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Dec 4, 2017

Why is there a knocking sound coming from my engine?

Why is there a knocking sound coming from engine? Before the compressed air-fuel mixture gas is ignited by a spark, the gas is partially exploded for certain reasons.

This phenomenon is called knocking, and the explosion speed of this abnormal combustion is very fast, and it may cause serious damage to the piston and cylinder head.


What can cause an engine to knock?
The normal combustion speed of the air-fuel mixture in the combustion chamber is 20 to 30 m/s. The combustion speed during the occurrence of knocking, or during abnormal combustion, will be extremely high, which is approximately 1,500 m/s.

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During this abnormal combustion, the impulse wave that is generated from it makes a knocking sound.

For an automobile engine, a bore diameter of approximately 110 mm is the threshold limit for preventing the occurrence of knocking.

 How can we prevent engine knocking?
1. Retard the ignition timing of the engine.

2. Remove the carbon deposit in the combustion chamber to decrease the compression ratio and to remove hot spots.

3. Use premium high octane gasoline to raise the ignition point of the fuel. The higher the octane numbers of the gasoline the higher the ignition point of the fuel. RON 95 or higher can be used.

4. Change the spark plug heat range (to cold type).

Using the above measures, knocking can be prevented. In most cases, high-performance engines are designed to use premium gasoline in order to obtain the maximum performance as well as to prevent knocking.

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