In Situ Observation of Different Soot Layers in a Model Filter Channel During Its Regeneration

To keep the air clean, wall-flow particulate filters are predominantly used in the exhaust gas after-treatment systems of combustion engines to remove reactive soot and inert ash particles. These filters consist of parallel porous channels with alternately closed ends, effectively separating particles by forming a layer on the filter surface. However, the particulate layer increases the pressure drop, requiring periodic regeneration. During regeneration, soot oxidation breaks up the particulate layer, while resuspension and transport of individual agglomerates may occur. These phenomena are influenced by gas temperature and velocity, as well as dispersity and the reactivity of the soot particles. Sustainable fuels can produce different types of soot with different reactivities and dispersities, therefore this study focuses on the influences of soot dispersity and reactivity by varying the reactive particle system. A model wall-flow filter channel is used for the investigation, enabling the detection of the layer break-up and detachment of particle structures from the filter surface over the entire channel length with a high-speed camera operating at 1000 fps. Recordings reveal significant differences in the behavior of the soot types. Image analyses provide insights into the visual layer break-up, structural size evolution, detachment dynamics, particle velocities, and the spatial and temporal distributions of detachment events. General parameters, including regeneration time, pressure drop, gas temperature and velocity as well as CO₂ concentration, further characterize the regeneration process. The results offer insights into the detachment and rearrangement behavior of differently dispersed and reactive particle structures in wall-flow filters, demonstrating that these characteristics can significantly influence the regeneration process.