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Stringent emissions legislation for diesel-powered vehicles, soon to go into effect, has led to new advances in both Diesel Oxidation Catalysts (DOC) and Diesel Particulate Filters (DPF). This paper reviews some of the new developments in DOC support design which lead to improved light-off behavior and higher overall emissions performance through lower thermal mass, higher Geometric Surface Area (GSA) and larger Open Frontal Area (OFA) than those afforded by the standard cordierite 400/6.5 cell configuration. The four different DOC supports examined in this paper include 400/4, 200/8, 300/8 and 400/6.5 - the last one serving as baseline.

Tempered float glass is commonly used for both side windows and backlites in the automotive industry. The success of such products is primarily attributed to high level of residual compression, following tempering, which provides abrasion resistance as well as 3X higher functional strength to sustain mechanical, vibrational and thermal stresses during the vehicle's lifetime. Certain applications of tempered glass, however, require mounting holes whose surface-finish must be controlled carefully to withstand transient tensile stresses during tempering. Simultaneously, the nature and magnitude of residual compression at the hole must provide sufficient robustness to bear mounting, vibrational and thermal stresses throughout the life of the vehicle. This paper presents (i) analysis of residual compression at the hole, (ii) measurement of biaxial strength of annealed glass with hole at center, and (iii) measurement of biaxial strength of tempered glass with hole at center.

The stringent emissions legislation has necessitated advances in the catalytic converter system comprising the substrate, washcoat technology, catalyst formulation and packaging design. These advances are focused on reducing light-off emissions at lower temperature or shorter time, increasing FTP efficiency, reducing back pressure and meeting the mechanical and thermal durability requirements over 100,000 vehicle miles. This paper reviews the role of cordierite ceramic substrate and how its design can help meet the stringent emissions legislation. In particular, it compares the effect of cell geometry and size on performance parameters like geometric surface area, open frontal area, hydraulic diameter, thermal mass, heat transfer factor, mechanical integrity factor and thermal integrity factor - all of which have a bearing on emissions, back pressure and durability. The properties of advanced cell configurations like hexagon are compared with those of standard square cell.

Significant advances in composition and the manufacturing process have led to thin wall cordierite ceramic substrates with low thermal mass, high surface area, and large open frontal area-properties that are critical for fast light-off, high conversion efficiency and low back pressure. Indeed, such substrates are ideal catalyst supports for meeting the ever-stringent emissions regulations, ala SULEV and ULEV, as demonstrated by recent performance data1. This paper focuses on the physical durability of 400/4 and 600/4 cordierite ceramic substrates. In particular, it presents strength, fatigue, and modulus data which influence the mechanical durability. In addition, it presents thermal expansion data which impact the thermal durability. Both of these durabilities are examined as a function of operating temperature.

An advanced three-way converter system with significant improvements in light-off performance, conversion efficiency, thermal stability and physical durability at high operating temperature is described. The converter system is comprised of a light-weight ceramic substrate with high surface area triangular cell structure, a new catalyst formulation with enhanced thermal stability and good substrate compatibility, and a durable packaging design which together lead to consistent improvements in high temperature performance and durability. Experimental data including FTP performance, canning trials, and high temperature vibration and thermal shock tests for both the advanced and standard three-way converter systems are presented.

The 290,000 vehicle-mile durability requirement for diesel/natural gas oxidation catalysts calls for robust packaging systems which ensure a positive mounting pressure on the ceramic flow-through converter under all operating conditions. New data for substrate/washcoat interaction, intumescent mat performance in dry and wet states, and high temperature strength and oxidation resistance of stainless steels, and canning techniques insensitive to tolerance stack-up are reviewed which help optimize packaging durability. Factors contributing to robustness of converter components are identified and methods to quantify their impact on design optimization are described. CERAMIC FLOW-THROUGH catalysts for diesel exhaust aftertreatment have met with much success since their introduction in 1993.

