Systems Durability of a Ceramic Racetrack Converter

The long-term durability of a ceramic racetrack converter is examined using the systems approach. Each of the converter components is characterized with respect to its behavior under simulated mechanical and thermal loads. In particular, the impact of three different washcoats on key physical properties, and the load vs. deformation characteristics of three different insulation mats are examined from mechanical and thermal durability point of view. Similarly, the can deformation at elevated temperature is taken into account to ensure adequate mounting pressure on ceramic monolith under all operating conditions.

The temperature distribution at the midbed of the catalyst during engine dynamometer testing, together with the component properties data, are then used in a finite element model to compute thermal stresses in the monolith as function of engine load and speed. The combined stresses in the monolith (including the effect of radial pressure from the mat) are compared with its high temperature strength and the probability of stress corrosion over the lifetime of the converter is examined using thermal fatigue data for the monolith. In this manner, the engine conditions and converter designs which limit the operating stresses to less than 50% of monolith strength are identified to ensure failure-free operation of the racetrack converter system.