Multiscale methods for the fundamental understanding of diesel soot mitigation

Doctoral thesis, 2011

Current regulations for diesel exhaust emissions cannot be met by engine improvements alone, and for this reason the diesel particulate filter (DPF) is a widely used aftertreatment component for the control of diesel particulate matter (PM). The DPF functions by trapping PM and destroying it by oxidation. The oxidation of the solid portion of PM, or soot, is a complex and non-linear process which can occur either with or without catalysts. In addition, lubrication-derived, incombustible ash accumulates in the DPF and over time accounts for a majority of the trapped mass in the DPF on average. As soot and ash accumulate in the DPF, the pressure drop over the filter increases, which negatively affects the fuel economy. Improved understanding of the fundamental properties of soot and ash leads to more efficient aftertreatment components. The work in this thesis consisted of two related focus areas, including diesel soot oxidation and the effects of ash accumulation on the DPF. An experimental method was developed to study the kinetics of the non-catalytic oxidation of carbon by O2, while a theoretical model was constructed to describe the relationship between carbon microsctructure and reactivity. The catalytic oxidation of carbon by O2 was studied by means of a recent nanofabrication technique where the carbon-catalyst contact could be accurately controlled. In addition, a system of both novel and established experimental techniques was used in this thesis to add to the fundamental understanding of lubrication-derived ash accumulation in the DPF.