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Natural Gas Engine 

Development Gaps

Natural Gas Vehicle Technology Forum – Brookhaven National Laboratory

Upton, New York

Bradley T. Zigler

14 January 2014

NREL/PR-5400-61425
2

Outline

• Review of current natural gas vehicle (NGV) 

offerings

• How to identify and address NGV 

development gaps

• Major NG engine development gap areas
3

Light-Duty NGV Offerings

OEM = original equipment manufacturer
4

Light-Duty NGV Offerings

General observations:

• Offerings are increasing in response to market

• EPA rules offer more flexibility for conversions

• OEMs have themselves reentered market along with 3rd party support

• Light-duty market is building range and diversity

EPA = U.S. Environmental Protection Agency
5

MD & HD NGVs

HD = heavy duty

MD = medium duty
6

MD & HD NGVs

• The “lighter” end of the market is 

covered with OEM options and 

conversions based on gasoline 

engines
7

MD & HD NGVs

• For the “heavier” applications, ESI 

offered the 7.6L Phoenix 
8

MD & HD NGVs

• For the “heavier” applications, ESI 

offered the 7.6L Phoenix 

... but ESI suspended operations 

in 2012 and CNG One Source / 

“new” ESI has not resumed 

production yet.
9

MD & HD NGVs

• For the “heavier” applications, ESI 

offered the 7.6L Phoenix 

... but ESI suspended operations 

in 2012 and CNG One Source / 

“new” ESI has not resumed 

production yet.

• A gap is formed in the ~6–8L 

range, and the California Energy 

Commission (CEC) conducted a 

funding solicitation in this area.
10

MD & HD NGVs

• For the “heavier” applications, ESI 

offered the 7.6L Phoenix 

... but ESI suspended operations 

in 2012 and CNG One Source / 

“new” ESI has not resumed 

production yet.

• A gap is formed in the ~6–8L 

range, and the California Energy 

Commission (CEC) conducted a 

funding solicitation in this area.

• Initial development of the 

Cummins Westport 6.7L ISB6.7 

G is now underway.
11

MD & HD NGVs

• The “heavy” end of the market is 

generally based on spark-ignition 

compressed natural gas (CNG) / 

liquefied natural gas (LNG) or 

compression–ignition dual fuel 

CNG / LNG + diesel conversions 

of diesel engines.
12

MD & HD NGVs

• The “heavy” end of the market is 

generally based on spark-ignition 

compressed natural gas (CNG) / 

liquefied natural gas (LNG) or 

compression–ignition dual fuel 

CNG / LNG + diesel conversions 

of diesel engines.

• The Cummins Westport 8.9L ISL 

G is popular and covers the lower 

power needs of many trucks.
13

MD & HD NGVs

• The Doosan Infracore 11L lean-

burn engine sells in limited 

numbers for repower applications, 

but its torque rating is comparable 

to ~ 9L.

• The “heavy” end of the market is 

generally based on spark-ignition 

compressed natural gas (CNG) / 

liquefied natural gas (LNG) or 

compression–ignition dual fuel 

CNG / LNG + diesel conversions 

of diesel engines.

• The Cummins Westport 8.9L ISL 

G is popular and covers the lower 

power needs of many trucks.
14

MD & HD NGVs

• The new Cummins Westport 

ISX12 G is addressing the 

important 11–12L range.

• The Doosan Infracore 11L lean-

burn engine sells in limited 

numbers for repower applications, 

but its torque rating is comparable 

to ~ 9L.

• The “heavy” end of the market is 

generally based on spark-ignition 

compressed natural gas (CNG) / 

liquefied natural gas (LNG) or 

compression–ignition dual fuel 

CNG / LNG + diesel conversions 

of diesel engines.

• The Cummins Westport 8.9L ISL 

G is popular and covers the lower 

power needs of many trucks.
15

MD & HD NGVs

• And Southwest Research Institute is 

working with Doosan on a significantly 

upgraded version of the 11L.

• The new Cummins Westport 

ISX12 G is addressing the 

important 11–12L range.

• The Doosan Infracore 11L lean-

burn engine sells in limited 

numbers for repower applications, 

but its torque rating is comparable 

to ~ 9L.

• The “heavy” end of the market is 

generally based on spark-ignition 

compressed natural gas (CNG) / 

liquefied natural gas (LNG) or 

compression–ignition dual fuel 

CNG / LNG + diesel conversions 

of diesel engines.

• The Cummins Westport 8.9L ISL 

G is popular and covers the lower 

power needs of many trucks.
16

MD & HD NGVs

• Westport Industries just ended 

production of the 15L HPDI dual 

fuel engine.

HPDI = High Pressure Direct Injection 
17

MD & HD NGVs

• Westport Industries just ended 

production of the 15L HPDI dual 

fuel engine.

• Cummins began initial 

development of the spark-ignited 

15L ISX15 G, but recently paused 

work on it.

?
18

MD & HD NGVs

• Westport Industries just ended 

production of the 15L HPDI dual 

fuel engine.

• Cummins began initial 

development of the spark-ignited 

15L ISX15 G, but recently paused 

work on it.

• Volvo announced that a new dual 

fuel (HPDI) D13-LNG engine will 

be available mid-2014.
19

Stakeholder Input is Critical

NGVTF uses a roadmap developed by the CEC as a foundation for its work. 

