What are the causes of engine knocking?
3 Answers
Engine knocking is caused by: 1. The ignition angle being too advanced. An excessively early ignition causes most of the fuel-air mixture to burn while the piston is still in the compression stroke. The unburned mixture then undergoes extreme pressure and auto-ignites, resulting in knocking. 2. Excessive carbon deposits in the engine. Excessive carbon buildup in the combustion chamber not only increases the compression ratio but also creates high-temperature hot spots on the carbon deposits, leading to engine knocking. 3. Overheating of the engine. Operating the engine in excessively hot environments, which raises the intake air temperature, or poor circulation of engine coolant can cause high-temperature knocking. 4. Incorrect air-fuel ratio. An overly lean fuel-air mixture raises the combustion temperature, which in turn increases the engine temperature and makes knocking more likely.
There are quite a few reasons for engine knocking, and I've encountered it several times over the years of driving. The most common cause is using low-octane gasoline—insufficient octane can lead to premature ignition under high temperature and pressure, resulting in abnormal combustion and knocking sounds. Problems with the ignition system, such as an overly advanced ignition timing setting, can also trigger this issue. Additionally, engine overheating is a critical factor; a faulty cooling system can cause cylinder temperatures to soar, leading to uncontrolled combustion. Carbon buildup on the piston crown reduces combustion chamber volume, advancing the ignition point. Lastly, mechanical factors like worn piston rings or poor valve sealing can cause imbalanced combustion. I recommend using high-quality fuel, avoiding sudden acceleration, and regularly maintaining the cooling system and cleaning carbon deposits. Otherwise, prolonged knocking can damage the engine's lifespan—never take it lightly while driving.
Last time I was driving, I noticed the engine was making a knocking sound, and after checking, I realized it was a detonation issue. The reason might be that I was trying to save money by using cheap fuel with low octane, which doesn't ignite properly under heat. Or it could be that the ignition timing was off, and old spark plugs tend to fire late. Engine overheating is another possibility; insufficient coolant or a broken fan can cause high temperatures. Too much carbon buildup reduces space, causing early ignition and leading to the same problem. Later, I switched to high-quality gasoline and replaced the spark plugs, and the improvement was immediate. Now, I've changed my driving habits, warming up the engine for a few minutes before starting and remembering to clean carbon deposits during maintenance, which has significantly reduced knocking. If you encounter similar issues, addressing them early saves time and trouble, otherwise, a breakdown on the road can be a real hassle.
