According to the official vehicle manual recommendation, the BYD Han should use 92 octane gasoline. In addition to checking the suitable gasoline grade in the vehicle manual, the BYD Han's fuel cap also 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. 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 gasoline grade—high compression ratio engines can also be tuned to use lower octane gasoline. This is because, besides the compression ratio, 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. If the BYD Han occasionally uses the wrong gasoline grade, simply switching back to the correct grade after consumption is sufficient. However, long-term 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 reduces 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. Due to the significantly lower octane number, the gasoline's ignition point decreases, causing premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance will arise during the upward stroke. This resistance makes the engine run very unstably. Mild knocking may only increase noise without significant engine damage, but severe knocking indicates serious engine issues. The vibrations not only affect driving stability but also cause abnormal wear on pistons and cylinders, potentially leading to cylinder scoring in severe cases.
