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.
Biodiesel has been used to reduce petroleum consumption and pollutant emissions. B20, a 20% blend of biodiesel with 80% petroleum diesel, has become the most common blend used in the United States. Little quantitative information is available on the impact of biodiesel on engine operating costs and durability. In this study, eight engines and fuel systems were removed from trucks that had operated on B20 or diesel, including four 1993 Ford cargo vans and four 1996 Mack tractors (two of each running on B20 and two on diesel). The engines and fuel system components were disassembled, inspected, and evaluated to compare wear characteristics after 4 years of operation and more than 600,000 miles accumulated on B20. The vehicle case history-including mileage accumulation, fuel use, and maintenance costs-was also documented. The results indicate that there was little difference that could be attributed to fuel in operational and maintenance costs between the B20-and diesel-fueled groups. No differences in wear or other issues were noted during the engine teardown. The Mack tractors operated on B20 exhibited higher frequency of fuel filter and injector nozzle replacement. Biological contaminants may have caused the filter plugging. A sludge buildup was noted around the rocker assemblies in the Mack B20 engines. The sludge contained high levels of sodium, possibly caused by accumulation of soaps in the engine oil from out-of-specification biodiesel. The Mack and Ford engines used similar pump-line nozzle fuel injection systems, but a much larger volume of fuel was recirculated in the larger Mack engines. This, along with duty cycle and engine loading, may account for the difference in performance of the two engine types operated on B20.
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Several configurations of truck tractor sleeper cabs were tested and modeled to investigate the potential to reduce heating and cooling loads. Two trucks were tested outdoors and a third was used as a control. Data from the testing were used to validate a computational fluid dynamics (CFD) model and this model was used to predict reductions in cooling loads during daytime rest periods. The test configurations included the application of standard-equipped sleeper privacy curtain and window shades, an optional insulated or arctic sleeper curtain, and insulated window coverings. The standard curtain reduced sleeper area heating load by 21% in one test truck, while the arctic curtain decreased it by 26%. Insulated window coverings reduced the heating load by 16% in the other test truck and lowered daytime solar temperature gain by 8˚C. The lowered temperature resulted in a predicted 34% reduction in cooling load from the model. Modeling also predicted doubling cab insulation could reduce cooling load by 35% and up to 54% with the sleeper curtain closed. Infrared images of the truck cabs identified other potential areas to reduce heat loss that included areas around window and door seals, at body and structural seams, and areas where insulation may be lacking around air circulation ducts.
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