Investigation On Spray And Combustion Performance Of Low Thrust Liquid Oxygen And Methane Rocket Engine

Low thrust liquid oxygen and methane rocket engine is investigated by analysis in theory,experiment,and simulation,which focus on the experiment of swirl-coaxial injectors,liquid-liquid impinging injectiors and gas-liquid impinging injectiors and also the simulation of the engine combustion process.Both the experiment and simultion resulets are invaluable for engineering design and optimization for the aimed kind of non-toxic propellants low thrust engine.Firstly, experiments were conducted to analyze discharge coefficient,the spray angle and the Sauter Mean Diameter(SMD).For the swirl-coaxial injector,with the increase of the air flow rate,the SMD of the central droplets increase,while the SMD of the marginal droplets decrease.The variation trend of the SMD value in same plane is gradually decreased from the center to the rim.Depending on the stripping effect of the gas,the increase of the ratio of gas and liquid can improve the atomization quality.With the increase of the gas injection pressure,the angle of the spray cone of the swirl-coaxial injectors decrease.When the injection pressure increases to a certain value,the angle of the spray cone remains unchanged.For gas-liquid impinging injector,the particle size distribution trend remains unchanged.For the liquid-liquid impinging injector,the distribution of the liquid spray in the spray field is not uniform,but the measurement of particle size distribution is homgeneous.With the increase of the liquid flow rate,the measurement value of the particle size declines rapidly.The axial velocity of the droplet increases first then decreases in radial direction.The axial velocity increases with the increase of gas injection pressure.The position of the droplet with the maximum velocity is not at the position of the droplet with the maximum SMD,while at the position bentween the largest droplet and the smallest droplet.Secondly,the simulation of the combustion and flow process in the combustion chamber of the engine was conducted by using the existing theoretical models,which focuses on the analysis of the liquid film cooling.Six simulation conditions were designed with the change of the mass fraction of the total propellant mass.The percentage of the coolant varied from 10% to 35%.The temperature distribution and the thrust performance of combustion chamber were compared,it is found that the temperature of the liquid film cooling region is obviously lower than that of central region of the combustion chamber,which is mainly due to the effect of liquid film evaporation and the convection heat transfer.With the increase of mass fraction of cooling liquid,the wall temperature of the combustion chamber declines.What is more,the amount of the outlet pressure,outlet velocity,and combustion efficiency also decreased,while the scope of the changes is not particularly obvious.Thus the reasonable range of the cooling mass flow rate is from 25% to 30%.Finally,this dissertation has completed the simulation of the combustion of the chambers whih both a longer and a shorter length.By comparing the effect of the three kinds of different lengths of the combustion chambers on the temperature field, liquid phase and methane volumetric fraction,it is found that the characteristic length of the chamber has some influence on the combustion flow field.With the increase of the characteristic length,the combustion efficiency can be improved and temperature in the chamber increases.With the increase of the chamber characteristic length,the liquid phase mass fraction in the downstream region decreases.The increase of residence time for the propellent in the combustion chamber,and the process of evaporation and combustion cause this phenomenon.It is not great for the liquid film cooling.So,the combustion chamber can not be too long, and the suitable characteristic length is 0.81 m.