Octane

Octane, colorless, liquid, highly flammable hydrocarbon, commonly used in gasoline. Since the 18 octane compounds vary in their molecular structure, they have different physical properties.

Octane number is the designation given to gasoline based on the amount of isooctane present. Fuels with a lower octane number have a larger amount of normal heptane and are prone to engine “knock,” which decreases the power of the engine.

See also: Hydrocarbon.