Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-II-9MODELLING OF DIESEL PARTICULATE FILTRATIONIN WALL-FLOW TRAPSS. Bensaid, D.L. Marchisio, D. Fino, G. Saracco, V. SpecchiaDipartimento di Scienza dei Materiali e Ingegneria Chimica - Politecnico di Torino,Corso Duca degli Abruzzi 24, 10129 Turin – ITALYTel./Fax: 011.564.4710/4699; corresponding author: e-mail: debora.fino@polito.itNowadays, soot emissions from Diesel engines can be reduced by physically trapping theparticles with on-board diesel particulate filters (DPFs). The investigation of soot filtration viaDPFs, and their regeneration, can be split into four sub-problems: i) the computation of themulti-phase flow field inside the DPF; ii) the description of the evolution of the filtercharacteristics as soot is deposited and filtered; iii) the formation of a soot cake in the DPFchannels; iv) the modeling of regeneration dynamics. Hence, the aim of this work is todevelop a mathematical model able to accurately describe each of these four mentioned steps.Two and three dimensional CFD simulations of the multiphase flow inside the filterchannels are carried out by resorting to an Eulerian-Eulerian approach. The interactionbetween the main phase and the soot particles is taken into account through the drag force,calculated according to Schiller and Naumann [1]. The influence of Brownian forces on thedrag force via the Stokes-Cunningham coefficient, and on particles trajectories in thechannels, is proven to be negligible.Fig. 1 shows the gas and soot velocity axial profiles inside the DPF channels at thebeginning of filtration (Fig 1-a), and the evolution of the gas velocity across the filter wallwith respect to the total amount of collected soot (Fig. 1-b). The accumulation of sootparticles into the filter pores modifies its characteristics: the porosity and the permeability ofthe filter decrease until a maximum value of deposited soot volume fraction is reached intothe porous media, thus making these regions impermeable to the dispersed phase and entailingthe formation of a soot layer onto the filter surface. A parameter of major importance inparticle interstitial filtration is the local efficiency, namely the probability of successfulcollections of soot particles onto fictitious spherical collectors constituting the channel walls,largely due to deposition from Brownian motions and interception. In the evaluation of theefficiency, calculated as indicated in literature [2], the size of the soot particles has a strongimpact. In the light of this consideration, our Eulerian-Eulerian approach is particularlyinteresting because it can be easily coupled with a population balance equation (PBE) for thedescription of poly-disperse solid-gas flows, resulting in a much lower computational timewhen compared with alternative Lagrangian-Eulerian approaches. The real soot distribution90