How things work: OMEGA modeling case study based on the 2018 Toyota Camry
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
WORKING PAPER 2018-03
How things work: OMEGA modeling case
study based on the 2018 Toyota Camry
Author: John German
Date: February 27, 2018
Keywords: CO2 emissions, fuel consumption, EPA modeling, OMEGA, Novation
The 2018 Toyota Camry incorpo- commissioned by the largest vehicle improve their analysis. The com-
rates eight technology upgrades that manufacturer association and per- m i t te e re co g n i ze s t h a t s u c h
are specifically modelled in the U.S. formed by Novation Analytics, are m e t h o d s a r e ex p e n s i ve b u t
Environmental Protection Agency’s inaccurate and underpredict future believes that the added cost is
Optimization Model for Reducing technology benefits. well justified because it produces
Emissions of Greenhouse Gases from more reliable assessments
Automobiles (OMEGA) and Lumped (Recommendation 8.3).1
Parameter Model (LPM). This large Background
number of simultaneous technology Modeling efficiency technology is As noted by the National Academy
upgrades makes the Camry an excel- complicated and difficult as there are of Sciences committee, the agencies
lent case study of how accurately the synergies and overlaps between tech- have developed sophisticated
EPA’s models project future technol- nologies. The efficiency impact of co m p u te r s i m u l a t i o n m o d e l s to
ogy benefits and handle synergies any technology varies depending on address technology synergies. The
between technologies. what other technologies are bundled EPA has developed its own full-
with it, the order in which the model vehicle computer simulation model,
This paper carries out that case study. adds technologies to a vehicle, and ALPHA, to estimate the effects of
It defines and adjusts for all differ- the characteristics of the vehicle. The individual technologies and tech-
ences between the 2015 and 2018 importance of accurately modeling nology packages. The ALPHA data
Camry and all differences between these synergies has been widely and outputs are used to calibrate
the EPA’s technology assumptions acknowledged and promoted. For the EPA’s Lumped Parameter Model
and technology on the 2018 Camry. example, the 2015 National Academy (LPM), which is used to account for
The results show that the actual CO of Sciences study on CAFE stated: synergies between technologies.
2
reductions of 18.6% achieved in the Finally, the EPA’s OMEGA model is
2018 Camry exceed the 17.7% reduc- Further, the committee notes used to assign the technology results
tions predicted by EPA models. This that the use of full vehicle simu- and synergies to 29 vehicle classes
confirms that the OMEGA and LPM lation modeling in combination and to assess the cost of compliance
models accurately predict both new with lumped parameter modeling
technology benefits and synergies and teardown studies contributed
1 Committee on the Assessment of
between technologies. If anything, substantially to the value of the Technologies for Improving Fuel Economy
they are somewhat conservative. Agencies’ estimates of fuel con- of Light-Duty Vehicles, Phase 2, Cost,
It also suggests that other studies sumption and costs, and it recom- effectiveness and deployment of fuel
economy technologies for light-duty vehicles
contradicting EPA model outcomes, mends they continue to increase (2015). https://www.nap.edu/read/21744/
including specifically a study the use of these methods to chapter/1#vii.
Acknowledgements: The author would like to thank Dan Meszler of Meszler Engineering Services for his assistance with the OMEGA model.
© INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION, 2018 WWW.THEICCT.ORGHOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
with standards. The LPM is built into • LPM-informed OMEGA tech- 2018 Toyota Camry. Compared with
the various OMEGA modeling runs.2 nology packages for the Prior the baseline 2.5L 2015 Camry, Toyota
Determination continue to fail added for the 2018 model eight new
reasonable tests for plausibil- or improved technologies used in
The issue ity. Notwithstanding EPA com- EPA modeling. This makes the 2018
B a s e d o n a st u d y by N ova t i o n ments to the contrary, the Alliance Camry an excellent test of the OMEGA
Analytics,3 the Alliance of Automobile believes that the plausibility limits model’s ability to account for syner-
Manufacturers (AAM) asserted in chosen remain appropriate. gies between technologies. This report
comments on the Reconsideration of assesses engine, transmission, and
• Only 18% of the Prior
EPA’s Final Determination that there road load improvements to the 2018
Determination’s technology pack-
was systematic bias in the LPM:4 Camry and compares CO2 projections
ages are traceable to the ALPHA
full vehicle simulations through the by the OMEGA model using the same
The AAM highlights the following technologies with actual CO2 reduc-
LPM. The underlying data for other
issues identified by the study for EPA’s tions in the 2018 Camry. If the vehicle
LPM-based assessments is unclear.
