Comparison of Real-World Fuel Use and Emissions for Dump Trucks Fueled with B20 Biodiesel Versus Petroleum Diesel

Diesel vehicles contribute substantially to emissions of NOx, an ozone precursor, and to particulate matter. Real-world in-use on-road emissions of selected diesel vehicles, fueled with B20 biodiesel and petroleum diesel, were measured during normal duty cycles using a portable emissions measurement system. Four categories of dump trucks were tested, including: (1) single rear axle with Tier 1 engines; (2) single rear axle with Tier 2 engines; (3) tandems with Tier 1 engines; and (4) tandems with Tier 2 engines. Each vehicle was tested for one day on B20 biodiesel and for one day on petroleum diesel. On average, there were 4.5 duty cycles per day. Each duty cycle can be represented as a combination of nine operating modes (idle, three levels of acceleration, three levels of cruise, deceleration, and dumping). Average fuel flow and emission rates on a mass per time basis varied substantially among the operating modes. Key factors responsible for the observed variability in fuel use and emissions include: operating mode, vehicle size, engine type, vehicle weight, and fuel. Average fuel use and CO2 emission rates were approximately the same for the two fuels, but average emission rates of NO, CO, HC, and PM decreased by 10, 11, 22, and 10 percent, respectively, for B20 biodiesel versus petroleum diesel. The observed decrease in NO emissions is different from results reported by others based on engine dynamometer testing. The difference may be because of the effect of real-world duty cycles versus standardized test procedures used in dynamometer testing, and requires further work to determine if the ratio of NO to total NOx is impacted by the duty cycle.