Ultra Low Sulfur

Ultra-low sulfur diesel ( ULSD) describes a new EPA standard for the sulfur content in on-road diesel fuel sold in the United States. This new regulation applies to all diesel fuel, diesel fuel additives and distillate fuels blended with diesel for on-road use, such as kerosene, however, it does not yet apply to train locomotives, marine, or off road uses. The EPA is also mandating the use of ULSD fuel in model year 2007 and newer diesel fuel engines designed for on-highway use. The EPA rule goes into effect for non-road, locomotive, and marine (NRLM) diesel fuel on June 1st, 2007.

The allowable sulfur content for ULSD (15 ppm) is much lower than the previous U.S. standard for Low Sulfur Diesel (LSD, 500 ppm), which not only reduces emissions of sulfur compounds (blamed for acid rain), but also allows advanced emission control systems to be fitted that would otherwise be poisoned by these compounds. These systems can greatly reduce emissions of oxides of nitrogen and particulates.

Because this grade of fuel is comparable to European grades, this standard may increase the availability of diesel-fueled passenger cars in the U.S., since engines will no longer have to be redesigned to cope with higher sulfur content. European diesels are both more advanced technologically and much more popular with buyers than those available in the U.S.

Additionally, the EPA is assisting manufacturers with the transition to tougher emissions regulations by loosening them for model year 2007 to 2009 light-duty diesel engines. As a result, Honda, Nissan, Subaru, Toyota, and others are expecting to begin producing diesel vehicles for the U.S. market to join those from Mercedes-Benz and Volkswagen.

According to EPA estimates, with the implementation of the new fuel standards for diesel, nitrogen oxide emissions will be reduced by 2.6 million tons each year and soot or particulate matter will be reduced by 110,000 tons a year.

Sulfur is a lubricant in diesel, so by lowering the sulfur content there may be a drop in the fuel's lubricity. There may also be a minor decrease in the energy content, by about 1%. This decrease in energy content may result in reduced fuel economy. To achieve the sulfur requirements for the new fuel standards, diesel manufacturers include an additive to keep the fuel flowing smoothly, and to prevent engine damage. A relatively cheap lubricious additive is biodiesel.

ULSD will run in any engine designed for the ASTM D-975 diesel fuels.