Simulation Study Of H₂/O₂ IVF System

IVF is an auxiliary power system which utilizes H2/O2 propellants and its ullage to accomplish power generation,tank pressurization,attitude control,and propellant settling.It integrates the upper stage fluids and power management to increase energy efficiency,reduce upper stage weight,and improve reliability.After comparing 4 IVF system schemes,factors that influenced the IVF system performance were concluded.Based on the third stage of a certain rocket,an IVF system scheme was designed,and the system mass flow rate,pressure and power equilibrium equation set was established.Based on AMESim/AMESet,a H2/O2 H2-rich O2 direct-injection internal combustion engine model was built and after reasonable simplification,the power characteristic was obtained.Using heating calculation program based on minimum gibs free energy method,the exothermic character of internal combustion engine was obtained.A cryogenic plunger pump model was built in AMESim.Adopting design of experiment method,the simulation results were sampled through Latin hypercube method.The static characteristic equation was obtained after fitting the results with response surface model.To handle the character-unknown heat exchanger,the lumped parameter method was adopted in programming supercritical hydrogen heat exchanger model and two phase flow oxygen heat exchanger model.The parameter equilibrium calculation was conducted based on system static characteristic equation set.The result was compared to that of the original scheme,and the influence of parameters and advantage in weight were analyzed.The result shows that the IVF system proposed can fulfill the needs of the third stage of a rocket,and is superior to traditional scheme in weight,adjustability,mission flexibility,reliability and power efficiency.The IVF power generation subsystem,mainly including H2/O2 internal combustion engine,starter/generator,controllers,etc was built by means of AMESim.Particularly internal combustion engine was built in transient model,which overcame the disadvantage of traditional way of simulating internal combustion engine generator with average model.With regard to the complexity of the system operating environment,a speed regulator based on radical basis function(RBF)neural network self-tuning PID algorithm was designed.The dynamic process simulation was conducted through AMESim/Simulink co-simulation.The method effectively improves the conventional PID controller.The result shows that the system can meet the demand of upper stage power consumption.Stability during start up and high speed regulation performance under variable working conditions are observed.Finally,a heat exchange cycle scheme was proposed.Based on AMESim,the heat exchange cycle system model was established,mainly including H2/O2 internal combustion engine,tube-shell heat exchanger,controllers,shunt valve,hydrogen heat exchanger,oxygen heat exchanger,etc.Taken the heat exchange cycle as 3-input 3-output controlled plant,uncoupled PID controllers were designed to regulate the temperature of outlet gas.3 working conditions,including hydrogen path and oxygen path simultaneously working,hydrogen path working only,oxygen path working only,were simulated.The effect of initial coolant temperature,initial heat capacity in start up process and the system dynamic characteristic under variable working conditions were analyzed.The result shows that the scheme can satisfy the heat exchange demand of the system,the controller designed has good dynamic performance in start up process and off-design process.