How is octane rating measured?
The octane rating of 2, 2, 4-trimethylpentane is set at 100 whilst that of a straight chain heptane is set at 0. A fuel can be tested by comparing it with these in a test engine. The ratio of heptane : 2, 2, 4-trimethylpentane is varied in the comparator mixture until it has the same ignition properties as the sample of fuel being used. The % of the 2, 2, 4-trimethylpentane in the mixture is then taken as the octane rating of the fuel