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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.

Two dimensional flame temperature distributions in D.I. diesel engine with high pressure fuel injection were measured by the image analysis of high speed photographs based on two color method. Effects of injection pressure and nozzle hole diameter on flame temperature distribution were examined. The flame temperature in the case of high pressure injection is higher than that in low injection pressure. The higher flame temperature in high pressure injection results from the rapid compression of burned gases. The KL value which is an index of soot density in the combustion chamber decreases as injection pressure increases. The higher oxidation rate of soot at the later period of combustion may contribute to a soot reduction in the case of high pressure injection.

A dissociated methanol fueled passenger car has been developed which shows improved transient driving and exhaust emission performance. In order to improve the transient performance, a mountable engine control unit, a new exhaust dissociator and a dissociated methanol flow control valve were developed among others and examined. The new exhaust dissociator has a extended heat transfer surface area and double injector to improve transient response and heat exchange efficiency. The dissociated methanol flow control valve which is controlled by intake manifold pressure works as a compensator for delayed dissociated methanol at transient driving. The high thermal efficiency and low exhaust emission level was observed for the transient driving as well as steady state driving.

Ignition and combustion of methanol in a spark-assisted methanol diesel engine were studied for the purpose of developing such an engine that is practical for actual vehicles. It became clear through investigations on combustion of methanol in a spark-assisted methanol diesel engine that methanol combustion proceeds mainly by flame propagation. Based on this finding, effects of such parameters as the injection direction, ignition position, ignition energy, compression ratio, injection timing and ignition timing were studied to obtain optimal conditions for methanol combustion. It was found through such studies that it is effective to form the mixture upstream of the spark, plug relative to the swirling direction and increase the inductive component of the ignition energy to achieve a high ignition stability.