Diesel fuel (or diesel, fuel oil, gas oil) is a liquid fuel composed of a mixture of heavier vapor-phase hydrocarbons and other additives.

Diesel is used as a fuel for most diesel engines. It is most often produced by the hydrogenation of fractions from the distillation of crude oil.

Ignition

The ignition of diesel fuel is an essential feature for its practical application in diesel engines. It is characterized by the so-called ignition delay. It is the time that elapses from the moment of injection of the diesel particle after the moment the particle starts to burn.

As this time depends on the composition and the distillation properties of diesel, but also on the design and operating parameters of the engine, a different parameter – cetane number (octane number for petrol) was introduced in practice. The cetane number represents the percentage by volume of cetane in mixture with alpha-methylnaphthalene, which has the same ignition delay on the test apparatus as the test fuel.