NUMERICAL-ANALYSIS OF THE TRANSIENT PERFORMANCE OF HIGH-TEMPERATURE MONOLITH CATALYTIC COMBUSTORS - EFFECT OF CATALYST POROSITY

The transient response of a high-temperature monolith catalytic combus tor was studied under various conditions. The aim of the study was to elucidate the significance of the catalyst porosity on the catalyst li ght-off. Numerical experiments were carried out using a one-dimensiona l mathematical model, which accounts for both heterogeneous and homoge neous reactions and allows heat conduction in the solid phase in the a xial direction. The most significant feature of the model is that it c onsiders the reactions on the interior surface as well as on the exter ior surface of the catalyst. This allows us to study the significance of the catalyst porosity on transient behavior. The effect of the poro sity was studied by varying the interior surface area, the washcoat th ickness and the effective diffusivity. Each of these parameters is a m easure of the effect of the catalyst porosity, directly or indirectly. The results of this study show that all of these parameters have an e ffect on the transient performance of the catalytic combustor except w hen the catalyst is preheated to a very high temperature. Thus, it is concluded that larger catalyst surface area will benefit catalytic ign ition. The results also show that the effect is more important at tran sient state than at steady state and that it depends on the type of fu el used for the combustion.