A three-dimensional numerical study of the effect of pulsating flow on conversion efficiency inside a catalytic converter

A study is made of the flow and conversion characteristics of the pulsating flow of an automotive catalytic converter. To investigate the unsteady flow effects of a dual monolithic catalytic converter of double-flow type, a numerical methodology coupled with wave action simulation based on gas dynamic theory is developed. The flow inside the converter is treated as three dimensional, unsteady compressible and isothermal. Conversion rates through the monolithic channels are calculated under the assumption of being diffusion controlled. The present study indicates that this integrated numerical model successfully represents the conditions of severe interaction among the exhaust flows, the extreme filling and the empty processes that affect the flow distribution and conversion efficiency. The simulation results also show that the level of flow maldistribution in the monolith heavily depends on the curvature and angles of separation streamline of the mixing pipe that homogenizes the exhaust gas from the individual cylinders. It is also found that, on a double-flow converter system, there are severe interactions of each pulsating exhaust gas flow at the junctions, and consequently junction geometry greatly influences the degree of flow distribution.