Based on NGV research, development, demonstration, and deployment gap 

analysis, and stakeholder views, this roadmap suggests the following would 

accelerate commercialization of NGV technologies in the market:

• Engine development and vehicle integration

• Fueling infrastructure and storage

• Technical and strategic studies

Source: http://www1.eere.energy.gov/cleancities/natural_gas_forum.html
20

• Past input directed co-funding for NG engine and vehicle research and 

development

o CEC – Initial development of Cummins Westport 11.9L (GTI)

o NREL (DOE/CEC/SCAQMD) – Final development of Cummins Westport 11.9L

o NREL (DOE/CEC/SCAQMD) – Development of Doosan 11L (SwRI)

o CEC – Initial development of Cummins Westport 6.7L (GTI)

o Other NG engine development

o Development of storage technologies

• What are current / future needs?

• NREL is assisting CEC in updating its NGV research roadmap

SCAQMD = South Coast Air Quality Management District

GTI = Gas Technology Institute

SwRI = Southwest Research Institute

Stakeholder Input is Critical
21

NG Engine Vehicle Development Gap Areas

• Some of the gaps are not limited to engines alone

o NGVs are dependent on vehicle availability, engine options, onboard fuel storage, fuel availability, etc....
22

NG Engine Vehicle Development Gap Areas

• Some of the gaps are not limited to engines alone

o NGVs are dependent on vehicle availability, engine options, onboard fuel storage, fuel availability, etc....

o Example: current expansion of Class 8 semi tractors with 

Cummins Westport ISX12 G and side-saddle tank / back of cab 

CNG storage (up to ~155 diesel gallons equivalent [DGE]) through 

companies like Agility
23

NG Engine Vehicle Development Gap Areas

• Some of the gaps are not limited to engines alone

o NGVs are dependent on vehicle availability, engine options, onboard fuel storage, fuel availability, etc....

o Example: current expansion of Class 8 semi tractors with 

Cummins Westport ISX12 G and side-saddle tank / back of cab 

CNG storage (up to ~155 diesel gallons equivalent [DGE]) through 

companies like Agility

o Additional on-board storage improvements are necessary:

– Higher capacity

– Smaller package

– Lighter package

– Lower cost

o R&D underway

– CEC – adsorptive technologies

– DOE’s Advanced Research Projects Agency - Energy (ARPA-E): 

advanced storage, lower cost home compression, etc....
24

NG Engine Development Gap Areas

• Increased engine efficiency

o Current trend in HD NG engines is spark-ignited, stoichiometric, 

cooled exhaust gas recirculation (EGR), with a three-way catalyst

o Need to reduce fuel efficiency penalty compared to diesel

o Low NG fuel costs may not last forever, so research is necessary now 

to reduce the fuel efficiency gap

– Reduce operating costs

– Increase range

– Address increasing concerns over greenhouse gases (GHGs)
25

NG Engine Development Gap Areas

• Increased engine efficiency

o Current trend in HD NG engines is spark-ignited, stoichiometric, 

cooled exhaust gas recirculation (EGR), with a three-way catalyst

o Need to reduce fuel efficiency penalty compared to diesel

o Low NG fuel costs may not last forever, so research is necessary now 

to reduce the fuel efficiency gap

– Reduce operating costs

– Increase range

– Address increasing concerns over greenhouse gases (GHGs)

• Potential pathways

o Improved fuel injection systems (port, direct)

o High dilution (EGR)

o High boost

o Improved ignition systems

o Reforming for syngas / H2 to extend ignition limits

o Low-temperature combustion strategies (like homogeneous charge 

compression ignition [HCCI])
26

NG Engine Development Gap Areas

• Reduced emissions

o Regulated emissions

– GHG / CO2 equivalence (concerns over tailpipe methane)

– Driving some regulated emissions lower

– CARB and SCAQMD R&D funding programs develop technology 

for sub-0.02 g/bhp-hr vs. 0.2 g NOx standard

o Unregulated emissions

– Ammonia (desire for sub-10 ppm)

o Will programs like California’s Carl Moyer Program incentivize sales of 

these engines?

o California is an important market and will influence future NG engine 

technologies. Meeting current standards isn’t enough.
27

NG Engine Development Gap Areas

• Reduced emissions

o Regulated emissions

– GHG / CO2 equivalence (concerns over tailpipe methane)

– Driving some regulated emissions lower

– CARB and SCAQMD R&D funding programs develop technology 

for sub-0.02 g/bhp-hr vs. 0.2 g NOx standard

o Unregulated emissions

– Ammonia (desire for sub-10 ppm)

o Will programs like California’s Carl Moyer Program incentivize sales of 

these engines?

o California is an important market and will influence future NG engine 

technologies. Meeting current standards isn’t enough.

• Potential pathways

o Same list as fuel efficiency enablers

o Cold-start / low-temperature catalyst operation focus

o Additional aftertreatment (selective catalyst reduction?)
28

NG Engine Development Gap Areas

• Engine development / certification process

o EPA / CARB HD emissions certification is challenging

– 22,000 hour / 435,000 mile “full useful life” requirement

o Unlike light-duty gasoline engines, which have bench-aging protocols 

for deterioration factor (DF) testing for emissions

o HD tests engine + aftertreatment system together in an accelerated 

manner (ideally very accelerated)

o This is a significant (cost, timing, resources) hurdle for engine OEMs 

(too big for some)

o Sales limited to 300 engines / year without this DF testing 

o This issue will become more challenging with increasing emissions 

standards (0.02 g/bhp-hr NOx)

o Coordinated development of catalyst aging protocols could satisfy EPA 

/ CARB needs and reduce the certification DF “hurdle” for OEMs
Thank you for your interest and 

feedback.

Bradley T. Zigler

brad.zigler@nrel.gov

303-275-4267