Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million (ppm) of sulfur content. The U.S. Environmental Protection Agency requires 80% of the highway diesel fuel refined in or imported into the United States (100% in California) to be ULSD. One hundred percent must be ULSD nationwide by December of 2010. Different requirements apply to non-highway diesel.
Ultra-low sulfur content in diesel fuel is beneficial because it enables use of advanced emission control technologies on diesel vehicles. The combination of ULSD with advanced emission control technologies is sometimes called Clean Diesel.
Nitrogen oxides (NOx) and particulate matter (PM) are the two most harmful diesel pollutant emissions. These emissions can be controlled with the use of catalytic converters (for NOx) and particulate traps (for PM). However, sulfur in amounts that used to be allowable in diesel fuel deactivates these devices and nullifies their emissions control benefits. Using ULSD enables these devices to work properly.
In general, ULSD should cause no noticeable impact on vehicle performance, although fuel economy might be slightly reduced because the process that produces ULSD can also reduce the fuel's energy content. Removing sulfur from diesel reduces lubricity. This issue can be resolved by the addition of additives prior to retail sale that increase lubricity. In addition, blending biodiesel with ULSD also increases lubricity.
Using ULSD in older diesel vehicles might affect fuel system components or loosen deposits in fuel tanks. These vehicles should be monitored closely for fuel system problems and premature fuel filter plugging during the transition to ULSD. New vehicles designed to use ULSD must never be fueled with a higher-sulfur fuel.
Additionally, like gasoline, ULSD is not seen as a “green” technology because it is produced from petroleum. It does not decrease our dependence on fossil fuels. However, biodiesel, biomass-to-liquids, coal-to-liquids, gas-to-liquids diesel, and hydrogenation-derived renewable diesel are inherently ultra-low sulfur fuels and could help meet ULSD requirements in the future. So while petroleum-based ULSD is not considered an alternative fuel under the Energy Policy Act of 1992 (EPAct), most ULSD fuels produced from non-petroleum and renewable sources are considered EPAct alternative fuels.
The U.S. consumption of diesel fuel steadily declined from 2007-2009. This is largely caused by the economic recession. However, increases in consumption in 2010 and 2011 may be indications of economic recovery.