(45f) A numerical Simulation Tool describing Particulate Depositions, Regeneration and Deposit Rearrangement Effects in Gas Filter Systems

Due to ever increasing demands regarding filtration processes, filter development is faced with the task to understand the process in a more detailed way. A great upcoming challenge in filter development is the reduction of diesel exhaust particulate emissions of passenger cars because of their harmful effects. Today aftertreatment devices, such as a Wall-Flow Diesel Particulate Filter (DPF) are used. The principle of a Wall-Flow DPF is based on the accumulation and oxidation of particles in the alternating open and closed channels of the filter. The pressure drop over the DPF and the fuel consumption of the passenger car increase with time of operation. For this reason, the deposited particulate filter cake must be regenerated occasionally. If catalytic additives are used in order to assist the regeneration, unburnable ash is produced in the filter channel which causes a permanent pressure drop and shortens the overall life-time of a DPF. So as to minimize complex and expensive investigations on engine test benches, a mathematical model has been developed describing the particulate loading and regeneration behavior of a DPF as well as the rearrangement of inert ash inside the filter channel depending on the type of regeneration. The model is integrated into a commercial CFD code (FLUENT) by means of user-defined subroutines (UDS). The CFD code was used for the calculation of the fluid flow and the particle tracks of different kinds of particles (e.g. soot, additives) in a two-dimensional model of the DPF. Herewith, the axial and radial structure of the deposited particles on and in the filter can be determined. In the UDS, models are implemented that calculate the particulate deposition places, the pressure loss, the separation efficiency, the regeneration behavior, and the ash rearrangement along the filter channel. By these means the basic operation conditions of a life-time cycle of a DPF can be described, starting from the ?green? filter and ending with its necessary technical service. The latter is required when the accumulated ash deposits lead to an inadmissible pressure loss over the DPF and have to be chemically removed. Experiments regarding the filtration and regeneration process of a Wall-Flow DPF where performed on an engine test bench at different operating points. In laboratory tests and computer tomography analyses performed after the engine test bench runs detailed information was gained about the particulate deposits inside the filter channels. Comparing the simulation results with the experimentally gained results, it can be seen that both sets of data concur.