Biodiesel can be blended and used in many different concentrations, including B100 (pure biodiesel), B20 (20% biodiesel, 80% petroleum diesel), B5 (5% biodiesel, 95% petroleum diesel) and B2 (2% biodiesel, 98% petroleum diesel). B20 is a common biodiesel blend in the United States.
ASTM International develops specifications for conventional diesel fuel (ASTM D975). These specifications allow for biodiesel concentrations of up to 5% (B5). Low-level biodiesel blends, such as B5 are ASTM approved for safe operation in any compression-ignition engine designed to be operated on petroleum diesel. This can include light-duty and heavy-duty diesel cars and trucks, tractors, boats, and electrical generators.
B20 (20% biodiesel, 80% petroleum diesel) is the most common biodiesel blend in the United States. B20 is popular because it represents a good balance of cost, emissions, cold-weather performance, materials compatibility, and ability to act as a solvent. Using B20 provides substantial benefits and avoids many of the cold-weather performance and material compatibility concerns associated with B100. Most biodiesel users purchase B20 or lower blends from their petroleum distributors or biodiesel marketers. Biodiesel blends of 20% (B20) or higher qualify for biodiesel fuel use credits under the Energy Policy Act of 1992.
B20 and lower-level blends generally do not require engine modifications. Engines operating on B20 have similar fuel consumption, horsepower, and torque to engines running on petroleum diesel. B20 has a higher cetane number (a measure of the ignition value of diesel fuel) and higher lubricity (the ability to lubricate fuel pumps and fuel injectors) than petroleum diesel.
However, not all diesel engine manufacturers cover biodiesel use in their warranties (see the National Biodiesel Board's OEM Information for those that do support the use of biodiesel blends). Because diesel engines are expensive, users should consult their vehicle and engine warranty statements before using biodiesel. Biodiesel blends between B6 and B20 must meet prescribed quality standards—ASTM D7467 (summary of requirements).
B100, or neat biodiesel, contains about 8% less energy per gallon than petroleum diesel. For B20, this could mean a 1% to 2% difference, but most B20 users report no noticeable difference in performance or fuel economy. Biodiesel has some emissions benefits, especially for engines manufactured before 2010. For engines equipped with selective catalytic reduction (SCR) systems, the air quality benefits are the same whether running on biodiesel or petroleum diesel. However, biodiesel still offers better greenhouse gas (GHG) benefits compared to conventional diesel fuel. The emissions benefit is roughly commensurate with the blend level; that is, B20 would have 20% of the GHG reduction benefit of B100.
B100 and other high-level biodiesel blends are less common than B5 or B20 due to a lack of regulatory incentives and pricing. B100 can be used in some engines built since 1994 with biodiesel-compatible material for parts, such as hoses and gaskets. B100 has a solvent effect and it can clean a vehicle's fuel system and release deposits accumulated from previous petroleum diesel use. The release of these deposits may initially clog filters and require filter replacement in the first few tanks of high-level blends.
When using high-level blends, a number of issues can come into play. The higher the percentage of biodiesel above 20%, the lower the energy content per gallon. High-level biodiesel blends can also impact engine warranties, gel in cold temperatures, and suffer from microbial contamination in tanks. B100 use could also increase nitrogen oxides emissions, although it greatly reduces other toxic emissions.
B100 requires special handling and may require equipment modifications. To avoid engine operational problems, B100 must meet the requirements of ASTM D6751, Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels (summary of requirements). ASTM Specification D6751 now includes a No.1-B and a No.2-B grade. The No.1-B grade has stricter limits on monoglycerides and filterability than the No.2-B grade. The No.1-B grade is a special purpose biodiesel grade for use in applications where low temperature operability is needed.