Diesel Fuels:

Diesel-fuel components

Diesel fuels consist of a large number of hydrocarbons which have boiling points in the range between about 180 C and 370  C. They are obtained by the step-wise distillation of crude oil.

Refineries are increasingly adding con version products (crack components) to diesel fuels. These are obtained from heavy oils by using fission (cracking) of larger modules into smaller ones by the application of heat, pressure, and catalysts.

Characteristic values

The requirements placed on diesel fuels are defined in national standards. The EN 590 standard applies in Europe, and DIN 51 601 in Germany. The most important parameters as stipulated in these standards are given below:

Cetane number, ignition quality.

Since the diesel engine operates without externally supplied ignition, following its injection into the hot, com pressed air in the combustion chamber, the diesel fuel must ignite of its own accord with the minimum possible delay (ignition lag).

Ignition quality is defined as that property of the fuel which serves to initiate diesel engine ignition. Ignition quality is expressed by the cetane number (CN). The higher the cetane number, the easier it is for the fuel to ignite.

Cetane, which has very good ignition qualities, is assigned the cetane number 100, whereas methyl naphthalene, which features poor ignition qualities, is given the cetane number 0. DIN 51 601 specifies a minimum cetane number of 45 for diesel fuels.

However, higher cetane numbers of around 50 are desirable for optimum operation of modern engines (quiet running, particulate emissions). High quality diesel fuels contain a large proportion of paraffins with high CN numbers. In contrast, aromatics of the kind found in crack components impair ignition quality.