The Effects of LNG Weathering on Fuel Composition and Vehicle Management Techniques

The Maryland Mass Transit Administration has operated four liquefied natural gas (LNG) transit buses since late 1993. LNG is unique among alternative fuels in that it has a short “shelf life.” As a result of heat gains, LNG fuel weathers at predictable rates, resulting in the potential loss of fuel mass and the potential loss of methane content. Early experience with LNG transit buses included engine failures due to insufficient octane caused by low methane content of the fuel. LNG systems can be managed to offset the effects of fuel weathering, given consistent fuel quality. Methods of predicting LNG fuel quality after weathering has occurred (both bulk and onboard storage tanks) are presented based on field experience. Vehicle operational management techniques that can reduce LNG weathering and possible engine damage are also presented. LNG is a viable alternative fuel for heavy-duty vehicles, offering good range and emissions, providing consistent quality LNG motor fuel is available and proper management of LNG weathering and vehicle operation occurs.