Comparison of real-world fuel use and emissions for dump trucks fueled with B20 biodiesel versus petroleum diesel

Diesel vehicles contribute substantially to the emissions of nitrogen oxides (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 by using a portable emissions measurement system. Four categories of dump trucks were tested: (a) trucks with a single rear axle and Tier 1 engines, (b) trucks with a single rear axle and Tier 2 engines, (c) tandem-rear-axle trucks with Tier 1 engines, and (d) tandem-rear-axle trucks with Tier 2 engines. Each vehicle was tested for 1 day while it was operating on B20 biodiesel fuel and for 1 day while it was operating on petroleum diesel fuel. 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). The average fuel flow and emissions rates on a mass-per-time basis varied substantially among the operating modes. The key factors responsible for the observed variability in fuel use and emissions included operating mode, vehicle size, engine type, vehicle weight, and fuel. Average fuel use and CO2 emissions rates were approximately the same for the two fuels; but the average emissions rates of NO, CO, hydrocarbons, and particulate matter PM decreased by 10%, 11%, 22%, and 10%, respectively, for B20 biodiesel fuel compared with those for petroleum diesel fuel. The decrease in NO emissions observed was different from the results reported by others, based on engine dynamometer testing. The difference may be because of the effect of real-world duty cycles versus the standardized test procedures used in dynamometer testing, and further work is required to determine whether the ratio of NO to total NOx is affected by the duty cycle.