What happens if you use 92 octane gasoline in a Volkswagen CC?

[DeMolly]

According to the official car manual recommendation, the Volkswagen CC should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the car manual, the Volkswagen CC can also check the fuel tank cap, which will also indicate the recommended grade. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Cars with an engine compression ratio between 8.6-9.9 should use 92 octane gasoline, while those with a compression ratio between 10.0-11.5 should use 95 octane gasoline. However, with the use of some new technologies, the gasoline grade cannot be solely determined by the compression ratio. High compression ratio engines can also be tuned to use lower octane gasoline because, apart from the compression ratio, other factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, the higher the gasoline grade, the higher the octane number and the better the anti-knock performance. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. If you occasionally use the wrong gasoline grade in a Volkswagen CC, you can simply switch back to the correct grade after using it up. However, if you consistently use the wrong gasoline grade for a long time, it may have the following effects: Using a higher octane gasoline in a vehicle that recommends a lower octane will not cause damage, but the increase in octane number will change the fuel's ignition point, leading to delayed combustion in the engine. This means the engine's power output and thermal efficiency will decrease, resulting in poorer performance. Using a lower octane gasoline in a vehicle that recommends a higher octane will cause engine knocking. Because the octane number is too low, the gasoline will ignite prematurely during the compression stroke before the spark plug fires. This premature ignition creates resistance during the upward stroke, making the engine run very unstable. If the knocking is mild, it may only increase noise without significant damage to the engine. However, if the knocking is severe, it indicates serious engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, even cylinder scoring.