Technical Report May 2015

Certification Test Approach for the Phase II 

Greenhouse Gas Regulations

Erik Dykes and Mihai Dorobantu, Eaton
Acknowledgements

The authors would like to recognize Eaton and its customer colleagues, specifically, the Environmental 

Protection Agency, Paccar, Navistar, Cummins, and Allison who provided the many hours of technical 

discussion and support to execute this work.
TABLE OF CONTENTS

I. Introduction........................................................................................................................................................4

II. Primary Certification Approach..........................................................................................................................4

Engine Fuel Mapping Procedure ............................................................................................................................4

The Greenhouse Gas Emission Model (GEM) Simulation ......................................................................................4

Powertrain Test Methodology ...............................................................................................................................5

III. Alternate Certification Approach – Fuel Mapping .........................................................................................6

IV. Test Configuration ..........................................................................................................................................6

Alternate Certification Approach – Engine Fuel Mapping......................................................................................6

Powertrain Test Methodology ...............................................................................................................................8

V. Certification Test Procedures.............................................................................................................................9

Alternate Certification Approach – Engine Fuel Mapping......................................................................................9

Powertrain Test Methodology ............................................................................................................................ 10

VI. Analysis........................................................................................................................................................ 11

Alternate Certification Approach – Fuel Mapping .............................................................................................. 11

Powertrain Test Methodology ............................................................................................................................ 15

VII. Conclusions.................................................................................................................................................. 18

Appendix A - Vehicle Configurations for Alternate Fuel Mapping Approach.......................................................... 20

Appendix B – Alternate Fuel Mapping Approach Test Results................................................................................ 21

Appendix C - Vehicle Configurations for Powertrain Test....................................................................................... 22

Appendix D – Powertrain Test Results.................................................................................................................... 23

Appendix D – Powertrain Test Results (Cont’d) ...................................................................................................... 24
I. Introduction

The United States Environmental Protection Agency (U.S. EPA) and the National Highway Traffic Safety 

Administration (NHTSA) are currently developing the testing protocols and stringencies for the second 

phase of the Heavy-Duty (HD) Greenhouse Gas (GHG) Regulations. The complementary U.S. EPA and 

NHTSA standards that make up the Heavy-Duty National Program apply to combination tractors (semitrucks), heavy-duty pickup trucks and vans, and vocational vehicles (including buses and refuse or 

utility trucks). The first phase of the HD GHG program went into effect in 2014 and will continue 

through 2018. A joint phase 2 effort is underway with the U.S. EPA and NHTSA to develop a more 

stringent HD Carbon Dioxide (CO2) standard beyond 2018. The analysis is focusing on technology, cost 

feasibility and methods to verify and track CO2 and fuel economy levels. The testing and certification 

protocols that are under development involve an engine fuel mapping procedure, updates to the 

accuracy, validity, and further refines the existing Greenhouse Gas Emission Model (GEM) and a 

powertrain test option that shows the deep engine-transmission integration fuel efficiency (FE)

benefits. The development of updated test procedures and certification methods to include the 

powertrain efficiencies ensure new technologies are credited for reduction in CO2 levels and ensure

the long-term investment development of new engine and transmission technologies.

II. Primary Certification Approach 

Engine Fuel Mapping Procedure

A 143-point engine fuel mapping procedure is being implemented in the regulation as the primary 

approach to characterize and construct a steady-state fuel map for use in the Greenhouse Gas 

Emissions Model (GEM). A fuel map is generated for each engine hardware and software combination 

over a series of steady-state engine operating points to determine a series at a minimum of 13 equally 

spaced speed points ranging from idle to the maximum speed and 11 equally spaced, normalized 

torque values ranging from zero torque to maximum torque at each of the speed points making a total 

of 143 steady state tests points. The normalized torque values are expressed as a percentage of 

maximum torque, at a given engine speed. This type of mapping approach is currently being 

developed for the European Commission, which is in the process of establishing test procedures and a 

vehicle simulation model Vehicle Energy Consumption Calculation Tool (VECTO) that will be used to

certify heavy duty vehicle CO2 emissions as part of the type-approval procedure. 

The Greenhouse Gas Emission Model (GEM) Simulation

The Greenhouse Gas Emission Model (GEM) was developed by the EPA as a means to track compliance 

with the proposed HD GHG and fuel efficiency standards which covers Class 7 and 8 tractors and Class 

2b-8 heavy-duty vehicles. The GEM is similar in concept to a number of vehicle simulation tools 

developed by commercial and government entities. The customized simulation model uses pre-defined 

parameters that are consistent across various manufacturers to predict the CO2 emissions from HD 

trucks by using a set of pull-down menus determined by the truck configuration (engine, transmission, 

driveline, vehicle frontal area, rolling resistance, mass, tire radius, aerodynamic drag, etc...) as shown in 

Figure 1. The GEM simulation model uses various inputs to characterize a vehicle’s configuration (such 

as weight, aerodynamics, and rolling resistance) and predicts how the vehicle would behave on the 

road when it follows a driving cycle (vehicle speed versus time). The agency uses these standardized 

input parameters in the simulation model for all seven proposed subcategories of combination 

tractors. The vehicle compliance model architecture, which is comprised of six systems: Ambient, 

Driver, Electric, Engine, Transmission, and Vehicle. The GEM produces a cycle-weighted grams 
CO2/ton-mile and gallons/1,000 ton-mile result which incorporates the drive cycle weightings of the 

ARB transient cycle, 55 mph cycle, and 65 mph cycle depending on class of vehicle.

