A West Virginia University (WVU) pump-to-wheels study is the first end-use paper to quantify and discuss the sources and amount of greenhouse-gas methane that is emitted across the natural gas supply chain. The collaborative study was carried out at the WVU Center for Alternative Fuels, Engines and Emissions (CAFEE) and was recently published by Environmental Science & Technology.
CAFEE scientists collaborated on the study with the Environmental Defense Fund (EDF) and a group of global natural gas industry leaders including the American Gas Association, Chart Industries, Clean Energy, Cummins, Cummins Westport, International Council on Clean Transportation, PepsiCo, Shell, Volvo Group, Waste Management, and Westport Fuel Systems. The results greatly expand on the very limited data on methane emissions from natural gas vehicles.
Westport Fuel Systems Inc., a global company that designs and manufactures advanced clean-burning fuel systems, commended the publication:
“This study offers a critical baseline by which ongoing product and technology enhancements can be measured, as it represents the first significant effort to quantify actual in-use methane emissions from natural gas filling stations and heavy-duty vehicles”, said Karen Hamberg, Vice-President of Natural Gas Industry and Government Relations. “Natural gas-fueled vehicles are expected to play a greater role in future transportation to meet the global regulatory trend for more stringent greenhouse gas emission (GHG) reductions. The natural gas vehicle industry has already implemented technology solutions to dramatically minimize, or in some cases, eliminate the largest sources of methane emissions from vehicle tailpipe, crankcase ventilation, and dynamic venting that were identified in the study.”
“We have seen global interest in Westport High Pressure Direct Injection 2.0 (Westport™ HPDI 2.0), a next generation natural gas technology that is optimal for heavy-duty vehicles. Westport™ HPDI 2.0 features further improvements to maximize the GHG benefits of natural gas, such as the capture of dynamic venting. It is the only natural gas engine technology that can achieve diesel engine efficiency within 1% with inherently low engine-out unburnt methane emissions.”
“For the North American market, the newly launched ISL G Near Zero 8.9L and ISB6.7 G engines from Cummins Westport Inc., our joint venture with Cummins Inc., feature closed crankcase ventilation that significantly reduces engine-related methane emissions while also meeting California Air Resources Board (“CARB”) optional low NOx standards”, added Hamberg.
The study says 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 (LNG) and eight compressed natural gas (CNG) refueling stations. Scientists also examined cryogenic boil-off pressure rise and pressure control venting from LNG storage tanks, using both theoretical and empirical modeling.
Although vehicle tailpipe and crankcase emissions were found to be the highest sources of methane, the research paper in its concluding discussion concurs with Westport’s position that manufacturers are already implementing preventative technologies in new natural gas vehicles.
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.
The study can be downloaded from here: pubs.acs.org/doi/abs/10.1021/acs.est.5b06059
Westport Fuel Systems is an NGV Global corporate member.
Endnote: Figure 5. Absolute and relative contribution of methane emissions by component for the base case scenario. Numbers represent the average methane loss per unit of fuel used (g/kg). The percentage values reflect the contribution of each source to the total PTW emissions.
(Source: West Virginia University; Westport Fuel Systems)
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