Technology Assessment for the Next 

Phase Heavy-Duty Greenhouse Gas 

Emission and Fuel Efficiency Standards

Houshun Zhang, Matt Spears, and Angela Cullen

Environmental Protection Agency

October 9, 2014
SAE INTERNATIONAL

Acknowledgement

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• EPA Team

• Byungho Lee, James Sanchez, Prashanth 

Gururaja, Kevin Newman, Paul Dekraker

• SwRI Team

• Joe Anthony, Jayant Sarlashkar, Anthony Phan, 

Brian Moczygemba, Charlie Roberts
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Outline

• GHG Phase II Update 

• Technology Assessment in Phase II

• Vehicle Model (GEM) Validations

• Chassis Dyno Test Variability

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Phase 1 - Highlights

 First ever Medium- & 

Heavy-Duty Standards

 Will reduce fuel 

consumption, CO2 

emissions, and 

operating costs for 

thousands of 

businesses

 Allows manufacturers to 

produce a single fleet of 

vehicles to meet 

requirement

 530 million barrels less oil 

 270 MMT lower GHGs

 $50 billion in fuel savings

 $49 billion in net benefits

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Phase 1 - Overview

HD Engines Vocational vehicle, regulated via the chassis

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Phase I GEM

Inertial/Braking

0-2%

Aerodynamic Loss

15-22%

Drivetrain

2-4%

Rolling Resistance

13-16%

Vehicle Auxiliary Loads

1-4%

Total Engine Loss

57-59%

EPA pre-specified

Allowed user inputs

• The Greenhouse Gas Emission Model (GEM) is a vehicle simulation tool being used by 

all vehicle OEMs for demonstrating compliance for the U.S. Greenhouse Gas Emission 

and Fuel Efficiency Standards

• GEM is run over three EPA drive cycles: 55mph, 65mph, and transient cycles

• Only up to 6 inputs are supplied by OEM, depending on regulatory subcategory

http://www.epa.gov/otaq/climate/gem.htm

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Inertial/Braking

Aerodynamic Loss

Vehicle Auxiliary Loads Rolling Resistance

Heat Rejection Exhaust Gas Friction Parasitic Loss Pumping Loss

Transmission Axles and Shaft

• Phase II will consider all possible technologies that can be evaluated in a chassis 

dyno cell in order to improve engine and vehicle efficiency

• A significantly upgraded version of GEM is being developed and validated to 

account for all possible technologies mentioned above

• GEM is intended for demonstrating compliance with the standards rather than for 

research and development or any other purpose

Total Engine Loss

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Phase II GEM
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Potential Assessment Options
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Engine Technology

• Phase II GEM is being developed to account for all engine technologies that 

are tested in an engine dyno

• Engine fuel map options

– Option A: a very well defined engine fuel could be developed from engine dyno testing and 

used in GEM 

– Option B: alternative method of evaluating the engine other than a traditional engine fuel 

map

Inertial / 

Braking

Aerodynamic 

Loss

Rolling 

Resistance

Vehicle Auxiliary 

Loads

Heat 

Rejection

Exhaust 

Gas

Friction Parasitic 

Loss

Pumping 

Loss

Transmission Axles and 

Shaft

Total 

Engine 

Loss

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Vehicle Technology

• OEM supplied aero drag and rolling resistance coefficients could be 

used to model the associated losses and

– Promote advanced aerodynamic technologies 

– Encourage low rolling resistance tires

Inertial / 

Braking

Aerodynamic 

Loss

Rolling 

Resistance

Vehicle Auxiliary 

Loads

Heat 

Rejection

Exhaust 

Gas

Friction Parasitic 

Loss

Pumping 

Loss

Transmission Axles and 

Shaft

Total 

Engine 

Loss

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Transmission Technology

• Transmissions, such as manual (MT), automated manual (AMT) and 

automatic (AT), can be modeled within GEM

– Phase I GEM only model MT

• GEM will allow OEM to enter transmission information, such as gear 

ratio vs. gear number

• GEM includes a shift strategy for each type of transmission

Inertial / 

Braking

Aerodynamic 

Loss

Rolling 

Resistance

Vehicle Auxiliary 

Loads

Heat 

Rejection

Exhaust 

Gas

Friction Parasitic 

Loss

Pumping 

Loss

Transmission Axles and 

Shaft

Total 

Engine 

Loss

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Driveline Technology

• Axle modeling parameters, such as axle ratio, could be input by OEM

• A pull-down menu could be specifically designed to recognize other 

axle technologies, such as 6x2 axle configurations

Meritor ECSA Smar 6x2 Dana’s dual range axle

Inertial / 

Braking

Aerodynamic Loss

Vehicle Auxiliary Loads Rolling Resistance

Heat 

Rejection

Exhaust 

Gas

Friction Parasitic 

Loss

Pumping 

Loss

Transmission Axles and 

Shaft

Total 

Engine 

Loss

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Pull-Down Menu Methodology

• A pull-down menu approach can be specifically designed to 

account for those technologies that are deemed inappropriate to 

model

– Axle technologies, such as Meritor ECSA Smar 6x2 and Dana’s dual range axle

– Transmission technologies, such as dual clutch transmissions or continuously 

variable transmissions

– Lightweight material, such as high strength steel, aluminum, thermoplastic

– Predictive cruise control (look ahead/smart coast ...)

