Experimental And Numerical Investigation On Combustion Characteristics Of Hydrogen/Oxygen Non-premixed Jet-flames Of Mini-lobed Nozzle

The micro-scale burners occupy an increasingly important position in the automotive,electromechanical,aerospace because of its advantages,such as,long life,high energy density,etc.In order to make micro-scale burners have more efficient and stable combustion,the study of micro-scale combustion characteristics has more important significance.In recent years,more and more researchers have done a lot of research on micro-scale combustion,but there are still many problems that need to be solved.In this paper,for the non-premixed jet combustion,compared with the traditional cylindrical nozzle,a symmetrical mini-lobed nozzle is proposed.The experimental study of small-scale cylindrical nozzle and symmetrical mini-lobed nozzle was carried out.Three-dimensional steady-state numerical simulations were performed on the hydrogen/oxygen non-premixed jets diffusion combustion in small-scale mini-lobed burner.The combustion characteristics were analyzed in detail.The effects of nozzle heat transfer,burner inlet parameters and combustion chamber parameters on the combustion characteristics were analyzed.It provides a certain theoretical basis and reference value for the further miniaturization of the size of the mixed combustion chamber and the combustion limit of the mini-lobed nozzle.Firstly,jet diffusion combustion experiments were performed on semi-confined space for cylindrical nozzle and symmetrical mini-lobed nozzle and got conclusions as: Symmetric mini-lobed nozzle have better combustion performance than cylindrical nozzle in semi-confined spaces.Secondly,numerical simulations of the symmetric mini-lobed nozzle with better combustion performance in a confined space were conducted to analyze the combustion performance,and the effect of heat transfer on the combustion characteristics of the nozzle wall was studied and got conclusions as: Due to the periodic petal structure of the lobe,a flow vortex is generated near the outlet of the nozzle so that the area of the interface where the fuel and oxidizer are mixed increases and the reaction is more severe at the position of 45 degrees in the circumferential direction.The heat transfer effect of the tube wall increases the reaction rate in the combustion chamber,and it also aggravates the reaction within the inner nozzle tube.Thirdly,the influence of burner inlet parameters on combustion characteristics was studied and got conclusions as: As the fuel inlet flow rate increases,the length of the flame increases,the reaction zone and reaction rate in the mixed combustion chamber increase,and the reaction zone and reaction rate inside the nozzle decrease.As the excess air coefficient increases,the reaction rate of the combustion chamber increases,the reaction zone accumulates toward the outlet of the nozzle and the central axis,and the reaction zone and reaction rate inside the nozzle increase.Finally,the influence of the parameters of the combustor on combustion characteristics was studied and got conclusions as: As the combustion chamber diameter increases,the chemical reaction rate increases,the hydrogen conversion rate increases,the reaction zone accumulates toward the nozzle outlet and the central axis,and the reaction zone and reaction rate inside the nozzle increase.In the working condition of the diameter of the combustion chamber is 10 mm and the fuel volume flow rate is 90ml/min,the thermal conductivity of the combustion chamber wall has little effect on the combustion characteristics.The central axis of the nozzle reaction,the central axis hydrogen conversion rate and the flame shape are basically the same,and the increase of the thermal conductivity slightly reduces the reaction rate in the combustion chamber.