General Knowledge - Chemistry - Discussion

If a fuel has an octane rating of 91 it means that it has auto-ignition (knock) characteristics which are the same as a blend of 91% isooctane and 9% heptane. i.e, zero octane means there is no octane.

Give me its structure.

The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane that would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For example, petrol with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the petrol contains just iso-octane and heptane in these proportions, but that it has the same detonation resistance properties. Because some fuels are more knock-resistant than iso-octane, the definition has been extended to allow for octane numbers higher than 100.

N-heptane is a long chain compound, that make radicals.

More number of radicals coupled with one another make high oil like structure burn sudden in manner make explosive.

That is called knocking in petrol engine.

Octane number is a rasio of Iso-octane(100) and n-haptane(0.0)

Octane nuber is used for rating the quality of petrol. If quntity of n-heptane in petrol is high then it is not a good fuel.