The monolithic, large frontal area (LFA), extruded ceramic substrates for diesel flow-through catalysts offer unique advantages of design versatility, longterm durability, ease of packaging and low Cost [1, 2]*. This paper examines the effect of cell density and cell size on catalyst light-off performance, back pressure, mechanical and thermal durability, and the steady-state catalytic activity. The factors which affect these performance characteristics are discussed. Certain trade-offs in performance parameters, which are necessary for optimum systems design, are also discussed. Following a brief discussion of design methodology, substrate selection, substrate/washcoat interaction and packaging specifications, the durability data for ceramic flow-through catalysts are summarized. A total of over 18 million vehicle miles have been successfully demonstrated by ceramic LFA catalysts using the systems design approach.

Ceramic preconverters have become a viable strategy to meet the California LEV and ULEV standards. To minimize cold start emissions the preconverter must light-off quickly and be catalytically efficient. In addition, it must also survive the more severe thermomechanical requirements posed by its close proximity to the engine. The viability of the ceramic preconverter system to meet both emissions and durability requirements has also been reported recently(1,2). This paper further investigates the impact preconverter design parameters such as cell density, composition, volume, and catalyst technology have on emissions and pressure drop. In addition, different preconverter/main converter configurations in conjunction with electrically heated catalyst systems are evaluated. The results demonstrate that ceramic preconverters substantially reduce cold start emissions. Their effectiveness depends on preconverter design and volume, catalyst technology, and the system configuration.

The motorcycle emissions regulations for both two-stroke and four-stroke engines, which are receiving worldwide attention, will go into effect in the very near future. To meet these regulations, the motorcycles will require a catalyst in conjunction with the muffler due to space limitations. The combination of high engine speeds, high vibrational acceleration, high HC and CO emissions, high oxidation exotherms, and stringent durability requirements, points to cordierite ceramic substrate as an ideal catalyst support. However, as an integral unit within the muffler, its packaging design must be capable of withstanding isothermal operating conditions which may exceed the upper intumescent temperature limit of the ceramic mat. This paper describes a durable packaging design for the ceramic catalyst which employs a hybrid ceramic mat, special end rings and gaskets, and high strength stainless steel can.

The stringent durability requirements approaching 100,000 vehicle miles for automotive substrates and 290,000 vehicle miles for large frontal area diesel substrates for 1994+ model year vehicles call for advanced packaging designs with thick ceramic mats and high mount densities. The latter result in high mounting pressure on the substrate and enhance its mechanical integrity against engine vibrations, road shocks and back pressure forces. A novel measurement technique which applies a uniform biaxial compressive load on the lateral surface of ceramic substrates, thereby simulating canning loads, is described. The biaxial compressive strength data obtained in this manner help determine the maximum mounting pressure and mat density for a durable packaging design. The biaxial compressive strength data for both round and non round substrates with small and large frontal area are presented.

The emissions regulations for the decade of 1990s are not only more stringent but are also required of vehicles other than passenger cars, for example both diesel and gasoline trucks as well as motorcycles. These latter applications involve different operating conditions in terms of space velocities, temperature profiles, and vibrational loads than those typical of passenger cars [1]*. In addition, the performance and durability requirements for these applications call for lower back pressure and longer service life. Furthermore, the space availability and the operating temperature range differ vastly so as to require special packaging designs to meet the durability requirements. This paper provides new data for ceramic insulating mats, both intumescent and non-intumescent [2,3], and ceramic substrates with thin and thick walls and square and triangular cell geometries [4], which are under development for non-passenger car applications indicated above.

The typical ceramic catalyst support for automotive application has a total volume of 1640 cm3. Approximately 10% of this volume is subjected to tensile thermal stresses due to a radial temperature gradient in service [1]*. These stresses are kept below 50% of the substrate strength to minimize fatigue degradation and to ensure long-term durability [2]. However, the tensile strength measurements are carried out in 4-point bending using 2.5 cm wide x 1.2 cm thick x 10 cm long modulus of rupture bars in which the specimen volume subjected to tensile stress is merely 3.2 cm3 or 0.2% of the total substrate volume [3]. Thus, a large specimen population is often necessary (50 specimens or more) to obtain the strength distribution representative of full substrate. This is particularly true for large frontal area substrates for diesel catalyst supports with an order of magnitude larger stressed volume. In this paper, the modulus of rupture data are obtained as function of specimen size.

