According to the official vehicle manual recommendation, Audi A4L should use 95 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle manual, you can also find it on the fuel tank cap, which will also be marked. Usually, the gasoline grade can also be determined based on the engine's compression ratio. Vehicles with an engine compression ratio between 8.6-9.9 should choose 92 octane gasoline, while those with a compression ratio between 10.0-11.5 should choose 95 octane gasoline. However, with the use of some new technologies nowadays, the gasoline grade cannot be solely determined by the compression ratio. A high compression ratio can also be adjusted to use lower-grade gasoline. This is because, apart from the compression ratio, other factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally speaking, 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 for Audi A4L, you just need to switch back to the correct grade after using it up. However, if you use the wrong gasoline grade for a long time, it may have the following impacts: For vehicles recommended to use lower-grade gasoline, using higher-grade gasoline by mistake will not cause damage, but the increase in octane number will change the ignition point of the fuel, leading to delayed combustion in the engine. This means both the engine's power output and thermal efficiency will decrease, and the actual feedback experience is poorer performance; For vehicles recommended to use higher-grade gasoline, using lower-grade gasoline will cause engine knocking. Because the octane number is much lower, the ignition point of the gasoline decreases and it may be ignited prematurely during the compression stroke. If detonation occurs before the spark plug ignites during the compression stroke, resistance will appear in the upward stroke. This resistance will make the engine run very unstably. If it is only mild knocking, the noise will increase, but the damage to the engine is not obvious. If there is obvious knocking sensation, it indicates that the engine's working condition is already very severe. The vibration not only affects driving stability but also causes abnormal wear of pistons and cylinders, and in severe cases, cylinder scoring may occur.
