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The ultimate purpose of the Catalytic Preconverter Vibration Program is the development of a method for evaluating and improving in-service mechanical robustness of ceramic catalytic converters. The program focuses on preconditioned and thermally aged close-coupled preconverters which may be subject to severe in-service engine and exhaust system vibrations. From a mechanical durability point of view, characterization of the substrate vibration response in the preconverter can is necessary to predict the possibility of adverse in-service substrate resonances. The substrate dynamic response was determined for preconverters canned with an intumescent mat material. Room temperature vibration measurements of preconditioned and thermally aged preconverters are presented. These vibration resonances were favorably correlated with static hot push-test results verifying the ability of a static measurement technique to predict dynamic response.

Application of new ultra-thinwall ceramic substrate technology to many new vehicle exhaust emission applications has lead to an interest in better understanding the pressures to which substrates are exposed during packaging operations. A recently identified thin film load cell technology has permitted a more analytical evaluation of pressure distributions that develop during ceramic substrate packaging. The optimum configuration of this technique for studying canning operations will be investigated as part of the study. In addition to identifying the characteristic pressure distributions created during canning processes, the impact of various process parameters on this distribution was also investigated.

More stringent emissions regulations, space limitations for catalytic converters in modern automotive applications, and new engine technologies constitute design challenges for today's engineers. In that context high cell density thinwall and ultrathinwall ceramic substrates have been designed into advanced catalytic converters. Whereas the majority of these substrates have a square cell geometry, a potential for further emissions improvement has been predicted for hexagonal cell structures. In order to verify these predictions, a ceramic substrate has been developed combining the features of high cell density, ultrathin cell walls, and hexagonal cell structure. Based on modeling data, the actual cell density and wall thickness of the hexagonal cell substrate will be defined. The performance of that substrate will be assessed by comparing experimental emissions results using two modern Volkswagen engines.

A bench scale thermal cycling device was designed and constructed to expose large numbers of converters to simulated automobile cycling conditions. Ceramic catalytic converter systems exposed to this thermal cycling technique were observed to experience equivalent or more severe aging, depending on the aging temperature, than isothermal exposures. Cyclic thermal exposures were examined for two mat basis weights. Each mat was examined at two gap bulk densities. Change in converter residual shear strength, as a function of accumulated thermal cycles, was observed to follow a logarithmic relationship. Results of thermal cyclic engine exposures showed a strong correlation with laboratory bench studies.

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.

To aid in the catalytic converter design and development process, a test apparatus was designed and built which will allow comparative evaluation of the durability of candidate mat materials under highly controlled thermal and vibration environments. The apparatus directly controls relative shear deflection between the substrate and can to impose known levels of mat material strain while recording the transmitted shear force across the mat material. Substrate and can temperatures are controlled at constant levels using a resistive thermal exposure (RTE) technique. Mat material fatigue after several million cycles is evident by a substantial decrease in the transmitted force. A fragility test was found to be an excellent method to quickly compare candidate materials to be used for a specific application. Examples of test results from several materials are given to show the utility of the mat material evaluation technique.