Is there any differences in knocking in petrol engine and that in diesel engine?

Answer 1

The knocking hammering sound in a diesel is just the normal sound made by the hi compression injection. The knocking in a gasoline engine is bad. It is caused by pre-ignition, usually caused by too low of an octane fuel or too advanced ignition timing. It will in time ruin a gasoline engine if you continue to run it with knocking (also called pinging) on acceleration or while climbing hills.