GPF modeling from pore-scale to the entire device

Petr  Koci, University of Chemistry and Technology, Prague, Czech Republic

Deposition of a catalytic material on or into the porous filter wall has become increasingly attractive in the automotive exhaust gas aftertreatment, because the resulting catalytic filter represents a compact multifunctional unit that can abate both gaseous and solid pollutants. Multi-scale modeling helps in understanding and quantification of the relationship between the filter microstructure and the entire device performance. The pore-scale models [1, 2] work with a 3D‑reconstructed porous filter wall obtained from X-ray tomography (XRT) scans, describing pore morphology as well as detailed spatial distribution of inert substrate and catalytic coating. Time-resolved XRT allows observing the formation of final coating structure with possible cracks during the washcoat drying. The XRT images are transformed into simulation mesh suitable for CFD computations of (i) gas flow through filter wall, (ii) component convection, diffusion and reaction, and (iii) soot particle transport and filtration.

Spatially averaged permeability and filtration efficiency predicted from the pore-scale simulations are then employed in a full-scale 1D+1D model of filter channels [3]. Local effectiveness factor with characteristic diffusion length is used to account for internal transport limitations of gas components conversion in the filter wall. The approach is demonstrated on several different GPFs with varying location (on-wall, in-wall, combined) and microstructure (particle and pore size) of the catalytic material. The model predictions are compared with the measured data from lab reactor and engine test bench, and it is shown how the actual catalyst distribution and structure affect the pressure drop, filtration efficiency and CO light-off curves at different flow rates.

References

[1] Kočí P., Isoz M., Plachá M., Arvajová A., Václavík M., Svoboda M., Price E., Novák V., Thompsett D. 3D reconstruction and pore-scale modeling of coated catalytic filters for automotive exhaust gas aftertreatment. Catalysis Today 320 (2019), 165-174. http://doi.org/10.1016/j.cattod.2017.12.025

[2] Plachá M., Kočí P., Isoz M., Svoboda M., Price E., Thompsett D., Kallis K., Tsolakis A. Pore-scale filtration model for coated catalytic filters in automotive exhaust gas aftertreatment. Chemical Engineering Science 226 (2020), 115854. https://doi.org/10.1016/j.ces.2020.115854

[3] Schejbal M., Štěpánek J., Marek M., Kočí P., Kubíček M. Modelling of soot oxidation by NO2 in various types of Diesel particulate filters, Fuel 89 (2010), 2365-2375. http://dx.doi.org/10.1016/j.fuel.2010.04.018