Mechanism And Characteristics Research On Solid Oxide Flame Fuel Cells

The solid oxide flame fuel cell directly combines a fuel-rich flame and a solid oxide fuel cell（SOFC）in a“no-chamber”setup,which is a promising fuel cell for distributed power systems.The reaction kinetics and characteristics of the flame fuel cell（FFC）were studied in this dissertation from the aspect of fuel cell type selection,fuel-rich flame,FFC unit and co-generation system.First,a two-dimensional model of the FFC was developed to quantitatively analyze the thermal stress and the failure probability of fuel cells with different structures brought by the rapid startup of the flame.A flame fuel cell setup was designed and built based on a Hencken-type flat flame burner.The start-up characteristics and thermal shock resistance of a planar SOFC and a micro-tubular SOFC were compared and studied.The experimental and numerical study on the thermal stress of the SOFC working in flame conditions provides a theoretical basis for the selection of the SOFC type and shows that the anode-supported micro-tubular SOFC is a proper choice for the FFC configuration.Second,a two-layer porous media burner with catalytic enhancement was used to increase the reforming efficiency of the burner.The effects of the equivalence ratio and the gas velocity on the temperature distribution inside the burner and the combustion products were studied.Using a burner efficiency based on lower heating values,up to50.0%of methane was converted to H₂and CO.The reforming efficiency of methane to H₂increased by 31.3%after the catalytic enhancement.A combined homogeneous and heterogeneous elementary reaction mechanism was developed for methane partial oxidation in the porous media burner with catalytic enhancement.A one-dimensional model was explored by coupling the combined mechanism with heat-transport and mass transport processes within the burner.The model is demonstrated to be a useful tool for understanding the reaction processes within the burner and for burner design optimization.The nickel catalyst mainly promoted the water-gas shift reaction,and the heterogeneous reactions were dominant in the region where the catalyst was loaded.Then,a FFC unit based on a porous media burner and a micro-tubular SOFC was designed and built.The influences of the flame operation conditions on the fuel cell electrochemical performance were studied.The fuel-rich methane flame provided suit able fuels and temperature environment for the operation of the SOFCs.Further,a FFC stack was successfully implemented for the first time.Four micro-tubular SOFCs were arranged in a parallel configuration,which reached 3.6 W at 0.6 V.A two-dimensional axisymmetric model of the FFC unit was developed based on the combustion model by further considering the chemical reactions,the electrochemical reactions,the heat transport,the mass transport and the charge transport processes inside the anode.The coupling mechanism of the fuel-rich flame and the SOFC anode was clarified.At last,a tri-generation system based on the FFC was proposed and analyzed for residential applications.Parametric analyses were conducted to investigate the effects of operation parameters on the system efficiency and the thermal-to-electrical ratio.The electric efficiency of the system is no more than 20%while the cogeneration efficiency can reach above 90%,indicating the suitability of the FFC-based system for cogeneration/trigeneration rather than power generation alone.