Otto Cycle PV Diagram made easy

What is the Otto cycle PV diagram?

The Otto cycle PV diagram is a diagram to show variations in the pressure and volume of the working substance/fluid during the various processes of the Otto cycle.

PV diagram

Otto cycle PV diagram and Actual PV diagram of otto cycle
V2=V3= Clearance volume;

various Processes of the otto cycle

The Otto cycle or constant volume cycle is the theoretical cycle for the spark-ignition engine. This cycle is so named as it was invented by ‘Otto’. In the air cycle analysis, the theoretical Otto cycle PV diagram is used.

With respect to the theoretical PV diagram for the Otto cycle

  • Line path 0-1 Induction or suction Process
  • Curve path 1-2 represents the adiabatic compression of air and air pressure is increased from P1 to P2 and the volume decreases from V1 to V2
  •  Line path 2-3 shows the supply of heat to the air at a constant volume and the pressure of the air increases from P2 to P3
  • Curve path 3-4 represents the adiabatic expansion of the air and the air pressure decreases from P3 to P4 and the volume increases from V3 to V4
  • Line Path 4-1 shows the rejection of heat by air at constant volume till the original state i.e. at the end of this process pressure and the volume of the air will be equal to P1 and V1 respectively.
  • Line Path 1-0 represent the Exhaustion Process
  • Net work done is equal to the area under the curve 1-2-3-4-1

Actual otto cycle PV diagram or the indicator diagram of the Otto cycle

The actual PV diagram of a Spark-ignition engine which works on the Otto cycle will differ from the theoretical PV diagram as shown in the figure. This is due to the non-instantaneous burning of the fuel and valve operation, incomplete combustion etc.

If you want to see the theoretical TS diagram of the Otto cycle then click/tap here

If you want to know more about the Otto cycle and its efficiency then click/tap here

If you want to compare the Diesel cycle with the Otto cycle to see which is better then click/tap here

If you want to check the PV diagram of the Diesel cycle then click/tap here

If you want to check the PV diagram of the Carnot cycle then click/tap here


  • Thermal Engineering by R.K Rajput
  • Internal Combustion Engine by M.L Mathur, R.P Sharma