Direct injection diesel engines are used in both light duty and heavy duty vehicles because of higher thermal efficiency compared to SI engines. However, due to only short time available for fuel-air mixing, combustion process depends on proper mixing. As a result, DI Diesel engine emits more NOx and soot into the atmosphere. Therefore, to achieve better combustion with less emission and also to accelerate the fuel-air mixing to improve the combustion, appropriate design of combustion chamber is crucial. Hence, in this work a study has been carried out using CFD to evaluate the effect of combustion chamber configuration on Diesel combustion with two different piston bowls. The two different piston configurations considered in this study are centre bowl on flat piston and pentroof offset bowl piston. Combustion pressure, heat release rate, flame structure, fuel injection on flow field, spray structure, droplet diameter, droplet velocity, Nox and soot emissions have been calculated and the best piston configuration has been arrived. As combustion studies could not be validated, the flow field studies are validated. From this study, it is concluded that pentroof offset bowl piston configuration is better.