Experimental And Numerical Studies On Planar And Cylingdrical Micro Combustors

As a branch of microelectromechanical systems,the micro power system based on hydrocarbon fuel combustion with high energy density has been a focus in scientific research.Researches on the performance of microscale combustion chambers have instructive significance for the design of micro power systems.In this thesis,the planar and cylindrical micro combustors are studied by experimental and numerical investigations.The simulation processes are carried out by the software Ansys fluent 16.0 with detailed chemical reaction mechanism and specific conditions denfined by user defined function(UDF).The main purpose of the thesis is to discuss the significant influence factors of microscale combustion,with the aim of strengthening flame stability and giving reasonable suggestions to the design and optimization of the micro combustors.The micro combustor is applied in the micro thermal photovoltaic(MTPV)system.As a key component of the MTPV,the improvement of the micro combustor radiation efficiency,as well as the enhancement of the wall temperature uniformity and flame stability can effectively improve the overall efficiency of the system and extend the cell life.A higher and more uniform temperature distributions enhance the power output.In this thesis,the results of the planar micro combustor applied for the micro thermophotovoltaic systems show that the porous media inserted in the combustor can greatly improve outer wall temperature of the combustor,the radiation energy and radiation efficiency are increased,and the flame stability is strengthened as well.Increasing the porosity of the porous media can effectively increase the outer wall temperature,and the flame position becomes less sensitive to the flow velocity.The characteristics of the bluff body and the thermal recirculation of the porous media are combined to ptimize the combustor structure.The aspect ratio of the bluff-body affects the distribution of the flow field,and thus the heat and mass transfer as well as the flame stability and the temperature distribution field of the outer wall are influenced.Increasing the width of the bluff body decreases the outer wall temperature and reduces the flame stability.In the optimized combustor with bluff body,the heat radiation performance of methane premixed combustion is greatly enhanced.There is a significant difference between the methane and hydrogen premixed combustion: There are two high temperature zones at the outer wall,and the temperature uniformity increases.The thermal performance of the outer wall is superior when porous media are tail half-filled to the cases fully filled with porous media and bluff body combustor.The flame dynamic characteristics were studied and analyzed in a cylindrical quartz tube combustor.The experimental investigation of premixed combustion of methane in the cylindrical combutor are carried out,and the periodic ignition and extinction asymmetric flames,symmetric V-shaped flames and oscillating and pulsating double-layer flames are observed.Considering the UDF to define the wall temperature and analysis flame stability characteristics,it is showed that the flame front shapes affect the flame stability since it influences the preheating effect of the flame on the unburned gas.A negatively stretched flame can improve flame stability and the flame stability decreases with a positively stretched flame front.The results of optimizing the cylindrical combustor by the casing inside the combustor show that the casing combustion can enhance the flame-wall thermal coupling effect,the outer wall temperature and flame stability are significantly improved.Therefore,the casing micro combustor is more suitable for a micro power systems.