The Reliability of Biodiesel Fuel
Research by scientists from the National Renewable Energy Laboratory (NREL) shows little performance difference between buses running on diesel fuel compared to buses running on B20, diesel fuel with a twenty percent blend of biodiesel.
The study, 100,000-Mile Evaluation of Transit Buses Operated on Biodiesel Blends (B20), consisted of a real life experiment involving a fleet of nine mass transit buses in the Denver Area.
B20 is the most common blend of biodiesel fuel on the market today. Proponents of biodiesel often cite both national security and environmental reasons for its use. We can help reduce our dependence on foreign oil by producing fuel from biomass that can be grown in many areas in United States. These fuels have the added advantage of being more environmentally friendly because their use produces fewer air pollutants than fuel derived totally from petroleum.
Because of the relatively brief history of biofuel production in the United States, there have been few opportunities to test those claims in real world situations. The nine busses involved in the NREL experiment were the same brand using the same engine. Additionally each bus traveled approximately 100,000 miles over the same route for a two year period. Fuel type was the only difference among the buses throughout the two year experiment. A group of four buses ran on diesel fuel. The other five buses ran on B20. After two years, each bus was evaluated in terms of four performance marks:
- engine performance
- fuel economy
- vehicle maintenance
Results of the tests are necessarily couched in terms of the sample population. Using a small fleet sample for comparative purposes carries the possibility that one non-fuel related problem connected to one bus in either the diesel or B20 group could distort the overall results of any one test. For example, a few of the diesel buses has transmissions problems during the course of the experiment, resulting in overall higher maintenance costs for the diesel group.
Comparing the two groups of buses, clogged fuel filters turned out to be the primary vehicle maintenance challenge associated with the B20 buses. Researchers assume that as the B20 storage tanks approached empty, the gunk collecting in them had more opportunities to be pumped out and into the bus gas tanks, causing the clogs.
Fuel economy for both sets of buses was statistically similar. Researchers assume that B20 use promotes less fuel efficiency because it has less total energy. At most, they discovered a 1.2% difference in fuel economy between the groups, with the diesel group performing slightly better.
Finally, only two buses were tested for emissions, providing little more that a starting point for evaluating the emissions reductions claims of biodiesel proponents. From that perspective, the emissions results offer some promise. The NREL reports, "The data show that for these vehicles on this test cycle, operation on B20 reduced all regulated pollutants, including NOx."
© 2007 Patricia A. Michaels