Biodiesel is a fuel-blending component produced from vegetable oils, animal fats, or waste grease by reaction with methanol or ethanol to produce methyl or ethyl esters. Pure biodiesel contains approximately 10 weight percent oxygen. It is typically blended with petroleum diesel at levels up to 20% (B20). The presence of oxygen in the fuel leads to a reduction in emissions of hydrocarbons (HC) and toxic compounds, carbon monoxide (CO), and particulate matter (PM) when biodiesel blends are burned in diesel engines. These reductions are robust and have been observed in numerous engine and vehicle testing studies. Engine dynamometer studies reviewed in a 2002 report from EPA however show a 2% increase in oxides of nitrogen (NOx) emissions for B20 leading some state regulatory agencies to consider banning the use of biodiesel and posing a potential barrier to expansion of biodiesel markets. Based on review of previous studies and new study results, NREL conclude that B20 has no net impact on NOx.

Effects of Biodiesel Blends on Vehicle Emissions (2006) [.pdf, 1926.8Kb]

URL: http://205.168.79.26/vehiclesandfuels/npbf/pdfs/40554.pdf