Pump-to-Wheels Methane Emissions from the Heavy-Duty Transportation Sector

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Transportation Engineering

Background:

• Methane emissions from the heavy-duty (HD) transportation sector have significant climate change implications but are not well-documented.
• Natural gas is increasingly used as a fuel in the HD sector, necessitating an understanding of associated methane emissions.

Purpose of the Study:

• To characterize pump-to-wheels (PTW) methane emissions from HD natural gas vehicles and their fueling infrastructure.
• To quantify methane leaks and losses throughout the natural gas supply chain for transportation.

Main Methods:

• Developed a novel measurement system for quantifying methane leaks and losses.
• Characterized engine-related emissions from various HD natural gas vehicles (transit buses, refuse trucks, over-the-road tractors).
• Assessed losses from compressed natural gas (CNG) and liquefied natural gas (LNG) fueling stations, including compression, fuel delivery, storage, and leaks. Modeled cryogenic boil-off and venting from LNG storage tanks.

Main Results:

• Vehicle tailpipe and crankcase emissions were identified as the primary sources of methane emissions.
• Quantified methane losses from both HD natural gas vehicles and CNG/LNG fueling stations.
• Established a methodology to express PTW emissions as a percentage of fuel throughput.

Conclusions:

• Methane emissions from HD natural gas vehicles and fueling infrastructure are a critical area for mitigation.
• The developed measurement system and data provide a foundation for accurate emissions forecasting.
• Further research and policy development are needed to reduce methane emissions in the HD transportation sector.