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The objective of this research project was to compare B20 (20% biodiesel fuel) and ultra-low-sulfur (ULSD) diesel-fueled buses in terms of fuel economy, vehicle maintenance, engine performance, component wear, and lube oil performance. We examined 15 model year (MY) 2002 Gillig 40-foot transit buses equipped with MY 2002 Cummins ISM engines. The engines met 2004 U.S. emission standards and employed exhaust gas recirculation (EGR). For 18 months, eight of these buses operated exclusively on B20 and seven operated exclusively on ULSD. The B20 and ULSD study groups operated from different depots of the St. Louis (Missouri) Metro, with bus routes matched for duty cycle parity. The B20- and ULSD-fueled buses exhibited comparable fuel economy, reliability (as measured by miles between road calls), and total maintenance costs. Engine and fuel system maintenance costs were also the same for the two groups after correcting for the higher average mileage of the B20 group.

In this study the effect of blending biodiesel (methyl soyester) with conventional diesel on emissions has been investigated. A 1991 MC Series 60 engine was employed and emissions of NOx, CO, THC, and PM were determined using the heavy-duty transient test. The fuels tested were a reference diesel, 20%, 35%, and 65% biodiesel blends in the reference diesel, as Well as 100% biodiesel. These tests show that as the percent biodiesel increased, the NOx, emission increased, while THC, CO and PM decreased. For 35% biodiesel, the composite NOx emission increased by nearly 1% while the composite particulate emission decreased by 26% relative to the reference diesel. The NOx increase of 1% was found to be statistically significant at the 99% level. For 100% biodiesel, the composite NOx increased by 11% while PM was decreased by 66%. CO was reduced by 47% and total hydrocarbon by 44%.