Wall-Flow Diesel Particulate Filters—Their Pressure Drop and Collection Efficiency

The present study investigates the pressure drop and filtration characteristics of wall-flow diesel particulate monoliths, with the aid of a mathematical model. An analytic solution to the model equations describing exhaust gas mass and momentum conservation, in the axial direction of a monolith cell, and pressure drop across its porous walls has been obtained. The solution is in very good agreement with available experimental data on the pressure drop of a typical wall-flow monolith. The capture of diesel particles by the monolith, is described applying the theory of filtration through a bed of spherical collectors. This simple model, is in remarkable agreement with the experimental data, collected during the present and previous studies, for the accumulation mode particles (larger than 0.1 μm). Although the model does not account for post-monolith particle formation, the dimensionless groups suggested by the filtration theory are found to correlate the data for the nuclei mode particles (smaller than 0.1 μm). The predictive power of the design equations established, and their ease of use make them indispensable tools for the rational engineering design of diesel particulate filters.