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The development of a stronger cordierite material with much less porosity than the current material allows the manufacture of substrates with the same strength as the current part but with proportionately thinner walls. In the process of analyzing the properties of this new substrate it was discovered that optimum performance can be realized by using specially chosen combinations of cell density and wall thickness. Using the properties of this new material and the equations which relate material and structural features to substrate performance, substrate designs have been identified which in one case minimize the back pressure while maintaining the catalyst performance at the present level, and in another case maximize the catalyst performance while maintaining the back pressure at the present level. Other optimum design points are also indicated.

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.

A rotary ceramic regenerator is the most efficient high temperature heat exchanger being considered for the automotive gas turbine application. Under the HVTE-TS program sponsored by the U.S. Department of Energy, our activities have focused on the identification and development of materials and on the development of hardware required for the extrusion of this product. Initially, five ceramic materials were identified which showed promise for meeting the performance criteria of the product. Of these five, lithium-aluminosilicate (LAS) glass and magnesium-aluminosilicate (MAS) ceramic batches were chosen. MAS materials had been developed for use in automotive catalyst supports and so have cost and processing advantages for automotive applications. Cellular MAS parts have been extruded, fired, finished, and supplied to Allison Engine Company for testing. LAS products have been in use for many years in gas turbine regenerators throughout the world.

In the preceding paper the specific heat capacity, substrate heat capacity, and energy requirements of two types of substrates were discussed in detail both from the standpoint of predictions from measured material property values as well as actual energy measurements on ceramic and metal products. This information is valuable for the catalyst designer because of the light-off impact of this energy requirement. Some material was also presented regarding the change in this energy requirement with washcoat loading. Other aspects of the substrate which could reasonably come into play to enhance the light-off characteristics of a catalyst are the rates of heat and mass transfer. The latter of these could reasonably be expected to drive the catalyst activity. In addition, the pressure drop which results from the substrate structure could influence and limit the choice of cell configurations and product shapes and sizes, thereby constraining the list of possible options.