Recently the analysis of air-fuel mixing and combustion has become important under the stringent emissions regulations of diesel engines. In the case of gasoline engines, the KIVA computer program has been developed and used for the analysis of combustion. In this paper, the calculations of combustion phenomena in DI diesel engines are performed by modifying the KIVA program so as to be applicable to multi-hole nozzles and arbitrary patterns of injection rate. The thermophysical and ther-mochemical properties of gasoline are altered to those diesel fuel.In order to investigate the ability of this modified program, the calculations are compared with the experiments on single cylinder engines concerning the pressure, flame temperature and mass change of chemical species in cylinders.Furthermore, the calculation for the heavy duty DI diesel engine is performed with this diesel combustion program. From this calculation results the gas flow, spray shapes, air-fuel mixing process, and combustion in this engine are investigated.