Research On System Scheme And Thrust Throttling Technology Of Liquid Oxygen Hydrocarbon Variable Thrust Rocket Engine

Variable thrust liquid rocket engine plays an important role in realizing soft landing of spacecraft on extraterrestrial bodies,improving the accuracy of orbital maneuver and rendezvous and docking,improving the flexibility of missiles and improving the performance of combined cycle engine.With the development of cryogenic propellant,battery and motor technologies,variable thrust liquid rocket engine using cryogenic motor pump has become a research hotspot.In this dissertation,the LOX/kerosene and LOX/CH4 variable thrust liquid rocket engines using motor pump are studied.Starting with the trajectory optimization of the variable thrust engine,the system scheme design is carried out.Moreover,the components and simulation parameters are provided for the system dynamics simulation.Finally,the closed-loop control research is carried out based on the open-loop results.In this dissertation,three typical flight modes are proposed for the ground vertical take-off and landing vehicle using variable thrust rocket engine,including vertical take-off and landing without translation,vertical take-off,translation and vertical landing,and vertical take-off,translation,vertical landing,and autonomous landing.The trajectory optimization of the above flight modes is carried out based on Gauss pseudospectral method.The results show that the Gauss pseudospectral method is suitable for the trajectory optimization of vertical take-off and landing vehicles.At the same time,the propellant consumption is reduced as much as possible,which increases the space left for the aircraft structure mass.On one hand,in mode 1,the thrust takes the form of quasi Bang-Bang control.However,in mode 2 and mode 3,the thrust takes the form of Bang-Bang control.On the other hand,the two norm term of thrust change rate is introduced into the optimization target by weight method,which can effectively suppress the thrust fluctuation.Multi cycle scheme designs of LOX/kerosene variable thrust rocket engine are carried out for the first time.For motor pump,pressure-fed and staged combustion cycle systems,the state and structure parameter distributions are given respectively.Further,the parametric analysis of influence factors on turbine flow ratio and pump power is carried out.Finally,different system schemes are compared from dry weight.The results show that,in terms of dry weight,due to the limitation of motor and battery mass,compared with the staged combustion cycle system,the motor pump system has no advantages.Based on the mission profile similar to that of the LOX/kerosene engine,different system schemes of LOX/CH4 variable thrust rocket engine system are designed.Firstly,the pump power performance and dry weight are studied for the motor pump system.Then,for the expander cycle system,the temperature estimation model of the cooling channel outlet under a constant mixing ratio is established.The state parameter distributions of single and double turbine schemes under different conditions are given,and these two throttling schemes are compared.Considering low chamber pressure of expander cycle and motor pump systems,a parallel electrothermal co-pressurization scheme is proposed by combining these two cycles,which can effectively improve chamber pressure at the rated condition.Furthermore,the concept of critical chamber pressure suitable for throttling conditions is proposed,and the variation laws of turbine fluid flow rate and critical chamber pressure are studied.Based on the system scheme of liquid oxygen kerosene variable thrust engine using motor pump,the dynamic simulation analysis is carried out.Firstly,the system dynamics models are established,especially considering the cooling channel model.Then,the time-domain analysis is carried out for different conditions,and the time-domain and frequency-domain results are analyzed for throttling conditions.Further,the short plate effect in system dynamic response and the method to control the short plate effect are proposed.The reason that the motor pump system has the anti-interference ability compared with the traditional turbine pump engine is given.Differential schemes for positive and negative throttling are obtained.Finally,the influence of oxygen and fuel buck arms on the closed-loop system stability is given.Based on open-loop response results,the control scheme design of liquid oxygen kerosene variable thrust rocket engine using motor pump is carried out.A dual control objective scheme with mixture ratio dependent on chamber pressure is proposed.The weight factors of oxygen and fuel buck arms are taken as control variables,and the control system framework is established by using uncoupled dual PI controllers.Based on the control system framework,the system simulation model is set up.Finally,the response characteristics of the closed-loop system under step and slope signals are analyzed respectively.The results show that,the proportional control mainly causes the fluctuation and oscillation of the control target.However,the integral control causes the steady-state error of the control target.