Sulphur

Diesel fuels contain sulphur in chemically bound form, depending on the crude-oil quality and the components used in the mixture. Crack components in particular have high sulphur contents, but these can be reduced by treatment with hydrogen at the refinery. Since sulphur is converted into sulphur dioxide (SO during combustion in the engine (this substance is environmentally hostile owing to its acidic reaction), maximum permitted sulphur content is limited by law.

It has been reduced in several stages in recent years, and since 1 Oct 1996 must not exceed 0.05% by weight in Europe. Of course in Australia we are still waiting to see these low levels 10 year later!!

The intention is to reduce the mass of emitted particulates which, in the case of catalytic exhaust gas aftertreatment, also contain sulphates in addition to soot.

Additives

Quality improvement by the addition of additives, as has been common practice with petrol for years now, has recently also become popular overseas for diesel fuels (super-grade or premium-grade diesel fuel). Additive packages are mostly used which have a multiple effect:

-Ignition improvers raise the cetane number and are responsible in particular for quieter combustion.

-Detergents to prevent nozzle coking.

-Corrosion inhibitors to prevent corrosion of metal parts (in the event of water being entrained into the fuel system).

    Anti-foaming agents to facilitate tank filling.

The overall concentration of additives is generally below 0.1%, so that the physical characteristics of the fuel, such as density, viscosity, and boiling curve do not change.