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As alternative fuel, natural gas holds a dominant position with widely distributed resources in the world and a low CO2 emission rate compared with the other fuels for automobile. Natural gas should be used in liquid phase (LNG) especially in automobile use due to considerations of energy density. Research and development was conducted for a practical LNG vehicle equipped with a LNG engine and LNG supply and engine control systems. The LNG engine system was given a high compression ratio, manifold gas injection, and spark ignition for the effective use of natural gas. For the components of LNG supply system, LNG tank, vaporizer, LNG control valve and gas injector were developed. The LNG tank and the LNG control valves were given super insulation constructions to prevent gas boil off. LNG was vaporized using heat from the radiator. The gas injector is controlled by a solenoid coil for optimum fuel supply. A computer using fuzzy logic was developed in part for the engine control system.

A new model to describe diesel combustion process has been developed. In this model diesel combustion field is divided into two zones, premixing and combustion. Turbulent mixing process is described by the stochastic approach in each zone separately. Comparison of calculations with experimental results showed that this model can predict the entire course of heat release and nitrogen-oxide formation precisely, under wide-spread conditions. Two-dimensional flame temperature distributions in the combustion field by the two color method were compared with simulation results. Both the measured and the calculated flame temperature distributions showed good agreements with each other. In the diesel combustion process, the injected fuel mixes with air entrained inside the spray. The mixture is thus formed, and ignites at several points. Random expansion of flamelets accelerates both mixing and combustion. Following this, fairly moderate diffusion combustion proceeds.