Diesel engines play a vital role in the power generation, transportation, marine applications etc. Intensive research efforts are ongoing for improving combustion efficiency, fuel consumption and exhaust emissions from diesel engines. To increase the combustion efficiency, turbulence plays a very important role in the combustion phenomenon of C.I engine. Hence even a small increase in the combustion efficiency will result in greater advantage. The turbulent motion of the mixture intensifies the better mixing. The turbulence can be increased by suitable designing of combustion chamber, which involves the geometry of cylinder head, inlet manifold and piston crown. In the present work, the experimental investigation of air swirl in the cylinder upon the per-formance and emission of a single cylinder direct injection diesel engine is presented. Turbulence is created in the engine cylinder by cutting trapezoidal grooves on the piston crown, three different configurations of the piston i.e. ,in the order of 2, 4, 8 are used to intensify the swirl for better mixing of air and fuel. A series of experiments are conducted on four stroke single cylinder direct in-jection diesel engine with grooved piston and compared with that of normal piston. Performance parameters such as brake power, specific fuel consumption, and thermal efficiencies are calculated based on the experimental analysis of the diesel engine .Emissions such as carbon dioxide, carbon monoxide, unburnt hydrocarbons, and NOx are measured.