Web exclusive posted August 13, 2008 at 10:41 a.m. CST

A year-long study conducted cooperatively by the National Biodiesel Board and the National Renewable Energy Laboratory has concluded that a B20 biodiesel blend operates comparatively with petroleum-based ultra-low sulfur diesel (ULSD).

The study evaluated the extended use of the two fuels in 15 St. Louis Metro Transit buses. Eight buses were fueled with a B20 blend of fuel for 12 months, while the other seven buses were fueled exclusively with ULSD. The 40-foot, model year 2002 buses were monitored for fuel economy, maintenance, engine performance, component wear and lube oil performance.

Results showed the B20 buses exhibited a 1.7 percent reduction in fuel economy, which is consistent with the fuel's lower energy output percentage as compared to petroleum diesel.

Fuel filters and fuel injectors needed to be replaced more frequently on the B20 buses. Poor fuel quality was ruled out as a factor. However, because maintenance workers didn't retain clogged parts as requested, researchers were unable to further determine a cause. It was speculated that an unusually cold spring could have been a factor.

Overall engine and fuel system maintenance was 35 percent higher for the B20 group but, according to the group's final report, bus-to-bus variability in maintenance indicates that percentage is not significant.

Lube oil samples that were collected throughout the year showed that B20 caused no harm and, in some cases, actually resulted in less soot and wear on metals than the ULSD samples.

The NBB and NREL are considering continuing the study for one more year to further evaluate how B20 affects engines and fuel systems.