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Natural gas vehicle (NGV) fuel energy storage density is a key issue, particularly in many heavy-duty applications where compressed natural gas may have unattractively low energy density. For these uses, benefits can be derived by using liquefied natural gas (LNG). From a market perspective, LNG can play a role for transportation because it is available in various areas of the United States and throughout the world. This paper provides a general overview of LNG use for vehicles and specifically an analysis of factors governing the behavior of this cryogenic fluid in a confined vessel. This is intended to provide an understanding of the cause/effect relation between LNG fuel composition, tank heat influx, and rate of fuel usage or storage time.

A dual-fuel conversion for the 3406-B Caterpillar marine diesel engine has been developed. The purpose of this conversion is to use lower priced natural gas as a fuel, thus providing substantial cost savings for large fuel consumers. The conversion applies dual-fuel technology to the smaller high-speed direct-injected diesel engine. Parameters are identified which allow a dual-fuel conversion to operate with similar performance as a diesel engine while simultaneously maintaining parameters that promote engine life. Test data is presented comparing various characteristics of both dual-fuel and diesel operation. Details of the conversion system are given. Data is presented showing fuel consumption, conditions leading to engine knock, conditions promoting methane flame propagation, and air-fuel ratios required for efficient combustion.