Figure 1: Greenhouse Gas Emission Model (GEM) main interface

EPA Greenhouse Gas Emission Model, Version 1.0. Available at http://www.EPA.GOV

Powertrain Test Methodology

A powertrain test includes both the engine and transmission coupled to a real-time vehicle model

which encompasses the remaining vehicle systems. The power absorber / generator (dynamometer) is 

connected directly to the transmission output shaft to act as the drive wheels of the test vehicle. The 

dynamometer accommodates the additional rotational inertia and speeds associated with the inclusion 

of the transmission and individual transmission gear ratios. The dynamometer generates speed and 

torque at the output side of the transmission to mimic a real world driving condition while fully 

exercising the engine and transmission controls. The transmission will cause the engine to mimic the 

same driving conditions as witnessed during the actual vehicle drive cycles. The GEM vehicles cycles 

can be utilized by the powertrain test so the results can be directly input into the GEM model for 

certification. Figure 2 depicts the actual powertrain system test configuration that is utilized to 

exercise the real vehicle controls. The powertrain test provides an opportunity to evaluate the complex 

interactions of engine and transmissions in a controlled, repeatable, high fidelity manner and 

quantifies the engine-transmission deep integration optimization. Powertrain testing is a tool that 

allows improved optimization of powertrain performance, emissions, and fuel economy and fully 

exercises the real engine and transmission controls through the vehicle model. 
Figure 2: Powertrain test configuration

III. Alternate Certification Approach – Fuel Mapping

An alternate certification approach was examined to characterize and construct a steady-state fuel

map for use in the Greenhouse Gas Emissions Model (GEM). An alternate method was investigated to 

determine if a feasible, reliable, repeatable, cost effected approach could be determined without 

adding additional test burden to the OEM. The procedure is addressed in detail under the certification 

test procedure section of this report. In summary the alternate method constructs a 9-point surface 

for each regulatory cycle (55 MPH with road grade, 65 MPH with road grade, and ARB) by generating

engine speed and torque profiles based on the intended applications and vehicle characteristics (mass, 

Crr, Cd, frontal area, axle ratio) using GEM. The profiles generated are then run on an engine 

dynamometer to determine the BSFC for each profile. The steady state BSFC maps are then input into 

GEM with the specific vehicle parameters to determine the vehicle BSCO2 certification results

IV. Test Configuration

This section includes a description of engine test cell used to generate the alternative certification 

approach for the engine fuel mapping as well as a description of the powertrain test set-up and 

methodology. The engine, aftertreatment system, transmission, test cell set-up and specific test cycles

utilized to generate the results are shown. The engine calibrations tested was emission certified for 

2013 CARB and EPA.

Alternate Certification Approach – Engine Fuel Mapping

The engine-only test cell as shown in Figure 3 was sized to accommodate a heavy-duty (HD) engine. A 

Cummins 15 liter ISX engine rated to 336kW (450 hp) with peak torque of 2375 Nm (1750 ft-lb) was 

used for the evaluation. A HD aftertreatment system was installed to meet the EPA and CARB 

emissions standards. The aftertreatment system utilized both a Diesel Particulate Filter (DPF) and a 

Selective Catalytic Reduction (SCR) system. To maintain a baseline condition for the DPF during testing

a DPF regeneration was forced prior to each set of tests to clean the DPF of stored particulates. The 

SCR system was operated during testing as would be witnessed in-vehicle operation to reduce NOx. 

The exhaust emissions were collected continuously using a Horiba Mexa7100D emission bench direct 
from the exhaust stream post aftertreatment system. The fuel was measured continuous during each 

test cycle using a ReSol RS438A-200 Fuel Flow Measurement System. The testing is completed using 

ultra low sulfur diesel fuel with a maximum sulfur concentration of 15 PPM. The engine intake air is 

temperature, humidity and pressure controlled to 25°C, 53% and 99kPa, respectively. All 

temperatures, pressures, fuel flow and emissions measurements were logged at a rate of 10 Hz.

Figure 3: Engine only configuration – alternative certification approach

The test cycles utilized for the engine-only alternate fuel mapping approach were generated using 

GEM. An example 65MPH speed and load trace used for the engine-only set-up is shown in Figure 4. 

Three separate vehicle configuration were input into the GEM model and the speed and load points 

generated for each of the regulatory cycles (ARB, 65MPH, and 55 MPH). A total of nine traces were 

generated for each cycle. A total of 27 engine tests were ran (3 vehicle configurations x 3 test cycles x 

3 axle ratios). Each individual cycle was repeated two times consecutively and emission data sampled 

during the second cycle. 

Figure 4: 65MPH engine-only cycle generated using GEM
Powertrain Test Methodology

The powertrain test cell as shown in Figure 5 was sized to accommodate a powertrain from a relatively 

heavy-duty vehicle. The vehicle test weight was 30,391 kg [67,000 lbs.]. The powertrain tested 

included a Cummins 15-liter ISX engine with an Eaton 10-speed automated manual transmission. The 

engine maximum rated performance was 336kW (450 hp) at 1800 rpm with peak torque of 2375 Nm 

(1750 ft-lb) at 1000 rpm and was operated using two separate calibrations; one base calibration for 

testing with the 10-speed UltraShift PLUS LAS transmission and an additional calibration with 

SmartTorque2 (ST2) technology for testing in conjunction with the 10-speed Fuller AdvantageTM (FASA) 

transmission. Both engine calibrations tested were emission certified for 2013 CARB and EPA. The 

dynamometer was sized to accommodate the engine’s peak torque multiplied by the transmission’s 

maximum gear reduction. The aftertreatment system utilized both a Diesel Particulate Filter (DPF) and 

a Selective Catalytic Reduction (SCR) system. To maintain a baseline condition for the DPF during 

testing a DPF regeneration was forced prior to each set of tests to clean the DPF of stored particulates. 

The SCR system was operated during testing as would be witnessed in-vehicle operation to reduce 

Nitric of Oxides (NOx). The exhaust emissions were collected continuously using a Horiba Mexa7100D 

emission bench direct from the exhaust stream post aftertreatment system. The fuel was measured 

continuous during each test cycle using a ReSol RS438A-200 Fuel Flow Measurement System. The 

testing is completed using ultra low sulfur diesel fuel with a maximum sulfur concentration of 15 PPM. 

