Comparison of Chemical Kinetic Mechanisms in Simulating the Emission Characteristics of Catalytic Converters

Engine exhaust systems need to undergo continuous modifications to meet increasingly stricter regulations. In the past, much of the design and engineering process to optimize various components of engine and emission systems has involved prototype testing. The complexity of modern systems and the resulting flow dynamics, and thermal and chemical mechanisms have increased the difficulty in assessing and optimizing system operation. Due to overall complexity and increased costs associated with these factors, modeling continues to be pursued as a method of obtaining valuable information supporting the design and development process associated with the exhaust emission system optimization. Insufficient kinetic mechanisms and the lack of adequate kinetics data are major sources of inaccuracies in catalytic converters modeling. This paper presents a numerical study that investigates the performance of different chemical mechanisms in simulating the emission conversion characteristics of catalytic converters during both steady state and transient conditions. The model considers the coupling effect of heat and mass transfer with the catalyst reactions as exhaust gases flow through the catalyst. The heat transfer model includes the heat loss due to conduction and convection. The effect of radiation is assumed to be negligible and is not considered. The resulting governing equations based on the conservation of mass, momentum and energy are solved by a tridiagonal matrix algorithm (TDMA) with a successive line under relaxation method. The performance of different chemical kinetic schemes is reviewed by comparing the results of numerical model with the experimental measurements.