attention for reconsideration of the meets or exceeds the OMEGA projec-
Prior Determination. • The LPM-based technology tions—seven years early—that would
package simulations appear to strongly support the accuracy of the
• The addition of power-to-weight have a high-efficiency, low-CO
2 EPA modeling.
and vehicle road load does little to bias, on average as compared to
improve the accuracy of the LPM. the underlying ALPHA data.
Model inputs
2 The EPA recently announced that as part of I n a m e e t i n g w i t h t h e AA M o n
The first step was to map the tech-
its efforts to improve modeling, the functions November 8, 2017, the EPA directly
performed by the LPM will be integrated nologies on the 2015 and 2018 Camry
into the ALPHA model. The EPA is making
addressed the LPM modeling issues
to the EPA’s technology codes. Table 2
the maps in ALPHA more realistic and raised by the AAM. 5 However, this
lists the technologies on each vehicle
replacing old “development” maps using report takes a different approach.
benchmarking of recent engines. These and the associated technology codes.
improvements are not considered here, as
Rather than argue about the merits
Technology changes coded into the
the improved model has not been released. of individual pieces of the modeling
model are highlighted in red, to make
However, a recent EPA presentation said: procedure, this report conducts a
“The revised fleet compliance modeling it easy to identify the changes from
methodology would be substantially similar
case study comparing LPM/OMEGA
2015 to 2018. Here is a brief descrip-
to the previous methodology, but with a set modeling of CO 2 reductions for a
tion of each technology:
of auto-calibrated response surface equations specific vehicle with the actual CO2
taking the place of the LPM.” (EPA Office of
Transportation and Air Quality, Powertrain
reduction achieved adopting a wide Oil and engine friction. The 2015
efficiency in EPA’s technical assessment to- range of technologies. Camry uses 0W-20 oil, and the 2018
date, and plans for ongoing updates Meeting
Camry uses 0W-16 oil. The EPA codes
with AAM and Global Automakers [2017, Previously, a meaningful comparison
September 21].) The EPA’s future modeling the base 2015 Camry with EFR1, or
revision thus should not significantly affect
could not be conducted because a
engine friction reduction 1, and LUB,
the results reported here. valid test of the EPA’s modeling
for use of 0W-20 engine oil viscosity.
3 The AAM contracted with Novation Analytics assumptions requires the simultane-
for a review of the LPM’s calibration from the While we have not been able to find
ous adoption of multiple technolo-
ALPHA model. That report, Evaluation of the quantification of the fuel economy
Environmental Protection Agency’s Lumped gies that the EPA assumed would be
benefits of 0W-16, it has lower friction
Parameter Model Informed Projections from widespread in 2025, and a suitable
the Proposed Determination, was provided at high temperatures, and there are
case-study vehicle did not exist. Now
to the EPA as Attachment 3 to the AAM’s suggestions that the fuel economy
comments on the Reconsideration of EPA’s one does after the redesign of the
Final Determination.
benefit could be significant.6 Also, EPA
4 AAM comments re: Request for Comment on modeling of ATK2 engines, or Atkinson
Reconsideration of the Final Determination 5 EPA Memorandum from Kevin Bolon to cycle engines for non-hybrid vehicles,
of the Mid-Term Evaluation of Greenhouse Docket EPA-HQ-OAR-2015-0827, Stakeholder
assumes that they have the EFR2, or
Gas Emissions Standards for Model Year Meeting with Novation Analytics and EPA
2022–2025 Light-Duty Vehicles; Request for summary presentation on Technical Response
Comment on Model Year 2021 Greenhouse to Assertions of ‘ALPHA-to-OMEGA Bias’.
