Peer Review for the PQA/Ricardo Report 

“A Study of Potential Effectiveness 

of Carbon Dioxide Reducing Vehicle 

Technologies” 
Peer Review for the PQA/Ricardo Report 

“A Study of Potential Effectiveness of 

Carbon Dioxide Reducing Vehicle 

Technologies” 

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

NOTICE 

This technical report does not necessarily represent final EPA decisions or 

positions. It is intended to present technical analysis of issues using data 

that are currently available. The purpose in the release of such reports is to 

facilitate the exchange of technical information and to inform the public of 

technical developments. 

EPA420-S-08-002 

January 2008 
 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

ANN ARBOR, MI 48105 

January 16, 2008 

OFFICE OF 

 AIR AND RADIATION 

MEMORANDUM 

SUBJECT: Peer Review for PQA/Ricardo Report on “A STUDY OF POTENTIAL 

EFFECTIVENESS OF CARBON DIOXIDE REDUCING VEHICLE 

TECHNOLOGIES” 

FROM: Cheryl Caffrey, Assessment and Standards Division 

Office of Transportation and Air Quality, U.S. Environmental Protection Agency 

In July 2007, US EPA contracted with Perrin Quarles Associates, Inc. who subcontracted with 

Ricardo, Inc. to perform vehicle simulation modeling to estimate the impact of various 

technology packages on carbon dioxide emissions. The resulting report from Ricardo provides a 

detailed assessment of the carbon dioxide emissions reduction potential of a large number of 

conventional vehicle technology packages involving engine and transmission technologies as 

well as improvements in aerodynamics, tires, and accessories. The PQA-Ricardo report is 

entitled “A Study of Potential Effectiveness of Carbon Dioxide Reducing Vehicle 

Technologies”. 

Prior to the release of the Final Report from Ricardo, Inc., EPA provided a draft copy of the 

report to three independent experts for external peer review, in accordance with EPA’s peer 

review guidelines. This EPA report contains documentation of the peer review process for the 

PQA-Ricardo study. 

This document contains three components. First is the summary of the peer reviewer’s 

comments and the response to those comments from EPA and/or Ricardo. Following this is the 

EPA charge letter to the peer reviewers which describes their task and what EPA requested from 

them in terms of deliverables. Lastly, is the peer reviewers submitted biographies and their 

comments on the draft PQA-Ricardo report. 
________________________________________________________________________ 

 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

ANN ARBOR, MI 48105 

OFFICE OF 

 AIR AND RADIATION 

DATE: January 16, 2008 

MEMORANDUM 

SUBJECT: EPA Response to Comments on Ricardo report entitled “A Study of Potential 

Effectiveness of Carbon Dioxide Reducing Vehicle Technologies”, Draft Final 

Report by peer reviewers Dennis Assanis, Chinu Bhavsar and Ron Graves 

FROM: Matt Brusstar, Advanced Testing Division 

Ben Ellies, Transportation and Climate Division 

Dave Haugen, ATD, Technology Development Group Manager 

Dennis Assanis (of Assanis & Associates, Inc.), Chinu Bhavsar (formerly of Ford Motor 

Company) and Ron Graves (of Oak Ridge National Laboratory) reviewed Ricardo’s report 

entitled “A Study of Potential Effectiveness of Carbon Dioxide Reducing Vehicle Technologies, 

Draft Final Report, November 2007”. 

This memo includes a summary of comments and responses and actions to comments from EPA 

and Ricardo. 

Comment: There were multiple comments about the executive summary lacking a discussion of 

results or conclusions drawn from the data, for example: “There should be more words 

summarizing the results (e.g., provide ranges of benefits), and assessing them critically (e.g., 

which technologies seem to incrementally or additively contribute the most), rather than just 

stating that the results are in the table below.” 

EPA’s Response: EPA and Ricardo discussed this before undertaking this work and agreed 

that the report would include only objective simulation results, without any subjective 

recommendations or conclusions. 

Comment: Multiple reviewers questioned why hybrid-electric vehicles (HEVs) were not part of 

the Ricardo study. 

EPA’s Response: Hybrid technologies are showing dramatic improvements in GHG 

reduction, as reflected by every major auto manufacturer’s plans to introduce some form of 

hybrid-electric vehicle. This major new group of drivetrain technologies are very complex, 
both to integrate into vehicles and to simulate through vehicle simulation models. Because 

of the limited time and resources available for this study, any vehicle simulation of GHG 

reductions from hybrid electric vehicles will be necessarily conducted in another, subsequent 

study. 

Comment: One reviewer mentioned that biofuels were not considered in this study. 

EPA’s Response: Although biofuels, renewable fuels and some alternative fuels have the 

potential to reduce GHG pollution, those benefits are realized primarily in their production 

rather than their consumption. Generally speaking, a vehicle powered on biofuels will not 

exhibit a significant reduction in tailpipe GHG emissions unless the vehicle is optimized for 

that fuel. Since there is very limited retail distribution network for fuels other than gasoline 

and diesel, within the near future it is unlikely that auto makers will manufacturer vehicles 

optimized for renewable fuels. Thus, the scope of this work is focused on vehicle fuels 

which are likely to be distributed nationally in broad and significant volumes. 

Comment: Multiple reviewers commented: “...the mostly-uniformly applied reductions in aero 

drag and rolling resistance are without supporting data or analysis. Perhaps this is covered in 

another study, but is conspicuously lacking the rigor of the remainder of the analysis. Aero and 

rolling loss factors for trucks are different than cars. Why?” 

“... what is the justification for the aero and rolling drag factors?” 

“...If there is data to support these assumptions, it should be included in the report.” 

EPA’s Response: To the extent that Ricardo was directed to evaluate representative vehicles 

in five vehicle classes, rather than the opportunities for improvement in individual and 

specific vehicles, a uniform reduction in aero-drag and rolling resistance were seen as the 

most appropriate means to project the gains available from these two technologies. 

A vehicle’s size and shape determine the amount of power needed to push the vehicle 

through the air at different speeds. Changes in vehicle shape or frontal area can therefore 

reduce GHG emissions. Areas for potential aerodynamic drag improvements include 

reduced frontal area as well as addition of skirts, air dams, underbody covers, and more 

aerodynamic side view mirrors. The technical literature consistently estimates that these 

design changes can provide at least a 10% improvement in aerodynamic drag coefficient in 

passenger cars, whereas 6%-10% Cd reduction is more realistic for trucks. Combining these 

drag coefficient improvements with a reduced frontal area equates to GHG reductions of 2% 

and 3% for trucks and cars, respectively. These numbers are in agreement with the technical 

literature and are supported by confidential manufacturer information. 

Based on a 2006 NAS/NRC report, a 10% rolling resistance reduction would provide a GHG 

emissions reduction of 1 to 2 percent – and at this level the tires would maintain similar 

traction and handling characteristics. Again, these numbers are in agreement with the 

technical literature and generally supported by confidential manufacturer information. 
Comment: A question raised was about the test cycles used for simulation: “Why the UDDS 

instead of LA92 cycles? Show example to indicate degree of sensitivity to drive cycle for 

representative technology package (LA92, for example, vs. UDDS).” 

EPA’s Response: Although EPA recently extended the fuel economy labeling methodology 

to 5 test cycles, most of the technology effectiveness data available today is based on EPA’s 

Urban and Highway Driving Schedule Tests. Extending this report to incorporate EPA’s 5-

cycles used in fuel economy labeling would have extended the deliverable date of the report 

beyond that where it could be used in EPA’s anticipated rulemaking process. 

Comment: “The report would be additionally instructive if the effect of reduced performance 

on CO2 emissions was shown for some example vehicles. 

EPA’s Response: The objective of this study was to estimate the GHG emissions reduction 

potential of technology packages while constraining the vehicles to performance levels 

equivalent to the baseline vehicles. Acknowledging that manufacturers might choose to 

trade performance against cost in achieving GHG reductions, EPA has assessed technologies 

without this performance-cost trade-off, and thus the reviewer’s comment highlights further 

reduction potential which was deemed beyond the scope of work at the time the report was 

commissioned. 

