Thermal design criteria for long-term durability of ceramic catalyst substrates

Abstract

The automotive industry has traditionally used ceramic honeycomb substrates as catalyst carriers. The long-term durability of a passenger car’s converter is assessed by examining the thermal stresses resulting from the temperature variations experienced under various driving conditions. These thermal stresses constitute the majority of the total stress that the ceramic catalyst substrate experiences while in service. The radial and axial temperature distributions were measured, and the thermal stress was calculated by using the thermal expansion coefficient according to the measured temperature. The threshold stress was determined from the fatigue constant, the required lifetime and the duration of the short term strength tests. The radial temperature variation was higher than the axial temperature variation, and the axial stress was higher than the radial stress because the thermal stress is dependent on the elastic modulus. The radial and axial stresses exist below the threshold thermal stress over the entire engine speed range.