Influence of the three way catalytic converter substrate cell density on the mass transfer and reaction resistances

Abstract The conversion of pollutants in automotive three way catalytic converter (TWC) channels is influenced by fluid mechanics, heat and mass transfer and catalytic reactions. The quantification of the total and relative importance of the physical and chemical phenomena involved is of major importance for the TWC performance optimization. In this paper, we present and implement a method to quantify the magnitudes of the external and internal mass transfer resistances as well as the chemical reaction resistance. The resistance quantification method was applied to analyze the influence of the TWC substrate cell density on the mass transfer and reaction resistances. Two TWCs with different cell density, referred to as TWC 200 cpsi and TWC 400 cpsi, were investigated. The experimental data were obtained under real world TWC operating conditions. For both TWCs and over the range of operating temperatures investigated the results reveal that (i) the magnitude of the reaction resistance is insignificant, (ii) the magnitude of the internal mass transfer resistance is higher than the magnitude of the external mass transfer resistance, and (iii) the washcoat thickness of the TWCs investigated ( δ C =30 μm) is so high that limits the contact between the reactants and the PCM. A comparison between the two TWCs indicates that (i) the magnitude of the external mass transfer resistance for the TWC 200 cpsi is higher than that for the TWC 400 cpsi, and (ii) the magnitude of both the internal mass transfer and the reaction resistance for the TWC 200 cpsi is lower than those for the TWC 400 cpsi. The present study also demonstrates that, keeping constant both the PCM loading and the washcoat mass, a TWC with high cell density along with a thinner washcoat layer allows reducing simultaneously the external and internal mass transfer limitations, which may enhance further the TWC conversions.