What is Knocking and Detonation?
Detonation or Knocking occurs when a highly compressed air-fuel mixture in the combustion chamber is fired, the flame front travels from the spark plug in an outward direction. As the charge continues to burn, pressure increases greatly. If the pressure in any part of the combustion chamber raises high enough, before the flame front reaches it, the heat from the compression will raise the temperature of the air-fuel mixture enough to ignite itself. This will produce two flame fronts that will therefore increase the burning rate. Instead of burning smoothly, a violent explosion occurs that cause heat and pressure waves. This can cause severe damaging to the engine. Detonation can be caused by a low grade of fuel, a bit of glowing hot carbon, excessively high compression ratio, or an overheated valve, etc.. This can ignite the "end gas" and thereby cause the formation of the second flame front.
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