Research Of The Non-Linear Pressure Coupled Response Characteristics Of Solid Propellant

The pressure-coupled response function of the solid propellant is the main influence factors of the combustion instability in the solid rocket motor.With the high requirement of the rocket motor performance in recent years,the performance of the propellant is also faced to the high standard.So the combustion characteristics of the propellant become more and more complicated.The basic parameters of the component,the processing of the propellant,even the different batches of the same processing,could influence their combustion characteristics,which would change the combustion response of the propellant.In addition,the motor operating parameters such as the pressure,the flight state and the acoustic characteristic in the motor chamber also affect the combustion response of the propellant.The slight change of the combustion response of the propellant could cause the nonlinear combustion instability phenomenon in the rocket motor.Therefore,the research of the pressure coupled response function of the solid propellant can be helpful to understand the mechanism of the combustion response.To establish the combustion response model to predict the pressure coupled response function(Rp)of the solid propellant,has scientific significance and engineering value to solve the combustion instability problem.Firstly,the nonlinear acoustic oscillation characteristics in the rocket motor chamber are analyzed,and the influence of the second order and third order acoustic mode on the nonlinear Rp function is established.The influence of the amplitude of oscillation on the response function is analyzed.Secondly,the experimental measurement method of linear and nonlinear Rp is established.And three kinds of propellant are tests,and the test results are compared with the nonlinear Rp model results.Thirdly,19 different formula propellants are tests in the T-burner under 6-10 MPa,and the influence rules of the parameter such as particle size,mixing ratio and content of AP,RDX and Al on the response function are obtained.Lastly,the pressure-coupled response model of the heterogeneous composite propellant(AP/HTPB)with muti-modal AP particles is established.Five different AP particle sizes are considered,and the pressure coupled response function are calculated and obtained the influence rules.The calculation results also compared with the results of experiments.The research work and main results of this paper are as follows:(1)The nonlinear Rp function model with consideration of the first order,second order and third order acoustic mode is established,and the influence of the amplitude of the oscillation on the nonlinear Rp is analyzed.The calculated results show that when the pressure oscillation amplitude increased from 1% to 30%,the nonlinear Rp value significantly increases larger than that of the linear Rp value.For example,the first mode nonlinear Rp value is increased by 4.2%~139.4%,the second mode nonlinear Rp value is increased by 18.27%~1074%,and the third mode nonlinear Rp value is increased by 1.7%~930%.The model can be used to analyze the characteristic of the nonlinear Rp in the real motor,which appear the nonlinear combustion instability.(2)An improved double pulsing T-burner test method is established for investigating and comparing the linear and nonlinear Rp function.Three kinds of propellants are used.Firstly,the linear Rp values are tested under 144Hz?175Hz?255Hz?340Hz and 670 Hz,which can be realized by changing the length of T-burner.Secondly,keeping the T-burner length constant and changing the pulser trigger manner.The nonlinear Rp values are tested under the same pressure with the linear Rp tests,and the oscillation of fundamental frequencies are set at 144 Hz and 175 Hz.Compared with the linear Rp values,the nonlinear Rp values of three kinds of propellants are significantly larger than the linear Rp values.Compared with the nonlinear model results,the error of the first,second and third mode nonlinear Rp value is 10%,17%,and 30% respectively.The results show that,the characteristic of nonlinear Rp could be estimated through the model,which could combine with parameter of the T-burner tests results and the acoustic characteristics of real motor chamber.(3)The experimental results also show that,the mean pressure has a great influence on the response function.In the whole oscillation frequency range,all the Rp values are increased when the mean pressure increases.(4)Under the same burning rate and pressure,the AP particle size distribution has a great influence on the response function.For the mono-modal and bi-modal AP propellants,when the content of the fine AP increases,the Rp value decreases when the oscillation frequency is less than 350Hz;and the Rp value increases when the oscillation frequency is larger than 350 Hz.For the three-modal and four-modal AP propellants,in order to reduce the Rp value,type I particle size of AP could be replaced by the type ? or type ? particle size of AP.(5)The pressure-coupled response model of the heterogeneous composite propellant(AP/HTPB)with muti-modal AP particles is established.The calculated results show that,the parameters of the particle size of AP,the mixing ratio of different size AP and the pressure have great influence on the Rp value.For example,the small size of AP particle enhances the high frequency response,and large size of AP particle enhances the low frequency response.The calculated results are agreed with the experimental results.