Gas Emissions Standards (EPA–HQ–OAR– EPA Office of Transportation and Air
2015–0827; FRL–9966–62–OAR). Submitted Quality, (December 18, 2017). https://www. 6 Tammy Neal, “The skinny on OW-16 oil,”
to Docket ID No. EPA–HQ–OAR–2015–0827 regulations.gov/document?D=EPA-HQ- National Oil & Lube News, June 30, 2017.
by AAM on October 5, 2017. OAR-2015-0827-10995 https://noln.net/2017/06/30/skinny-ow-16-oil/.
2 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2018-03HOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
engine friction reduction 2, package.7 Fuel injection. Gasoline Direct Injection and no aero for 2015 to LRRT2 and
The modeling of the 2018 Camry was (DI) was added for the 2018 Camry Aero1 for 2018.
run with both EFR1+LUB and EFR2 engine and is coded as such.
coding to evaluate the sensitivity of Table 1. Road load coefficients for 2015
this assumption, but the EFR2 case is Atkinson cycle and cooled EGR. Both
and 2018 Toyota Camry.
considered to be more appropriate. technologies were added for the 2018
Camry and are coded as such. The 4-cylinder – 3,500
Cam phasing. The 2015 Camry uses Camry engine has a 13.0:1 compres- pounds ETW
variable valve timing on both intake sion ratio and does not have fast Coefficients 2015 2018
and exhaust camshaft (dual VVT-i, engine warmup. Note that ATK2 in the A 27.232 21.006
where “i” means intelligent control). EPA modeling is based on an engine
B 0.04319 0.17604
The EPA codes the base 2015 Camry as with a 14.0:1 compression ratio and
C 0.019374 0.016028
VVT.8 The 2018 Camry adds an electric fast engine warmup, with a lower CO2
motor on the intake camshaft for faster penalty on the cold start portion of the ETW = Equivalent test weight.
and more precise control, but the EPA Federal Test Procedure (FTP). See Appendix A for discussion of road load
coefficients.
has no coding to reflect this, and the
benefits are unknown and likely to be Rolling resistance and aerodynamic
drag. The 2018 Camry has significantly Performance. While not a technology
small. So the 2018 model is also coded
lower road load coefficients, as shown change, the EPA’s modeling assumes
as VVT.
in Table 1. The road load is about 15% that vehicles maintain constant levels
Transmission. The 2015 Camry uses a lower at 15 mph and 10% lower at 40 of performance when adding technol-
6-speed automatic transmission with mph. Weighted by the speeds on the ogy. Thus, any change in performance
electronic controls, which Toyota calls FTP and highway cycle, the average also needs to be evaluated for trad-
ECT-i. The 2018 Camry also uses ECT-i road load reduction is about 11% eoffs with efficiency. Performance is
and increases the number of gears to (see Appendix A for details). This is proportional to the power-to-weight
eight. The 2015 transmission clearly reflected in the modeling by reducing ratio of the vehicle, so both weight
fits the TRX11 transmission code defi- both aerodynamic drag and rolling and performance changes need to be
nition, and the 2018 transmission, the resistance, using low rolling resistance evaluated. The base 2015 and 2018
TRX21 code. tires (LRRT), by 10%. This is handled by Camrys were both tested at 3,500
changing the model inputs from LRRT1 equivalent test weight (ETW), and
Steering. Both the 2015 and the 2018
Camry use electric power steering
Table 2. Actual Camry technology, 2015 and 2018, and EPA coding. Changes from the
(EPS). Note that there is an error in the 2015 Camry to the 2018 Camry are highlighted in red.
EPA’s coding for the 2015 Camry, as path
0 for the Camry does not include EPS. Actual Camry technology EPA coding
To correct for the presence of EPS on 2015 2018 path 0 2015 2018
the baseline 2015 Camry, we modeled Oil 0W-20 0W-16 LUB LUB LUB / —
scenarios with and without EPS.
