Filtration modelling in wall-flow particulate filters of low soot penetration thickness

Abstract

Wall-flow particulate filters are the basis to meet particulate emission standards concerning number and mass limits. The required balance between filtration efficiency and pressure drop demands the availability of computational tools able to predict and diagnose their combined response. In this paper a filtration model coupled with a gas dynamic particulate filter (PF) model based on the theory of packed beds of spherical particles is presented. The model takes as main assumption the experimentally well-known low soot penetration inside the porous wall. From this basis the description of the changes in filtration efficiency, pressure drop and deposits distribution are approached as a function of the soot loading level. The soot penetration inside the porous wall is shown to be a critical parameter dependent on the Peclet number. The transition from deep bed to cake filtration regime is also analysed accounting for macro-and micro-scale transition. Finally, the model is validated against experimental data obtained from several PFs. Flow properties advection along channels and the appropriate definition of the soot penetration and deposition dynamics lead to great accuracy in the modelling of the filtration efficiency, both overall and as a function of the particle size, as well as pressure drop.

On the Impact of Particulate Matter Distribution on Pressure Drop of Wall-Flow Particulate Filters

“…The maximum pressure drop is always found when the onset of the particulate layer is placed close to the monolith inlet. This means that the worst loading conditions of the DPF are determined by an homogeneous particulate layer along the whole channel, which is the natural profile towards soot loading processes' convergence [28]. These results evidence the interest for soot and ash accumulation in the rear end of the inlet channels.…”

“…According to the results presented in [28] and as the boundary condition for the modeling work, the particulate layer porosity before the first water injection event is known to be 0.65. This data were obtained assuming that the representative collector unit diameter in the particulate layer is that of the mode of the particle size distribution (69 nm).…”

“…The porous wall has been kept saturated with a soot penetration thickness of 2%. These characteristics are based on the results obtained from the modeling of the soot loading process up to the first water injection event, which are described in [28]. Therefore, the objective has been to identify the main trends in particulate layer properties' variation that provide the pressure drop after a pre-DPF injection event.…”

“…Besides permeability, the change in porous wall properties also determines the fluid-dynamic field in the inlet channels as the soot loading takes places and governs the variation in filtration efficiency [28]. Brownian diffusion, interception and inertial deposition mechanisms are considered to compute the filtration efficiency of an isolated collector unit.…”

Late Fuel Post-Injection Influence on the Dynamics and Efficiency of Wall-Flow Particulate Filters Regeneration

“…The amount of soot cumulated in the DPF determines the dynamics of the filtration [40] and regeneration [38], as well as the pressure drop [41]. The variation in the soot mass inside the DPF is modelled as a function of the filtrated and oxidised soot amounts per unit of time according to Equation 14,…”