Using CFD Simulation as a Tool to Identify Optimal Operating Conditions for Regeneration of a Catalytic Diesel Particulate Filter

Abstract

In the work presented in this paper, CFD-based simulations of the regeneration process of a catalytic diesel particulate filter were performed with the aim of identifying optimal operating conditions in terms of trade-off between time for regeneration and peak temperature. In the model, all the soot trapped inside the filter was assumed to be in contact with the catalyst. Numerical results have revealed that optimization can be achieved at low inlet gas velocity by taking advantage of the high sensitivity of the soot combustion dynamics to the availability of oxygen. In particular, optimal conditions have been identified when operating with highly active catalysts at sufficiently low inlet gas temperatures, so as to lie on the boundary between kinetics-limited regeneration and oxygen transport-limited regeneration. As catalyst activity is increased, this boundary progressively shifts towards lower inlet gas temperatures, resulting in lower peak temperatures and shorter times for filter regeneration. Under such conditions, in order to further speed up the process while still ensuring temperature control, it is essential to keep the filter adequately hot, thus minimizing the time required for the preheating phase, which may be a significant part (up to 65%) of the total time required for regeneration (preheating plus soot consumption).

The Issue of Soot-Catalyst Contact in Regeneration of Catalytic Diesel Particulate Filters: A Critical Review

“…Thus, once a high dispersion with a deep penetration of catalyst into the macro-pores of the filter walls is assured (Figure 5), in order to optimize the contact between soot and catalyst, thus making regeneration of the DPF a truly catalytic process, it is essential to minimize the thickness of the cake layer, approaching its disappearance. This conclusion is supported further by the results of CFD-based simulations of soot combustion dynamics in a catalytic DPF showing that, once it is assumed that all the soot trapped inside the filter walls is in contact with the catalyst, fast and at the same time safe (i.e., low-temperature) regeneration is not feasible [40][41][42] unless the accumulation of soot in the form of cake on top of the catalytic walls is prevented [42][43][44]. Indeed, catalytic oxidation of the soot trapped inside the walls is only a pilot causing violent ignition of the soot cake, whose fast combustion process leads to high peak temperatures [40][41][42].…”

“…In addition, as already mentioned in Section 3, avoiding the accumulation of cake is of paramount importance in preventing high temperature excursions that arise under conditions of fast regeneration, possibly causing damage to the catalytic DPF. However, in the absence of cake, fast low-temperature regeneration can be carried out provided that operating conditions are properly chosen [42][43][44]. In this respect, Figure 8 shows the operating map of a catalytic DPF in the plane maximum filter temperature, Tmax, versus In addition, under controlled regeneration conditions (i.e., constant oxygen concentration and temperature of the inlet gas), enhanced soot oxidation and higher regeneration efficiency were found for the catalytic DPF with hexagonal cells.…”

Performance of Diesel Soot Oxidation in the Presence of Ash Species

“…The difference may be caused by the mass of the carbon black particles. Compared with ash up and ash down stratification methods, the tight contact stratification method increases the contact surface of carbon black and ash particles, which is beneficial for the heat transferring and the diffusion of oxygen within the particles. , …”

Most Recent Advances in Diesel Engine Catalytic Soot Abatement: Structured Catalysts and Alternative Approaches

“…In this way, an optimal temperature is assured in the DPF, avoiding severely high temperatures during the regeneration, which can result in filter damages. Di Sarli et al have recently performed CFD-based simulations of the regeneration process of a single-channel catalytic DPF [93]. The authors developed the model assuming (i) the absence of the soot cake layer, and (ii) all the soot entrapped within the porous channel of the filter was in contact with the catalyst.…”