Design of Durable Catalytic Converters from Mat Material Coupon Fragility Data, 18-9291

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Principal Investigator
James F. Unruh

Inclusive Dates: 01/01/2002 - Current

Background - 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 modern day catalytic converter consists of a coated converter substrate packaged in protective mat material and housed in a metallic can to contain the hot exhaust gases. The mat material plays a critical role in protecting the substrate from engine- and road-induced vibrations and exhaust-induced thermal and pressure stresses. However, little or no consideration is given to the mat material dynamic properties during the converter design effort. Nevertheless, converter design acceptance is based on accelerated hot vibration aging tests where the converter is subjected to engine-induced, high-temperature exhaust gases with a high level of shaker-induced can vibration, often at 75 g's or higher.

Approach - The objective of the investigation is to demonstrate that catalytic converter durability design can be accomplished in a cost-effective manner using a fundamental mechanical modeling approach employing coupon level mat material fragility data. Fragility data of a candidate mat material, in the form of mat material shear stiffness and material loss factor, will be generated and used in a design procedure to predict converter substrate resonance at selected elevated temperatures. Direct comparison of the predicted converter resonance to measured data from assembled converters will be used to demonstrate the usefulness of the coupon level mat material fragility data for converter preliminary design.

Accomplishments - A coupon level mat material fragility test apparatus was developed from an existing SwRI patented fragility test apparatus design. The test apparatus can provide mat durability data for a wide range of operational temperatures, up to 1,000 °C, with a controlled thermal gradient across the mat of 100 to 200°C, while controlling the mat material gap bulk density. A candidate mat material was chosen for the investigation, and a series of coupon tests were carried out to provide a mat material properties database ranging in temperatures from 280 °C to 800 °C and gap bulk densities from 0.8 to 1.0 g/cm3. Employed in a conventional converter configuration, the nonlinear mat material response with respect to shear deformation was modeled as an equivalent single degree of freedom oscillator, allowing frequency response prediction to imposed can base motion. A series of full-scale converters were assembled and tested for resonant frequency response at various substrate temperatures. Predictions of the assembled converters response were also made using the coupon level mat material database properties. Converter resonant frequency comparisons were very good with conservative amplification prediction.

SwRI-patented mat material fragility test apparatus uses water cooling to protect the shaker and instrumentation during high-temperature operation

Predicted versus measured converter frequency response functions employing SwRI design procedures and mat material database.

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