Real-World Measurement and Evaluation of Duty Cycles, Fuels, and Emission Control Technologies of Heavy-Duty Trucks

The purpose of this study is to assess the robustness of relative comparisons of emission rates between fuels and technologies to differences in real-world duty cycles on the basis of in-use measurements of five heavy-duty diesel vehicles (HDDVs). Prior comparisons of biodiesel and ultra-low-sulfur diesel emissions, recent changes in emission standards applicable to HDDVs, and typical emission control technologies used in these vehicles are reviewed. The study methodology includes field measurements with a portable emission measurement system and related instruments and sensors for five HDDVs operated in normal service by professional drivers on multiple round-trip routes within North Carolina. Duty cycles and emission rates are quantified on the basis of the manifold absolute pressure, which is an indicator of engine load. Variability in engine load for each observed round trip is quantified on the basis of the cumulative distribution function of normalized manifold absolute pressure. The effect of variability in duty cycles on fuel-based emission rates for nitrogen oxides, carbon monoxide, hydrocarbons, and particulate matter is evaluated. Comparisons are made for emissions of three trucks operated on B20 biodiesel and ultra-low-sulfur diesel. Furthermore, comparisons of five trucks with model years ranging from 1999 to 2010 illustrate the impact of different emission standards and emission control technologies on real-world emission rates. A key finding is that relative comparisons pertaining to fuels and technologies are robust to variability in observed duty cycles.