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Technical Paper

Systems Design for Ceramic LFA Substrates for Diesel/Natural Gas Flow- Through Catalysts

1995-02-01
950150
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.
Technical Paper

Advances in Durability and Performance of Ceramic Preconverter Systems

1995-02-01
950407
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.
Technical Paper

High Temperature Compressive Strength of Extruded Cordierite Ceramic Substrates

1995-02-01
950787
High temperature modulus of rupture (MOR) data, published previously, show that the ceramic catalyst supports get stronger with temperature due to the absence of water vapor and closure of microcracks which would otherwise act as stress concentrators [1, 2 and 3]*. The increased MOR value is partially responsible for the excellent durability of ceramic catalyst supports at high temperature. In this paper, we will present the compressive strength data of ceramic substrates at high temperature, namely the crush strength along B-axis and biaxial compressive strength of the whole substrate. Since the honeycomb strength is directly related to that of the individual cell wall, the compressive strength should also increase with temperature similar to the modulus of rupture. Accordingly, the ceramic substrates are capable of supporting higher mounting pressures exerted by the intumescent mat at high temperature [4].
Technical Paper

Strength and Thermal Shock Resistance of Segmented Wall-Flow Diesel Filters

1986-03-01
860008
The physical properties, including modulus of rupture, structural modulus and thermal expansion coefficient of segmented, large frontal area, ceramic wall-flow diesel filters are presented. The effect of cement composition, its coverage and segmentation pattern on these properties and on the failure modes during strength testing is discussed. Using these properties the mechanical and thermal integrities of LFA filter are computed and compared with those of monolithic filter,. The paper discusses both the high efficiency (EX-47, 100/17) and low efficiency (EX-66, 100/25) filter compositions.
Technical Paper

Long-Term Durability of Ceramic Honeycombs for Automotive Emissions Control

1985-02-01
850130
Ceramic honeycomb structures have been used successfully as catalyst supports in gasoline-powered vehicles for the past ten years. They are currently the leading candidate for trapping and oxidizing the carbonaceous particulate emissions in diesel-powered vehicles. In both of these applications the long term durability of the ceramic substrate is of prime importance. This, in turn, depends on the physical properties of cellular structure, cyclic nature of service loads and design of the mounting assembly. This paper examines the nature and dependence of both the mechanical and thermal stresses in the substrate on its geometry, properties, mounting parameters, and the operating conditions. It also compares the observed failure modes with those predicted by the theory. The paper concludes with a set of recommendations for optimal systems design and acceptable operating conditions which will promote the long term durability of the ceramic substrate.
Technical Paper

Failure Modes During Static and Impact Loading of Light-Weight Rectangular Glass Headlamps

1984-04-01
840745
An approximate analytical solution for stress distribution in the rectangular lens of a glass headlamp due to static and impact loading is presented. Both low mass/high velocity and high mass/low velocity impact data and the resulting failure modes are discussed. Generally, glass headlamp lenses break either due to Hertz stress (front surface under high localized tension), or due to flexural stress (back surface under tension due to bending), or the combination of two. Failure due to flexural stress is illustrated by a star-crack, while that due to Hertz stress is illustrated by a Hertzian cone or “bullet hole” in the lens. The failure mode during low mass/high velocity impact is predominantly Hertzian while that during high mass/low velocity impact is flexural for lenses 0.120″ to 0.150′ thick. No significant differences are observed in the impact resistance of standard and light-weight lenses in this thickness range.
Technical Paper

Dynamic Fatigue Data for Cordierite Ceramic Wall-Flow Diesel Filters

1991-02-01
910135
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.
Technical Paper

High Temperature Creep Behavior of Ceramic and Metal Substrates

1991-02-01
910374
The high temperature creep data for radial specimens, cut from metal and ceramic substrates and subjected to compressive loads representative of mounting and thermal pressure are presented as function of load and temperature. These data show that the creep resistance of metallic specimens under sustained loading varies with temperature and is orders of magnitude lower than that of ceramic specimens. The observed creep deformation in metallic specimens reduces their open frontal area and hydraulic diameter with potentially adverse impact on pressure drop across the metallic substrate.
Technical Paper

Optimization of Substrate/Washcoat Interaction for Improved Catalyst Durability

1991-02-01
910372
The substrate/washcoat systems which preserve both the mechanical and thermal attributes of cordierite substrates are most desirable for prolonged durability of automotive catalysts. This paper provides a micromechanics viewpoint of substrate/washcoat composite whose properties are predictable, measurable and relevant to catalyst durability. The micromechanics model helps quantify substrate/washcoat interaction which controls the long-term catalyst performance. Three different examples of substrate/washcoat systems are used here to illustrate the optimization process during the development of new substrates or washcoat technologies to meet the more stringent emission and durability requirements of advanced catalysts for the 1990s.
Technical Paper