Engine friction EFR1 EFR1 EFR1 / EFR2
Accessories. The 2018 Camry added Cam phasing dual VVT-i VVT-iE (I) VVT VVT VVT
variable cooling and a variable oil Transmission 6A w ECT-i 8A w ECT-i TRX11 TRX11 TRX21
pump, meaning that both are com- Steering electric electric EPS EPS
puter-controlled for increased effi-
var. cooling &
ciency. This fits the EPA definition Accessories IACC1
oil pump
o f I ACC 1 ( i m p rove d a cce ss o r i e s
package 1), so IACC1 is added for the Fuel injection SPI DI + SPI DI
2018 Camry. Atkinson cycle 13:1 CR ATK2
EGR cooled cEGR
Rolling resistance -11.3 % LRRT1 LRRT1 LRRT2
7 Note that LUB is removed from the model
inputs when EFR2 is added, as LUB is Aero Cd = 0.28 road load Aero1
included in the EFR2 package.
3,500 3,500
8 Note that the LPM codes dual-VVT as dual Weight (ETW)
cam phasing.
pounds pounds
WORKING PAPER 2018-03 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 3HOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
even their curb weight differed by less Table 3. Actual CO2 emissions for 2015 and 2018 Camry compared with modeled results
than 10 pounds. However, the 2018 for specific technology packages.
Camry engine has significantly greater
% reduction vs
power than the 2015 Camry, with gCO2 /mi Model 2015 Camry
horsepower increasing by 14% from
Actual reduction
178 to 203 and torque rising by 8% veh. Model v no-tech Actual Model
from 170 ft-lb to 184 ft-lb. In addition, OMEGA tech path 0 237.5 15.2%
the number of transmission gears
2015 actual 232.0 234.7 16.2%
increased from six to eight, which also
increases performance by keeping 2018 actual w/o EFR2 188.9 189.9 32.2% 18.6% 19.1%
the engine at higher rpm after each 2018 actual 188.9 187.9 32.9% 18.6% 19.9%
shift and providing higher gear multi- Adjustments Adj. Model CO2 adj.
plication for launch. While the actual 14:1 to 13:1 CR 188.9 18.6% 19.0% + 1.2%
performance improvement is clearly +10% performance 188.9 18.6% 17.7% + 1.5%
more than 10%, for the purposes of
this comparison the performance gain
part this reflects that the 2015 baseline to 14:1 is 0.9%.11 Modeling in this paper
is conservatively estimated at 10%.
CO2 in the modeling is 2.7 g/mi higher conducted with Autonomie found
This reduces the downward adjust-
than the actual readings. The percent- that the fuel-consumption reduction,
ment of the modeled fuel economy to
age reductions from 2015 to 2018 were if performance is maintained, is 1.32
reflect the fuel economy/performance
19.9% for the modeling results and times the brake efficiency improve-
tradeoff and thus causes the modeled
18.6% for the actual 2018 Camry. ment. So increasing the compression
fuel economy to be slightly overstated.
ratio from 13:1 to 14:1 would reduce fuel
However, this is not the most appro- consumption by 1.19%. Applying this to
priate comparison, as the modeling
Analysis results assume a 2025 powertrain with
the 2018 Camry modeling narrows the
percent reduction from 19.9% to 19.0%
Table 3 presents actual CO2 emissions additional optimization and improve- percent—only 0.4% more than the
for the 2015 and 2018 Camry from ments beyond those incorporated in actual reduction of the 2018 Camry
EPA test car lists and compares the the 2018 Camry and assume constant compared with the 2015 Camry.
findings with the modeled results for vehicle performance. As noted above,
the technology packages applied spe- the 2018 Camry uses a 13.0:1 com- OMEGA assumed constant perfor-
cifically to the Camry.9 pression ratio, while EPA modeling mance for all of the modeling results.