Comment: “What is the convention for the technology package identifiers? It is not intuitive 

(i.e. Z, 1, 15, 15a, 15b, etc.?).” 

EPA’s Response: EPA provided Ricardo with technology packages and included identifiers 

for each package that were arbitrarily chosen for project management purposes. It would be 

errant to assume the identifiers have any meaning whatsoever. 

Comment: Multiple reviewers questioned along the lines of: “Page 6: The friction-reduction 

factor is consistent for all technology packages, in spite of the technology packages using 

different sized engines.” 

EPA’s Response: The engine friction reduction factor was provided by EPA as a general 

input representing reasonable fuel efficiency improvements applicable to all engines. It 

includes not only the effects of engine friction reduction, but also the use of lower-friction 

lubricants. 

Comment: “Most of the technology options explored seem to favor gasoline packages over 

diesels. The presentation of the results in chapter 7 selects four categories, all for gasoline 

engines, creating the appearance of imbalance” 

EPA’s Response: Currently, diesels represent less than 1% of the light-duty market in the 

United States, although more stringent GHG and/or fuel economy regulations will certainly 

encourage increases in diesel market penetration. EPA feels that given all the technologies 

considered, diesels were adequately represented in terms of options available to reduce GHG 

emissions using conventional fuels. EPA is comfortable with Ricardo’s presentation in 
chapter 7’s highlight of the synergies between independent technologies when packaged on 

the same engine. 

Comment: “The reference and use of a “known factor” for every fuel, mentioned in section 

2.10.2 to derive CO2 benefits from fuel economy results, is confusing. It would be desirable to 

show the analysis behind the ‘known factor” that was used to convert fuel consumption savings 

to vehicle CO2 equivalent output—do these include upstream CO2 factors, or the effect of CH4 

emissions? A brief discussion of the sources of uncertainty associated with the use of this factor 

equivalent should be added.” 

EPA’s Response: EPA provided Ricardo with constant tailpipe GHG conversion rates (that 

include contributions of CH4) which Ricardo applied to consumption of gasoline and diesel 

fuels in the simulated test cycles. These numbers are based on outputs from the Department 

of Energy’s GREET model and do not include upstream CO2 factors (GHG emitted during 

production of the fuel). The intent of this project was to evaluate the effects of vehicle 

technologies with common fuels (rather than to investigate variability in the fuels 

themselves). 

Comment: “It should be mentioned that these might be market dependent. In European and 

Japanese markets where they have low sulfur and better quality fuels and different customer 

performance expectations (than US), it may be possible to deploy certain advance technologies 

earlier than the US.” 

EPA’s Response: Ricardo’s technology readiness estimates described in the report are 

implicitly for the U.S. market only. 

Comment: “The focus on homogeneous stoichiometric GDI, at the request of EPA, seems to 

be unnecessarily too restrictive. Also, it is questionable whether a 1.5 increase in compression 

ratio can be realized without partial stratified, lean operation with GDI.” 

EPA’s Response: 

a) EPA is unaware of any demonstrated technical pathway for meeting Tier 2 emissions 

levels with a lean combustion gasoline system, given the potential sulfur levels in gasoline in 

today’s U.S. market. In absence of requirements for lower-sulfur gasoline, we believe it will 

be quite difficult to make a stratified lean-burn GDI “Bin 5” vehicle to the U.S. market in the 

near-term. 

b) EPA defers to Ricardo’s technical expertise in this area, but recognizes that this level of 

compression ratio increase is consistent with GDI engines available today. 
Comment: ”Technology options are quantized into discrete bins, when in fact we could very 

well see in production hybrid versions of the options much sooner (e.g., GDI/HCCI dualmode).” 

EPA’s Response: A prime objective of this study was to quantify the synergies and 

effectiveness of representative mechanisms, rather than explore specific realizations of 

specific mechanisms. In this case, Ricardo modeled the HCCI packages with only a limited 

HCCI operating range, outside of which they operated as spark ignition GDI engines so these 

technologies actually were considered as “hybrid” versions of HCCI as suggested by the 

reviewer. 

Comment: “There should have been a mention of the cam torque actuated phaser system in 

section 5.1.1. This type of phaser provides fast response and reduces energy consumption.” 

EPA’s Response: A prime objective of this study was to quantify the synergies and 

effectiveness of representative mechanisms, rather than explore specific realizations of 

specific mechanisms. EPA is aware of this specific form of variable valve timing and 

recognizes there are likely to be various implementations of each technology which cannot 

all be represented individually in the scope of this work. 

Comment: “Cylinder deactivation operating zone (section 3.3) would be dependent on the 

number of cylinders and engine displacement to vehicle weight ratio. As such those parameters 

should be incorporated in a detailed analysis.” 

EPA’s Response: EPA agrees and commissioned this report with this level of detail in 

mind. Ricardo built an individual vehicle simulation model for each technology package and 

vehicle combination. Thus, EPA accepts that these dependencies are accounted for in the 

results. 

Comment: ”Table 1-1 and Table 1-2 have conflicting clutches for technology package Z (one 

is a dry clutch; the other is a wet clutch)...” 

EPA’s Response: Both of the “Z” technology packages have a dual-clutch transmission. 

The specific type of DCT is a further detail which, although resulting in different levels of 

transmission efficiency, was not intended to confuse the reader. Several technologies, for 

example wet clutch DCTs and dry clutch DCTs, are applied differently between vehicle 

classes. In this case, Ricardo confirmed that a dry clutch DCT is an appropriate design for 

the standard car, while the wet clutch DCT is appropriate for other vehicle classes. 

Comment: ”What does it mean to “consider” NVH, but not quantify it?” 

EPA’s Response: The level of customer-accepted NVH is a subjective measure that is not 

subject to accepted industry-wide measurements techniques, metric quantifications and 

uniformly accepted levels. EPA requested that Ricardo use engineering judgment based on 

their vast experience in providing this form of NVH engineering services to the automotive 
industry to highlight any technology implementation that might cause a degradation in NVH 

that would be objectionable to the driver. 

Comment: “Page 49: The stated BMEP limits for naturally aspirated (13.5 bar) and boosted 

(in excess of 20 bars) engines seem too high for automotive applications...” 

EPA’s Response: Recent market data confirms Ricardo’s use of these levels of BMEP. For 

example, Toyota’s 3.5L engine (Lexus G350) is rated at 274 ft-lb of peak torque, which 

equates to about 13.5 bar BMEP for a naturally aspirated engine. Similarly, GM’s 

turbocharged 2.0L engine (Solstice GXP) achieves 260 lb-ft of torque (or 22.1 bar BMEP). 

Comment: “P59. Diesel. The system shown in Fig 5-19 is only high-pressure (HP) loop EGR. 

A better balance between in-cylinder emissions and aftertreatment required may be achieved 

with HP plus low-pressure loop EGR. EGR loop catalysts may not be adequately effective to 

prevent fouling.” 

EPA’s Response: A prime objective of this study was to quantify the synergies and 

effectiveness of representative mechanisms, rather than explore specific realizations of 

specific mechanisms. The system shown represents the modeling approach used for the 

vehicle simulation results reported. 

Comment: “Page 2: What does “unadjusted” refer to in the statement: “The unadjusted 

results for the EPA city, highway, and combined cycles. . .”?” 

EPA’s Response: The term “unadjusted” implies raw laboratory or unadjusted fuel economy 

results, as opposed to “adjusted” results which are modified to better reflect real-world 

driving conditions. Refer to 40 CFR 600.206 for further details. 

Comment: “Table 1-6 (and other corresponding tables): Define in the text what is meant by 

“FDR”, especially since transmission technology variances include gearless systems such as 

CVTs.” 

EPA’s Response: FDR – or Final Drive Ratio – is applicable even to continuously variable 

transmissions. As is the case with a traditional step-gear transmission, the operating gear (or 

theoretical torque conversion) ratio of a CVT is then multiplied by the FDR to provide the 

overall vehicle driveline gear ratio. 

