Ultra-Low Sulfur Diesel Changes Fuel Chemistry

ULSD Changes Fuel Chemistry 

At the same time as engines are undergoing radical design changes, the fuel industry also is subject to new mandates. In an effort to help the environment, most parts of the world now require that sulfur be removed from diesel. With so many simultaneous changes to both fuel and fuel systems, it is not surprising that there are some unintended consequences.

Sulfur occurs naturally in crude oil. In diesel, it not only contributes to particulate matter in exhaust, but also prevents emissions control through exhaust after-treatment devices, such as diesel particulate filters. In order to reduce harmful emissions, most of the world has enacted measures that reduce sulfur content in diesel, which can otherwise be as high as 5000 ppm. Low sulfur diesel is considered to be under 500 ppm, while ultra low sulfur diesel (ULSD) is almost sulfur-free at no more than 15 ppm. In North America, Europe, South Africa, Australia and portions of Asia, Ultra Low Sulfur Diesel is mandated and virtually all new equipment requires ULSD for proper function. 

Reducing sulfur content has clear advantages, but also has some disadvantages. The hydrocracking or ​hydrodesulphurization process used to remove sulfur also removes most nitrogen and oxygen compounds and increases saturates, which causes the formation of paraffin. In removing sulfur, nitrogen and oxygen, many beneficial properties are reduced or eliminated. 
Diesel pump

Lubricity: Natural lubricity improvers, these compounds protected engines from wear. 

Shelf life: These natural anti-oxidants helped delay the formation of fuel degradation products and extend diesel life.
Biological growth inhibitors: Microbial colonies can thrive without the presence of these natural microbe inhibitors which helped limit the bacteria or fungi's ability to multiply. 

Conductivity enhancer: Sulfur prevented electrostatic discharge by helping to dissipate electrical charge. 

The use of additives is now required to compensate for the relative absence of these compounds and the positive effects they had on fuel. Much of the chemistry added to replace the function of sulfur, nitrogen and oxygen is generally referred to as surfactant. Surfactants are soap-like materials. They have a significant impact on how water acts in fuel and, as a result, have dramatically changed the level of filtration and coalescing efficiency. This represents a significant change to fuel chemistry.