Air Standard Otto cycle:
The air-standard-Otto cycle is the idealized cycle for the spark-ignition internal combustion engines. This cycle is shown on P-V diagram. The Otto cycle 1-2-3-4 consists of following four process:
Process 1-2: Reversible adiabatic compression of air.
Process 2-3: Heat addition at constant volume.
Process 3-4: Reversible adiabatic expansion of air.
Process 4-1: Heat rejection at constant volume.
 

Mean Effective Pressure is defined as the ratio of the net work done to the displacement volume of the piston.