The engine intake air is temperature, humidity and pressure controlled to 25°C, 53% and 99kPa, 

respectively. All temperatures, pressures, fuel flow and emissions measurements were logged at a rate 

of 10 Hz.

Figure 5: Heavy-Duty (HD) powertrain test cell configuration

Three regulatory drive cycles were tested to verify the Powertrain methodology 1) the California Air 

Resources Board (ARB) Transient cycle, 2) a 65 mph [105 kph] cycle with road grade, and 3) a 55 mph

[88 kph] cycle with road grade. Each individual cycle was repeated two times consecutively and 

emission data sampled during the second cycle. Figure 6a shows a vehicle speed trace for the ARB 

transient test cycle having an average vehicle speed of 15.3 mph [24.6 kph] and a maximum speed of 

47.5 mph [76.5 kph]. The cycle distance is 2.8 miles. The transient cycle is operated for 668 seconds 

and emissions collected the entire duration. Figure 6b shows a vehicle speed trace for the 65 mph test 

with road grade. The road profile was fully reflective of real world driving as it included a +/- 2% grade 
change with a cycle distance of 12.4 miles. Figure 6c shows a vehicle speed trace for the 55 mph test 

with road grade. The road profile was fully reflective of real world driving as it included a +/- 2% grade 

change with a cycle distance of 12.5 miles.

Figure 6: a) California Air Resources Board (ARB) transient cycle, b) 65 mph [105 kph] cycle with road 

grade, and c) 55 mph [88 kph] cycle with road grade

V. Certification Test Procedures

Alternate Certification Approach – Engine Fuel Mapping

An alternate certification approach was evaluated for mapping the brake specific fuel consumption 

(BSFC) of an engine. An alternate method was investigated to determine if a feasible, reliable, 

repeatable, cost effected approach could be achieved in place of the primary approach of a 143-point 

steady state engine fuel mapping procedure being implemented in the phase 2 HD GHG regulation. 

The vehicle application range was first determined with the intent of selecting the correct range to test 

the engine to its full operating capacity. The method investigated generated an engine speed and 

torque profile based on the intended applications for each of the regulatory drive cycles (55 mph cycle 

with road grade, 65 mph cycle with road grade, and ARB transient). Three separate pre-defined vehicle 

configuration were used to generate the regulatory cycles through the GEM simulation tool. The predefined vehicle configurations were chosen to span a wide range of engine speed over vehicle speed 

[rpm/mph] values that the engine may be subject. A total of 9 tests were generated for each 

regulatory cycle. Once the speed and torque traces were created the profiles were then used to 

construct a total of 27 engine tests (3 generic vehicles x 3 test cycles x 3 axle ratios). Each of the test 

cycles was then run on an engine dynamometer to generate a nine (9) point BSFC surface plot for each 

regulatory cycle. The engine BSFC data generated was input into GEM and used with the specific set of 

vehicle parameters (tire size, Crr, Cd, axle ratio, transmission gear ratio, and mass) to generate the 

vehicle CO2 [g/ton-mile] certification results as shown in Figure 7. 

(a) (b) (c)
Figure 7: Procedure for alternate certification approach – engine fuel mapping

Powertrain Test Methodology

A powertrain test methodology was developed to recommend a powertrain test procedure using 

actual hardware in-place of EPA’s GEM simulation tool to determine brake specific fuel consumption 

(BSFC). The test methodology as shown in Figure 8 provided an opportunity to evaluate the complex 

interactions of engine and transmissions in a controlled, repeatable, high fidelity manner, quantifying 

any engine-transmission deep integration optimization that may not be captured in GEM. The 

powertrain test procedure first defined the intended application range for the powertrain being 

evaluated, and for each regulatory drive cycle determined the correct range of vehicle applications. 

The intent of selecting the correct vehicle application range was to test the powertrain to its full 

operating space. A set of matrices were then generated for each regulatory cycle (ARB transient, 

65mph cycle with road grade, and 55mph cycle with road grade) from the powertrain test results using 

the decided application range as shown in Figure 8. A total of 27 powertrain tests were executed 

assuming 3 drive cycles x 3 vehicles x 3 axle ratios. The cycle work was calculated using GEM for the 

specific vehicle parameters (Cd, Crr, frontal area, and mass) for each drive cycle. The specific cycle 

work was then used to interpolate from the matrix generated from the powertrain test the actual BSFC 

point. The single BSFC point was then input into GEM to determine the final certification data. If a 

specific vehicle cycle work or axle ratio is outside the vehicle application range tested, then 

interpolation is not valid and a powertrain test for that vehicle may be necessary. 
Figure 8: Powertrain test methodology

VI. Analysis

Alternate Certification Approach – Fuel Mapping

The BSFC surface plots shown in Figure 9 represent GEM simulation runs for the alternate approach 

completed on 192 different truck configurations over each regulatory drive cycles (55, 65 mph SS and 

ARB transient). Average engine speed divided by average vehicle speed (denoted as N/V) has been 

used as a map axis to represent the nature of the engine speed operation on the cycle. Engine cycle 

work has been used as a second map axis to represent the engine loading on the cycle. The BSFC 

results provided a well behaved surface plot for each of the drive cycles. The initial GEM results 

showed promise for the alternate map approach providing a well behaved surface for extrapolation. 

Figure 9: a) ARB Transient, b) 65 MPH, c) 55 MPH GEM BSFC surface plots – 192 truck configurations

Three separate pre-defined vehicle configuration were used to generate the test cycles through GEM. 

