What Causes Engine Knocking?
2 Answers
Engine knocking causes: 1. Overly advanced ignition timing: Excessively early ignition causes most of the air-fuel mixture to burn while the piston is still in the compression stroke. The remaining unburned mixture then undergoes extreme pressure and spontaneously combusts, resulting in knocking. 2. Excessive carbon buildup in the engine: Severe carbon deposits in the combustion chamber not only increase the compression ratio but also create high-temperature hot spots on the carbon surface, leading to engine knocking. 3. Overheating engine: Operating in excessively hot environments causes elevated intake air temperatures or poor engine coolant circulation, both contributing to engine overheating and knocking. 4. Incorrect air-fuel ratio: An overly lean fuel-air mixture raises combustion temperatures, which increases engine temperature and makes knocking more likely. 5. Low fuel octane rating: Octane rating indicates a fuel's resistance to knocking. Higher octane fuels have better anti-knock properties. High-compression engines with greater combustion chamber pressure are prone to knocking when using low-octane fuels with poor knock resistance.
That annoying knocking sound from engine detonation actually has many causes. From my work experience, the most common one is ignition timing that's too early, where the spark plug ignites the fuel before the piston reaches the proper position, causing abnormal combustion. Another factor is gasoline with too low octane rating - using cheaper fuel with poor anti-knock properties makes it prone to premature ignition. Carbon buildup is also a key issue, as deposits on cylinder walls create hot spots that prematurely ignite the air-fuel mixture. Additionally, faulty oxygen sensors or air-fuel ratio sensors can make the mixture too lean or too rich, increasing knock risk. My regular advice is to periodically check spark plug condition, calibrate ignition timing, and maintain carbon cleaning frequency. Don't forget to inspect the cooling system, as overheating can accelerate the problem. In short, paying attention to small preventive details can save you from major repair headaches.
