The Pennsylvania State University
The Graduate School
College of Engineering
EXTENSIONS TO THE TIME LAG MODELS
FOR PRACTICAL APPLICATION TO ROCKET ENGINE STABILITY DESIGN
A Dissertation in
Mechanical Engineering
by
Matthew J. Casiano
© 2010 Matthew J. Casiano
Submitted in Partial Fulfillment of the Requirements for the Degree of
Doctor of Philosophy
August 2010
The dissertation of Matthew J. Casiano was reviewed and approved* by the following:
Domenic A. Santavicca Professor of Mechanical Engineering Co-chair of Committee
Vigor Yang Adjunct Professor of Mechanical Engineering Dissertation Advisor Co-chair of Committee
Richard A. Yetter Professor of Mechanical Engineering
André L. Boehman Professor of Fuel Science and Materials Science and Engineering
Tomas E. Nesman Aerospace Engineer at NASA Marshall Space Flight Center Special Member
Karen A. Thole Professor of Aerospace Engineering Head of the Department of Mechanical and Nuclear Engineering
*Signatures are on file in the Graduate School
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ABSTRACT
The combustion instability problem in liquid-propellant rocket engines (LREs) has remained a tremendous challenge since their discovery in the 1930s. Improvements are usually made in solving the combustion instability problem primarily using computational fluid dynamics
(CFD) and also by testing demonstrator engines. Another approach is to use analytical models.
Analytical models can be used such that design, redesign, or improvement of an engine system is feasible in a relatively short period of time. Improvements to the analytical models can greatly aid in design efforts.
A thorough literature review is first conducted on liquid-propellant rocket engine (LRE) throttling. Throttling is usually studied in terms of vehicle descent or ballistic missile control however there are many other cases where throttling is important. It was found that combustion instabilities are one of a few major issues that occur during deep throttling (other major issues are heat transfer concerns, performance loss, and pump dynamics). In the past and again recently, gas injected into liquid propellants has shown to be a viable solution to throttle engines and to eliminate some forms of combustion instability. This review uncovered a clever solution that was used to eliminate a chug instability in the Common Extensible Cryogenic Engine (CECE), a modified RL10 engine.
A separate review was also conducted on classic time lag combustion instability models.
Several new stability models are developed by incorporating important features to the classic and contemporary models, which are commonly used in the aerospace rocket industry. The first two models are extensions of the original Crocco and Cheng concentrated combustion model with feed system contributions. A third new model is an extension to the Wenzel and Szuch double- time lag model also with feed system contributions.
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The first new model incorporates the appropriate injector acoustic boundary condition which is neglected in contemporary models. This new feature shows that the injector boundary can play a significant role for combustion stability, especially for gaseous injection systems or a system with an injector orifice on the order of the size of the chamber. The second new model additionally accounts for resistive effects. Advanced signal analysis techniques are used to extract frequency-dependent damping from a gas generator component data set. The damping values are then used in the new stability model to more accurately represent the chamber response of the component. The results show a more realistic representation of stability margin by incorporating the appropriate damping effects into the chamber response from data. The original
Crocco model, a contemporary model, and the two new models are all compared and contrasted to a marginally stable test case showing their applicability. The model that incorporates resistive aspects shows the best comparison to the test data. Parametrics are also examined to show the influence of the new features and their applicability. The new features allow a more accurate representation of stability margin to be obtained.
The third new model is an extension to the Wenzel and Szuch double-time lag chug model. The feed system chug model is extended to account for generic propellant flow rates.
This model is also extended to incorporate aspects due to oxygen boiling and helium injection in the feed system. The solutions to the classic models, for the single-time lag and the double-time lag models, are often plotted on a practical engine operating map, however the models have presented some difficulties for numerical algorithms for several reasons. Closed-form solutions for use on these practical operating maps are formulated and developed. These models are incorporated in a graphical user interface tool and the new model is compared to an extensive data set. It correctly predicts the stability behavior at various operating conditions incorporating the influence of injected helium and boiling oxygen in the feed system.
