ANL/ESD/02-4

The Potential Effect of Future Energy-Efficiency and

Emissions-Improving Technologies on Fuel

Consumption of Heavy Trucks

Center for Transportation Research

Argonne National Laboratory

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under Contract W-31-109-Eng-38, for the

United States Department of Energy
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ANL/ESD/02-4

The Potential Effect of Future Energy-Efficiency and

Emissions-Improving Technologies on Fuel

Consumption of Heavy Trucks

by A. Vyas, C. Saricks, and F. Stodolsky 

Center for Transportation Research, Energy Systems Division,

Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439

August 2002

Work sponsored by U.S. Department of Energy

Energy Information Administration

Office of Integrated Analysis and Forecasting

Demand and Integration Division
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contact:

Director, Energy Systems Division

Argonne National Laboratory

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Telephone (630) 252-3724

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and Publishing Division (for more information, see IPD’s home page:

http://www.ipd.anl.gov).

This report is printed on recycled paper.

ANL/ESD/02-4 THE POTENTIAL EFFECT OF FUTURE ENERGY-EFFICIENCY AND EMISSIONS-IMPROVING

TECHNOLOGIES ON FUEL CONSUMPTION OF HEAVY TRUCKS
iii

Contents

Acknowledgments ................................................................................................................... v

Abstract.................................................................................................................................... 1

1 Introduction ....................................................................................................................... 3

2 Technology, Costs, and Market Penetration Potentials of Fuel-Efficiency-Enhancing

Technologies for Medium and Heavy Freight Trucks: Projections to 2025 ..................... 5

2.1 Methodology ............................................................................................................ 5

2.2 Technologies, Assumptions, and Potential Effects .................................................. 6

2.2.1 Non-Engine Technologies ............................................................................. 6

2.2.2 Powertrain Technologies ............................................................................... 10

2.3 Market Penetration Profiles...................................................................................... 13

2.4 References for Section 2 .......................................................................................... 16

3 Technology, Costs, and Fuel Effects of Meeting 2007 and Later Emission and 

Fuel Content Standards for Medium and Heavy Freight Trucks: Projections to 2025 ..... 19

3.1 Current State of Technology .................................................................................... 19

3.1.1 Standards and Test Procedures through 2004................................................ 19

3.1.2 Engine/Combustion Controls and Equipment Retrofits ................................ 21

3.1.3 Present and Near-Term Prospective Exhaust Controls.................................. 21

3.1.4 Additional Technologies Available Today and in the Near Future ............... 22

3.2 Impact of 2007 and Later Standards ........................................................................ 24

3.2.1 Timing of Phase-In for Both Vehicular Emission Limits and 

Fuel Properties............................................................................................... 24

3.2.2 Technologies Expected to be Proven/Capable of Commercialization 

by 2006 .......................................................................................................... 25

3.2.3 Pollutants for Which Final Control Set Remains Undefined or

Flexible .......................................................................................................... 25

3.3 Onboard Fuel Efficiency Effects of 2007 and Later Standards................................ 26

3.3.1 Speculation on Parasitic Losses..................................................................... 26

3.3.2 Decrease in Maximum Potential Engine Efficiency...................................... 34

3.4 Technology Cost Estimates and Credits Other than Efficiency Penalties................ 34

3.5 Emerging Low-Emission Technologies and Their Prospects for 

Commercialization after 2010.................................................................................. 35

3.5.1 Fuel Cells....................................................................................................... 35

3.5.2 Diesel Electric Hybrids.................................................................................. 35
iv

3.5.3 Effects of Synthetic Diesel Fuel .................................................................... 35

3.5.4 The “All Electrically Controlled” Engine...................................................... 35

3.6 References to Section 3............................................................................................ 36

4 Conclusions ....................................................................................................................... 39

Figures

1 Market Penetration Profile for Aerodynamics-Improving Technologies

for Class 7 and Class 8 Trucks .......................................................................................... 14

2 Market Penetration Profile for Fuel-Cell-Operated Auxiliaries for Class 7 and

Class 8 Trucks ................................................................................................................... 15

3 Market-Share-Weighted Fuel Economy Benefits of Aerodynamic Devices — New

Class 7 and Class 8 Trucks................................................................................................ 15

4 FTP Transient Cycle.......................................................................................................... 20

Tables

1 Class 2b and Class 3 Truck Technologies and Their Potential Effects, Cost, and

Market Shares.................................................................................................................... 27

2 Classes 4–6 Truck Technologies and Their Potential Effects, Cost, and

Market Shares.................................................................................................................... 29

3 Class 7 and Class 8 Truck Technologies and Their Potential Effects, Cost, and

Market Shares.................................................................................................................... 32
v

Acknowledgments

The authors thank John Maples and Susan Holte of the Energy Information Administration,

U.S. Department of Energy, for their guidance and support. The authors also thank Roy Cuenca

of Argonne National Laboratory for his technical advice on fuel-economy-improving

technologies. Thanks are due to our technical editor Kevin A. Brown and to Kerri Schroeder, also

of Argonne, who provided word processing support. Although many persons helped make this

report possible, the authors are solely responsible for its contents.
vi
1

Abstract

Researchers at Argonne National Laboratory analyzed heavy-duty truck

technologies to support the Energy Information Administration’s long-term

energy use projections. Researchers conducted an analysis of several technology

options that have potential to improve heavy truck fuel economy and emissions

characteristics. The technologies are grouped as fuel-economy-enhancing and

emissions-improving. Each technology’s potential impact on heavy truck fuel

economy has been estimated, as has the cost of implementation. The extent of

technology penetration is estimated on the basis of truck data analyses and

technical judgment. 
2
3

Section 1

Introduction

The Energy Information Administration (EIA) within the U.S. Department of Energy

projects future energy use by various energy consuming sectors. The EIA has developed a

modeling tool called the National Energy Modeling System (NEMS) for developing these

projections, which are published as the Annual Energy Outlook (AEO). The transportation sector

component of NEMS projects energy use by several categories. One of these categories includes

heavy-duty trucks. The heavy-duty trucks include all freight-carrying trucks with a gross vehicle

weight (GVW) exceeding 8,500 lb. For its projection work for the 2002 AEO, EIA asked

Argonne National Laboratory (Argonne) to identify future energy-efficiency and emissionsimproving technologies and their effects on heavy-duty truck fuel economy.

The objective of Argonne’s work was to provide the EIA with a set of technologies,

associated impacts on fuel economy, and potential market penetration for each technology. Two

sets of technologies, one aimed at enhancing fuel economy and the other aimed at enhancing

emissions characteristics, were evaluated. This report summarizes the methodology used and

estimated impacts of these technologies on truck fuel economy.
4
5

Section 2

Technology, Costs, and Market Penetration

Potentials of Fuel-Efficiency-Enhancing

Technologies for Medium and Heavy

Freight Trucks: Projections to 2025

This section describes the methodology used in identifying promising technologies, their

potential impacts, and their market penetration potentials.

2.1 Methodology

The project team developed information from various sources to identify truck technologies

that are most likely to be introduced during the next two decades. A few of the technologies

included in the analysis represent research sponsored by the U.S. Department of Energy (DOE).

The technologies were in two groups: those affecting the powertrain and those affecting nonengine loads. The Technology Roadmap for the 21st Century Truck Program, prepared by the

U.S. Department of Energy, Office of Heavy Vehicles Technology (OHVT), was used in

estimating the potential energy savings of various technologies (DOE 2000). Several other

publications were used to obtain information about technologies and their impacts on fuel

economy. 

Projecting the market penetration of new technology is normally done by applying one or

more models to predict market share. The EIA uses a vehicle choice model for projecting market

penetration by new technologies and alternative fuels in the light-duty sector. Projections from

this model are based on data collected through consumer preference surveys. A similar model was

not available for the heavy-duty sector. The light-duty vehicle selection is highly affected by such

behavioral variables as perceived image of owning a given vehicle, while the heavy-duty vehicle

selection is affected by intended use, cost, and benefits. Some simple payback models exist that

evaluate incremental cost of a technology and estimated fuel savings. Since the future year fuel

prices were not available during this analysis, an approach based on technical judgment was

employed, although it is acknowledged that pressures imposed by fuel price and perhaps future

petroleum supply security concerns will be important accelerants to the promulgation of these

technologies. Thus, our projections reflect less than what would be “maximum feasible”

penetration for any forecast year, given manufacturing and supply constraints.

Each technology’s potential fuel savings was evaluated against its cost. Further, the potential

maximum market penetration was then evaluated in terms of segments of trucks that may obtain

the maximum benefits. An introduction year was selected on the basis of a technology’s status of

development, and a time interval for reaching the maximum market penetration was assigned.

With an estimated market introduction date and maximum market penetration, a demand curve

was plotted that shows sales of the new technology over time. There are two regimes in the

market penetration curve: (1) initial penetration, where the market is constrained by

manufacturing capability and lack of consumer awareness, and (2) mature market, where supply

quickly responds to demand. We characterized two cases: a medium-technology case (by
6

considering relatively low-cost and less-innovation-dependent technologies) and a hightechnology case by including higher-cost and more-innovation-dependent technologies.

Argonne performed a literature search on advanced truck technologies for estimating the

future fuel economy of three groups of trucks: light medium (GVW classes 2B and 3), heavy

medium (GVW classes 4–6), and heavy-duty (GVW classes 7 and 8). The most reliable data were

the potential fuel economy of the advanced class 8 tractor-trailer and the advanced class 2B-6

medium-duty hybrid truck, which are subjects of detailed studies (Stodolsky et al. 1998; An et al.

1999; DOE 2000; Englar 2001). The least-reliable data were the future costs of all technologies.

For the less-reliable data, we relied on the collective judgment of several Argonne researchers.

Both retrofit and replacement technologies were assessed. Much of the cost information had to be

estimated by using the costs of typical current production technologies because the advanced

technologies do not yet exist in production. In a few cases, DOE cost goals were used.

The impacts on fuel economy were determined by grouping the technology as either one that

reduces non-engine or parasitic losses (those that affect the energy needed to propel the vehicle

— e.g., rolling resistance, aerodynamic drag, and auxiliary load) or one that reduces engine losses

(e.g., improved lubrication, increased peak cylinder pressure, and improved thermal

management). The introduction year also depended, in part, on the schedule of upcoming

emission standards. In model year 2004, emission standards are scheduled to be tightened

significantly (EPA 1997), which requires many new technologies (Browning 1997). While many

emissions control technologies (like exhaust aftertreatment) will reduce fuel economy, some will

actually improve fuel economy (like higher fuel injection pressure). Market penetration curves

were developed for each technology on the basis of earlier Argonne work (Mintz and Vyas 1991;

Teotia et al. 1999 and 2001). These curves also characterized market penetration of new

technologies constrained by manufacturing capacity and lack of consumer awareness. 