assumes 14.0:1, the Camry does not However, the 2018 Camry has sig-
Comparing the “2018 actual” row, have the fast engine warmup assumed nificantly better performance than
where EFR2 is included in the 2018 in EPA modeling, and the 2018 Camry the 2015 Camry, as noted above. For
Camry technology, the reductions has at least 10% better performance modeling purposes, the overall per-
achieved by the 2018 Camry do not than the 2015 Camry. formance gain was conservatively
quite match the reductions projected
estimated to be 10%. While there is no
by EPA modeling. The actual CO2 emis- Based on a 2014 paper by Speth et al.,10 consensus on the tradeoff between
sions are very close, just 1.0 g/mi, or the brake efficiency improvement for performance and fuel consumption,
0.5%, higher than the modeled result. In increasing compression ratio from 13:1 it can be derived from the impacts of
11 This is extrapolated from the modeled
9 The file MS_Control_in2025AB_20161118_ 10 Raymond L. Speth, Eric W. Chow, Robert results, as the benefits of increasing
icm_aeoR_ScenarioPackages was used to Malina, Steven R. H. Barrett, John B. Heywood, compression ratio decrease as the baseline
generate the model results. A description of and William H. Green, “Economic and compression ratio increases. For example,
the OMEGA model and links to download the Environmental Benefits of Higher-Octane the paper found that increasing the
model, including this file, can be found at: Gasoline,” Environmental Science & compression ratio from 10.5:1 to 11.5:1 would
https://www.epa.gov/regulations-emissions- Technology, 2014, 48 (12), 6561-6568 DOI: improve brake efficiency by 1.9%, or more
vehicles-and-engines/optimization-model- 10.1021/es405557p. https://pubs.acs.org/doi/ than twice the 0.9% benefit of increasing
reducing-emissions-greenhouse-gases abs/10.1021/es405557p from 13:1 to 14:1. See Appendix B for details.
4 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2018-03HOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
weight reduction on fuel economy.12 Comparison with footprint the OMEGA model properly accounts
Reducing weight by 10% results in for synergies between technologies
targets
about a 5.2% decrease in fuel con- and does not overpredict technology
sumption with a 10% increase in The 2018 2.5L Camry meets its 2022 benefits. In fact, its projections are most
acceleration. Reducing weight by 10% footprint target without any consid- likely conservative.
while maintaining constant levels of eration of air conditioning or off-cycle
performance, for example by down- credits, without weight reduction, and Another unavoidable conclusion is that
sizing the engine, results in about a without any kind of hybridization, not the Novation critique of EPA modeling
6.6% decrease in fuel consumption. even stop/start.13 Just maximizing off- is demonstrably wrong. There is clearly
Thus, the impact of increasing per- cycle credits of 10 grams of CO2 per no systematic bias in the LPM, and
formance by 10% results in roughly a mile (g CO2/mi) and air conditioning the 2018 Camry can easily meet its
1.5% increase in fuel consumption or efficiency credits of 5 g CO2 /mi would 2025 targets without hybridization
CO2 emissions. allow the Camry to almost meet the beyond possibly a stop/start system.
2024 targets. The Camry still has seven This further suggests that Novation’s
Applying this performance adjustment years to make modest improvements analyses are not properly constructed
to the 2018 Camry modeling drops the and can easily reach its 2025 target and that the bias exists in Novation’s
modeled reduction from 19.0% to 17.7% by adding a stop/start system, with modeling, not the EPA’s.
—significantly less than the actual modest reductions of weight, aerody-
18.6% reduction of the 2018 Camry namic drag, or tire rolling resistance, or
versus the 2015 Camry. even petitioning the EPA for additional APPENDIX A
off-cycle credits beyond those listed in Rolling resistance and
Note that this result does not account the off-cycle menu. aerodynamic drag
for calibration improvements from
2018 to 2025. Minor improvements Road load coefficients are generated
to technologies and calibrations are Conclusion using a coast-down test on a track.
routine and will certainly increase the For a given vehicle weight, the longer
Before considering differences in perfor- it takes for the vehicle to lose velocity,
CO2 reduction that can be achieved mance, OMEGA modeling of the tech-
with this technology set by 2025. the lower the tire rolling resistance
nology improvements in the 2018 Camry or aerodynamic drag, or both. The
Also note that a likely conservative almost exactly matches the actual
adjustment was made for the impact vehicle speed versus time curve is
reductions achieved by the vehicle after fitted using A, B, and C coefficients,
of the improved performance of the adjusting for technology differences,
2018 Camry on fuel economy, plus no where the A coefficient is a fixed value
such as lower compression ratio and regardless of speed, B is a function of
adjustment was made for the lower higher CO2 after cold start. However, this
cold start fuel consumption included vehicle speed, and C is a function of
does not take into account the much the square of vehicle speed.
by OMEGA in their ATK2 technology, higher performance of the 2018 Camry.
