Gasoline engine is prone to knock. To analyze the knock phenomenon, we need to understand the reason and solve the problem according to the crux.
The combustible mixture of gasoline engine is ignited by high pressure at first. Then, the combustion flame takes the spark plug as the center and spreads outward to ignite the mixture in the combustion chamber, which is a normal combustion process. If the rest of the mixture ignites itself before the flame reaches, the combustion is called detonation.
Detonation is not allowed to happen in the normal operation of the engine. It will lead to the deterioration of the parts of the engine cylinder block, the shortening of the service life, even the rapid destruction. It will also reduce the engine power and increase the fuel consumption.
Causes of knock:
1. Detonation will produce shock wave suddenly in the cylinder and impact on all sides, which will make the piston, cylinder wall, connecting rod and crankshaft of the engine vibrate strongly and produce irregular metal knocking sound;
2. The temperature of cooling system is too high;
3. Incomplete combustion of fuel and black smoke from the exhaust gas;
4. The engine power decreases and the fuel consumption increases.
Solutions:
1. Reduce the ignition advance angle;
2. Use gasoline of the specified brand (octane number);
3. Remove the carbon deposit in the combustion chamber;
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