A total of 9 tests were generated for each regulatory cycle (3 pre-defined vehicles x 3 axle ratios). The 

cycles were then configured and run on engine dynamometer. Average engine speed divided by 

average vehicle speed (denoted as N/V) has been used as a map axis to represent the nature of the 

engine speed operation on the cycle. Engine cycle work has been used as a second map axis to 

represent the engine loading on the cycle. BSFC surface plots were generated using a grid fit method 

for each cycle as shown in Figure 10. The BSFC relationship is well behaved as also observed from the 

65

70

75

80

11 12 13 14 15

160

170

180

190

200

N/V [rpm/mph]

ARB Transient

Work [bhp-hr]

BSFC [g/bhp-hr]

10

20

30

40

25 30 35 40 45 50

140

160

180

200

N/V [rpm/mph]

65MPH SS

Work [bhp-hr]

BSFC [g/bhp-hr]

10

15

20

25

30

20 25 30 35 40

140

160

180

200

N/V [rpm/mph]

55MPH SS

Work [bhp-hr]

BSFC [g/bhp-hr]

a) b) c)
GEM simulation outputs shown in Figure 9. The results provide a well behaved surface for 

extrapolation. 

Figure 10: a) ARB transient, b) 65 mph, c) 55 mph BSFC surface plots

To validate the engine BSFC surface fit two additional vehicle configurations were generated to provide 

values that fell between the original 3 vehicle configurations. The speed and load traces were 

generated through GEM and ran using the engine-only set-up for each of the drive cycles (ARB 

Transient, 65 MPH, and 55 MPH). Average engine speed divided by average vehicle speed (denoted as 

N/V) has been used as a map axis to represent the nature of the engine speed operation on the cycle. 

Engine cycle work has been used as a second map axis to represent the engine loading on the cycle. 

The new BSFC points as generated fell on the surface plot between the original points as shown in 

Figure 11.

Figure 11: a) ARB transient, b) 65 mph, c) 55 mph BSFC surface plots with fit points

The primary and alternate BSFC fuel mapping approaches were compared as shown in Figure 12. The 

alternate approach performed similar or better than the primary approach as witnessed. The alternate 

approach seems to capture well the transient content of the cycle as seen when comparing the two 

approaches. The 55 and 65 cycles for the two approaches output similar results as shown in the plot, 

however for ARB, the results from alternate engine mapping (Cycle Average map based approach) are

better than the results from steady state engine map based approach. The alternate approach for 

both the steady state and transient tests fall on the mean average line as well as the primary approach

for the 55 and 65 MPH cycles.

60

65

70

10 11 12 13 14 15

140

160

180

200

N/V [rpm/mph]

ARB

Work [bhp-hr]

BSFC [g/bhp-hr]

15

20

25

25 30 35 40 45

130

140

150

160

170

N/V [rpm/mph]

65 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

15

20

25

25 30 35 40

140

150

160

170

N/V [rpm/mph]

55 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

60

65

70

10 11 12 13 14 15

140

160

180

200

N/V [rpm/mph]

ARB

Work [bhp-hr]

BSFC [g/bhp-hr]

15

20

25

25 30 35 40 45

130

140

150

160

170

N/V [rpm/mph]

65 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

15

20

25

25 30 35 40

140

150

160

170

N/V [rpm/mph]

55 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

a) b) c)

a) b) c)
Figure 12: BSFC comparison between alternate and steady state map approach

To validate the engine BSFC comparison plot two additional vehicle configurations were generated to 

provide values that fell between the original 3 vehicle configurations. The speed and load traces were 

generated through GEM and ran using the engine-only set-up for each of the drive cycles (ARB 

Transient, 65 MPH, and 55 MPH). The new BSFC points as generated and shown in Figure 13 trended 

as seen from the original BSFC points as shown in Figure 12. The alternate approach for both the 

steady state and transient tests fall on the mean average line as well as the primary approach for the 

55 and 65 MPH cycles.

Figure 13: BSFC comparison between alternate and steady state map approach with fit points

Table 1 shows the cycle times for the primary and alternate engine fuel mapping approaches. The 

engine warm-up times are the same for both methods taking the engine temperatures approximately 

20 minutes to stabilize per 40 CFR 1065.510(b)(2). To maintain a baseline condition for the DPF during 

testing a DPF regeneration was forced prior to running each approach to clean the DPF of stored 
particulates. The emission bench was purged with Nitrogen and calibrated before testing was 

launched and after every 40 minutes of test cycle time. Each purge and calibration took 20 minutes. 

The primary and alternate approaches had 2.4 and 5.9 hours of emission calibration time, respectively. 

The primary approach stabilized the engine for 90 seconds at each of the 143 steady state points and 

measured emissions for the last 30 seconds, reporting the mean values. The total test time for the 

primary approach was 4.5 hours. The alternate approach ran nine different vehicle configurations for 

the three different regulatory cycles (3 generic vehicles x 3 test cycles x 3 axle ratios). The ARB 

transient, 65 MPH cycle with grade, and 55 MPH cycle with grade times were 1336, 1443, and 1693 

seconds, respectively as each of the cycles were repeated twice consecutively and emissions measured 

during the second cycle. The first cycle of each test sequence was used to pre-condition the system. 

The total test time to complete the 27 different tests was 5.6 hours. The total pre-condition time was 

5.6 hours for the 27 different tests. The test and emission calibration times can be reduced for the 

alternate approach if the amount of pre-conditioning is decreased. The alternate approach could be 

reduced by only running one preconditioning cycle per three test cycles completed. This would reduce 

the amount of preconditioning time to 1.9 hours and also reduced the emission calibration time to 1.1

hours as shown in Table 1 (alternate - reduce pre-conditioning). 

