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The Maryland Mass Transit Administration conducted an LNG transit bus demonstration in Baltimore, Maryland. A refueling facility was constructed and maintenance facilities were modified to provide support for the demonstration. During the demonstration operational data were collected on the buses and facilities. Problems encountered with the vehicle LNG fuel systems are reviewed and discussed. This paper summarizes the findings and operation of the LNG fleet during the demonstration and projects future LNG vehicle and operational costs.

This project demonstrates the use of M85 as an alternative fuel for vehicle operation. The fleets chosen for this demonstration experienced driving conditions typical for most vehicles, i.e., interstate highways and suburban traffic. Four generations of flexible fuel vehicles (FFVs), the 1986 and 1989 Ford Crown Victoria and the 1991 and 1993 Ford Taurus, were used in individual fleet operation. The demonstration spanned a period of over seven years from 1988 through 1995 and approximately 220 vehicle-years of M85 FFV operational data were collected. These data were analyzed to create a comprehensive knowledge base for fuel economy, emissions, driveability, acceleration, maintenance and wear characteristics of FFVs. A comparison of the overall performance of these vehicles with conventional gasoline vehicles was made. Important experience in the design, construction and maintenance of M85 refueling facilities was obtained over the duration of this project.

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.