Comment: Regarding Figure 4-5: “Why are the CO2 output levels for the base simulated 

vehicles not compared against the actual values? This is done for the fuel economy numbers. 

EPA’s Response: That calculation can be made by applying the gasoline GHG emissions 

factor to each of the baseline vehicles. 
Comment: There were multiple comments on the effect of technologies on vehicle weight, and 

the treatment of vehicle weight in the study. For example: “...Some technologies such as a 

diesel engine with a complicated emission control system could significantly affect vehicle 

weight with a corresponding negative effect on gas mileage and CO2 emission.” 

“In general there seems to be inadequate attention or discussion about weight differences among 

the technology packages. Are we to assume that all engine and transmission options had same 

weights? At least there should be some discussion of this. Specific example: boosted, 

downsized engines, pp. 50-51” 

Ricardo’s Response: “The intent was to make the study weight-neutral to the extent that no 

vehicle would change ETW class. Downsizing of diesels will offset heavier aftertreatment 

and may result in lower vehicle weight.” 

Comment: “More discussion of uncertainties in the analysis should be presented along with 

the findings, to add perspective. The report should not characterize the study as “scientific” 

unless data uncertainty is discussed and shown (in appropriate situations). In a less rigorous 

manner, the authors should still address the uncertainty associated with critical assumptions.” 

Ricardo’s Response: “The study was performed in a scientific and consistent manner, based 

on accurate modeling of the physics involved. Uncertainties from the simulation method are 

negligible, but the variations in applying the technologies to a vehicle (i.e. differences in 

actual specification, design, and calibration) are much greater than can be projected for a 

class of vehicles.” 

Comment: “Although numerous publications are cited for data, much of the input data are 

held as proprietary and undisclosed. This could give rise to the results of the study being 

challenged. Ricardo has an excellent international reputation, but will it be sufficient to deflect 

doubts as to accuracy of input data and assumptions? An alternate would be to use more data 

from the public domain.” 

Ricardo’s Response: “Ricardo data is proprietary information and cannot be released to 

the public. However, Ricardo's libraries and experience spans the world's manufacturers and 

product lines. Further, Ricardo used as much public-domain information as possible in the 

study. However, there was insufficient data available for the detailed simulation performed 

and so it was supplemented and verified against Ricardo proprietary data.” 

Comment: “Page 28: What is the “BSFC modifier” based on?” 

Ricardo’s Response: “It is based on proprietary Ricardo data.” 
Comment: “Page 28: It appears as though the simulation neglects the electrical loads on the 

alternator system when the radiator uses an electric fan (as is the case in all nontruck vehicles). 

Please clarify.” 

Ricardo’s Response: “These loads were included in the base vehicle electrical load and so 

were included for all cases with electric fan in the base configuration.” 

Comment: “Page 35: the statement that the comparison simulated and actual vehicle results 

shows “noticeable difference” is too subjective (there is a “noticeable difference” in all of 

them). Given the challenges involved in generating consistently rigorous sets of data for all 

cases and various subjective assumptions involved in the analysis, please correct the language 

and use appropriate words other than “scientific” and “significant”.” 

Ricardo’s Response: “The study was performed in a scientific and consistent manner, based 

on accurate modeling of the physics involved. However, the differences between the 

simulation results and measured data are largely due to differences between the input data 

which attempts to describe an average vehicle and, in some cases, measurements from an 

individual vehicle.” 

Comment: “P40. It would be useful to see the BSFC data that show the impact of cam 

phasers, said to be widely used. Hence the data should be relatively non-sensitive. Similarly, 

the valve control options are seen later as having major impact on fuel efficiency. The lack of 

supporting data in the report leaves the reader questioning the results.” 

Ricardo’s Response: “While the technology might be widely used, this is Ricardo 

proprietary data and cannot be shared. Ricardo invests significant time and effort in 

benchmarking the industry to obtain this data.” 

Comment: “Figure 3-3 (and other corresponding figures): Why do required power curves 

become constant at a certain speed for various loads? Does the heat removal with oil flow not 

increase with speed after a certain point?” 

Ricardo’s Response: “Heat removal does not increase above a certain speed because the 

oil flow from a conventional pump is limited by a pressure regulator. Although the 

conventional pump power continues to increase with speed, the flow through the engine does 

not.” 

Comment: “Page 82: This “torque-to-weight” ratio is very confusing, and doesn’t really 

contribute any meaning to the study. This review suggests you remove it (and its corresponding 

figure) from the discussion.” 

Ricardo’s Response: “The torque-to-weight ratio relates to the load levels that the engine 

runs at on a drive cycle, hence vehicles with a low torque-to-weight ratio will run at higher 

engine loads and so benefit less from camless technology.” 
Comment: “Table 7-9. We have seen diesel applications in prototype light trucks getting 35­

50% higher “tank mileage” than SI with similar performance (published). 20% gain seems very 

conservative. With good PCCI systems, we should see aftertreatment penalties closer to 3%. 

Consider including a simple explanation why 20% is the correct value in view of more optimistic 

published reports.” 

Ricardo’s Response: “The transmission was not changed and so the diesel engine operating 

points were not optimized. Refer to the discussion in Sec 7.2 and the footnote at the bottom of 

the table stating that optimization was not performed for each step.” 

Comment: “Engine up shift RPM for a V8 (p 26) appears to be too high. I believe this needs to 

be rechecked.” 

Ricardo’s Response:“P. 28 shows min speed for V8 upshift to be 1150rpm. This may vary 

based on vehicle stiffness but it is not out of line with industry practice.” 

Comment: “The fuel economy/CO2 benefits of a camless valvetrain depend on the power 

consumption of the camless system as well as the operating domain (cylinder deactivation, six 

cycle etc). These parameters should have been used for modeling and included in the report.” 

Ricardo’s Response:“Sec 5.1.7 discusses the power consumption issue, and sec 5.1.7.1 

discusses the operating domains enabled with camless. Sec 5.1.7.2 and 5.1.7.3 discuss the 

source of the data (published) and the power consumption issue again. Additionally, Sec 7.3 

specifically calls out camless and HCCI as low readiness technologies requiring long-term 

development.” 

Comment: “Section 3.4: It is assumed that electric power steering consumes no steering input 

on the EPA drive cycle and therefore that there is no parasitic loss from it. This is true, but there 

has to be some adjustment for generating electric energy for steering use. The electric energy 

consumed in steering will have an undetermined negative impact on fuel economy/CO2.” 

Ricardo’s Response:“The reviewer is correct that there will be an undertermined negative 

impact on FE/CO2, depending on the amount of steering done. Unless the amount of steering 

input is defined we cannot determine the impact. This study only considered the EPA city and 

hiwhway cycles and straight-ahead accelerations, so no steering inputs were included. They 

would be of off-center steering inputs. In addition, the parasitic loss from the PS pump 

during straight ahead driving offsets the negative impact of the electrically-driven pump.” 

Comment: “To a technical reader, Tables 7-5 through 7-9 are some of the more interesting. 

How much influence is there from the sequence in which technologies are added?” 

Ricardo’s Response:“Ricardo did not examine any other sequences for technology 

additions than those prescribed by EPA already stated in the study, so we cannot quantify the 

influence. 
EPA’s Response: The affect of technology-pairing and its accounting in a technology 

application sequence is an interesting and relevant issue that EPA intends to address in 

subsequent work. 

Comment: “P 30- Start Stop model. The model or strategy appears to hinge on coolant 

temperature as the principal signal to manage the on-off cycle. Is it well-established that the 

coolant temperature is indicative of the exhaust catalyst temp that is so crucial for emission 

controls? I would have thought a catalyst temp monitor would have been desired.” 

Ricardo’s Response: “(Coolant temperature) is indicative of exhaust temperature but there 

are other considerations that make using catalyst temperature (undesirable). Specifically, the 

coolant temperature is slower to warm up than catalyst temperature and so the engine should 

not be shut off until up to a minimum (coolant) temperature. 

Comment: “P60. Did the engine-out NOx map include much operation in PCCI modes? 

