ASTM Standards
The first national biodiesel specification in the USA has been the ASTM standard D 6751, “Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels”, adopted in 2002. The D 6751 standard covers biodiesel (B100) used as a blending component with petroleum diesel fuels. Requirements and test methods of the D 6751 standard are discussed in detail in the Biodiesel Fuel Standards paper.
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No standards currently exist in the USA that would cover neat biodiesel (B100) or biodiesel blends for use as automotive fuels. An ASTM specification for B20 blend of 20% biodiesel and 80% of petrodiesel—one of the most common biodiesel blends in the United States—is under development.
US Military Specifications
In the absence of a national standard, the US military has developed its own specifications for B20 biodiesel blends. B20 meeting the requirements has been approved for use in Army engines and vehicles other than combat and tactical vehicles. The basic specification is defined in the “Commercial Item Description: Diesel Fuel, Biodiesel Blend (B20)” [CID-A-A-59693A, 15 Jan 2004], according to which B20 shall consist of 20±1 % (by vol.) of biodiesel conforming to ASTM D 6751 and a balance of No 2-D or 1-D diesel fuel conforming to ASTM D 975 or to the military specification A-A-52557. The standard further specifies a number of properties and test methods for the B20 blend.
Additional technical requirements are included in solicitations for the purchase of B20 biodiesel blend which are issued periodically by the Defense Energy Support Center (DESC). The military specifications are expected to be superseded by the ASTM standard for B20, when finalized. Notably, the military solicitations typically require that, in the event that a Federal, State, or local environmental requirement is more stringent than the military specification, the contractor shall deliver B20 fuel that complies with the more stringent requirement. The DESC solicitations also require that the B100 product used for blending be EPA registered (in accordance with 40 CFR Part 79, Registration of Fuels and Fuel Additives).
While the CID-A-A-59693A standard does not include a fuel stability specification, it advises against using biodiesel blends that have been stored for longer than six months from the date of manufacture, or which have an acid number of 0.3 mg KOH/g or higher.