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Biodiesel

12 November 2002

The US Environmental Protection Agency (EPA) released a draft technical report titled “A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions” (EPA 420-P-02-001), which quantifies the emission effects of biodiesel fuel and its blends.

There has been increasing interest in the use of biodiesel as a substitute for petroleum-based diesel fuel. Since several studies have found emission benefits from the use of biodiesel, some States have been considering mandating the use of low levels of biodiesel in diesel fuel. The wide spread of emission data in the literature, however, makes it difficult to quantify the associated emission benefit. The EPA report will establish technical guidelines which will assist in claiming emission credits in relation to biodiesel use.

The EPA analyzed 80 literature studies, and chose 39 studies to develop correlations between the biodiesel content in the blend and its emission effect. The chosen studies met certain criteria, including the use of commercial heavy-duty highway engines and the FTP Transient test cycle. Consequently, the results are valid for heavy-duty highway engines. It was determined that biodiesel reduces the emissions of HC, CO, and PM, while increasing the emissions of NOx. The average emission effects of 20% blend (B20) and neat biodiesel found by the study are shown in the following table.

Average Biodiesel Emission Effect, % change
PollutantB20 BlendNeat Biodiesel
NOx+2+10
PM-10-47
CO-11-48
HC-21-67

Fuel economy penalty due to lower heat value is estimated at 1-2% for running B20, and at 4.6-10.6% for running neat biodiesel.

The report includes also a comprehensive analysis of emission impact of such factors as engine technology, biodiesel source, or cetane number. Due to limited data, it was not possible to make conclusions on the impact of biodiesel on emissions from light-duty and nonroad engines. Analysis of biodiesel impact on selected air toxics reveled that while some of them (including aldehydes) were reduced by biodiesel, no effect could be determined with others. The magnitude of air toxics reduction, if any, was much smaller than that of HCs.

EPA accepts comments on the draft report by 31 December 2002. Comments should be sent to David Korotney, korotney.david@epa.gov.

Download the report

Source: US EPA