US Federal Diesel Fuel

Regulatory Requirements

In parallel with the 1994 emission standards for heavy-duty diesel engines, the EPA introduced new requirements for highway diesel fuel. Effective October 1, 1993, a new sulfur limit of 0.05% (500 ppm) superseded the earlier ASTM specification of 0.5%. The 0.05% sulfur fuel was termed “low sulfur” diesel. In addition, the EPA required either a minimum cetane index of 40 or a maximum aromatic content of 35%. These requirements applied to all areas of the USA except Alaska. Diesel fuel not intended for on-road use was required to be dyed red.

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Further significant reductions of sulfur levels in highway diesel fuel were legislated by the EPA as a part of the 2007-2010 emission regulations for heavy-duty engines [66 FR 5135-5193, 18 January 2001]. Fuel of maximum sulfur content of 15 ppm (wt.)—called “ultra low sulfur diesel” (ULSD)—was required to be available beginning in mid-2006. Other fuel properties remain unchanged. The ULSD fuel was legislated as a “technology enabler”, to facilitate the use of sulfur-sensitive catalyst-based emission technologies on MY2007 and later heavy-duty engines, as well as on Tier 2 compliant light duty diesel vehicles.

The ULSD implementation schedule was as follows:

  • 1 June 2006: Refinery level and importers
  • 1 September 2006: Terminal level (downstream of the refinery/importer, except for retail outlets and wholesale consumers)
  • 15 October 2006: Retail level (including wholesale consumers)

California (CARB Diesel)

Effective October 1, 1993, the California ARB adopted a diesel fuel specification limiting the sulfur and aromatics in commercially available diesel fuel. Starting in January 2005, California diesel fuel was required to meet a minimum lubricity specification as well. This fuel, commonly referred to as the CARB diesel, is mandatory for use in a variety of applications including both highway and off-road vehicles. The limits and applicability have evolved as follows:

  • 1993.10—Sulfur limited to a maximum of 500 ppm and aromatics to 10% or equivalent. Applicable to on- and off-road vehicles but not stationary engines, locomotives and marine vessels.
  • 2004.12—CARB diesel requirement extended to stationary sources (applies to on- and off-road motor vehicles and nonvehicular sources other than locomotives and marine vessels).
  • 2005.01—CARB diesel required to meet a lubricity requirement of a maximum wear scar diameter of 520 microns by ASTM D6079, the High Frequency Reciprocating Rig (HFRR).
  • 2006.06—Sulfur in CARB diesel limited to 15 ppm.
  • 2007.01—CARB diesel requirement extended to intrastate locomotives and marine engines (within the SCAQMD, CARB diesel must be sold to harborcraft operators beginning 2006.01).