The cycle of compression in both the engines are different in the thermodynamic terms. The spark ignition engine is a gasoline or petrol engine which is based on the otto cycle. It uses a spark generated by the electric supply from the battery to ignite the petrol fuel to generate the power. Whilst, the compression ignition engine, also known as a diesel engine is based on a diesel thermodynamic cycle and ignites the fuel in the cylinder using the compression of the fuel from pistons. This is the main reason that the capacity of the diesel engine is more than a petrol engine.