As a check, we calculated the improvement in fuel economy of a Class 8 tractor-trailer on

the basis of our estimates. Under the assumption that a set of major technologies is adopted, the

fuel economy of the truck rises from a baseline value of 6.2 mpg (for new trucks in VIUS 2000)

to 10.1 mpg. This mileage is consistent with an industry goal of a 10-mpg truck, as described by

Merrion (1994) and adopted by DOE (DOE 1997 and 2000).

2.2 Technologies, Assumptions, and Potential Effects

Various technologies that were evaluated, key assumptions, and estimated potential effect on

fuel economy of heavy trucks are described in this section.

2.2.1 Non-Engine Technologies

The non-engine technologies reduce a vehicle’s parasitic losses. The potential improvement

in fuel economy of such technologies was developed primarily from earlier studies (Mintz and

Vyas 1991; Stodolsky et al. 1999; DOE 2000, and Englar 2001) and adjusted to match the

average speed of a truck duty-cycle (a more comprehensive study would model each use within

the truck classes to estimate the detailed impact of duty cycle on fuel economy). The improved

non-engine technologies are classified in four broad groups: (1) those reducing aerodynamic drag,
7

(2) those reducing rolling resistance, (3) those affecting better management of auxiliaries, and

(4) those reducing empty vehicle mass. In most of the cases, several technologies were identified

within each group. 

Aerodynamic Drag. The effects of reducing aerodynamic drag are a strong function of

vehicle speed because the power needed to overcome aerodynamic drag varies as the cube of

speed. Heavy-duty trucks classed as long-haul travel mostly at highway speeds (65 mph), while

medium-duty trucks travel mostly at lower speeds (approximately 45 mph is the maximum speed

observed in WVU’s suburban driving schedule by Clark et al.). Therefore, the benefits of reduced

aerodynamic drag are significant for most heavy-duty trucks.1

 We assume some advanced dragreduction treatments can be retrofitted onto the existing fleet. The aerodynamic forces are

estimated to require 21.3% of the energy used by a class 8 truck at 65 mph steady speed (DOE

2000). The Government-Industry Research Partnership under the 21st Century Truck Program

proposes a 20% reduction in aerodynamic energy usage, which is equivalent to a 4.5%

improvement in fuel economy. We have also included a new DOE-sponsored technology under

the high-technology case — pneumatic blowing — that is expected to further reduce aerodynamic

drag. The technology involves pressurized air blowing through selected points on the exterior

surface of a truck. The technology has already been applied to reduce aircraft drag and increase

stability. The technology is claimed to have the potential to save energy, even after deducting

energy expended for the generation of pressurized air (Englar 2001).

For class 7 and class 8 heavy trucks, four technologies were identified for reducing

aerodynamic drag: 

1. Cab top deflectors, sloping hood, and cab side flares; 

2. Closure or coverage of the gap between tractor and trailer, aerodynamic

bumper, underside air baffles, and wheel well covers; 

3. Trailer leading and trailing edge curvatures; and 

4. Pneumatic blowing. 

The first technology involving cab top deflectors is on the market and can be retrofitted to

existing trucks.

For class 8 heavy-duty trucks, we assume that drag-reduction technologies would improve

fuel economy by 10.8% (Englar 2001; Stodolsky et al. 1999); for heavier medium trucks

(classes 4–6), we assume that they would improve fuel economy by 7.5%; and for lighter

medium-duty trucks (classes 2B and 3), we assume that they would improve fuel economy by

2.5%. We assume that the costs of drag reduction vary substantially for heavy trucks. With a

pneumatic blowing system, the cost could be as high as $5,250. In terms of development, the

pneumatic blowing system is at the laboratory stage; further research may help to lower the initial

 

1

 The clear exception in this class is refuse haulers and concrete mixers, which travel at very low

average speeds. A more complete study would differentiate among uses within the heavy-duty truck class.
8

cost of this technology. The cost for the heavier medium trucks would be $1,950 for the

maximum benefits; for the lighter medium trucks, the cost would be proportionately lower at

$600.

Rolling Resistance. Three rolling-resistance-reducing technologies were identified for the

class 8 heavy trucks: 

1. Low-resistance tires, 

2. Super single tires, and 

3. Pneumatic blowing to provide some lift and thereby reduce rolling resistance. 

The first two technologies are mutually exclusive. The share of energy required to overcome

rolling resistance is estimated as 12.8% for the class 8 trucks (DOE 2000). The joint GovernmentIndustry Research Partnership under the 21st Century Truck Program proposes a 40% reduction in

rolling resistance energy, which is equivalent to a 5.4% increase in fuel economy.

Energy expended in overcoming rolling resistance is directly proportional to speed and

mass, implying that the fuel economy of heavier trucks that travel at high speeds can benefit

significantly from reductions in this resistance. Low-resistance tires have been on the market for

some time, but some types require higher inflation pressure and frequent monitoring. These

requirements may have limited the extent of their penetration. The low-resistance tires can be

used by the existing class 8 trucks and are estimated to improve fuel economy by 3%. The super

single tires can be used only in new class 8 trucks and are estimated to improve fuel economy by

about 2–3% (Stodolsky et al. 1999; DOE 1997). We assume a 3% improvement with super

singles. For both groups of medium trucks, we assumed only one technology — the lowresistance tires — that would improve fuel economy by 2.5%. We assume an incremental cost of

$15–20 per low-resistance tire for the heavy-duty trucks, with 18 tires replaced every 60,000

miles; we also assume that 10 tires are replaced for the heavier medium-duty trucks and six tires

are replaced on lighter medium-duty trucks every 50,000 miles. The super singles are considered

only for the heavy-duty trucks, with eight super singles at an incremental cost of $30–40 for 16

regular tires, replaced every 60,000 miles (Bridgestone 1996). 

The use of pneumatic blowing to provide a slight lift to the trailing axles is being researched

(Englar 2001). The technology has a potential to increase fuel economy by more than the

assumed 1.2% in this analysis. Safety and road dust issues associated with this technology have

not yet been researched. We assigned the technology a low 1.2% fuel economy gain, assuming

that it would not be deployed 100% of the time. A cost of $500 — in addition to the cost of

$2,500 assigned to pneumatic blowing for reducing aerodynamic drag – was assigned for pipes,

jets, valves, and additional controls.
9

Accessory Load. The heavy and medium trucks have several auxiliaries operated through

their engines: 

• Air compressor, 

• Hydraulic pumps, 

• Coolant pump, 

• Engine oil and fuel pumps, 

• Fans, and 

• Air conditioning compressor. 

Since most of these auxiliaries operate all the time while engine is turned on (even when not

needed), they consume some energy. The engine also runs the alternator that provides electric

power for lighting, windows, mirror adjustment, heating, audio entertainment devices, and cab

comforts. Many class 8 trucks are being equipped with an on-board personal computer, an

Internet connection through the cab top dish antenna, a refrigerator, a microwave oven, a coffee

maker, and video entertainment devices. 

Two alternative (mutually exclusive) technologies for reducing accessory load were

considered: (1) electric auxiliaries and (2) fuel-cell-operated auxiliaries. The first option of

having electrically operated auxiliaries is expected to increase the fuel economy of heavy-duty

trucks by 1.5% at an additional cost of $500. For medium trucks, this option was treated as a part

of engine technologies as either an integrated starter-alternator or a hybrid powertrain. The

second alternative of fuel-cell-operated auxiliaries included in the high-technology case was

considered feasible for heavy-duty trucks only because it would not be cost-effective for medium

trucks. DOE is sponsoring research on fuel cell technology with cost goals of $30–35/kW. The

target is to have the technology introduced by 2010. Also, all major vehicle manufacturers have

their own fuel cell programs. We assumed that fuel-cell-operated auxiliaries would be ready for

introduction by 2012. We also assumed that the original equipment manufacturers would install

small (~5 kW) fuel cell units, thereby reducing cost. Currently, a few small diesel-engineoperated power units are available, but because they are offered as an add-on, their per-kW cost is

much higher than what truck engine manufacturers could achieve. The technology is expected to

increase fuel economy by 6% at an additional cost of $1,500. Aside from continuous operation

during long distance driving, the heavy-duty truck engines are often kept idling during rest stops

(Stodolsky et al. 2000). The use of fuel-cell-operated accessories has potential to reduce such

idling and further improve the overall fuel economy of heavy-duty trucks.

Vehicle Mass. Lightweight materials allow weight-limited trucks to increase carrying

capacity (thereby reducing the number of trucks for a given tonnage of freight hauled) and allow

improvements in fuel economy for those trucks that “cube out” (i.e., are volume limited). We

assume that an unloaded tractor-trailer weighs 26,000 lb and that the use of aluminum, plastics,

and other high-strength, lightweight materials reduces the weight by 4,500–9,000 lb. Assuming
10

that a loaded cubed-out tractor-trailer weighs 60,000 lb, the use of lightweight materials would

reduce the loaded truck mass by 7.5–15%. 

Argonne has attempted to simulate the effect of mass reduction on the fuel economy of

heavy trucks through the National Renewable Energy Laboratory’s Advanced Vehicle Simulator

Model, ADVISOR (Wipke et al. 1998 and 1999). Because there are no established driving

schedules for heavy trucks, the Argonne simulations relied on a few driving schedules developed

by the West Virginia University (WVU) that are included in ADVISOR (Clark et al. 1999).

While simulating a class 8 truck on WVU Intercity Driving Schedule, a fuel economy gain of

0.6% was observed for each 1% mass reduction from 65,000 lb to 58,000 lb. The maximum speed

during the simulation was 61 mph, and the average running speed (excluding stops) was 37.5

mph. Most intercity class 8 trucks average a much higher speed than 37.5 mph. The gain in fuel

economy due to mass reduction could be higher than 0.6% at higher average speeds. We assumed

a 0.66% increase in fuel economy for each 1% weight reduction and estimated fuel economy

increases as 5–10%. While simulating a class 6 truck on a WVU Suburban Driving Schedule, a

fuel economy gain of 0.48% was observed for each 1% mass reduction from 22,600 lb to 21,800

lb. The maximum speed during the simulation was 44.8 mph, and the average running speed was

21.5 mph. The potential fuel economy gains for medium trucks, both heavy- and light-, were

capped at 5% since they are less likely to be weight- or volume-limited, and so the use of

expensive lightweight material would not be cost-effective.

2.2.2 Powertrain Technologies

Powertrain technologies increase the efficiency of the engine and transmission, thereby

increasing the overall fuel economy. These technologies are synergistic and their effects are

multiplicative, as compared with non-engine technologies, the effects of which are additive.

