Axial Mounting for Converters and Filters - Acs Industries inc - #1

Sivanandi Rajadurai, Shiju Jacob, Chad Serrell , Rob Morin, Jeff Archembault, Zlatomir Kircanski, Scott Mackenzie ■ ACS Industries

Abstract

Introduction

Conventional converter mounting, using radial mounting mats and wiremesh supports, is very effective in three-way catalytic convert­ers and diesel oxidation converters used in light duty vehicles [1-7]. However, in some situations, the aspect ratio (diameter/length) of the diesel oxidation catalytic converter substrate is too high due to the large diameter and short length of the substrate. In such cases, the radial mounting is not sufficient to provide the required sup­port [8]. Also due to the large size, high bulk density and high ther­mal expansion coefficient of the diesel particulate filter substrate, the conventional mounting system cannot provide the necessary radial mounting pressure [9-11]. Axial support along with the con­ventional radial support is preferred in mounting diesel particu-late filters. This is possible due to the continued changes on the converter internals. Axial support flanges and metal retainer ring supports are extensively used in non-road emission control system designs. Knitted wiremesh support seals are used to protect sub­strate breakage due to hard surface contacts. These wiremesh seals provide axial and/or radial mounting supports also [12,13]. The shape and size of the wiremesh seals are designed to match the canning process and the converter/filter internal components.

Particulate Filter Elements

Different types of wall flow filter elements are used in diesel par-ticulate matter control systems. Physical attributes of silicon car­bide, cordierite and aluminum titanate filter elements are given in Table 1. The bulk density of the filter materials vary from 0.45 g/cc to 0.75 g/cc. The thermal properties also vary due to the

Wiremesh seals used in diesel particulate filter mounting provide cushion to accommodate the linear tolerances of the components and also give additional axial and/or radial mounting forces. Seals are suitably selected to match the canning process and the com­ponent's design. Different types of seals are engineered to provide axial mounting support for diesel particulate filter. The axial sup­port system is designed to give more mounting force as the a-axis crush strength of the filter element is higher (20-30 bars). The L-seal provides combination of axial and radial mounting forces for the DPF. The L-shaped radially held axial seal, with a tapered radial leg, is designed to provide the required axial force with a minimum radial force contribution. These tapered seals can be inserted on the substrate after stuffing the substrate into the shell. The Axial seal provides only axial mounting force for DPF assem­bly. Axial seals are engineered to fit the shell and the cone of the filter assembly. Axial support seals with different wire geometry, wire diameter and material densities are studied to optimize the compression characteristics of the seal. A cyclic compression test with in-situ heating is performed to study the effect of temperature on the mounting force of the seal. The compression characteristics are optimized to overcome the system expansion and contraction during thermal cycling due to regeneration of the diesel particu-late filter.

Figure 1: Force exerted on DPF

Table 1: Diesel niter physical properties