Combining Biodiesel and Exhaust Gas Recirculation for Reduction in NO x and Particulate Emissions

The coupled elimination of NO x and particulate matter (PM) in diesel exhaust was investigated by combining biodiesel, exhaust gas recirculation (EGR), and diesel particulate filtration (DPF). The combustion of biodiesel fuels, being oxygenated hydrocarbons, produces less partial oxidation products such as CO, volatile organic hydrocarbons, and particulate soot. EGR requires auxiliary particulate filtration due to the increased soot that is produced while the reliability of the DPF regeneration requires a minimum exhaust temperature and NO x /PM ratio. We employed a heavy-duty chassis dynamometer system to quantify the synergistic effects of biodiesel, EGR, and soot filtration for a vehicle having a drive cycle with a low exhaust temperature. The biodiesel/EGR/DPF system performance was assessed in terms of NO x and PM emissions for low-temperature operation. The combination of biodiesel and EGR was shown to produce significantly less NO x and PM for a refuse truck operated at low load. The combination of biodiesel and EGR replaces gas phase O2 from air with nascent oxygen in the fuel, resulting in up to a 40% reduction in both PM and NO x compared to the use of ultralow sulfur diesel (ULSD) without EGR. The decrease in PM and corresponding increase in the NO x /PM ratio has a beneficial effect on DPF operability due to a more favorable oxidation stoichiometry. Another advantage of this system is the possibility of optimizing NO x reduction by increasing the amount of EGR, while staying within the prescribed limits of favorable DPF operation.