According to a recent report in the journal Environmental Science & Technology, biodiesel can be used in regular diesel engines without modifying them and produces significantly less pollutants. The researchers are from West Virginia University in Morgantown, WV, and the National Renewable Energy Laboratory in Golden, CO, and the study was funded by the U.S. Department of Energy.
"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% biodiesel fuel and 65% conventional diesel fuel. They found that this emitted significantly less carbon monoxide and moderately less hydrocarbons and particulate matter compared to 100% petroleum diesel.
"The potential of biodiesel to reduce emissions is quite significant," says Gautam. "There is a 25% reduction in particulate emissions alone." Emissions of carbon monoxide declined by 12 to 14%, and hydrocarbons by 10%, 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% reduction in particulate emissions to the lower aromatic and sulfur content of biodiesel fuel, and its greater oxygen content.
In Delaware, a pilot program announced recently will use a 20% soybean-based biodiesel, 80% conventional diesel blend in its fleet of state-owned cars and trucks. The program will last six months and burn 40,000 gallons of soybean-based fuel.
"We'll be looking to see what the fuel performance is, we'll be looking to see what the equipment maintenance costs are," said Anne P. Canby, state transportation secretary. "Just imagine a few years out that you're tailing a little too close to a DOT truck and you get something that smells like french fries."