Q4Engineering Chemistry
Question
Q.4 Define octane number of a fuel.
Answer
The Octane Number is a highly specific, standardized empirical numerical scale utilized universally to mathematically quantify the absolute anti-knock quality and combustion performance of spark-ignition (gasoline/petrol) engine fuels.
In automotive engineering chemistry, 'knocking' is the highly destructive, explosive premature auto-ignition of the unburned fuel-air mixture strictly inside the engine cylinder.
The absolute Octane Number is rigorously defined as the exact volumetric percentage of highly stable iso-octane (2,2,4-trimethylpentane, which is arbitrarily assigned an octane rating of exactly 100) mathematically present in a completely standardized test mixture containing exactly normal-heptane (which is extremely prone to knocking and assigned a rating of exactly 0).
If a commercial petrol sample exhibits the exact same knocking characteristics as a specific mixture containing strictly 87% iso-octane and 13% n-heptane, its definitive Octane Number is rigidly certified as 87.