Characterization of the oxidation kinetics and morphology of diesel particulates

We summarize recent studies of the impact of fuel variations on the oxidation characteristics and morphology of diesel particulates generated in engine dynamometer experiments at both Oak Ridge National Laboratory and Pennsylvania State University. Results from these studies to date indicate that fueling with pure biodiesel and biodiesel-blends produces particulates with significantly different properties compared to conventional diesel fuels. These differences include higher volatiles content and higher devolatilized surface area for high biodiesel particulates. TEM measurements of the nanoscale lamella structure of devolatilized biodiesel particulates also indicate a more open structure, which is more accessible to oxygen penetration. Oxidation rate measurements of devolatilized diesel particulates with molecular oxygen reveal that normalizing the observed oxidation rates with surface area makes it possible to model the kinetics of both conventional and biodiesel-blended particulates with a single set of Arrhenius parameters. These measurements also indicate that the surface area of both particulates evolves in a complex but consistent way as oxidation proceeds. We suggest a general approach for modeling this area evolution and discuss the resulting implications for understanding changes in particle morphology with oxidation.