what is the importance of aniline point?
First we’ve to know two definitions,
i) Aniline Point : Aniline point is defined as the minimum temperature at which equal volumes of anhydrous aniline and oil mix together.
ii) Diesel Index : Diesel index is a measure of ignition quality of fuel and this can be expressed as follows
Diesel Index = (Aniline Point in oF X oAPI)/ 100
Now from the definition we can understand that aniline being an aromatic compound freely mixes with aromatic,so a low aniline point indicates low diesel index and high aniline point indicates that the fuel under test in highly paraffinic and its diesel index is also high.Highly paraffinic compounds show low Self Ignition Temperature( SIT – the lowest temperature at which the fuel start to ignite without an external source of ignition),but fuel rich in aromatics have high SIT burns later causing ignition delay and gives rise to what is known as diesel knock. And because diesel knocking is destructive for an engine,high self ignition temperature is avoided by using oil having high diesel index,i.e.,of high aniline point.