What fraction of operating range? The 60-75% LNT reduction may be a bit high for a very 

effective PCCI engine.” 

Ricardo’s Response: “PCCI was not used in the maps and that is why 60-75% effectiveness 

is stated. With aggressive application of PCCI not as much aftertreatment would be required 

and the fuel penalty would be lower.” 

Comment: “P62. The 550C regeneration temperature for DPF is rather high if a catalyzed 

device is used. Balance point temps are more like 350C. Would this lower the fuel penalty in the 

simulation?” 

Ricardo’s Response: “"The 550°C regeneration temperature is to facilitate active 

regeneration, whereby extra hydrocarbons are used to trigger a regeneration event. 

""Balance point"" is a term useful for catalyzed DPF systems where there is continuous 

passive regeneration of the DPF, usually by the reaction of NO2 with the carbon in the DPF. 

While a 350°C balance point temperature seems reasonable; the usefulness of the metric is 

suspect because it depends greatly on the specific test protocol used to estimate it. (That is, 

what else changes when one changes exhaust gas temperature?) The expectation is that 

LDD systems need some active regeneration capability, especially if the DPF is downstream 

of the deNOx device.” 

Comment: “References to the methodology as “scientific” based on a “physics-based 

modeling approach” are somewhat misleading. The descriptors “scientific” and “physicsbased’ for the model must be reconciled with evidence to the contrary in the paper. For 

instance, in some cases, there are steady-state dyno test data behind an engine map featuring a 

certain technology. In other cases, available data were scaled based on empirical/proprietary 

factors (i.e., “BSFC modifiers” and “empirical formula derived from several transmissions”-p. 

28, GHG-CO2 conversion factors). Please verify and correct the statements so as to create a 

realistic impression of the vehicle simulation.” 
 Ricardo’s Response: “The study was performed in a scientific and consistent manner, 

based on accurate modeling of the physics involved. The input data and maps were 

accumulated through several means, including test data and scaling of known quantities. 

Science can deal with empirical (measured) data as well as purely mathematically-derived 

data.” 

Comment: “It would be helpful to include a summary that defines the theoretical boundaries 

for CO2 reduction potential for powertrains, i.e., what can be achieved if the engine operated at 

the best efficiency all of the time allowing for some degradation during the warm up period. This 

would form a basis for a quick check on the validity of combining various technologies” 

EPA’s Response: The approach referred to above is used in the “lumped-parameter” 

technique of estimating impacts of multiple technologies (EPA used a similar approach in 

initially estimating technology synergies for its rule). The Ricardo modeling work was 

commissioned to validate EPA’s preliminary estimates drawn from theoretical potentials, not 

vice versa. EPA intends to publish a technical document that explains and compares results 

generated from both the “lumped-parameter” technique and Ricardo’s vehicle simulation 

results. 

General Editorial Comments 

The remaining comments were those consisting of an editorial nature (formatting and 

typographical suggestions). These comments, as appropriate, are reflected in Ricardo’s final 

report. As such, these comments have not been addressed in this document. 
Charge Letter Example: 

November 2, 2007 

Peer Reviewer 

(address) 

Dear Peer Reviewer: 

Thank you for agreeing to review the paper entitled A Study of the Potential Effectiveness of Carbon 

Dioxide Reducing Vehicle Technologies, October 2007, prepared by PQA/Ricardo, Inc. The paper 

was prepared in support of the Greenhouse Gas Rulemaking (GHG). The vehicle modeling 

paper is enclosed. 

We are working to continually improve estimates of GHG emission reduction from incorporation 

of technologies, and in this paper we were particularly interested in how particular technologies 

or technology packages differently affect different categories of automobiles. The five 

categories we examined include: small car, small MPV, large MPV, large car, small truck. 

Technologies include: variable valve train timing and lift systems, cylinder deactivation, 

turbocharged/down size engine, advanced transmission technologies, stop-start, diesel, etc. The 

performance criteria of the technology packages were compared to the performance criteria of 

current production vehicles through baseline modeling. Performance criteria such as “launch” 0-

30 mph, “on-ramp” 30-50 mph, “traditional acceleration” 0-60 mph, “passing” 50-70 mph, 

sustained grade capability at cruise speed, transmission shifting business and other NVH issues, 

Tier 2-bin 5 emissions and FTP cycle CO2 emissions levels (also available in terms of MPG) 

were considered and matched as practicable in the simulations of the final packages. Also 

presented should be some incremental vehicle simulation runs, which should enable a better 

understand of the synergistic consequences of combining multiple technologies to reach more 

stringent vehicle GHG standards. 

In regard to reviewing the enclosed report, please use the following criteria: 

1) clarity/understandability, 

2) reasonableness of methodology and assumptions, 

3) appropriateness of data, and 

4) recommendations for any alternate methodologies and/or data. 

When making recommendations, please make a distinction between clearly defined 

improvements that can be readily made based on data reasonably at hand to EPA and 

improvements that are more exploratory or dependent on data not readily available to EPA. The 

comments should be sufficiently detailed to allow thorough understanding by EPA or other 

parties familiar with the work. 

Your comments should be provided as an enclosure to a cover letter that clearly states your 

name, the name and address of your organization, what material was reviewed, a summary of 

your expertise and qualifications and a statement that you have no real or perceived conflicts of 

interest. The comments should be sent in care of Cheryl Caffrey to the following address: 
U.S. EPA 

Office of Transportation and Air Quality 

Assessment and Standards Division 

2000 Traverwood Drive 

Ann Arbor, MI 48105 

Also, send the cover letter and comments by e-mail to Cheryl Caffrey at caffrey.cheryl@epa.gov 

(provide comments in MS Word or a format that can be imported into MS Word so we can create 

a document that lists both your comments and our responses to these comments). Please do not 

provide the peer review materials or your comments to anyone else. 

We would appreciate receiving the results of this peer review in the shortest time frame possible, 

preferably by November 16. If you have any questions about what is required in order to 

complete this review, or if you find you need additional background material, please contact 

Matt Brusstar by phone at (734)214-4791 or by the email at brusstar.matt@epa.gov . 

As has been discussed with you, you will be paid a flat fee of $3,000 for this peer review. This 

fee was calculated based on an estimated 12 hours of review time at a rate of $250 per hour. In 

your cover letter, please indicate the number of hours spent on the review; spending fewer or 

more hours than our estimate will not affect the fee paid for this work, but will help us improve 

our future estimates. A purchase order form is also included hosing payment information. You 

may expect to receive payment in full within fourty-five (45) days of submitting your invoice 

and comments to Cheryl Caffrey. 

Thank you again for your time and consideration. 

Sincerely, 

Enclosure 
________________________________________________________________________________________ 

Reviewer Bio: 

AAI 

Assanis & Associates, Inc. 

3108 West Dobson Place 

Ann Arbor, MI 48105 

Tel: (734) 213-2513 

Fax: (734) 213-2512 

aai@comcast.net 

December 4, 2007 

Cheryl Caffrey 

U.S. EPA 

Office of Transportation and Air Quality 

Assessment and Standards Division 

2000 Traverwood Drive 

Ann Arbor, MI 48105 

Dear Cheryl: 

With this cover letter you will find my comments on the paper entitled, A Study of the 

Potential Effectiveness of Carbon Dioxide Reducing Vehicle Technologies, dated 

November 9, 2007. I received this report via email from EPA on November 9, 2007. 

The comments are organized according to the guidance in the November 2, 2007 

transmittal letter signed by Dr. Haugen of EPA. 

