Contribution of Surface Catalysis and Gas Phase Reaction to Catalytic Combustor Performance.

Abstract

Abstract : Engineering studies with catalytic combustors in the main burner and afterburner of aircraft propulsion systems have been concerned with the attainment of high combustion efficiency and flame stabilization of fuel-air mixtures outside the conventional flammability limits. The development of such devices that will perform at optimum efficiency over a broad range of operating conditions requires a detailed understanding of the flow of a reactive gas through ducts with catalytic walls, in which both hetorogeneous (wall) and homogeneous (gas) chemical reaction kinetics can occur. Of special interest to our study is the evaluation of the relative contributions of surface-catalyzed and gas-phase reactions to the total heat release rate in a catalytic combustor over a range of operating variables that include gas flow velocity, catalyst temperature, surface reactivity , and fuel-air ratio. Two catalytic combustor systems were employed. One involved stagnation point boundary layer flow with a catalytically active flat surface, the other duct flow in a multichannel catalytic monolith. The experimental studies were supplemented by theoretical calculations of heat release rates and temperature profiles based on models appropriate to the geometry and fluid dynamics of each catalytic combustion system. The result of our studies with dilute propane-air gas mixture and platinum coated surfaces have demonstrated that in both combustor configurations the gas phase combustion can be initiated by the wall-catalyzed reaction.