Biodiesel is renewable fuel made by chemically combining natural oils from soybeans (or cottonseeds, canola, etc.; animal fats, or even recycled cooking oil) with an alcohol such as methanol (or ethanol).
Biodiesel fuels are usually more expensive than petrodiesel, but biodiesel burns with less particulate and with no sulfur or aldehydes, producing less harmful and irritating tailpipe emissions. NOx sometimes increases with biodiesel, but after-treatment devices benefit from the lack of sulfur in biodiesel. The improved lubricity and zero sulfur content of biodiesel result in longer maintenance intervals, longer engine and fuel system life, and lower emissions.
Biodiesel fuel is compatible with petrodiesel and may be used 100% (B100) in place of petrodiesel, or may be blended with petrodiesel. A typical blend would be 20% biodiesel with 80% petrodiesel fuel (B20).
Biodiesel tends to clean petrodiesel residues from the fuel system, so fuel filters may require frequent servicing for the first few tank fills.