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TABLE OF CONTENTS
LIST OF FIGURES ...... vii
LIST OF TABLES ...... xi
NOMENCLATURE ...... xii
ACKNOWLEDGEMENTS ...... xxv
Chapter 1 Introduction...... 1
1.1 Motivation ...... 1 1.2 Background ...... 3 1.2.1 Time-Lag-Based Combustion Instability Models ...... 3 1.2.2 Liquid-Propellant Rocket Engine Throttling ...... 4 1.3 Objective ...... 5
Chapter 2 Liquid-Propellant Rocket Engine Throttling ...... 8
2.1 Throttling Review ...... 11 2.1.1 High-Pressure-Drop Injectors...... 11 2.1.2 Dual-Manifold Injectors ...... 30 2.1.3 Gaseous Injection ...... 41 2.1.4 Multiple Chambers ...... 47 2.1.5 Pulse Modulation ...... 49 2.1.6 Throat Throttling ...... 54 2.1.7 Variable Area Injectors ...... 58 2.1.8 Hydrodynamically Dissipative Injectors ...... 70 2.1.9 Combined Methods ...... 72 2.2 Review Summary ...... 73 2.2.1 High-Pressure-Drop Injectors Summary ...... 73 2.2.2 Dual-Manifold Injectors Summary ...... 74 2.2.3 Gaseous Injection Summary ...... 76 2.2.4 Multiple Chambers Summary ...... 77 2.2.5 Pulse Modulation Summary ...... 77 2.2.6 Throat Throttling Summary ...... 78 2.2.7 Variable Area Injectors Summary ...... 79 2.2.8 Hydrodynamically Dissipative Injectors Summary...... 80
Chapter 3 Time Lag Stability Models ...... 81
3.1 Research Goal, Strategy, and Objectives ...... 85 3.2 Gunder and Friant Time Lag Model ...... 89 3.3 Summerfield Time Lag Model ...... 91 3.4 Crocco and Cheng Monopropellant Time Lag Chug Model ...... 93 3.5 Crocco and Cheng Bipropellant Time Lag Model ...... 105 3.6 Notes on Crocco and Cheng Chug Time Lag Models ...... 110
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3.7 Natanzon Monopropellant Chug Time Lag Model ...... 111 3.8 Crocco and Cheng Longitudinal High Frequency Time Lag Model ...... 112 3.9 Control Engineering Background ...... 120 3.10 Stability Diagrams, Gain Margin and Phase Margin ...... 123 3.11 Wenzel and Szuch Time Lag Models ...... 127
Chapter 4 Stability Model for a Damped Wave Equation in a Mean Flow with Concentrated Combustion ...... 130
4.1 Model Development ...... 132 4.1.1 Injector Boundary Condition ...... 141 4.1.2 Injector Admittance ...... 144 4.1.3 Nozzle Boundary Condition ...... 153 4.2 Model Formulation ...... 155
Chapter 5 Damping from Typical Engine Data ...... 161
5.1 Engine Data Analysis ...... 165 5.2 NASTRAN Acoustic Model of Chamber ...... 166 5.3 Engine Chamber Damping Estimate ...... 172
Chapter 6 Concentrated Combustion Model Study ...... 176
Chapter 7 Effects of Helium Introduced in an Injector on a Throttled Engine ...... 191
7.1 Parametric Formulation of the Wenzel and Szuch Model ...... 193 7.2 Parametric Formulation of a Modified Szuch Model ...... 202 7.3 Chug Stability Code ...... 205 7.3.1 Wenzel and Szuch Single-Time Lag Model Solution ...... 206 7.3.2 Wenzel and Szuch Double-Time Lag Model Solution ...... 211 7.4 Fluid Boiling ...... 214 7.5 Homogeneous Two-Phase Flow ...... 217 7.6 CECE Data and Analysis ...... 221
Chapter 8 Summary and Future Work...... 236
8.1 Summary ...... 236 8.2 Future Work ...... 240
Appendix A Exponential Coefficients from Equation 4.38 ...... 242
Appendix B Example Hilbert Transform Problem ...... 244
Appendix C MATLAB Concentrated Combustion Stability Code ...... 246
Appendix D MATLAB Chug Stability Code ...... 249
REFERENCES ...... 266
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LIST OF FIGURES
Figure 1.1: Cartoon of a Chamber Pressure Measurement Spectrum ...... 6
Figure 1.2: Stability Plot showing a Stable Operating Point and Neutral Stability Curves .... 7
Figure 2.1: Characteristic Velocity Efficiency from Project Thumper35 ...... 18
Figure 2.2: Chart of Throttling Techniques from Project MX-79431 ...... 20
Figure 2.3: Chug Stability Limits of Three Injector Configurations37 a) Low-Pressure- Drop Inj. b) Middle-Pressure-Drop Inj. c) High-Pressure-Drop Inj...... 21
