3D reconstruction and pore-scale modeling of coated catalytic filters for automotive exhaust gas aftertreatment

This paper introduces a newly developed methodology for the pore-scale simulation of flow, diffusion and reaction
in the coated catalytic filter. 3D morphology of the porous filter wall including the actual distribution of
catalytic material is reconstructed from X-ray tomography (XRT) images and further validated with the mercury
intrusion porosimetry (MIP). The reconstructed medium is then transformed into simulation mesh for
OpenFOAM. Flow through free pores in the substrate as well as through the coated zones is simulated by
porousSimpleFoam solver, while an in-house developed solver is used for component diffusion and reactions.
Three cordierite filter samples with different distribution of alumina-based coating ranging from in-wall to onwall
are examined. Velocity, pressure and component concentration profiles are calculated enabling the prediction
of permeability and component conversion depending on the actual microstructure of the wall. The
simulation results suggest that the gas predominantly flows through remaining free pores in the filter wall and
cracks in the coated layer. The mass transport into the coated domains inside the filter wall is enabled mainly by
diffusion. Large domains of compact catalytic coating covering complete channel wall result in a significant
increase of pressure drop as the local permeability of the coating is two orders of magnitude smaller than that of
bare filter wall.