The present paper investigates effect of piston bowl geometry on combustion and emissions. One of the important parameters which affect the combustion in diesel engine is piston geometry. In this study four different piston geometries (HEMISPHERICAL, OMEGA, SINGLE CURVED, DOUBLE CURVED) have been selected for comparative study. Numerical investigation has been carried out using commercially available code AVL FIRE which is a finite volume based code .Automatic mesh generation feature of code is utilized for modelling. For validation of numerical model, simulation results of baseline shape have been validated with experimentally available results. Simulation has been carried out for various piston geometries while keeping parameters such as speed, compression ratio and mass of fuel injected constant. The study has been carried out at full as well as half load .A comparative study for in-cylinder pressure, rate of heat rejection, velocity and temperature field, turbulence kinetic energy has been performed .Emission and performance parameters like SOOT, NO ,efficiency and BSFC have been studied. The results indicated that omega shaped piston works best for the current setup. As compared to baseline shape of hemisphere, it gives 12% higher NO but 19% less SOOT. Also, the efficiency and BSFC are better for omega shaped piston.