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Model-based evaluation of diesel particulate filter structures

: Dannowski, M.; Beckert, W.; Adler, J.; Michaelis, A.

Fraunhofer-Institut für Algorithmen und Wissenschaftliches Rechnen -SCAI-, Sankt Augustin:
1st Conference on Multiphysics Simulation - Advanced Methods for Industrial Engineering 2010. Proceedings. CD-ROM : June 22-23, 2010, Bonn, Germany
Sankt Augustin: Fraunhofer SCAI, 2010
8 S.
Conference on Multiphysics Simulation <1, 2010, Bonn>
Fraunhofer IKTS ()

Within the last years modern diesel applications had to satisfy increasingly challenging European exhaust emission standards, especially the Euronorm 5 and 6. All the automotive firms focused her efforts to reduce soot emissions by developing new after treatment systems. Common concepts for diesel exhaust after treatment systems rely on Diesel Oxidation Catalysts (DOC), Diesel Particulate Filter (DPF) and NOx absorbers. The most effective of these systems is the DPF, actually providing filtration rates better than 90 %. The geometry of the DPF structure has an important influence on its performance. Simulation offers a valuable tool for the evaluation and optimisation of various DPF designs. The present paper demonstrates the usage of the COMSOL multi physics code for modelling DPF systems. The complete model is based on a single pair of DPF channels composed of inlet / outlet channel, porous wall and the ash layer. Alternating plugs sealing the inlet- and outlet channels force the soot loaded exhaust gas to flow through the porous walls, where the soot is deposited into porous structure and at a growing soot cake layer. It is advantageous to separate the modelling of a DPF into several stages. In a first stage the pressure drop over the complete DPF channel structure unit cell is analysed in a CFD-analysis, also incorporating nonlinear pressure loss contributions due to flow contraction and expansion at the channel in and outlets. The pressure difference across the porous walls and the soot cake follows from Darcy's Law. In a next stage the soot deposition with its effect on the permeability of the porous walls and initiation of soot cake growth is included into the analysis. Phenomenological approximations on a continuum level are applied to account for the different microscopic and molecular processes of soot deposition within and at the surface of the porous wall structures . There is a strong both way interaction between gas flow field and soot deposition. The model results are compared to experimental measures of the DPF filter segments. A further level of model analysis is necessary to account for non-ideal effects of the measuring system.