The variation of pressure inside the cylinder with respect to volume for two stroke petrol engine can be represented. The pressure drops closer to atmosphere level from the opening of exhaust port and thereafter remains at the same level till the piston comes back in its return smoke to close the exhaust port. The compression and expansion follow any one of isentropic, polytropic or isothermal laws. Heat addition is at constant volume in SI engine. For two stroke diesel engine the only change in the pv diagram is the constant pressure heat addition process.
