Vehicle effect:

The presence of Sulphur in diesel fuel can lead to the corrosion and wear of engine components and this can have a significant effect on engine life. As the Sulphur level decreases, the relative engine life increases.

During combustion, the formation of Sulphur oxides and water vapour combine resulting in Sulphur acids (sulphuric and sulphurous acids). During combustion, nitrogen from the air is also oxidised, forming nitrogen oxides (NOx) which in turn become nitric and nitrous acids. These acids are extremely corrosive to engine components, so good quality engine oil fortified with appropriate levels of neutralising agents are necessary to protect the engine components from damage.

Exhaust Gas Re-circulation (EGR), is now widely used in Light Duty and Passenger vehicles and to a lesser extent also in heavy duty engines. EGR effectively returns a portion of the exhaust gas back to the engine under part-load operating conditions.

Since NOx formation is extremely sensitive to temperature, by replacing some of the intake air with inert exhaust gas, the flame temperature can be reduced by a small amount and the NOx emissions can be reduced without seriously affecting the combustion efficiency.

The exhaust gas is usually cooled before returning it to the engine via the intake manifold and the small amount of sulfuric acid in the exhaust may condense, and this presents a risk of internal engine corrosion.

The lower the Sulphur level in the diesel fuel, the lower the risk of internal engine corrosion.