Octane Number Blending

Octane Number Blending

Octane numbers are blended on a volumetric basis using the blending octane numbers of the components. True octane numbers do not blend linearly, thus it is necessary to use blending octane numbers in calculating the octane number of the blend. Blending octane numbers can be estimated from empirical correlations that have been developed over the years. Blending octane numbers, when added on a volumetric average basis, will give the true octane of the blend, as can be obtained from standard test using CFR test engines.

(True Octane Number of a blend) ON = Σ xi∗ ONi

Where xi is the volume fraction of component i in the blend, and ONi is the blending octane number of component i.

For example, if you have

• a light naptha stream with a blending octane number = 75
• a reformate with a blending octane number = 86

and would like to get a gasoline of ON = 83, what would be the volume fraction of reformate (x) in the blend?

• ON = x(86) + (1-x)(75) = 83
• x = 0.73

So, you need 73% by volume of reformate in your blend. Additive concentration may be calculated the same way, and ON for multicomponent blends can be calculated the same way for research or motor octane numbers.