What is throttle knock?

Engine "super knock", also known as low-speed pre-combustion, is a unique abnormal combustion phenomenon in supercharged direct injection gasoline engines. When the engine inhales the mixture of fuel vapor and air, during the compression process, because the fuel is mixed with low-ignition substances, before the spark plug is ignited, the fuel mixture will automatically deflagrate, forming a new ignition point, and the flame will spread outward at a speed several times higher than the normal combustion, so that the cylinder wall will be impacted and vibrated, which is called knocking. Simply put, knocking is a manifestation of abnormal combustion chamber pressure.

Phenomenon at the time of explosion

When a slight knock occurs, the engine will emit a crisp and discontinuous metal knocking sound, while when a serious and continuous knock occurs, the engine will emit a continuous metal knocking sound, and the engine power will also be significantly reduced.

What was the cause of the explosion?

The air-fuel ratio of 1 is incorrect, and the lean mixture increases the combustion temperature, thus increasing the engine temperature.

The octane number of fuel is too low, and the octane number is an index of antiknock. The higher the octane number, the stronger the antiknock performance, and the lower the octane number, the easier it is to knock.

3 the cleanliness of fuel is not enough. Some physical substances and chemical impurities contained in fuel, including some aromatic substances, will cause spontaneous combustion during engine compression, leading to knocking.

There is too much carbon deposition in the combustion chamber, because the actual volume of the cylinder becomes smaller and the compression ratio increases when the carbon deposition is serious. At the same time, the carbon deposit has poor heat dissipation ability in high temperature environment, and it will always burn red, so that the high-temperature compressed mixture will be randomly ignited by the high-temperature carbon deposit in the cylinder in addition to the sequential spark plug, leading to deflagration.

5 The engine temperature is too high, the intake air temperature of the engine is too high in a too hot environment, or the cooling water circulation of the engine is not good, which will cause the engine to knock at high temperature.

6 ignition angle is too early. In order to make the piston gain power immediately after the compression stroke and enter the power stroke, it is usually ignited in advance before the piston reaches the top dead center. However, premature ignition will make most of the oil and gas burn while the piston is still in the compression stroke, and the unburned oil and gas will spontaneously ignite under great pressure, resulting in knocking.

The solution to knocking is as follows.

1. Use fuel that meets the engine compression ratio.

2. Avoid "procrastination" driving.

3. Regularly clean the carbon deposit in the oil circuit and nozzle.

4. Avoid high temperature: check the coolant level regularly, check the oil change regularly to avoid long-term intense driving, and often monitor the water temperature when driving in summer.

5. Appropriate selection of high-quality fuel additives. For example, the fuel additive containing PNF stock solution can solve the engine knock problem to some extent.