Development of a CFD Model to Study the Hydrodynamic Characteristics and the Soot Deposition Mechanism on the Porous Wall of a Diesel Particulate Filter

A two dimensional CFD model has been developed to study the mechanism of soot deposition on the porous wall surface in a Diesel Particulate Filter (DPF). The goal is to improve understanding of the soot deposition and its interaction with the hydrodynamic behaviour of the device. The KIVA3V CFD code and pre-processor were modified to simulate a single channel in a DPF. The code was extended to solve the conservation equations in porous media materials, to account for the sticking of particles on a porous surface and to evaluate the increasing resistance to the flow as the soot inside the trap accumulates. The code is already configured to track Lagrangian particles and these were modified to represent the soot particles in the flow. The code pre-processor was modified to allow definition of a double-symmetric geometry and to specify porous cells. The numerical model can predict the hydrodynamic performance and pressure drop of a clean particulate filter with results compared to experimental data and simple one-dimensional DPF models. The soot cake layer thickness on the porous wall increases in time with a spatial distribution determined by the fully coupled particle-hydrodynamics in the gaseous flow. As the soot cake increases in thickness, it alters the particle laden gaseous flow profiles. A set of unsteady simulations were run to steady state, at different loading conditions and the results have been compared with the experimental data available from literature. An extensive set of simulations has been carried out and an analysis of the spatial distribution of kinetic energy in the system (as a function of Reynolds number and of the geometric features of the trap) has been done, in order to study the correlation between the velocity field inside the channels and the soot deposition profile.

The simulation results have been compared with the results of a CFD commercial code (Fluent) and with the results of a 1D simulation code, based on Bissett's approach and developed by the authors.

The model can be used as a tool to predict the pressure drop across a Diesel Particulate Filter, the velocity profile inside the channels, and to study the deposit of soot along a porous surface as a function of time.