Experimental and Computational Investigation of Particle Filtration Mechanisms in Partially Damaged DPFs

Abstract

<div class="section abstract"><div class="htmlview paragraph">Understanding the filtration mechanisms in partially damaged Diesel Particulate Filters is very important for the design of exhaust systems with efficient On-Board Diagnosis functionality, especially as new threshold limits have been recently applied for particulate mass leakage. Two common types of DPF failure are included in this study, namely rear plug removal and internal failure due to uncontrolled regeneration with excessive deposit loading. Initially, the two respective filters were loaded on the engine bench with particle measurement upstream and downstream, and then they were disassembled and sectioned to study the deposit distribution. The analysis of the second filter revealed several modes of failure that should be expected under real-life conditions such as material accumulation in the inlet channels, substrate melting, and crosswise and diagonal crack development. Moreover, a computational model with the necessary adjustments is used to simulate the loading experiments and interpret the underlying filtration mechanisms. The processed results reveal small effects of temperature and mass flow rate on the filtration efficiency and a comparatively stronger impact of the total deposit loading. The local deposit loading is uniform in the intact segments, while it is non-uniform with a minimum value at the failure location in the unplugged and internally damaged segments. This finding is consistent with the wall flow predicted by the model, whereas some discrepancies of the model can be attributed to a secondary collection mechanism.</div></div>

Numerical Study of Flow and Particle Deposition in Wall-Flow Filters with Intact or Damaged Exit

“…The size of the plugs and whether they are permeable or not can also affect the particle behavior in the entrance flow region of the filter. The present study provides for the first time numerical results of particle deposition at the frontal surface of the wall-flow filter, which are consistent with visual observations from experiments (see, for example, Reference [43]). The removal of the rear plugs leads to a considerable particle leakage that has to be determined and quantified.…”

“…However, the presence of recirculations has a pronounced effect on the distributions of velocity and pressure and, thus, they affect indirectly particle deposition. The numerical results on the particle deposition process in intact filters and damaged filters with missing plugs are consistent with recent experimental findings [43]. For instance, the experiments indicate clearly that the deposit soot accumulates almost uniformly in the central region of the intact filter, whereas the deposit loading is gradually reduced from the entrance of the defective filter obtaining a zero value at its exit.…”

“…The particulate traps under investigation are those studied experimentally in Haralampous et al [43]. The side of each square channel is h c = 1.2 mm, the thickness of the porous walls is h w = 0.3 mm, while their dimensionless values are H c = 1 and H w = 0.25, respectively.…”

“…The temperature is θ 0 = 540 K throughout the domain, the fluid density is ρ = 0.6509 kg m −3 , and its dynamic (kinematic) viscosity is µ = 2.54 The porosity of the walls and plugs is w = 0.52 and their permeability is k w = 6.18 × 10 −13 m 2 , while the average size of obstacles in the porous domain is d p,ob = 27.7 µm. These values correspond to the clean wall case examined experimentally in [43]. The results shown here were obtained based on Equations (5) to (7) in order to model F DR , while Equations (3) and (4) were used in the verification tests.…”

Filtration efficiency and pressure drop modelling of particulate filters with rear plug damage

“…Recently, Haralampous et al 24 presented experimental results of two damaged filters, the first with partial plug removal and the second compromised during uncontrolled regeneration with excessive deposit loading. The destructive analysis conducted after the loading tests showed non-uniform profiles of deposit loading, qualitatively similar to the numerically predicted.…”