Impacts of biodiesel on particulate emissions control

With the expanding use of bio-derived diesel fuels, their effect on emissions controls has become an important issue. This is particularly true for diesel particulate filters (DPFs), which capture incompletely burned particulates from engine exhaust and oxidize those particulates to prevent excessive backpressure. We describe results from comparisons between diesel particulates generated with a modern light-duty engine fueled with conventional ultra-low sulfur diesel (ULSD) fuel and particulates generated with biodiesel blends at the 5%, 20% and 100% level (B5, B20, and B100, respectively). Several complementary experimental techniques, including temperature programmed desorption and oxidation, and pulsed isothermal oxidation, high-resolution transmission electron microscopy and surface area measurements by BET were employed to characterize the particulates. From these measurements we developed a kinetic oxidation model to account for differences in reactivity. Oxidation of the fixed carbon components of the each fuel's particulates was found to follow a consistent Arrhenius rate relationship with an activation energy of 113 ± 6 kJ/mol when normalized to the instantaneous BET surface area. An oxidation model for the combined effects of volatiles and fixed carbon was found to compare well with experimental data.