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 inuse 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.

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Plug-in hybrid electric vehicle (PHEV) technology may reduce fuel consumption and tailpipe emissions in many medium-and heavyduty vehicle vocations, including school buses. The true magnitude of these reductions is best assessed by comparative testing over relevant drive cycles. The National Renewable Energy Laboratory (NREL) collected and analyzed real-world school bus drive cycle data, and selected similar standard drive cycles for testing on a chassis dynamometer. NREL tested a first-generation PHEV school bus equipped with a 6.4 L engine and an Enova PHEV drive system comprising a 25-kW/80 kW (continuous/peak) motor and a 370volt lithium ion battery pack. For a baseline comparison, a Bluebird 7.2 L conventional school bus was also tested. Both vehicles were tested over three different drive cycles to capture a range of driving activity. Relative to the baseline school bus, the PHEV fuel savings in charge-depleting (CD) mode ranged from slightly more than 30% on the Urban Dynamometer Driving Schedule for Heavy Duty Vehicles and Rowan University Composite School Bus Cycle drive cycles to a little over 50% on the Orange County Bus cycle. However, the larger fuel savings lasted over a shorter driving distance, as the fully charged PHEV school bus would initially operate in CD mode for some distance, then in a transitional mode and finally in a charge-sustaining (CS) mode for continued driving. The test results indicate that a PHEV school bus can achieve significant fuel savings during CD operation relative to a conventional bus. In CS mode, the tested bus showed small fuel savings and somewhat higher nitrogen oxides (NOx) emissions than the baseline comparison bus. Further refinements to realize hybridization fuel savings in CS mode and calibrations focused on reducing NOx could lead to both higher fuel economy and lower NOx emissions in the next generation PHEV bus design.

The National Renewable Energy Laboratory (NREL) evaluated the performance of diesel, compressed natural gas (CNG), and hybrid electric (equipped with BAE Systems' HybriDrive propulsion system) transit buses at New York City Transit (NYCT). CNG, Gen I and Gen II hybrid electric propulsion systems were compared on fuel economy, maintenance and operating costs per mile, and reliability. These comparisons are based upon comparable service years; the second year in service for CNG and Gen II hybrids, and the second and third years in service for the Gen I hybrids. Conventional diesel buses provided a baseline comparison for fuel economy. Both the CNG and hybrid propulsion systems are alternatives to standard diesel buses and allow for reductions in petroleum use and emissions (usually focused on reductions of particulate matter and oxides of nitrogen).The Gen I hybrid buses exhibited 88% and 37% higher fuel economy than CNG and conventional diesel buses, respectively. The average fuel economy for the Gen II hybrid buses was 5.9% lower than the Gen I hybrid buses. Fuel economy decreased for all bus groups during summer operation due to air conditioning load. However, the hybrids exhibited the most dramatic seasonal fluctuation.The average total maintenance cost per mile for the Gen II hybrid buses was 39% lower than the Gen I hybrid buses, while the CNG buses' average was 5% higher than the Gen I hybrid buses. Total propulsion-related systems maintenance costs per mile were 55% lower for the Gen II hybrid buses than the Gen I hybrid buses, while the CNG buses were 5% lower than the Gen I hybrid buses.The Gen I hybrids experienced a 4.8% traction battery failure rate per year during evaluation year 1, and a 3.3% failure rate per year during evaluation year 2. BAE Systems utilizes lead-acid chemistry Hawker batteries.Hybrid buses are expected to have reduced brake reline frequency because they use regenerative braking. The Gen I hybrid buses accumulated more than two times the mileage of the CNG buses before requiring their first brake reline.

Six 2001 International Class 6 trucks participated in a project to determine the impact of gas-to-liquid (GTL) fuel and catalyzed diesel particle filters (DPFs) on emissions and operations from December 2003 through August 2004. The vehicles operated in Southern California and were nominally identical. Three vehicles operated "as-is" on California Air Resources Board (CARB) specification diesel fuel and no emission control devices. Three vehicles were retrofit with Johnson Matthey CCRT® (Catalyzed Continuously Regenerating Technology) filters and fueled with Shell GTL Fuel. Two rounds of emissions tests were conducted on a chassis dynamometer over the City Suburban Heavy Vehicle Route (CSHVR) and the New York City Bus (NYCB) cycle. The CARB-fueled vehicles served as the baseline, while the GTL-fueled vehicles were tested with and without the CCRT filters. Results from the first round of testing have been reported previously (see 2004-01-2959). The second round results were compared to the CARB specification diesel fuel baseline. Over the CSHVR cycle, the GTL Fuel (no filter) reduced oxides of nitrogen (NO x), hydrocarbon (HC), and particulate matter (PM) emissions by 13%, 46%, and 21%, respectively, and increased carbon monoxide (CO) by 11%. The GTL Fuel and the CCRT filter virtually eliminated the HC, CO, and PM emissions and reduced NO x emissions by 22%, a statistically significant reduction. Testing over the NYCB cycle also revealed emission reductions are possible with GTL Fuel. Compared to the CARB specification diesel fuel, the GTL Fuel provided statistically significant reductions in NO x , HC, and PM emissions by 11%, 58%, and 16%, respectively. A 10% increase in CO emissions was also noted, although not statistically significant. With the CCRT filter, the HC, CO, and PM emissions were reduced by over 95%. A statistically significant NO x reduction of 20% was observed. Reductions from round 2 were notably larger than those in round 1. To determine if the changes observed between rounds were "real", a statistical analysis was performed. The analysis found that CO emissions were higher without the filter in round 2, while no changes were observed for HC or PM emissions. The NO x emissions were significantly higher in round 1 for the NYCB cycle only. The fleet was followed for operability for 6 months and accumulated ~20,000 miles. Driver feedback for the vehicles operating on the GTL Fuel and CCRT filters was very positive. An analysis determined that the fuel economy with the combination of GTL Fuel and CCRT filters decreased by 8%. Evaluation of the maintenance NREL/CP-540-38221. Posted with permission.