This propensity to premature ignition is measured by the octane rating of the fuel, where 2,2,4-trimethylpentane (isooctane) has an arbitrary value of 100, and heptane has a value of zero.
Esta propensión á ignición prematura é medida polo índice de octano do combustible, onde o 2,2,4-trimetilpentano (isooctano) ten un valor arbitrario de 100, e heptano ten un valor de cero.