This paper describes a simplified three-dimensional modeling of the mixture formation and combustion processes in a direct injection (D.I.) diesel engine. The fuel-air mixing and combustion processes in the D.I. diesel engine can be characterized by the combined effects of some processes, such as spray trajectory, fuel vaporization, gas motion, combustion, and dispersion of gaseous components and enthalpy. Each process was computed by a simple sub-model based on the experimental results and empirical equations. The dispersion process was, however, computed by solving the conservation equations of the gaseous components and enthalpy by the finite difference technique. The sub-models were combined for predicting the three-dimensional distributions of the gaseous components and the temperature in the combustion chamber, and finally the cylinder pressure, heat release rate, engine performance and pollutant emissions (NO and soot). An application of this model was made to a small D.I. diesel engine with a bore of 78 mm and a stroke of 86 mm. The computation was made under various intake swirl ratios and piston cavity diameters. Reasonable agreement between computed and experimental results for these engine variables demonstrate that, with appropriate adjustments to the empirical coefficients of each model, the model produces qualitatively realistic predictions of the in-cylinder processes and engine performance.