St. Louis, Missouri – A 12-month evaluation by the U.S. National Renewable Energy Laboratory (NREL) of buses operating on B20 biodiesel found that the buses exhibited only a 1.76 per cent lower fuel economy than buses using ultra low sulphur diesel (ULSD), but that reliability and maintenance costs were comparable. B20 biodiesel is a mixture of 80 per cent petroleum diesel and 20 per cent renewable-fuel biodiesel.
The evaluation was undertaken on buses in the St. Louis, Missouri Metro fleet and was conducted by NREL and the National Biodiesel Board. The study is the first B20 in-fleet study using buses equipped with EGR valves, and the first to compare B20 to ULSD. It involved 15 40-foot model-year 2002 transit buses with Cummins engines; eight operated exclusively on B20 and seven on petroleum USLD. The groups operated from different depots at St. Louis Metro, but the routes were matched for duty cycle parity.
Average fuel economy over the 12-month period for the ULSD buses was 3.58 mpg US (65.7 L/100 km), while average economy for the B20 buses was 3.52 mpg US (66.8 L/100 km).
Average reliability values, measured by miles between road calls (MBRC), were 2,375 for the ULSD and 2,627 for the B20 groups. MBRCs for the engines and fuel systems were much higher for the B20 buses, with 6,924 for ULSD and 8,211 for B20. The B20 study group had a higher incidence of fuel filter and fuel injector replacements, and analysis of the fuel samples did not indicate poor fuel quality; the researchers said that while the B20 fuel may have been the cause, the high mileage of the bus could also have been a factor, and that additional data will be compiled during the study’s second year to determine any impact of the renewable fuel. Lube oil analysis indicated no harm and some potential benefits with B20 use, including lower levels of soot and wear metals. Viscosity, total base number and corrosive metals were generally more positive with ULSD use, but qualities for the B20 buses were still within acceptable limits.