What is Diesel Fuel?

Words by Andrew Leimroth

Photography by Caravan & Motorhome

Nobody is game to ask what diesel fuel is. As a result, it is a very misunderstood topic. So, what is diesel fuel? Diesel fuel is obtained from the residue (basically the gunk left at the bottom of the drum) of crude oil after the more volatile fuels have been removed during the distilling process (heating of crude oil). So, why are we paying so much? Your guess is as good as mine! It is about 18% heavier in composition than petrol. It consists mainly of hydrocarbons that range from C10 to C24 (10 to 24 carbon atoms with various configurations of hydrogen atoms attached to the carbon atoms). Petrol is usually in the C7 to C11 range, while kerosene, commonly used for jet engine fuel, is weighted just between diesel and gasoline in the C12 to C15 range. The higher the number of carbon atoms, the heavier the product.

Before shipment from the petroleum distillery, the composition of diesel fuel may be varied by the distilling facility, depending on the location of the distillation facility and weather – specifically, the temperature at the time of distillation. This is where you may hear, ‘winter’ or ‘summer’ diesel fuel. The heavier diesel fuel will tend to thicken, or solidify in cold weather, unlike petrol, which is basically unaffected by colder temperatures.

Diesel fuel is lighter than other petroleum-based products, such as other lubricating oils. With a flash point (flash point of a chemical refers to the lowest temperature at which that chemical, in liquid form, will produce combustible vapours that will ignite with a flame) of roughly 50°C to 100°C, depending on the method of distillation, diesel is not as volatile as either kerosene or petrol.

Sulphur in diesel fuel has a definite effect on the wear of the internal components of the engine, such as piston ring, pistons, and valves. High additive lubricating oils are desired when high sulphur fuels are used because the corrosive effects of sulphur combining with water vapour during combustion forms acids, which damage and wear components. Sulphur in diesel fuel can also attack and corrode injection system components in addition to contributing to combustion chamber and injection system deposits. So, as you can see, low sulphur diesel isn’t so bad after all.

Good filtration is needed on diesel vehicles because it is heavier than petrol and thus will hold dirt particles in suspension for a longer period than petrol.

In summary, diesel is a very simple fuel that, if looked after, will give your vehicle many years of trouble-free service.

Safe Driving

Andrew