Design Considerations for Diesel Flow-Through Converters

1992-02-01
920145
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.
Technical Paper

Size Effect on the Strength of Ceramic Catalyst Supports

1992-10-01
922333
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.
Technical Paper

New Developments in Packaging of Ceramic Honeycomb Catalysts

1992-10-01
922252
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.
Technical Paper

Cell Design for Ceramic Monoliths for Catalytic Converter Application

1988-10-01
881685
The shape and size of the unit cell of a ceramic monolith have a profound influence on its geometric and mechanical properties. These, in turn, affect the catalytic performance, converter durability and vehicle drive-ability. This paper presents the important relationships between cell geometry and monolith's open frontal area, geometric surface area, hydraulic diameter, bulk density, structural rigidity, strength and heat transfer characteristics of the monolith; both the square and triangular cells are considered. These relationships provide a rational basis for selecting the cell shape and size which will yield the best balance between the various performance requirements, i.e. light-off characteristics, conversion efficiency, back pressure and long-term dutability. It is shown that certain tradeoffs are necessary in selecting the final cell geometry which is best accomplished by prioritizing the various performance requirements.
Technical Paper

Systems Approach to Packaging Design for Automotive Catalytic Converters

1990-02-01
900500
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.
Technical Paper

Experimental Verification of Residual Compression in Tempered Automotive Glass with Holes

2003-01-18
2003-26-0012
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.
Technical Paper

Performance and Durability of Advanced Ceramic Catalyst Supports

2003-01-18
2003-26-0015
As emissions regulations become more stringent, catalyst supports with higher cell density, smaller wall thickness, higher surface area and lower thermal mass become more desirable for faster light off and higher conversion efficiency. Simultaneously, however, washcoat formulation and loadings have to be adjusted to yield higher and more stable B.E.T. area at operating temperatures representative of close-coupled application. The thermal mass contribution of advanced washcoat system to catalyst supports with 600/4 and 900/2 cell structures may approach or even exceed that of uncoated substrates. Under such high washcoat loadings, the composite properties of advanced catalysts may be affected adversely in terms of their physical durability, notably in close-coupled application. This paper focuses on potential solutions to light-off performance and FTP efficiency, via optimization of substrate/washcoat interaction, geometric design and the mounting system.
Technical Paper

Thin Wall Ceramic Catalyst Supports

1999-03-01
1999-01-0269
The stringent emissions regulations, notably for cold start, have led to design modifications in each of the converter components, notably the catalyst support. With the faster light–off requirement, the catalyst support must have a lower thermal mass so as to reach the 50% conversion temperature as quickly as possible. Simultaneously, for higher warmed–up efficiency, the catalyst support must offer higher geometric surface area. Similarly, for improved fuel economy and for preserving engine power, the catalyst support must exert lower back pressure. Indeed, these three performance requirements might be met by certain thin wall ceramic substrates, including 400/4.5 and 600/4.3, which have 22% lower thermal mass, 25% higher geometric surface area and 8% larger open frontal area than the standard 400/6.5 substrate. Testing by automakers and international laboratories on engine dynamometers has verified the above advantages of thin wall substrates.
Technical Paper

High Temperature Strength Behavior of Ceramic Versus Metal Substrates

1990-10-01
902170
The high temperature strength and deformation behavior of ceramic and two different metal substrates were measured in the 25°-1200°C temperature range in uniaxial and biaxial bending using rectangular bars and circular discs, respectively, prepared from the substrates. The data show that both of the metal substrates exhibit permanent deformation and lose their load carrying capability by an order of magnitude above 800°C. The ceramic substrate, on the other hand, preserves its strength and behaves elastically over the entire temperature range exhibiting neither permanent deformation nor cell distortion. These data suggest that the upper use temperature for metal substrates could be significantly lower than that for ceramic substrates to meet 50-100K vehicle mile durability
Technical Paper

Ceramic Converter Technology for Automotive Emissions Control

1991-09-01
911736
This paper reviews the development and successful application of ceramic catalytic converters for controlling automotive exhaust emissions. It presents the scientific rationale for designing the high surface area substrate to meet both performance and durability requirements. This is followed by a step-by-step design process for each of the converter components. The initial design stage focuses on understanding automaker's requirements and optimizing component design commensurate with them. The intermediate stage involves laboratory testing of converter components in simulated environment and ensuring component compatibility from durability point of view. The final design stage addresses the critical tests on converter assembly to ensure performance and field durability. In addition, it examines the necessary trade-offs and associated design modifications and evaluates their impact on warranty cost for system failure.
Technical Paper

Advanced Three-Way Converter System for High Temperature Exhaust Aftertreatment

1997-02-24
970265
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.
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