Also as requested, here is a brief summary of my qualifications, prepared as a third person 

biographical summary: 

Dr. Assanis received the B.Sc. degree in Marine Engineering from Newcastle University, 

England in 1980, and four graduate degrees from the Massachusetts Institute of 

Technology: S.M. in Naval Architecture and Marine Engineering (1982), S.M. in 

Mechanical Engineering (1982), Ph.D. in Power and Propulsion (1985) and S.M. in 

Management from MIT's Sloan School of Management (1986). He has worked as 

Assistant and Associate Professor (with tenure) at the University of Illinois at UrbanaChampaign from 1985-1994. He joined The University of Michigan in 1994 as Professor 

of Mechanical Engineering. He has served as the Founding Director of the 

interdisciplinary graduate program in Automotive Engineering between 1996 and 2002, 

and subsequently as Chair of the Department of Mechanical Engineering from 2002- 

2007. In parallel, he has revitalized the Mechanical Engineering Department’s teaching 

and research efforts in internal combustion engines. He currently serves as the Director 

of the Automotive Research Center, the Director of the Walter E. Lay Automotive 

Laboratory, and the Director of the Multi-University Consortium on Homogeneous 
Charge Compression Ignition Engine Research. He is also the Co-Director of the 

General Motors Collaborative Research Laboratory on Engine Systems. He is an 

international authority in the field of internal combustion engines, and has published over 

250 articles in journals and international conference proceedings. 

His expertise encompasses both modeling methodologies and experimental techniques 

for studies of the fundamental thermal, fluid and chemical phenomena that occur in 

advanced internal combustion engines and exhaust catalysts so as to develop systems 

with significantly improved fuel economy and dramatically reduced emissions. He is a 

Fellow of the Society of Automotive Engineers. He is an editorial board member of 

several journals and has organized or chaired over 60 sessions at international technical 

conferences. He is also the President of the engine consulting company Assanis & 

Associates, Inc. 

As requested in the transmittal letter, I hereby affirm that I have no real or perceived 

conflict of interest as a reviewer of the subject report. I am pleased to have been given 

the opportunity to review this report and make a modest contribution to EPA’s 

rulemaking process. Please feel free to contact me for clarifications on any of the review 

comments. 

Sincerely, 

Dennis N. Assanis 

Enclosure: 

Review comments on A Study of the Potential Effectiveness of Carbon Dioxide Reducing 

Vehicle Technologies, dated November 9, 2007 
Report Review on 

“A Study of Potential Effectiveness of Carbon Dioxide Reducing 

Vehicle Technologies” 

Ricardo, Inc. 

November 9, 2007 

SUMMARY COMMENTS 

The objective of this reported study is to identify the relative impact of novel and 

advanced vehicle technologies on fuel economy and greenhouse gases – specifically 

carbon dioxide (CO2). The objective is pursued by comparing different “packages” of 

advanced vehicle technology using a model-based vehicle simulation software in 

conjunction with experimental data and empirical rules. Vehicles comprising five 

different platforms are evaluated. Representative vehicles from each platform are 

identified for relevance and for limited validation of the simulation predictions for the 

baseline case. In the spirit of improving the quality of the study and the report, the 

reviewer provides several general and detailed comments for consideration by the 

contracting agency and the authors of the report. 

Overall, the report attempts to undertake an analytical technology assessment study of 

significant scope in a short amount of time. It does a fairly competent job at analyzing a 

select number of technologies and packages, mostly aimed at improving the gasoline IC 

engine and to a less extent the diesel engine. However, several promising technologies 

and fuel options for IC engine technologies (other than gasoline and diesel) which can 

make a significant contribution to the improvement of mpg and reduction of CO2 

emissions have not been considered, or even mentioned at all. A primary example of this 

is the hybridization of gasoline engines (other than mild start/stop options) which is in 

production today, achieving significant CO2 benefits. Another major omission is any 

mention of biofuels, which from the standpoint of a life cycle analysis have strong 

potential for reduction of CO2 emissions and CO2 sequestration. 

As it is, the executive summary of the report is not adding much value to the entire 

document. It merely recycles tabulated results that are repeated in other chapters of the 

document in exactly the same form, without any attempt of summarizing key findings for 

the reader. On the other hand, it goes into great length to provide disclaimers of what 

Ricardo was tasked to do and not to do. There is a place for this, such as in a preface, but 

the executive summary should provide to the reader a concise synopsis of the scope, the 

approach followed and the major fact findings – while being sensitive to not drawing 

conclusions. I recommend that all detailed tabulated results should be in the appendix, 

listed once and referenced throughout the report. I would also like to see a consistent and 

high-level “train of thought” throughout the summary with some very specific statements 

and reasoning for narrowing down the technology and fuel options to the ones selected. 

In general, the report is unnecessarily lengthy at places, while too laconic at other places. 

The draft can definitely benefit from re-organization and better balancing of its chapters. 
There is unnecessary duplication of tables that can be in the appendix and referenced. 

The reviewer attempts to point out further opportunities for shortening the report in the 

section providing “Detailed Comments”. On the other hand, Chapters 4 and 6 are very 

skinny and should be merged with other chapters. There should be more words 

summarizing the results (e.g., provide ranges of benefits), and assessing them critically 

(e.g., which technologies seem to incrementally or additively contribute the most), rather 

than just stating that the results are in the table below. More discussion of uncertainties 

present in the analysis should be presented along with specific findings so as to enable 

the reader to place the findings into proper perspective. In general, figures were not 

introduced in the text in the style they should. All figures and tables should be explicitly 

referred to and discussed in the text. Furthermore, figures must be identified by their 

figure number, not their relative position to the text. For example, Page 52 states 

“Typical cylinder pressure diagrams for recompression HCCI are provided in the first 

figure below.” 

References to the methodology as “scientific” based on a “physics-based modeling 

approach” are somewhat misleading. The afore-quoted statements suggest that the 

simulation is composed of rigorous, first-principle expressions for the various phenomena 

without using “correlations”, “empirical formulas”, and “phenomenological models”. Are 

these conditions truly met? Certain clues indicate that the latter is not the case. For 

instance, in some cases, there are steady-state dyno test data behind an engine map 

featuring a certain technology. In other cases, available data were scaled based on 

empirical/proprietary factors. For example, page 28 states “the models applies a BSFC 

modifier”, page 21 gives a multiplier factor for CO2 emissions, and page 28 states “based 

on an empirical formula derived from several transmissions. . . “. Please verify and 

correct the statements so as to create a realistic impression of the vehicle simulation. 

Related, and perhaps more important, the report should not characterize the study as 

“scientific” unless data uncertainty is discussed and shown (in appropriate situations). To 

be completely rigorous, no data can be claimed to be relevant or significant unless there 

is a way to quantify uncertainty. Realizing that this study does not probably need to go 

into such rigor, the author(s) should still address the uncertainty associated with critical 

assumptions. For example, page 35 states that the comparison between simulated and 

actual vehicle performs shows “noticeable difference”. This reviewer also sees a 

“noticeable difference” in all of the listed fuel economies. Whether these “noticeable 

differences” are significant or not is presently indeterminable. Given the challenges 

involved in generating consistently rigorous sets of data for all cases and various 

subjective assumptions involved in the analysis, please correct the language and use 

appropriate words other than “scientific” and “significant”. 

The author(s) occasionally write(s) in past tense. The report could be written in present 

tense (unless referring to specific actions that took place in the past, such as, “the engine 

was operated at x speed and y load”). A reader will always be reading the report in the 

present. 
GENERAL TECHNICAL COMMENTS 

In certain cases, technology options are quantized into discrete bins, when in fact we 

could very well see in production hybrid versions of the options much sooner. For 

instance, GDI/HCCI employing spark-ignition for part of the range (start-up and high 

load) and HCCI combustion mode for all other regimes. In many ways, HCCI is a 

combustion mode that can be realized through the integration of several of the technology 

packages presented and should not be viewed as a strap-on option. While camless is one 

way to enable HCCI (and will require a longer time horizon), HCCI can be realized via 

the use of cam profile switching/phasing and mechanical lift control. This is 

acknowledged in the report under the HCCI technology discussion of Chapter 5. If this 

option were to be pursued, the claimed benefits of the mechanical VVA systems can be 

augmented. At present, it is not clear which of the possible benefits of the VVA 

packages have been harnessed in each case (improvement of volumetric efficiency, 

elimination/reduction of throttling to reduce pumping losses, cylinder deactivation to 

reduce pumping losses, compression ratio variation to increase fuel economy and avoid 

knock, alteration of the combustion process by modulating trapped residual, etc). Overall, 

a more systematic analysis of technology package combinations is warranted as several 

are synergistic but not additive. Section 7.2 acknowledges this fact and is a start, but falls 

short of doing a comprehensive analysis. 

