octane number

noun

1. (of gasoline) a designation of antiknock quality, numerically equal to the percentage of isooctane by volume in a mixture of isooctane and normal heptane that matches the given gasoline in antiknock characteristics.

octane number

noun

1. a measure of the quality of a petrol expressed as the percentage of isooctane in a mixture of isooctane and n -heptane that gives a fuel with the same antiknock qualities as the given petrol

octane number

1. A numerical representation of the ability of a fuel to resist knocking when ignited in the cylinder of an internal-combustion engine. The octane number of a given fuel is determined by comparing the amount of knocking that fuel causes when combusted with the amount of knocking caused by two standard reference fuels, isooctane (which resists knocking and has an octane number of 100) and heptane (which causes knocking and has an octane number of 0). The octane number is then assigned as the percentage of isooctane required in a blend with normal heptane to match the knocking behavior of the fuel being tested.

Word History and Origins

Origin of octane number¹

First recorded in 1930–35

Example Sentences

Mid-grade gasoline will typically have an octane number between 88 and 90, and it offers better performance than standard gas.

From Seattle Times

The higher the octane number, the greater the fuel’s resistance to detonation.

From New York Times

The branching means there are more tertiary carbon atoms to stabilize pressure-induced radicals, reducing premature ignition and increasing the octane number.

From Nature

In blending avgas, distillers have to add tetra-ethyl lead to protect the valve-seats on the exhaust side of the engine from erosion, while raising the fuel’s octane number and preventing the engine from “knocking”.

From Economist

Now that you know what the octane number means, it’s important to understand what makes each fuel type useful and unique.

From Seattle Times