Biodiesel fuel is produced by alcohol – usually methanol or ethanol – chemically reacting with vegetable oils, animal fats or recycled cooking greases. It can be used neat (pure) or blended with petroleum-based diesel fuel. The most popular type of biodiesel now used is a 20 percent blend, or B20. It’s also used in a 2 percent blend with diesel, primarily for added lubricity.
Biodiesel has about 90 to 95 percent of the energy content found in No. 2 diesel but contains no aromatics or sulfur. It has a high cetane number (related to ignition capabilities) and offers good lubricating qualities. Biodiesel suppliers say a 2 percent blend of biodiesel may replace the lubricity lost with low-sulfur fuels. The fuel is sensitive to cold weather and requires anti-freezing treatments. Biodiesel acts like a detergent additive and will loosen and dissolve fuel tank and fuel line sediments. It also acts like a solvent and may pose problems for seals and other rubber components in pre-1994 engines.
It reduces carbon monoxide, sulfur dioxide and particulate emissions by significant amounts but may produce higher levels of NOx (oxides of nitrogen) emissions. Since it is sulfur-free, biodiesel can be used with aftertreatment devices that require low-sulfur fuel.
B20 costs 13 to 22 cents more per gallon than diesel, and B100 – 100 percent pure biodiesel – runs from $1.25 to $2.25 per gallon depending on purchase volumes and delivery costs.
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy