Should SUVs Use 92 or 95 Octane Gasoline?

[Sara]

SUVs can use 92 octane gasoline. This octane rating is recommended in the vehicle's official owner's manual. In addition to checking the appropriate gasoline grade in the owner's manual, the fuel filler cap will also indicate the recommended octane rating. Typically, the octane rating can also be determined based on the engine's compression ratio. Vehicles with a 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. If the compression ratio is higher, 98 octane gasoline is recommended. However, with the application of new technologies, the octane rating cannot be solely determined by the compression ratio. High-compression engines can also be tuned to use lower-octane gasoline because factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, the higher the octane rating, 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 an SUV occasionally uses the wrong octane rating, simply switch back to the correct one after the current tank is used up. However, long-term use of the wrong octane rating can have the following effects: For vehicles designed for lower octane ratings, using higher octane gasoline will not cause damage, but the increased octane number can alter the fuel's ignition point, leading to delayed combustion in the engine. This reduces the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles designed for higher octane ratings, using lower octane gasoline can cause engine knocking. Because the octane number is significantly lower, the reduced ignition point may cause premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance will be generated during the upward stroke. This resistance makes the engine run very unevenly. If the knocking is mild, it may only increase noise without significant engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to cylinder scoring in severe cases.