Cycle Primary

[Hours]

Alternate

[Hours]

Alternate – Reduced PreConditioning [Hours]

Engine Warm-Up 0.3 0.3 0.3

DPF Regeneration 1.0 1.0 1.0

Emission Purge & Calibration 2.4 5.9 1.1

Pre-conditioning 3.3 5.6 1. b9

Time at Test 1.2 5.6 5.6

Total Time 8.3 18.4 9.9

Table 1: Total test time for engine fuel mapping for primary and alternate approaches

Tables 2 and 3 show a comparison of the GEM simulated and engine test results for both engine brake 

specific fuel consumption (BSFC) [g/bhp-hr] and brake specific Carbon Dioxide (BSCO2 ) [g/ton-mile]. 

The payload of the vehicle was assumed to be 19 ton for calculation of the BSCO2 results. The results 

show that the engine and GEM simulations correlate very well for the 55MPH and 65MPH with road 

grade, but the ARB transient cycle had a slightly higher offset. The higher BSFC and BSCO2 offset for 

the ARB transient can be directly related to the dissimilarities between the steady state fuel map 

utilized and the transient ARB cycle completed.

Regulatory Cycles ARB

[g/bhp-hr]

65 MPH

[g/bhp-hr]

55 MPH

[g/bhp-hr]

Engine BSFC GEM 163.6 145.2 145.4

Engine-Only 172.3 147.5 148.1

Difference [%] 5.3% 1.6% 1.9%

Table 2: Comparison of GEM versus engine-only BSFC results
Regulatory Cycles ARB

[g/ton-mile]

65 MPH

[g/ton-mile]

55 MPH

[g/ton-mile]

Engine BSCO2 GEM 120.8 73.7 63.5

Engine-Only 129.7 72.6 61.9

Difference [%] 7.4% 1.6% 2.5%

Table 3: Comparison of GEM versus engine-only BSCO2 results

Powertrain Test Methodology

The BSFC surface plots shown in Figure 14 represent GEM simulation runs for the powertrain test 

methodology completed on 3 different truck configurations over three different regulatory drive cycles 

(55, 65 mph SS and ARB transient). Average powertrain speed divided by average vehicle speed 

(denoted as N/V) has been used as a map axis to represent the nature of the powertrain speed 

operation on the cycle. Powertrain cycle work has been used as a second map axis to represent the 

engine loading on the cycle. The BSFC results provided a well behaved surface plot for each of the 

drive cycles. The initial GEM results showed promise for the powertrain test option providing a well 

behaved surface for extrapolation.

Figure 14: a) ARB transient, b) 65 mph SS, c) 55 mph SS BSFC GEM BSFC surface plots

Three separate pre-defined vehicle configuration were used to generate the powertrain test. A total of 

9 tests were executed for each regulatory cycle (3 pre-defined vehicles x 3 axle ratios). Average 

powertrain speed divided by average vehicle speed (denoted as N/V) has been used as a map axis to 

represent the nature of the powertrain speed operation on the cycle. Powertrain cycle work has been 

used as a second map axis to represent the powertrain loading on the cycle. BSFC surface plots were 

generated using a grid fit method for each cycle as shown in Figure 15. The BSFC relationship is well 

behaved for the ARB, 55 mph, and 65 mph as also observed from the GEM simulation outputs shown in 

Figure 14. 

20

25

30

10 10.5 11 11.5 12

160

170

180

190

200

N/V [rpm/mph]

ARB

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25 30 35 40 45

140

150

160

170

N/V [rpm/mph]

65 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25 30 35 40

140

150

160

170

N/V [rpm/mph]

55 MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

a) b) c)
Figure 15: a) ARB transient, b) 65 mph SS, c) 55 mph SS BSFC surface plots

To validate the engine BSFC surface fit two additional vehicle configurations were generated to provide 

values that fell between the original 3 vehicle configurations. The configurations were input into the 

vehicle model and the powertrain test completed for each of the drive cycles (ARB Transient, 65 MPH, 

and 55 MPH). The new BSFC points as generated fell on the surface plot between the original points as 

shown in Figure 16. 

Figure 16: a) ARB transient, b) 65 mph SS, c) 55 mph SS BSFC surface plots with fit points

Tables 4 and 5 show a comparison of the GEM simulated and powertrain test results for both the 

powertrain brake specific fuel consumption (BSFC) [g/bhp-hr] and brake specific Carbon Dioxide 

(BSCO2) [g/ton-mile]. The payload of the vehicle was assumed to be 19 ton for calculation of the 

BSCO2 results. The 9 tests executed for each regulatory cycle were averaged to determine the overall 

cycle results. The results show that the GEM simulation and actual powertrain tests correlate very well 

for the 55MPH and 65MPH with road grade as well as the ARB transient. 

Regulatory Cycles ARB 

[g/bhp-hr]

65 MPH 

[g/bhp-hr]

55 MPH 

[g/bhp-hr]

Powertrain BSFC GEM 181.9 153.5 154.0

Powertrain 180.9 148.8 150.5

Difference [%] 0.5% 3.1% 2.3%

Table 4: Comparison of GEM versus powertrain BSFC results

15

20

25

10

10.5

11

11.5

12

160

170

180

190

200

N/V [rpm/mph]

ARB

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25

30

35

40

140

150

160

170

N/V [rpm/mph]

65MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25

30

35

140

150

160

170

N/V [rpm/mph]

55MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

15

20

25

8

9

10

11

12

160

180

200

220

N/V [rpm/mph]

ARB

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25 30 35 40

140

150

160

170

N/V [rpm/mph]

65MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

20

25

30

25

30

35

140

150

160

170

N/V [rpm/mph]

55MPH

Work [bhp-hr]

BSFC [g/bhp-hr]

a) b) c)

a) b) c)
Regulatory Cycles ARB 

[g/ton-mile]

65 MPH 

[g/ton-mile]

55 MPH 

[g/ton-mile] 

