The design of portable power generation units using small-scale thermal engines requires a deep understanding of combustion and heat transfer processes at the microscale. Sophisticated CFD models accounting for flow-field description, combined heterogeneous and homogeneous chemical reactions and heat transfer mechanisms, have been used to delineate the stable combustion regimes of methane- and propane-fueled catalytic honeycomb microcombustors. Stability diagrams of hydrocarbon-fueled catalytic microreactors, in terms of maximum allowable heat losses to the environment versus channel inlet velocity, have identified favorable reactor wall materials for steady-state microreactor operation. Metallic materials (such as FeCr alloy) display wider combustion stability envelopes compared to ceramic materials (e.g. cordierite), owing to the higher upstream heat transfer through the microreactor walls, which in turn enhances the preheating of the incoming fuel/air mixture. Comparison between different hydrocarbon fuels, namely methane and propane, revealed a significant impact of fuel transport properties on microreactor stability, particularly on the high-velocity (blow-out) branch of the stability envelope. While methane is less reactive than propane, both catalytically and in the gas phase, it compensates more efficiently for heat losses towards the environment than propane, owing to its higher diffusive transport towards the catalytic surface.
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General Energy Research Department (ENE)
