What happens if you fill a car designed for 98 octane with 92 octane fuel?

[DelSophie]

Using 92 octane gasoline in a car designed for 98 octane can cause engine knocking due to the difference in octane ratings: 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 98 octane gasoline contains 98% isooctane and 2% n-heptane. Additionally, 98 octane gasoline has stronger anti-knock properties. Using 92 octane fuel with lower anti-knock properties can easily lead to engine knocking. Gasoline is a mixture, and the octane number we commonly refer to indicates the fuel's anti-knock index (i.e., octane rating). Strictly speaking, 92 octane and 98 octane gasoline should not be mixed, although their chemical compositions and other aspects are relatively similar. However, to ensure vehicle safety, they should be used separately. Some regions still offer lower-grade 90 octane gasoline. Mixing this with higher-grade gasoline can result in knocking, insufficient power, reduced spark plug lifespan, and increased exhaust emissions. 98 octane gasoline typically has a density above 0.74, while 92 octane gasoline has an octane rating equivalent to a mixture of 92% isooctane and 8% n-heptane. The advantages of 98 octane gasoline are "two highs and two lows": higher anti-knock performance and power output, along with lower harmful substances and exhaust emissions. 98 octane gasoline's strong anti-knock properties prevent premature ignition under high pressure, ensuring the engine operates at the optimal ignition timing without affecting power output. The octane number directly represents the fuel's anti-knock performance—the higher the number, the better the anti-knock properties. Anti-knock performance refers to gasoline's ability to resist knocking during combustion in the engine. It is the primary indicator of gasoline's combustion efficiency. Knocking occurs when gasoline burns abnormally in the engine. The octane rating measures gasoline's resistance to knocking—higher octane means better anti-knock performance. Engines with higher compression ratios generate higher combustion chamber pressures. Using low-octane gasoline in such engines increases the risk of knocking. Important Notes: Choosing the correct gasoline octane is crucial. Most vehicles have the manufacturer's recommended octane rating printed inside the fuel filler cap. Follow this guidance when refueling. Higher octane gasoline is not always better. The engine's compression ratio must match the gasoline's octane rating. Using high-octane gasoline in a low-compression engine may reduce knocking but can alter ignition timing, leading to increased carbon deposits in the cylinders. Prolonged use can shorten the engine's lifespan. Using low-octane gasoline in a high-compression engine can cause knocking and accelerate wear and tear on engine components.