Thermal Shock Study of a Converter Package for a Drive Cycle

A drive cycle where the engine speed is a function of time is used to generate boundary conditions for a close-coupled converter since the engine out determines not only the emission control performance of a catalytic converter but also its durability. With the flow data a transient CFD simulation is run, and outputs such as brick temperature distribution, mat temperature distribution and shell temperature distribution are predicted. Orthotropic properties of the substrate, temperature dependent mat properties, natural convection and radiation are accounted for in the numerical model. A transient conjugate heat transfer model is implemented where the momentum and energy equations for both solids and fluids are coupled. From the transient temperature distribution of brick, shell and mat, a thermo-mechanical analysis was performed for the converter during the engine cycle, and the converter durability parameter thermal shock was studied. The results indicate that a full converter assembly approach is necessary since the type of insulation, exhaust-seals and shell material significantly affect this parameter. It is also observed from prediction that the thermal shock is not constant over the length of the catalyst but is seen to decrease along its length till the mid-bed and then predicted to rise proportionally to the exothermic catalytic reactions. To support this study correlations between experimental and computational data are presented and discussed.