What is engine knocking in cars?
3 Answers
There are several main reasons that cause engine knocking: 1. Overly advanced ignition timing. To ensure the piston receives power immediately upon entering the power stroke after the compression top dead center, ignition usually occurs before the piston reaches the top dead center (because it takes time from ignition to complete combustion). Excessively advanced ignition causes most of the fuel-air mixture to burn while the piston is still in the compression stroke, leading the unburned mixture to auto-ignite under extreme pressure, resulting in knocking. 2. Excessive carbon buildup in the engine. Excessive carbon deposits in the combustion chamber not only increase the compression ratio (generating high pressure) but also create hot spots on the carbon deposits, causing engine knocking. 3. Incorrect air-fuel ratio. A too lean fuel-air mixture raises combustion temperatures, which increases engine temperature and makes knocking more likely. 4. Low fuel octane rating. The octane rating is an indicator of a fuel's resistance to knocking. The higher the octane rating, the stronger the anti-knock properties. High-compression engines have higher combustion chamber pressures, making them more prone to knocking if low-octane fuel is used.
I've been a long-haul truck driver for decades and have experienced many instances of engine knocking. Knocking sounds like the engine is pinging or rattling, especially noticeable when climbing hills or accelerating. The main cause is using low-octane gasoline—its low octane rating makes it prone to abnormal combustion in the cylinders. Ignition timing that's too early can also cause the flame front to collide with the piston, creating noise. Excessive carbon buildup on the cylinder walls, which increases compression ratio, is another common issue. Knocking is more likely to occur in summer when the engine overheats. My advice is to use high-quality gasoline, regularly inspect the ignition system, and clean internal engine carbon deposits periodically. Don't underestimate knocking—ignoring it long-term can shorten engine life, increase fuel consumption, and even damage cylinders. Whenever I hear unusual noises, I immediately slow down and check to prevent further hardware damage. Prevention is always better than repair, and that's crucial.
I've only had my car for a little over a year, and I was quite alarmed when I heard a knocking sound from the engine on the highway last time. After researching, I understood it was engine knocking, which essentially means abnormal combustion of fuel causing explosive noises. It might be because I used cheaper gasoline with insufficient octane rating, or there's too much carbon buildup in the engine. The problem tends to occur more easily during hot summer temperatures. A friend reminded me that a malfunctioning ignition system could also be a cause. Now, I've developed the habit of only using higher-grade gasoline and avoiding heavy-load driving. If the knocking persists, I need to get it checked at the garage immediately—delaying could wear out internal components. New drivers should take note: this isn't just a minor noise; it can affect engine performance. Regular maintenance and cleaning can prevent a lot of trouble. Learning these lessons has made me feel more at ease while driving.