While diesels are considered as an optional package, most of the technology options 

explored seem to favor the gasoline package. Furthermore, the results of chapter 7 

present selected results in four categories, seemingly all for gasoline engines. This 

creates the appearance of imbalance. 

The reference and use of a “known factor” for every fuel, mentioned in section 2.10.2 to 

derive CO2 benefits from fuel economy results, is confusing. It would be desirable to 

show the analysis behind the ‘known factor” that was used to convert fuel consumption 

savings to vehicle CO2 equivalent output. Do these CO2 equivalent emissions include the 

CO2 released during the production of the respective fuels, or just the use (i.e. 

combustion) of the respective fuels? If the latter, different engine technologies may yield 

different combustion efficiencies and methane concentrations (which could be 

significantly different than the values reported in Table 2-8). Some language should be 

added to the report to identify the sources of uncertainty associated with the use of this 

factor equivalent. 

The focus on homogeneous stoichiometric GDI, at the request of EPA, seems to be 

unnecessarily too restrictive. Some GDI engines in production operate under the lean 

stratified mode when at part-load conditions, yet operate at homogenous stoichiometric 

conditions when requiring full power. This report seems to suggest that GDI engines 

operate with “one or the other” strategy, which limits the technology benefit to the 

identified charge cooling effect. Would the charge cooling effect alone really offer up to 

a 1.5 times increase in compression ratio? It is more plausible that the combined effects 

of stratified charge, lean mixture, and cooling effect could result in this benefit. 
DETAILED COMMENTS 

• Table of contents is missing the “front matter” contents (i.e. title page, table of 

contents, list of figures, etc). 

• Example of past tense language: Page 1, “Vehicle performance metrics were 

considered an important part. . . “ 

• Inconsistency observed between CO2 and CO2. 

• A clear objective is not stated in the Executive Summary. The motivation for this 

study as listed on Page 1 conflicts with the motivation listed on Page 13. Page 1 

states “The intended purpose of this study is to serve as an input to the EPA in its 

rule-making effort. . .” while Page 13 states “To overcome the limitations of the 

previous studies, the objective of the present study. . .” 

• Page 2: What does “unadjusted” refer to in the statement “The unadjusted results 

for the EPA city, highway, and combined cycles. . .”? 

• Page 3: It is not clear if there are two time-ratings or three time-ratings. Are the 

time ratings 1) in production now, 2) in production in 5 years, and 3) in 

production in 10 years? Or are the time ratings 1) in production now, and 2) in 

production in 5 – 10 years? 

• What is the convention for the technology package identifiers? It is not intuitive 

(i.e. Z, 1, 15, 15a, 15b, etc.?). 

• Table 1-1 and Table 1-2 have conflicting clutches for technology package Z (one 

is a dry clutch; the other is a wet clutch). This error exists in similar tables where 

the technology package is described. 

• Page 6: The friction-reduction factor is consistent for all technology packages, in 

spite of the technology packages using different sized engines. 

• Page 6: “. . .tables to distinguish their higher level of uncertainty. . .”: how is 

uncertainty quantified? 

• Table 1-6 (and other corresponding tables): Define in the text what is meant by 

“FDR”, especially since transmission technology variances include gearless 

systems such as CVTs. 

• Table 1-6 (and other corresponding tables): Should “Distance at 3 sec” be 

provided in units of miles (as opposed to meters), since the base convention used 

throughout is English system of units (the obvious and appropriate exception 

being g/mile of emissions). 

• Page 13, in the first statement under section 2.3: Correct “the modeling 
approached used” to “modeling approach”. Also, change “forward-facing” to 

“forward-looking” which is more standard terminology and to be consistent with 

what is mentioned in page 1. 

• Page 13: What does it mean to “include torques”, as mentioned in the statement 

“The model physics includes torques. . .” 

• Page 14: Can Tables 2-1 and 2-2 be combined, and perhaps orientated in 

landscape fashion to conserve space (or at least be easier on the reader)? 

• Table 2-3 (and other corresponding tables): Can’t the column headers be 

orientated horizontally, for ease on the reader (and create less white space). 

• Page 21: For convenience to the reader, please describe in more detail what the 

EPA’s “ETW” is, and how it is calculated. 

• Page 28: What is the “BSFC modifier” based on? 

• Page 28: It appears as though the simulation neglects the electrical loads on the 

alternator system when the radiator uses an electric fan (as is the case in all nontruck 

vehicles). Please clarify. 

• Page 28: What does it mean to “consider” NVH, but not quantify it? 

• Page 30 (and other instances): Should the 42V / 14V transformer be referred to 

such, as opposed to “DC-DC converter”? 

• Page 30: Example of past tense, “The 42V stop-start included. . . “ 

• Page 31: Replace statement that reads “It is assumed that the energy. . .” with “It 

is shown that the energy . . .” since you actually run a computation to verify this. 

• Page 31: In the statement that reads “requiring less that 1 kJ”, replace “that” with 

“than”. 

• Figure 3-2 (and other corresponding figures): Please define AC drive efficiency, 

and why it is seemingly used as a metric for these components. 

• Figure 3-3 (and other corresponding figures): The legend is confusing, and 75% 

required power legend identifier is unclear. 

• Figure 3-3 (and other corresponding figures): Why do required power curves 

become constant at a certain speed for various loads? Does the heat removal with 

oil flow not increase with speed after a certain point? 

• Figure 3-5: Cannot read y-axis label. 
• Figure 4-5: Why are the CO2 output levels for the base simulated vehicles not 

compared against the actual values? This is done for the fuel economy numbers. 

• Page 39-40: Should benefits to reduction of other emissions be identified if it is 

not part of the objective of this study? It seems to only be done for cam phaser 

technology; the implications of other technologies on NOx and HC emissions are 

not discussed. 

• Figure 5-3 (valve profile) is unclear. 

• Page 46, statement that reads “No major changes to engine architecture are 

required compared to a port fuel injection engine”: Is this statement really true? 

Don’t you have to add a high pressure fuel injection system? 

• Page 49: The stated BMEP limits for naturally aspirated (13.5 bar) and boosted 

(in excess of 20 bars) engines seem too high for automotive applications. Perhaps 

for 15L heavy-duty turbocharged diesel engines it is possible to reach 20 bar 

BMEP, however this reviewer believes a number closer to 12 bar BMEP is 

appropriate for full load turbocharged diesel automotive engines. 

• Page 49: What is the final paper number of the quoted SAE paper? Currently, the 

“accepted abstract” paper number is cited. 

• Figure 5-10 is an excellent example of how uncertainty bars on the data can 

indicate to the reader where differences in BSFC become significant. 

• Figure 5-11: Perhaps re-orientate the legend so that “Turbo SIDI I4” reads over 

top of its corresponding data set (and same is true then for “NA V8”). 

• Page 52: Leave out the statement that reads “HCCI is also known as . . .”. The 

current “name count” of HCCI combustion is over 20. 

• Figures 5-14 – 5-16. Why are these figures in the report? They are not discussed 

in the text and really don’t contribute anything to the discussion. 

• Page 58: The reviewer suggests to change the statement “Diesel engines gain 

efficiency through high compression ratios and significantly reduced throttling or 

pumping losses” to “Compression ignition, diesel engines enjoy an efficiency 

advantage compared to spark-ignition engines due to their higher compression 

ratios, and overall fuel lean, unthrottled operation.” 

• Figure 5-19 (and other corresponding figures): A throttle is not listed in the text. 

While it is assumed that the throttle is used to help control EGR flow, it should 

either be discussed as such in the text or be removed from the figure so as to not 

mislead the reader about diesel engines. 
• Page 66 contains too much white space. 

• Figure 5-25 through Figure 5-27 are too small. 

