Knocking and Detonation (Thermal Engineering)

Basically both knocking and detonation are phenomenon which cause same effect

i.e abnormal engine sound.

Knocking

1. It is the result of rapid burning of end charge.
2. When end charge gets pre-ignited and pressure wave/flame front produced collides with original wave/flame front. 
3. This is generally observed at the end of combustion.

Detonation

1. It results due to instantaneous burning of large amount of charge. 
2. This is observed at the starting of combustion.

A general term Knock can be used for the sound caused by both knocking and detonation.