Analysis of Transient Thermal and Conversion Characteristics of Dual-Monolith Catalytic Converter with Palladium and Palladium/Rhodium Catalysts

Abstract

We used a one-dimensional monolithic catalyst model to predict the transient thermal and conversion characteristics of a dual monolithic catalytic converter with a Palladium only (Pd-only) catalyst and a Palladium/Rhodium (Pd/Rh) catalyst. Prior to the numerical investigation of the dual-catalyst converter, we modified the pre-exponential factor and activation energy of each reaction for both catalysts to achieve acceptable agreement with experimental data under typical operating conditions of automobile applications. We validated the conversion behavior of the lumped parameter model for each catalyst against different engine operating conditions.

Two higher cell density substrates, Pd-only catalyst (600cpsi/3.9mil) and Pd/Rh catalyst (600cpsi/4mil), for faster light-off and improved warm-up performance are used in this study and the two monoliths has been connected without the space between monoliths. As a result of the constriction of the monoliths, a slight temperature drop through the interface between two substrates occurred due to thermal contact resistance. Therefore, to examine the heat transfer mechanism through the conforming rough surfaces, we theoretically determined the thermal joint conductance between monoliths in contact by using existing theory and correlation. The adequacy of the considered theory and correlation for thermal joint conductance was elucidated by the relevance of heat transfer phenomena across the joint. Also, we performed parametric investigations to examine how the overall temperature drop across the joint and exhaust gas emissions were affected by the apparent contact pressure and mass flow rate of the exhaust gas.