CFD simulation of the effect of upstream flow distribution on the light-off performance of a catalytic converter

Abstract

This paper describes the evolutions of the distributions of temperature and concentration in the monolith during the cold-start period and the effects of the flow distributions in the monolith on the performance of a catalytic converter using numerical simulation. The effects of the flow distributions on the light-off, warm-up performance and the temporal variation of the solid temperature were studied through numerical simulation. The following conclusions were obtained from the predicted light-off curves and the steady conversion efficiency: (1) The light-off time increases and the total outlet conversion efficiency reduces as the flow uniformity index decreases, which is in good agreement with experimental results. (2) The conversion efficiency decreases due to the reduction of residence time caused by the increase of the velocity as the radius is reduced. The analyses on the distribution of temperature in the monolith show that the temperatures of the solid in the area near the front face of the substrate rise as the radius increases, and the radial gradient of the temperature of the solid becomes greater as the flow uniformity index decreases. An experiment on the flow distribution in a catalytic converter with a honeycomb spherical arc was conducted. Experimental results show that the flow distribution in the monolith can be improved greatly by installing the honeycomb spherical arc in the tapered inlet header with a penalty of a relatively small increase of pressure drop.