Diesel fuel is a mixture of hydrocarbons obtained by distillation of crude oil. The important properties which are used to characterize diesel fuel include cetane number (or cetane index), fuel volatility, density, viscosity, cold behavior, and sulfur content. Diesel fuel specifications differ for various fuel grades and in different countries. Diesel—whose first engine concept was designed to use coal dust as the fuel—recognized that liquid petroleum products might be better fuels than coal. The engine was re-designed for operation with liquid fuels, resulting in a successful prototype in 1895. Both the engine and the fuel still bear the name of Diesel. ydrocarbons of three major classes: (1) paraffinic, (2) naphthenic (or cycloparaffinic), and (3) aromatic hydrocarbons. Unsaturated hydrocarbons (olefins) rarely occur in the crude. It should be noted that the terms ‘paraffinic’ and ‘naphthenic’ seem to be obsolescent; we use them because they are still common in the petrochemical industry. In modern chemistry, the respective groups of hydrocarbons are called alkanes and cycloalkanes.
