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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.

An attempt is made to develop solenoid operated injectors for diesel engines, to inject natural gas directly into the combustion chamber at high pressure. These new injectors have the size of conventional diesel injectors with small but powerful solenoids located in the former spring chamber, and the spring is moved to a location closer to the nozzle. To provide fast opening and closing of the nozzle, a multiobjective optimization method is used to select the design variables of the injector. The mathematical model used for optimization is developed with the help of experimental results obtained from the solenoid force measurements at transient conditions. The optimization results did show good dynamic performance of the injector, despite the use of a small size solenoid actuator.

In our earlier papers on thermocontrolled tank storage system, we presented the basic concept of storing natural gas and the results from optimization of the vessel design. In this paper we are presenting optimization results of the entire storage system, assuming that the vehicle is running in a certain pre-scheduled pattern. Two kinds of vehicles have been considered for investigation, a city bus with a continuous running schedule and a car with a short run-park schedule. The initial waiting time, parking time, safe pressure ratio and range of the two vehicles have been investigated and then optimized to define the performance requirements.

A new concept of a semicryogenic tank for storage and supply of natural gas into the cylinders of an internal combustion engine is presented. It allows the gas to be pressurized before injection and uses the heat entering the tank as the means to evaporate the natural gas introduced in a liquid phase to the tank. To limit the heat transfer to the tank and the gas pressure increase, the semicryogenic tank has to be well insulated. However, it has to be also preheated to accelerate the gas pressure increase, as required. To maintain the right pressure and temperature of natural gas an electronic control of the semicryogenic tank is needed. The gas preheating system uses the waste heat of engine exhaust gases and, therefore, contributes to the increase of the thermal efficiency of the engine through the injection of hot natural gas.

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.