Three groups of powertrain technologies were included: 

1. Those improving transmission efficiency, 

2. Those improving diesel-engine-based powertrain efficiency, and 

3. Those improving gasoline-engine-based powertrain efficiency. 

Transmission. High-efficiency transmission technologies are aimed at reducing mechanical

losses in these components by 25–30% (DOE 1997; 2000), resulting in an improvement in fuel

economy of about 1–3% (Stodolsky et al. 1999; DOE 1997). Actual efficiency improvements are

a function of duty cycle, with a higher efficiency improvement possible during congested driving

(An et al. 1999). The 21st Century Truck Program estimates a 2.3% energy use by transmission at

65 mph steady speed and proposes a 30% reduction, which is equivalent to a 0.7% gain in fuel

economy. The energy use would be much greater in city driving; consequently, we assume a

higher gain of 2% in all truck classes due to improvements in the transmission and in its

lubricants (Ehlbeck et al. 1991).

Diesel Engine. This category is applicable to all diesel-engine trucks with differing

technology menus for class 7 and class 8 heavy-duty trucks and class 2B-6 medium trucks.
11

According to the 1997 Vehicle Inventory and Use Survey (VIUS), heavy-duty (classes 7–8)

trucks use 69% of all fuel used by heavy trucks, heavier medium (classes 4–6) trucks use 14%,

and lighter medium (classes 2B–3) trucks use 17% (VIUS 2000). Also — according to the 1997

VIUS — 98% of the new heavy-duty (classes 7–8) trucks, nearly 68% of the new classes 4–6

(heavier medium) trucks, and slightly more than 2% of the new class 2B-3 (lighter medium)

trucks have diesel engines. The joint Government-Industry Research Partnership under the 21st

Century Truck Program estimates the energy losses within a diesel engine to be 60% (DOE

2000). Although these losses seem very high, the diesel engine is the most efficient of all internal

combustion engines. Homogeneous charge compression-ignition (HCCI) combustion is the

subject of some proposed research. HCCI is a cross between spark-ignition and compressionignition (diesel) combustion, whereby well-mixed air and fuel are ignited. Combustion occurs

spontaneously and homogeneously without flame propagation. Because of the very lean charge,

local flame temperature is low, thereby drastically lowering NOx emissions. Because the HCCI

concept is at a research program evaluation stage, we did not explore the impacts of HCCI

engines. Once some progress is made and preliminary results are available, we recommend that

the impacts of this technology be assessed in future studies of truck fuel economy and emissions.

Four diesel engine technologies were identified for heavy-duty (classes 7–8) trucks: 

1. Internal friction reduction, 

2. Increased peak cylinder pressure, 

3. Improved fuel injection and more efficient combustion, and 

4. Reduced waste heat and improved thermal management. 

Reducing internal friction is estimated to improve the fuel economy of heavy-duty trucks by 2%

and increase peak cylinder pressure by 4% (DOE 2000). Improved fuel injection encompasses

such technologies as electronic fuel injection (e.g., electronic unit injectors and common rail

injectors), electronic unit pump and electronic distributor pump systems (Browning 1997), and

other technologies that would be developed with a better understanding of diesel spray

(ANL 2000). Gains in fuel economy are estimated as 6% (DOE 2000). DOE is supporting

research on reducing waste heat and improving thermal management. More efficient

turbochargers and turbocompounding are among various options under this technology group.

The technology is projected to improve heavy-duty truck fuel economy by 10%. Incremental

costs for the four technology groups are estimated at $500, $1,000, $1,500, and $2,000,

respectively. 

Four diesel engine technologies were also identified for medium trucks: 

1. Turbocharging and direct injection; 

2. Integrated starter alternator with idle off and limited regenerative braking

capability; 
12

3. Lower internal friction, improved fuel injection, and more efficient

combustion; and 

4. Hybrid electric powertrain.

Because heavier (classes 4–6) medium trucks and lighter (classes 2B–3) medium trucks are used

differently, improvements in fuel economy were projected to be lower for the lighter trucks. The

lighter trucks are less likely to carry loads, but they are used more for services by farmers,

utilities, craftsmen, construction contractors, and delivery companies (VIUS 2000).

Turbocharging and direct injection are estimated to improve the fuel economy of heavier medium

trucks by 8% and of lighter medium trucks by 5% at a cost of $1,000 and $700, respectively. 

The integrated starter-alternator technology would enable electrical operation of such

auxiliaries as fuel, coolant, vacuum, and hydraulic pumps. The technology would also reduce the

amount of engine idling at traffic lights and in congested traffic and provide limited regenerative

braking capability. The technology is estimated to improve fuel economies of both subgroups by

5% at a cost of $1,200. Through lower internal friction, improved fuel injection, and more

efficient combustion, the fuel economy of medium trucks is estimated to improve by 8% at a cost

$2,000. 

A hybrid electric powertrain with associated engine power reduction improves the fuel

economy of a car substantially (in the range of 21–200%), particularly in congested driving (An

et al. 2001; Santini et al. 2002). When the gains not directly associated with the hybrid powertrain

are subtracted, the estimated range of fuel economy gain is 21–96%. Hybrid electric cars cost

$3,000–5,000 more than similar models equipped with conventional engines (CarPoint 2001).

Hybrid electric powertrains are projected to improve the fuel economy of medium trucks by 40–

71% (An et al. 2000; DOE 2000). We estimate a 40% improvement at a cost of $6,000–$8,000.

Gasoline Engines. Most of the heavy-duty (classes 7–8) new trucks are equipped with diesel

engines (VIUS 2000), and, consequently, no gasoline engine technologies were characterized for

them. Four technology groups were characterized for medium truck gasoline engines: 

1. Electronic fuel injection, double overhead cams, and multiple valves; 

2. Integrated starter alternator with idle off and limited regenerative braking

capability; 

3. Direct fuel injection; and 

4. Hybrid electric powertrain. 

Use of electronic fuel injection is common in light-duty gasoline engines. Its use would

become more prevalent in medium trucks because of the more stringent emissions standards

(Browning 1997). Double overhead cams and multiple valves have increased engine specific

power and, thereby, reduced the specific fuel consumption in cars. Although the average fuel

economy of cars has not improved over the last 15 years because of demand for better
13

performance, these technologies have potential to improve the fuel economy of gasoline-powered

trucks, which, in commercial service, are more sensitive to fuel cost. These technologies are

estimated to increase the fuel economy of medium trucks by 5% at a cost of $700–1,000. As in

the case of diesel engines, the integrated starter-alternator technology would enable the use of

electric accessories, reduce the amount of idling at traffic lights and in congested driving, and

provide limited regenerative braking capability. The technology is estimated to improve medium

truck fuel economy by 5% at a cost of $1,000–1,200. 

The gasoline direct injection (GDI) (also referred to as spark-ignition direct-injection –

SIDI) technology has potential to improve gasoline engine fuel economy by 22–24% (Cole et al.

1998 and 1999). However, it is unlikely to meet the emissions standards without emissions

control equipment that require frequent regeneration. When fuel consumption for regeneration is

accounted for, the gain in the fuel economy is estimated to be 8–10% (Stovell et al. 1999). The

14% fuel economy penalty for regeneration was estimated in laboratory experiments and

potentially can be reduced to 10% or less. We estimated a 12% gain in fuel economy for this

technology at a cost of $700–1,000. 

As discussed above, the hybrid powertrain technology is expected to improve fuel economy

by about 40–70% (An et al. 1999; DOE 2000). We estimate a 45% improvement in fuel economy

at a cost of $6,000–8,000. The estimated improvement in fuel economy for the hybrid technology

is higher for the gasoline–powered medium trucks because they usually have lower laden weight

and fewer annual miles, indicating that they are used in congested conditions (VIUS 2000). 

2.3 Market Penetration Profiles

A new technology entering the market would compete with an existing technology, and its

market share would depend on the benefits (or utility) it provides and cost/penalties (or disutility)

it imposes. A new technology’s extent of penetration is usually limited during the introductory

period because only a small fraction of the buyers adopt it. When others learn from these early

buyers and production-related issues are resolved, its rate of market penetration would rise. The

rate of market penetration would eventually slow down when a large majority of buyers that

benefit from the technology have adopted it. The market penetration over time would follow a

classical S-shaped curve. Researchers and marketing professionals have investigated new

technology market penetration and substitution and have developed mathematical models for

projecting such market penetration pattern for new technologies (Mansfield 1961;

Blackman 1974; Paul 1979; Bass 1980; Teotia and Raju 1986).

Our data for each technology included possible year of introduction, maximum market

penetration, and estimated period for achieving the maximum market penetration. To develop

market penetration profiles for the truck technologies listed in Tables 1–3 in Section 3, we

adapted a logit function formulation in which function F{t} defines the market share of a new

technology at time t. The old technology share, if any, would be 1 – F{t}. We selected the

following functional form, which uses two parameters, δ and β, to determine the shape of the

curve (Santini 1989):

t = δ + β ln[F{t}/(1− F{t})] + μ .
14

Here, δ and β are coefficients that determine the shape of the market penetration curve, and

μ is the error term. The term δ defines the midpoint in time for the symmetric market penetration

curve represented by the above equation, while β determines the rate at which the new technology

would penetrate the market. We selected values of δ and β to reflect the potential maximum

penetration and when it was likely to happen. Figures 1 and 2 show market penetration curves for

two representative technologies.

Each technology’s potential of increasing fuel economy of various trucks is shown in

Tables 1–3 in Section 3. Collectively, these technologies can improve truck fuel economy

substantially. However, their impact on the on-road truck fleet and overall new truck fuel

economy will be different at different points in time. For example, four aerodynamic-improving

technologies for class 8 heavy trucks are listed in Table 3. These four technologies differ in

introduction year, fuel economy benefit, and maximum penetration. Their market penetration

profiles also differ significantly. Consequently, the market-share-weighted combined benefits of

the technologies would be different at different points in time. Figure 3 shows the market-shareweighted benefits of these aerodynamic-improving technologies on new-truck fuel economy.

0%

5%

10%

15%

20%

25%

30%

35%

40%

2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025

Year

Share of New Trucks

Figure 1 Market Penetration Profile for Aerodynamics-Improving Technologies for

Class 7 and Class 8 Trucks (closing/covering gap between tractor and trailer, aerodynamic

bumper, underside baffles, and wheel well covers)
15

0%

3%

6%

9%

12%

15%

2010 2012 2014 2016 2018 2020 2022 2024 2026

Year

New Truck Share

Figure 2 Market Penetration Profile for Fuel-Cell-Operated Auxiliaries for

Class 7 and Class 8 Trucks

Figure 3 Market-Share-Weighted Fuel Economy Benefits of Aerodynamic

Devices — New Class 7 and Class 8 Trucks
16

2.4 References for Section 2

An, F., et al., 2001, “Evaluating Commercial and Prototype HEVs,” presented at SAE

International, 2001 Annual Congress and Exposition, paper 2001-01-0951, Warrendale, Pa.

An, F., et al., 2000, “Scenario Analysis of Hybrid Class 3–7 Heavy Vehicles,” presented at SAE

International, 2000 Annual Congress and Exposition, paper 2000-01-0989, Warrendale, Pa.

An, F., et al. 1999, “Fuel and Emissions Impacts of Heavy Hybrid Vehicles,” presented at the

ISATA, paper no. 99CPE015, Vienna, Austria, June.

