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Liquefied natural gas (LNG) use as a heavy-duty vehicle fuel is increasing. Current generation high-horsepower natural gas engines used in trucks and buses typically require fuel supply pressures in the range 75 to 120 psig. LNG delivered to the fueling station usually has a saturation pressure of roughly 10 psig. A variety of approaches may be used to provide the required fuel pressure increase. Each approach involves a different on-vehicle fuel system design, and LNG station capabilities must accommodate vehicle fuel system requirements. This paper describes various LNG vehicle fuel system design strategies including key tradeoffs, implications on station requirements, and developmental status. The most commonly used fuel system design receives and stores the LNG in the vehicle tank at a saturation pressure at least equal to the engine fuel supply pressure requirement.

Liquefied natural gas, commonly referred to as LNG, is gaining popularity as an alternate fuel for heavy duty automotive applications. The use of LNG as an alternate fuel for automotive applications is in its early stages and is not yet defined by any standards. While technology improvements are common within the automotive industry, changes in fuel formulation are usually minor and evolutionary in nature. Technology advancement may play a dominant role in defining the LNG fuel standard of tommorrow but, the emergence of LNG as an alternate automotive fuel requires LNG to shed its “cryogenic mystique” and assume properties which can be understood by the automotive user. The two industries, cryogenic and automotive, represent sophisticated, mature technologies, each individually understood within its respective industry.

This paper will establish the production quality for LNG vehicular fuel which will accommodate engine manufacturers' specifications for fuel quality at the engine. The potential degradation of the fuel from the time it leaves the production plant until it reaches the engine will be examined via a series of scenarios. The impact of engine manufacturers' fuel specifications will be translated into a vehicle fuel production specification which the consumer must utilize in selecting an acceptable fuel supplier.

This paper will establish the fuel quality necessary for use as a modern CNG and/or LNG vehicular fuel which will accommodate efficient performance and low emissions. The premise of using either BTU content and/or Wobbe index as a reliable means of fuel quality identification for vehicular fuel will be explored and discounted. Standards for transportation grade LNG will be developed.