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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.