ANL: Argonne National Laboratory

ANL, 2000, “X-Ray Vision: Taking a Hard Look at Fuel Sprays and Combustion,”

TransForum 3:1, Argonne, Ill.

Bass, F.M., 1980, “The Relationship Between Diffusion Rates, Experience Curves, and Demand

Elasticities for Consumer Durable Technological Innovations,” Journal of Business 53(3):s51–

s67.

Blackman, A.W., 1974, “The Market Dynamics of Technological Substitutions,” Technological

Forecasting and Social Change 6:41-63.

Bridgestone, 1996, “Bridgestone Tire Price and Data Book,” Bridgestone Technical Publications,

Nashville, Tenn. 

Browning, R., 1997, “Technologies and Costs for On-Road Heavy-Duty Engines Meeting 2004

Emissions Standards,” Society of Automotive Engineers Technical paper no. 973256, Society of

Automotive Engineers, Warrendale, Pa. 

CarPoint 2001, “MSRP Data on Toyota Prius and Corolla,” at

http://carpoint.msn.com/Vip/Overview/Toyota/Prius/New.asp and

http://carpoint.msn.com/Vip/Overview/Toyota/Corolla/New.asp

Clark, N.N., et al., 1999, “Application of the New City-Suburban Heavy Vehicle Route (CSHVR)

to Truck Emissions Characterization,” in Special Publication SP-1459, Topics in General

Emissions, pp. 1–15, paper 1999-01-1467, SAE International, Warrendale, Pa.

Cole, R.L., R.B. Poola, and R. Sekar, 1999, Emissions and Fuel Economy of a Vehicle with a

Spark-Ignition, Direct-Injection Engine: Mitsubishi Legnum GDI, Argonne National Laboratory

report ANL/ESD-TM-149, Argonne, Ill.

Cole, R.L., R.B. Poola, and R. Sekar, 1998, “Exhaust Emissions of a Vehicle with a DirectInjection Engine,” pp. 67–77 in Direct Injection: Engines, Emissions, and Aftertreatment, SAE

International Report SP-1399, Warrendale, Pa.

DOE: U.S. Department of Energy
17

DOE, 1994, Assessment of Costs and Benefits of Flexible and Alternative Fuel Use in the

U.S. Transportation Sector, Technical Report Fourteen: The Potential of Alternative Fuels in

Nonroad Vehicles to Reduce Reliance on Imported Energy Sources, U.S. Department of Energy,

Office of Policy, unpublished.

DOE, 1997, OHVT Technology Roadmap, U.S. Department of Energy, Office of Heavy Vehicle

Technologies, report DOE/OSTI-11690 (DE98001287), Washington, D.C., Oct. 

DOE, 2000, Technology Roadmap for the 21st Century Truck Program: A Government-Industry

Research Partnership, U.S. Department of Energy, Office of Heavy Vehicles Technologies,

report 21CT-001, Washington, D.C.

Ehlbeck, J.M., and M. von Mayenburg, 1991, “Increasing Heavy-Duty Truck Fuel Economy,” in

the Transactions of the SAE, SAE paper no. 912662, SAE International, Warrendale, Pa.

Englar, R.J., 2001, “Advanced Aerodynamic Devices to Improve the Performance, Economics,

Handling, and Safety of Heavy Vehicles,” SAE International Annual Congress and Exposition,

paper 2001-01-2072, Warrendale, Pa.

EPA: U.S. Environmental Protection Agency

EPA, 1997, Emission Standards Reference Guide for Heavy-Duty and Nonroad Engines,

U.S. Environmental Protection Agency, Office of Air and Radiation, publication no. EPA420-F97-014, Washington, D.C., Sept.

Mansfield, E., 1961, “Technical Change and Rate of Imitation,” Econometrica 29:741-765.

Merrion, S., 1994, “Diesel Engine Design for the 1990s,” Fortieth L. Ray Buckendale Lecture,

Society of Automotive Engineers publication SP-1011, Society of Automotive Engineers,

Warrendale, Pa.

Mintz, M., and A. Vyas, 1991, Forecast of Transportation Energy Demand through the Year

2010, Argonne National Laboratory report ANL/ESD-9, Argonne, Ill. 

Paul, R.A., 1979, The Impact of Future Diesel Emissions on the Air Quality of Large Cities,

U.S. Environmental Protection Agency Report EPA-45075-79-005, Research Triangle Park, N.C. 

Santini, D.J., 1989, “Interactions among Transportation Fuel Substitution, Vehicle Quantity

Growth, and National Economic Growth,” Transportation Research Part A 23(3):183–207. 

Santini, D.J., et al., 2002, “Hybridizing with Engine Power Reduction,” Transportation Research

Board, Eighty-First Annual Meeting, paper 02-4095, Washington, D.C.

Stodolsky, F., L. Gaines, and A. Vyas, 2000, Analysis of Technology Options to Reduce the Fuel

Consumption of Idling Trucks, Argonne National Laboratory report ANL/ESD-43, Argonne, Ill.
18

Stodolsky, F., A. Vyas, and R. Cuenca, 1999, unpublished information, Argonne National

Laboratory, Argonne, Ill.

Stodolsky, F., et al., 1998, “Lifecycle Analysis for Freight Transport,” presented at the Total Life

Cycle Conference and Exposition, Society of Automotive Engineers Technical Paper no. 982206,

Graz, Austria, Dec. 

Stovell, C., et al., 1999, “Emissions and Fuel Economy of 1998 Toyota with a Direct Injection

Spark Ignition Engine,” SAE International Paper no. 1999-01-1527, Warrendale, Pa.

Teotia, A.P., et al., 2001, Macroeconomic Impacts of Clean Diesel Engines, Phase 2 Report:

U.S.-Produced Clean Diesel Engines and SIDI Gasoline Engines for Selected Light Trucks,

Argonne National Laboratory report ANL/ESD/TM-164, Argonne, Ill.

Teotia, A.P., et al., 1999, Assessing Economic Impacts of Clean Diesel Engines, Phase 1 Report:

U.S.- or Foreign-Produced Clean Diesel Engines for Selected Light Trucks, Argonne National

Laboratory report ANL/ESD/TM-155, Argonne, Ill.

Teotia, A.P.S., and P.S. Raju, 1986, “Forecasting the Market Penetration of New Technologies

Using a Combination of Economic Cost and Diffusion Models,” Journal of Product Innovation

and Management 4:225–237.

VIUS, 2000, 1997 Vehicle Inventory and Use Survey: Micro Data Compact Disk and

Documentation, Bureau of the Census, Washington, D.C.

Wipke, K., M. Cuddy, and S. Bunch, 1999, “ADVISOR 2.1: A User-Friendly Advanced

Powertrain Simulator Using a Combined Backward/Forward Approach,” in IEEE Transactions on

Vehicular Technology, Special Issue on Hybrid and Electric Vehicles, Columbus, Ohio.

Wipke, K., et al., 1998, “ADVISOR 2.0: A Second-Generation Advanced Vehicle Simulator for

Systems Analysis,” Proceedings of North American EV and Infrastructure Conference and

Exposition, Phoenix, Ariz., Dec. 3–4.
19

Section 3

Technology, Costs, and Fuel Effects of

Meeting 2007 and Later Emission and Fuel

Content Standards for Medium and Heavy

Freight Trucks: Projections to 2025

3.1 Current State of Technology

3.1.1 Standards and Test Procedures through 2004

Beginning with the 1998 model year and effective through model year 2003, federally

certified heavy-duty diesel engines are subject to the following emission standards (units of

g/bhp-h):

Total HC CO NOx PM

1.3 15.5 4.0 0.10a, 0.05b

a Applicable to over-the-road heavy-duty diesel

trucks and truck tractors.

b Applicable to heavy-duty transit buses; 0.05

certification value must meet 0.07 g/bhp-h in

use.

The corresponding California standards, effective as of model year 1996, are:

Non-Methane HC TOTAL HC CO NOx PM

1.2 1.3 15.5 4.0 0.05

As of 2004, California and federal standards for NOx will be harmonized at the following

increased stringency levels (manufacturer selects compliance option):

OPTION 1: NMHC + NOx = 2.4 NMHC n/a

OPTION 2: NMHC + NOx = 2.5 NMHC = 0.5

(The second option corresponds to a NOx standard of approximately 2.0 g/bhp-h, which is equal

to a 50% reduction from the prior year.) Through 2003, levels must be certified to 10 years or

110,000 miles (whichever comes first) for vehicles up to 19,500 lb GVW, to 10 years or

185,000 miles for vehicles weighing between 19,500 and 33,000 lb, and to 10 years or

290,000 miles for vehicles weighing more than 33,000 lb. Emission warranties must be honored

for five years or 50,000 miles. Beginning in 2004, although the warranty period/accrual remains

the same, the certification values for the 33,000-pound and higher GVW ratings increase to 13

years or 435,000 miles. Note that, pursuant to a consent decree regarding in-use violation of

existing standards that was reached by EPA, the U.S. Justice Department, and truck engine
20

manufacturers, all 2004 requirements have been moved forward to October 2002, for the subset

of manufacturers that signed the decree and have been found guilty of this violation. Most diesel

engines have already demonstrated that they are capable of meeting the 2004 non-methane

hydrocarbon (NMHC) limits with engine parameter modifications, since diesel fuel combusts

efficiently and is characterized by low volatility/minimal evaporation. However, the NOx

component of the new standard poses a more formidable challenge because of the requirement to

simultaneously meet the stringent 1998 PM limits. There is a physical trade-off between PM and

NOx emissions such that, ceteris paribus, if one is controlled to a low level, the other increases. 

The EPA transient emission certification cycle (FTP) for heavy-duty truck engines, codified

in CFR Title 40, Part 86.1333, is shown in Figure 4. Emission testing is performed by using a DC

or AC electric engine dynamometer. The four phases of the cycle represent light urban traffic

conditions with frequent stops and starts (the New York Non-Freeway [NYNF] component);

crowded urban traffic with few stops (Los Angeles Non-Freeway [LANF] component); crowded

expressway traffic in high-speed, “saw-tooth” mode (Los Angeles Freeway [LAFY] component);

and repetition of the NYNF. The cycle is conducted twice — the first time from cold shutdown

and the second with a warm start after an engine-off time of 20 minutes as soon as the first run

has been completed. The 1,200-s (20-min) run time for each cycle would cover an on-road

distance of approximately 10.3 km (6.4 mi) at an average speed of 30 km/h (19 mph). Recently, a

chassis dynamometer urban driving schedule has been added to 40 CFR Part 86 because of the

increasing amount of heavy-duty testing that is being performed on such equipment. The profile

of this cycle mimics much of the FTP, but it is only 1,060 s in duration and covers only 8.9 km at

an average speed of 30.4 km/h.

