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.