• Tables 7-1 (and other corresponding tables): Why are the base conditions not 

provided for comparison to the performance data? 

• Page 82: This “torque-to-weight” ratio is very confusing, and doesn’t really 

contribute any meaning to the study. This review suggests you remove it (and its 

corresponding figure) from the discussion. 

• Page 84: Statement that reads “The effect on fuel economy and CO2. .. “ should 

be pluralized. 
Reviewer Bio: 

November 16, 2007 

Chinu Bhavsar 

1415 Packard 

Ann Arbor, Mi 48104 

To: 

U.S. EPA 

Office of Transportation and Air Quality 

Assessment and Standards Division 

2000 Traverwood Drive 

Ann Arbor, Mi 48105 

Attn: Ms. Cheryl Caffrey 

Subject: Review of the paper entitled A Study of the Potential Effectiveness of Carbon Dioxide 

Reducing Vehicle Technologies, Draft dated November 9 2007, prepared by PQA/Ricardo, 

Dear Ms. Caffrey 

In response to the EPA purchase order EP08B000029 for peer review of the subject report, and 

Dr. David Haugen's letter dated November 2, 2007, I am submitting my comments and 

recommendations per the attached document. 

I feel that I have the right experience and qualifications to review the subject report. Here is a 

brief summary of my qualifications and expertise. 

I am a retired engineer with MS degree in Mechanical Engineering from Stanford University. I 

worked at Ford Motor Company for 36 years prior to my retirement in October 2005. I spent 

most of these years at Ford on developing advanced and research powertrain (Engine & 

Transmission) technologies. Of those years around 5 were spent on vehicle performance and 

fuel economy modeling methodologies. I also chaired Ford's powertrain Fuel Economy Forum 

the purpose of which was to monitor and prioritize engine, transmission and vehicle technologies 

that improve vehicle fuel economy and reduce GHG emissions. 

At the present time I am retired and I have no real or perceived conflict of interest that could 

possibly affect my analysis and review of the subject paper. 

I have spent a total of eighteen (18) hours to review the paper and provide my comments 

Thank you for giving me the opportunity to review the paper. 

Sincerely, 

 Chinu Bhavsar 

 Tel: 734-678-1096 or 734-663-5861 

 Email:cpbhavsar@comcast.net 
REVIEW OF THE PAPER ENTITLED 

A STUDY OF THE POTENTIAL EFFECTIVENESS OF CARBON DIOXIDE 

REDUCING VEHICLE TECHNOLOGIES, DRAFT DATED NOV 2007 BY 

PQA/RICARDO INC. 

(By: Chinu Bhavsar) 

Introduction: This report is being provided to EPA in response to a purchase order request from 

EPA to review the subject paper and provide comments. I have reviewed the paper and offer the 

following comments. 

Clarity/understandability 

There is a large volume of detailed and reasonably accurate information in the report. It appears 

that Ricardo Inc. has used excellent modeling and analytical methods to predict vehicle CO2 

emissions and performance for the various technology bundles EPA requested. 

I suggest that the report could further be improved to make it more concise and comprehensible. 

It is my opinion there is too much information in the body of the report; some of it is redundant 

and the report could be better organized to make it more presentable. 

Here are my specific recommendations and comments for each section of the report 

Executive summary: Pages 7 thru 11: Show CO2 benefit for only one FDR for each package 

identified by EPA. There is no need to clutter the executive summary with all of the details for 

various FDR's. Those details are already and should be only in the appendix. Removing FDR 

details would have no significant impact on the findings of the report 

Pages 14-15 combine tables 2-1 and 2-2. There is no need to repeat information from table 2-1 

in table2-2 

Pages 16 through 20 FDR rows could be eliminated by stating, "Various FDR's were used" 

Pages 36 & 37 can be eliminated or moved to the appendix. Page 38 (fig 4-5) is sufficient to 

indicate that the modeling used correlates very well with the test data. 

Section 5.0: most of the description of individual technologies should be moved to the appendix. 

This is like an encyclopedia of advanced powertrain technologies. Only the relevant data (source 

of efficiency maps, maps & logic used for modeling etc) should be left in section 5.0. 

There should have been a mention of the can torque actuated phaser system in section 5.1.1 this 

type of phaser provides fast response and reduces energy consumption 
Section 6.0: Technology readiness estimates: It should be mentioned that these might be market 

dependent. In European and Japanese markets where they have low sulfur and better quality 

fuels and different customer performance expectations (than US), it may be possible to deploy 

certain advance technologies earlier than the US. 

Section 7.0 Show only CO2 benefit and move fuel economy to the appendix. 

Reasonableness of methodology and assumptions. 

Ricardo appears to have used state of the art methodology to conduct vehicle CO2 emission and 

performance predictions. They have used appropriate parameters and constraints to define 

acceptable operating zones for various technologies. However, I am not clear on one topic. Did 

the analysis include the effect each technology had on vehicle weight? Some technologies such 

as a diesel engine with a complicated emission control system could significantly affect vehicle 

weight with a corresponding negative effect on gas mileage and CO2 emission. 

Cylinder deactivation operating zone (section 3.3) would be dependent on the number of 

cylinders and engine displacement to vehicle weight ratio. As such those parameters should be 

incorporated in a detailed analysis. 

Engine up shift RPM for a V8 (p 26) appears to be too high. I believe this needs to be rechecked. 

The fuel economy/CO2 benefits of a camless valvetrain depend on the power consumption of the 

camless system as well as the operating domain (cylinder deactivation, six cycle etc). These 

parameters should have been used for modeling and included in the report. 

Section 3.4: It is assumed that electric power steering consumes no steering input on the EPA 

drive cycle and therefore that there is no parasitic loss from it. This is true, but there has to be 

some adjustment for generating electric energy for steering use. The electric energy consumed in 

steering will have an undetermined negative impact on fuel economy/CO2 

Appropriateness of data 

Ricardo has used in house benchmark data and technology development data where available. 

They have used data from external sources when they did not have internal data. This is very 

appropriate 

Since I do not have access to the Ricardo in house data, I am not in a position to judge the quality 

of such data. But I would like to state that the results of the analysis in some cases produce 

higher fuel economy/CO2 benefits than my experience would indicate. I recommend that the 

results for the following packages be rechecked 

Package Z for Standard vehicle class 

Package 16 for full size vehicle class 
Package 6b for large MPV vehicle class 

Package 10 for truck vehicle class 

Section 6.1.1 & 6.1.2 Data supplied by EPA: If there is data to support these assumptions, it 

should be included in the report. 

Recommendations for any alternate methodologies and /or data 

It would be helpful to include a summary that defines the theoretical boundaries for CO2 

reduction potential for powertrains. I.e. what can be achieved if the engine operated at the best 

efficiency all of the time allowing for some degradation during the warm up period. This would 

form a basis for a quick check on the validity of combining various technologies. 

Conclusion: The quality and content of the report are excellent. Certain modifications in the 

presentation of the analysis and results are recommended to improve clarity and understanding. 

Without these changes the report is difficult to follow even for a person well informed on the 

topic. 

This review has been for prepared for EPA and submitted to them on Nov 16th, 2009 by: 

Chinu Bhavsar, a retired automotive engineer 

1415 Packard 

Ann Arbor, MI 48104 
Reviewer Bio 

Cheryl Caffrey 

U.S. EPA 

Office of Transportation and Air Quality 

Assessment and Standards Division 

2000 Traverwood Drive 

Ann Arbor, MI 48105 

Dear Cheryl: 

With this cover letter you will find my comments on the paper entitled, A Study of the Potential 

Effectiveness of Carbon Dioxide Reducing Vehicle Technologies, dated November 9, 2007. I received 

this report via email from EPA on November 9, 2007. The comments are organized according to 

the guidance in the November 2, 2007 transmittal letter signed by Dr. Haugen of EPA. 

