What is diesel fuel?

Written by Capt. Jeff Werner
Written by Captain Jeff Werner

Diesel fuel is a very complex mixture of thousands of individual compounds with carbon numbers between 9 and 23 (the number of carbon atoms per hydrocarbon molecule). Most of these compounds are members of the paraffinic, napthenic or aromatic classes of hydrocarbons (HC).

These three classes have different chemical and physical properties. The different relative proportion of these three classes is one of the factors that make one diesel fuel different from another. It influences fuel properties and affects its performance.

Up until 35 years ago, refineries used only about 50% of a barrel of crude oil to make distillates such as gasoline, jet fuel and diesel. The remainder of the barrel of crude oil went to “residual oil”. Today, as a result of different refining techniques and additive packages, the refinery uses 90% or more of the same barrel of crude, which clearly has consequences for fuel stability.

More than 90% of the debris on filter elements and the sludge in your fuel tank is organic material, fuel and oil breakdown residue. In most cases, this debris is acidic and not good for your engine. It causes corrosion in injectors, pumps and storage tanks. The solids that form as a result of the inherent stability of the fuel and the natural process of degradation will accumulate in the bottom of your tank. The sludge will form a coating or bio-film on the walls and baffles of the tank, plug your filters and impact combustion efficiency. Eventually it will clog fuel lines and ruin your equipment.

Capt. Jeff Werner, a Licensed USCG Master, has sailed professionally throughout the world. He is also the Diesel Doctor, helping to keep your boat’s fuel clean and bright.

If you have additional questions for Capt. Jeff Werner, please email him [email protected].