The large frontal area cordierite ceramic flow-through converter for diesel emissions must meet the 290K vehicle mile durability requirement, almost a six fold increase over that of automotive converters. This paper compares the size, the geometry and the operating conditions of automotive vs. diesel converters and suggests ways to design the converter system to meet the challenging durability requirements without compromising its performance with respect to back pressure and conversion efficiency. It is shown that the mechanical durability of the system, which is critical for meeting the 290K vehicle mile durability, can best be met by ensuring good compatibility between the substrate and washcoat and by designing a rugged packaging system with positive mounting pressure under all driving conditions.

The dynamic fatigue data for two different cordierite ceramic wall-flow diesel filter compositions, EX-54 and EX-66, are obtained at 200° and 400°C using the 4-point bend test. These compositions offer larger mean pore size and experience lower pressure drop than the EX-47 composition, and hence are more desirable for certain applications. Their fatigue behavior in the operating temperature range is found to be equivalent or superior to that of EX-47 composition which helps promote filter durability. The fatigue data are used to arrive at a safe allowable stress, which would ensure the required 290K vehicle mile durability. The paper also discusses the impact of mean pore size on high temperature strength and fatigue properties and their effect on filter durability.

This paper addresses the packaging design for monolithic cordierite ceramic converters to meet the new, stringent durability requirements of the 1990's, while minimizing warranty cost for the automaker. These objectives are best met by using a systems approach during the early phases of packaging design, i.e. by examining design interactions between the ceramic monolith, alumina coating, ceramic mat or wiremesh mounting material with seals, stainless steel can, heatshields, and associated peripheral components. Failure of any one of these components can prove detrimental to converter durability. In this paper we take advantage of overall understanding of the observed failure modes and individual component behavior, and present new data for optimizing the total converter durability through initial design. In particular, the impact of symmetric gas entry, monolith contour, clamshell anisotropy, mount density, stiffener ribs, and heatshield insulation on total durability is highlighted.

The high temperature dynamic fatigue data for the catalyst support composition, EX-20, 400/6.8, are presented. These data indicate that the fatigue effects are more severe when the substrate temperature in the peripheral region is near 200°C. The major impact of high temperature fatigue is the slow degradation of substrate’s initial strength while in service. Such a degradation must be taken into account in designing the total converter package to meet life requirements. For the EX-20, 400/6.8 substrate, approximately 50% of its initial strength is available to withstand the combined stresses from mechanical, thermal, and vibrational loads in service. At temperatures well above 200°C, the available design strength can be as high as 65% of substrate’s initial strength. The fatigue theory, the measurement technique, and the application of fatigue data to long term durability of cordierite substrates are discussed.

Under certain operating conditions when the combined stresses in a ceramic wall-flow diesel filter from mechanical, thermal, and vibrational loads exceed its threshold strength, the fatigue effects become important. This paper reviews the theory of static and dynamic fatigue, and presents fatigue data for Coming's high efficiency filter composition (EX-47, 100/17) in the temperature range 25° - 400°C which is representative of the stressed peripheral region during regeneration. The measurement and analysis of fatigue data, together with the implication on long-term durability of cordierite ceramic filters, is discussed.

Thermal stresses constitute a major portion of the total stress which the ceramic wall flow filter experiences in service. The primary source of these stresses is the temperature gradients, both in radial and axial directions, which attain their maximum values during regeneration. The level of particulate loading, the flow rate, the filter size and the mounting design govern the severity of temperature gradients which, together with physical properties and aspect ratio of the filter, dictate the magnitude and distribution of thermal stresses. The filter, the mounting, and the regeneration conditions should be so designed as to minimize these stresses to insure reliable and fracture free performance of the filter throughout the lifetime of the vehicle. In this paper we present a thermal stress model, based on finite element method, which computes stresses in the axisymmetric filter subjected to linear or step temperature gradients in radial and axial directions.