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

Principal Investigator
James F. Unruh

Inclusive Dates: 01/01/02 - 12/31/02

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 gasses. 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. 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.

Approach - Fragility data of a candidate mat material, in the form of mat material shear stiffness and material loss factor, is to 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 is 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 provided mat durability data for a wide range of operational temperatures, up to 1,000°C, with a controlled thermal gradient across the mat while controlling the mat material gap bulk density. A candidate mat material was chosen for the investigation and a series of full-scale converters were assembled and tested for resonant frequency response at various substrate temperatures. A mat material fragility database was generated in the temperature range from 280°C up to 800°C for a range gap bulk densities to allow characterization of the mat material for a wide range of potential converter applications. A design procedure was developed that made use of the database to predict resonant frequency response characteristics of the previously tested assembled converters. The non-linear 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. Predictions of the assembled converter response were made using the coupon level mat material database properties. Converter resonant frequency comparisons were very good with conservative amplification prediction.

The 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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