You should not add 92 octane gasoline after filling up with 95 octane. If you accidentally use the wrong gasoline grade occasionally, simply switch back to the correct grade after consumption. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles designed for lower octane, using higher octane gasoline will not cause damage, but the increased octane rating alters the fuel's ignition point, leading to delayed combustion in the engine. This reduces both the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles designed for higher octane, using lower octane gasoline can cause engine knocking. Since the octane rating 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 develop during the upward stroke. This resistance makes the engine run very unevenly. Mild knocking may only increase noise without obvious engine damage, but severe knocking indicates serious engine issues, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to cylinder scoring. Besides checking the recommended gasoline grade in the car's manual, you can also find it on the fuel cap. Generally, the gasoline grade can also be determined by the engine's compression ratio. Cars with a compression ratio between 8.6-9.9 should use 92 octane, while those between 10.0-11.5 should use 95 octane. However, with modern technologies, the compression ratio alone is not the sole determinant. High-compression engines can be tuned to use lower octane gasoline due to other factors like ignition timing, turbocharging technology, and Atkinson cycle technology. Generally, higher octane gasoline has a higher octane rating and better anti-knock properties. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane.
