 20 and 40 grams per year scheduled to

begin in 2005 and impose instead a requirement for an unspecified maximum leakage rate for A/C

systems with a GWP greater than 150 beginning in 2007. The specific maximum leakage rate and

associated test procedure are to be developed. So, while the amendments somewhat relax near term

requirements, longer term requirements were made more stringent.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-5

percent lower than HFC-152a. Finally, CO2 systems represent a practical lower limit

with a GWP of unity (by definition).

In this assessment, direct refrigerant emissions were investigated for six

alternative vehicle A/C systems: current HFC-134a, two levels of enhanced (i.e., reduced

leakage) HFC-134a, HFC-152a, propane, and CO2. Enhanced HFC-134a systems are

based on the proposed EU levels of refrigerant leakage of 40 and 20 grams per year,

which reflect regular leakage reductions of about 20 and 60 percent relative to current

HFC-134a systems. All alternatives except CO2 assume an effective refrigerant recovery

and recycling program in both the service and end-of-life industries. The absence of such

a program will lead to emission rates considerably larger than those assumed in this

evaluation. The CO2 system evaluation included one practical assessment of a system

with a leakage rate controlled to 50 grams per year and one “ impractical” assessment of a

system with annual leakage equivalent to a complete system charge. The “ impractical”

system assessment is intended solely to illustrate the insensitivity of overall CO2 system

GHG emission rates to refrigerant leakage assumptions - it is not intended to represent a

viable market system.

Table D-1: Basic Environmental Characteristics of Selected Refrigerants [2,8,14]

Refrigerant Compound Name Formula ODP

a GWPb

CFC-12 Dichlorodifluoromethane C(Cl)2F2 1 8500

HFC-134a 1,1,1,2-Tetrafluoroethane C2F4H2 0 1300

HFC-152a 1,1-Difluoroethane C2F2H4 0 120

HC-290 Propane C3H8 0 20

R-744 Carbon Dioxide CO2 0 1

a ODP is “ Ozone Depletion Potential” as defined by the U.S. Environmental Protection Agency in 40

CFR Part 82. The ODP scale is based on CFC-11 (trichlorofluoromethane, C(Cl)3F) so that the

indicated ODP of a compound is defined as the ratio of its impact on ozone to the impact of the same

mass of CFC-11.

b GWP is “ Global Warming Potential” as defined by the U.S. Environmental Protection Agency in 40

CFR Part 82. The GWP scale is based on CO2 (carbon dioxide) so that the indicated GWP of a

compound is defined as the ratio of its impact on global warming to the impact of the same mass of

CO2.

Indirect Mass-Based A/C Emissions: Increased vehicle tailpipe CO2 emissions

due to the mass of A/C systems was estimated through an engineering assessment of the

energy required to move mass. Using fundamental physical relations, it is possible to

estimate the incremental CO2 emitted for a given incremental change in vehicle mass

(i.e., that due to the presence of the A/C system). This rate of change is estimated to be

about 111 pounds of CO2 per 100 pounds per 10,000 miles. Given this relationship and

the associated mass of various A/C system alternatives, incremental tailpipe CO2

emissions can be estimated.

Current A/C system mass is on the order of 30-35 pounds. For this assessment, a

value of 33 pounds was assumed. Based on data for current evaluation systems, CO2 A/C
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-6

systems were assumed to have an additional one pound mass. [1] This differential is

considerably less than differentials estimated by other researchers, but is based on actual

component masses for a baseline HFC-134a system and its CO2 equivalent. Empirical

mass information for comparable A/C systems using other refrigerants is limited, but

theoretical calculations by previous researchers have estimated that enhanced HFC-134a,

HFC-152a, and hydrocarbon refrigerants would allow mass reductions of about 8 percent

relative to current systems. [8]

Due to potential safety issues, HFC-152a, hydrocarbon, and CO2 systems could

require measures not currently needed on current HFC-134a systems. These measures

could include active safety systems such as automatic vehicle cabin ventilation and A/C

system evacuation or physical separation of the A/C system refrigerant from the vehicle

cabin through the use of secondary A/C system cooling loops. If utilized, secondary loop

systems may increase overall system mass, but empirical data is limited. However, given

that secondary loop systems would consist of all of the components of the base system,

plus an additional heat exchanger, a small pump to move coolant through the secondary

loop, the secondary loop plumbing, the secondary loop coolant, and a secondary loop

coolant reservoir, it seems likely that overall system mass will increase significantly.

Based on the weight of current vehicle pumps, current system heat exchangers, current

coolant lines, and the secondary coolant itself, a total secondary loop mass penalty of 8 to

9 pounds, or a mass increase of about 25 percent relative to current single loop systems

seems likely.

40

Indirect Energy-Based A/C Impacts: In addition to the indirect GHG impacts

associated with A/C system mass, indirect GHG emission impacts also accrue during A/C

system operation due to the energy demands of the system compressor and cabin fan.

Since A/C system usage varies with climate, it is not possible to quantify an operational

GHG impact that applies to all areas. Areas with significant cooling demands will

promote higher indirect GHG emissions. Areas with low cooling demands may have

overall A/C-related GHG impacts that only modestly exceed those associated with direct

 

40

It should be noted that subsequent to the completion of the A/C portion of this study, the details of the

various A/C systems included in the SAE Alternate Refrigerant Cooperative Research Program (ARCRP)

were released. The ARCRP was initiated by the Society of Automotive Engineers (SAE) to evaluate the

energy efficiency of various mobile A/C systems. As tested in the ARCRP, the mass differential between

a comparable enhanced HFC-134a and CO2 system was indicated to be about 8 pounds, substantially

greater than that assumed in this study. However, both the HFC-134a and CO2 systems had masses less

than assumed in this study, at about 24 pounds for HFC-134a (versus 30 in this study) and 32 pounds for

CO2 (versus 34 in this study). Additionally, the ARCRP included a secondary loop system, with an

incremental mass estimated to be about 17 pounds (versus 8 in this study). If A/C mass-based emissions

are recalculated using these estimates, overall A/C system emissions, as presented in Table D-4 below,

would be reduced at average A/C operating conditions by about 2 percent for HFC-134a, non-secondary

loop HFC-152a, and non-secondary loop propane systems, while emissions for a non-secondary loop CO2

system would be reduced by about 1 percent. Under the same operating conditions, emissions from

secondary loop HFC-152a and secondary loop propane systems would increase by about 1 percent under

average A/C operating conditions, while secondary loop CO2 emissions would increase by about 2

percent. Changes would be proportionally larger under low average operating conditions and

proportionally smaller under high average operating conditions. Since the author of this study has not

had an opportunity to critically review the systems included in the ARCRP, it is not possible to more fully

evaluate the mass differentials associated with the ARCRP data. Regardless, these data certainly are as

valid as any other published data reviewed for this study and should be considered accordingly.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-7

and indirect mass-based emissions. Thus, indirect operational impacts must be viewed as

a range across specific geographic areas.

Indirect operational emissions can be reduced in two principal ways, through

component design and through the use of alternative refrigerants. Most current vehicle

A/C systems in the U.S. rely on pneumatically (freeze point) controlled fixed

displacement compressors (FDCs) that provide a constant flow of refrigerant for any

given demand. System control is generally limited to cycling the compressor on and off

to maintain evaporator surface temperature above the point at which condensed water

from the ambient air would freeze and inhibit system performance. The resulting

inability to continuously adjust refrigerant flow to meet cooling demand is relatively

inefficient. Alternative system designs are available and can be used to promote

increased A/C efficiency. For example, externally controlled variable displacement

compressors (VDCs) can be utilized to provide a dynamic system response, allowing the

flow of refrigerant to be varied continuously in accordance with cooling demand. This

can result in a significant efficiency improvement for most cooling demands. It is

important to note that similar efficiency gains may also be possible through the

incorporation of external controls in FDC systems. Such control could rely on rapid

clutch cycling to provide the dynamic system response currently lacking from most A/C

designs. It is not the intent of this study to specify a particular technology path to be

employed by any or all manufacturers, but rather to illustrate the potential efficiency

improvements that are possible through system redesign. Therefore, while this study

bases its conclusions on a system utilizing an externally controlled VDC, it should not be

assumed that all solutions providing similar efficiency improvement will rely on this

same technology. Efficiency gains can also be achieved through the use of improved

heat exchangers, the addition of suction line heat exchangers, and the incorporation of

enhanced air management strategies. Through such technologies, the overall efficiency

of HFC-134a systems can be improved through system redesign, without any alteration

of the system refrigerant. The replacement of HFC-134a with an alternative refrigerant is

a second area of potential operational efficiency improvement. To the extent that

alternative refrigerant systems are more or less efficient than HFC-134a systems, overall

system efficiency for a given cooling demand will be affected accordingly.

As stated above, an appropriate set of evaluation conditions must first be defined

in order to estimate the operational impacts of current A/C systems and the potential

influences of alternative systems. Compressor (and therefore A/C system) load varies

with a number of operating and design factors. Among these are cooling demand (which

is a function of solar radiation, ambient temperature, and humidity), compressor

displacement (which is generally a function of vehicle size), compressor shaft speed

(which varies with engine speed), airflow (which varies with vehicle speed), and system

operating mode (fresh air mode versus recirculation mode). Figure D-1, developed by

W.O. Forrest at Delphi, illustrates the typical magnitude of such variation for an A/C

system utilizing a freeze point controlled FDC of 210 cubic centimeters (cc)

displacement. [5]

For this assessment, a vehicle miles of travel (VMT) weighted average set of

evaluation conditions has been developed to compare alternative A/C system operational

emissions. Impacts in most areas will, of course, vary somewhat from those estimated, in
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-8

accordance with local conditions. In an effort to characterize the practical extent of this

variation, the assessment also includes emission estimates for areas with below and above

average cooling demands. Data from the National Renewable Energy Laboratory

(NREL) were used to quantify typical vehicle cooling demands in the U.S. [7] NREL

subjected meteorological data for a geographically diverse set of U.S. cities to detailed

“ thermal comfort” analysis to estimate the frequency and conditions associated with

typical vehicle A/C usage. Table D-2 presents the resulting estimates.

Figure D-1: Illustrative Variation in Power Demand for a Pneumatically Controlled

210 cc FDC A/C System [5]

Note: The power demand figures include the effect of compressor “ on/off” cycling as

required to maintain efficient evaporator function.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-9

Table D-2: Frequency of Use and Typical Conditions during A/C System Operation

Average Conditions when A/C Operating

State

2002

Annual VMT

(million miles)

Number

of Cities

Represented

Percent of

VMT with

A/C On

Temperature

(degrees C)

Temperature

(degrees F)

Relative

Humidity

(percent)

Specific

Enthalpy

(kJ/kg)

United States 2,855,756 116 34 25 77.0 69 60.9

Louisiana 43,295 2 50 27 80.6 81 73.8

Florida 178,367 4 57 27 80.6 80 73.2

Alabama 57,515 4 43 27 80.6 76 71.5

Mississippi 36,429 1 52 27 80.6 75 70.6

Tennessee 68,229 3 40 27 80.6 74 70.5

Hawaii 8,886 1 69 27 80.6 73 69.0

Arkansas 30,080 1 43 27 80.6 72 68.8

Kansas 28,443 2 33 27 80.6 69 68.5

Oklahoma 45,731 2 40 27 80.6 69 68.2

South Carolina 47,290 1 50 27 80.6 70 67.7

Texas 221,026 11 49 27 80.6 69 67.6

Georgia 108,321 5 41 26 78.8 74 67.3

Missouri 68,163 3 33 26 78.8 74 67.2

North Carolina 92,894 3 38 26 78.8 74 67.1

Nebraska 18,719 1 26 25 77.0 76 65.5

Maryland 57,249 1 28 26 78.8 71 64.6

Virginia 77,450 2 31 25 77.0 77 64.3

Kentucky 46,841 2 30 25 77.0 75 64.1

Indiana 72,523 3 32 25 77.0 74 63.7

Iowa 30,847 1 26 25 77.0 71 62.4

Illinois 105,401 4 25 25 77.0 71 62.0

Delaware 8,875 1 28 25 77.0 72 61.7

West Virginia 20,005 1 27 24 75.2 77 61.7

Pennsylvania 104,476 3 26 25 77.0 71 61.6

New Jersey 69,942 2 23 25 77.0 69 60.2

Minnesota 54,562 1 20 24 75.2 73 60.0

Ohio 107,861 5 25 24 75.2 72 59.5

New York 133,057 4 21 25 77.0 67 59.3

Connecticut 31,205 2 21 24 75.2 73 59.1

Michigan 100,144 4 24 24 75.2 71 58.8

South Dakota 8,499 1 23 25 77.0 63 58.7

Wisconsin 58,746 2 17 23 73.4 77 58.6

Rhode Island 8,142 1 17 24 75.2 71 58.0

North Dakota 7,336 2 19 24 75.2 67 57.4

Massachusetts 53,266 2 16 23 73.4 71 54.9

Vermont 9,677 1 18 23 73.4 70 54.8

New Mexico 22,789 1 32 26 78.8 42 53.5

Arizona 51,334 2 58 30 86.0 32 52.9

Montana 10,395 1 18 25 77.0 47 51.7

Colorado 43,545 3 21 24 75.2 47 51.3

Wyoming 9,007 1 15 23 73.4 50 51.1

California 320,942 7 29 22 71.6 68 50.8

Utah 24,564 1 26 26 78.8 37 49.2

Maine 14,727 1 37 23 73.4 57 48.6

Nevada 17,966 2 41 23 73.4 52 48.5

Oregon 34,578 3 42 23 73.4 56 48.2

Idaho 14,167 1 23 25 77.0 37 45.7

Washington 54,776 2 25 21 69.8 58 44.4

New Hampshire 12,578 1 19 26 78.8 31 42.8

Alaska 4,896 1 6 17 62.6 67 37.6

Notes: (1) VMT data are from the Federal Highway Administration, Highway Statistics 2002. [15]

(2) Data for the number of cities from which state data are developed, percent of VMT with A/C operating, average temperature

and average humidity with A/C operating are from the National Renewable Energy Laboratory. [5]

(3) Data on the specific (ambient) enthalpy with A/C operating are calculated from average temperature and humidity data, in

conjunction with calculated standard atmospheric pressure for the population-weighted elevation of represented cities.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-10

As indicated in Table D-2, the NREL data estimate state-specific VMT-weighted

average temperature and relative humidity during A/C operation to range from 63-86oF

(17-30oC) and 31-81 percent respectively. Weighting the individual state data by VMT,

produces estimates of U.S. average conditions during A/C usage of 77oF (25oC) and 69

percent relative humidity. Because both temperature and humidity affect the amount of

energy that must be removed (as heat) from ambient air to produce a desired level of

cooling, the conversion of these data to specific enthalpy provides a more robust measure

of average cooling demand for a given area. Specific enthalpy indicates the energy per

unit mass, which for ambient air can be calculated from temperature and humidity data at

a given atmospheric pressure. The NREL data available for this assessment did not

include pressure data, so pressures were estimated for each of the 116 cities in the NREL

dataset on the basis of elevation and standard U.S. atmospheric pressures. The resulting

estimates of specific enthalpy during A/C system use are presented in Table D-2, and

range from about 38-74 kilojoules (kJ) per kilogram (kg). The U.S. average estimate is

61 kJ/kg. It should also be noted that solar load also affects A/C usage. Local solar load

is considered by NREL for each of the 116 U.S. cities in their dataset and is reflected in

Table A-2 through its impact on the parameter “ percent of VMT with A/C on.”