– Idle reduction

– Automated tire inflation systems

– Start-Stop

Inertial / 

Braking

Aerodynamic 

Loss

Vehicle Auxiliary Loads Rolling Resistance

Heat 

Rejection

Exhaust 

Gas

Friction Parasitic 

Loss

Pumping 

Loss

Transmission Axles and 

Shaft

Total 

Engine 

Loss

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Phase II GEM Features

• Model upgrade examples

– Engine controller

• Engine fuel cut-off algorithm during braking and deceleration

• More stable engine idle speed controller

– Transmission model

• Manual Transmission – upgraded

• Automatic Transmission – newly developed

• Automated Manual Transmission – newly developed

– Driver model

• Distance-Based Driver is developed and validated

• Vehicle tests for model validation include over 130 vehicle variants

– Class 6 Vocational Box Truck with AT

– Class 6 Vocational Tow Truck with AT

– Class 8 T700 Tractor with AMT

– Class 8 Cascadia Tractor with MT

– Refuse Truck with AT

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GEM Validation – Class 8 T700 Tractor

• GEM has been validated against chassis dyno tests covering over 40 

vehicle variants. GEM has been correlated to within +/- 5% of the chassis 

test results

2

3

4

5

6

7

8

9

10

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2 4 6 8 10 GEM [MPG]

Chassis Dynamometer [MPG]

55 MPH

65 MPH

CARB

Parcel

Utility

WHVC

1:1

1:1-5%

1:1+5%

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GEM Validation- Class 6 Tow Truck

• GEM is validated against chassis dyno test over 40 vehicle variants. 

Excellent agreements between GEM and tests have been obtained.

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7

8

9

10

11

12

13

14

15

16

6 8 10 12 14 16 GEM result [MPG]

Powertrain Test [MPG]

1:1

55 mph

65 mph

ARB

Utility

Parcel

WHVC

+5% Line

-5%

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GEM Validation - Class 6 Box Truck

• GEM is validated against chassis dyno test over 40 vehicle variants. 

Excellent agreements between GEM and tests are obtained

5

6

7

8

9

10

11

12

13

14

5 7 9 11 13 GEM [MPG]

Chassis Dynamometer [MPG]

55 MPH

65 MPH

CARB

Parcel

Utility

WHVC

1:1

1:1-5%

1:1+5%

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GEM Validation – Refuse Truck

• GEM is validated against chassis dyno test over 6 vehicle variants. Good 

agreements between GEM and tests have been obtained

2

3

4

5

6

7

2 3 4 5 6 7 GEM [MPG]

Chassis Dynamometer [MPG]

55 MPH

65 MPH

CARB

Utility

WHVC

1:1

1:1-5%

1:1+5%

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GEM Validations 

against 130 Vehicle Variants

U.S. Environmental Protection Agency

2

4

6

8

10

12

14

16

2 4 6 8 10 12 14 16

GEM (MPG)

Experimental Tests (MPG)

1:1

1:1+5%

1:1-5%

Results

• GEM has been validated against chassis dyno tests covering 130 vehicle 

variants. Excellent agreements between GEM and tests have been 

obtained.

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• Driver behavior

— Pedal inputs

— Shift schedule

• Transmission temperature

Chassis Testing Variability (1)

Chassis Dynamometer CO2 Comparison

0

20

40

60

80

100

120

0 100 200 300 400 500 600 CO2 Mass Rate, kg/hr

Time, Seconds

Run 1

Run 2

At low load, the driver’s 

behavior difference only 

slightly affected CO2.

Pedal variability affects 

CO2 emissions more at 

higher loads.

0

10

20

30

40

50

60

70

80

90

100

0 100 200 300 400 500 600 Accelerator Pedal Positon, %

Time, Seconds

Run 1 Human driver has significantly Run 2 different behavior for each test.

Pedal Position % CO2 Mass Rate (kg/hr)

Time (sec)

Time (sec)

7.34

7.53

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7.1

7.2

7.3

7.4

7.5

7.6

7.7

35 55 75 95

Fuel Economy, MPG

Transmission Temperature, degC

CAC Temperature 46C

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• Tire temperature

Chassis Testing Variability (2)

500

550

600

650

700

750

800

850

900

950

1000

00:00 05:46 11:31 17:17 23:02 28:48 34:34 Dynamometer Roll Force [N] 

Time [Min:Sec]

With driveshaft

~270 N after 30 min. from cold

Average Tire Temperature Change = 9.7 degC

Average Tire Pressure Change = 45 kPa

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• Thermal management

• Aftertreatment temperature

• Accessory load

Chassis Testing Variability (3)

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

100

150 200 250 300 350 400 Fuell Rate (L/hr)

Fuel Rate for -15% Crr Condition

5.54 mpg (Run 940)

5.313 mpg (Run 944)

5.25 mpg (Run 951)

5.39 mpg (Run 952)

5.29 mpg (Run 957)

Runs WithActive Thermal 

Managment

Thermal management 

impact during idle

Fueling Rate (L/hr)

Time (s)

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Conclusions

• A full vehicle model – GEM, has been developed and 

comprehensively validated against testing data covering 130 

vehicle variants, and excellent agreement between GEM and tests 

has been obtained

• Variability in chassis dyno test results not only impact GEM 

validations if not modeled correctly, but also impact test procedure 

considerations

• GEM is able to assess performance of those technologies that are 

being and will be developed at OEM level, which are intended to be 

put into production to reduce GHG emissions and improve fuel 

efficiency of heavy-duty vehicles 

• EPA is conducting Peer Review on Phase II GEM

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