EM3-1: Impact of Filtration Velocities and Particulate Matter Characteristics on Diesel Particulate Filter Wall Loading Performance(EM: Exhaust Emission Control and Measurement,General Session Papers)

Abstract

The catalytic oxidation (low temperature oxidation) of Particulate Matter (PM) deposited on a catalyst coated Diesel Particulate Filter (DPF) is important to DPF regeneration process. It was found that PM/catalyst contact (fraction of PM which resides in the wall) plays a crucial role on catalytic oxidation effectiveness. Despite extensive technology development in recent years, the lack of fundamental understandings on the nature of the contact between PM and DPF substrate resulting from engine exhaust flow rates and PM characteristics still exists. The goal of this study is to gain more fundamental understanding on PM characteristics depositing on DPF and how engine exhaust flow rates impact DPF wall loading performance. Two engine operating conditions of the same engine speed and torque but distinct PM characteristics were selected for this study. Diesel exhaust was sampled through the newly developed Diesel Exhaust Filtration Analysis system (DEFA) holding a wafer disk made of the same substrate material as a full-scale DPF. The wafer disk also had similar wall thickness and pore geometry as the full-scale DPF substrate. Washcoat variations on the wafer (washcoat and catalyzed washcoat) were available. Previous work from our research group has shown that the pressure drop and filtration efficiency measured from the DEFA are similar to that of the full-scale DPF. The loaded wafers were then analyzed in a thermal mass analyzer that measures the semi-volatile organic fraction (SOF) as well as soot and sulfate fractions of PM. Two filtration velocities were also selected to study their impact on PM wall filtration. Preliminary results indicate that PM partitioning on a wafer disk are similar to that found on gravimetric analysis. Relative OC (SOF + sulfate) magnitudes are similar for all PM mass loading. Filling the wafer disks with the same engine mode but different filtration velocities affects the wafer filtration performance. This in turn alters the amount of PM trapped in the wall and soot cake as well as soot/SOF contents. Filling wafer disks with the same filtration velocity but different PM characteristics also affects wall loading performance and soot/SOF partitioning.