As shown in Figure D-1 above, A/C compressor power consumption varies with

ambient conditions. Using the NREL data to reflect average ambient operating

conditions, average compressor power consumption can be estimated. Essentially, this

involves interpolating between the various consumption curves presented in Figure D-1

to arrive at a typical average consumption rate. The temperature and humidity test

conditions defined in Figure D-1 can be converted to approximate specific enthalpies as

shown in Table D-3. From these data, it is clear that tests conducted at 27oC (80.6oF) and

60 percent relative humidity differ from U.S. average A/C operating conditions by only

about 2 percent. Moreover, high average A/C use conditions typical of the southeastern

U.S. (Louisiana in particular) are approximately midway between A/C system tests

conducted at 32oC (89.6oF) and 50 percent relative humidity and 38oC (100.4oF) and 40

percent relative humidity. Finally, A/C system tests conducted at 16oC (60.8oF) and 80

percent relative humidity are within 4 percent of the low average A/C usage conditions

encountered in Alaska.

Because weather extremes in the U.S. can vary from average by a significant

extent, it is important to evaluate the potential impact of such extremes. Temperatures in

southwestern states such as Arizona can climb above 110oF fairly often in the summer

months. However, during these excursions, humidity levels are generally limited to

about 20 percent or lower. As indicated in Table D-3, the approximate enthalpy for 45oC

(113oF) and 20 percent relative humidity is about 77 kJ/kg, or about 4 percent higher than

the high average A/C use conditions representative of the southeastern U.S. Thus, it

appears that the range associated with average A/C usage conditions across the U.S. is

quite robust in its ability to reflect the broad range of A/C operating conditions.

Using these data, representative A/C system operational GHG impacts can be

estimated. However, since A/C system design varies across vehicles, it is first necessary

to develop a representative A/C system. Although there is limited penetration of

VDC-based systems, pneumatic freeze point controlled FDC-based systems continue to

dominate the U.S. market. Thus, the baseline A/C system for this assessment is a
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-11

Table D-3: Approximate Enthalpies of Typical A/C System Test Conditions

Test Conditions

Temperature

(degrees C)

Temperature

(degrees F)

Relative

Humidity

(percent)

Specific

Enthalpy

(kJ/kg)

Figure D-1 -- Condition 1 38 100.4 40 82.3

Figure D-1 -- Condition 2 32 89.6 50 71.4

Figure D-1 -- Condition 3 27 80.6 60 62.2

Figure D-1 -- Condition 4 22 71.6 70 52.3

Figure D-1 -- Condition 5 16 60.8 80 39.6

Figure D-1 -- Condition 6 10 50.0 90 27.8

Comparable Ambient Conditions

U.S. Average A/C Conditions 25 77.0 69 60.9

U.S. High Average (Louisiana) 27 80.6 81 73.8

U.S. Low Average (Alaska) 17 62.6 67 37.6

U.S. High Temperature 45 113.0 20 77.0

SC03 Cycle Conditions 35 95.0 40 72.3

pneumatic freeze point controlled FDC-based system. Compressor displacement varies

considerably across the U.S. market. The smallest cars can utilize compressors with

displacements below 150cc, while larger light trucks can rely on compressor

displacements over 200 cc. For this evaluation, it is assumed that typical compressor

sizes range from about 150 cc for a compact car to 210 cc for a large SUV, so that

average compressor displacement is about 180 cc given current vehicle sales shares.

Since A/C system load is approximately proportional to compressor displacement, the use

of a single average compressor displacement should produce reasonably accurate fleet

average GHG impact estimates given the overall uncertainty associated with the various

A/C system operational and emission parameters. As a result, a single 180 cc

displacement pneumatically controlled FDC system was evaluated.

Evaluations were also performed for several alternative systems. The initial

alternative to the baseline HFC-134a system is an enhanced HFC-134a system that takes

advantage of available efficiency improving technologies. For this evaluation, an

externally controlled VDC-based system with automatic air recirculation was evaluated

as the enhanced system. Other approaches such as improved heat exchangers or

externally controlled FDC-based systems with rapid cycling algorithms may be able to

provide similar levels of improvement, but the intent of the evaluation was not to

proscribe specific technological approaches, but to evaluate viable CO2 reduction levels.

Therefore, while the levels of CO2 emissions developed for this evaluation are based on

the comparison of an internally controlled FDC system to an externally controlled VDC

system, it is the CO2 emissions levels that are of interest, not the specific technology path

undertaken to achieve them.

The efficiency improvement that could result from the use of externally controlled

VDC systems with automatic air recirculation was evaluated using existing research data

as presented in Figures D-2 and D-3. Figure D-2, as developed by W.O. Forrest and M.S.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-12

Bhatti at Delphi, presents the relative power consumption of comparable A/C systems

utilizing a variety of technologies, including a pneumatically controlled FDC system,

both pneumatically and externally controlled VDC systems, and an externally controlled

VDC system in combination with air management strategies. [6] The test conditions for

these data are virtually identical to U.S. average A/C operating conditions. Figure D-3,

also developed by Forrest, illustrates how the compressor power requirements of an

externally controlled VDC system in combination with enhanced air management

strategies vary with ambient conditions. [5] The variation in compressor power with

changing ambient conditions for a comparable pneumatically controlled FDC system was

previously presented in Figure D-1 above. It is important to recognize that these figures

are illustrative only in that they are based on systems that are larger than that assumed for

an average A/C system in this evaluation. This evaluation assumes a 180 cc average

pneumatically controlled FDC system displacement, and all system load estimates have

been adjusted to reflect this reduced displacement.

To accurately consider the impacts of an enhanced externally controlled

VDC-based system employing an air intake management strategy to force cooled air

recirculation, the relations presented in Figures D-1, D-2, and D-3 were adjusted to

reflect a 180 cc base FDC system as well as to factor out the benefits of a reduced

reheating strategy (since the impacts of series reheat were not assumed in the baseline

A/C system consumption).

41 As indicated in Figure D-2, the efficiency benefits of air

intake management are expressed incremental to those of reduced reheating. To factor

out the reduced reheating efficiency benefits, the ratio of power demand with both

reduced reheat and air intake management to power demand with only reduced reheat

was applied to VDC power demand without either the reduced reheat or air intake

management strategies. Similarly, the base (180 cc) system displacement adjustment was

accomplished by normalizing the power demands for the VDC system to those of the

corresponding base FDC system and treating the normalized power demand as

representative of the efficiency benefits associated with a non-specific FDC system

replacement.

Since the power consumption of both internally and externally controlled A/C

systems varies with both engine speed and ambient conditions as indicated in Figures D-1

and D-3, the relationships presented in those figures must be processed to derive

estimated consumption impacts for a given set of conditions. For this study, the curves

presented in Figures D-1, D-2, and D-3 were reconfigured to estimate power demand

over a range of ambient conditions at a single engine speed of 1500 rpm. Demand at

 

41

It should be noted that in the enhanced externally controlled A/C system, the combination of external

control, variable compressor displacement, and automatic air management do derive significant efficiency

improvements through a reduction in the level of series reheat required to maintain a given passenger

cabin temperature. However, since this study assumes a manually controlled baseline A/C system for

which the impacts of series reheat were assumed to be minimal, it was appropriate to exclude the

efficiency benefits from reduced series reheat from the impact calculations of this study. This does not

imply that these benefits will not accrue, simply that no credit for them is taken in this study. In effect,

the efficiency benefits for the enhanced A/C system assumed in this study relative to a baseline system in

which series reheat is significant (i.e., an automatic climate control system) will be greater than estimated

in this study. For example, while this study estimates a power consumption reduction of about 55 percent

for the enhanced A/C system, Forrest and Bhatti estimate a reduction of 75 percent for the exact same

system [6].
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-13

1500 rpm was selected as most appropriate for a determination of average U.S. impacts

based on an analysis of engine speeds over typical driving cycles. Figure D-4 presents

the resulting power demand curves.

As might be expected, the power demand curves show the greatest benefit of

externally controlled VDC systems to be in the mid range of typical ambient conditions

encountered during A/C system operation. At ambient conditions inducing higher

cooling demand, the operating displacement of the externally controlled VDC system

approaches that of an internally controlled FDC system and benefits decline. Benefits

also decline at low ambient, low cooling demand conditions because the on time for an

internally controlled FDC clutch cycling system is small, thereby reducing the level of

excess power demand available for reduction. Using the presented relationships, the

specific efficiency improvements for an externally controlled VDC-based A/C system

employing an air intake management strategy can be estimated for average, high average,

and low average U.S. A/C operating conditions.

Alternative Refrigerant Impacts on Energy Demand: HFC-152a has been

shown to have physical, thermodynamic, and transport properties similar or superior to

those of HFC-134a, while the corresponding properties for hydrocarbon refrigerants are

generally also similar or superior to the hydrofluorocarbon refrigerants. Thus, A/C

systems utilizing HFC-152a or propane refrigerants should be
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-14

Figure D-2: Variation in Power Demand for Various A/C System Technology

Relative to a 215 cc Pneumatically Controlled FDC System [6]

Note: The power demand figures include the effect of compressor “ on/off” cycling

as required to maintain efficient evaporator function at ambient conditions

of 26.7oC (80.1oF) and 60 percent relative humidity (approximately 61 kJ/kg

specific enthalpy). “CVC” stands for Compact Variable Compressor, “ p”

stands for pneumatically controlled, “ e” stands for externally controlled,

“ SHSR” stands for Series Reheat Reduction Strategy, “ AIM” stands for Air

Inlet Mixture (i.e., forced recirculation), and “ TXV” stands for Thermal

Expansion Valve.

Figure D-3: Ambient Impacts on Power Demand for an Externally Controlled VDC

System with Enhanced Air Management [5]
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-15

Figure D-4: Power Demand for the Pneumatically Controlled FDC and Externally

Controlled VDC Systems at 1500 rpm Engine Speed

capable of transferring heat more efficiently than similar HFC-134a systems. Existing

research for HFC-152a appears to confirm this, where data consistently show improved

efficiency. [14,16-18] Moreover, it appears that this improvement increases with ambient

enthalpy. A regression analysis of available data shows an 11 percent efficiency

improvement for enthalpies in the 80 kJ/kg range, declining to about 5 percent in the 60

kJ/kg range. Because available evaluation data were limited to the lower end of this

range, the regression was not extrapolated, but instead held constant at a 5 percent

improvement for low enthalpy conditions.

As with HFC-152a, there is limited available data for propane systems. [14,18] A

regression analysis of available data indicated no significant slope, so a simple arithmetic

average was selected as the most appropriate approach to estimating power demand

reduction for propane systems. The average reduction relative to HFC-134a systems is 3

percent.

The power demand impacts of CO2-based A/C systems have been subject to

considerable debate. Early theoretical calculations predicted poor performance for CO2

systems relative to HFC-134a. [8] Those calculations were predicated on a series of

thermodynamic properties of CO2 (primarily its low critical temperature) that implied

poor performance relative to HFC-134a. However, considerable research has

demonstrated that in practice CO2 systems can perform better than HFC-134a systems for

a wide range of operating conditions. [19-21] This apparent discrepancy results from the

fact that CO2 possesses better heat transfer properties than HFC-134a, and CO2 systems

0

1

2

3

4

5

6

20 30 40 50 60 70 80 90

Specific Enthalpy (kJ/kg)

A/C

S

ystem

L

oad (k

W)

0.0

0.5

1.0

1.5

2.0

L

oad

Relative to

U.S. A

verage

Pneumatically Controlled FDC @1500 Erpm

Externally Controlled VDC @1500 Erpm

EC-VDC with Automatic Recirculation @1500
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-16

operate at reduced pressure ratios resulting in higher compressor efficiency. For this

evaluation, recent research conducted at the University of Illinois was used to estimate

CO2 system power demand. [21] This research was selected specifically because it

compares the performance of a CO2 system to an enhanced HFC-134a system of

equivalent compressor and evaporator design and size. Using these data, the estimated

power demand reductions for average, high average, and low average U.S. A/C operating

conditions are 8 percent, 1 percent, and 20 percent respectively.

42

As mentioned above, HFC-152a, propane (as well as other hydrocarbon-based

systems), and CO2 A/C systems all present certain safety risks beyond those of HFC-134a

systems. HFC-152a and propane are considered to be flammable (albeit HFC-152a to a

lesser extent than propane), while CO2 is considered to be toxic due to physiological

effects at moderately high concentrations and its ability to asphyxiate at sufficiently high

concentrations. A risk assessment for all three systems is currently being conducted

through a cooperative government/industry process to determine the extent of imposed

risk. Based on the results of that assessment, it is possible that one or more of these

refrigerants may be restricted from use in traditional A/C systems where the system

evaporator is located inside the passenger cabin (behind the instrument panel).

Alternatively, the basic system design could remain unchanged, but added safety

equipment could be required to detect and respond to refrigerant leaks (e.g., by

automatically lowering vehicle windows). At this time, it is unclear how the risk

assessment process will conclude.

Based on the current uncertainty regarding the level of risk imposed by

HFC-152a, propane, and CO2 systems, it is appropriate to examine the impacts of

potential system designer response to possible risk constraints. One particular response,

the use of secondary loop A/C systems, could significantly impact the power-demand

estimates for each of the systems. In a secondary loop system, the primary system

refrigeration loop is analogous to current A/C system designs, except that: (1) it is located

entirely outside the passenger cabin, and (2) the evaporator is coupled to a secondary

fluid refrigeration loop rather than cabin-bound air ducts. The secondary loop fluid,

generally a water/glycol mixture, transfers heat from passenger cabin-bound air to the

primary refrigerant. Thus, the secondary loop system isolates the passenger cabin from

the primary refrigerant, but also adds complexity and incremental power demand. The

incremental power demand is due to both a pump required to move the secondary fluid

through its circuit and the incremental efficiency losses associated with an additional heat

exchange operation.

Research has been performed to evaluate the power demand impacts associated

with secondary loop systems. [14, 16] Although empirical data are somewhat limited,

there is sufficient consistency to indicate that incremental demand is on the order of

10-25 percent. Since regression analysis indicates no significant slope between power

 

42

It should be noted that subsequent to the completion of the A/C portion of this study, summary data from

the SAE Alternate Refrigerant Cooperative Research Program (ARCRP) were released. The ARCRP was

initiated by the Society of Automotive Engineers (SAE) to evaluate the energy efficiency of various

mobile A/C systems. The released summary data imply a CO2 efficiency benefit of about 7 percent

relative to an enhanced HFC-134a system, quite consistent with the 8 percent benefit assumed in this

study.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-17

demand impacts and system operating conditions, incremental system power demand was

estimated through arithmetic averaging at about 18 percent.

43

Costs: Estimating the cost of the A/C system alternatives is somewhat difficult

given the research nature of most of the evaluated options. Nevertheless, previous

researchers have produced some estimates. [22, 23] However, in many cases, biases have

been demonstrated in favor of one option or another and, as a result, it is sometimes

difficult to rationalize the various available cost estimates. For example, the cost of an

incremental safety system may be applied to one refrigerant and not another, or the costs

of safety considerations overlooked entirely. In this evaluation, an attempt is made to

correct for these inconsistencies so that presented costs may differ somewhat from those

presented in the public references. Basically, the following cost assumptions are

employed:

• The cost associated with the upgrade of current system components to a

system that includes an externally controlled variable displacement

compressor with electronic controls and reduced leakage hoses and

connections is estimated to be $40. This cost applies to all evaluated A/C

alternatives.

• HFC-152a and propane systems accrue no additional component costs, except

as related to safety as noted below.

• CO2 systems accrue an additional $20 cost associated with the upgrade of

system hoses and components for higher pressure operating conditions, so that

the total system component cost for CO2 systems is estimated to be $60.

• For non-secondary loop designs, HFC-152a, propane, and CO2 systems are

assumed to require additional safety equipment, including in-cabin leak

sensors and engine compartment evacuation valves. An additional cost of

$22.50 is assumed for all three alternatives.

