Inertial Contributions to the Pressure Drop of Diesel Particulate Filters

Wall-flow Diesel particulate filters operating at low filtration velocities usually exhibit a linear dependence between the filter pressure drop and the flow rate, conveniently described by a generalized Darcy's law. It is advantageous to minimize filter pressure drop by sizing filters to operate within this linear range. However in practice, since there often exist serious constraints on the available vehicle underfloor space, a vehicle manufacturer is forced to choose an “undersized” filter resulting in high filtration velocities through the filter walls. Since secondary inertial contributions to the pressure drop become significant, Darcy's law can no longer accurately describe the filter pressure drop. In this paper, a systematic investigation of these secondary inertial flow effects is presented. The investigation has lead to an analytical approximation shown to be in remarkable agreement with both experimental data collected in the laboratory with a variety of filters and with detailed 3-D Computational Fluid Dynamics calculations. The inclusion of these additional inertial losses to available filter pressure drop models enables more accurate predictions of pressure drop of Diesel particulate filters under all practical ranges of exhaust flow.