which is also conservative. After properly adjusting for the perfor- The 2018 Camry had significantly
mance gains, the 2018 Camry achieved lower A and C road load coefficients
a CO2 reduction of 18.6%, significantly than the 2015 Camry, although the B
12 Details of the calculation of the tradeoffs greater than the 17.7% predicted by the coefficient was higher (see Table A-1).
between fuel economy and performance adjusted OMEGA modeling. And this
are in Appendix B. Note that Appendix B
also provides an example of the 2018 Honda is without accounting for seven more
Table A-1. Road load coefficients for 2015
Accord, which uses a similar turbocharger years of development and calibration
system on both the base 1.5L and the
and 2018 Toyota Camry.
improvements and the reductions in
optional 2.0L engines. Compared with the
1.5L Accord engine, the 2.0L engine increases cold start fuel consumption modeled by 4-cylinder – 3,500
horsepower by 31% from 192 to 252, and OMEGA, plus a likely conservative per- pounds ETW
torque, by 42% from 192 ft-lb to 273. Using formance adjustment. This confirms that Coefficients 2015 2018
the 6-speed manual as the control (as the
automatics are different for the 1.5L and the A 27.232 21.006
2.0L), the 1.5L is rated at 30 mpg and the 13 John German, “Technology Leapfrog:
B 0.04319 0.17604
2.0L at 26 mpg, or 13% lower. So, for every Or, all recent auto technology forecasts
10% increase in performance on this engine, underestimate how fast innovation is C 0.019374 0.016028
fuel economy decreased by about 4%—or happening,” ICCT blog, September 25,
over 2.5 times the amount calculated from 2017. https://www.theicct.org/blog/staff/ ETW = Equivalent test weight.
the weight-reduction formulas. technology-leapfrogging
WORKING PAPER 2018-03 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 5HOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
Figure A-1 illustrates the total road
2018 vs 2015 Camry Road Load
load from the A, B, and C coefficients
120 24%
at different vehicle speeds.
Road Load (pound-force)
Percentage difference between
Figure A-2 shows the speed 100 20%
distribution on the FTP and highway
2018 and 2015 Camry
test cycles. Weighting the 2015 and 80 16%
2018 2.5L Camry road load (blue and
red lines in Figure A-1) by the FTP 60 12%
speed distribution (blue line in Figure
A-2) yields an average road load 40 8%
reduction of 12.8%, and weighting by
the highway speed distribution (red 20 4%
line in Figure A-2), 10.4%. Finally,
2015 2018 % reduction
weighting the FTP and highway 0 0%
results by 55% city and 45% highway 0 5 10 15 20 25 30 35 40 45 50 55 60 65
yields an overall average road load Vehicle speed (mph)
reduction of 11.3%.
Figure A-1. Road load comparison of 2018 and 2015 2.5L Camry.
APPENDIX B FTP and Highway Test Cycle Speed Distribution
Performance tradeoffs with 120 24%
fuel economy
2018 Camry %
Percentage difference between
100 20%
The tradeoff between performance reduction in
# seconds at vehicle speed
road load
and fuel consumption is difficult
2018 and 2015 Camry
80
to calculate. Theoretically the fuel- 16%
consumption increase with improv- 60
ing performance should diminish in 12%
the future as engines improve fuel 40
Highway
consumption at low engine loads. No FTP 8%
consensus has been reached on how 20
to quantify the tradeoff. 4%
0
0 5 10 15 20 25 30 35 40 45 50 55 60 65
The approach taken here is to derive
the performance versus fuel economy -20 0%
FTP # sec Hwy # sec % reduction
tradeoff from the impacts of weight
reduction on fuel economy. Reducing Figure A-2. FTP and highway test cycle speed distributions and related reductions in
weight affects both fuel consump- road load for 2018 Camry compared with 2015 Camry.
