Numerical Study On Flame Stability And Combustion Characteristics Of Non-premixed Combustion In Asymmetric Vortex Micro-combustors

With the rapid development of micro-electromechanical system（MEMS）technology,micro equipment such as micro machinery,portable electronics,communication and sensing equipment keep emerging and are widely used in aerospace,military,communication and biomedical fields.Most existing micro devices use electrochemical batteries as energy sources.However,electrochemical batteries have low energy density,large volume and short working time,and hydrocarbon fuels have higher energy density than electrochemical batteries.Therefore,the micro power system based on hydrocarbon fuel combustion is expected to replace traditional batteries and provide energy for micro devices.The micro-combustor is the core component of the micro power system.The flame stability in the micro-combustor directly affects the output power and total energy conversion efficiency of the micro power system.Improving the flame stability in the micro-combustor is of great significance to the micro power system.At present,micro-combustor using premixed combustion mode are widely used in micro-power systems because of their high combustion efficiency,relatively simple structure and easier manufacturing.The non-premixed micro-combustor requires physical preparation time before combustion because of the indoor mixing process,which makes the overall combustion time of the reactants longer and the flame stable combustion in the micro-combustion chamber difficult.At the same time,its structure is relatively complex,and there are many inconvenience in manufacturing and using in the micro power system,so it is less used in the micro power system.However,the non-premixed micro-combustor fuel is stored separately from the oxidizer,which has better safety performance.At the same time,it does not require a premixing device,which makes it possible to use in micro-power systems.In this thesis,an asymmetric vortex micro-combustor using non-premixed combustion is proposed to improve the flame stability of micro-scale non-premixed combustion.The micro-combustor can be used as a component of a micro-power system based on fuel combustion.In this thesis,the flame stability and combustion characteristics in the asymmetric vortex micro-combustor,as well as the influence of the inlet on its combustion and heat transfer performance are numerically studied and analyzed.The main work is as follows:（1）In order to improve the stability of the non-premixed combustion flame of the micro-burner,based on the asymmetric vortex combustion theory,an asymmetric vortex micro-burner for H₂/air non-premixed combustion is proposed.The feasibility of the vortex combustion flame improving the flame stability of the micro non-premixed burner is studied through numerical simulation.And the effect of air mass flow rate and hydrogen/air equivalent ratio on flame stability in asymmetric vortex micro-combustors.The results show that the corner reflux region,the center reflux region and the low velocity region in the asymmetric vortex micro-combustor have obvious anchoring effect on the flame.The central reflux area plays a major role in anchoring the flame root,which can prevent the flame from being blown downstream of the burner and improve the stability of the non-premixed flame.（2）The micro-combustor as the core component of micro power systems,the vortex micro premixed burner combustion performance will affect the performance of micro power systems.In Chapter 3,the combustion characteristics of H₂/air non-premixed combustion in the combustion chamber of asymmetric vortex micro-combustors are studied,including mixing performance,combustion efficiency,center line temperature,wall temperature,heat loss and heat loss rate,as well as the air mass flow rate,equivalent ratio,and the influence of wall materials on the combustion characteristics of asymmetric vortex micro-combustors.The results show that when the air mass is 0.5×10^-5kg/s to3.5×10^-5kg/s,the fuel in the asymmetric vortex micro-combustor basically realizes complete combustion,and the combustion efficiency is close to 100%（3）In order to improve the asymmetric vortex combustion and heat transfer performance of the micro-combustor,asymmetric vortex micro-combustor is studied through numerical simulation of tangential rectangle air inlet height to width ratio and fuel inlet size and position of micro-combustor flame structure and wall average temperature and the influence of radiation efficiency and power.The results show that the flame of a micro-combustor with a larger air inlet height to width ratio and a smaller diameter with a fuel inlet close to the air inlet can be more stable in the combustion chamber,and the average wall temperature,radiation power and radiation efficiency are higher.