Currently, there is a shortage of emissions data from diesel engines of the age and types commonly used by the Department of Defense (DoD), especially those burning alternative fuels such as biodiesel. The objective of this project was to obtain air pollution emission factors for diesel engines fueled with various types and blends of biodiesel. Measurements were made for carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) in accordance with Environmental Protection Agency (EPA) testing standards and duty cycles. The project also included measurements of hazardous air pollutants (HAP) as well as speciation of HC emissions and characterization of PM emissions.

Biodiesel is a nontoxic, biodegradable fuel made from organic fats and oils that serves as a replacement, substitute, and enhancer for petroleum diesel. Biodiesel may be blended with petroleum diesel in all existing diesel engines with little or no modification to the engines. Various concentrations of five fuels were tested, including two baseline petroleum fuels, a soy biodiesel, and two yellow grease biodiesel fuels. Ten DoD-operated diesel engines were evaluated, including engines used for on-road, off-road, and portable power applications. The primary criteria used to select these engines were their widespread use by DoD, and selected engines were supplied by various DoD facilities.

The emissions tests were performed using a combination of various standardized stationary and transient driving test cycles, static and actual on-road testing in locations with varying climates and altitudes, and at different duty cycles and load points. Testing performed on B20 biodiesel fuels (i.e., 20% biodiesel) identified three significant results. First, there were no consistent trends over all engines tested. Second, there were no statistically significant emissions differences between biodiesel fuels manufactured from yellow grease or soy oil feedstocks. Finally, extensive statistical analyses indicated no statistically significant differences in CO, HC, NOx, or PM emissions between a B20 biodiesel and California Air Resources Board (CARB)-certified Ultra Low Sulfur Diesel (ULSD).

The project’s results differed significantly from those previously reported by the EPA. Of particular interest is the fact that, for actual DoD fleet diesel engines fueled with biodiesel, there was no statistically significant increase in NOx emissions. These differences may be attributable to the use of ULSD as the base fuel instead of Diesel Fuel No. 2, only installed engines were tested, and tested DoD engines were generally much newer. In addition, it was shown that there is no statistical difference in CO, HC, NOx, or PM emissions between B20 and CARB certified ULSD, which is the required diesel fuel for on-road use in California as of June 2006. The emissions data obtained in this project will help DoD more effectively evaluate future use of biodiesel. (Project Completed - 2006)