Figure 2.4: Hydraulic Characteristics with Throttling of a Liquid Oxygen Shear Coaxial Injector37 ...... 22
Figure 2.5: SSME Low Power Level Chamber Pressure45, 46 ...... 27
Figure 2.6: CECE shown at Multiple Power Levels49 ...... 29
Figure 2.7: CECE at 30% Power Level Showing Ice Formation47, 48 ...... 29
Figure 2.8: Triplet-Element Dual-Manifold Injector53-55 a) Hardware Photo b) Schematic Diagram ...... 32
Figure 2.9: Dual-Manifold Injection Flow System Schematic53-55 ...... 33
Figure 2.10: Dual-Manifold Flow Control Schemes56-59 a) Parallel Scheme b) Series Scheme ...... 36
Figure 2.11: Dual-Manifold Throttling Performance with Series Valve Configuration58 ...... 36
Figure 2.12: XLR-129 Dual-Manifold Preburner Config.62-73 a) Complete Injector b) Close-up of Oxidizer Dual-Manifold Configuration ...... 38
Figure 2.13: XLR-129 Dual-Inlet Swirl Coax Oxidizer Element62-73 ...... 38
Figure 2.14: HIPERTHIN Platelet Dual-Manifold Injector Design74 ...... 40
Figure 2.15: System Pressures vs. Fuel Flow Rate with a Constant Secondary Mixture Ratio83 ...... 45
Figure 2.16: System Pressures vs. Fuel Flow Rate with a Constant Secondary Oxidizer Pressure83...... 45
Figure 2.17: Advanced Maneuvering Propulsion Technology Advanced Development Engine89-94 ...... 48
Figure 2.18: Pulse-Width Modulation Throttling Approaches97 ...... 51
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Figure 2.19: Pulsing Performance Comparisons99 a) Comparison of Steady and Pulsing Performance b) Steady Performance c) Pulsing Performance at 150 msec Pulse Width ...... 52
Figure 2.20: Dual-Mode Throttling Performance99 ...... 53
Figure 2.21: Reaction Motors, Inc. Restrictor Device100 ...... 55
Figure 2.22: Triplet Impinging-Jet Variable Area107 ...... 61
Figure 2.23: Swirl-Cup Variable Area107 ...... 62
Figure 2.24: Theoretical Specific Impulse for Triplet Impinging-Jet Variable Area Injector107 ...... 62
Figure 2.25: LMDE Nominal Duty Cycle29, 86, 108-111 ...... 64
Figure 2.26: LMDE Engine Layout108, 109 ...... 64
Figure 2.27: LMDE Engine Specific Impulse Prior to Throat Erosion108 ...... 66
Figure 2.28: Gaseous Propellant Variable Area Injector Engine Schematic116 ...... 68
Figure 2.29: Pintle Injector Operation Illustration121-123 ...... 69
Figure 3.1: Cartoon Describing Time Lag ...... 83
Figure 3.2: Cartoon Describing Interaction Index ...... 84
Figure 4.1: Schematic of a Manifold for Admittance Estimate ...... 145
Figure 4.2: Elemental Volume for Compliance Estimate ...... 146
Figure 4.3: Schematic of a Manifold and Injector Orifice for Admittance Estimate ...... 148
Figure 4.4: Lumped Element for Inertance Estimate ...... 151
Figure 5.1: Autospectrum of the Component Gas Generator Chamber Pressure Measurement ...... 166
Figure 5.2: Engine Hot Gas Property Distribution ...... 167
Figure 5.3: Engine Cold Gas Property Distribution ...... 168
Figure 5.4: Property Distribution in FEM ...... 169
Figure 5.5: 1L Acoustic Mode (504 Hz) ...... 169
Figure 5.6: Autocorrelation, Envelope, and Exponential Fit of 2nd Acoustic Mode ...... 172
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Figure 5.7: Autocorrelation, Envelope, and Exponential Fit of 5th Acoustic Mode ...... 173
Figure 5.8: Frequency Dependent Damping ...... 174
Figure 6.1: Chug and Concentrated Combustion Model Schematics ...... 177
Figure 6.2: Models Collapsed for Verification ...... 178
Figure 6.3: Legend for Figure 6.4 to Figure 6.7 ...... 181
Figure 6.4: Chamber Response (Oxidizer Pressure Drop Variation) ...... 182
Figure 6.5: Injector Response (Oxidizer Pressure Drop Variation) ...... 183
Figure 6.6: Burning Response (Oxidizer Pressure Drop Variation) ...... 183
Figure 6.7: Open-Loop Transfer Function (Oxidizer Pressure Drop Variation) ...... 184
Figure 6.8: Legend for Figure 6.9 ...... 185
Figure 6.9: Open-Loop Transfer Function (Injector Boundary Condition Variation) ...... 186
