preignition

The ignition of fuel in an internal-combustion engine before the spark passes through the fuel, resulting from a hot spot in the cylinder or from too great a compression ratio for the fuel.

An ignition of the combustible charge of fuel and air in an internal-combustion engine before the piston, on its compressing stroke, has reached the inner dead-center, or completed the normal compression of the charge. See ignition, 5.

Ignition in an internal-combustion engine while the inlet valve is open or before compression is completed.

The premature detonation of a fuel charge in Four-stroke cycle engines.