"Biodiesel" Fuel Could Reduce Truck Pollution

Diesel fuel made from natural renewable sources such as vegetable oils or animal fats lowered air-polluting emissions of heavy trucks in a trial study, according to researchers. They say the so-called "biodiesel" fuel can be used in regular diesel engines without modifying them.

The finding is reported in the March 1 print edition of the journal Environmental Science & Technology by researchers from West Virginia University (WVU) in Morgantown, W. Va., and the National Renewable Energy Laboratory in Golden, Colo. It was initially published on the journal's web site on Feb. 9. The peer-reviewed journal is published by the American Chemical Society, the world's largest scientific society.

"Biodiesel fuel may have the potential to reduce our nation's reliance on imported oil and to improve air quality," said Mridul Gautam, Ph.D., a professor in the university's Department of Mechanical and Aerospace Engineering and one of the authors of the study. The scientists studied a blend of 35 percent biodiesel fuel and 65 percent conventional diesel fuel. They found that this emitted significantly less carbon monoxide and moderately less hydrocarbons and particulate matter, compared to 100 percent petroleum diesel.

"The potential of biodiesel to reduce emissions is quite significant," says Gautam. "There is a 25 percent reduction in particulate emissions alone." Emissions of carbon monoxide declined by 12 to 14 percent, and hydrocarbons by 10 percent, he added.

Biodiesel fuel is made by a reaction of vegetable oils with methanol or ethanol. The result is a less viscous, more volatile fuel. The truck engines ran just as efficiently on the biodiesel mix as on conventional diesel fuel (i.e., the average miles per gallon were essentially the same).

The research team found slightly elevated levels of nitrous oxide (NOx) emissions with the biodiesel blend. Changing the ignition timing of the engines reduced NOx emissions.

The reduction in carbon monoxide emissions is probably due to the higher oxygen content of the biodiesel fuel, the researchers say. More oxygen means the fuel is burned more completely. More complete burning also helps reduce hydrocarbon emissions.

The researchers attributed the 25 percent reduction in particulate emissions to the lower aromatic and sulfur content of biodiesel fuel, and its greater oxygen content.

The biodiesel study at West Virginia University was funded by the United States Department of Energy's Office of Transportation Technologies. The research team also included WVU scientists Donald W. Lyons, Nigel N. Clark and Wen-Guang Wang (now at Ford Motor Company in Dearborn, Mich.) and Paul Norton from the National Renewable Energy Laboratory.