Figure 6.10: Comparison to Double-Time Lag Model ...... 187
Figure 6.11: Bode Plot for Comparison to Marginal Test Data ...... 189
Figure 7.1: GUI Display for Single-Time Lag Model Example ...... 207
Figure 7.2: Nyquist Diagram for Single-Time Lag Example ...... 208
Figure 7.3: Pressure Drop Stability Plot for Single-Time Lag Example ...... 209
Figure 7.4: Parametric Space Curve for Single-Time Lag Example ...... 210
Figure 7.5: Frequency Variation for Single-Time Lag Example ...... 210
Figure 7.6: Nyquist Diagram for Double-Time Lag Example ...... 211
Figure 7.7: Pressure Drop Stability Plot for Double-Time Lag Example ...... 212
Figure 7.8: Parametric Space Curve for Double-Time Lag Example ...... 213
Figure 7.9: Frequency Variation for Double-Time Lag Example ...... 213
Figure 7.10: 1964 RL10 Injector with Window into Oxidizer Dome183 ...... 214
Figure 7.11: Close-up of Window into Oxidizer Dome183 ...... 215
Figure 7.12: Boiling shown through the Window in the Oxidizer Dome during Chug183 ...... 216
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Figure 7.13: Helium Gas - Liquid Oxygen Mixture in Window of Oxidizer Manifold183 ...... 218
Figure 7.14: Liquid Oxygen - Helium Gas Mixture Sound Speed ...... 220
Figure 7.15: Contour Plot of Chug Data showing the Stable Test Point Analyzed ...... 223
Figure 7.16: Nyquist Diagram for the Stable Test Point ...... 224
Figure 7.17: Pressure Drop Stability Plot for Stable Test Point ...... 225
Figure 7.18: Contour Plot of Chug Data showing the Unstable Test Point Analyzed ...... 227
Figure 7.19: Pressure Drop Stability Plot for Unstable Test Point ...... 227
Figure 7.20: Frequency Plot for Unstable Test Point ...... 228
Figure 7.21: Neutral Stability Condition with Vapor Oxidizer at 0.44% ...... 229
Figure 7.22: Scatter Plot of Data showing the Marginally Unstable Test Point during Helium Injection ...... 230
Figure 7.23: Nyquist Diagram for the Marginally Unstable Test Point during Helium Injection ...... 231
Figure 7.24: Pressure Drop Stability Plot for the Marginally Unstable Test Point during Helium Injection ...... 231
Figure 7.25: Scatter Plot of Data showing the Stable Test Point during Helium Injection .... 232
Figure 7.26: Pressure Drop Stability Plot for the Stable Test Point during Helium Injection ...... 232
Figure 7.27: Stability Map for Unstable Test Point with and without Feed System Effects .. 234
Figure B.1: Example Showing a Signal and its Envelope ...... 244
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LIST OF TABLES
Table 2.1: Summary of Information from Reviewed Projects, Research Tasks, and Investigations ...... 14
Table 5.1: Test Property Distribution ...... 170
Table 5.2: Frequency Dependent Damping ...... 174
Table 6.1: Input Parameters for Examples in this Chapter Except where Noted ...... 179
Table 6.2: Additional Parameters for Verification Example ...... 179
Table 6.3: Additional Parameters for Parametric Example ...... 181
Table 6.4: Additional Parameters in Modified Crocco Model Comparison Example ...... 185
Table 6.5: Double-Time Lag Model Input Parameters ...... 186
Table 6.6: Additional Test Case Example Parameters ...... 188
Table 7.1: Model Inputs for Test Cases ...... 223
Table D.1: Excel Input File Format ...... 249
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NOMENCLATURE
Symbols
A amplitude function in Equation 5.10
A coefficient in Equation 7.48
2 A cross-sectional area ⎣⎡in ⎦⎤
A empirical constant in Equation 2.2 − [ ]
A state matrix
A nozzle exit area ⎡in2 ⎤ e ⎣ ⎦
A feedline cross-sectional area ⎡in2 ⎤ f ⎣ ⎦
A orifice cross-sectional area ⎡in2 ⎤ o ⎣ ⎦
A nozzle throat area ⎡in2 ⎤ t ⎣ ⎦
⎡ in3 ⎤ Aˆ complex coefficient in Equation 4.43 ⎢ ⎥ lb s ⎣⎢ f ⎦⎥
a example characteristic equation coefficient in Equation 3.95
a oxidizer exponential empirical coef. or generic exponential empirical coef.
