What is knocking?

  • The air-fuel mixture burns moderately and uniforms at a rate in the cylinder of internal combustion (IC) engine.
  • The metallic or rattling sound in the cylinder of internal combustion engine due to explosive violent combustion of the air-fuel mixture is known as knocking.
  • In a petrol engine, if the combustion rate air diesel mixture initiated due to compression of air becomes very slow then a large amount of fuel is collected in the cylinder.
  • This accumulated fuel burns violently and non-uniformly producing a loud sound. This is known as diesel knock.

Knocking is also produced due to

  • Nature of fuel
  • Engine design
  • The shape of the engine head
  • Running conditions

Disadvantages of knocking

  • knocking increases the engine noise and engine runs roughly due to crankshaft vibrations.
  • If knocking is high, it may break the piston.
  • It decreases power output and efficiency of the machine.
  • Deposition of unguent carbon increase in the engine increase due to knocking.

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