An increasing environmental concern for diesel particulate emissions has led to the development of efficient and robust diesel particulate filters (DPF). Although the main function of a DPF is to filter solid particles, the beneficial effects of applying catalytic coatings in the filter walls have been recognized. The catalyzed DPF technology is a unique type of chemical reactor in which a multitude of physicochemical processes simultaneously take place, thus complicating the tasks of design and optimization. To this end, modeling has contributed considerably in reducing the development effort by offering a better understanding of the underlying phenomena and reducing the excessive experimental efforts associated with experimental testing. A comprehensive review of the evolution and the most recent developments in DPF modeling, covering phenomena such as transport, fluid mechanics, filtration, catalysis, and thermal stresses, is presented in this article. A thorough presentation on the mathematical model formulation is given based on literature references and the differences between modeling approaches are discussed. Selected examples of model application and validation versus the experimental data are presented.

The objective of this study is to explain the physical and chemical mechanisms involved in the operation of a catalyzed diesel particulate filter. The study emphasizes on the coupling between reaction and diffusion phenomena (with emphasis on NO2 “back-diffusion”), based on modeling and experimental data obtained on the engine dynamometer. The study is facilitated by a novel multi-dimensional mathematical model able to predict both reaction and diffusion phenomena in the filter channels and through the soot layer and wall. The model is thus able to predict the species concentration gradients in the inlet/outlet channels, in the soot layer and wall, taking into account the effect of NO2 back diffusion. The model is validated versus engine dyno measurements. Two sets of measurements are employed corresponding to low-temperature “controlled” regenerations as well as high-temperature “uncontrolled” conditions. Good agreement is observed between measured and computed results in both regeneration modes. It is concluded that at low temperatures, the main reaction mechanism involves NO2 produced on the catalytic sites and partially diffusing back to the soot layer (re-cycling). At high temperature regeneration modes, NO2 is not favored due to chemical equilibrium limitations and therefore the main reaction path involves oxygen reaction with soot.

Pressure drop modelling is a subject of special interest for the design and control of diesel particulate filters. Based on previous experience, an improved pressure drop model is presented. Special emphasis is given on the soot permeability properties and its dependence on temperature and pressure. With the assumption of uniform wall flow distribution throughout the channel length, it is possible to derive an analytic expression for pressure drop calculation. The main difference with previously proposed analytic expressions lies in the inclusion of gas density dependence on local pressure, which necessitates an iterative calculation procedure. The importance of this improvement is illustrated parametrically. The new model is validated against experimental data on an engine bench, using a double filter configuration to ensure constant filter soot loading throughout the test.