What is the Difference Between High and Low Gasoline Octane Ratings?
3 Answers
Gasoline octane ratings are determined by the octane number of the gasoline. The higher the octane number, the stronger the anti-knock capability of the gasoline, and the higher the octane rating. The anti-knock performance indicator of gasoline is called the octane number, which is the gasoline octane rating. Generally, engines with high compression ratios require gasoline with higher octane ratings, while engines with low compression ratios use gasoline with lower octane ratings to ensure normal vehicle operation. Below is a related introduction: 1. Principle: Generally, engine operation consists of a repetitive cycle of "intake-compression-combustion-exhaust-intake" in the cylinders. The compression ratio is the ratio of the cylinder volume when the piston is at the farthest and nearest points in its stroke. The best way to reduce fuel consumption costs is to increase the engine's compression ratio. Increasing the compression ratio can alter the piston stroke, compressing the air-fuel mixture more intensely, which results in a stronger combustion reaction and more complete combustion. However, the compression ratio of a car is not easily changed and is matched with an indicator, namely the gasoline's anti-knock performance indicator, known as the octane number, which is the gasoline octane rating. 2. Composition of gasoline: Standard gasoline consists of isooctane and n-heptane. Isooctane has excellent anti-knock properties with an octane number of 100, while n-heptane has poor anti-knock properties and is prone to knocking in gasoline engines, with an octane number of 0. Generally, if a gasoline's octane rating is 0, it means the gasoline contains 90% isooctane and 10% n-heptane.
Gasoline octane ratings primarily indicate differences in anti-knock properties, with higher octane fuel offering better resistance to engine knocking. Simply put, high-compression engines require higher octane fuel—many turbocharged models need 95 octane or above. Using lower octane can cause knocking and piston slapping sounds. In my decade-plus as a mechanic, I've seen many owners use the wrong fuel, resulting in increased carbon deposits and reduced power. Lower octane fuel suits naturally aspirated engines better, being more economical. Always check your owner's manual before refueling—don't compromise for savings or prestige. Remember, octane rating doesn't correlate with cleanliness—Sinopec's 92 and 98 octane fuels contain similar detergent additives. The key is matching your engine's compression ratio. Long-term use of incorrect fuel may damage piston rings, leading to repairs costing thousands.
I have a deep understanding of gasoline octane ratings, as my two family cars use different grades. The numbers 92, 95, and 98 don't indicate fuel quality differences—the core factor is how the octane rating affects anti-knock performance. Higher-octane fuel withstands compression better, which is why high-displacement track cars need 98-octane to perform at their peak. For regular cars, there's no need to use premium fuel. I've tested the same car with both 92 and 95 octane—the cost difference was 0.3 RMB per kilometer with virtually no power difference. Forcing high-octane fuel into a low-compression engine can actually lead to incomplete combustion and clogged fuel injectors. Gas station attendants always remind us to check the fuel cap label—if the manufacturer specifies 92-octane, don't arbitrarily switch to 95. With fuel prices so high, choosing the right octane rating is the most practical way to save money.
