What is engine knock?

Engine knock, also known as detonation, occurs when unburned fuel in the combustion chamber ignites prematurely before the flame front from the main combustion process reaches it. This can lead to a sudden increase in pressure and temperature, causing a knocking or pinging sound. It is a destructive phenomenon that can significantly damage the engine if not addressed.

In terms of understanding the mechanics behind this, engine knock is often associated with high compression ratios, low-octane fuel, and high temperatures. Normal combustion involves a smooth, controlled burn of the air-fuel mixture, which should ignite in a consistent manner following the spark plug firing. When the unburned fuel ignites at the wrong time or places within the combustion cycle, it leads to an erratic combustion process, resulting in the characteristic knocking sound.

Recognizing the signs of engine knock is crucial for maintaining engine health, as prolonged detonation can result in severe engine damage, including damaged pistons, bearings, and the cylinder head.