What does engine knocking mean?

[Allison]

Engine knocking occurs when the air-fuel mixture undergoes abnormal combustion inside the engine cylinder after being compressed by the piston. Here are the causes of engine knocking: 1. Excessive carbon deposits in the engine: Over-accumulation of carbon in the combustion chamber increases the compression ratio, creating hot spots on the carbon surface that lead to engine knocking. 2. Engine overheating: High intake air temperature in hot environments or poor engine coolant circulation can cause elevated engine temperatures and result in knocking. 3. Abnormal air-fuel ratio: An excessively lean fuel-air mixture raises combustion temperatures, increasing engine temperature and causing knocking. 4. Low octane rating: The octane rating indicates a fuel's resistance to knocking. Higher octane fuels have better anti-knock properties. High-compression engines with greater combustion chamber pressure are more prone to knocking when using low-octane fuel.