| The development of a new type of high performance space propulsion system which is the main development direction of future space propulsion has attracted by the scholars from different countries.Ammonium dinitramide(ADN)based liquid monopropellant propellant has shown the broad application prospect currently.It has been regarded as the next generation propellant,which could replace the traditional mopropellant hydrazine propellant that apply on the attitude and orbit control of satellite.The key engineering problems for the atomization,evaporation,heat and mass transfer of porous media,catalytic decomposition and combustion process should be discussed,and it has shown the significant effect on the specific impulse performance,reliability and economy.In this paper,the high performance of ADN based thruster is regared as the research background,and the actual green space non-toxic ADN based propellant is used as the working fluid.The atomization characteristics of ADN based propellants is obtained through the test.Furthermore,the simulation results of ADN-based thruster is investigated through the numerical simulation method.The influence of propellant ratio variation is discussed.The results could provide support for further research on small space thruster design and atomization combustion mechanism research.A test device for the study of swirl atomization characteristics of ADN based propellants has been established.The swirl nozzle is designed based on the principle of maximum flow.The dynamic image of swirl spray and droplet size distribution were obtained by combined using the method of high speed photography and Malvin particle size analyzer.The swirl atomization characteristics of ADN based monopropellant are studied,and based on the analysis of swirl spray configuration,the development and evolution characteristics of swirl atomization process are clarified.The effects of injection pressure,spray hole structure parameters,tangential hole structure parameters and swirl chamber structure parameters on macro and micro characteristics of swirl atomization are discussed.The effects of injection parameters and nozzle structure parameters on the breakup length,spray cone angle and average particle size are obtained.It is found that the increasing of injection pressure,reducing the length and diameter of the nozzle,increasing of swirl chamber height and increasing of tangential hole quantity are conducive to improving the spray characteristics.At the same time,the optimal value of the tangential hole number and the diameter of the swirl chamber has been found to increase the spray characteristics.The relationship between primary and secondary effects of the structure parameters on atomizing characteristics is discussed.It is found that the swirl chamber diameter and height are key factors influencing the nozzle cone angle and breakup of liquid film length,respectivity,and the tangential hole number is the key factor affecting the average droplet size.The influence of nozzle structure parameters on the macro and micro characteristics of ADN based propellant swirl atomization is revealed.The physical and mathematical model of ADN based thruster is established by counpling the spray model which is based on the nozzle atomization characteristics of the experimental results,evaporation model,mass transfer in porous media model,by considering thermal dispersion non-isothermal heat transfer model and the simplified chemical kinetic model.The evaporation rate formula of the droplet is obtained through experimental results.Firstly,the heat release characteristics of ADN based propellant are obtained based on differential scanning calorimetry.The propellant droplet evaporation process of non touch wall state based on the Leidenfrost effect is investigated.The droplet shape change process and droplet survival time at differernt wall temperature are achieved.The Leidenfrost temperature between the ADN based propellant droplets and quartz glass is obtained.The fitting formula of droplet survival time is established.According to the established mathematical and physics model,temperature distribution characteristics of thruster is discussed.Component distribution characteristics is analysed along the central axis and the thruster catalytic bed exit section and combustion chamber exit section.The relationship between ADN,methanol,important intermediate of AN,N2O,NO2,HCOOH,CO2 and H2O and other components is clarified.The reaction zone and degree of the catalytic decomposition and combustion reaction are revealed.At the same time,the effect of ADN based propellant composition ratio changing on the difference between the temperature distribution and components is analysed.The optimal ratio of propellant components that conducted to the thruster performance improving is achieved.The effects of thruster key parameters,including the catalytic bed operatingparameters,injection pressure and thruster structure parameters,on the catalytic decomposition and combustion processes are analyzed.The distribuation of temperature,and the reactant and important intermediate products at the catalyst bed exit section and the combustion chamber exit section is discussed.The influence of thruster key parameters on the catalytic decomposition and combustion mechanism is revealed.The results show that the porosity increases,the preheating temperature increasing,increasing injection pressure is beneficial to improve the performance of specific impulse thruster,and the preheat temperature of 420 K could start the thruster,the optimal catalytic bed length and diameter values of the thruster is obtained.The relationship between primary and secondary effects of the thruster start parameters on specific impulse perfomence is discussed.It is found that the dominant factor for improving the specific impulse thruster performance is thruster diameter,and porosity has shown a relatively small effect on the specific impulse perfomence.It is beneficial for the design of ADN-based thruster and ignition experiment research. |
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