Ultra-Low Emission Engines

Fleets that move goods and people throughout the nation rely on vehicles powered by domestically produced natural gas because it is both economical and clean-burning. Natural gas vehicles (NGVs) use proven, reliable technology to take advantage of a domestic energy source. The relative low cost of natural gas, combined with unmatched reductions of smog-forming emissions of nitrogen oxides (NOx), has led to significant market growth and more vehicle and fueling options than ever before. This is especially important in metropolitan areas throughout the nation where medium- and heavy-duty engines are the number one source of toxic air contaminants and ozone-forming emissions of NOx.

The Cleanest Available Heavy-Duty Engine

In September 2015, the U.S. Environmental Protection Agency and the California Air Resources Board certified the world’s first heavy-duty engine that emits oxides of nitrogen (NOx) at levels so low they are considered “near-zero.” The 8.9-liter engine from Cummins Westport, certified to CARB’s most stringent low-NOx emission standard of 0.02 g/bhp-hr NOx, is 90% cleaner than the cleanest available diesel engine. It offers 320 horsepower / 1,000 lb-ft torque, and is a great fit for transit, refuse, and truck applications.

In 2018, CARB certified a larger 12-liter version of Cummins Westport’s natural gas engine to the same 0.02 g/bhp-hr NOx standard. This NZE engine offers 400 horsepower / 1,450 lb-ft torque making it well suited for heavy-duty regional-haul trucks, vocational, refuse applications, and motorcoach.

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Cummins Westport L9N engine

Cummins Westport ISX12N engine

An on-road truck with a natural gas near-zero engine is:
90% Cleaner
than the EPA’s current heavy-duty NOx emission standard.

HD BEV Equivalent
based on comparing NOx emissions associated with HD battery-electric vehicle (BEV) charging (even states like CA, OR, and WA, that have the cleanest electrical grids in the nation).

Learn how grid equivalency was evaluated:

The Most Cost Effective Option to Reduce NOx Emissions

Dollar-for-dollar, NGVs deliver the most cost effective NOx emissions reductions across multiple medium- and heavy-duty applications. The calculations shown below assume the deployment of the cleanest commercially available model for each application.

Short/Regional Haul Trucks

School Buses


Refuse Trucks

Transit Buses

(Source: NGVAmerica, 2017)

Commercially Available Across Numerous Applications

NGVs are available from national OEMs with established sales and service networks. Retrofit and repower options are also available from a variety of manufacturers. To view the latest vehicle availability, use the U.S. Department of Energy Alternative Fuel and Advanced Vehicle Search tool.

Available NGV Applications Include:

(Source: NGVAmerica, 2017)

Low NOx Certified Vehicles

Certification (g NOx/ bhp-hr)
CARB-Certified HD Low NOx Engine
CARB Certification Executive Order(s)
OEM Materials

0.02 g NOx/ bhp-hr
ROUSH CleanTech V10 6.8L CNG Engine

0.02 g NOx/ bhp-hr
Cummins-Westport ISLG 8.9L CNG Engine

0.02 g NOx/ bhp-hr
Greenkraft V8 8.0L Engine

0.02 g NOx/ bhp-hr
Encore Tec 6.8L CNG Engine

0.05 g NOx/ bhp-hr
Encore Tec 6.0L CNG Engine

0.05 g NOx/ bhp-hr
Cummins-Westport ISBG 6.7L CNG Engine

0.1 g NOx/ bhp-hr
ROUSH CleanTech V10 6.8L CNG Engine