What Is Diesel Cycle? What Are The Four Processes Of Diesel Cycle

Diesel cycle is also called as constant pressure cycle. The diesel engine operates on this cycle. This cycle also contains four processes, out of which two processes are adiabatic, the third one is constant pressure process and forth process is constant volume process.Diesel cycle is an air-standard cycle (a combustion process), which is used to design mostly compression ignition engines. Generally, these engines are heavier than petrol engines.

diesel cycle

Processes In Diesel Cycle-


  1. 1–2= Adiabatic compression
  2. 2–3= Heat addition at constant pressure
  3. 3–4= Adiabatic expansion
  4. 4–1= Heat rejected at constant volume

Following is the pressure vs volume graph for a diesel cycle.

diesel Cycle

Isentropic Compression (Process 1–2)

  • This process is called isentropic as there is no heat transferred (adiabatic) to or from the system and it is a reversible process.
  • The gas inside the cylinder is compressed isentropically from a volume V1 to V2.
  • The ratio of V1 and V2 is referred to as the compression ratio.
  • Work is done by the piston on gases (negative work Win), which means external work has to be done to compress the gases.
  • This process is characterized by the compression stroke of the 4-stroke cycle.


diesel cycle

Isobaric Heat Addition (Process 2–3)-

Add Comment