Engine knocking

Knocking or pinging in internal combustion engines occurs when the fuel ignites before the spark occurs at maximum compression. As the cylinder may still be in the compression cycle, the eary ignition may damage the cylinder.

Knock is detonation within the cylinder. Uncontrolled combustion. It is not the same as pinging/pinking which is pre-ignition.

Knocking can typically be prevented by higher octane gasoline, reduction of in cylinder temperature (cooling or compression reduction), or the addition of "lead" to the gasoline.

To the driver, knocking can be detected as "knocking" or "pinging" noise during hard acceleration.