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To increase the operational range of the vehicle equipped with direct injection gas supply and to eliminate the problems associated with the cryogenic pumps, a composite high pressure vessel is proposed for use as a thermocontrolled tank in vehicles. The test results showed that the liquefied natural gas can be brought from atmospheric pressure to the high pressure required for direct injection in a reasonable time period. Based on these results a mathematical model for the heat transfer to the natural gas was developed and simulated. Three different aspects of gas storage, namely, the initial operational temperature, the gas to vessel mass ratio and the gas weight to vessel volume ratio have been investigated and formulated as objectives for optimization. Due to the presence of different conflicting objectives, the problem was formulated as a nonlinear multi objective optimization problem and then solved.

A new electronically controlled fuel system is proposed for direct injection of natural gas in diesel engine. It consists of the solenoid controlled injectors interfaced with a metering valve under stepper motor control. This system proved to operate well in different configurations with metering valve being located at various distances from the injector; two injectors interfaced by one metering valve were also tested. In all cases, the required maximum and minimum gas doses were obtained, either by the change of the metering valve flow area or the injector opening time. The gas dose was measured using a special closed chamber. The conclusions drawn from these tests were used for the proposal of improvement of the injector design in order to reduce its size and weight and obtain more reliable operational characteristics.