Fundamentals of Engine Control
Fundamentals of Engine Control
Fundamentals of Engine Control
Dr. Sanjay Garg Chief, Controls and Dynamics Branch Ph: (216) 433-2685 FAX: (216) 433-8990 email: sanjay.garg@nasa.gov
http://www.lerc.nasa.gov/WWW/cdtb
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Outline
The Engine Control Problem Safety and Operational Limits Historical Engine Control Perspective Modeling and Simulation Basic Control Architecture Advanced Concepts
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N1
Dual Shaft High Pressure and Low Pressure Two flow paths bypass and core Most of the thrust generated through the bypass flow Core compressed air mixed with fuel and ignited in the Combustor Two turbines extract energy from the hot air to drive the compressors Glenn Research Center
Controls and Dynamics Branch
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Thrust (T) cannot be measured, use Fuel Flow WF to Control shaft speed N (or other measured variable that correlates with Thrust Pump fuel T = F(N) Accessories flow from
fuel tank
Control Throttle
Pilots power request Compute desired fuel flow Meter the computed fuel flow Inject fuel flow into combustor
Sensor
Measure produced power
Valve / Actuator
Determine operating condition
Fuel nozzle
No
Power desired?
Yes
Control Logic
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Foreign objects Birds, Ice, stones Air mass flow ~2 tonne/sec 8mm+ Shaft movement 2.8m Diameter 50 000g centrifugal acceleration >100g casing vibration to beyond 20kHz 1100+C Metal temperatures 10 000rpm 0.75m diameter
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Operational Limits
N2 LPC - Low Pressure Compressor HPC - High Pressure Compressor HPT - High Pressure Turbine LPT - Low Pressure Turbine N1 - Fan Speed N2 - Core Speed
N1
Structural Limits:
Maximum Fan and Core Speeds N1, N2 Maximum Turbine Blade Temperature Safety Limits: Adequate Stall Margin Compressor and Fan Lean Burner Blowout minimum fuel Operational Limit: Maximum Turbine Inlet Temperature long life
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Idle power
Max. power
GE I-A (1942)
Fuel flow is the only controlled variable. - Hydro-mechanical governor. - Minimum-flow stop to prevent flame-out. - Maximum-flow schedule to prevent over-temperature Stall protection implemented by pilot following cue cards for throttle movement limitations
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Engine control logic is developed using an engine model to provide guaranteed performance (minimum thrust for a throttle setting) throughout the life of the engine - FAA regulations provide a minimum rise time and maximum settling time for thrust from idle to max throttle command
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Engine Modeling
Steady State performance obtained from cycle calculations derived from component maps obtained through detailed component modeling and component tests Corrected parameter techniques used to reduce the number of points that need to be evaluated to estimate engine performance throughout the operating envelope Dynamics modeled through inertia (the rotor speeds), combustion delays, heat soak and sink modeling etc. Computationally intensive process since it is important to maintain mass/momentum/energy balance through each component Detailed thermo-dynamic cycle decks developed and parameters adjusted to match engine test results Simplified models generated to develop and evaluate control design Glenn Research Center
Controls and Dynamics Branch
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Bypass Nozzle
VBV VSV Fuel LPT Core Nozzle
Aero-Thermodynamics
Compressor/Fan Maps: PR, Corr. Flow & Efficiency as functions of Shaft Speed & R-line Turbines: Corr. Flow and Efficiency as functions of Shaft Speed & PR
Dynamics
Two physical states: fan speed, core speed Actuator/sensor dynamics: first-order lags Combustion delay
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blowout
Limits are implemented by limiting fuel flow based on rotor speed Maximum fuel limit protects against surge/stall, over-temp, overspeed and over-pressure Minimum fuel limit protects against combustor blowout Actual limit values are generated through simulation and analytical studies
R N2
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P2 T2
P25 T25
Ps3 T3 WF36
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Thrust command
Acceleration/ Deceleration schedule The various control gains K are determined using linear engine models and regulator linear control theory Fan speed
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Math Model
Prob Form
Control Logic
Eval
Good to Go
Yes
Spec Met? No
Hardware Testing
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Nf limit
20 15 10 5 0 10 20
50
demand
10
20
0 x 10
4
10
20
Wf/Ps30 (pph/psi)
60 40 20 0 0 10 20
Wf (pph)
50 40 30 20 0 10
20
9500
Nc (rpm) T48 (R)
Ps30 (psia)
Nc limit
2000 1500
T48 limit
Ps30 hi limit
10 20 Time (s)
1000
10 20 Time (s)
10 20 Time (s)
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Fan SM
10
15
20
25
PRFan
2000
3000
4000
Fan
40 30
LPC SM
20 6% margin 10
PRLPC
LPC
50 40 25 20 stall line 15% margin chop burst
HPC SM
30 20 10 0 5 15% margin
PRHPC
25
15 10 5
10 15 Time (s)
20
100
150
200
HPC
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Actuator Positions
Sensor Sensor Estimates Validation & Fault Detection Sensor Measurements On Board
Ground Level
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Thrust
Degradationinduced shift
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Adds the following logic elements to existing FADEC: A model of the nominal throttle to desired thrust response An estimator for engine thrust based on available measurements A modifier to the Fan Speed Command based on the error between desired and estimated thrust - Since the modifier appears prior to the limit logic, the operational safety and life remains unchanged
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EPDMC Evaluation
Thrust response for Typical Mission
With EPDMC Throttle to thrust response is maintained no uncommanded thrust asymmetry Without EPDMC
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Detect stall precursive signals from pressure measurements. Develop high frequency actuators and injector designs. Actively stabilize rotating stall using high velocity air injection with robust control.
Injector
Rotor scoop
Intake
Demonstrated significant performance improvement with an advanced high speed compressor in a compressor rig with simulated recirculating flow
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Summary
Provided an overview and historical perspective of engine control design The control design enables smooth and safe operation of the engine from one steady-state to another through implementation of various limits There are tremendous opportunities to improve and revolutionize aircraft engine performance through proper use of advanced control technologies
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References
H. Austin Spang III and Harold Brown, Control of Jet Engines, Control Engineering Practice, Vo. 7, 1999, pp. 1043-1059 Jonathan A. DeCastro, Jonathan S. Litt, and Dean K. Frederick, A Modular Aero-Propulsion System Simulation of a Large Commercial Aircraft Engine, NASA TM 2008-215303. Jeffrey Csank, Ryan D. May, Jonathan S. Litt, and Ten-Huei Guo, Control Design for a Generic Commercial Aircraft Engine, NASA TM-2010-216811 Sanjay Garg, Propulsion Controls and Diagnostics Research in Support of NASA Aeronautics and Exploration Mission Programs, NASA TM 2011-216939.
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