Combustion characteristics of small alkanes on noble metal
surfaces in pre-mixed homogeneous-heterogeneous hybrid systems
In conventional thermal combustion fuel and air in inflammable proportions are contacted with an ignition source to ignite the mixture which will then continue to burn. Flammable mixtures of most fuels are normally burned at relatively high temperatures, which inherently results in the formation of substantial emissions of nitrogen oxides. In purely catalytic combustion systems, there is little or no nitrogen oxides formed in a system which burns the fuel at relatively low temperatures. The present study is focused primarily upon the combustion characteristics of small alkanes on noble metal surfaces in pre-mixed homogeneous-heterogeneous hybrid systems. The homogeneous-heterogeneous combustion characteristics small alkanes on noble metal surfaces are investigated to gain a greater understanding of the mechanisms of flame stabilization and to gain new insights into how to design pre-mixed combustors with improved stability and robustness. The essential factors for design considerations are determined with improved combustion characteristics. The primary mechanisms responsible for the loss of flame stability are discussed. The present study aims to explore how to effectively operate catalytically stabilized combustion. Particular emphasis is placed upon the catalytic combustion characteristics of small alkanes in the pre-mixed hybrid systems. The results indicate that the combustion effluent is characterized by high thermal energy and typically by low nitrogen oxides content. Precise tuning of the combustion process is needed to establish a balance between stable combustion and low emissions. Simply changing the combustor geometry to maintain near-stoichiometric ratios will not avoid nitrogen oxides formation. The catalytic reactor oxidizes substantially all of the ingested fuel and produces thermal energy. Adiabatic combustion systems, from a practical standpoint, have relatively low heat losses, thus substantially all of the heat released from the combustion zone of such systems appears in the effluent gases as thermal energy for producing power. Catalytic oxidation has the disadvantage that the physical reaction surface which must be supplied for complete oxidation of the fuel increases exponentially with decreasing inlet temperatures, which greatly increases the cost of the combustor and complicates the overall design. The operating temperature is determined by the theoretical adiabatic flame temperature of the fuel-air admixture passed to the combustor and thus is dependent on the initial temperature of the air as well as the amount of fuel contained therein. The temperature of the catalyst zone is controlled by adjusting the composition and initial temperature of the fuel-air admixture as well as the uniformity of the mixture.
Keywords: Combustion; Metals; Designs; Fuels; Alkanes; Oxidation