Explain knocking in diesel

In a diesel engine, if the combustion rate of air diesel mixture initiated due to compression of air becomes very slow then a large amount of fuel collected in the cylinder. This accumulated fuel burns violently and non uniformly producing a loud sound this is known as diesel knock.

Knocking and chemical constitution of a fuel

Internal combustion (IC) engines use petrol (gasoline) or diesel as fuel. The air mixture is ignited in the cylinder either by an electric spark (as in ignition engine) or by compressing air (as in compression ignition engine). The gas formed pushes the piston down.