Octane rating

An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without causing engine knocking. The higher the octane number, the more compression the fuel can withstand before detonating. Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates the resistance to detonating under pressure without a spark.

Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine. In broad terms, fuels with a higher octane rating are used in higher-compression gasoline engines, which may yield higher power for these engines. The added power in such cases comes from the way the engine is designed to compress the air/fuel mixture, and not directly from the rating of the gasoline.^[1]

In contrast, fuels with lower octane (but higher cetane numbers) are ideal for diesel engines because diesel engines (also called compression-ignition engines) do not compress the fuel, but rather compress only air, and then inject fuel into the air that was heated by compression. Gasoline engines rely on ignition of compressed air and fuel mixture, which is ignited only near the end of the compression stroke by electric spark plugs. Therefore, being able to compress the air/fuel mixture without causing detonation is important mainly for gasoline engines. Using gasoline with lower octane than an engine is built for may cause engine knocking and/or pre-ignition.^[2]

The octane rating of aviation gasoline was extremely important in determining aero engine performance in the aircraft of World War II.^[3] The octane rating affected not only the performance of the gasoline, but also its versatility; the higher octane fuel allowed a wider range of lean to rich operating conditions.^[3]

^ Stauffer, Eric; Dolan, Julia A.; Newman, Reta (2008). "Flammable and Combustible Liquids". Fire Debris Analysis. pp. 199–233. doi:10.1016/B978-012663971-1.50011-7. ISBN 978-0-12-663971-1.
^ Dabelstein, Werner; Reglitzky, Arno; Schütze, Andrea; Reders, Klaus; Brunner, Andreas (2016). "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_719.pub3. ISBN 978-3527306732.
^ ^a ^b Haitch, Richard (3 December 1978). "Who Helped Win Battle of Britain". New York Times. Retrieved 29 July 2021. The new fuel was called BAM 100, or 100/130 octane, the latter designation because it gave the British aircraft up to 30 percent more horsepower when taking off and climbing than ordinary 100 octane would have given.

[1] Stauffer, Eric; Dolan, Julia A.; Newman, Reta (2008). "Flammable and Combustible Liquids". Fire Debris Analysis. pp. 199–233. doi:10.1016/B978-012663971-1.50011-7. ISBN 978-0-12-663971-1.

[Ullmann-2] Dabelstein, Werner; Reglitzky, Arno; Schütze, Andrea; Reders, Klaus; Brunner, Andreas (2016). "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16_719.pub3. ISBN 978-3527306732.

[Haitch1978-3] Haitch, Richard (3 December 1978). "Who Helped Win Battle of Britain". New York Times. Retrieved 29 July 2021. The new fuel was called BAM 100, or 100/130 octane, the latter designation because it gave the British aircraft up to 30 percent more horsepower when taking off and climbing than ordinary 100 octane would have given.

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