Turbulent flow field in a four cylinder direct injection (DI) diesel engine combustion chamber has been simulated using computational fluid dynamics (CFD). A commercial CFD code, namely Fluent was used to model 3D flow field. Three different geometrical shapes of combustion chamber were considered in the flow analysis in order to clarify the effect of combustion chamber geometry on the flow field characteristics. The simulation results showed that the bowl shapes of the combustion chambers greatly influenced the pressure, velocity and temperature distributions at the end of the compression stroke. Therefore, it has been concluded that geometry of combustion chamber could be optimized using CFD