The Environmental Protection Agency (EPA) requires all highway diesel fuel offered for sale in the United States to be a cleaner-burning diesel fuel, designated Ultra Low Sulfur Diesel (ULSD) fuel, by December 1, 2010. ULSD contains a maximum 15 parts-per-million (ppm) sulphur.
While the EPA regulates how diesel fuel is consumed, it is the American Society for Testing and Materials (ASTM) that classifies diesel fuel into grades. With the number of sulphur grades growing and to provide greater precision, as of October 2010, the ASTM Standard designation "Sxxx" distinguished grades by sulphur rather than by more general descriptors like "Low Sulfur" as done previously.
For example, S5000 grades correspond to the "regular" sulphur grades, the previous No. 1-D and No. 2-D, while S500 grades correspond to the previous "Low Sulfur" grades. S15 grades were not in the previous grade system and are referred to as "Ultra-Low Sulfur" grades or ULSD.
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Grade No. 1 Fuels
Grade No. 1 diesel fuels are designated DS15, DS500 and DS5000. Grade No. 1-D S15 is a special-purpose, light middle distillate fuel used in diesel engines requiring a fuel with a maximum 15 ppm sulphur and higher volatility than Grade No. 2-D S15 fuel. Grade No. 1-D S500 is similar but for those applications requiring a fuel with maximum 500 ppm sulphur, while Grade No. 1-D S5000 is for applications requiring a fuel with a maximum 5,000 ppm sulphur.
Grade No. 2 Fuels
Grade No. 2 diesel fuels are designated DS15, DS500 and DS5000. Grade No. 2-D S15 is a general purpose, middle distillate fuel for diesel engine applications that require a fuel with no more than 15 ppm sulphur and is designed for variable speed and load conditions. Grade No. 2-D S500 is similar but for applications that require a fuel with at most 500 ppm sulphur while Grade No. 2-D S5000 is for applications with at most 5,000 ppm sulphur.
Grade No. 4-D Fuel
Grade No. 4-D is a heavy distillate fuel --- a blend of distillate and residual oil --- and is intended for use in low and medium-speed, non-automotive diesel engines where speed and load are mostly constant.
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