In October of 2004, the Air Pollution Prevention and Control Division of the U.S. EPA's National Risk Management Research Laboratory investigated the emissions from a diesel-powered tractor-trailer operating along a highway at near-zero grade. In place of a dynamometer and standard dilution tunnel, the Diesel Emissions Aerosol Laboratory (DEAL) was used to sample both the exhaust plume of the truck and the background environment, which eliminated the contributions of other vehicle emissions to the plume measurements. The primary thrust of the research was to compare the truck’s emissions when using low sulfur (15 ppm) diesel fuel (base fuel) with those when using a 20% soy-based biodiesel blend (B20). These comparisons were made for two speeds (56 and 105 km/h) and load conditions—21,350 and 33,850 kg gross vehicle weight (GVW). Each time the fuel was changed, the truck was returned to the dealer to have the filters replaced, the old fuel removed, and the new fuel added. The highway traversed during the bulk of the measurements was a level section of US-70 in eastern North Carolina near the town of New Bern. After 20 days of primary experiments near New Bern were completed, an additional two days were spent driving a section of Virginia’s I-77 between Exits 1 and 8, which is near the town of Fancy Gap, VA, to investigate the effect of road grade on diesel emissions. The truck used standard pump fuel during this phase of the research. The DEAL was instrumented to measure total hydrocarbons (THC), carbon monoxide (CO), carbon dioxide (CO2), oxides of nitrogen (NOX), fine particulate matter (PM-2.5—PM with an aerodynamic diameter equal to or less than 2.5 µm) and the chemical composition of selected gas- and particle-phase air pollutants. Using B20 in place of the base fuel reduced nearly all emissions under nearly all combinations of speed and GVW examined, but the greatest reduction was in PM emission factors. For example, at the higher GVW and 56 km/h, using B20 reduced emissions of NOX by 9%, CO by 8%, THC by 20%, and PM by 68% compared with the base fuel. At the lower GVW and 105 km/h, using B20 reduced emissions of NOX by 5%, CO by 13%, THC by 18%, and PM by 19% compared with the base fuel. Changes in GVW at a given speed and fuel type had a smaller effect on emissions than changes in speed for a given load and fuel type. With regard to chemical composition, both black carbon (which approximates elemental carbon content) and particle-phase polycyclic aromatic hydrocarbons decreased at all speed and load conditions when using B20 in place of the base fuel. Also, B20 produced less C17-C31 alkanes when compared to the base fuel.
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