Time‐lapse visualization of diesel particulate filter active‐regeneration using field emission scanning electron microscopy

: Regeneration of diesel particulate filter (DPF) is a complicated process due to its high operating temperature and associated oxidation of soot on the filter substrate. Several oxidation mechanisms of diesel soot have been proposed based reaction kinetics, but more information about the oxidation phenomena is needed in a practical system, i.e., soot oxidation on a DPF substrate. In this work, the DPF regeneration process was, for the first time, visualized at the particle scale ex-situ, in time-lapse series, using field emission scanning electron microscopy (FE-SEM). Time-lapse transformation of soot cake layer on a real DPF was followed from initiation through the complete regeneration process. In parallel, transformation of the soot primary particle diameter was directly measured using high-resolution transmission electron microscopy. FE-SEM visualization clearly showed shrinkage of the soot cake layer on the DPF wall as oxidation progressed. Furthermore, diameter distribution analysis revealed a trend of shrinkage of the nano-scale soot primary particles during oxidation, supporting the FE-SEM observations of the micron-scale shrinkage of the agglomerated soot cake layer. Fragmentation of the shrunken soot cake layer was also observed and is suspected to be a result of locally higher gas flow that depends on surface pore morphology of the filter substrate. This article is protected by copyright. All rights reserved.