what is the use of pv diagram for diesel cycle?

What is the use of PV diagram for diesel cycle?

Diesel cycle comprises various processes that determine the performance of the engine. To better understand the variations in the pressure and volume of the working substance/fluid during these processes for studying the performance of the diesel engine, a PV diagram for diesel cycle is used.

Diesel Cycle PV diagram

PV diagram for diesel cycle, Diesel cycle PV diagram
r=Compression Ratio; Q1=heat supplied; Q2=Heat rejected;

With respect to PV diagram of the diesel cycle

  •  path 0-1 Induction or suction Process
  • 1-2 Adiabatic compression.
  • 2-3 Addition of heat at constant pressure.
  • 3-4 Adiabatic expansion.
  • 4-1. Rejection of heat at constant volume.
  • Area Under the curve 1-2-3-4 represents net work done

Working of the Diesel cycle referring to the PV diagram in the Piston Cylinder Engine

Piston cylinder engine to illustrate the function of the Diesel cycle using PV diagram.
Figure shows Piston Cylinder Compression Ignition Engine

At point 1, the cylinder is full of air at a certain pressure and volume, denoted by P1 and V1. Next, the piston compresses the air adiabatically until it reaches point 2, where the pressure and volume become p2 and V2. 

Then, heat is added to the system at a constant pressure, causing the volume to increase to V3, which is known as the point of cut-off, at point 3. 

After that, the air expands adiabatically to reach point 4, where the pressure and volume become p4 and V4. 

Finally, the air rejects heat to the cold body at a constant volume until it returns to its original state at point 1.

If you want to know more about the Diesel 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 Otto 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