The following processes take place during one cycle of an Internal Combustion Engine.

  1. Suction
  2. Compression
  3. Expansion
  4. Exhaust
IC Engine Schematic
Fig :- General Diagram of Parts of an Internal Combustion Engine


  • The charge which is usually a mixture of air and fuel is drawn into the engine during suction.
  • Due to the downward movement of the piston, the charge is taken inside the engine because the pressure inside is less than atmospheric pressure.
  • After the charge has entered the engine, the pressure equates and the inlet valve closes.
  • The piston moves down during the entire process i.e., it will move from TDC (Top Dead Center) to BDC (Bottom Dead Center).

Compression & Expansion :-

  • During compression, the pressure inside the engine cylinders rises, i.e., the pressure goes above atmospheric pressure.
  • This happens due to the piston moving upwards i.e. from BDC to TDC.
  • After the compression processes spark plug produces sparks, which will ignite the air-fuel mixture.
  • Then an explosion takes place inside the engine, because of which there is high pressure rises inside the cylinder.
  • Hence piston starts moving from TDC to BDC at very high speed, thereby converting the chemical energy to mechanical work.


  • After the expansion processes or power stroke is completed then the burnt gases, as well as some amount of unburned charge, will be exhausted from the engine cylinder.
  • So, the piston will start from BDC to TDC, the inlet valve is closed and the exhaust valve is open, the gases inside the engine are exhausted or sent out from the engine to the atmosphere.

In this way the processes inside an engine gets completed.

Nikhil Picture

About the Author: Cadet Nikhil Kumar Choudhary is a first-year student at the Tolani Maritime Institute, Pune and currently taking up Marine Engineering, where he developed the gift of declamatory and is said to have eloquent writing skills. His chief incentive of writing is to convey about Marine Technology and Machines.

Similar Posts


Hey Visitor! Let us know what are you thinking about this post!

This site uses Akismet to reduce spam. Learn how your comment data is processed.