The Sylphy should use 92-octane gasoline, as recommended in the vehicle's official user manual. In addition to checking the appropriate fuel grade in the user manual, you can also find this information on the fuel tank cap, which typically indicates the recommended fuel type. Generally, the fuel grade can also be determined based on the engine's compression ratio. Vehicles with a compression ratio between 8.6 and 9.9 should use 92-octane gasoline, while those with a compression ratio between 10.0 and 11.5 should use 95-octane gasoline. If the compression ratio is even higher, 98-octane gasoline is recommended. However, with the advent of new technologies, the compression ratio alone is no longer the sole determinant of fuel grade. Engines with high compression ratios can now be tuned to use lower-octane fuel. Other factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology, also play a role. 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. If the Sylphy is occasionally filled with the wrong fuel grade, simply switching back to the correct grade after consumption is sufficient. However, prolonged use of the wrong fuel grade can have the following effects: For vehicles designed for lower-octane fuel, using higher-octane gasoline will not cause damage, but the increased octane rating 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 fuel, using lower-octane gasoline can cause engine knocking. The significantly lower octane rating lowers the fuel's ignition point, causing premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance is created during the upward stroke. This resistance makes the engine run very unevenly. Mild knocking may only increase noise without noticeable engine damage, but severe knocking indicates serious engine issues. The vibrations not only affect driving stability but can also cause abnormal wear on pistons and cylinders, potentially leading to severe engine damage like cylinder scoring.