tion and performance. Most studies
only technology variant.14 The results 0.467 %, and 0.447% per % change
of the impacts of weight reduction
of this evaluation revealed average in vehicle mass for vehicles executing
have found that a 10% weight reduc-
CO 2 emission changes of 0.456%, the NEDC, WLTP low road-load, and
tion directly results in about a 4.5%
WLTP high road-load cycles, respec-
decrease in fuel consumption. To tively. While not listed in this report, the
14 Dan Meszler, John German, Peter Mock,
generalize the CO 2 effects of mass and Anup Bandivadekar, CO2 reduction same methodology applied to the US
reduction, as part of an ICCT study on technologies for the European car and cycles revealed average CO2 emission
European post-2020 CO2 standards, van fleet: a 2025-2030 assessment
methodology and summary of compliance changes of 0.596% and 0.426% per
ICCT performed a detailed analysis of costs for potential EU CO2 standards, % change in vehicle mass for vehicles
26 technology packages developed (ICCT: Washington, DC, November, 2016). executing the FTP and highway test
https://www.theicct.org/sites/default/
by FEV (spanning all modeled vehicle files/publications/EU-Cost-Curves_ICCT_ cycle, respectively. Weighting the FTP
classes) where mass reduction was the nov2016.pdf and highway results by 55%/45% yields
6 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION WORKING PAPER 2018-03HOW THINGS WORK: OMEGA MODELING CASE STUDY BASED ON THE 2018 TOYOTA CAMRY
an average of 0.520% per % change in weight reduction. Thus, the impact on 192 ft-lb for the 1.5L. Using the 6-speed
vehicle mass. fuel economy of increasing perfor- manual as the control, because the
mance by 10% is roughly the fuel- automatics are different for the 1.5L
However, 10% weight reduction also economy impact without correcting and the 2.0L, the 1.5L is rated at 30
improves performance by 10%. Modeling for performance, or 1 – 5.2% = 94.8%, mpg and the 2.0L at 26 mpg, or 13%
of the impact of weight reduction while divided by the fuel-economy impact lower. So, for every 10% increase in
maintaining constant levels of perfor- after correcting for performance, or horsepower, fuel economy decreased
mance—for example, by downsizing 1 - 6.6% = 93.4%. This yields about a by 4.3%, and for every 10% increase
the engine—is difficult, as it is affected in torque, fuel economy dropped by
1.5% increase in fuel consumption or
by powertrain characteristics, vehicle 3.2%. Overall, for a 10% gain in perfor-
CO 2 emissions with a 10% improve-
attributes, and how the performance mance, fuel economy fell by roughly
ment in performance.
is adjusted. A more reliable method 4%. This is over 2.5 times the amount
is to evaluate the change in the total The 2018 Honda Accord provides a calculated from the weight-reduction
energy required to drive a vehicle over quick check on the accuracy of this formulas, indicating that the perfor-
a specific drive cycle. ICCT developed calculation. The vehicle offers a good mance adjustment used for the 2018
such a method as part of the 2016 comparison, using a similar 4-cylinder Camry is most likely conservative.
ICCT study on European post-2020 turbocharger system on both the base
CO2 standards. It was later applied to Table B-1. 2018 Honda Accord performance
1.5L and the optional 2.0L engines,
the US FTP and highway test cycles to and fuel economy comparison.
and each engine can be paired with
generate lightweighing benefit inputs a manual 6-speed transmission. This
to the OMEGA model.15 Because the 2018 Honda Accord w/ M6 transmission
minimizes the confounding factors of
relationship between the various road- different engine types, number of cyl-
HP ft-lb MPG
load parameters (i.e., mass, rolling inders, and transmissions. 1.5L 192 192 30
resistance, and aerodynamic drag) 2.0L 252 273 26
varies across vehicles, estimates were As shown in Table B-1, the 2.0L engine % change 31.3% 42.2% -13.3%
made for six different types of vehicles. is rated at 252 horsepower, 31% more MPG decrease
The mid-size car estimate was a 6.6% than the 1.5L’s 192. The 273 ft-lb of per 10% HP/ft-lb -4.3% -3.2%
decrease in fuel consumption for a 10% torque for the 2.0L is 42% higher than increase
15 Nic Lutsey, Dan Meszler, Aaron Isenstadt,
John German, and Josh Miller, Efficiency
technology and cost assessment for 2025-
2030 light-duty vehicles, (ICCT: Washington,
DC, 22 March, 2017). https://www.theicct.
org/publications/US-2030-technology-cost-
assessment
WORKING PAPER 2018-03 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION 7You can also read