Powertrain BSCO2 GEM 117.7 73.6 63.7

Powertrain 119.3 69.9 61.3

Difference [%] 1.3% 5.0% 3.7%

Table 5: Comparison of GEM versus powertrain BSCO2 results

Powertrain results comparing a SmartAdvantage and baseline powertrains are shown in Table 6. The 

baseline powertrain is a standard ISX engine and Eaton 10-speed line haul transmission. The 

SmartAdvantage powertrain is a deeply integrated Eaton and Cummins powertrain solution of the ISX 

engine and Eaton 10-speed line haul transmission. These two powertrains were tested on the 

powertrain dynamometer against potential regulatory drive cycles (65 and 55 mph with up to +/- 2% 

grade, and the ARB transient cycle) under various weightings of the drive cycles that correspond to 

either long haul, or mixed city delivery and high speed, and with multiple vehicle configurations. The 

test show 3.4 – 4.9% GHG reduction of the SmartAdvantage powertrain versus the baseline, with 

greater than 98% repeatability coefficient as shown in Table 7. 

Powertrain ARB

[g]

65 MPH

[g]

55 MPH

[g]

Baseline 2.32 6.00 5.05

SmartAdvantage 2.02 5.79 5.07

Application Cycle weights Fuel

Line haul 86% 65mph, 9% 55mph, 5%ARB 3.4%

Mixed city / high speed 22% 65mph, 28% 55 mph, 50% ARB 4.9%

Table 6: Fuel consumption [kg] measured against 3 drive cycles (top) and % fuel improvement across 

two different drive cycle weightings (bottom) 

The improvements are due to active controls shared between the engine and transmission as well as 

advanced lubrication strategies. The GEM simulation of these powertrains can only account for 

approximate 100 rpm engine down-speeding in top gear because the overdrive ratios of the two 

transmissions are 0.73 and 0.796, which results in approximate 1% fuel savings when in top gear. The 

balance of the 3.4 – 4.9% GHG reduction is due to the deep integration between the engine and 

transmission and the advanced lubrication system in the transmission that are not modeled in GEM. 

This is an example where powertrain testing accounts for advanced technologies not modeled in GEM.

Table 7 represents six 55 mph cycles with road grade that were repeated consecutively over multiple 

days. The tests were repeated to verify test-retest reliability for the powertrain set-up. The 

repeatability coefficient showed a probability of greater than 98% between the two worst case cycles 

representing that the absolute difference measured between two test cycles showed a very high 

correlation of repeatability.
Powertrain 

Test

55 MPH Cycle

Cycle Work [bhp-hr] BSFC [g/bhp-hr] N/V [rpm/mph] FE [mpg]

PT #1 27.0 151.7 26.9 4.10

PT #2 27.0 150.6 26.9 4.07

PT #3 27.0 152.1 26.9 4.11

PT #4 27.0 151.0 26.9 4.08

PT #5 27.0 151.4 26.9 4.09

PT #6 27.0 152.8 26.9 4.13

CoR 

Std. Dev.

Difference

Difference

100%

0.00

0.0%

0.0

98.5%

0.80

1.4%

1.8

100%

0.00

0.0%

0.0

98.5%

0.02

1.5%

0.06

Table 7: Powertrain cycle to cycle repeatability

VII. Conclusions

The Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration 

(NHTSA) are currently developing the testing protocols and stringencies for the second phase of the 

Heavy-Duty (HD) Greenhouse Gas (GHG) Regulations. The testing and certification protocols that are 

under development involve an engine fuel mapping procedure, updates to the accuracy, validity, and 

further refinement of the existing Greenhouse Gas Emission Model (GEM) and a powertrain test 

option. 

An alternate fuel mapping method was investigated and tested by a consortium of vehicle, engine, and 

transmission OEM’s to determine if a feasible, reliable, repeatable, cost effective alternate to the 

primary steady state fuel mapping approach could be developed. The alternate method tested 

provided a scheme of a reduced number of test points creating an average map which provided the 

same accuracy as the primary engine fuel mapping method. The overall test burden to collect the 

engine BSFC data for the alternate approach was shown to be roughly double as executed in this study 

while supplying equivalent accuracy to the primary approach. The pre-conditioning portion of the 

alternate approach can be reduced to decrease the overall test burden as still obtain the accuracy and 

repeatability of the data sets. The alternate method average BSFC map was well behaved as also 

observed from the GEM simulation outputs. The alternative approach also produced CO2 results that 

agreed with the vehicle data as well as the primary mapping approach. The primary and alternate fuel 

mapping approaches were compared and the alternate performed similar or better than the primary

capturing better the transient content of the cycle. To further validate the alternate engine BSFC 

mapping approach two additional vehicle configurations were generated to verify the surface fit. The 

additional points generated verified that the BSFC points as predicted fell on the surface plot 

generated from the original points for each of the test cycles (ARB, 65 MPH, & 55 MPH).

A powertrain test methodology was also developed and shown to be a controlled, repeatable, high 

fidelity solution to meet the agencies GHG verification needs. The powertrain procedure is able to 

show the specific GHG emissions and fuel efficiency improvements from powertrain enhancements 

that would otherwise not be recognized in simulation, engine testing, or full vehicle evaluation. 

Powertrain testing provided a consistent and repeatable measure independent of vehicle platform or 

powertrain technology and includes conditions reflective of real-world operation. Vehicle parameters 

such as road friction, vehicle mass, rolling radius, wheel inertia, vehicle frontal area, drag coefficient 
and final drive ratio were implemented into the driver model to reflect on-road vehicle operation of a 

class 8 vocational truck as defined by EPA in the GEM model as part of the GHG phase 1 rule. The 

powertrain was tested using regulatory cycles (ARB, 65mph and 55mph) and were fully reflective of 

real-world driving as they included a +/-2% road grade profile. The BSFC results provided a well 

behaved surface plot for each of the drive cycles. To validate the powertrain BSFC mapping approach 

two additional vehicle configurations were generated to verify the surface fit for each cycle. The 

additional points verified that the BSFC points as predicted fell on the surface plot between the original 

points generated.

