Operational Evaluation of In-Use Emissions and Fuel Consumption of B20 Biodiesel versus Petroleum Diesel-Fueled Onroad Heavy-duty Diesel Dump Trucks and Nonroad Construction Vehicles

Abstract

Diesel vehicles contribute substantially to statewide emissions of NOx, an ozone precursor, and to particulate matter. North Carolina Department of Transportation (NCDOT) is conducting a pilot study to demonstrate the use of B20 biodiesel fuel on approximately 1,000 vehicles in selected areas of the state; there are plans to extend the use of B20 fuel to a much larger number of vehicles in all 100 counties in North Carolina. Real-world in-use onroad and nonroad emissions of selected heavy-duty diesel vehicles, including those fueled with B20 biodiesel and petroleum diesel, were measured during normal duty cycles using a portable emissions measurement system (PEMS). Each vehicle was tested for one day on B20 biodiesel and for one day on petroleum diesel, for a total of 68 days of field measurements. The vehicles were operated by drivers assigned by NCDOT. Each test was conducted over the course of an entire workshift, and there were approximately 2 to 10 duty cycles per shift. Each duty cycle is comprised of a uniquely weighted combination of operating modes based on vehicle speed, acceleration, and typical modes of activities. Average emission rates on a mass per time basis varied substantially among the operating modes. Average fuel use and emissions rates increased 26 to 35 percent when vehicles were loaded versus unloaded. The use of B20 instead of petroleum diesel lead to a slight decrease (approximately 2 to 10 percent depending on the vehicle) in NO emission rate and significant decreases (approximately 10 to 30 percent depending on the vehicle) for opacity, HC, and CO, respectively. These trends are similar to nonroad vehicles. Factors that were responsible for the observed variability in fuel use and emissions include: operating mode, vehicle size, engine tier and size, vehicle weight, and fuel. In particular, emission rates were also found to decrease significantly when comparing newer, higher tier vehicles to older ones. Recommendations were made regarding operating strategies to reduce emissions, choice of fuel, and the need for future work to collect real-world duty cycle data for other vehicle types.