West Virginia University (WVU) scientists at the Center for Alternative Fuels, Engines and Emissions (CAFEE) have conducted a new study on methane emissions from heavy-duty natural gas vehicles (NGVs) and refueling stations.
The report, recently published by Environmental Science & Technology, greatly expands on very limited data on methane emissions from NGVs and has been publicly supported by the Environmental Defense Fund and numerous organizations from the natural gas industry, including a variety of NGVAmerica members.
“The natural gas vehicle industry has taken a proactive approach to reducing methane emissions, and this study provides a valuable baseline from which to understand emissions from natural gas vehicles and fueling stations on a pump-to-wheels basis,” says NGVAmerica President Matthew Godlewski. “The findings confirm that many of the technologies being deployed on the latest generation of natural gas engines and refueling infrastructure are dramatically lowering emissions and continue to make natural gas the ‘greenest’ choice for fleets across North America.”
As reported, the researchers studied 22 natural gas-fueled transit buses, refuse trucks and over-the-road tractors and six liquefied natural gas (LNG) and eight compressed natural gas (CNG) refueling stations.
Today’s NGVs provide significant environmental benefits, including the lowest emissions of nitrogen oxides (NOx), particulate matter and other pollutants that directly affect public health. Additionally, the latest engines (which were not among those studied as part of this research) include closed-crankcase systems and other upgrades that optimize operation and increase efficiency. For these new spark-ignited natural gas engines, these changes have resulted in a more than 70% reduction in methane emissions compared with engines produced only a few years ago.
The study found that emissions from natural gas stations and refueling infrastructure contributed less than 20% of the methane emissions examined. New technologies and best practices at CNG and LNG stations with dispensers, compressors, boil off gas management systems for storage tanks, and other equipment are lowering these emissions even further, and the study provides a solid baseline to demonstrate future improvements.
Although the WVU study did not examine the increasing role of renewable natural gas (RNG), recent studies have found that RNG (captured from landfills, wastewater treatment and other sources) can reduce total greenhouse emissions by more than 80%. NGVAmerica estimates that 20%-30% of all natural gas used for transportation is now low-carbon RNG. According to the U.S. Environmental Protection Agency, RNG accounts for the largest share of cellulosic biofuel currently sold in the U.S.
“NGVAmerica applauds the cooperative approach taken with this study and will incorporate its findings in the ongoing work of our Technology & Development Committee that is continuously evaluating further product enhancements and best practices,” says Godlewski.
CAFEE scientists collaborated on the study with the 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.
WVU says that a Scientific Advisory Panel comprising academic experts in the fields relevant to the study served as independent advisors, reviewing the appropriateness of the methodologies, results and statistical methods.
Click here for the study’s release.