• For secondary loop designs, the incremental cost of a secondary loop is

assumed to be $50 and this estimate is independent of the primary loop

refrigerant. Thus HFC-152a, propane, and CO2 systems with secondary loops

all reflect this incremental cost. However, the added cost of the safety

equipment described above ($22.50) is subtracted out of secondary loop

systems, so that the net incremental cost is $27.50.

 

43Here also, it should be noted that subsequent to the completion of the A/C portion of this study, summary

data from the SAE Alternate Refrigerant Cooperative Research Program (ARCRP) were released. The

ARCRP was initiated by the Society of Automotive Engineers (SAE) to evaluate the energy efficiency of

various mobile A/C systems. The released summary data imply a secondary loop efficiency disbenefit of

about 18-20 percent relative to an enhanced HFC-134a system. This is entirely consistent with the 18

percent estimate assumed in this study.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-18

Based on these estimates, both the total incremental system cost for each A/C

option as well as the cost per ton of associated CO2 (or CO2 equivalent) reductions can be

estimated. presents the derived GHG reduction, cost, and cost effectiveness estimates.

For convenience in comparing these data to other CO2 control strategies, cost

effectiveness estimates are presented both in terms of CO2 and carbon. As indicated, for

average U.S. A/C usage conditions, the cost effectiveness of the various A/C alternatives

ranges from -8 to -43 dollars per ton CO2 (-31 to -158 dollars per ton carbon), with the 40

gram enhanced HFC-134a system being the most cost effective.

44 However, the

enhanced HFC-134a system provides only about 70-75 percent of the benefits of

HFC-152a, propane, or CO2 systems. In high average usage areas, the cost per ton drops

even further due to the proportionally higher emission reductions associated with greater

A/C system usage. Conversely, in low average usage areas, the cost per ton rises

dramatically due to low system usage rates.

 

44 Negative cost effectiveness estimates indicate a situation in which consumers derive a net cost savings

through reduced fuel usage
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-19

Table D-4: Estimated A/C System GHG Reductions, Cost, and Cost Effectiveness

A/C System Type

Total

Equivalent

CO2

(kg/year)

Total

Equivalent

CO2

(kg/life)

Total

CO2

Reduction

(kg/life)

Incremental

System

Cost

($)

Cost

Benefit

($/ton CO2)

[see Note 2]

Cost

Benefit

($/ton C)

[see Note 2]

U.S. Average Operating Conditions

Baseline HFC-134a 464.1 5,569.2 Baseline 0.00 Baseline Baseline

Enhanced HFC-134a (40 gram/yr leakage) 260.6 3,127.2 2,442.0 40.00 -43.09 -158.01

Enhanced HFC-134a (20 gram/yr leakage) 229.6 2,755.2 2,814.0 40.00 -37.40 -137.12

HFC-152a (20 gram/yr leakage) 170.1 2,041.2 3,528.0 62.50 -25.22 -92.47

HFC-152a with SL (20 gram/yr leakage) 195.3 2,343.6 3,225.6 90.00 -13.95 -51.16

Propane (20 gram/yr leakage) 167.8 2,013.6 3,555.6 62.50 -24.62 -90.27

Propane with SL (20 gram/yr leakage) 194.7 2,336.4 3,232.8 90.00 -13.08 -47.96

CO2(porous) 164.8 1,977.6 3,591.6 82.50 -19.95 -73.16

CO2 with SL (porous) 190.0 2,280.0 3,289.2 110.00 -8.42 -30.87

CO2(50 gram/yr leakage) 164.2 1,970.4 3,598.8 82.50 -19.91 -73.01

CO2 with SL (50 gram/yr leakage) 189.4 2,272.8 3,296.4 110.00 -8.40 -30.80

High U.S. Average Operating Conditions

Baseline HFC-134a 866.1 10,393.2 Baseline 0.00 Baseline Baseline

Enhanced HFC-134a (40 gram/yr leakage) 520.2 6,242.4 4,150.8 40.00 -51.25 -187.91

Enhanced HFC-134a (20 gram/yr leakage) 489.2 5,870.4 4,522.8 40.00 -47.03 -172.45

HFC-152a (20 gram/yr leakage) 405.6 4,867.2 5,526.0 62.50 -38.84 -142.42

HFC-152a with SL (20 gram/yr leakage) 472.5 5,670.0 4,723.2 90.00 -29.47 -108.06

Propane (20 gram/yr leakage) 420.3 5,043.6 5,349.6 62.50 -37.46 -137.34

Propane with SL (20 gram/yr leakage) 489.8 5,877.6 4,515.6 90.00 -27.23 -99.86

CO2(porous) 429.5 5,154.0 5,239.2 82.50 -33.46 -122.68

CO2 with SL (porous) 501.8 6,021.6 4,371.6 110.00 -21.91 -80.33

CO2(50 gram/yr leakage) 428.9 5,146.8 5,246.4 82.50 -33.41 -122.51

CO2 with SL (50 gram/yr leakage) 501.2 6,014.4 4,378.8 110.00 -21.87 -80.20

Low U.S. Average Operating Conditions

Baseline HFC-134a 146.5 1,758.0 Baseline 0.00 Baseline Baseline

Enhanced HFC-134a (40 gram/yr leakage) 119.9 1,438.8 319.2 40.00 88.62 324.93

Enhanced HFC-134a (20 gram/yr leakage) 88.9 1,066.8 691.2 40.00 40.92 150.06

HFC-152a (20 gram/yr leakage) 34.7 416.4 1,341.6 62.50 36.19 132.68

HFC-152a with SL (20 gram/yr leakage) 40.5 486.0 1,272.0 90.00 61.22 224.48

Propane (20 gram/yr leakage) 30.5 366.0 1,392.0 62.50 34.88 127.88

Propane with SL (20 gram/yr leakage) 36.6 439.2 1,318.8 90.00 59.22 217.14

CO2(porous) 32.2 386.4 1,371.6 82.50 49.56 181.72

CO2 with SL (porous) 38.1 457.2 1,300.8 110.00 74.86 274.48

CO2(50 gram/yr leakage) 31.6 379.2 1,378.8 82.50 49.30 180.77

CO2 with SL (50 gram/yr leakage) 37.5 450.0 1,308.0 110.00 74.45 272.97

Notes: (1) SL signifies “ Secondary Loop” and the indicated gram per year leakage defines the system design standard. Porous indicates a

CO2 system that is recharged annually and is included only to illustrate the insensitivity of CO2 emissions performance to leakage

rate. Lifetime emissions are based on a 12 year estimated life.

(2) Cost benefit calculations include accrued fuel savings due to indirect emission reductions, estimated using the following

assumptions: 19.5 pounds CO2 per gallon of gasoline, 12 years/150,000 miles vehicle life, 4.5 percent annual decline in travel, 12

years of fuel savings, $1.50 per gallon fuel price, and a 12 percent annual discount rate for future savings.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-20

In considering overall A/C system GHG reduction potential, there are several

issues that should be recognized. Each issue, however, could demand the focus of

significant investigation beyond the scope of this evaluation. The following list presents

a basic overview of a variety of these issues, and where appropriate indicates where

estimates produced in this evaluation might be subject to uncertainty based on future

related developments.

• Basic research into A/C approaches that differ fundamentally from the

approaches included in this evaluation has been conducted. For example,

basic theoretical work related to systems such as metal hydride heat

pumps, absorption cycles, heat pipes, and turbocharger-driven

compression has been reported. However, none of these approaches has

achieved a level of development that allows an accurate determination of

practical feasibility, impact, or cost to be estimated in any way that would

allow for reasonable comparison to more advanced alternatives. For this

reason, such options are not considered in this evaluation.

• Similarly, there are a number of vehicle design parameters unrelated to the

A/C system itself that affect A/C energy demand. For example, cabin

design, window glazing, interior color, instrument panel design, cabin

ventilation, and myriad other parameters can all affect occupant comfort

and, therefore, A/C demand. Although worthy of investigation, the

analysis of the cost effectiveness of such design strategies relative to the

cost of more efficient A/C systems is beyond the scope of this evaluation.

• The feasibility of onboard diagnostic (OBD) systems to detect reduced

refrigerant charge levels has been demonstrated and such systems could be

used to enforce mandated refrigerant leakage rates if imposed. Such

systems would add costs beyond those assumed in this evaluation, but

could be considered as part of a regulatory program that, for example,

might allow the continued use of HFC-134a with appropriate low level

OBD detection safeguards.

• The ability to CO2 systems to retain a specified charge over time has not

yet been demonstrated in use. CO2 systems operate at much higher

pressures than current vapor compression systems and this poses a

significant leakage challenge for CO2 system designers. Typical operating

pressures for CO2 systems are about 500-700 psia on the low pressure side

and 1400-1900 psia on the high pressure side, as compared to 40-65 psia

on the low pressure side and 200-350 psia on the high pressure side for

HFC-134a systems. Thus, CO2 systems must be able to prevent

refrigerant leakage while operating at pressures 7-10 times greater than

those of current systems. While prototype systems have been developed

and tested, some uncertainty remains about the ability of CO2 systems to

perform adequately in consumer use. It should be noted that this primarily

a marketability issue, and is not important from an emissions perspective.

To demonstrate this fact, this evaluation included a “ porous” CO2 system
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-21

that required a complete refrigerant refill annually and, as presented

above, the emissions performance of this system is virtually identical to a

“ tight” CO2 system. However, the cooling performance is the critical

factor from a consumer perspective and a porous system is not a viable

A/C alternative. Based on progress to date, it seems likely that adequate

system design can be achieved, but the issue should not be dismissed at

this point in system development.

• The ability of HFC-152a, propane, and CO2 systems to meet acceptable

safety requirements is currently being evaluated. Both HFC-152a and

propane represent potential flammability concerns, while CO2 presents

toxic concerns related to mental acuity and asphyxiation. Possible

responses include the installation of safety systems, which have already

been demonstrated, or the use of secondary loop A/C systems. This

evaluation includes the effect of both approaches on estimated system

performance and cost, but it in unclear whether an ongoing

government/industry risk assessment will conclude that either approach is

adequate to address all safety issues.

• Electric A/C compressors may offer further efficiency advantages over

current belt driven systems. These advantages primarily result from the

ability to control compressor speed independent of engine speed, which

becomes especially important on hybrid electric vehicles (HEV) and

conventional gasoline vehicles utilizing engine-off at idle technology.

Adapting A/C system capacity to cooling demands through compressor

speed variation, as opposed to the compressor displacement variation

approach employed in VDC systems, offers volumetric efficiency

advantages that result in additional reductions in system energy-demands.

Some of the volumetric efficiency gain is lost to reduced power

transmission efficiency (electric drive efficiencies are typically in the 65

percent range, whereas belt drive efficiency generally exceeds 95 percent),

but it appears that the net gain could be positive. However, current 12 volt

electric systems are not adequate to handle the additional power demands

imposed by electric compressors. Migration of vehicles to 42 volt

systems, as is being discussed for a variety of power consumption reasons

other than A/C, would enable electric compressor use. However, given

the uncertainty of a 42 volt future in the 2009-2015 timeframe of this

study, electric compressors have not been considered as a large market

A/C option. Nevertheless, electric A/C systems can be expected to

achieve a modest level of market penetration in accordance with HEV, 42

volt, and engine-off at idle technology.

• As described above, the current A/C system technology for this evaluation

was assumed to utilize pneumatically controlled fixed displacement

compressor technology. However, it should be recognized that there are

current variable displacement compressor systems in the U.S. market and
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-22

that the externally controlled VDC market share can be expected to

increase through the 2009-2015 timeframe. In the absence of regulatory

consideration of A/C system impacts on fuel consumption, vehicle

manufacturers have little incentive to switch to VDC systems for fuel

consumption benefits. However, in some cases, manufacturers do have an

incentive to switch to external control VDC systems to improve vehicle

driveability and “feel.” The incremental engine load associated with FDC

clutch cycling is sufficiently large on small output engines to cause

perceptible and perhaps unacceptable driveability concerns for some

vehicles and customers. Thus, some manufacturers have been moving

toward VDC systems in the small engine market to improve customer

acceptance. In markets dominated by small displacement engines such as

Europe and Japan, the market share of VDC systems is growing

dramatically, but this same level of growth is not expected in the U.S.

Average engine displacement in the EU is less than 2 liters, as opposed to

nearly 3.5 liters in the U.S., with only about 6 percent of U.S. light duty

vehicle sales reflecting engines under 2 liters displacement. Since larger

engines respond less dramatically to compressor clutch cycling, the

performance-based incentive for VDC systems is substantially less in the

U.S. For example, even if VDC systems were installed on all light duty

vehicles with displacements of 2 liters or less, the total U.S. new vehicle

market share of VDC systems would be less than 15 percent through the

2009-2015 timeframe. If application was extended to all engines of 2.5

liters or less, the market incentive would double to about 30 percent,

further increasing to about 40 percent at 3 liters or less. Given continuing

dominance in the U.S. market, a pneumatically controlled FDC-based

system was utilized as the baseline A/C system technology in this

evaluation. Nevertheless, it should be recognized that some fraction of the

U.S. market already incorporates VDC technology and that this presence

will impose a modest error on total fleetwide emission impacts derived

from the evaluation-assumed baseline conditions.

• Some research cites the ability of CO2 systems to also perform in reverse

(as heat pumps) and provide vehicle heating benefits as a major benefit of

moving to CO2 systems. Such ability would be most important in high

efficiency vehicle applications with low waste heat availability. This

evaluation has not considered such benefits for two primary reasons.

First, it is not clear that operating the A/C compressor to support heat

pump operation is the most efficient approach to supplying vehicle heat.

Clearly, such operation would increase A/C system usage rates

dramatically. Second, the ability of a CO2 system to operate as a heat

pump is not unique. Existing residential and commercial applications, as

well as recent vehicle research, demonstrates that vapor compression cycle

refrigerants possess the same ability.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-23

• In accordance with the costing methods for other portions of this study,

alternative A/C system costs include only the estimated high volume

variable costs of components and do not consider the fixed costs

associated with system introduction (e.g., engineering, and any

incremental production, manufacturing, or assembly plant costs). For A/C

systems, fixed costs to the vehicle manufacturer should be modest since

the systems are generally purchased from suppliers and not manufactured

by the vehicle manufacturer. Nevertheless, this approach can result in the

omission of barriers to marketability and should be considered

accordingly. Similarly, costs external to initial vehicle manufacture have

also not been considered. This primarily involves service industry costs

such as the cost of replacing recycling equipment, diagnostic tools, etc.,

but can also include additional consumer costs if service and maintenance

differences exist across system alternatives. These omitted costs can vary

considerably across the various systems. For example, with the exception

of the potential replacement of the system desiccant to ensure

compatibility, HFC-152a can effectively be used in current HFC-134a

systems (i.e., it is virtually a “ drop-in” replacement). With HFC-152a and

propane, service equipment will need to be upgraded or replaced and both

HFC-134a and alternative refrigerant equipment will need to be

maintained during the switchover period. In the case of CO2 systems, the

service industry should incur no need for recycling equipment, but will

require leak detectors and appropriate high pressure service equipment.

However, if service intervals are shorted for CO2 systems, consumers

would incur additional costs.

• As stated previously, this evaluation assumes effective refrigerant

recycling in both vehicle service and end-of-life disposal practices. If

actual practices are ineffective, direct refrigerant emission impacts will be

up to 3.5 times greater than estimated in this study, and total GHG impacts

(direct plus indirect) will increase by about 50 percent for U.S. average

operating conditions. The potential impacts of enforcing refrigerant

recycling should be considered in the overall evaluation of alternative

refrigerants. The negative effects of ineffective recycling practices decline

in step with the GWP of A/C system refrigerant, so that the potential

negative impacts of HFC-152a, propane, and CO2 systems are

significantly less than those for HFC-134a systems. CO2 systems reflect a

lower bound risk since direct emissions from CO2 systems have a zero net

GWP, allowing the complete elimination of refrigerant recycling

requirements.