-20

0

20

40

60

80

100

120

0 150 300 450 600 750 900 1050

Percent

% Maximum Rated RPM

0

20

40

60

80

100

120

0 150 300 450 600 750 900 1050

Seconds

Percent

% Maximum Rated Torque

Figure 4 FTP Transient Cycle
21

3.1.2 Engine/Combustion Controls and Equipment Retrofits

Successful commercialization of increasingly sophisticated computer-assisted common rail

direct-injection designs, applied primarily to light-duty diesel engines, resulted in significant

breakthroughs in diesel engine fuel and combustion management during the 1990s. This

development was on par with the transition to full fuel injection technology for spark ignition

engines and enabled a much greater degree of emission control within the engine than was

possible under the previous indirect injection (swirl chamber) approach to diesel fuel

management. Engine manufacturers have generally been able to achieve the 1998–2003 standards

by combining higher fuel injection pressures, for better atomization and thus more complete burnup of combustion particles, with cooled exhaust gas recirculation for engine-out NOx control

(cooler combustion produces less NOx). They have also found that adding a supplementary

sulfur-tolerant oxidation catalyst can further decrease or virtually eliminate the soluble organic

fraction of tailpipe particulate mass and number at normal operating temperatures. 

To bring socially sensitive heavy diesel vehicles (such as older large transit and school buses

operating in urban areas) into compliance with current standards, the application of retrofit

devices — especially catalytically regenerated particulate traps and/or oxidation catalysts — is on

the increase. Using traps requires the availability of ultra-low-sulfur (≈15 ppm) diesel fuel, while

applying oxidation catalysts generally does not.

3.1.3 Present and Near-Term Prospective Exhaust Controls (including

aftertreatment)

The EPA has expressed considerable confidence that the combined technologies of catalytic

particulate traps and NOx adsorbers can meet 2004 and later heavy-duty diesel standards on

vehicles equipped with OEM engines (EPA 2000). The NOx adsorber acts as a retaining reservoir

for NOx emissions, stored as nitrogen dioxide following direct exhaust NO oxidation over a

catalyst, until a vehicle’s exhaust stream becomes sufficiently oxygen poor (momentarily fuelenriched) to promote reduction to N2; the adsorbed nitrogen dioxide is then released for

conversion to nitrogen and carbon dioxide over a three-way reduction catalyst bed. Computercontrolled metering of the enriched exhaust stream is believed to minimize excess fuel loss:

current best performance for prototype adsorbers averages 2–3% excess fuel during pre-reduction

enrichment events. These systems appear to function most effectively at exhaust temperatures

between 200o

C (approximate catalyst “light-off” temperature) and 450°C, which represents the

exhaust temperature range for over 90% of most diesel engine operations. However, for the

reduction catalyst to function reliably (assuming that it is based, as at present, on catalytic

washcoats of precious metal—rhodium and platinum), low-sulfur fuel will be required. Also,

because certification testing will begin before after-treatment devices reach full operating

temperature, diesel vehicles will have higher initial emission transients (“cold starts”), as have

been problematic for years in spark ignition engines. (At the current diesel emission standards,

cold transient and stabilized emission rates are virtually identical.) Even very low levels of fuel

sulfur can cause sulfates to build up on the adsorber surface, inexorably impairing its efficiency

unless a high temperature (>500o

C) transient can be generated in the exhaust to induce the sulfate

to mobilize. If desulfation must be performed frequently, as is the case with fuel containing more

than 15 ppm sulfur, overall performance is likely to degrade over time as a result of reduced
22

durability and sintering of the coating. Also, regular desulfation can produce undesirable

odiferous compounds, such as hydrogen sulfide (H2S), that may have to be “cleaned up” by a

supplementary oxidation catalyst before leaving the tailpipe.

In dual adsorber/catalytic regenerating trap concepts currently under review, the particulate

matter treatment occurs first (upstream) such that the adsorber works with a NO-rich but PMdepleted exhaust gas flow. One question is whether this type of arrangement — with the addition

of an adsorber for sulfur oxides positioned downstream of the trap but upstream of the NOx

controls — could successfully intercept sufficient sulfur and sulfate particles to permit acceptable

and long-lived high-sulfur-tolerant operation of the overall adsorber/reduction catalyst system.

The EPA has examined the mechanics of this system and has not been persuaded that catalyzing

particulate traps with SOx adsorbers can intercept enough of the sulfur in diesel fuels with a sulfur

content greater than 15 ppm to sustain NOx adsorber operation at the required control efficiency

(DOE 2000a). Also, SOx adsorbers would likely have to increase in volume approximately

proportional to average fuel sulfur content, rendering them impractical at a sulfur content above

30 ppm or so.

3.1.4 Additional Technologies Available Today and in the Near Future

Other near-term proposals for NOx control — some of which are already in limited use —

include selective catalyst reduction (SCR) by means of fuel mixing with a compound (such as

urea) that promotes chemical reduction, direct excess nitrogen injection into the combustion

chamber, and non-thermal plasma-assisted catalysts. Caterpillar Corp. has recently claimed a

“breakthrough in engine technology” that couples a hydraulically activated, electronically

controlled unit injector fuel system with a proprietary “advanced combustion emissions reduction

technology.” Caterpillar claims that the combined systems will enable an emission treating

system in the company’s on-highway truck diesel engines that (1) can meet 2007 and later

emission standards and (2) is far simpler than other available or developing options (Caterpillar,

Inc., 2001). Speculation is that the control strategy Caterpillar is developing will involve NOx

reduction with plasma-assisted catalysis (see below) (Pacific Northwest National

Laboratory 2001).

Although touted as an effective retrofit option, we do not believe that, beyond rigidly

controlled centrally refueled fleets, SCR has a long-term future in the trucking industry.

Originally disseminated as a means for stopgap compliance with the consent decree

manufacturers signed to avoid litigating the in-use high NOx excursions EPA discovered to be a

“deliberate” operating strategy, SCR requires that manufacturers add a separate reservoir of urea,

up to 25 gal in the case of heavy-duty diesel trucks, to the fueling system. Moreover, without

closed-loop combustion control, large amounts of ammonia (NH3) can be released (“ammonia

slip”) as a by-product of the NOx reduction reaction. Ammonia has an unpleasant odor and can

form large quantities of secondary fine particulates when present with the nitrate and sulfate ions

found in vehicular exhaust streams. Truckers have little incentive (save deliberately programmed

performance degradation or overall loss of engine functionality) to ensure that the urea is “topped

up” — and when the urea reservoir is exhausted, catalytic NOx reduction no longer occurs. This

technology holds little promise of ever being a “value-added” solution to stringent mobile source

NOx control.
23

Injection of a nitrogen-enriched combustion air stream in lieu of exhaust gas recirculation

has two advantages: (1) better control of combustion air properties (as recirculated exhaust often

contains undesirable constituents that can impair efficient compression) and (2) better

management of combustion temperature. Moreover, a higher nitrogen-to-oxygen ratio can retard

the rate of NOx formation in the cylinder. The principal drawback in the near term is the

experimental nature of this technology: unless intake air can be split into nitrogen-enriched and

oxygen-enriched streams on board, say, by some yet-to-be-perfected osmotic process, nitrogen

cylinders would have to be incorporated, raising the same inadequate restocking issues as SCR.

However, with a developmental time horizon of 2025, small, lightweight osmotic membranes

could be perfected sufficiently to improve long-term prospects for this option. The same can be

said of non-thermal plasma-assisted catalysts, which, when perfected at lower voltage and power

requirement than at present, would generate NO-oxidizing ions across charged metal plates in lieu

of through-oxidation catalysts, thus saving the expense of precious metals.

At the lighter end (10,000–14,000 lb) of the heavy-duty slate, a way for truck and engine

manufacturers both to meet stringent NOx and PM emission standards and to bypass the

uncertainties about future diesel fuel properties is to commit to producing more clean-burning

gaseous-fueled trucks. This strategy would also enable these manufacturers to obtain sufficient

“low-emission bin” certifications to offset the potentially higher-emission certifications for their

diesel and gasoline offerings.

Gasoline-fueled vehicles in the lighter classes (up through 14,000 lb), most of which are

already catalyst-equipped, seem destined to be able to meet regulated standards by 2005, but if

there is an emerging preference for diesel in these categories, compliance is not assured for those

vehicles. Thus, CNG and, potentially, dedicated propane-fueled trucks could meet an important

need in this market segment, unless spark-ignition engines regain dominance and gasoline is their

fuel of choice. 

Note that engine tuning to control NOx to ever-more stringent levels works against

compliance (by combustion regulation alone) with the carbon monoxide standard (15 g/bhp-h) for

heavy-duty diesels. Thus, the oxidation catalyst now applied for particulate reduction may also

prove essential to future maintenance of regulated CO limits.
24

3.2 Impact of 2007 and Later Standards

3.2.1 Timing of Phase-In for Both Vehicular Emission Limits and Fuel

Properties

Beginning in the 2007 model year and phasing in to 100% over a four-year period, all

federally certified on-road heavy-duty diesel engines will be subject to the following emission

limits (g/bhp-h):

Non-Methane HCa CO NOx PM HCHOb

0.14 15.5 0.2 0.01 0.016

a NMHC

b Formaldehyde

The required minimum phase-in rate for each manufacturer’s new production fleet is as follows:

2007: 25%; 2008: 50%; 2009: 75%; 2010: 100%.

For heavy-duty gasoline-fueled vehicles in the 8,500–14,000-lb gross vehicle weight (GVW)

classes (i.e., 2b and 3), the corresponding standards (g/bhp-h) are:

Weight (lb) NMHC CO NOx PM HCHO

8,500–10,000 0.195 7.3 0.2 0.02 0.032

10,000–14,000 0.230 8.1 0.4 0.02 0.040

Full compliance with the above standards is required in the 2008 model year. In the case of

both NOx and PM, this represents a 90% reduction from 2004 standards and a better than 98%

reduction from the standards in place in 1988. The EPA (EPA 2000) leaves no doubt in its

Regulatory Impact Analysis (RIA) for these 2007 and later truck standards that it holds diesel fuel

of a very low sulfur content (in any case, no greater than about 15 ppm) to be an indispensable

prerequisite to the attainment of these standards. The reason is that the control technologies the

RIA identifies as being capable of achieving required reductions in tailpipe emissions will not

function properly, except with low-sulfur fuel. We should therefore consider that the general

availability of such fuel in a time frame consistent with the schedule for phasing in the new

standards will be a given, or, conversely, that the new exhaust limits will be delayed if litigation

or other circumstances delay the availability of such fuel. For this analysis, we take the view that

both low-sulfur diesel fuel and ultra-clean diesel emission control technologies that do not

significantly degrade fuel economy will be available somewhat ahead of the mandated schedule,

enabling engine manufacturers who so choose to take advantage of advance banking incentives

for their out-year fleet offerings. A force countervailing such incentives is the strong customer

specification-driven nature of the heavy-duty truck market, which renders this already lowvolume product even less subject to emission control cost spreading since each manufactured unit

may be uniquely specified.
25

3.2.2 Technologies Expected to be Proven/Capable of

Commercialization by 2006

For as long as the sulfur content of diesel fuel remains at or near current levels, sulfurtolerant NOx and PM control methods will be required. Urea-based selective catalyst reduction

for NOx control is already in use in some heavy-duty fleets, although fleet managers generally

assume the responsibility for ensuring on-board availability of urea, not vehicle operators.

