CBSE Class 11-science Answered

The cetane number of a diesel oil is the percentage of cetane (hexadecane) by volume in a mixture of cetane and ? -methyl naphthalene which has the same ignition property as the fuel oil under consideration. The cetane number of 1-methylnaphthalene is zero and of hexadecane is 100.

Octane number is used for measuring the knocking character of fuel used in petrol engine. The octane number of a given sample may be defined as the percentage by volume of iso-octane present in a mixture of iso-octane and n-heptane which has the same knocking performance as the fuel itself.

Isooctane (upper) has an octane rating of 100 whereas n-heptane has an octane rating of 0.