In diesel and gasoline engines, it becomes increasingly important to filter soot emissions from the exhaust. Soot emissions can be reduced by forcing the soot particles to be trapped physically through an installed diesel particulate filter (DPF). The DPF is one of the most essential after-treatment devices invented to reduce particulate matter from diesel engines discharge. For optimal protection of environment, the international emission standards become stricter and mandatory for more countries.
The goal of this study was to use computer simulations (GeoDict) to design a better DPF with lower pressure drop, higher filter efficiency and longer life time. The key parameter that governs the DPF performance is the ceramic filter media. Therefore, the simulation steps contain modeling the ceramic filter media, simulating the air flow through the filter media, simulating the transport and deposition of soot particles, the conversion of deposited particles into a porous media, determining the soot layer packing density and the soot layer's viscuous flow resistivity. The simulations provide all the details on deposition location and pressure drop over time.
Soot particles to be filtered are much smaller than the computational grid size. Therefore, when soot particles deposit, they do not fully fill the computational cell, but rather form a permeable media inside and on top of the ceramic filter. The solver allows to control how much a cell can get filled, and how much resistivity to the flow the cell will have, depending on the degree of filling. Sub-voxel-sized soot particles form a filter cake which is modeled as porous media with locally varying permeability. These soot particles do most of the work to filter more particles.
The simulation results show that initially a fast increase in pressure drop occurs during the depth filtration regime. Afterwards, it follows with a long, slower pressure drop increase during the cake filtration regime. The simulation results agree very well with the experimental data provided by Fraunhofer IKTS. Modifications were carried out to shorten the depth phase and to reduce the presssure drop during cake phase. This work confirms a key step in virtual material design. The outcome of the simulation studies led to a granted patent for the particulate filter.