Physical and chemical processes in micro-scale heat-recirculating systems with improved flame stability and combustion characteristics

Numerical simulations are conducted to gain insights into system performance and to determine what changes can be made to improve the robustness and stability of catalytically stabilized combustion in a micro-scale system with a heat-recirculating structure. Detailed kinetics are used for modeling the system in computational fluid dynamics. Methods of applying a heat-recirculating structure to the channel walls are employed, which may be utilized with presently existing designs of micro-scale combustion systems. The factors affecting combustion stability are determined for the system. The objective of this study is to investigate the essential characteristics of catalytically stabilized combustion in a micro-scale heat-recirculating system so as to gain a greater understanding of the mechanisms of flame stabilization. Particular focus is placed on determining essential factors for design considerations of the system with improved flame stability and combustion characteristics so that the system operates more efficiently. The results indicate that there must be sufficient residence time for the fuel-air mixture to diffuse and reach substantially complete reaction at the catalyst surface. In practice, when employing gas velocities which provide laminar flow, the pattern of flow of the entering gases at the initial portion of the flowthrough paths will resemble turbulent flow until the flow pattern becomes settled. The reactions can more precisely be controlled with respect to degree of completion, reaction conditions, response to change in reaction conditions, and the like. The reaction conditions required to provide an advantageous result may depend in part upon the particular reaction being conducted and the nature of the catalytically-active components contained on the catalyst. Both heat transport and diffusion of active particles must be considered essential for ignition. Combustion terminates when equilibrium is achieved between the total heat energies of the reactants and the total heat energies of the products. The adiabatic flame temperature of fuel-air admixtures at any set of conditions is established by the ratio of fuel to air. In mass transfer controlled catalytic reactions, one cannot distinguish between a more active catalyst and a less active catalyst because the intrinsic catalyst activity is not determinative of the rate of reaction.