Literature is very sparse with respect to systematic evaluation of the effectiveness of fleet SCR

programs, but a recurring problem observed in some open-loop SCR retrofit applications is

“ammonia slip,” in which excess reductant (urea) builds up on the catalyst surface and is

eventually rejected as high ammonia exhaust transients. Recent tests have shown the ability to

control this problem (Sluder and West 2002) and raised the possibility that the ammonia needed

for the catalytic reduction reaction can actually be produced on-board from the propulsion fuel,

thus obviating the urea reservoir and taking the vehicle operator “out of the loop” of emissions

control. Unfortunately, the fuel economy penalty with these prototype units generally exceeds

15% (Ogunwumi et al. 2002). Most NOx retrofit programs are not expected to survive after 15

ppm sulfur fuel becomes universally available and the requirements of the EPA consent decree on

NOx emission compliance are met. However, investigations are under way to provide catalytic

reduction through other agents, including the use of injected diesel fuel itself as a reactant (socalled hydrocarbon or volatile organic compound selective catalyst reduction). Like on-board

ammonia generation, this approach currently bears a significant fuel economy penalty. Whatever

NOx reduction technique is ultimately adopted, closed-loop (closed crankcase) emission controls

will become standard by 2006 on all sizes of diesel engine/powertrain systems, just as they have

been for many years in spark-ignition vehicles.

For PM control, retrofit with regenerating exhaust particulate traps is well under way for

heavy-duty vehicles — such as school and transit buses, refuse haulers, and pick-up and delivery

trucks — that operate predominantly in urban areas. These retrofits require low-sulfur (i.e., less

than 50 ppm) diesel fuel for full control effectiveness. Activity is especially vigorous in southern

California, where such retrofits are eligible for funding under the Carl Moyer emission mitigation

program, and in New York City, where transit buses have undergone, or will soon be undergoing,

retrofit.

3.2.3 Pollutants for Which Final Control Set Remains Undefined or

Flexible

As implied above, there remains a wide choice of options for advanced NOx control, and

assuming availability of 15 ppm sulfur diesel fuel, no one technique has yet been identified as

superior. Heavy-duty engines must now be emission-certified to as many as 435,000 miles of

operation (Class 7 and 8), so durability of the emission control equipment set is critical. The EPA

endorses the NOx adsorber-based solution, but without a commercial product, estimates of

effective service life, maintenance intervals, and costs for these systems are highly speculative.

Perfecting an SCR system employing clean diesel fuel itself (rather than urea) as the reducing

agent, such that 90% NOx removal is achieved (nothing approaching this level is now in view),

could result in a control platform that does not require operator intervention and is lighter-weight

and more reliable than adsorbers or plasma catalysts. For the lighter (Class 2b–3) heavy-duty
26

trucks, migration of a portion of that fleet to hybrid electric power could obviate some of the

Stage IV controls needed for conventional vehicles. Thus, joint control of NOx and particulates in

2b–3 diesel-electric hybrids may be achievable with exhaust gas recirculation and an oxidation

catalyst (and possibly passive SCR) as the only required exhaust aftertreatment.

3.3 Onboard Fuel Efficiency Effects of 2007 and Later Standards

Although the 21st Century Truck program has articulated a fuel economy penalty goal of no

more than five percent to achieve 2007 and later emission standards (DOE 2000a, p. 4-14), truck

and bus engine manufacturers are determined to meet these stringent standards without any net

loss in fuel efficiency because customers would strongly resist a loss in fuel economy, especially

given past expectations of performance. Meeting this need will require that any new parasitic or

system efficiency losses attributable to additional emission control devices and techniques be

offset by fuel economy gains across all truck size classes. In Tables 1–3, we indicate that fuel

efficiency gains will remain equal to or slightly ahead of emission-control-related fuel penalties,

such that no new model-year vehicle will prove inferior in performance or fuel consumption to its

predecessors per unit of work output. Thus, the following discussion should be considered only in

light of the net fuel economy information in Tables 1–3, which for any model year chosen should

show either a gain or zero overall loss. However, obstacles to achieving this goal remain

formidable, as documented in recent technical papers cited herein.

3.3.1 Speculation on Parasitic Losses

The incremental mass of add-on equipment for treating emissions, which is variable by

engine size/displacement but increasingly subject to minimization through the use of advanced

materials, will impose a fuel economy penalty on heavy diesel trucks that would otherwise not

have occurred. There are other possible sources related to the control of exhaust emissions that

would sacrifice fuel efficiency. A common technique for NOx control generally modulated

through engine or manifold vacuum ported to the cylinder intake valves is recirculating some

fraction of cylinder-out gas from the exhaust manifold back to the combustion chamber after

compression by a supercharger and cooling by an intercooler. On light-duty vehicles, before

closed-loop control and real-time on-board diagnostics became standard, carbon build-up in the

vacuum lines could impair the recirculation process, resulting in an increased pumping load.

More importantly, as mechanical controls occasionally allow EGR application to drift beyond

50%, soot formation increases as excess fuel is needed for combustion (Guzman 1997). Given the

introduction of electronic closed-loop control and mature EGR technology in heavy diesel trucks,

this problem is not expected to recur, and placing a turbine in the exhaust stream can meet the

needs of supercharger air compression. 

Although catalyst diesel particulate traps should be fully automated with respect to burnoff

of collected matter and recharging, backpressure will build up before all required cleaning

functions (including ash blowout and removal) are triggered by a sensor. Excess fuel

consumption during this period could reach 2% (DOE 2000b).
27

Table 1 Class 2b and Class 3 Truck Technologies and Their Potential Effects, Cost, and Market Shares

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

Base Base over-the-road mpg =11.4.Aerodynamics I Lower coefficient of drag through

hood and cab configuration, bumper,and underside baffles.

2.5 2002 80 $600

RollingResistance

I Low-rolling-resistance tires. 2.5 2004 75 $180

Transmission I Advanced transmission with lock-up,

electronic controls, and reducedfriction.

2.0 2005 100 $750

Auxiliaries I Electrical auxiliaries (vacuum pump,

hydraulic pump, radiator fan) withintegrated starter/alternator.

Please see integratedstarter/alternator under dieseland gasoline engines.

II Electrical auxiliaries (vacuum pump,

hydraulic pump, radiator fan, HVAC,brakes) with hybrid electricpowertrain.

Please see hybrid electricpowertrain under diesel andgasoline engines.

Diesel Engine I Turbocharged, direct injection

engine.

5.0 2003 25 $700

II Integrated starter/alternator with idle

off and limited regenerative braking.

5.0 2005 25 $1,200 MPG gain and cost account for

larger alternator and inverterand for electrical auxiliaries.

III Improved engine with lower friction,

better injectors, and efficientcombustion.

10.0 2012 15 $2,000

IV Hybrid electric powertrain.* 40.0 2010 15 $6,000 Includes mpg gains and cost

due to all-electric auxiliaries.

EmissionControl—NOx

I Exhaust gas recirculation and timing

retard + selective catalytic reductionfor higher emitters.

2002/3 10 $250 3–5 These are interim approaches

that will systematically bephased out after 2006.

DOE 2000: 21CT-001,"Technology Roadmap orthe 21st Century TruckProgram" (December2000)

II Nitrogen-enriched combustion air. 2003 30*** $500 0.5 Enhancement of EGR likely to

be supplanted by adsorbersystems unless fuel sulfurissues remain unresolved.

Automotive EngineeringInternational, June, July2001

III Non-thermal plasma catalyst. 2007 25 $1,000 1–2 Alternative to nitrogen

enrichment but commercialintroduction will be later than forenrichment.

DOE 2000: 21CT-001

IV NOx adsorber (integrated) system. 2007 75 $1,500 2–4 Cost includes 1/2 NO--> NO2

oxidation catalyst cost +downstream "cleanup" catalyst.

EPA420-R-00-026(December 2000—Dieselvehicle standards RIA)and several SAE papers
28

Table 1 (Cont.)

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

EmissionControl—PM

I Diesel oxidation catalyst (organics). 2001/2 95 $150 0.5 Added mass penalty only. EPA420-R-00-026

[NOTE: Fuelcompositionchanges for CI PMand NOx control

are possible inboth the short andlong term, but willnot affectemission controlsystemtechnology]

II – IV Catalytic diesel particulate filter. 2006 85 $1,000 1–2 Regeneration and ash clearing

will have to be accomplishedautomatically.

EPA420-R-00-026; DOE2000: 21CT-001

EmissionControl—C/CO

I – IV Diesel oxidation catalyst. 2001/2 95 $150 0.5 50/50 allocation to PM control. EPA420-R-00-026

II – IV Closed crankcase system. 2005 95 $50 ---

Gasoline Engine I Electronic fuel injection, DOHC, and

multiple valves.

5.0 2003 55 $700

II Integrated starter/alternator with idle

off and limited regenerative braking.

5.0 2005 30 $1,000 MPG gains and cost account for

larger alternator and inverterand for electrical auxiliaries.

III Direct injection (GDI). 12.0 2008 25 $700

IV Hybrid electric powertrain.* 45.0 2010 8 $6,000 Includes mpg gains and cost

due to all-electric auxiliaries.

EmissionControl—PM

I – IV Improved oxidation catalyst. 2005 95 $250 0.25 50/50 allocation to HC/CO

control. 

EPA420-R-00-026 

EmissionControl—NOx

I – II EGR/spark retard. 2002 75 $25 1–2 Retard will be phased out

gradually. 

EPA420-R-00-026 

II – IV Oxygen sensors. 2003 90 $75 --- 50/50 allocation to HC/CO

control. 

EPA420-R-00-026 

III – IV Secondary air/closed loop system. 2008 80 $50 --- Displaces retard and some

EGR; needed for optimumsensor function. 

EPA420-R-00-026 

EmissionControl—HC/CO

I – IV Oxygen sensors. 2003 90 $75 --- 50/50 allocation to NOx control. EPA420-R-00-026 I – IV Evap. canister w/improved system

vacuum, materials, and connectors.

2003 95 $50 --- Elimination of diurnal (soak),

running, and resting losses.

EPA420-R-00-026

II – IV Improved oxidation catalyst. 2005 95 $250 0.25 50/50 allocation to PM control. EPA420-R-00-026

Vehicle Mass(Tare)

I Mass reduction through highstrength, lightweight material.** 5.0 2010 20 $1,300
29

* Under high-technology case, this technology will penetrate sooner.** Half of the fuel economy gains would be under the high-technology case.***Contingent on development of practical on-board air separation system and significant lag in fuel sulfur phasedown. This option selected in preference to "lean-NOx" catalysts, the

development of which is still plagued by high fuel penalties and low efficiency.

