Research On The Variable Thrust Scheme Of Heavy Staged Combustion Cycle LOX/LH2 Engine

Based on variable thrust demand of the 220 t staged combustion cycle LOX/LH2 engine of our country,this paper discusses the principle of variable thrust liquid rocket engine,expounds theoretical schemes of the variable thrust engine.Also the paper puts forward three variable thrust schemes for the engine,which takes some typical variable thrust systems over the world into consideration.And then in order to determine the best scheme,the paper uses the means of static simulation to take calculation and analysis.Finally,it preliminary discusses the control system of variable thrust.This paper discusses the variable thrust simulation model of each component of liquid rocket engine by means of engine nonlinear analysis.The propellant property parameter model adopts the thermodynamic function built in the EES simulation software.The elements models of combustion chamber,injector,pipeline,valve and throttle are nonlinear equations which are frequently-usedin the static simulation of engine.Based on previous theoretical researches,this paper sets up a one-dimensional heat transfer model of thrust chamber cooling jacket independently.And so as to verify the reliability of the model,it uses the experimental data of a large thrust LOX/LH2 engine to make a contrast.At the same time,the mentioned one-dimensional heat transfer is inserted into the engine model in a modular fashion,instead of the practice of separately solvingon this part previously.Thereinto,the models of centrifugal pump and turbine are built with the modular idea and inserted into the engine model.On the basis of engine components models,this paper uses three equilibrium relationships to set an engine variable thrust simulation model,thereinto,the three relationships are pressure balance,flow balance,and power balance.Then taking the balancing calculation,the paper confirms the rated condition parameters and some structure parameters of the engine.Also it uses the simulation model to test above-mentioned three variable thrust schemes,of which takes the 100% to 50% of the variable thrust simulation,and the ±5% of the variable mixing ratio simulation.The results of simulation show that the valve opening change do not vary monotonicallyin the process of thrust decreasing for the oxidizing gas throttling solutions and gas shunting in front of the turbine solutions.And the variation range of precombusor mixing ratio of the two schemes are larger than the single channel regulation scheme.Besides,thrust change of three solutions in the process of mixing ratio adjustment are within the acceptable range.Ultimately this paper finds that the single channel regulation scheme is the best of the three.After determining the engine variable thrust scheme,the method of real-time measurement of engine thrust and mixing ratio are put forward,and the control scheme of engine thrust and mixing ratio are preliminarily discussed.In the aspect of thrust regulation,the closed-loop control of thrust regulator is proposed by using chamber pressure signal,and the mixing ratio control valve is controlled by the opening signal of thrust control valve in the open-loop to keep the mixing ratio fixed.The mixing ratio regulation is to use the measured mixing ratio signal to control the mixing ratio control valve in the closed-loop,to adjust the mixing ratio at a certain thrust level.