Reasons behind knocking in CI engines

Knocking in CI engines
Knocking in CI engines

In this article, we are going to shed some light on reasons behind the Knocking in CI engines which is also called as Abnormal Condition of the engine.

Knocking in CI engines:

  • In spark ignition engines (SI engines), at the end part of the gas, if flame speed and delay period are low in the combustion chamber, produce detonation in SI engine. In the case of the CI engine, it was the first part of the gas which causes the Knocking in CI engine and rough running of the engine.
  • In CI engines, when fuel is injected in the combustion chamber and combustion occurs by the way of the autoignition system. When the period of injection of fuel is long, an excess amount of fuel starts to inject in the combustion chamber. Then there is a large amount of fuel accumulate in the combustion chamber due to longer injection of fuel or delay period.
  • When there is uncontrolled combustion, the amount of fuel accumulated in the combustion chamber suddenly explodes. It increases the rate of pressure rise in the combustion chamber and ultimately high pressure. This high rate of pressure rise in the internal combustion engine is equivalent to a sudden increase in load on the engine.
  • Also high and increasing pressure of gases in the chamber affects the whole engine structure during the pressure equalization process. Due to this, you will hear a thudding sound from the engine, the same sound is called Knock or Knocking in CI engine.
  • From the above explanation, we can conclude that the knocking in CI engines occurs if the delay period of injection is longer than the usual condition.

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