Experimental And Numerical Investigations On Combustion And Agglomeration Characteristics Of Solid-Fuel Ramjet

Solid fuel ramjet(SFRJ)has the advantages of simple structure,high reliability,high specific impulse,low cost and safe for storage and transportation.Hence,SFRJ can be used as the power device for various missiles and projectiles for supersonic flight.Due to the performance of solid fuel ramjet is very complex,more extensive basic research work is necessary,such as poor flame stability,easy extinguishing,low combustion efficiency of metal particles,etc.These problems greatly hinder the application of solid fuel ramjet.In this work,the ignition and combustion performance of Al/Mg fuel-rich propellants,multiphase nonequilibrium chemical reaction and agglomeration mechanism of aluminum particles are studied,which is helpful to improve the comprehensive combustion and flow performance of solid fuel ramjet.The main research work is as follows:Firstly,a CO2 laser ignition and combustion experimental system is established to study the ignition characteristics of Al/Mg fuel-rich propellant.The physical and chemical process of Al/Mg fuel-rich propellant ignition is analyzed in detail.The ignition model and combustion dynamics model are established.The ignition delay time is studied theoretically and experimentally.The mathematical model is established to indicate the relationship between ignition delay time and laser heat flux,ambient pressure,initial temperature.The model is verified by the experiments of nitramine propellant and Al/Mg fuel-rich propellant.Secondly,the combustion characteristics of Al/Mg fuel-rich propellant are studied through CO2 laser ignition and combustion system.The combustion characteristics of Al/Mg fuel-rich propellant under different ambient pressures,oxygen concentration and Al/Mg content ratio are studied by experimental and theoretical analysis.Based on the B-number theory,a theoretical and mathematical model of the combined effect of ambient pressure and oxygen concentration on burning rate is established.The model fits well with the experimental results,which shows that it is suitable for predicting the burning rate of Al/Mg fuel-rich propellant under different pressure and oxygen concentration.Meanwhile,the effects of ambient pressure and oxygen concentration on the temperature distribution of combustion wave are also studied.Thirdly,a set of software is developed to study the decomposition and combustion characteristics of Al/Mg fuel-rich propellant in the near burning surface region.Based on the turbulence model and detailed combustion dynamics model with 16 species and 16 chemical reactions,the finite volume method is used to solve the gas-phase N-S equations and solidphase control equations discretely.The numerical simulation results are verified by comparing with the experimental data.The effects of pressure,oxygen concentration and magnesium content on combustion wave temperature,turbulent viscous coefficient and mass distribution of combustion products of Al/Mg fuel-rich propellants are analyzed.Fourthly,the agglomeration process and mechanism of Al/Mg fuel-rich propellant are studied by means of high-speed camera,scanning electron microscope and laser particle size analyzer.The combustion process of Al/Mg fuel-rich propellant is recorded by high-speed camera.It is observed that the aluminum particles would break away from the burning surface after agglomeration,and secondary agglomeration occurred.Under different ambient pressures,the microstructure of the combustion products and the aggregation behavior of aluminum particles are further analyzed.Based on the classical pocket theory and particle size analysis experiments,a new agglomeration size prediction model is established.It can be used to predict the agglomeration size on the burning surface and the new agglomeration size formed by the secondary agglomeration after detaching from the burning surface.Compared with the empirical model and the typical pocket model,this model is more in line with the experimental results.Fifthly,a direct-connection test system platform for solid fuel ramjet is established,on which the ground direct-connection test of solid fuel ramjet fueled with Al/Mg fuel-rich propellant is carried out to study the effects of inlet temperatures on the combustion performance,the microstructure and size of the agglomerates.With the increase of inlet temperature,the size of the agglomerates decreases,the pressure and temperature in the afterburning chamber increase,and the thrust increases,which makes the propellant burn more fully.The characteristic speed,specific impulse and combustion efficiency of the solid fuel ramjet increase.