• Finally, the evaluation also does not consider emissions resulting from the

energy used to produce refrigerants. Refrigerant leakage prior to vehicle

charging is considered in the estimation of direct emissions, but energy

used to power manufacturing and distribution equipment is not considered.

Generally, all alternatives will require energy to produce and it may be
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-24

that energy required to produce natural fluids such as CO2 will be

somewhat less than that required to produce HFCs, but such analysis is

beyond the scope of this evaluation.

D.1.1. AVL CRUISE Simulation Modeling

To validate the analytical estimates of the stand-alone evaluation, several

CRUISE simulations were conducted for baseline HFC-134a systems using

pneumatically controlled FDC technology and alternative HFC-152a systems using

externally controlled VDC technology with automatic air recirculation. To facilitate the

simulation modeling, compressor power demand curves were developed for each of the

A/C systems. Initial compressor demand estimates were developed from the curves

presented previously in Figure D-2, which indicate the demands of several alternative

system designs including those investigated in this exercise.

All CRUISE modeling related to A/C was performed for U.S. average ambient

conditions during A/C operations, which as described above are estimated to be

equivalent to a specific enthalpy of 60.9 kJ/kg. The data summarized in Figure D-2 are

associated with ambient test conditions of 80.1 °F and 60 percent relative humidity,

which is equal to a specific enthalpy of approximately 61 kJ/kg. Accordingly, the data

presented in Figure D-2 are quite consistent with average U.S. operating conditions and

no adjustments for ambient conditions were employed.

Nevertheless, several adjustments unrelated to ambient conditions were

undertaken. First, the data presented in Figure D-2 correspond to a 215 cc base

compressor displacement. First, power demands were scaled down to reflect a more

“ typical” 180 cc system using a simple proportionality approach. Second, since Figure

D-2 presents data at the compressor shaft, engine crankshaft power was estimated by

applying a power transmission efficiency factor. For this adjustment, a belt transmission

efficiency of 97 percent was assumed. Third, the impacts of a “reheat reduction strategy”

(designated as SRHR in Figure D-2) were removed from CRUISE analysis by

normalizing the "SRHR&AIM" (reheat reduction plus automatic air recirculation) loads

to the "SRHR" (reheat reduction alone) and applying the resulting ratios to the externally

controlled variable displacement compressor curve without either reheat reduction or

automatic air recirculation.

45

Finally, the system power associated with the cabin blower

motor was assumed to be 0.25 kW and was added to the resulting consumption curves for

both the baseline pneumatically controlled FDC-based system and the alternative

externally controlled VDC-based system.

Figure D-5 presents the resulting A/C load curves provided to AVL for CRUISE

modeling. It is perhaps worth noting that these curves are analogous to those previously

presented in Figure D-4, except that engine speed is held constant in Figure D-4, while

specific enthalpy is held constant in Figure D-5. The analytical evaluation described

above assumed an average engine speed of 1500 rpm and estimated A/C GHG impacts

 

45As indicated in the discussion for the stand-alone analysis, series reheat reduction impacts are factored

out of the impact calculations in this study, not due to a lack of expected benefits, but rather because the

baseline system assumed in this study is a manually controlled A/C system for which series reheat is

presumed to be minimal. Series reheat reduction should be an integral component of an enhanced system

designed to maximize efficiency at an automatically controlled cabin temperature.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-25

for various ambient conditions. The CRUISE simulations investigate only a single

ambient condition (i.e., U.S. average), but treat engine speed on a robust basis according

to the specific drive cycles evaluated.

46

Figure D-5: A/C System Power Demand Versus Engine Speed

AVL performed several additional processing steps prior to actual CRUISE

modeling. First, the generic 180 cc demand curves presented in Figure D-5 were

converted into vehicle class specific curves in accordance with estimated class-specific

compressor displacements of 150 cc for the small car class, 170 cc for the large car class,

and 210 cc for all three truck classes.

47 As described above for the development of the

180 cc curves, this adjustment assumed proportionality between system power demand

 

46

It is perhaps worth noting that subsequent to the completion of the A/C portion of this study, summary

data from the SAE Alternate Refrigerant Cooperative Research Program (ARCRP) were released. The

ARCRP was initiated by the Society of Automotive Engineers (SAE) to evaluate the energy efficiency of

various mobile A/C systems, and included the investigation of several advanced A/C systems relying on

externally controlled VDCs and improved heat exchangers. Although the engine speeds covered by the

summary data extend only from about 600-1700 rpm, the power consumption data for the ARCRP

enhanced HFC-134a system over this speed range tracks quite closely with the power demand curve for

the externally controlled VDC-based system used in this study (as presented in Figure D-5).

Unfortunately, the ARCRP does not include comparable consumption data for a typical “ unimproved”

baseline A/C system.

47Actual compressor sizes in the truck classes cover a wide range of displacements, and 210 cc is probably

near the upper end of the range. Therefore, the use of 210 cc as the compressor size for the three truck

classes could overstate A/C-related energy consumption by 15-20 percent for a significant fraction of

trucks. So, while the percentage improvement in A/C-related energy consumption is accurate for all

vehicles in the truck classes, absolute CO2 emissions due to A/C may be overstated by up to 5 grams per

mile for the baseline A/C system and up to 2 grams per mile for the advanced system.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 1000 2000 3000 4000 5000 6000

Engine RPM

Power (kW)

0.00

0.67

1.34

2.01

2.68

3.35

4.02

4.69

5.36

6.03

6.71

Power (hp)

180 cc Pneumatically Controlled FDC System

Externally Controlled VDC System with Air Management
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-26

and compressor displacement. Second, AVL applied a 5 percent power demand

reduction to the externally controlled VDC system curves for all five vehicle classes to

simulate the benefit that is expected with HFC-152a refrigerant. Finally, AVL converted

the class-specific demand curves into crankshaft torque curves and performed simulation

modeling for both the baseline and alternative A/C systems by adding the A/C system

loads to existing “ non-A/C” simulations for two technology packages in the large car

class and one technology package in each of the small car, small truck, and minivan

classes.

Since A/C system simulation modeling was only performed for five of the

technology packages, CRUISE results were investigated to determine if a generalized

impact could be developed. Figure D-6 presents the impacts estimated by CRUISE for

each of the five pneumatically controlled FDC system simulations and each of the five

externally controlled VDC system simulations. The CRUISE outputs are indicated by the

open markers (diamonds for the FDC system and circles for the VDC system). As

indicated, there is considerable scatter for the FDC system, with estimated incremental

CO2 impacts varying by as much as 25 grams per mile (g/mi).

Figure D-6: CRUISE-Predicted A/C Impacts

Note: FDC in this figure refers specifically to a pneumatically controlled FDC-based A/C

system. VDC refers specifically to an externally controlled VDC-based A/C system with

enhanced air management.

0

10

20

30

40

50

60

70

80

90

200 220 240 260 280 300 320 340 360

A/C-Off CO2(g/mi)

As Reported

A/C-O

n

C

O2 Increase (g/mi)

0

5

10

15

20

25

30

35

40

45

Per 100cc A/C-O

n

C

O2 Increase (g/mi)

FDC Data (unnormalized) VDC Data (unnormalized)

FDC Data (per 100cc Disp) VDC Data (per 100cc Disp)

SC M ST

V

LC LC
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-27

Scatter for the VDC system is also significant, covering a range of about 15 g/mi.

However, if the CRUISE outputs are adjusted to account for the differing compressor

sizes across vehicle classes, much of the scatter goes away. This is reflected in the solid

markers of Figure D-6 (diamonds for the FDC systems and circles for the VDC systems),

where the full FDC scatter is now encompassed within a range of about 7 g/mi and the

full VDC system scatter is encompassed within a range of about 5 g/mi.

Based on the resulting similarity in A/C system impacts per 100 cc compressor

displacement, generalized A/C system impacts were estimated to be 33.0 g/mi per 100 cc

for the base FDC system and 15.1 g/mi per 100 cc for the alternative VDC system. These

impact estimates are also plotted in Figure D-6 as the solid and dashed lines respectively.

As indicated, they represent the data for the five CRUISE simulations quite well.

Accordingly, the generalized impact estimates are believed to be reasonable estimates of

the impact of A/C systems on vehicle GHG for a wide range of technologies (as indicated

in Figure D-6, the CRUISE modeling covered CO2 emission rates ranging from 220 to

340 g/mi). On this basis, the generalized impact estimates have been applied to the full

range of CRUISE simulation results presented in Chapter 3 above.

References

1. Collier, S. et al., Modine Manufacturing Company, “ Adapting a Vehicle from a

R134a to a R744 (CO2) AC System,” presented at the SAE Alternate Refrigerants

Symposium, Phoenix, Arizona, July 16, 2003.

2. U.S. Environmental Protection Agency, “ Greenhouse Gases and Global Warming

Potential Values, Excerpt from the Inventory of U.S. Greenhouse Emissions and

Sinks: 1900-2000,” Office of Atmospheric Programs, U.S. Greenhouse Gas

Inventory Program, April 2002.

3. 6FKZDU] : NR-Recherche GmbH, “ Emission of Refrigerant R-134a from Mobile

Air-Conditioning Systems, Annual Rate of Emission from Passenger-Car

Air-Conditioning Systems up to Seven Years Old,” 360 09 006, prepared for the

German Federal Environment Office, September 2001.

4. 6FKZDU] : HW DO NR-Recherche GmbH, “ Establishing the Leakage Rates of

Mobile Air-Conditioners,” B4-3040/2002/337136/MAR/C1, prepared for the

European Commission (DG Environment), April 17, 2003.

5. Forrest, W.O., Delphi, “ Air Conditioning and Gas Guzzler Tax Credits,”

2002-01-1958, Society of Automotive Engineers, Inc., 2002.

6. Forrest, W.O. and Bhatti, M.S., Delphi Harrison Thermal Systems, “ Energy Efficient

Automotive Air Conditioning System,” 2002-01-0229, Society of Automotive

Engineers, Inc., 2002.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-28

7. Johnson, V.H., National Renewable Energy Laboratory, “ Fuel Used for Vehicle Air

Conditioning: A State-by-State Thermal Comfort-Based Approach,” 2002-01-1957,

Society of Automotive Engineers, Inc., 2002.

8. Bhatti, M.S., Delphi, “ Global Warming Impact of Automotive Air Conditioning

Systems,” 982929E, Society of Automotive Engineers, Inc., 1998.

9. Fischer, S. K. et al., Oak Ridge National Laboratory, “ Total Environmental Warming

Impact (TEWI) Calculations for Alternative Automotive Air-Conditioning Systems,”

970526, Society of Automotive Engineers, Inc., 1997.

10. Petitjean, C. et al., Valeo Climate Control, “ TEWI Analysis for Different Automotive

Air Conditioning Systems,” 2000-01-1561, Society of Automotive Engineers, Inc.,

2000.

11. Clodic, D. et al., Ecole des Mines de Paris, “ Refrigerant Emissions Along the MAC

System Lifetime,” presented at the EU Mac Summit, Brussels, Belgium, February

10-11, 2003.

12. Hill, W. et al., General Motors, “ Life Cycle Analysis Framework, A Comparison of

R134a and R134a Enhanced Systems,” presented at the SAE Alternate Refrigerants

Symposium, Phoenix, Arizona, July 15-17, 2003.

13. Vainio, M., European Commission, “ Life Cycle Climate Performance [LCCP] in

Mobile Air Conditioning,” presented at the EU Mac Summit, Brussels, Belgium,

February 10, 2003.

14. Ghodbane, M., Delphi, “ An Investigation of R152a and Hydrocarbon Refrigerants in

Mobile Air Conditioning,” 1999-01-0874, Society of Automotive Engineers, Inc.,

1999.

15. Federal Highway Administration, “ Highway Statistics 2002,” FHWA-PL-03-010,

Table VM-2, 2003.

16. Ghodbane, M., Delphi, “ On Vehicle Performance of a Secondary Loop A/C System,”

2000-01-1270, Society of Automotive Engineers, Inc., 2000.

17. Ghodbane, M. et al., “ R-152a Mobile A/C with Directed Relief Safety System,”

presented at the SAE Alternate Refrigerants Symposium, Phoenix, Arizona, July

15-17, 2003.

18. Maclaine-cross, I., The University of New South Wales, “ Hydrocarbon Refrigerants

for Car Air Conditioners,” presented at the Seminar on ODS Phase-out: Solution for

the Refrigeration Sector, Kuta, Bali, Indonesia, May 5-7, 1999.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-29

19. Yin, J.M. et al., University of Illinois, “ TEWI Comparison of R744 and R134a

Systems for Mobile Air Conditioning,” 1999-01-0582, Society of Automotive

Engineers, Inc., 1999.

20. McEnaney, R.P. et al., University of Illinois, “ Performance of the Prototype of a

Transcritical R744 Mobile A/C System,” 1999-01-0872, Society of Automotive

Engineers, Inc., 1999.

21. Hrnjak, P. et al., “ Design and Performance of Improved R-744 System Based on

2002 Technology,” presented at the SAE Alternate Refrigerants Symposium,

Phoenix, Arizona, July 15-17, 2003.

22. Commission of the European Communities, “ Proposal for a Regulation of the

European Parliament and of the Council on certain fluorinated greenhouse gases,”

COM (2003) 492 final, 2003/0189 (COD), August 11, 2003.

23. Unattributed, “ Alternative Refrigerants Assessment Workshop,” presented at the

SAE Alternate Refrigerants Symposium, Phoenix, Arizona, July 15-17, 2003.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page D-30
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-1

Appendix E: Methane and Nitrous Oxide

Emissions
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-2

Appendix E: Methane and Nitrous Oxide Emissions

E.1. Introduction

In addition to CO2 emissions, which are discussed throughout the other sections

of this report, light duty vehicle GHG emissions also include methane (CH4) and nitrous

oxide (N2O). Although emissions of these compounds are generally orders of magnitude

lower than emissions of CO2, the global warming potential (GWP

48

) of both CH4 and

N2O is greater than that of CO2. Methane is estimated to have a GWP 23 times that of

CO2, while the GWP of N2O is estimated to be 296 times that of CO2. [1] As a result, it

may be important to consider these emissions in determining the overall GHG impact

potential of light duty vehicles.

Naturally emitted methane, principally a product of vegetative decay and

digestive processes, is estimated to comprise about 40 percent of total atmospheric

methane. The principal anthropogenic (manmade) methane sources in the U.S. are

landfills, agriculture, coal mining, and natural gas extraction and distribution, which

together account for over 90 percent of manmade emissions. In contrast, highway

vehicles and nonroad equipment are estimated to produce less than one percent of

manmade methane. Since 1990, manmade methane emissions in the U.S. are estimated

to have declined by about 15 percent, primarily due to recovery practices in the coal and

landfill industries. [2]

Almost 60 percent of N2O emissions result from natural processes, primarily

bacterial breakdown of soil nitrogen, ocean upwelling, and stratospheric

photo-dissociation and oxidation.

Agricultural fertilization and solid waste denitrification are estimated to be

responsible for the bulk of U.S. manmade N2O emissions (about 70 percent), but nearly

20 percent are estimated to be produced by highway vehicles and nonroad equipment.

Moreover, over 90 percent of the highway vehicle and nonroad equipment emissions

share is estimated to be produced by light duty highway vehicles as a direct result of

catalytic emissions conversion. Since 1990, manmade N2O emissions in the U.S. are

estimated to have remained mostly unchanged, although emissions from light duty

vehicles have increased by about 30 percent (an increase offset by reductions in industrial

and agricultural emissions). [2]

Methane emissions from vehicles represent a product of incomplete combustion.

