What Causes Engine Knock?
2 Answers
The specific causes of engine knock are as follows: 1. Excessively advanced ignition timing: To ensure the piston receives power immediately after the compression top dead center, ignition typically occurs before the piston reaches top dead center (since it takes time for complete combustion). Overly advanced ignition causes most of the air-fuel mixture to burn while the piston is still in the compression stroke, leading to extreme pressure on the unburned mixture, which then auto-ignites, resulting in knock. 2. Excessive carbon buildup in the engine: Heavy carbon deposits in the combustion chamber not only increase the compression ratio (creating high pressure) but also form hot spots on the carbon surface, causing engine knock. 3. Overheating of the engine: Operating in excessively hot environments or poor engine coolant circulation can lead to high engine temperatures, resulting in knock. 4. Incorrect air-fuel ratio: An overly lean air-fuel mixture raises combustion temperatures, which in turn increases engine temperature, making knock more likely. 5. Low fuel octane rating: The octane rating indicates a fuel's resistance to knock. Higher octane fuels have better anti-knock properties. High-compression engines have higher combustion chamber pressures, and using low-octane fuel increases the risk of knock.
I've been driving for decades, and the knocking sound of engine detonation is all too familiar to me. The most common cause is using low-octane gasoline. If a high-compression engine uses the wrong fuel, it can lead to premature ignition of the air-fuel mixture, causing detonation. Additionally, if the ignition timing is set too early or the computer adjustment malfunctions, problems can easily arise. Too much carbon buildup in the combustion chamber can also increase hot spots, leading to premature combustion. I remember once on a long trip, the knocking was very loud, and after inspection, it turned out to be severe carbon buildup in the intake tract. Cleaning it improved the situation significantly. Ignoring it for too long can lead to cylinder wear or piston damage, so timely repairs are essential. It's recommended to always use the recommended high-octane gasoline when refueling and to regularly clean the engine to maintain good combustion, ensuring smooth driving.
