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Modeling, Simulation and Control of a Propellant MixerThis paper addresses some modeling and control issues for a mixing chamber used in rocket engine testing at NASA Stennis Space Center. The mixer must combine high pressure liquid hydrogen (LH2) and gaseous hydrogen (GH2) to produce and output flow that meets certain thermodynamic properties before it is fed into a test article. More precisely, this paper considers that the quantities to be tracked and/or regulated are mixer internal pressure, exit mass flow, and exit temperature. The available control inputs are given by three value positions, namely those of the GH2, LH2 and exit valves. The mixer is modelled by a system of two nonlinear ordinary differential equations having density and internal energy as states. The model must be simple enough to lend itself to subsequent feedback controller design, yet its accuracy must be tested against real data. For this reason, the model includes function calls to thermodynamic property data. Some structural properties of the resulting model that pertain to controller design, such as controllability and uniqueness of the equilibrium point are shown to hold. Validation of the model against real data is also provided. As a first control approach, a small-signal (linear) model is developed based on the nonlinear model and simulated as well. Pulse disturbances are introduced to the valve positions and the quality of the linear model is ascertained by comparing its behavior against the nonlinear model simulations. Valve control strategies that simulate an operator-in-the-loop scenario are then explored demonstrating the need for automatic feedback control. Classical optimal single-output and multi-output Proportional/Integral controllers are designed based on the linear model and applied to the nonlinear model with excellent results to track simultaneous, constant setpoint changes in desired exit flow, exit temperature, and mixer pressure, as well as to reject unmeasurable but bounded additive step perturbations in the valve positions. A feedback linearization controller is designed and used to achieve tracking and regulation of the outputs over an extended range of the variables of interest.
Document ID
20040013427
Acquisition Source
Stennis Space Center
Document Type
Conference Paper
Authors
Richter, Hanz
(NASA Stennis Space Center Stennis Space Center, MS, United States)
Barbieri, Enrique
(Houston Univ. TX, United States)
Figueroa, Fernando
(NASA Stennis Space Center Stennis Space Center, MS, United States)
Date Acquired
August 21, 2013
Publication Date
July 20, 2003
Subject Category
Fluid Mechanics And Thermodynamics
Report/Patent Number
SE-2002-11-00076-SSC
Meeting Information
Meeting: 39th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
Location: Huntsville, AL
Country: United States
Start Date: July 20, 2003
End Date: July 23, 2003
Sponsors: American Society of Mechanical Engineers, Society of Automotive Engineers, Inc., American Society for Electrical Engineers, American Inst. of Aeronautics and Astronautics
Funding Number(s)
CONTRACT_GRANT: NAS13-98033
CONTRACT_GRANT: NASW-99027
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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