You are here

Biodiesel Basics

July 30, 2013 - 2:43pm


Biodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant greases.

What is Biodiesel?

Biodiesel is a liquid fuel made up of fatty acid alkyl esters, fatty acid methyl esters, or long-chain mono alkyl esters. It is produced from renewable sources such as new and used vegetable oils and animal fats and is a cleaner-burning replacement for petroleum-based diesel fuel. It is nontoxic and biodegradable.

Like petroleum diesel, biodiesel is used to fuel compression-ignition (diesel) engines. B20, which is 20% biodiesel and 80% petroleum diesel, is the most common biodiesel blend in the United States.

Biodiesel Blends

Biodiesel can be legally blended with petroleum diesel in any percentage. The percentages are designated as B20 for a blend containing 20% biodiesel and 80% petroleum diesel, B100 for 100% biodiesel, and so forth.

B20—the most common biodiesel blend in the United States—is 20% biodiesel and 80% petroleum diesel. Using B20 avoids many of the cold-weather performance and material compatibility concerns associated with B100.

B20 can be used in nearly all diesel equipment and is compatible with most storage and distribution equipment. B20 and lower-level blends generally do not require engine modifications. Not all diesel engine manufacturers cover biodiesel use in their warranties, however. Users should consult their vehicle and engine warranty statements before using biodiesel. It is similarly important to use biodiesel that meets prescribed quality standards (ASTM D6751-07b).

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. Greenhouse gas and air quality benefits of biodiesel are roughly commensurate with the blend; B20 use provides about 20% of the benefit of B100 use and so forth.

B100 or other high-level biodiesel blends can be used in some engines built since 1994 with biodiesel-compatible material for parts such as hoses and gaskets. As biodiesel blend levels increase significantly beyond B20, however, a number of concerns come into play. Users must be aware of lower energy content per gallon and potential issues with impact on engine warranties, low-temperature gelling, solvency/cleaning effect if regular diesel was previously used, and microbial contamination.

B100 use could also increase nitrogen oxides emissions, although it greatly reduces other toxic emissions. All these issues can be handled, but currently B100 use might be best for professional fleets with maintenance departments prepared to deal with this fuel.

More Information

Visit the Alternative Fuels and Advanced Vehicles Data Center to learn more about biodiesel.