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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.

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.

Preconverters and close-coupled main converters are viewed as key components in advanced emission systems to help the auto industry comply with tightened emission regulations in North America and Europe. Due to their close position to the exhaust manifold when compared to current main catalysts, the mechanical and thermal durability requirements on such close-coupled converters are significantly increased. A set of representative preconverter systems, with respect to back pressure and surface area, ceramic and metal substrate material was exposed to a 100 hour engine aging cycle, which is equivalent to approximately 80,000 kilometers under European driving conditions. This aging cycle is used by the German Autoconsortium (ZDAKW). In order to address the high thermal load in a close-coupled position, the preconverter inlet gas temperature has been elevated to a maximum of 950 °C at stoichiometry. Maximum preconverter midbed temperature has been found close to 1000 °C.

Characterization of diesel particulate filters requires test methods that permit rapid and accurate assessment of important performance requirements. The operation of the filter is comprised of two primary functions, particle filtering and filter soot regeneration. One challenge facing implementation of diesel filter technology lies with the difficult process of regenerating the filter after accumulating a full complement of soot. This paper will primarily focus on laboratory bench testing methods developed to study the regeneration characteristics of filters under a variety of test conditions. To rapidly assess the performance of many filters it was important to develop laboratory techniques that approximate engine exposure conditions. A simulated soot loading process and a well-controlled regeneration test method were developed.

Wall-flow filter technology has been used for many years to remove particulate emissions from a select number of diesel engine exhaust systems. Significant implementation of diesel particulate filters will require the definition of regeneration strategies that permit the filters to be regularly and durably purged of accumulated non-volatile particulates. This paper will examine the laboratory-bench characterization of filter responses to the wide variety of input conditions to which they may be exposed in practice. The lab-bench filter characterization will be done as a function of generic independent variables such as flow rate, inlet temperature, oxygen content and soot loading. The testing will be conducted on uncatalyzed filters for this preliminary study. The characterization approach will examine such dependent variables as completeness of regeneration and maximum exotherm temperatures.

The characterization of the thermal and vibration environment of the exhaust systems of three modern day diesel engines, with displacements ranging from 1.9 liter to 12.7 liter, was carried out to support the development of exhaust after treatment components. Tri-axial accelerometer and in pipe thermocouple measurements were recorded at several locations along the exhaust systems during vehicle acceleration and steady driving conditions up to 70 mph. The vehicles were loaded to various gross weight configurations to provide a wide range of engine load conditions. Narrow band and octave band vibration power spectral densities are presented and conclusions are drawn as to the spectral content of the exhaust vibration environment and its distribution along the exhaust system. Temperature time histories during vehicle acceleration runs are likewise presented to indicate expected peak exhaust temperatures.

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.

Automotive catalytic converters must provide a very high level of mechanical and thermal durability to maintain performance during their 100,000 to 150,000 mile life expectancy. The work reported herein characterizes the converter as a base (can) excited spring (mat material) supported mass (substrate). A mat material coupon test apparatus was developed for the purpose of providing parameter data for the converter model in the form of stiffness and material loss factor data as a function of shear deflection across the mat. An intumescent mat material was chosen and its dynamic properties evaluated for a range of converter operating parameters. The mat material response properties were placed into a mat material database as a function of gap bulk density, substrate temperature, and temperature gradient across the mat.