New WVU study examines pump-to-wheels methane emissions from the natural gas-fueled heavy-duty transportation sector

 CAFEE mobile testing vehicle

A study of methane emissions from heavy-duty natural gas-powered vehicles and refueling stations by West Virginia University scientists at the Center for Alternative Fuels, Engines and Emissions, recently published by Environmental Science & Technology, greatly expands on very limited data on methane emissions from natural gas-fueled vehicles. The WVU pump-to-wheels study is the first end-use paper in a collaborative scientific research series designed to measure and better understand the sources and amount of greenhouse-gas methane that is emitted across the natural gas supply chain.

Natural gas-fueled vehicles are expected to play an increasing role in meeting future transportation fuel needs. By relying on a cleaner-burning fossil fuel, natural gas engines can produce fewer greenhouse gas emissions than diesel – but only if methane emissions are kept low. WVU researchers are applying the study’s data to develop models to forecast methane emissions from the future heavy-duty transportation sector. This published data and forthcoming report can help the industry target improvements in engine technologies and fueling operations, and identify best practices for minimizing emissions.

“Natural gas vehicle and dispensing technology has evolved steadily. We characterized methane emissions from real-world operations to support well-informed projections of future pump-to-wheels contributions from heavy-duty vehicle use,” said Nigel Clark, George Berry Chair of Engineering and professor of mechanical and aerospace engineering.

Researchers looked at methane emissions from the pump-to-wheels sector of the natural gas supply chain and characterized emissions factors for each major source associated with currently manufactured heavy duty vehicles and fueling systems. The researchers studied 22 natural gas-fueled transit buses, refuse trucks and over-the-road tractors, and six liquefied natural gas and eight compressed natural gas refueling stations. Scientists also examined cryogenic boil-off pressure rise and pressure control venting from LNG storage tanks, using both theoretical and empirical modeling. Vehicle tailpipe and crankcase emissions were found to be the highest sources of methane. 

CAFEE scientists collaborated on the study with Environmental Defense Fund and a group of industry leaders including: the American Gas Association, Chart, Clean Energy, Cummins, Cummins Westport, International Council on Clean Transportation, PepsiCo, Shell, Volvo Group, Waste Management, and Westport Innovations. Sponsors provided access to vehicles or facilities. Equipment for testing was also provided by a number of other industry participants or rented. 

A Scientific Advisory Panel comprised of academic experts in the fields relevant to the study served as independent advisors, reviewing the appropriateness of the methodologies, results and statistical methods.

A detailed website for the study can be found online.

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