Growing demands on reduction of Internal Combustion Engine fuel consumption with increase of its performance new designs and optimization of existing ones are introduced. Air motion in CI Engine influences the atomization and distribution of fuel injected in the air charge. Better atomization of Injected fuel allows for a more complete burn and helps to reduce the engine Knock. A four stroke compression ignition engine with power 9 H.P and rated speed 1500 rpm is selected for the present work to investigate the performance characteristics. The swirl motion of the air is an important parameter in optimizing the performance of the engine. In order to increase the air velocity in the inlet manifold a convergent-divergent nozzle is used. The rise in velocity with the use of nozzle generates turbulence at the exit of the manifold which facilitates for better combustion of injected fuel. The Performance characteristics were calculated without nozzle and with out nozzle in the inlet manifold and compared