Powertrain dynamometer test rigs have been developed on which the entire powertrain, including the 

real controllers, can be tested against drive cycles. These test rigs and procedures offer ways to 

quantify the GHG performance of deeply integrated and highly optimized powertrains. PT utilizes

established testing protocols (CFR) producing high fidelity data. The powertrain test captures real 

world performance differentiation among drivetrains as shown with the deeply integrated Eaton and 

Cummins SmartAdvantage powertrain which provided a 3.4 – 4.9% GHG reduction versus the baseline 

under various weightings of the drive cycles that correspond to either long haul, or mixed city delivery 

and high speed.

The PT methodology test-to-test repeatability was examined by running six 55 MPH cycles 

consecutively and verifying the consistency of the test and set-up. The repeatability coefficient showed 

a probability of greater than 98% and also exhibited a low standard deviation for the powertrain

configuration tested. Both the high repeatability coefficient and low standard deviation values indicate 

that the cycle to cycle correlation for the powertrain tests were very repeatable. The cycle to cycle 

correlation also indicates that the powertrain test procedure is very robust and a reliable method for 

verifying performance, emissions, and fuel economy in a controlled, repeatable, high fidelity manner. 

Powertrain dynamometers as extensions of engine dynamometers, where the motor is connected to a 

transmission output shaft rather than the engine flywheel, and the controls simulate a vehicle route, 

rather than the usual engine cycles. From this perspective, the powertrain dynamometer has the 

advantage of relative small incremental capital costs (less than $600,000 capital investment in 

converting an engine test cell to a powertrain test cell). In the context of certification, the calibration 

of a new powertrain is also a small incremental effort relative to the engine dynamometer calibration. 

Thus a new powertrain can be installed and calibrated by experienced staff in less than two weeks, 

while a variation can be installed in two days. 
Appendix A - Vehicle Configurations for Alternate Fuel Mapping Approach

Vehicle 

Configuration

Aero Drag 

Coefficient

Vehicle 

Mass [kg]

Frontal 

Area [m2]

Tire Radius 

[m]

Rolling 

Resistance

1 0.7 30391 9.8 0.489 0.006

2 0.55 30391 9.8 0.489 0.0053

3 0.41 30391 9.8 0.489 0.0045

4 0.625 30391 9.8 0.489 0.0057

5 0.48 30391 9.8 0.489 0.0049
Appendix B – Alternate Fuel Mapping Approach Test Results

Cycle

Vehicle 

Configuration

Actual Engine Cycle 

Work [bhp-hr]

Engine BSFC

[g/bhp-hr]

CO2

[g/ton-mile]

N/V

[rpm/mph]

FDR

55MPH 1 36.49 147.2 64.9 18.3 2.64

55MPH 1 36.52 146.8 72.2 19.8 2.85

55MPH 1 36.96 147.2 73.1 21.4 3.08

55MPH 2 31.76 147.4 57.3 18.4 2.64

55MPH 2 32.08 147.1 63.4 19.8 2.85

55MPH 2 32.23 148.6 64.4 21.4 3.08

55MPH 3 27.28 149.2 50.0 18.3 2.64

55MPH 3 27.67 149.6 55.8 19.8 2.85

55MPH 3 27.76 149.5 56.0 21.4 3.08

55MPH 4 37.90 146.4 71.5 19.1 2.75

55MPH 4 34.45 148.0 68.8 20.6 2.97

55MPH 5 29.79 149.0 59.8 19.1 2.75

55MPH 5 29.91 148.8 59.7 20.6 2.97

65MPH 1 41.42 145.8 80.89 18.4 2.64

65MPH 1 42.33 145.8 82.67 19.8 2.85

65MPH 1 43.25 147.5 85.33 21.4 3.08

65MPH 2 36.31 146.2 70.90 18.3 2.64

65MPH 2 36.76 146.9 72.16 19.8 2.85

65MPH 2 37.29 148.3 73.94 21.4 3.08

65MPH 3 31.25 148.2 61.96 18.4 2.64

65MPH 3 31.24 148.2 61.94 19.8 2.85

65MPH 3 31.41 150.6 63.22 21.4 3.08

65MPH 4 38.96 146.0 76.70 19.1 2.75

65MPH 4 39.79 147.3 79.14 20.6 2.97

65MPH 5 33.42 147.2 66.11 19.1 2.75

65MPH 5 33.89 148.7 67.73 20.6 2.97

ARB 1 13.32 171.2 135.56 66.3 2.64

ARB 1 13.10 169.5 131.98 64.6 2.85

ARB 1 12.87 170.2 130.84 63.5 3.08

ARB 2 13.09 173.4 135.04 65.8 2.64

ARB 2 12.58 171.7 128.57 64.6 2.85

ARB 2 12.42 171.5 126.95 63.5 3.08

ARB 3 12.48 174.7 130.39 65.8 2.64

ARB 3 12.02 173.9 124.36 64.4 2.85

ARB 3 11.98 174.5 123.98 63.5 3.08

ARB 4 13.14 172.8 135.54 66.4 2.75

ARB 4 12.63 172.6 129.66 63.3 2.97

ARB 5 13.14 172.8 135.54 66.4 2.75

ARB 5 12.18 174.1 126.11 63.3 2.97
Appendix C - Vehicle Configurations for Powertrain Test

Vehicle 

Configuration

Aero Drag 

Coefficient

Vehicle 

Mass [kg]

Frontal 

Area [m2]

Tire Radius 

[m]

