Compression Ratio 10:1 - Should I Use 92 or 95 Octane?

[LeVivian]

For an engine with a compression ratio of 10:1, both 92 and 95 octane gasoline can be used. The specific choice should be based on the recommendation in the vehicle's official owner's manual. In addition to checking the appropriate gasoline grade in the owner's manual, you can also find this information on the fuel filler cap, which typically indicates the recommended octane rating. Generally, the gasoline grade 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. However, with the application of new technologies, the compression ratio alone is no longer the sole determinant of the appropriate gasoline grade. Even engines with high compression ratios can be tuned to use lower-octane gasoline because other factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology, also play a role. Generally, the higher the gasoline 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. Occasionally using the wrong gasoline grade is not a problem as long as you switch back to the correct grade after the tank is empty. However, prolonged use of the wrong gasoline grade can have the following effects: For vehicles designed for lower-octane gasoline, using higher-octane gasoline will not cause damage, but the increased octane number may alter the fuel's ignition point, leading to delayed combustion in the engine. This can reduce the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles designed for higher-octane gasoline, using lower-octane gasoline can cause engine knocking. Because the octane number is significantly lower, the fuel's ignition point decreases, causing premature ignition during the compression stroke. If the fuel ignites before the spark plug fires, it creates resistance during the upward stroke. This resistance can make the engine run very unevenly. If the knocking is mild, it may only increase noise without noticeable damage to the engine. However, if the knocking is severe, it indicates serious engine issues. The vibrations not only affect driving stability but can also cause abnormal wear on the pistons and cylinders, potentially leading to cylinder scoring in severe cases.