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Study Provides Roadmap to Lower Methane Emissions
November 8, 2017

Following the recent decrease in the price of natural gas, interest has increased throughout industry and in the scientific community to discover ways to use it as a cleaner replacement for diesel fuel. Although natural gas vehicles (NGV) currently make up a small market share, they are predicted to grow significantly over the next few decades.

Study Co-PI Dr. Johnson searches for natural gas leaks during the audit of equipment at a compressed natural gas (CNG) station. Credit: West Virginia University.

However, there is a formidable challenge as researchers try to balance the positives against the negatives. The primary component of natural gas is methane, a cleaner burning, low carbon fuel, the positive side. But methane is also a powerful greenhouse gas already shown to have detrimental environmental impacts when released into the atmosphere, the negative side.

According to information from West Virginia University (WVU), researchers at the Center for Alternative Fuels, Engines, and Emissions at WVU have completed a new study that builds upon recent heavy-duty natural gas vehicle methane emission measurements to model methane emissions from a future, much larger vehicle fleet. Details of the research, published in the Journal of Air and Waste Management Association illustrate the predicted methane emissions rates from a 2035 natural gas fleet based on technologies adopted and best management practices employed.

The paper, “Future Methane Emissions from the Heavy-Duty Natural Gas Transportation Sector for Stasis, High, Medium, and Low Scenarios in 2035,” used data from a prior study to project various scenarios in order to evaluate potential emissions reductions of technological advances and best management practices. The study did not look at the full suite of vehicles on the road today but rather focused on vehicles and engines currently under production as these represented those most likely to populate the fleet in 2035. Consequently, the study does not estimate emissions from the current fleet.

“We considered both liquefied natural gas and compressed natural gas technologies employed in a future fleet and considered a range of engine applications including over-the-road and refuse trucks and buses,” explained Nigel Clark, professor of mechanical and aerospace engineering and George Berry Chair at WVU. “Our first study served to highlight fuel losses meriting future attention and we assess the impacts of their potential reductions within this study.”

This study found that the biggest reduction in emissions would come from implementing closed crankcase ventilation systems on heavy-duty natural gas spark ignition engines. Adherence to best practices during fueling and fuel station management could also have a significant impact on the amount of methane leaked through reduction in manual venting of liquid nitrogen gas (LNG) tanks and proper design of station and fleet combinations. In addition to current and new technologies, regulation and policy may lead to further developments that could reduce methane emissions.

“While the models in this paper provide valuable insights on technological and management practice improvements to reduce methane emissions as the natural gas fleet grows, the study only looks at the emissions from the fleet and associated infrastructure, or the ‘pump-to-wheels’ emissions. However, to understand fully the climate benefits of an industry swing from diesel to natural gas, the full ‘well-to-wheels’ emissions must be considered,” noted Joe Rudek, lead senior scientist, Environmental Defense Fund.

Support for this paper was provided by the Environmental Defense Fund, Cummins, Cummins Westport, Royal Dutch Shell, the American Gas Association, Chart Industries, Clean Energy, the International Council on Clean Transportation, PepsiCo, Volvo Group, Waste Management and Westport Innovations. Support was also provided by West Virginia University’s George Berry Chair endowment and the WVU Transportable Chassis Testing Laboratory personnel.

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