The article presents a modern approach for studying the combustion process in the DI Diesel engines developed for passenger car. The mixing controlled combustion model has been chosen for estimation the rate of heat released in the combustion chamber as well as the Arrhenius equation was used for ignition delay determination. The injection rate was calculated by means of constant injection pressure as well. Zero dimensional thermodynamic models have been used for estimation the in-cylinder parameters. All of the models were implemented as a computational code in Matlab. Finally, in-cylinder parameters variation such as pressure, temperature, rate of heat released etc., were studied at two engine operating points.