What causes combustion knocking in an engine?

Combustion knocking, also referred to as engine knocking or pinging, is primarily caused by a sharp increase in pressure within a cylinder before the intended ignition timing. This phenomenon occurs when the air-fuel mixture ignites too early in the compression stroke, resulting in a rapid and uncontrolled rise in pressure. This creates a shock wave within the cylinder that causes the characteristic knocking sound.

This early ignition can lead to uneven combustion, which not only affects engine performance but can also cause damage over time. When the pressure rises abruptly rather than steadily, it can lead to vibrations and noise due to the excess force acting on engine components.

While inadequate fuel delivery, excessive carbon buildup, and poor quality fuel can all contribute to engine performance issues and may lead to conditions that favor knocking, they do not directly cause the sharp pressure peaks associated with combustion knocking. The key factor in this situation is the premature ignition that results in sudden spikes in cylinder pressure.