(426g) Modeling of Soot Oxidation in Diesel Particulate Filters Incorporating Cake Layer Microstructure

Tightening of emission norms around the world has led to the widespread adoption of diesel particulate filter (DPF) technology as the method of choice for reducing particulate emissions from diesel vehicles. However, oxidation of the trapped soot and efficient regeneration of DPFs continue to be challenges for practical implementation of these devices in the exhaust stream. Most regeneration models in the literature assume fixed surface area and density for the soot cake, which may not always be valid.

In this work, we examine the oxidation of the soot cake layer formed on a DPF, by treating the cake as a random assembly of particles of different sizes. A model is developed to generate the soot microstructure, in three dimensions over a small part of the inlet channel of a DPF. This is done by a Monte Carlo simulation implemented at two levels: first, to generate randomly the positions (centers) of the individual soot particles constituting the cake; and second, to generate the diameters of the soot particle so that they are according to a prescribed moment of the soot particle size distribution.

Each soot particle is assumed to oxidize according to the shrinking particle mechanism, and the combustion of the entire assembly of soot particles is coupled to the oxygen partial pressure profile in the bed. Reconfiguration of the bed is allowed in order to maintain connectivity as the bed combusts, until complete burnout of the bed is achieved. Different possible methods in which the soot cake can be re-configured are discussed, and sensitivity of the final oxidation rate to each of these reconfiguration mechanisms is shown.

Under specific conditions, the simplifying assumption of constant specific area is shown to hold. Results are also presented for the evolution of bed density, total soot surface area and surface area per unit mass of (remaining) soot. Overall the model presents a generalized description of soot cake oxidation and can be used to gain insights into the regeneration behavior of DPFs.