Also as requested, here is a brief summary of my qualifications, prepared as a third-person 

biographical summary: 

Ron Graves joined Oak Ridge National Laboratory in 1976 after receiving his PhD in 

Mechanical Engineering from the University of Tennessee. As a graduate student he conducted 

research on the use of anhydrous ammonia as an engine fuel, ultimately including experiments in 

a vehicle in a student competition. He is presently a member of the Engineering Science and 

Technology Division, and is the Director of the Fuels, Engines, and Emissions Research Center 

(FEERC) with programmatic, technical, and strategic responsibility for this Department of 

Energy (DOE) User Facility and the numerous projects conducted therein. Ron was national 

project manager for the DOE Alternative Fuels Utilization Program from 1984-1990. He 

continues in a prominent role in that as well as other DOE fuels and engines programs. In 1997 

he was chosen by DOE as the technical coordinator for the Diesel Crosscut Team and continues 

in that role. He was a member of the DOE/Industry Advanced Petroleum Based Fuels (APBF) 

Steering Committee, the DOE program that contributed heavily to the EPA rule for lowering 

sulfur in diesel fuel in December 2000. He led the emission control subteam for the 21st Century 

Truck Technical Roadmap. In 2002, he was appointed as ORNL’s representative to the DOE 

21st Century Truck Partnership “Lab Council” to facilitate government-industry interactions in 

that initiative. He is an invited member of the FreedomCAR Advanced Combustion & Emission 

Control Tech Team. Ron has a record of approximately 55 publications and reports that 

encompass subjects in fossil energy, internal combustion engines, fuels, and materials. He has 

been invited to deliver tutorial presentations in major technical conferences as well as 

informative talks to non-technical audiences. He is a Fellow of the Society of Automotive 

Engineers and has organized or chaired over twenty technical sessions at technical conferences. 

He has three patents, with one additional in progress. He is a licensed Professional Engineer in 

the State of Tennessee. 

As requested in the transmittal letter, I hereby affirm that I have no real or perceived conflict of 

interest as a reviewer of the subject report. I am pleased to have been given the opportunity to 
review this report and make a modest contribution to EPA’s rulemaking process. Please feel free 

to contact me for clarifications on any of the review comments. 

Sincerely, 

Ronald Graves, PhD 

Center Director 

Fuels, Engines, and Emissions Research Center 

Oak Ridge National Lab at NTRC 

2360 Cherahala Blvd 

Knoxville, TN 37932 

Enclosure: 

Review comments on A Study of the Potential Effectiveness of Carbon Dioxide Reducing Vehicle 

Technologies, dated November 9, 2007 
Review Comments on 

A Study of Potential Effectiveness of 

Carbon Dioxide Reducing Vehicle Technologies 

November 9, 2007 Draft 

Submitted by 

Ron Graves 

Oak Ridge National Laboratory 

November 18, 2007 

Clarity and Understandability (this section of review comments also includes minor editing, 

grammar, word-processing issues) 

Many comments and questions that came to mind while reviewing this report could be covered 

in a Preface added to this report, written by EPA. Why no hybrids in the study? What 

justification for aero and rolling drag factors? Why the UDDS instead of LA92 cycles? 

In the Executive Summary inform reader straightaway that CO2 and more customary measure of 

mpg are related merely a conversion factor based on fuel properties. Figure 1-1. 

Section 1.3. Technology misspelled 

Table 1-1 Start off without using so many acronyms. Improving this may be as simple as using 

smaller font in table to allow more complete wording. If acronyms essential, define them up 

front. 

For clarity, define the “combined” mpg and CO2 values and state whether any correction factors 

were applied. 

P13. First line of 2.4. that should be than 

P35. Last paragraph. ....vehicle data was attributed.... Should be were 

The technology descriptions are informative and clear for the most part. 

P59 Last line typo ....Tier 2 Bin 5 (T2B5).... 

Tables 7-5 through 7-19 presently include the baseline vehicle characteristics. This adds clarity 

and ease of reading. Recommend including baseline info in Tables 7-1 through 7-4. 

Table 7-5. The list of incremental actions does not appear to be consistent with Package Z. 

Where are CCP, DVVL effects in Table 7-5? Other similar tables appear to be consistent with 

package descriptions. 
To a technical reader, Tables 7-5 through 7-9 are some of the more interesting. 

In tables 7-5 through 7-9, how much influence is there from the sequence in which technologies 

are added. A comment on this would be useful. 

Reasonableness of Methodology and Assumptions 

Page 3 and in Exec Summary, the mostly-uniformly applied reductions in aero drag and rolling 

resistance are without supporting data or analysis. Perhaps this is covered in another study, but 

is conspicuously lacking the rigor of the remainder of the analysis. Aero and rolling loss factors 

for trucks are different than cars. Why? 

In section 7 we see that the 20% aero drag reduction produces incremental benefits as great or 

greater than most powertrain options, furthering the need to explain the reasonableness of this 

assumption. At least cite any thorough analysis to establish feasibility. 

Section 2.1, the philosophy of maintaining vehicle performance in the analyses is commendable 

and appropriate. The report would be additionally instructive if the effect of reduced 

performance on CO2 was shown for some example vehicles. 

P 15, Sect 2.8. The reader is left to assume that other powertrains like hybrids are being 

addressed separately by EPA. 

P 30- Start Stop model. Engine shut-off/restart is certainly an effective technology for reducing 

idling fuel use. The model or strategy appears to hinge on coolant temperature as the principal 

signal to manage the on-off cycle. Is it well-established that the coolant temperature is indicative 

of the exhaust catalyst temp that is so crucial for emission controls? I would have thought a 

catalyst temp monitor would have been desired. 

It is apparent that the impact of the cost of the technology options is beyond the scope of this 

study. Nonetheless, the cost or price will tend to have great impact on implementation of any 

technology. 

Appropriateness of data 

See many of comments in previous section. 

Although numerous publications are cited for data, much of the input data are held as proprietary 

and undisclosed. This could give rise to the results of the study being challenged. Ricardo has 

an excellent international reputation, but will it be sufficient to deflect doubts as to accuracy of 

input data and assumptions. An alternate would be to use more data from the public domain. 

P40. It would be useful to see the bsfc data that show the impact of cam phasers, said to be 

widely used. Hence the data should be relatively non-sensitive. Similarly, the valve control 

options are seen later as having major impact on fuel efficiency. The lack of supporting data in 

the report leaves the reader questioning the results. 
P.50-51. Boosted downsized engines might be expected to have less weight. The report does 

not address this. Does the vehicle simulation account for weight differences of any of the 

powertrains? The boosted-downsized engine would appear to have the greatest weight reduction 

potential. 

P54. Outlook for HCCI. We are likely to see some partial use of HCCI modes within 5 years. 

P59. Diesel. The system shown in Fig 5-19 is only high-pressure (HP) loop EGR. A better 

balance between in-cylinder emissions and aftertreatment required may be achieved with HP 

plus low-pressure loop EGR. EGR loop catalysts may not be adequately effective to prevent 

fouling. 

P60. Did the engine-out NOx map include much operation in PCCI modes? What fraction of 

operating range? The 60-75% LNT reduction may be a bit high for a very effective PCCI 

engine. 

P62. The 550C regeneration temperature for DPF is rather high if a catalyzed device is used. 

Balance point temps are more like 350C. Would this lower the fuel penalty in the simulation? 

In general there seems to be inadequate attention or discussion about weight differences among 

the technology packages. Are we to assume that all engine and transmission options had same 

weights? At least there should be some discussion of this. 

Table 7-9. We have seen diesel applications in prototype light trucks getting 35-50% higher 

“tank mileage” than SI with similar performance (published). 20% gain seems very 

conservative. With good PCCI systems, we should see aftertreatment penalties closer to 3%. 

Consider including a simple explanation why 20% is the correct value in view of more 

optimistic published reports. 

Recommendations for Alternate Methods 

See comments in previous section. 

Show examples to indicate degree of sensitivity to drive cycle for representative technology 

package (LA92, for example, vs UDDS). 

The report would be additionally instructive if the effect of reduced performance on CO2 

emissions was shown for some example vehicles. 

The report overall deserves high praise for its breadth and thoroughness, especially considering 

the accelerated schedule for performing the simulations and writing the document.