Should the ES use 92 or 95 octane fuel?

[VanLevi]

According to the official vehicle user manual recommendation, the ES should use 92 octane gasoline. In addition to checking the appropriate gasoline grade in the vehicle user manual, the ES can also check it on the fuel tank cap, which will also be marked. Usually, the fuel 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, those with a compression ratio between 10.0-11.5 should choose 95 octane gasoline, and if the compression ratio is higher, 98 octane gasoline should be selected. However, with the use of some new technologies nowadays, the fuel grade cannot be determined solely by the compression ratio. A high compression ratio can also be tuned to use lower octane gasoline. This is because, besides 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 the ES occasionally uses the wrong gasoline grade, simply switch back to the correct grade after using it up. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended to use lower octane gasoline, using higher octane gasoline 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 both the engine's power output and thermal efficiency will decrease, and the actual feedback experience is reduced performance. For vehicles recommended to use higher octane gasoline, using lower octane gasoline can cause engine knocking. Because the octane number is too low, the gasoline's ignition point is reduced, causing it to ignite prematurely during the compression stroke. If the fuel ignites before the spark plug fires during the compression stroke, resistance will occur during the upward stroke. This resistance will make the engine run very unstable. If it's mild knocking, it only increases noise and does not cause significant damage to the engine. However, if there is noticeable knocking, it indicates that the engine's condition is already very severe. The vibration not only affects driving stability but can also cause abnormal wear on the pistons and cylinders, and in severe cases, even cylinder scoring.