What Causes the Crisp Sound of Metal Striking in a Car?

[StPresley]

This phenomenon is an abnormal combustion condition known as knocking or detonation, which commonly occurs in gasoline engines under low-speed, high-load conditions. Below are the relevant details:1. Impact: After the air-fuel mixture in the cylinder is ignited by the spark, the flame front spreads outward at a certain speed, releasing heat and causing the pressure and temperature inside the cylinder to rise. The distant mixture is affected by thermal radiation and pressure propagation, leading to an increase in its pressure and temperature as well. Before the flame front reaches it, this mixture auto-ignites, effectively creating multiple ignition points within the cylinder, which sharply increases the rate of heat release.2. Heat Release Rate: The rapid increase in the heat release rate causes the temperature to rise quickly and the pressure to change drastically, forming pressure waves that propagate back and forth within the cylinder. These waves strike the combustion chamber walls, causing them to vibrate and produce the knocking sound.