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Difference between SI Engine and CI Engine

Difference between SI Engine and CI Engine:

SI and CI Engines are used to generate heat energy and further heat is converted into mechanical energy to run the vehicle. SI engine required a spark plug to ignite the air-fuel mixture. but in CI engine it ignites the air-fuel mixture with the help of high compression ratio.

SI Engine(Spark Ignition Engine):


  1. SI Engine required spark plug to burn the fuel.
  2. SI engine has less compression ration than CI engine
  3. Petrol is used in SI engine.
  4. SI engines have low thermal efficiency.
  5. The carburetor is used in SI engine to supply the fuel to the engine.
  6. Operating pressure is less in Si engine.
  7. Cost of running is more, but less maintenance.
  8. Si Engine is easy to start.
  9. It has low cranking effort.
  10. The temperature of exhaust gas is high.
  11. SI engines have less weight than CI engines.
  12. It develops less vibrations, low sounds, etc.
  13. This type of engines are used for light weight vehicles.

CI engine(Compression Ignition Engine):


  1. CI engines burn the fuel with the help of high compression ratio.
  2. CI engines have high compression ratio.
  3. Diesel is used in CI engine.
  4. CI Engines have high thermal efficiency.
  5. Injectors are used in CI engine.
  6. Operating pressure is high in CI engines.
  7. Cost of running is less but more maintenance.
  8. CI engine is difficult to start.
  9. It has a high cranking effort.
  10. The temperature of exhaust gas is low.
  11. Ci engines have more weight than SI engines.
  12. It produces high vibratuions and more sounds.
  13. This type of engines are used for heavy weight vehicles.

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