49

Ideally, such emissions would be converted to CO2 and water as they pass through the

catalytic aftertreatment systems that are universally used on today’s vehicles to meet

 

48 GWP indicates the global warming effectiveness of a compound relative to that of CO2, so that the

GWP of a compound indicates the estimated ratio of its impact on global warming to the impact of the

same mass of CO2.

49

In the case of some automotive fuels, especially natural gas, methane comprises a substantial

portion of the fuel itself. As a result, both incomplete combustion and fuel evaporation or venting can

result in substantial methane emissions. Since this study focuses on gasoline and diesel vehicle emissions,

methane-based fuels are not explicitly considered, but readers should recognize the increased methane

emissions potential of such fuels.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-3

existing criteria pollutant emission standards. However, as the simplest hydrocarbon,

methane is less reactive than all other hydrocarbons and can pass through aftertreatment

systems more easily than other hydrocarbon species. While catalyst system design can be

tailored to more effectively convert CH4, it is important to recognize that this conversion

will not result in the reduction of methane-based GHG emissions to zero. Since catalytic

action will produce 2.75 grams of CO2 for every gram of methane converted, the

elimination of unburned methane through catalysis can achieve a considerable net

reduction in GHG, but that reduction is capped at 88 percent.

50,51 Of course, this same

cap exists for improving in-cylinder fuel combustion characteristics, as any “ displaced”

methane will lead to an increase in CO2 emissions. Only reduced fuel use can provide a

complete reduction in methane-based GHG emissions.

N2O emissions result almost entirely from activity within the catalytic

aftertreatment systems of vehicles. Several test programs have demonstrated that

engine-out N2O emissions are consistent with background N2O concentrations within the

limits of detectability (approximately 0.01 grams per mile). [3-6] N2O appears to be

associated with low temperature NOx (oxides of nitrogen) reduction, being formed as an

intermediary reaction product.

52

[3,4] Although the body of research on the specific

formation chemistry of N2O is considerably less than that of other automotive emission

species, the low temperature reaction mechanism is quite consistent with observed

experimental emissions data. As a result, it is widely believed that the control of vehicle

N2O emissions is a function of improved aftertreatment systems.

A detailed discussion of vehicle methane emissions and the potential for future

reductions follows in Section E.2. Section E.3 presents a similar discussion for N2O

emissions. Finally, Section E.4 presents a summary of associated conclusions.

E.2. Methane Emissions

As indicated in Section E.1, methane is emitted from light duty vehicles due to the

incomplete combustion of fuel in the vehicle engine and the incomplete oxidation of

engine-out methane in current catalytic aftertreatment systems. It is important to

recognize, however, that current vehicles produce and emit substantially less methane

than their older counterparts and, even in the absence of additional regulation, it is almost

certain that future vehicles will exhibit even lower emission rates. Although there are

currently no specific emission standards for methane, existing standards for non-methane

organic compounds do effectively result in reduced methane emissions through the

design and implementation of advanced combustion and catalyst technologies.

Emissions control of organic compounds has evolved over the years. While the

latest (i.e., Tier 2 federal and LEV II California) standards are characterized in terms of

non-methane organic gases (NMOG), other current (e.g., Tier 1 federal) and previous

(e.g., Tier 0 federal) standards are, or have been, characterized in terms of non-methane

 

50

(x CH4)×(23 GWP) → (2.75x CO2)×(1 GWP), so maximum reduction potential = [(2.75x)/(23x)]-

1 = 88 percent.

51 Conversion of one gram of CH4 also produces 2.25 grams of water, which is the most prevalent

GHG. However, the GWP of methane accounts for its indirect production of water. [1]

52

2NO + CO → N2O + CO2, which ideally is followed by N2O + CO → N2 + CO2.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-4

hydrocarbons (NMHC) or total hydrocarbons (THC). While only THC standards

explicitly require the control of CH4 emissions, since by definition both NMHC and

NMOG exclude CH4, all have effectively reduced methane emissions since the

technologies and control strategies implemented to reduce NMHC also reduce the

production and emission of methane. For example, engine technologies designed to

reduce hydrocarbon emissions through improved combustion characteristics, reduce the

full range of hydrocarbon emissions. Similarly, improved catalytic aftertreatment

techniques that increase hydrocarbon conversion efficiency reduce both NMHC and

methane emissions. While aftertreatment systems may preferentially oxidize NMHC due

to its inherently higher reactivity, any improvement in oxidation efficiency will also

increase the oxidation of methane. Therefore, even in the absence of explicit GHG-based

limits, methane emissions should continue to decline as combustion and aftertreatment

efficiencies are further improved.

Since methane emissions are measured as part of the standard vehicle certification

process in the U.S., there is an extensive library of certification data that can be used to

assess both the historic and current methane emission rates of light duty vehicles. Even

so, a considerable degree of processing is required to assemble and analyze these data.

For this study, a smaller 39 vehicle dataset developed by the California Air Resources

Board (ARB) was utilized to estimate methane emission rates. [7] This ARB dataset was

used for several reasons, including the following:

• The dataset represents emissions data for actual in-use vehicles and, therefore,

provides an indication of actual in-use methane and N2O emission rates.

• The dataset includes a wide range of vehicle model years, allowing a wide

range of emissions levels to be analyzed.

• The dataset includes THC, NMHC, CH4, NOx, and N2O emissions

measurements for all 39 vehicles.

Generally, the ARB data was collected between 2000 and 2002 as part of the

agency’s 16th Vehicle Surveillance Program (VSP). Overall, the VSP, which is

conducted periodically, is a much larger (than 39 vehicles) investigation of the in-use

vehicle fleet, intended to evaluate such issues as the cost effectiveness of the state’s

vehicle emissions inspection program, in-use emissions deterioration rates, in-use

evaporative emission rates, in-use speciation profiles, and alternative test cycles. This

study looked at only a subset of the full VSP dataset, since N2O emissions were not

collected for all study vehicles. Moreover, only VSP data collected over the standard

FTP-75 driving cycle were analyzed to avoid any potential confounding issues related to

driving cycles. As indicated, these criteria constrain the overall dataset size to 39

vehicles.

The vehicles included in the VSP are California-based light duty vehicles. Since

federal and California vehicle emission standards have varied over the years (and

continue to do so), this might be cause for variation in estimated emission rates from

those expected in the rest of the U.S. However, it is expected that any such variation will

be minor for several reasons. First, for pre-1993 vehicles, the differences between the

federal and California hydrocarbon standards are minor. Second, much of the federal

fleet now consists of vehicles certified to the National Low Emissions Vehicle (NLEV)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-5

standards, which are similar to the California Low Emission Vehicle (LEV) standards.

Third, the estimated emission rate is determined as an average across vehicles and the

variation between individual vehicles is at least as large as the variation between federal

and California standards. Finally, the data are primarily used to derive emission rate

ratios as opposed to absolute emission rates. These ratios are then applied to applicable

federal certification standards to develop expected federal emission rates, so that the

absolute emission levels of the California data are primarily a reference point rather than

a final emissions estimate.

Figure Eí1 and Table Eí1 provide an overview of the vehicle fleet represented in

the VSP dataset used for this study. As indicated, vehicles span a 21 model year range of

1981 through 2001, with odometer readings ranging from 1,700 to 326,000 miles. Most

of the 39 test vehicles (31) are passenger cars, but there are also 8 light duty trucks.

Thus, trucks are underrepresented in the test sample. The test vehicles do, however,

represent a wide range of engine sizes, with displacements ranging from one to five liters.

Figure E-1: Mileage and Model Year of Vehicles in the ARB VSP Dataset

Note: Solid markers indicate data for 1993 and newer vehicles, open markers

indicate data for 1992 and older vehicles. The sloping solid line is a simple

linear trendline that is not used for any specific purpose other than to determine

the general year-to-year rate of mileage change (6,640 miles). The dashed lines

indicate the mileage bounds applied to a secondary data analysis described in

detail below.

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1980 1985 1990 1995 2000 2005

Vehicle Model Year

Odometer (miles)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-6

Table E-1: Summary Descriptive Data for Vehicles in the ARB VSP Dataset

Model

Year

Vehicle

Make

Vehicle Model

Disp

(liters)

Odometer

(miles)

Vehicle

Class

1981 Chevrolet Van 20 5.0 140,642 MDV

1983 Chevrolet Caprice Classic Station Wagon 5.0 129,370 PC

1984 Volvo DL 4-Door 2.3 140,508 PC

1985 Chevrolet Blazer 2.8 101,625 LDT1

1986 Saab 900 2.0 153,916 PC

1986 Cadillac El Dorado Biarritz 4.1 64,505 PC

1986 Toyota Camry LE 2.0 326,358 PC

1986 Mercury Capri GS 3.8 68,251 PC

1987 Cadillac El Dorado 2-Door 4.1 172,416 PC

1988 Toyota Corolla FX 1.6 97,947 PC

1989 Chevrolet Geo Metro LSi 1.0 163,882 PC

1989 Toyota Tercel Hatchback 1.5 234,588 PC

1990 Nissan Pathfinder XEV6 3.0 153,896 LDT2

1991 Pontiac Transport 3.1 124,716 LDT2

1991 Chrysler Lebaron LE 3.0 94,121 PC

1991 Cadillac Sedan DeVille 4.9 53,804 PC

1992 Pontiac Grand Am 4-Door 3.3 88,497 PC

1993 Cadillac Sedan DeVille 4-Door 4.9 101,147 PC

1993 Mercury Villager GS 3.0 123,070 LDT2

1993 Toyota Corolla 1.6 162,332 PC

1993 Nissan Sentra XE 1.6 78,016 PC

1993 Toyota Camry LE 4-Door 2.2 89,252 PC

1993 Acura Integra LS 3-Door 1.8 81,987 PC

1994 Ford Taurus GL 4-Door 3.0 51,773 PC

1994 Toyota Camry XLE 3.0 110,134 PC

1995 Chevrolet Geo Prism LSi 1.6 118,082 PC

1995 Plymouth Neon 4-Door 2.0 63,752 PC

1995 Toyota Camry LE 2.2 78,773 PC

1996 Dodge Ram 1500 5.2 116,400 MDV3

1996 Mazda 626 LX 2.0 104,185 PC

1996 Toyota Camry LE 2.2 49,631 PC

1997 Ford Expedition XLT 4.6 73,598 MDV3

1997 Mazda Miata 1.8 65,733 PC

1998 Dodge Neon 4-Door 2.0 76,375 PC

1999 Ford Taurus SE 3.0 69,617 PC

2000 Volkswagen GTI Turbo 1.8 31,959 PC

2000 Toyota 4Runner 2WD 2.7 39,252 LDT2

2000 Saturn Saturn SL 4-Door 1.9 31,973 PC

2001 Ford Taurus LS 3.0 1,724 PC
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-7

Figure E-2: CH4 Emission Rate Versus THC Emission Rate

FTP Bag 1 FTP Bag 2

FTP Bag 3 Composite FTP

Note: The dotted and solid lines indicate regression-based relations. Dotted lines include all data, solid lines exclude

outliers (defined as datapoints that vary from the average CH4/THC or THC/CH4ratio by more than two

standard deviations).

Table E-2: Regression Statistics for CH4 (g/mi) Versus THC (g/mi)

All Data Outliers (±2σ) Removed

Statistic

Bag 1 Bag 2 Bag 3 Composite Bag 1 Bag 2 Bag 3 Composite

Intercept 0.0000 0.0201 0.0175 0.0000 0.0000 0.0165 0.0137 0.0000

Slope 0.0803 0.1227 0.0963 0.1220 0.0753 0.1223 0.1047 0.1190

r

2

0.64 0.67 0.62 0.67 0.83 0.82 0.84 0.86

n (obs) 39 39 39 39 36 36 35 36

Slope and intercept statistics are selected at 95 percent confidence level.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Measured THC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Measured THC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Measured THC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Measured THC (g/mi)

Measured CH4 (g/mi)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-8

Figure E-3: CH4 Emission Rate Versus NMHC Emission Rate

FTP Bag 1 FTP Bag 2

FTP Bag 3 Composite FTP

Note: The dotted and solid lines indicate regression-based relations. Dotted lines include all data, solid lines exclude

outliers (defined as datapoints that vary from the average CH4/NMHC or NMHC/CH4ratio by more than two

standard deviations).

Table E-3: Regression Statistics for CH4 (g/mi) Versus NMHC (g/mi)

All Data Outliers (±2σ) Removed

Statistic

Bag 1 Bag 2 Bag 3 Composite Bag 1 Bag 2 Bag 3 Composite

Intercept 0.0000 0.0248 0.0213 0.0000 0.0000 0.0201 0.0160 0.0000

Slope 0.0857 0.1282 0.0986 0.1342 0.0806 0.1328 0.1132 0.1326

r

2

0.59 0.57 0.54 0.58 0.80 0.76 0.80 0.82

n (obs) 39 39 39 39 36 37 35 36

Slope and intercept statistics are selected at 95 percent confidence level.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5

Measured NMHC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5

Measured NMHC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5

Measured NMHC (g/mi)

Measured CH4 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.0 0.5 1.0 1.5 2.0 2.5

Measured NMHC (g/mi)

Measured CH4 (g/mi)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-9

The relationship between measured methane and measured THC emission rates,

as well as the relationship between measured methane and measured NMHC emission

rates, was investigated. Figure Eí DQG 7DEOH (í SUHVHQW WKH UHVXOWV RI WKH 7+&

analysis, while Figure Eí DQG 7DEOH (í SUHVHQW WKH UHVXOWV RI WKH 10+& DQDO\VLV $V

expected, statistically significant relations between both CH4 and THC and CH4 and

NMHC were found (of course, a valid relation for either implies a valid relation for the

other). As shown in Tables Eí DQG (í YDOLG UHODWLRQV H[LVW IRU DOO WKUHH EDJV RI WKH

FTP, but the CH4 fraction of HC increases in Bag 2. This is expected since Bag 2 reflects

hot stabilized catalyst operation, wherein NMHC conversion efficiencies will be at their

maximum. Although CH4 conversion will also increase in Bag 2, efficiency will

generally be below the peak efficiencies for NMHC due to the decreased reactivity of

methane.

As shown in Table E-2, methane generally constitutes about 7.5 to 12 percent of

THC emissions, with the smaller fractions being observed in Bags 1 and 3 of the FTP,

during which the catalyst has not yet attained peak conversion conditions and NMHC

emissions are highest.

53 Relative to NMHC, Table E-3 shows that the methane emission

rate generally ranges from 8 to 13 percent of that for NMHC. This is in good agreement

with algebraic expectations, where a 10± percent increase in emissions fraction would be

expected in moving the relationship base from THC to NMHC.

54

From a composite

emissions standpoint,

CH4 = 0.119 (THC)

or

CH4 = 0.133 (NMHC)

Assuming the THC coefficient to be precise, the algebraic NMHC equivalent

coefficient would be 0.135 (0.119/(1-0.119)). This varies from the regression-based

coefficient by less than 2 percent, so the independent regression analysis results are quite

consistent.

As indicated by the VSP data, as THC (and NMHC) is reduced, methane is also

reduced in a proportional manner. Thus, as vehicle technology advances to meet stricter

organic compound emission standards, it is reasonable to expect that methane emissions

will also decline. However, since it could be possible to derive similar relationships from

data for equivalently emitting vehicles tested at different mileage accumulations

throughout their deterioration cycle, a secondary analysis was performed to ensure that

this was not the case with the VSP data.

 

53 Note that both Tables Q-2 and Q-3 include “ All Data” and “ Outliers Removed” statistics. The

former includes data for all 39 dataset vehicles. The latter excludes data for vehicles with either CH4/X or

X/CH4 ratios that vary from the average ratio by more than ±2 standard deviations, where X indicates the

independent parameter (i.e., either THC or NMHC). Data identified as outliers are indicated in Figures Q-2

and Q-3 as solid markers.

