Volvo S90: Should I Use 92 or 95 Octane Gasoline?

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Volvo S90 should use 95 octane gasoline, as this is the recommended fuel grade specified in the vehicle's official user manual. In addition to checking the appropriate gasoline grade in the user manual, the fuel cap of the Volvo S90 will also indicate the recommended grade. Typically, 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 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 even higher, 98 octane gasoline is recommended. However, with the application of new technologies, the compression ratio alone cannot determine the required gasoline grade, as high compression ratio engines can also be tuned to use lower octane fuel. This is because factors other than compression ratio, 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 you occasionally use the wrong gasoline grade in your Volvo S90, simply switch back to the correct grade after the current tank is used up. However, prolonged use of the wrong gasoline grade can have the following effects: For vehicles recommended to use lower octane gasoline, using a higher octane grade 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 recommended to use higher octane gasoline, using a lower octane grade can cause engine knocking. The significantly lower octane number lowers the fuel's ignition point, causing premature ignition during the compression stroke. If the fuel ignites before the spark plug fires, resistance will occur during the upward stroke. This resistance makes the engine run very unstably. If the knocking is mild, it may only increase noise without obvious engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, and in severe cases, cylinder scoring.