Engine knock

[袁春凤 (Tiffany)]

Engine knock

In a gasoline engine, when the mixture (fully mixed with air and fuel) enters the combustion chamber at the intake stroke, the piston compresses it at the compression stroke. When the spark plug ignites the high-pressure mixture, the pressure generated by the combustion is converted to the power of the engine.

The right side of the high compression ratio setting, more prone to detonation, so the need to use high octane fuel to avoid detonation.

It is precisely because the combustion of the engine is very complex, so the need for a fairly accurate design and control, a little control error or abnormal, will cause abnormal combustion, and "detonation" is a kind of abnormal combustion. Simply speaking, knock is abnormal pressure in combustion chamber caused by abnormal combustion.

Causes of detonation

Firstly, the mixture burns in the combustion chamber, and the flame is spread around by the ignition point in a "wave", so it takes a short time from ignition to the complete combustion of oil and gas.

Second, although oil and gas need to be ignited by spark plugs, too high temperature, high pressure environment will also make oil and gas spontaneous combustion.

Generally, detonation is caused by the fact that the flame has not completely diffused after the ignition of oil and gas in the combustion chamber, and the long-range unburned oil is spontaneously ignited because of high temperature or high pressure. The impact between the flame and the normal burning flame produces great pressure, which makes the engine produce abnormal knock.