54

If CH4/THC = x and CH4/NHMC = y, then y = CH4/(THC-CH4) = CH4/(THC-THC(x)) =

CH4/(THC(1-x)) =

x/(1-x). So if x ≅ 0.10, then y = 0.11 ≅ 1.1x.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-10

In this secondary analysis, the VSP data were split into two component datasets,

one for 1992 and earlier vehicles (17 vehicles) and one for 1993 and newer vehicles (22

vehicles). This split was selected on the basis that organic compound emission standards

generally shifted in stringency beginning in 1993 when the first Tier 1 vehicles were

required to be sold in California. Light duty vehicles from model years 1981 through

1992 were certified to Tier 0 emission standards. Organic compound emission standards

continued to evolve throughout the 1990s as differing numbers of LEV vehicles were

sold, but the VSP dataset analyzed for this study does not contain sufficient information

to pinpoint the certification class of each vehicle. Nevertheless, there is no question that

a split based on the 1993 model year is biased toward Tier 0 vehicles on the pre-1993

side and Tier 1/LEV vehicles on the 1993 and newer side. Thus, there is a clear

distinction between the relative emissions control design of the two data subsets.

55

Table E-4 indicates the results of the data subset analysis. To factor out the

influence of mileage accumulation to the maximum extent possible, statistics were

calculated on a stratified basis by 50,000 mile increment mileage accumulation bins.

Statistics were then compared across the two samples only when five or more datapoints

were present in comparable mileage bins. This results in comparisons for two mileage

bins, 50,000-100,000 miles and 100,000-150,000 miles. As indicated, the 1993 and

newer vehicle organic emissions have generally declined by 50 to 70 percent for THC,

NMHC, and CH4 relative to comparable mileage 1992 and older vehicles. To truly

confirm the lack of mileage bias, a comparison of the 100,000-150,000 mile data for

1993 and newer vehicles to the 50,000-100,000 mile data for 1992 and older vehicles

indicates that the minimum reduction in THC, NMHC, and CH4 emission rates is between

30 and 50 percent, with the 50 percent reduction being applicable to methane. Clearly,

methane emissions have declined between the two periods, while methane-to-THC and

methane-to-NMHC ratios have remained relatively stable as described above. Therefore,

it should be possible to estimate both current and future certification emission rates for

methane on the basis of the derived relations.

Using the CH4-to-NMHC regression results and U.S. light duty vehicle

certification standards for NMOG, the methane emission rates for current and future

vehicles were estimated. Since the regression relations are based on NMHC emissions,

as opposed to NMOG emissions, the NMOG standards were converted to NMHC

equivalent standards using the allowable certification adjustment factor of 1.04 as

specified in the Code of Federal Regulations.

56 A certification compliance margin of 30

percent was also assumed, consistent with assumptions utilized for the CO2 emissions

analysis portion of the study. So in effect, the target NMHC emission rate for a given

NMOG standard is equal to:

0.70

1.04

NMOG Standard Target NMHC × 











=

 

55 Despite the seeming clarity of this distinction, t-tests were conducted for the two samples. This

testing indicates that the probability of the two samples being from the same population is <0.1 percent for

THC, NMHC, and CH4.

56

40 CFR §86.1810-01(p) allows NMOG emissions to be estimated as NMHC emissions times 1.04.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-11

For Tier 1 standards, which were expressed in terms of NMHC, the NMOG

adjustment was not performed. For Tier 0 standards, which were expressed in terms of

THC, the NMOG adjustment was similarly not performed and the NMHC portion of

THC was estimated using the Tier 0 NMHC-to-THC standard ratio developed by the U.S.

Environmental Protection Agency (EPA) for natural gas vehicles (0.34/0.41).

57

Estimated methane emission rates were then developed on the basis of the previously

described regressions as:

CH4 = 0.133 (Target NMHC)

The resulting emission rates are presented in Table E-5. As indicated, estimated

emission rates range from 0.039 g/mi for a Tier 0 passenger car to 0.010 g/mi for a 2002

“fleet average” NLEV vehicle. Perhaps the best indication of the accuracy of these

estimated emissions can be gleaned from a comparison of the estimated Tier 1 passenger

car emission rate of 0.029 g/mi to the estimated 100,000 mile methane emission rate for

1993 and newer vehicles from the ARB VSP dataset used to develop the CH4 to NMHC

regression relations. Although the 1993 and newer vehicles in the ARB dataset are

likely to reflect a mix of LEV I and Tier 1 vehicles, the fleet average LEV standard for

NMOG was dominated by Tier 1 vehicles through the late 1990s. Thus, it is reasonable

to expect that the ARB dataset for 1993 and newer vehicles is similarly dominated by

Tier 1 vehicles. In fact, a basic regression analysis of these data indicate an expected

100,000 mile methane emission rate of 0.034 g/mi, which compares well with the

certification estimated rate for Tier 1 vehicles of 0.029 g/mi. As a result, it seems likely

that the estimated methane emission rates presented in Table E 5 provide a reasonably

accurate depiction of current and future emissions.

 

57 Because natural gas vehicles have inherently higher methane emission rates than gasoline vehicles, the

EPA established an equivalent stringency Tier 0 standard for natural gas vehicles in terms of NMHC. A

standard of 0.31 g/mi NMHC was determined to be equivalent to the 0.41 g/mi Tier 0 THC standard for

gasoline vehicles.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-12

Table E-4: Average Hydrocarbon Emission Rates for Split VSP Database

Pre-1993 Vehicles 1993 and Newer Vehicle

Organic

Species

Odometer

(miles)

Average

Emission

Rate

(g/mi)

Number

of

Observations

Average

Emission

Rate

(g/mi)

Number

of

Observations

Percent

Change

(a)

0-50,000 0 0.115 5

50,000-100,000 0.464 6 0.223 10 -52%

100,000-150,000 0.943 5 0.314 6 -67%

150,000-200,000 0.823 4 0.335 1

200,000-250,000 0.714 1 0

250,000-300,000 0 0

300,000-350,000 0.461 1 0

All Data 0.704 17 0.228 22 -68%

THC

50,000-150,000 0.682 11 0.257 16 -62%

0-50,000 0 0.106 5

50,000-100,000 0.381 6 0.200 10 -47%

100,000-150,000 0.830 5 0.271 6 -67%

150,000-200,000 0.750 4 0.296 1

200,000-250,000 0.613 1 0

250,000-300,000 0 0

300,000-350,000 0.398 1 0

All Data 0.614 17 0.202 22 -67%

NMHC

50,000-150,000 0.585 11 0.227 16 -61%

0-50,000 0 0.009 5

50,000-100,000 0.089 6 0.024 10 -73%

100,000-150,000 0.120 5 0.044 6 -63%

150,000-200,000 0.079 4 0.039 1

200,000-250,000 0.110 1 0

250,000-300,000 0 0

300,000-350,000 0.062 1 0

All Data 0.095 17 0.027 22 -72%

CH4

50,000-150,000 0.103 11 0.032 16 -69%

Notes: (a) Only stratifications with five or more component datapoints are included.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-13

Table E-5: Estimated Methane Emission Rates

Certification Level

NMOG

Standard

(g/mi)

NMHC

Target

(g/mi)

Predicted

CH4

(g/mi)

CO2

Equivalent

(g/mi)

Change

from

PC Tier 0

Change

from

PC Tier 1

Change

from

02 NLEV

Tier 2,Bin 1/ZEV 0.000 0.000 0.000 0.000 -100% -100% -100%

Tier 2,Bin 2/SULEV 0.010 0.007 0.001 0.021 -98% -97% -91%

Tier 2,Bin 3/ULEV I/ULEV II 0.055 0.037 0.005 0.113 -87% -83% -50%

Tier 2,Bin 4 0.070 0.047 0.006 0.144 -84% -78% -37%

Tier 2,Bin 5/LEV I/LEV II 0.090 0.061 0.008 0.185 -79% -72% -19%

Tier 2,Bin 6 0.090 0.061 0.008 0.185 -79% -72% -19%

Tier 2,Bin 7 0.090 0.061 0.008 0.185 -79% -72% -19%

Tier 2,Bin 8 0.125 0.084 0.011 0.257 -71% -61% +13%

TLEV 0.156 0.105 0.014 0.320 -64% -52% +41%

Passenger Car Tier 1 0.310 0.217 0.029 0.662 -26% 0% +191%

Passenger Car Tier 0 0.422 0.295 0.039 0.900 0% +36% +296%

2002 NLEV Fleet Average 0.111 0.075 0.010 0.227 -75% -66% 0%

2002 LEV Fleet Average 0.101 0.068 0.009 0.207 -77% -69% -9%

2010 LEV Fleet Average 0.050 0.034 0.004 0.103 -89% -85% -55%

Notes: (1) For NMOG standards, the equivalent NMHC standard equals the NMOG standard divided by

1.04.

(2) For all fleet average standards, passenger car and LDT1/2 standards are weighted by 55 percent

and LDT3/4 standards are weighted by 45 percent on the basis of the 2009 Martec market forecast

described in Chapter 2 of the study report. Basically, the entire large truck and minivan classes

are assumed to be LDT3/4, as is 60 percent of the small truck class.

(3) The target emissions level is 70 percent of the applicable standard.

(4) Predicted CH4 equals the target NMHC emissions times 0.133.

(5) CO2 equivalent emissions equal CH4 emissions times 23 (the GWP of CH4).

Table E-5 also indicates that by 2009, methane emissions can be expected to

decline by about 19 percent, to 0.008 g/mi (about 0.2 g/mi CO2 equivalent), from the

estimated 2002 fleet average emission rate of 0.010 g/mi. This reduction will come about

due to the imposition of the Tier 2 program and the improved combustion and

aftertreatment efficiencies it is expected to promote. Since the Tier 2 program is already

adopted, the incremental costs that will accrue to capture this methane reduction benefit

are already accounted for under the Tier 2 program and thus no additional cost is incurred

from a GHG perspective. As is also indicated, it is possible to promote further methane

reductions through even further advances in combustion and aftertreatment efficiency.

However, since the total expected CO2 equivalent emission rate in 2009 is less than 0.2

g/mi, the overall GHG reduction potential is quite limited. For example, adding

advanced technology required to certify vehicles to the Tier 2, Bin 3 level will reduce

emissions by another 40 percent, but this translates into an absolute CO2 equivalent

reduction of less than 0.1 g/mi. Technology capable of meeting Tier 2, Bin 2 levels will
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-14

increase the added reduction to almost 90 percent, with the absolute reduction increasing

to about 0.15 g/mi CO2 equivalent.

As additional emission reduction potential is clearly occurring “ at the margin”

due to already low methane emission rates, the cost effectiveness of additional reductions

is relatively high. In developing the NLEV program, the EPA estimated the incremental

retail cost of a ULEV I vehicle relative to a LEV I vehicle at $30. [8] This estimate

properly reflects the technology required to reduce NMOG emissions from Tier 2, Bin 5

levels to Tier 2, Bin 3 levels while holding NOx control constant, and is generally

consistent with similar cost impacts estimated by the ARB. [9] As indicated in Table

E-6, this implies a cost effectiveness of about $2,500 per ton of equivalent CO2 reduction,

assuming all associated costs are attributed to methane reduction.

ARB estimates for the incremental retail cost of a SULEV vehicle relative to a

ULEV II vehicle provide similar insight into the cost effectiveness of controlling methane

to the Tier 2, Bin 2 level. These costs are estimated at about $70 per vehicle after

correcting for the increased rhodium loading estimated to be needed for reducing ULEV

II NOx to SULEV levels. [10] This implies a cost effectiveness of about $3,700 per ton

of equivalent CO2 for reducing methane from Tier 2, Bin 5 to Tier 2, Bin 2 levels, or a

marginal cost effectiveness of about $4,600 per ton of equivalent CO2 for reducing

methane from Tier 2, Bin 3 levels. Of course, reductions of NMOG also accrue, which

could be used to offset a portion of the imposed cost. Since methane reductions accrue in

proportion to NMOG reductions, it seems most logical to consider future methane

reduction as an integral component of Tier 2 and LEV II program reviews. This would

maintain a consistent approach to continued program development, while properly

reflecting both the criteria and GHG emission benefits of such programs.

It is also important to note that the methane relationships presented in this study

are derived from data for stoichiometric control technology. Existing research indicates

that, unlike NMHC conversion, the methane conversion efficiency of typical

stoichiometric three-way catalysts falls off fairly rapidly at lean conditions. [11] This is

likely due to the reduced exhaust temperatures associated with lean combustion and, as a

result, methane emissions for combustion technologies such as lean gasoline direct

injection and diesel may need to be investigated further as detailed research data become

available. At the same time, it is also likely that the excess air combustion

Table E-6: Cost and Cost Effectiveness of Methane Reductions

Reduction Strategy

CH4

Change

(g/mi)

CO2

Equivalent

Change

(g/mi)

Marginal

Cost

Cost

Effectiveness

($/ton CO2)

Tier 2,Bin 5 to Tier 2, Bin 3 0.003 0.072 $ 30 $ 2,526

Tier 2,Bin 5 to Tier 2, Bin 2 0.007 0.164 $ 100 $ 3,683

Tier 2,Bin 3 to Tier 2, Bin 2 0.004 0.092 $ 70 $ 4,584

Notes: (1) Cost effectiveness is based on a lifetime mileage estimate of 150,000 miles.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-15

associated with such technologies will produce lower engine-out methane emissions than

is the case with stoichiometric technology, but this should be confirmed during

certification testing.

In the absence of specific data on advanced lean burn technology, this study relies

on an estimated methane emission rate derived from the EPA’s MOBILE6.2 emission

factor model for light duty diesel passenger cars and trucks. [15] The EPA model was

executed for two evaluation years, 2002 and 2009, and methane emission rates were

calculated as the difference between model-estimated THC and NMHC emission rates.

The resulting methane emission rate, 0.005 g/mi, was identical for both evaluation years

and is, in a general sense, quite consistent with the emission rates presented in Table E-5

for stoichiometric technology. An emission rate of this magnitude certainly reflects

inherently low methane emissions, given that it is equivalent to emissions associated with

highly advanced aftertreatment technology (i.e., Tier 2, Bin 3 technology). Moreover, the

emission rate also appears to be reasonably consistent with the methane emission rates of

larger diesel engines as measured in several emissions test programs. For example, a test

program conducted by the Center for Environmental Research and Technology at the

University of California-Riverside found the average methane emission rate of fifteen

1982 though 1996 light and medium heavy duty diesel vehicles to be 0.011 g/mi. [16]

Therefore, in the absence of more representative test data, a lean burn emission rate of

0.005 g/mi has been assumed for this study.

E.3. Nitrous Oxide Emissions

As indicated in Section E.1, N2O is emitted from light duty vehicles due to the

incomplete reduction of engine-out NOx emissions in current catalytic aftertreatment

systems. However, as was the case with methane emissions, it is important to recognize

that current vehicles produce and emit substantially less N2O than their older

counterparts. Moreover, even in the absence of additional regulation, it is almost certain

that future vehicles will exhibit even lower emission rates. Although there are currently

no specific standards that directly limit emissions of N2O, existing standards for NOx do

effectively result in reduced N2O emissions through the design and implementation of

advanced combustion and catalyst technologies.

