Experimental investigation of formation mechanisms and rearrangement phenomena of reactive-inert particle layers in cross-flow filters in gas cleaning applications

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Cross-flow or wall-flow filters are nowadays a standard component in exhaust gas aftertreatment and reduce particulate emissions from internal combustion engines by removing ash and soot particles. After reaching a critical pressure drop due to the layer formation, the filter is regenerated. The soot particles are oxidized by a continuous (C-NO2) or discontinuous (O2) reaction. This results in a layer break-up. Particulate structures can be detached and transported along the filter channel. In this process, the deposition pattern of the homogenous layer can result in a channel filling. The break-up behavior of the particle layer is a decisive process that depends on the layer composition and the soot reactivity. The aim of the overall project consists of the structured investigation of the relationship be-tween the particle layer of reactive and inert particles and the rearrangement processes (layer break-up – resuspension - transport) of particulate structures during O2- as well as NO2-based regeneration in a model filter channel. In the first project phase, an experimental setup was developed in which the rearrangement processes of resuspended particulate structures during O2-based regeneration can be investigated in a model filter channel. The layer break-up, resuspension and transport of agglomerates is observed over the entire channel length with a high-speed camera and analyzed in terms of resuspension location, agglomerate size and velocity. The developed methods and existing knowledge on the resuspension processes serve as a basis for the objectives de-fined in the second funding period. The goal of the second project phase is therefore to fundamentally investigate the influence of soot reactivity (high reactive vs. low reactive) and soot dispersity as well as the oxidation gas (NO2 vs. O2) on the rearrangement processes in a wall-flow filter. The resulting findings are subsequently used to elucidate the inconsistency from the literature that the resulting deposition patterns in a wall-flow filter are dependent on the oxidation gas used (continuous regeneration (NO2) homogenous layer; discontinuous regeneration (O2) channel filling). The hypothesis is pursued that it is not the oxidation gas but the fundamental particle-technological processes that determine the rearrangement behavior. Through the defined adjustment of process parameters (e.g. flow velocity, temperature) and the generation of particle layers with known composition (reactive inert ratio), the knowledge obtained can also be extended to other fields of application, e.g. newly developed fuels with altered soot reactivities and soot concentrations in the exhaust gas. This provides a fundamental understanding of the processes occurring during the filtration of ash and soot particles.