The Optimum Cell Density for Wall-Flow Monolithic Filters: Effects of Filter Permeability, Soot Cake Structure and Ash Loading

A major challenge in the development of diesel filter systems is the selection of the appropriate filter medium in terms of its geometric configuration (cell density, wall thickness) and its physical properties (porosity, pore size). This selection aims to achieve minimization of the filter pressure drop as well as more efficient filter regeneration.

The aim of the present work is to provide engineering criteria to support the design and selection of suitably sized wall-flow monolithic filters for diesel particulate control. The approach followed in the present paper is to employ a comprehensive, experimentally validated mathematical framework taking into account the effects of filter structure (cell density, filter dimensions, wall thickness, permeability), soot cake microstructure and its evolution under varying exhaust flow conditions, as well as ash accumulation, in order to derive optimal configurations and sizing criteria of monolithic filters that can be used for specific applications. A major result concerns the derivation of nomographs giving the optimum cell density for honeycomb filters under the combined constraints of given filter volume, exhaust flow, temperature, as well as different soot and ash loadings inside the filter. These nomographs are expected to facilitate the task of selection and reliable life-cycle deployment of diesel particulate filters.