Although the existing body of research on N2O emissions is somewhat limited,

available research does provide for a basic theoretical understanding of the N2O

formation process that is consistent with available test data. At low catalyst

temperatures, NOx reduction by carbon monoxide (CO) is believed to proceed according

to the following pathway:

58

[3,4]

2 2 2

2 2

N O CO N CO

2NO CO N O CO

+ → +

+ → +

As indicated, N2O is formed as an intermediate reaction product, which can be

emitted due to low temperature inefficiencies in carrying out the subsequent dissociation

 

58 The indicated reactions are simplified depictions of a more complex catalytic reaction process, but they

effectively present the important elements of the N2O formation process.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-16

reaction. The N2O formation reaction appears to dominate up to about 300oC. At higher

catalyst temperatures, N2O formation ceases as the NOx reduction reaction proceeds in

accordance with the single step reaction:

2NO + CO → N2 + CO2

Thus, N2O formation is primarily a function of catalyst warmup. This has been

confirmed through several research testing programs that clearly show N2O formation

rates peaking during vehicle start-up operations as the aftertreatment catalyst moves

through its warm up stage. In effect, measured FTP emissions of N2O are dominated by

emissions during Bag 1 and Bag 3 of the driving cycle. [3,4,12]

Of course, the same dominance of Bag 1 and 3 emissions would occur for an

engine-out exhaust species undergoing inefficient conversion due to low catalyst

temperatures. However, several test programs have demonstrated that engine-out N2O

emissions are consistent with background N2O concentrations, so that there is little

uncertainty but that N2O emissions are formed within the aftertreatment catalyst and not

within the vehicle engine. [3-6] At the same time, it should be recognized that N2O can

form within the combustion chamber through reactions with intermediate combustion

products such as:

HCO NO N O CO

HN NO N O H

2

2

+ → +

+ → +

However, such N2O is also rapidly removed to create OH radicals:

N2O + H → N2 + OH

so that engine-out N2O is very low. [3]

Given the demonstrated formation mechanism, it is widely believed that the

control of vehicle N2O emissions is a function of improved aftertreatment systems. As

was the case with organic compounds (see Section E.2), emissions control of NOx (and

thus NO) has evolved over the years. Both advanced engine technologies and improved

catalytic aftertreatment techniques have reduced NOx emissions to a fraction of that

emitted by older vehicles. For example, a 2002 model year vehicle emits about 80

percent less NOx than a 1981 era vehicle. By 2009, the reduction will increase to about

95 percent through continuing combustion and aftertreatment improvements. As was the

case with methane, these improvements should result in decreases in N2O emissions

commensurate with increases in catalytic aftertreatment efficiency. As will be shown

below, typical N2O emissions are approaching levels associated with non-catalyst

vehicles, but it is likely that a reasonable lower limit for N2O emissions will continue to

be greater than would be the case if catalytic aftertreatment systems were eliminated. Of

course, associated increases in criteria pollutant emissions (i.e., HC, CO, and NOx) due to

catalyst removal would be several orders of magnitude larger than the net reduction in

N2O.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-17

Expectations for continued N2O reductions are consistent with existing research.

In a review of N2O emissions research, the EPA generally found that emission factors

decline for three-way catalyst equipped vehicles as NOx control efficiency increases. [13]

Similarly, a recent test program conducted under rigorously controlled conditions across

a set of controlled usage vehicles found a clear relationship between NOx aftertreatment

efficiency and N2O emissions, as depicted in Figure Eí4. [4] Nevertheless, to confirm

this relationship, the 39 vehicle ARB VSP dataset previously described in Section E.2

above was utilized to estimate study-specific N2O emission rates. [7] While 39 vehicles

is certainly a limited dataset, it should be recognized that unlike methane, N2O is

generally not measured as part of the standard vehicle certification process in the U.S., so

there is not an extensive library of available N2O data. In fact, the VSP dataset includes

approximately the same volume of N2O emission rate data as all previous test programs

combined. Moreover, it provides a snapshot of emissions from actual in-use vehicles.

Figure E-4: N2O Emission Rate Versus NOx Conversion Efficiency [4]

Since the VSP dataset was previously described in Section E.2, readers are

referred to that section for additional background. Figure Eí1 and Table Eí1 of Section

E.2 provide an overview of the vehicle fleet represented in the VSP dataset. For this

study, the relationship between measured N2O and measured NOx emission rates was

investigated. Figure Eí5 and Table Eí7 present the results of this analysis. As expected

from the findings of previous researchers, statistically significant relations between N2O

and NOx emissions were found. As shown in Table Eí7, valid relations exist for all three

bags of the FTP after outliers were removed.

59 When all data were considered, valid

relationships were found for Bags 2 and 3, but not Bag 1. The lack of a Bag 1

relationship prior to the removal of outliers is the result of a single vehicle with very high

 

59 Consistent with the methane analysis described in Section Q.2, outliers are identified as vehicles with

either N2O/NOx or NOx/N2O ratios that vary from the average ratio by more than ±2 standard deviations.

Data identified as outliers are indicated in Figure Eí DV VROLG PDUNHUV
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-18

NOx and very low N2O emissions (a carbureted 1981 Chevrolet Van with 5.1 g/mi NOx

and 0.02 g/mi N2O). Data for this vehicle are consistent with very low aftertreatment

efficiency, as N2O emissions approach those of non-catalyst vehicles. This same vehicle

was also identified as an outlier for both the Bag 3 and composite cycle analyses, but

because N2O emissions decline substantially for all vehicles during Bag 2, it was

sufficiently consistent with the other VSP data for the Bag 2 analysis.

As shown in Table Eí7, N2O generally is emitted at a rate about 2 to 3 percent of

the NOx emission rate, except during the start portions of the FTP cycle (i.e., Bags 1 and

3) when an additional 0.02 to 0.03 g/mi is emitted. Over the full cycle, the N2O emission

rate is equal to about 3 percent of the NOx emission rate plus 0.015 g/mi:

N2O = 0.0295 (NOx) + 0.0150

Thus, as NOx is reduced, N2O is also reduced proportionally to a lower limit of

0.015 g/mi. Such a finding is quite consistent with previous research, where maximum

N2O formation occurs during catalyst warmup, from about 100oC to 300oC for new

catalysts or 200oC to 400oC for aged catalysts.

Figure Eí6 illustrates the sensitivity of N2O formation to catalyst temperature.

Since all catalysts will pass through the maximum N2O formation temperature band after

vehicle startup, there is a period of time during which N2O emissions increase while NOx

declines (as NO is converted to N2O). After the catalyst passes this band, both NOx and

N2O conversion efficiencies increase and additional N2O emissions are generally

proportional to NOx emissions. Thus, the volume of N2O generated during initial catalyst

warmup represents a practical lower limit for current three-way catalyst technology and

N2O reductions below this level will require significant advances in warmup

characteristics.

Interestingly, the shift in the N2O formation window to higher temperatures with

catalyst aging results in a rather uncommon phenomenon relative to other emission

species affected by catalyst aftertreatment. For aged catalysts, such as those represented

in the ARB VSP dataset analyzed in this study, N2O emissions during Bag 3 generally

equal or exceed those of Bag 1. This is due to the fact that the shift upwards in the N2O

formation temperature band can result in a somewhat longer period during Bag 3 (as

compared to Bag 1) in which catalyst temperatures are within the band.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-19

Figure E-5: N2O Emission Rate Versus NOx Emission Rate

FTP Bag 1 FTP Bag 2

FTP Bag 3 Composite FTP

Note: The dotted and solid lines indicate regression-based relations. Dotted lines include all data, solid lines exclude

outliers (defined as datapoints that vary from the average N2O/NOx or NOx/N2O ratio by more than two

standard deviations).

Table E-7: Regression Statistics for N2O (g/mi) Versus NOx (g/mi)

All Data Outliers (±2σ) Removed

Statistic

Bag 1 Bag 2 Bag 3 Composite Bag 1 Bag 2 Bag 3 Composite

Intercept 0.0491 0.0000 0.0272 0.0183 0.0301 0.0000 0.0249 0.0150

Slope 0.0000 0.0283 0.0275 0.0207 0.0191 0.0285 0.0362 0.0295

r

2

0.00 0.46 0.31 0.32 0.21 0.45 0.43 0.48

n (obs) 39 39 39 39 35 37 35 35

Slope and intercept statistics are selected at 95 percent confidence level.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 1 2 3 4 5 6

Measured NOx(g/mi)

Measured N O2 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Measured NOx(g/mi)

Measured N O2 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Measured NOx(g/mi)

Measured N O2 (g/mi)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.0 1.0 2.0 3.0 4.0 5.0 6.0

Measured NOx(g/mi)

Measured N O2 (g/mi)
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-20

Figure E-6: N2O Formation Rate Versus Catalyst Temperature [14]

As was the case with the methane analysis described in Section E.2, a secondary

statistical analysis was conducted to ensure that the derived N2O-to-NOx relations were

not simply a function of equivalently emitting vehicles measured at different mileage

accumulations during their deterioration cycle. In this secondary analysis, the VSP data

were split into two component datasets, one for 1992 and earlier vehicles (17 vehicles)

and one for 1993 and newer vehicles (22 vehicles). As described in more detail in

Section E.2, this split was selected on the basis of a general shift in emission standard

stringency beginning in 1993 when the first Tier 1 vehicles were required to be sold in

California.

60

Table Eí8 indicates the results of the data subset analysis. To factor out the

influence of mileage accumulation to the maximum extent possible, statistics were

calculated on a stratified basis by 50,000 mile increment mileage accumulation bins.

Statistics were then compared across the two samples only when five or more datapoints

 

60 T-tests indicate that the probability of the two samples being from the same population is about 0.2

percent for NOx and about 3 percent for N2O.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-21

were present in comparable mileage bins. This results in comparisons for two mileage

bins, 50,000-100,000 miles and 100,000-150,000 miles. As indicated, the 1993 and

newer vehicle emissions have generally declined by 30 to 50 percent for N2O and 50 to

60 percent for NOx relative to comparable mileage 1992 and older vehicles. Clearly, N2O

emissions have declined between the two periods, while N2O-to-NOx ratios have

remained relatively stable as described above. Therefore, it should be possible to

estimate both current and future certification emission rates for N2O on the basis of the

derived regression relations.

Using the N2O-to-NOx regression results and U.S. light duty vehicle certification

standards for NOx, the N2O emission rates for current and future vehicles were estimated.

As with the methane analysis discussed in Section E.2, a certification compliance margin

of 30 percent was assumed, consistent with assumptions utilized for the CO2 emissions

analysis portion of the study. So in effect, the target NOx emission rate for a given NOx

standard is equal to:

Target NOx = NOx Standard × 0.70

Estimated N2O emission rates were then developed on the basis of the previously

described regression as:

N2O = 0.0295 (NOx) + 0.0150

The resulting emission rates are presented in Table E-9. As indicated, estimated

emission rates range from 0.046 g/mi for a Tier 0 passenger car to 0.021 g/mi for a 2002

“fleet average” NLEV vehicle. Perhaps the best indication of the accuracy of these

estimated emissions can be gleaned from a comparison of the estimated Tier 1 passenger

car emission rate of 0.027 g/mi to the estimated 100,000 mile N2O emission rate for 1993

and newer vehicles from the ARB VSP dataset used to develop the N2O-to-NOx

regression relations.

61 As described in Section E.2, the 1993 and newer vehicles in the

ARB dataset are likely to reflect a mix of LEV I and Tier 1 vehicles, but the fleet average

LEV requirements were such that Tier 1 vehicles were sold in substantial quantities

through the late 1990s. Thus, it is reasonable to expect that the ARB dataset for 1993 and

newer vehicles is similarly dominated by Tier 1 vehicles. In fact, a basic regression

analysis of these data indicate an expected 100,000 mile N2O emission rate of 0.029 g/mi,

which compares well with the certification estimated rate of 0.027 g/mi.

The estimated N2O emission rate for Tier 1 vehicles also compares favorably with

emission rates estimated by the EPA. [13] As published, the EPA estimated N2O

emission rates for Tier 1 vehicles of 0.046 g/mi for passenger cars and 0.064 for light

duty trucks appear to be much higher than the estimate of 0.027 g/mi from Table E-9.

However, the EPA emission rates are for a 285 ppm sulfur gasoline, while those

estimated in this study are for low sulfur California fuel.

 

61

Since the certification standards used to develop the estimated N2O emission rate are 100,000 (or

120,000) mile standards, measured emissions at 100,000 miles are an appropriate comparison metric.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-22

Table E-8: Average NOx and N2O Emission Rates for Split VSP Database

Pre-1993 Vehicles 1993 and Newer Vehicle

Organic

Species

Odometer

(miles)

Average

Emission

Rate

(g/mi)

Number

of

Observations

Average

Emission

Rate

(g/mi)

Number

of

Observations

Percent

Change

(a)

0-50,000 0 0.098 5

50,000-100,000 0.709 6 0.339 10 -52%

100,000-150,000 1.901 5 0.747 6 -61%

150,000-200,000 1.548 4 0.444 1

200,000-250,000 0.688 1 0

250,000-300,000 0 0

300,000-350,000 0.801 1 0

All Data 1.261 17 0.400 22 -68%

NOx

50,000-150,000 1.251 11 0.492 16 -61%

0-50,000 0 0.009 5

50,000-100,000 0.035 6 0.025 10 -29%

100,000-150,000 0.065 5 0.033 6 -50%

150,000-200,000 0.056 4 0.039 1

200,000-250,000 0.015 1 0

250,000-300,000 0 0

300,000-350,000 0.036 1 0

All Data 0.048 17 0.024 22 -49%

N2O

50,000-150,000 0.049 11 0.028 16 -43%

Notes: (a) Only stratifications with five or more component datapoints are included.

As described further below, sulfur has been shown to have a significant influence

on N2O emission rates, as might be expected given its detrimental influence on catalyst

efficiency. Thus, the EPA emission rates are not directly comparable with those

estimated in this study. The EPA did, however, test two Tier 1 vehicles on both the 285

ppm sulfur gasoline and indolene containing 24 ppm sulfur. The results of this

comparative testing showed that N2O emission rates were reduced by 28 and 49 percent

on the low sulfur fuel.

62 While this is certainly a limited test sample, it does indicate that

the EPA estimated N2O emission rates, when corrected for fuel sulfur content, are more

likely within a range of 0.024 to 0.046 g/mi, which is reasonably consistent with the

0.027 g/mi emission rate estimated in this study. As a result, it seems likely

 

62 One Tier 1 vehicle had measured N2O emission rates of 0.039 g/mi with 24 ppm sulfur and 0.054 g/mi

with 285 ppm sulfur, for a net emission rate reduction of 28 percent. The second Tier 1 vehicle had

measured N2O emission rates of 0.115 g/mi with 24 ppm sulfur and 0.227 g/mi with 285 ppm sulfur, for

a net emission rate reduction of 49 percent.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-23

Table E-9: Estimated N2O Emission Rates

Certification Level

NOx

Standard

(g/mi)

NOx

Target

(g/mi)

Predicted

N2O

(g/mi)

CO2

Equivalent

(g/mi)

Change

from

PC Tier 0

Change

from

PC Tier 1

Change

from

02 NLEV

Tier2,Bin 1/ZEV 0.000 0.000 0.015 4.4 -67% -45% -28%

Tier2,Bin 2/SULEV 0.020 0.014 0.015 4.6 -66% -44% -26%

Tier2,Bin 3 0.030 0.021 0.016 4.6 -66% -43% -25%

Tier2,Bin 4 0.040 0.028 0.016 4.7 -66% -42% -24%

Tier2,Bin 5/LEV II/ULEV II 0.070 0.049 0.016 4.9 -64% -40% -21%

Tier2,Bin 6 0.100 0.070 0.017 5.0 -63% -38% -18%

Tier2,Bin 7 0.150 0.105 0.018 5.4 -61% -34% -13%

Tier2,Bin 8 0.200 0.140 0.019 5.7 -58% -30% -8%

LEV I/ULEV I 0.300 0.210 0.021 6.3 -54% -23% +2%

PC Tier 1/TLEV 0.600 0.420 0.027 8.1 -40% 0% +32%

PC Tier 0 1.500 1.050 0.046 13.6 0% +68% +122%

2002 NLEV Fleet Average 0.276 0.193 0.021 6.1 -55% -24% 0%

2002 LEV Fleet Average 0.262 0.183 0.020 6.0 -56% -25% -1%

2010 LEV Fleet Average 0.061 0.043 0.016 4.8 -65% -41% -21%

Notes: (1) For all fleet average standards, passenger car and LDT1/2 standards are weighted by 55 percent

and LDT3/4 standards are weighted by 45 percent on the basis of the 2009 Martec market forecast

described in Chapter 2 of the study report. Basically, the entire large truck and minivan classes

are assumed to be LDT3/4, as is 60 percent of the small truck class.

