What indicators are used to classify gasoline grades?
2 Answers
Automotive gasoline grades are classified by Motor Octane Number (MON) into five grades: 66, 70, 75, 80, and 85. The numerical grade indicates the octane number measured by the Motor method, with grades 75, 80, and 85 suitable for high-end vehicles. The GB489—86 "Gasoline Specifications" stipulate three grades: 66, 70, and 85, with the numerical grades representing the octane number measured by the Motor method. More details are as follows: 1. Grade issuance time: The new standard GB484—89 issued in 1989 stipulates that automotive gasoline grades are classified by Research Octane Number (RON) into three grades: 90, 93, and 97. The numerical grades indicate the octane number measured by the Research method. For the same gasoline, the octane number measured by the Research method is 8~10 units higher than that measured by the Motor method, with Motor Octane Number = Research Octane Number × 0.8 + 10. 2. Meaning of gasoline grades: Simply put, gasoline grades represent the anti-knock coefficient, or octane number. The so-called 90, 93, and 97 unleaded gasoline grades indicate that they contain 90%, 93%, and 97% of the highly anti-knock "iso-octane," respectively, meaning they contain 10%, 7%, and 3% of the poorly anti-knock n-heptane, respectively.
Gasoline grades are classified by octane rating, which indicates the fuel's resistance to knocking. Knocking refers to that annoying pinging sound in the engine, which harms the engine and is quite bothersome. The higher the octane rating, the less likely the gasoline is to auto-ignite under high pressure. Therefore, higher-grade fuels like 91 octane have better anti-knock properties and are suitable for high-compression engines such as sports cars. The higher the compression ratio, the more sensitive the engine becomes, making it prone to issues with lower-grade gasoline. Having driven for many years, I've seen many people carelessly use lower-grade fuel, resulting in engine vibration, reduced power, and in severe cases, potential piston damage. Actually, octane ratings are globally standardized—for example, US 87 octane is roughly equivalent to China's 92 octane. The key when choosing fuel is to follow the vehicle manual's recommendation rather than guessing blindly, otherwise your car might throw a tantrum.
