Flash point

The flash point is the temperature at which a combustible liquid gives off just enough vapour to the air surrounding it that the vapour/air mixture above the liquid can be ignited by an ignition source. Diesel fuels have a flash point above 55��C. For example, petrol content of less than 3% in the diesel fuel can reduce the flash point to such an extent that ignition is possible at room temperature.

Boiling range

The position of the boiling range influences parameters which are important for the operating behaviour of the diesel fuel. Although extension of the range towards lower temperatures leads to a fuel which is suitable for cold operation, the cetane number is reduced at the same time, and this impairs the lubrication properties in particular. However, poorer lubrication properties increase the risk of fuel-injection equipment wear.

If, on the other hand, the final boiling point temperature is increased, which is desirable in order to achieve better utilization of crude oil, this can lead to increased soot production and nozzle coking (deposit of combustion residues).

Density

The diesel fuel��s calorific value depends on a good approximation to its density, and increases with increasing density. Therefore, if fuels with greatly differing densities are used with the fuel injection pump kept at the same setting, (volume metering by the pump is constant), shifts occur in the mixture composition owing to the fluctuations in the calorific values, which in turn leads to increased soot emission for high densities, and a reduction in output power for low densities.