(2) The target emissions level is 70 percent of the applicable standard.

(3) Predicted N2O equals the target NOx emissions times 0.0295 plus 0.0150.

(4) CO2 equivalent emissions equal N2O emissions times 296 (the GWP of N2O).

that the N2O emission rates estimated in this study provide for a reasonably accurate

depiction of current and future emissions.

Table E-9 indicates that by 2009, N2O emissions can be expected to decline by

about 21 percent, to 0.016 g/mi (about 4.9 g/mi CO2 equivalent), from the estimated 2002

fleet average emission rate of 0.021 g/mi. This reduction will come about due to the

imposition of the federal Tier 2 program and the improved combustion and aftertreatment

efficiencies it is expected to promote. Since the Tier 2 program is already adopted, the

incremental costs that will accrue to capture this N2O reduction benefit are already

accounted for under the Tier 2 program and thus no additional cost will accrue from a

GHG perspective.

However, as is also indicated, the 2009 N2O emission rate is approaching the

lower emissions limit (estimated in this study as 0.015 g/mi) imposed by the necessity of

conventional three-way catalysts to pass through the warmup temperature band during

which the bulk of N2O formation occurs. Faster excursions to catalyst temperatures

above about 400oC could allow even this lower limit to be “ broken,” but there is no

available data with which to access the likelihood of significant breakthroughs in this
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-24

area. It is also important to recognize that the EPA estimates that N2O emissions for

non-catalyst vehicles are in the range of 0.017-0.019 g/mi. [13] This is actually a bit

higher than the lower limit emission rate estimated in this study and so is not necessarily

a precise comparative datapoint, but the clear implication is that emission rates for

catalyst equipped vehicles are approaching those for non-catalyst vehicles.

Nevertheless, it is possible to promote modest additional N2O reductions through

further advances in aftertreatment efficiency. For example, adding advanced technology

required to certify vehicles to the Tier 2, Bin 2 level will reduce emissions by a additional

6 percent, but that translates into an absolute CO2 equivalent reduction of less than 0.3

g/mi. As was the case for methane, since additional emission reduction potential is

occurring “ at the margin” due to already low emission rates, the cost effectiveness of

additional reductions is relatively high. ARB estimates for the incremental retail cost of a

SULEV vehicle relative to a ULEV II vehicle provide insight into the cost effectiveness

of controlling N2O to the Tier 2, Bin 2 level. These costs are estimated at about $80 per

vehicle. [10] As indicated in Table E-10, this implies a cost effectiveness of about

$1,600 per ton of equivalent CO2 reduction, assuming all associated costs are attributed

to N2O reduction. Of course, as described in Section E.2, reductions of methane also

accrue, as do reductions in NOx and NMOG, which could be used to offset a portion of

the imposed cost. As both the N2O and methane reductions accrue in proportion to NOx

and NMOG reductions, it seems most logical to consider these reductions as integral

components of Tier 2 and LEV II program reviews, as opposed to independent GHG

considerations. This would maintain a consistent approach to continued program

development, while properly reflecting both the criteria and GHG emission benefits of

such programs.

Table E-10: Cost and Cost Effectiveness of N2O Reductions

Reduction Strategy

N2O

Change

(g/mi)

CO2

Equivalent

Change

(g/mi)

Marginal

Cost

Cost

Effectiveness

($/ton CO2)

Tier 2,Bin 5 to Tier 2, Bin 2 0.001 0.305 $ 80 $ 1,585

Added Reduction due to CH4 0.164

Total GHG Reduction 0.001 0.469 $ 80 $ 1,031

Notes: (1) Cost effectiveness is based on a lifetime mileage estimate of 150,000 miles.

As was the case with the methane analysis presented in Section E.2, it is

important to note that the N2O relationships presented in this study are derived from data

for stoichiometric control technology. Existing research indicates that the N2O formation

rate over typical three-way catalysts is quite sensitive to perturbations in air-fuel ratio. At

both very rich and very lean conditions, N2O formation is low due to high active site
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-25

adsorption rates for non-NO species (CO under rich conditions and oxygen under lean

conditions). However, at slightly rich and slightly lean conditions, significant NO

adsorption occurs while additional free sites for subsequent N2O dissociation are limited.

[17] Thus, for stoichiometric technology, N2O is minimized as air-fuel ratio control is

optimized. Since future emission standards will result in the introduction of further

advances in mixture control as well as continuing improvements in catalyst light off

performance, the expectation of continuing N2O emission reductions for stoichiometric

technology, as suggested by the Table E-9 emission rates, is reasonable.

Current diesel engines emit relatively low levels of N2O due to the absence of

catalytic reduction technology. However, the introduction of lean burn aftertreatment

technology targeting NOx control, whether for advanced gasoline or diesel engines, could

alter current lean burn N2O emission rates. [18,19] Lean burn aftertreatment technology

such as NOx adsorbers or selective catalytic reduction (SCR) systems must function

under mixture regimes well removed from stoichiometry. Under such conditions and

depending on the effectiveness of associated control strategies, N2O formation could be

significant. Current research indicates that N2O concerns may be more pronounced with

SCR systems, but due to the ongoing nature of lean burn aftertreatment system

development, it is not possible to assign a reliable N2O emission rate to any lean burn

systems at this time. Given the awareness of aftertreatment developers to N2O emission

concerns, it seem reasonable, however, to assume that design goals will be for emission

rates equal to or less than those for current stoichiometric systems. Therefore, for

purposes of this study, N2O emission rates for lean burn technologies are assumed to be

the same as those for 2009 (i.e. Tier 2, Bin 5) stoichiometric technology. Clearly, the

validity of such an assumption should be monitored as such systems enter the

marketplace.

N2O decomposition catalysts have been patented and are in the initial stages of

investigation in the industrial sector. However, these systems are essentially untested in

the automotive sector and are likely to face significant challenges such as mechanical and

thermal durability, as well as potential sensitivity to exhaust contaminants such as sulfur.

[20] Given the ability of the aftertreatment industry to produce the highly effective

catalyst systems available in the automotive sector today, there is little doubt that with

sufficient leadtime, effective N2O decomposition catalysts could be introduced.

However, given continuing N2O reductions, the cost effectiveness of additional N2O

decomposition solutions is uncertain. Due to the lack of a prototype system on which to

base a costing analysis, no specific cost estimates are developed for this study, but such

systems could be considered if alternative lean burn solutions are not found.

Finally, existing research has demonstrated the sensitivity of N2O formation to

fuel sulfur content. [3,4,13] Test data show N2O emission rate increases of up to 300

percent when fuel sulfur is increased from 20 to 300 ppm. However, this is not

considered to be a significant issue in this study as existing federal and California rules

require the sulfur content of both gasoline and diesel fuel to be less than 30 ppm on

average in the timeframe considered. Thus, all N2O emission rates estimated in this study

assume low sulfur fuel availability. Current emission rates for in-use vehicles may be

higher than indicated, but those rates should decline as low sulfur fuels assume a

dominating market share over the next few years. Moreover, in any established
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-26

regulatory structure, emission rates would almost certainly be measured over existing

certification cycles for which low sulfur fuels are commonly used.

E.4. Summary

As described in Sections E.2 and E.3 above, emission rates for methane and

nitrous oxide have been estimated using an emissions testing dataset for in-use vehicles

provided by the ARB. Table E-11 presents a summary of the estimated emission rates.

In general, current emissions of both methane and N2O appear to be quite low relative to

emissions of CO2, estimated at about 0.2 and 6 grams CO2 equivalent per mile of travel.

Moreover, as shown in Figures Q-7 and Q-8, emission rates of both compounds have

declined substantially over the last two decades.

A combined CO2 equivalent emission rate of about 6 g/mi compares to typical

tailpipe CO2 emission rates for current light duty vehicles that range from about 250 g/mi

for small cars to 500 g/mi or more for large trucks. Thus, the combined GHG impact of

methane and N2O represents from 1-2 percent of the total CO2 equivalent emissions from

light duty vehicles (ignoring the GHG impacts of emitted water vapor). As presented

elsewhere in this study, advanced technology vehicles could achieve reduced CO2

emission rates in the 2009 to 2015 timeframe of between 150 and 250 g/mi. In this same

timeframe, the combined impact of methane and N2O emissions is estimated to decline to

about 5 g/mi, so the combined GHG impact of these species could increase to between 2

and 3 percent of the total GHG impact of light duty vehicles if low CO2 emission

technologies are introduced in significant volumes.

Reductions in methane and N2O emissions beyond those expected to occur by

2009–2015 are possible. However, because the total possible reduction is capped at 5

g/mi CO2 equivalent, these reductions tend to be relatively expensive from a cost

effectiveness standpoint, ranging upwards from about $1,000 per ton of CO2, as detailed

in Sections E.2 and E.3 above. These estimates should be considered in the context of a

current absence of regulatory controls on either methane or nitrous oxide. In this

absence, research into potential reduction technologies and costs, as well as emission

rates is somewhat limited. So it is possible that future developments will improve the

cost effectiveness of additional reductions. However, barring significant error in the

estimated emission rates, the absolute level of reductions possible at any cost is quite

limited.

Table E-11: Estimated Methane and N2O Emission Rates

Methane Nitrous Oxide

Basic Technology Configuration

2002 2009-2015 2002 2009-2015

Grams per Mile - Expressed as Direct Methane or Nitrous Oxide

Stoichiometric 0.010 0.008 0.021 0.016

Lean Burn 0.005 0.005 0.016 0.016

Grams per Mile - Expressed as CO2 Equivalent

Stoichiometric 0.23 0.18 6.1 4.9

Lean Burn 0.12 0.12 4.9 4.9
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-27

Figure E-7: Methane and N2O Emission Rates by Certification Class

Figure E-8: CO2 Equivalent Methane and N2O Emission Rates by Vehicle

Certification Class

0.039

0.029

0.010

0.008

0.046

0.027

0.021

0.016

0.00

0.01

0.02

0.03

0.04

0.05

Tier 0 Tier 1 2002 NLEV 2009 Tier 2, Bin 5

Vehicle Certification Class

10

0

K

Mile E

missio

n

Rate (g/mi)

Methane

Nitrous Oxide

Between 2002 and 2009, methane declines by 19 percent and

nitrous oxide declines by 21 percent. Relative to Tier 0 vehicles,

these represent declines of 79 and 64 percent respectively.

0.90

0.66

0.23 0.18

13.6

8.1

6.1

4.9

0

2

4

6

8

10

12

14

16

Tier 0 Tier 1 2002 NLEV 2009 Tier 2, Bin 5

Vehicle Certification Class

10

0

K

Mile C

O2 E

q

uivalent (g/mi)

Methane

Nitrous Oxide

Between 2002 and 2009, methane declines by 19 percent and

nitrous oxide declines by 21 percent. Relative to Tier 0 vehicles,

these represent declines of 79 and 64 percent respectively.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-28

E.5. References

1. Intergovernmental Panel on Climate Change, “Climate Change 2001: The Scientific

Basis,” Contribution of Working Group I to the Third Assessment Report, 2001.

2. U.S. Energy Information Administration, “ Emissions of Greenhouse Gases in the

United States, 2002,” DOE/EIA-0573(2002), October 2003.

3. Baronick, J. et al., Volkswagen AG, “Impact of Sulfur in Gasoline on Nitrous Oxide

and Other Exhaust Gas Components,” 2000-01-0857, Society of Automotive

Engineers, Inc., 2000.

4. Meffert, M.W. et al., Ethyl Corp., “ Analysis of Nitrous Oxide Emissions from Light

Duty Passenger Cars,” 2000-01-1952, Society of Automotive Engineers, Inc., 2000.

5. Koike, N. and Odaka, M., Traffic Safety and Nuisance Research Institute, “ Methane

and Nitrous Oxide (N2O) Emission Characteristics from Automobiles,” 960061,

Society of Automotive Engineers, Inc., 1996.

6. Ballantyne, V.F. et al., Environment Canada, “Nitrous Oxide Emissions from Light

Duty Vehicles,” 940304, Society of Automotive Engineers, Inc., 1994.

7. California Air Resources Board, Emissions Test Data Collected in 2000-2002 under

the 16th Vehicle Surveillance Program (VSP16).

8. U.S. Environmental Protection Agency, “ Analysis of Costs and Benefits of a

National Low Emission Vehicle Program,” prepared by E.H. Pechan & Associates,

Inc. (Pechan Report No. 97.11.002/446.006), December 1997.

9. California Air Resources Board, “ Low-Emission Vehicle and Zero Emission Vehicle

Program Report,” 1996.

10. California Air Resources Board, “ Proposed Amendments to California Exhaust and

Evaporative Emission Standards and Test Procedures for Passenger Cars,

Light-Duty Trucks and Medium-Duty Vehicles ‘LEV II’ and Proposed Amendments

to California Motor Vehicle Certification, Assembly-Line and In-Use Test

Requirements ‘Cap 2000’,” Staff Report: Initial Statement of Reasons, September

18, 1998.

11. Corbo, P. et al., Istituto Motori - CNR, “ Methane Dedicated Catalysts for

Heavy-Duty Natural Gas Engines,” 961087, Society of Automotive Engineers, Inc.,

1996.
Reducing Greenhouse Gas Emissions from Light-Duty Motor Vehicles Page E-29

12. Odaka, M. et al., Traffic Safety and Nuisance Research Institute, Ministry of

Transport, Japan, “ Deterioration Effect of Three-way Catalyst on Nitrous Oxide

Emission,” 980676, Society of Automotive Engineers, Inc., 1998.

13. U.S. Environmental Protection Agency, “ Emissions of Nitrous Oxide from Highway

Mobile Sources,” EPA420-R-98-009, August 1998.

14. Koike, N. et al., Traffic Safety and Nuisance Research Institute, Ministry of

Transport, Japan, “ Reduction of N2O from Automobiles Equipped with Three-Way

Catalysts - Analysis of N2O Increase Due to Catalyst Deactivation,” 1999–01–1081,

Society of Automotive Engineers, Inc., 1999.

15. U.S. Environmental Protection Agency, MOBILE6.2 Mobile Source Emission

Factor Model, model and users guide available at http://www.epa.gov/otaq/m6.htm

as of May 7, 2004.

16. Norbeck, J. et al., Center for Environmental Research and Technology,

“Characterizing Particulate Emissions from Medium- and Light Heavy-Duty

Diesel-Fueled Vehicles,” 98-VE-RT2E-004-FR, University of California at

Riverside, September 1998.

17. Jobson, E. et al., Volvo Technological Development, “Nitrous Oxide Formation

Over Three-Way Catalyst,” 940926, Society of Automotive Engineers, Inc., 1994.

18. Corning, Inc., “ Auto Emissions Special Report: The Future of Clean Diesel,” Auto

Emissions, Number 14, Fall 1999.

19. Oak Ridge National Laboratory, Fuels, Engines and Emissions Research Center,

“ Post-combustion emissions control,”

http://feerc.ornl.gov/capabilities/aftertreatment.html (as of May 7, 2004).

20. Kubsh, J., Manufacturers of Emission Controls Association, “Nitrous Oxide

Emissions from Light-duty Vehicles,” presented at the California Air Resources

Board Greenhouse Gas Symposium, March 2003.