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This paper employs a systematic approach to packaging design and testing of a system and its components in order to determine the long term durability of light duty diesel filters. This effort has utilized a relatively new aluminum titanate filter technology as well as an advanced support mat technology engineered to provide superior holding force at lower temperatures while maintaining its high temperature performance. Together, these two new technologies form a system that addresses the unique operating conditions of diesel engines. Key physical properties of both the filter and the mat are demonstrated through laboratory testing. The system behavior is characterized by various laboratory techniques and validation procedures.

This paper provides elastic analysis of compressive stresses in the matrix and skin regions of automotive substrates during 3D- and 2D-isostatic strength testing. The matrix region is treated as transversely isotropic material and the skin region as isotropic material, each with their independent elastic properties. Such a solution helps quantify load sharing by the matrix and skin regions which, in turn, affect compressive stresses in each region. The analysis shows that the tangential compressive stresses in the skin and matrix differ significantly at the interface due to high stiffness ratio of skin versus matrix. The resulting strain in the skin is more severe for thin and ultrathin wall substrates and may lead to localized bending of interfacial cells thereby inducing premature failure. Methods to reduce compressive strain in both the matrix and skin without affecting performance-related advantages are discussed.

A concern has been expressed regarding the durability of the ceramic thin wall and ultra-thin wall substrates under severe thermal and mechanical conditions. Damage that might result from these conditions would most likely lead to a reduction in catalyst performance. One of the potential damage mechanisms for automotive catalysts is erosion resulting from the impingement of particles onto the front face of the catalyst system. A basic study of the particulate erosion phenomenon of cellular ceramic substrates was undertaken in order to determine, in a controlled setting, the substrate, particulate, and flow conditions that might bring this damage about. This report will discuss a room temperature study of the effects of particle size, particle density, gas flow rate, cellular part orientation, and cellular design parameters on the erosion of ceramic substrates.

The design of a canned ceramic oval converter, 77mm by 146.8mm, is described along with subsequent demonstration of its high temperature (1050°C) durability. A new mat deterioration phenomenon was recognized, and will be described. The mat deterioration results from sintering of the vermiculite and glass fiber structure when exposed to temperatures greater than approximately 1000°C. Due to the extremely high temperature experienced in the supporting mat of an oval converter exposed to 1050°C, an alternative mat configuration was utilized to eliminate potential mat sintering. An inner layer of non-intumescent mat (1500g/m2) was used in conjunction with an outer layer of intumescent mat (3100g/m2). The inner mat provided sufficient thermal protection to the outer intumescent mat, maintaining considerable holding pressure on the ceramic substrate. A tourniquet closure technique was developed to uniformly compress a hybrid mat system around the entire perimeter of the oval converter.

Significant particulate emission reductions of diesel engines can be achieved using diesel particulate filters (DPFs). Ceramic wall flow filters with a PM efficiency of >90% have proven to be effective components in emission control. The challenge for the application lies with the development and adaptation of a reliable regeneration strategy. The main focus is emission efficiency over the legally required durability periods, as well as over the useful vehicle life. It will be shown, that new DPF systems are characterized by a high degree of integration with the engine management system, to allow for initiation of the regeneration and its control for optimum DPF protection. Using selected cases, the optimum combination and tuning will be demonstrated for successful regenerations, taking into account DPF properties.

In this study quantitative techniques were established to assess the low temperature durability of commercially available mat systems. A new low temperature dynamic resistive thermal exposure (LT-RTE) test method was developed. The mats were evaluated in thermal cycling with maximum substrate skin temperatures from 280°C to 450°C. Results indicate that at low use temperatures the residual shear strength of the mat fell to ∼5-15KPa following 280°C cycling. Under the same LT-RTE exposure conditions an equivalent mat system, following thermal preconditioning to 500°C for 3 hours, possessed a residual shear strength of ∼30KPa. An alternative mat system with a lower shot content fiber was also evaluated, following the same thermal preconditioning previously described. This alternative mat was found to exhibit substantially higher residual shear strengths following LT-RTE aging. A residual shear strength of ∼95KPa was observed for this alternative mat following 280°C LT-RTE aging.

Stringent emissions standards with 95+% conversion efficiency requirements call for advanced ceramic catalyst supports with thinner walls, higher cell density and optimum cell shape. The extrusion technology for cellular ceramics has also made significant progress which permits the manufacture of advanced catalyst supports. Similarly, modifications in cordierite chemistry and the manufacturing process have led to improved microstructure from coatability and thermal shock points of view. The design of these supports, however, requires a systems approach to balance both the performance and durability requirements. Indeed as the wall gets thinner, the contribution of washcoat becomes more significant in terms of thermal mass, heat transfer, thermal expansion, hydraulic diameter and structural stiffness - all of which have an impact on performance and durability. For example, the thinner the wall is, the better the light-off performance will be.

The oven shock test is an accelerated test which is often used to quantify the thermal durability of both coated and uncoated ceramic substrates. The test calls for heating the substrate for 30 minutes in an oven, which is preheated to specified temperature, and then cooling it in ambient environment for 30 minutes. Such a cycle induces axial and tangential stresses, during cooling, in the skin region whose magnitude depends on physical properties, oven temperature, radial temperature gradient and the aspect ratio of substrate. In addition, these stresses vary with time; their maximum values occur as soon as the substrate is taken out of the oven. This paper evaluates the severity of thermal stresses as function of above factors and estimates the probability and mode of failure during cooling using thermocouple data. Methods to reduce these stresses are discussed.