Table 2 Classes 4–6 Truck Technologies and Their Potential Effects, Cost, and Market Shares

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

Base Base over the road mpg = 7.9Aerodynamics

I Cab top deflector (same height at the

trailing van), sloping hood, cab sideflares.

2.5 Current 50 $750 Assuming that currently only

10% of trucks have suchdevices.

II Closing/covering of gap between cab

and van, aerodynamic bumper,underside air baffles, wheel wellcovers.

4.0 2004 50 $800

III Van leading and trailing edge

curvatures.

1.0 2005 50 $400

RollingResistance

I Low-rolling-resistance tires. 2.5 2005 50 $280

Transmission I Advanced transmission with lock-up,

electronic controls, and reducedfriction.

2.0 2005 100 $900

Auxiliaries I Electrical auxiliaries (vacuum pump,

hydraulic pump, radiator fan) withintegrated starter/alternator.

Please see integratedstarter/alternator under dieseland gasoline engines.

II Electrical auxiliaries (vacuum pump,

hydraulic pump, radiator fan, HVAC,brakes) with hybrid electricpowertrain.

Please see hybrid electricpowertrain under diesel andgasoline engines.

Diesel Engine I Turbocharged, direct injection engine

with better thermal management.

8.0 2004 25 $1,000

II Integrated starter/alternator with idle

off and limited regenerative braking.

5.0 2005 35 $1,200 MPG gain and cost account for

larger alternator and inverterand for electrical auxiliaries.

III Improved engine with lower friction,

better injectors, and efficientcombustion.

8.0 2008 25 $2,000

IV Hybrid electric powertrain.* 40.0 2010 15 $8,000 Includes mpg gains and cost

due to all-electric auxiliaries.

EmissionControl—NOx

I Exhaust gas recirculation and timing

retard + selective catalytic reductionfor higher emitters.

2002/3 10 $400 3–5 These are interim approaches

that will begin to be phasedout after 2006.

DOE 2000: 21CT-001, "21stCentury Truck ProgramRoadmap" (DOE 2000)

II Nitrogen-enriched combustion air. 2003 30*** $700 0.5 Enhancement of EGR likely to

be supplanted by adsorbersystems unless fuel sulfurissues remain unresolved.

DOE 2000 21CT-001
30
31

Table 2 (Cont.)

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

III Non-thermal plasma catalyst. 2006 25 $1,200 1–2 Alternative to nitrogen

enrichment but commercialintroduction will be later.

Automotive EngineeringInternational, June, July2001 EPA420-R-00-026(December 2000—Dieselvehicle standards RIA) andseveral SAE papers

IV NOx adsorber (integrated) system. 2006 90 $2,000 2–4 Cost includes 1/2 NO--> NO2

oxidation catalyst cost +downstream "cleanup" catalyst.

EmissionControl—PM

I Diesel oxidation catalyst (organics). 2001/2 95 $200 0.5 Added mass penalty only. EPA420-R-00-026

[NOTE: Fuelcompositionchanges for CI PMand NOx control

are possible inboth the short andlong term, but willnot affectemission controlsystemtechnology]

II – IV Catalytic diesel particulate filter. 2006 95 $1,250 2–3 Regeneration and ash clearing

will have to be accomplishedautomatically.

EPA420-R-00-026; DOE2000: 21CT-001

EmissionControl—HC/CO

I – IV Diesel oxidation catalyst. 2001/2 95 $200 0.5 50/50 allocation to PM control. EPA420-R-00-026

II – IV Closed crankcase system. 2005 95 $65 ---

Gasoline Engine I Electronic fuel injection, DOHC, and

multiple valves.

5.0 2003 35 $1,000

II Integrated starter/alternator with idle

off and limited regenerative braking.

8.0 2005 25 $1,200 MPG gains and cost account for

larger alternator and inverterand for electrical auxiliaries.

III Direct injection (GDI). 12.0 2008 25 $1,000

IV Hybrid electric powertrain.* 45.0 2010 15 $8,000 Includes mpg gains and cost

due to all-electric auxiliaries.

EmissionControl—PM

I – IV Improved oxidation catalyst. 2005 95 $350 0.25 50/50 allocation to HC/CO

control. 

EPA420-R-00-026 

EmissionControl—NOx

I – II EGR/spark retard. 2002 75 $25 1–2 Retard will be phased out

gradually. 

EPA420-R-00-026 

II – IV Oxygen sensors. 2003 90 $75 --- 50/50 allocation to HC/CO

control. 

EPA420-R-00-026 

III – IV Secondary air/closed loop system. 2008 80 $50 --- Displaces retard and some

EGR; needed for optimumsensor function. 

EPA420-R-00-026 
32

Table 2 (Cont.)

Technology

Area

Stage Technology Type MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%)

Comments Sources Consulted

EmissionControl—HC/CO

I – IV Oxygen sensors. 2003 90 $75 --- 50/50 allocation to NOx control. EPA420-R-00-026 I – IV Evap. canister w/improved system

vacuum, materials, and connectors.

2003 95 $50 --- Elimination of diurnal (soak),

running, and resting losses.

EPA420-R-00-026

II – IV Improved oxidation catalyst. 2005 95 $350 0.25 50/50 allocation to PM control. EPA420-R-00-026

Vehicle Mass(Tare)

I Mass reduction through highstrength, lightweight material.** 5.0 2007 20 $2,000

* Under high-technology case, this technology will penetrate sooner.** Half of the fuel economy gains would be under the high-technology case.***Contingent on development of practical on-board air separation system and significant lag in fuel sulfur phasedown. This option selected in preference to "lean-NOx" catalysts

whose development is still plagued by high fuel penalties and low efficiency
33

Table 3 Class 7 and Class 8 Truck Technologies and Their Potential Effects, Cost, and Market Shares

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

Base Base over the road mpg = 6.2.Aerodynamics I Cab top deflector (same height at the

trailer), sloping hood, cab side flares.

2.0 Current 70 $750 Assuming that currently only

25% of the line haul truck havesuch devices.

II Closing/covering of gap between

tractor and trailer, aerodynamicbumper, underside air baffles, andwheel well covers.

2.5 2005 40 $1,500

III Trailer leading and trailing edge

curvatures.

1.3 2005 50 $500

IV Pneumatic blowing.* 5.0 2010 30 $2,500

RollingResistance

I Low-rolling-resistance tires. 3.0 2005 66 $550 Assuming 2 steering and 16

trailing tires. 

II Super singles. 3.0 2008 33 $700 Excluding the front axle.

Frication reduction throughpneumatic lift.

III Pneumatic blowing.* 1.2 2015 25 $500 Assuming that compresssor,

piping, and blow control areincluded in stage IV ofaerodynamic improvements.Additional cost is for selectiveblowing and control.

Transmission I Advanced transmission with lock-up,

electronic controls, and reducedfriction.

2.0 2005 100 $1,000

Auxiliaries I Electrical auxiliaries (air compressor,

hydraulic pump, radiator fan). 

1.5 2005 50 $500 MPG gain and cost account for

larger alternator and inverter. 

II Fuel-cell (with reformer) -operated

auxiliaries (HVAC included).*

6.0 2012 15 $1,500 Stage I and II are mutually

exclusive.

Diesel Engine I Internal friction reduction through

better lubricants and improvedbearings.

2.0 2005 66 $500 The MPG gain reduced to allow

for higher peak cylinderpressure. 

II Increased peak cylinder pressure. 4.0 2006 40 $1,000

III Improved injectors and more efficient

combustion.

6.0 2007 40 $1,500

IV Reduced waste heat and improved

thermal management.**

10.0 2010 35 $2,000
34 Table 3 (Cont.)

Technology

Area Stage Technology Type

MPG

Gain

(%)

Intro

Year

Max

Share

by 2025

(%)

System

Hardware

Cost

Fuel

Economy

Penalty

(%) Comments Sources Consulted

EmissionControl—NOx

I Exhaust gas recirculation and timing

retard + selective catalytic reductionfor higher emitters.

2002/3 10 $500 3–5 These are interim approaches

that will begin to be phased outafter 2006.

DOE 2000: 21CT-001,"21st Century TruckProgram Roadmap"(DOE 2000)

II Nitrogen-enriched combustion air. 2003 30*** $750 0.5 Enhancement of EGR likely to

be supplanted by adsorbersystems unless fuel sulfurissues remain unresolved.

DOE 2000: 21CT-001

III Non-thermal plasma catalyst. 2007 25 $1,250 1–2 Alternative to nitrogen

enrichment but commercialintroduction will be later.

Automotive EngineeringInternational, June, July2001 EPA420-R-00-026(December 2000--Dieselvehicle standards RIA)and several SAE papers

IV NOx adsorber (integrated) system. 2007 90 $2,500 2–4 Cost includes 1/2 NO--> NO2

oxidation catalyst cost +downstream "cleanup" catalyst.

EmissionControl--PM

I – IV Diesel oxidation catalyst (organics). 2001/2 95 $250 0.5 Added mass penalty only. EPA420-R-00-026

[NOTE: Fuelcompositionchanges for CI PMand NOx control

are possible inboth the short andlong term, but willnot affectemission controlsystemtechnology]

II – IV Catalytic diesel particulate filter. 2006 95 $1,500 1–2 Regeneration and ash clearing

will have to be accomplishedautomatically.

EPA420-R-00-026; DOE2000: 21CT-001

EmissionControl--HC/CO

I – IV Diesel oxidation catalyst. 2001/2 95 $250 0.5 50/50 allocation to PM control. EPA420-R-00-026

II – IV Closed crankcase system. 2005 95 $75 ---

Vehicle Mass(Tare)

I Mass reduction through highstrength, lightweight material.** 10.0 2005 30 $2,000 MPG gains account for less energy use by volumeconstrained commodities and

fewer trips by weightconstrained commodities.

* Under high-technology case.** Half of the fuel economy gains would be under the high-technology case.***Contingent on development of practical on-board air separation system and significant lag in fuel sulfur phasedown. This option selected in preference to "lean-NOx" catalysts, the

development of which is still plagued by high fuel penalties and low efficiency.
35

NOx adsorber regeneration will also require injection of small amounts of diesel fuel for light

off and desorption of stored NO for downstream catalysis under rich-burn conditions. This

process may result in additional fuel use beyond combustion for propulsion of 2–4%, depending

on system maturity (EPA 2000, pp. III-35 through III-48). 

The incremental energy requirement for periodic desulfation of the NOx adsorber and

catalyst at a temperature of up to 750oC — a procedure necessary for proper adsorber function

when fuel sulfur content exceeds about 3 ppm — is estimated at 1–2% (Dearth et al. 1998). This

efficiency would be considerably better than what has been achieved in recent prototype testing.