Rolling 

Resistance

1 0.7 30391 9.8 0.489 0.006

2 0.55 30391 9.8 0.489 0.0053

3 0.41 30391 9.8 0.489 0.0045

6 1.4 37989 19.6 0.489 0.013

7 1.4 30391 19.6 0.489 0.013

8 0.7 37989 9.8 0.489 0.0065

9 0.41 15195 9.8 0.489 0.0065

10 0.41 22000 9.8 0.489 0.0065

11 0.53 30391 9.8 0.489 0.0065

12 0.5 30391 9.8 0.489 0.0045
Appendix D – Powertrain Test Results

Cycle Vehicle 

Configuration

Powertrain Cycle 

Work [bhp-hr]

Powertrain BSFC

[g/bhp-hr]

CO2

[g/ton-mile]

N/V

[rpm/mph]

FDR

55MPH 1 33.90 148.4 70.17 26.9 2.64

55MPH 1 33.86 149.1 70.40 26.9 2.85

55MPH 1 33.89 148.7 70.48 23.0 3.08

55MPH 2 29.48 150.6 61.18 24.8 2.64

55MPH 2 29.40 150.7 61.05 23.0 2.85

55MPH 2 29.44 150.1 60.89 26.8 3.08

55MPH 3 25.27 151.6 52.39 26.9 2.64

55MPH 3 25.29 153.0 52.66 26.9 2.85

55MPH 3 25.28 152.3 52.86 26.9 3.08

55MPH 11 31.16 152.4 66.11 26.9 2.64

55MPH 12 27.05 154.9 58.55 26.9 2.64

55MPH 11 31.10 153.4 66.48 26.9 2.85

55MPH 12 27.03 155.0 58.76 18.3 2.85

55MPH 11 31.19 152.6 66.22 19.8 3.08

55MPH 12 27.06 156.7 59.44 21.4 3.08

55MPH 1 33.89 148.7 70.12 18.3 2.64

55MPH 1 33.85 148.3 69.80 19.8 2.85

55MPH 11 31.16 151.2 65.86 21.4 2.64

55MPH 12 27.02 151.0 57.30 18.3 3.08

55MPH 12 27.02 151.7 57.78 19.8 3.08

55MPH 12 27.02 150.6 57.49 21.4 3.08

55MPH 12 27.02 152.1 58.00 18.3 3.08

55MPH 12 27.02 151.0 57.74 18.3 3.08

55MPH 12 27.02 151.4 57.78 19.8 3.08

55MPH 12 27.02 152.8 58.37 19.8 3.08

65MPH 1 39.55 145.9 81.00 21.4 2.64

65MPH 1 39.72 147.5 81.08 21.4 2.85

65MPH 1 39.82 149.2 81.95 26.9 3.08

65MPH 2 33.91 146.6 68.97 26.9 2.64

65MPH 2 34.09 148.1 69.53 23.0 2.85

65MPH 2 34.15 149.9 70.45 24.8 3.08

65MPH 3 28.51 148.7 58.13 23.0 2.64

65MPH 3 28.57 150.5 58.77 26.8 2.85

65MPH 3 28.59 152.9 59.32 26.9 3.08

65MPH 11 35.55 149.4 73.95 26.9 2.64

65MPH 12 31.09 151.2 65.49 26.9 2.64

65MPH 11 35.64 150.7 74.42 26.9 2.85

65MPH 12 31.26 152.3 66.02 26.9 2.85
Appendix D – Powertrain Test Results (Cont’d)

Cycle Vehicle 

Configuration

Powertrain Cycle 

Work [bhp-hr]

Powertrain BSFC

[g/bhp-hr]

CO2

[g/ton-mile]

N/V

[rpm/kph]

FDR

65MPH 1 39.52 146.5 80.53 18.3 2.64

65MPH 1 39.82 149.4 81.75 21.4 2.85

65MPH 11 35.53 146.9 72.73 18.3 2.64

65MPH 12 31.29 150.8 65.34 21.4 3.08

65MPH 12 31.29 150.5 65.48 21.4 3.08

65MPH 12 31.28 150.9 65.52 21.4 3.08

65MPH 12 31.30 153.0 66.10 21.4 3.08

65MPH 12 31.29 151.5 65.61 21.4 3.08

65MPH 12 31.29 151.2 65.54 21.4 3.08

65MPH 12 31.29 151.2 65.41 21.4 3.08

ARB 1 11.10 181.1 125.09 57.0 2.64

ARB 1 11.28 179.1 125.68 56.5 2.85

ARB 1 11.57 176.3 125.36 56.2 3.08

ARB 2 10.71 183.0 120.75 56.6 2.64

ARB 2 10.89 180.9 120.72 56.0 2.85

ARB 2 11.11 178.2 121.22 56.1 3.08

ARB 3 10.22 185.9 110.69 56.9 2.64

ARB 3 10.44 183.9 112.65 56.0 2.85

ARB 3 10.74 179.7 111.53 56.2 3.08

ARB 6 17.90 168.2 203.39 65.7 2.64

ARB 7 16.10 168.9 169 59.5 2.64

ARB 8 13.78 174.2 148.04 59.6 2.64

ARB 9 5.97 232.8 84.41 54.7 2.64

ARB 10 10.08 187.5 113.86 55.3 2.64

ARB 6 18.74 166.0 199.85 62.7 2.85

ARB 7 16.17 170.7 170.38 60.0 2.85

ARB 8 13.80 173.9 146.58 58.1 2.85

ARB 9 5.92 234.8 84.4 54.7 2.85

ARB 10 8.39 199.0 101.73 54.8 2.85

ARB 6 18.61 166.0 198.07 61.0 3.08

ARB 7 16.36 168.7 171.54 58.3 3.08

ARB 8 13.75 173.8 147.23 59.2 3.08

ARB 9 5.93 236.1 86.06 55.8 3.08

ARB 10 8.42 199.5 102.48 55.5 3.08