100,000-Mile Evaluation of Transit Buses Operated on Biodiesel Blends (B20)

Nine identical 40-ft. transit buses were operated on B20 and diesel for a period of two years - five of the buses operated exclusively on B20 (20% biodiesel blend) and the other four on petroleum diesel. The buses were model year 2000 Orion V equipped with Cummins ISM engines, and all operated on the same bus route. Each bus accumulated about 100,000 miles over the course of the study. B20 buses were compared to the petroleum diesel buses in terms of fuel economy, vehicle maintenance cost, road calls, and emissions. There was no difference between the on-road average fuel economy of the two groups (4.41 mpg) based on the in-use data, however laboratory testing revealed a nearly 2% reduction in fuel economy for the B20 vehicles. Engine and fuel system related maintenance costs were nearly identical for the two groups until the final month of the study. Component replacements near the end of the study on one B20 bus caused average maintenance costs to be higher for the B20 group ($0.07 vs. $0.05 per mile). However, engine and fuel system maintenance costs varied widely from bus-to-bus so the $0.02 per mile average difference between the two groups is not statistically significant. There was no significant difference in miles between road calls. Analysis of B20 samples during the study period revealed early problems with fuel blending. There also were occasional fuel filter plugging events for the B20-fueled buses that were likely caused by out of specification biodiesel, however the exact cause could not be conclusively determined. Oil analysis results indicate no additional wear metals from the use of B20, with similar rates of TBN and ZDDP decay. Soot levels in the lubricant were significantly lower for the B20 vehicles. Laboratory chassis emissions tests comparing the in-use B20 and petroleum diesel on the CSHVC cycle showed reductions in all measured pollutants, including a reduction in nitrogen oxides.