This efficiency does not account for the potential reduction in the cost-effectiveness of NOx

removal over time due to a fall-off in adsorber efficiency caused by sintering of portions of the

active catalyst matrix (Parks et al. 2002; Monroe and Li 2002).

3.3.2 Decrease in Maximum Potential Engine Efficiency (combustion

cooling, EGR)

EGR and cooled (or N2-enriched) combustion air each has the property of diminishing the

potential work output that could be obtained from the compression ignition (diesel) cycle per unit

energy input if optimal temperature and fuel/air mix could be retained. Such diminution has

always been interpreted as a “cost of doing business.” The attributable increase in brake-specific

fuel consumption has been measured, as a function of excess air introduced to the cylinder, to

reach about 2% relative to best case (stoichiometric) combustion conditions before engine

performance falls off dramatically (Robert Bosch GmbH 2000).

Plasma arc recharge, like NO release from an adsorber, draws on available fuel for its energy

requirement. The excess fuel use penalty is up to 3% (European Fuels News 1999). 

3.4 Technology Cost Estimates and Credits Other than Efficiency Penalties

The capital costs of the new technologies, including amortization of R&D, are shown in

column 7 of Tables 1–3. While based on estimates documented by the U.S. EPA (2000), they

incorporate a premise based on past cost studies from EPA Regulatory Impact Analyses that the

EPA’s approach can underestimate fully allocable cost by one-third or more. Thus, costs, where

shown, are conservatively inflated 50% above the EPA’s unit estimates (i.e., a multiplier of

1.5 times fixed + variable costs). Although it is not yet field-proven, these estimated cost

increments could be mitigated by a credit of 10% or more for reduced vehicular maintenance

requirements because of the future use of predominantly electronic (rather than mechanical)

control systems for many emission control functions. In fact, the EPA has assigned a reducedmaintenance savings credit (1999 dollars), ranging from $150 (lighter medium-duty diesel trucks)

to $600 (heavy heavy-duty diesel trucks), to the application of 2007 and later emission-control

technologies (EPA 2000, Chapter V). 
36

3.5 Emerging Low-Emission Technologies and Their Prospects for

Commercialization after 2010

3.5.1 Fuel Cells

Fuel-cell-based propulsion is not considered a viable option for the commercial heavy truck

market. Major advancements in vehicular fuel cell durability, weight, and cost will indeed occur

over the next ten to fifteen years. However, it is generally conceded that the demanding peak

power requirements of the heavy-duty fleet will restrict fuel cell application in commercial trucks

to (1) propulsion in a subset of the light-duty fleet (i.e., trucks and vans less than 8,500 lb) and,

possibly, to (2) supplemental powering of auxiliaries in a stopped heavy vehicle. The latter

application is basically that of a stationary generator introduced to preclude extended engine

idling (DOE 2000a). Both of these applications are expected to emerge before 2010 and

accelerate penetration thereafter.

3.5.2 Diesel Electric Hybrids

Tables 1 and 2 indicate the anticipated time frame of introduction (about 2010) and

penetration of diesel hybrid trucks into the heavy-duty fleet. Note that this technology is not

considered a viable option for the heaviest trucks and tractors, and it is for only a subset of lighter

heavy-duty trucks by 2025 (DOE 2000a). However, where these hybrid systems can provide

power adequate for a truck’s mission (recall that in a true hybrid, the heat engine will be

significantly downsized and used predominantly to meet peak power requirements, in order to

maximize overall efficiency gains), using all-electric auxiliaries will yield additional benefits in

terms of fuel economy and emission reduction. 

3.5.3 Effects of Synthetic Diesel Fuel

Using natural-gas-based synthetic diesel fuel with its zero-sulfur, zero-aromatic (straightchain) hydrocarbon properties will bring immediate and significant reduction in particulate,

sulfate, and toxic emissions from heavy diesel trucks. The consensus is that creating a significant

market for such a fuel will depend on (1) a major domestic increase in the cost and decline in the

supply reliability of conventional petroleum and petroleum products and (2) the economic

attractiveness of constructing large synthetic petroleum refineries at or near remote natural gas

fields. The second condition would open up the opportunity to ship liquid rather than gaseous

product from these fields, which would alleviate costly investment in new, often undersea, gas

transmission pipelines. Serious discussions are under way to bring more of such plants on-line by

2010, and at least two gained commitments for construction start by the end of 2002.

3.5.4 The “All Electrically Controlled” Engine

Generally independent of the pace of development of hybrid-electric technology, the

evolution of functional control systems of heavy-duty trucks from all-mechanical to partmechanical, part-electrical, and, finally, all-electrical will proceed with the introduction of 42-V

battery systems. Significant fuel savings are possible by decoupling belt-driven devices, such as

various pumps, from the engine through the use of electronically controlled electric drives. In

addition, electronic control of combustion and aftertreatment could provide additional benefits to
37

fuel economy and emissions. Thus, while we have not explicitly credited all-electric engine

control functionality with specific benefits to emission and fuel economy in this report, neither

have we assigned them separable costs, as they will be integral to truck operation on all heatengine and electrochemical propulsion pathways.

3.6 References to Section 3

Caterpillar, Inc., 2001, “Caterpillar’s Emission-Control Technology,” Automotive Engineering

International, p. 30, June.

Dearth, M.A., et al. (Ford Motor Co), 1998, “Sulfur Interaction with Lean NOx Traps: Laboratory

and Engine Dynamometer Studies,” SAE paper no. 982595, Oct. 

DOE: U.S. Department of Energy

DOE, 2000a, Technology Roadmap for the 21st Century Truck Program: A Government-Industry

Research Partnership, DOE-DOD/21CT-001, Oak Ridge, Tenn., Dec. 

DOE, 2000b, Phase I Interim Data Report No. 4: Diesel Particulate Filters – Final Report,

Diesel Emission Control – Sulfur Effects (DECSE) Program, Oak Ridge, Tenn., pp. 20–21;

40-41, Jan. 

EPA: U. S. Environmental Protection Agency

EPA, 2000, Regulatory Impact Analysis: Heavy-Duty Engine and Vehicle Standards and

Highway Diesel Fuel Sulfur Control Requirements, EPA420-R-00-026, Office of Air and

Radiation, Washington, D.C., Dec. 

European Fuels News, 1999, Hart Publications Europe, Inc., T.L. Wright, ed., 3:18, Sept. 22. 

Guzman, H., 1997, “Understanding Exhaust Gas Recirculation Systems,” 1997, AutoInc

Magazine XLV:(1, 12). 

Monroe, D.R., and W. Li, 2002, “Desulfation Dynamics of NOx Storage Catalysts,” paper no.

2002-01-2886, presented at 2002 SAE Powertrain & Fluid Systems Conference & Exhibition,

reprinted from Diesel Particulate Systems and Gaseous Emissions, publication no. SP-1723, SAE

International, Warrendale, Pa.

Ogunwumi, S., et al, 2002, “In-Situ NH3 Generation for SCR NOx Applications,” paper no. 2002-

01-2872, presented at 2002 SAE Powertrain & Fluid Systems Conference & Exhibition, reprinted

from Diesel Particulate Systems and Gaseous Emissions, publication no. SP-1723, SAE

International, Warrendale, Pa.

Pacific Northwest National Laboratory, 2001, “PNNL Reduces Noxious Emissions,” Automotive

Engineering International, pp. 44–46, July.
38

Parks, J., et al., 2002, “Durability of NOx Absorbers: Effects of Repetitive Sulfur Loading and

Desulfation,” paper no. 2002-01-2880, presented at 2002 SAE Powertrain & Fluid Systems

Conference & Exhibition, reprinted from Diesel Particulate Systems and Gaseous Emissions,

publication no. SP-1723, SAE International, Warrendale, Pa.

Robert Bosch GmbH, 2000, Automotive Handbook (Fifth Edition), Stuttgart (De), p. 435 and

p. 501. 

Sluder, C.S., and B.H. West, 2002, “Effects of Regeneration Conditions on NOx Adsorber

Performance,” paper no. 2002-01-2876, 2002 SAE Powertrain & Fluid Systems Conference &

Exhibition, reprinted from Diesel Particulate Systems and Gaseous Emissions, publication no.

SP-1723, SAE International, Warrendale, Pa.
39
40

Section 4

Conclusions

We have analyzed and presented the results of several technologies for improving energy

and emissions characteristics of heavy trucks (gross vehicle weight classes 2b–8). The analysis

involved estimating fuel economy impacts of these technologies, probable cost, and potential

market penetration. We compiled the estimates of the impacts on fuel economy from several

sources and presented the most likely estimates. Each technology was characterized on the basis

of current status, regulations, and most likely production methods. On the basis of the resulting

estimates in terms of costs and market penetration, we have come to the following conclusions:

• The fuel economy of heavy trucks can be improved substantially by reducing parasitic

and accessory loads and using a more efficient powertrain. Some of the technologies are

estimated to have high initial cost and, consequently, will penetrate niche markets.

• The fuel economy of class 8 trucks can be improved to 10 mpg or slightly more by using

the known technologies that reduce aerodynamic and rolling loads, increasing the use of

lightweight materials, and improving diesel engine efficiency.

• The fuel economy of medium trucks in the classes 4–6 GVW group could be improved

substantially by using a hybrid electric powertrain. However, given experience with

hybrid electric cars, this option would be attractive only for trucks that have high annual

use.

Nominal losses in potential maximum fuel economy and moderately higher acquisition costs

are associated with the addition of (1) emission control aftertreatment equipment and (2) modified

combustion management techniques for meeting impending exhaust emission standards for

particulate matter, oxides of nitrogen, and (potentially) carbon monoxide. The losses associated

with these techniques are expected to be offset in commercial production engines by gains in fuel

economy that result from implementing the efficiency measures cited above, and so the net fuel

efficiency loss compared to engines meeting less-stringent standards is expected to be zero. The

leading anticipated control strategies are as follows:

• Addition of adsorber aftertreatment, in conjunction with ultra-low sulfur diesel fuel

(ULSD), for compliance by medium and heavy trucks with the 2004 and later NOx

standards. 

• Also, if ULSD is generally available, requisite control of fine PM can be achieved by

using a catalytic diesel particulate filter that (1) could gradually supplant the oxidation

catalysts now (in the absence of a stringent NOx standard) widely applied and (2) may

still be needed after 2007 for CO control.

• Control measures already established for gasoline-fueled light trucks and automobiles

can be extended to spark-ignition light and medium heavy (classes 2b–6) trucks, given
41

the availability of low-sulfur gasoline. However, application of oxidation catalysts will

be much lower for the heavy (classes 5–6) end of the range because of constraints

related to the size of catalyst. 

As stated above, the pace at which these developments will occur is likely to be significantly

affected by fuel price — and especially by a general perception that petroleum product prices will

continue to rise. Exploration of market adoption of these technologies as a function of fuel cost

was not a component of the current effort, but it should be incorporated in future analysis.