a real coefficient in Equation A.1 − [ ]
B coefficient in Equation 7.48
B empirical constant in Equation 2.2 − [ ]
B nozzle boundary condition ratio relationship in Equation 3.88 − [ ]
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⎡ in3 ⎤ Bˆ complex coefficient in Equation 4.43 ⎢ ⎥ ⎣⎢lbf s ⎦⎥ b converging nozzle geometric parameter for exit flowrate − [ ] b example characteristic equation coefficient in Equation 3.95 b fuel exponential empirical coefficient b real coefficient in Equation A.1 − [ ]
C coefficient in Equation 7.48
C compliance ⎡⎤lb in2 lb ⎣⎦mf
C generic pressure coefficient ⎡lb in2 ⎤ ⎣ f ⎦
C open-loop transfer function
C air chamber compliance ⎡lb in2 lb ⎤ A ⎣ mf⎦
C C coefficients in Equation 4.39 ⎡lb in2 ⎤ A , B ⎣ f ⎦
C discharge coefficient − d [ ]
C manifold compliance ⎡lb in2 lb ⎤ m ⎣ mf⎦
C C coefficients in Equation 4.42 ⎡lb in3 ⎤ 1 , 2 ⎣ m ⎦
C C coefficients in Equation 4.43 ⎡lb in2 ⎤ 1 , 2 ⎣ f ⎦
C3 C4 unknown coefficients referred to for Equation 4.43[in s] , c damping coefficient ⎡lb s in⎤ ⎣ f ⎦ c example characteristic equation coefficient in Equation 3.95 c sound speed in s [ ]
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critical damping coefficient ⎡ ⎤ cc ⎣lbf s in⎦
cph phase speed [in s]
ct nozzle throat sound speed [in s] c∗ c-star [in s]
D diameter in [ ]
D feedline diameter in f [ ]
Dj jet diameter in Equation 2.2[in]
Do orifice diameter [in]
Ea process accumulation level [rate⋅ s]
force ⎡⎤ F ⎣⎦lbf
⎡ lb s ⎤ F fuel engine gain in Equation 7.5 f ⎢ 2 ⎥ ⎣lbm in ⎦
F total thrust ⎡⎤lb T ⎣⎦f
F fuel engine parameter in Equation 3.107 − [ ] f frequency [Hz] f friction factor [−] f instantaneous rate of the relevant processes [rate]
⎡lb⋅ in2 ⎤ G admittance (mass flow rate-to-pressure ratio) ⎢ m ⎥ lb⋅ s ⎣⎢ f ⎦⎥
xv
2 2 ⎡ EUin ⎤ ⎡⎤in G spectral density function gain in autocorrelation ⎢ ⎥ e.g. ⎢⎥ ⎣ Hz ⎦ , ⎣⎦Hz
⎡ 2 ⎤ lbm ⋅ in Gi injector admittance ⎢ ⎥ ⎣⎢ lbf ⋅ s ⎦⎥
G normalized admittance − [ ]