Study On The Atomization And Combustion Characteristics Of LOX/Methane Pintle Injectors

Having the advantages of simple structure,non-toxic,high specific impulse,stable combustion and wide scale of thrust adjustment,LOX/CH4 variable-thrust pintle rocket engines show wide application prospect.Breakup progress of conical sheets,atomization characteristics and combustion performance of pintle injectors were studied through theoretical analysis,experimental study and numerical simulation.In addition,the influences of structural parameters of pintle injectors were analyzed,expecting to provide a reference for the designing of variable-thrust engines.Firstly,design criteria of pintle injectors were obtained.Flow rate regulating characteristics in different shapes of propellants injection channels were theoretical investigated.And the results show that pintle injectors have the ability of achieving any format of propellants flow rate regulating curve.Next,breakup process on conical sheets of pintle injectors was studied.Similarities and differences between pintle injectors and swirl injectors were analyzed.Linear unstable theoretical model of irrotational conical sheets was established,and the dispersion equations were solved.Then,influences of parameters like injection pressure drop on breakup process of conical sheets were analyzed.Compared with experimental results,an empirical correlation for parameter C and(7)(8)0lnbη η were obtained,and variation laws of breakup length,breakup time and wave length with structural parameters were studied.The results indicate that the theoretical model of irrotational conical sheets can used qualitative analysis of breakup process of conical sheets of pintle injectors.Then,using Marvin measuring instrument and high-speed photography,steady atomization characteristics of pintle injectors were studied.And variation laws of SMD,drop distribution homogeneity factors and atomization cone angles with gas-liquid mass flow ratio and slit width were analyzed.The experimental results show that when the gas-liquid mass flow ratio was larger than 0.206,with the effects of aerodynamic force,the atomization boundary could be divided into two zones,the upper zone was contraction stage,while the lower zone was equal-diameter stage.Last,numerical simulation on pintle engines was conducted.The influences of the main structural parameters of pintle injector and combustor on flow field structures and combustion performance were studied.The results show that there exist two recirculation zones,which can improve combustion stability and efficiency of the engines.Gas temperature near the first-half combustion wall was low,which reduced the demand of engine cooling system.In addition,there existed a reactants “enclosed area” in the combustor of circularity pintle engines,which had a significant effect on improving combustion efficinency.Thus,to improve combustion efficiency,the inner fuel injection channels of pintle engines should be designed as injection orifices.