- 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.