In gasoline engine, when the mixture (air and fuel fully mixed) enters the combustion chamber in the intake stroke, the piston compresses it in the compression stroke. After the spark plug ignites the high-pressure mixture, the pressure generated by its combustion is converted into the power of engine operation.

發動機燃燒雖可以用三言兩語簡單的形容，但光是內燃機的燃燒研究，不知已造就了多少博、碩士論文，甚至許多學者、工程師窮其一生都在研究燃燒的學問，所以要真正了解發動機，是要花很多工夫的。

Although engine combustion can be simply described in a few words, I don't know how many doctoral and master's theses have been produced in the combustion research of internal combustion engine alone. Even many scholars and engineers have spent their whole lives studying the knowledge of combustion. Therefore, it takes a lot of effort to really understand the engine.

右側高壓縮比設定，比較容易引起爆震，因此需要使用高辛烷值的燃油避免爆震

The setting of high compression ratio on the right side is easy to cause knock, so it is necessary to use fuel with high octane number to avoid knock

正是因為發動機的燃燒十分復雜，所以需要有相當精確的設計與控制，稍有一點控制失誤或是失常，便會造成不正常燃燒，而“爆震”就是一種不正常燃燒。簡單的說，爆震是不正常燃燒所導致的燃燒室內壓力失常。

It is precisely because the combustion of the engine is very complex, so it needs to have quite accurate design and control. A little bit of control error or abnormality will cause abnormal combustion, and "knock" is a kind of abnormal combustion. In short, detonation is the abnormal pressure in combustion chamber caused by abnormal combustion.

造成爆震主要有以下幾點原因：

The main reasons for knock are as follows:

一、點火角過于提前：

1、 Too early ignition angle:

為了使活塞在壓縮上止點結束后，一進入動力沖程能立即獲得動力，通常都會在活塞達到上止點前提前點火(因為從點火到完全燃燒需要一段時間)。而過于提早的點火會使得活塞還在壓縮行程時，大部分油氣已經燃燒，此時未燃燒的油氣會承受極大的壓力自燃，而造成爆震。

In order to make the piston obtain power immediately after entering the power stroke at the end of compression TDC, it is usually ignited in advance before the piston reaches TDC (because it takes a period of time from ignition to complete combustion). If the ignition is too early, most of the oil and gas will burn when the piston is still in the compression stroke. At this time, the unburned oil and gas will bear great pressure and spontaneously ignite, causing detonation.

二、發動機過度積碳：

2、 Excessive carbon deposition in engine:

發動機于燃燒室內過度積碳，除了會使壓縮比增大(產生高壓)，也會在積碳表面產生高溫熱點，使發動機爆震。

Excessive carbon deposition in the combustion chamber will not only increase the compression ratio (produce high pressure), but also produce high temperature hot spots on the surface of carbon deposition, which will make the engine knock.

三、發動機溫度過高：

3、 Engine temperature too high:

發動機在太熱的環境使得進氣溫度過高，或是發動機冷卻水循環不良，都會造成發動機高溫而爆震。

If the engine is too hot, the intake air temperature is too high, or the engine cooling water circulation is not good, it will cause the engine high temperature and knock.

四、空燃比不正確：

4、 Incorrect air fuel ratio:

過于稀的燃料空氣混合比，會使得燃燒溫度提升，而燃燒溫度提高會造成發動機溫度提升，當然容易爆震。

If the fuel air mixture ratio is too thin, the combustion temperature will increase, and the increase of combustion temperature will increase the engine temperature, which is easy to knock.

五、燃油辛烷值過低：

5、 Low octane number of fuel:

辛烷值是燃油抗爆震的指標，辛烷值越高，抗爆震性越強。壓縮比高的發動機，燃燒室的壓力較高，若是使用抗爆震性低的燃油，則容易發生爆震。

Octane number is an index of knock resistance of fuel. The higher the octane number is, the stronger the knock resistance is. The engine with high compression ratio has high pressure in combustion chamber. If the fuel with low shock resistance is used, it is easy to knock.