Controls of Aero Gas Turbine Engines

National Level Workshop on Recent
Trends in Aerospace Propulsion
Controls of Aero Gas Turbine
Engines
16 February 2012
Rohan M Ganapathy
Undergraduate, Dept of Aeronautical
Engineering,
Hindusthan College of Engineering and
Technology, Coimbatore

Lecture flow
• Controls
• Requirements
• Mechanical
• FADEC
• Integrated propulsion
• Continued challenges
srb-hcet-001

Gas Turbine Components
• The basic gas turbine engine comprises of
a number of main components
• Intake casing
• Compressor
• Combustion chamber
• Turbine
• Jet pipe
• Exhaust nozzle.
• srb-hcet-002

Fuel Supply & Engine Thrust
• The fuel supply input into the engine in
conjunction with the starting and ignition
systems sets the gas turbine cycle into
operation resulting in
 Rotational speeds of engine with
consequent production of thrust.
 In turn, this thrust helps in forward
movement of the aircraft when the
engine is installed into it.

Control Variable : Fuel Flow
• Control of fuel flow into main combustion
chamber can be done in response to a
number of parameters
• Engine rotational speed bears a direct
relationship with the turbine entry
temperature and this is one of the
parameters used to control fuel flow to the
engine

Power Lever Angle – Rotational
Speed

PLA-Rotational Speed
block diagram
• Outer and Inner loops
• PLA demand creates N demand
• N demand creates valve position demand
• Valve position causes fuel flow input
• Engine rotational speed results as output
• Two feedback loops based on valve
position and engine rotational speed
sensor fed into loop

Requirements of Fuel Control
• The control of the gas turbine rotational speed
is achieved through modulation of the fuel
flow by the pilot through the power lever angle
(PLA) operation.
• For the transient condition such as
acceleration and deceleration, this quantum of
fuel flow would be different.

Requirements of Fuel Control-
[contd]
• Further the fuel flow is to be made a
function of altitude and forward speed
depending upon the flight envelope
prescribed for the engine and its
corresponding aircraft installation.
• Therefore, there is a basic need to control
this variable called the fuel flow and this
needs to be done automatically in order to
minimize pilot work load.

Phases of engine operation
• Starting
• Ground idling
• Acceleration , Deceleration
• Slams , Chops
• Shutdown
• Cruising
• Flight idling
• Max dry , Afterburner/Reheat

Typical Governor Characteristics

GT Control Variables
• To meet increasing demands for obtaining
precise performance of engine the number
of control variables has increased from
simple fuel control to multi controls.
• Variabilility in inlet guide vanes, exhaust
nozzle, stator vanes, bypass bleed, reheat
fuel flow, etc., are typical control variables
that have evolved over the decades.

Simplified fuel systems for turbo-propeller
and turbo-jet engines – RR Manual

Mechanical Control System
Configuration
• Mechanical elements added to cater for above
control variables
• 3-Dimensional cams, spool sleeve combinations, air
potentiometer networks, servo devices, moving
pivots and beam governors, etc all added to make
the fuel control system as a very complicated
mechanical computer

Typical 2 spool requirements
• Complete engine control considering all
the control variables
• Translation of fuel flow, biased w.r.t.
engine intake temperature and engine
intake temperature so as to control LP
spool / HP spool speed
• All speed governing of spool speeds
biased w.r.t. engine intake temperature

(contd)
• Rising idle speed characteristics to
prevent flameout
• Prescription of Ndot control
• Scheduling Exhaust nozzle area,
Afterburner fuel flow, Inlet Guide Vanes
and Stator vanes as a functions of PLA
• Ensuring engine safety by limiting values
of Spool speeds, TET, JPT, Pressure
Ratio, etc.

(contd)
• Ensuring performance of engine control
systems under extremes of environments
in relation to Temperature, Vibration, EMI,
Nuclear exposure, Dust, Fire, etc
• Ensuring data transfer between
engine/airframe and airframe/engine
• Ensuring high reliability levels of system
so that MTBF is quite high
• Ensuring system architecture is fault
tolerant

Evolution of [FADEC] system
• Basic hydromechanical elements/devices
enjoyed high reliability
• Initial Trimming controls through
electrical/electronic means deployed in the
nature of limited authority trim on the basic
system
• Early engines like Spey, Pegasus, RB211
• These trimming systems offered redundancy in
the sense that adequate safety was assured
even after failures of the main control function

FADEC System (contd)
• With suitable packaging of electronic
components/circuits supervisory sort of
electronic control system was configured
• This system improved performance when it was
operated and its failure would not hazard
engine/airframe mission
• The disadvantage was that the complicated
heavy hydromechanical system had to be
carried and the supervisory authority system
could not achieve the full performance potential

• The Analog computer and controller [ used in the
Olympus 593 of the Concorde] had its attendant
problems with environment effects and
temperature changes
• The digital computer outpaced the analog
computer in terms of capability to store huge
amounts of data, functional insensitiveness to
environmental effects and temperature

RHMPDV
IHPP
DECU
FSP
MECU
RHFCU
Compressor VG
Main Burners
Reheat
burners
Nozzle actuators
Fuel in Manual Fuel Control Linkage
Engine & System Feed back
PLA
Demonstrator Engine with Digital Controller

• The digital computer provided the basic ability
and flexibility for quick changes especially
during development through the embedded
software changes
• With advances in electronic
components/circuits and their improvement
in reliability coupled with packaging heralded
the beginning of the full authority digital
engine control[ FADEC]

• With need to build in defined control laws,
redundancy management, mission
requirements, precise engine operation with
optimum fuel burn, health monitoring and
diagnostics, the FADEC system is a fairly
standard system in gas turbine engines, Civil
and Military [ Pegasus, M88, Trent 1000,etc]
• A fully integrated flight propulsion control
system is available in many aircraft/engine
flight systems today [ LCA]

CVG
CONTROL
MAIN
FUEL
CONTROL
REHEAT
FUEL
CONTROL
NOZZLE
CONTROL
DECU
LANE 1
DECU
LANE 2
ALTERNATORIGNITION
BOX
ENGINE & FEED
BACK SENSORS
ENGINE & FEED
BACK SENSORS
28 V
AIRCARFT
BATTERYMISSION
COMPUTER
1553 B
BUS
1553 B
BUS
PLA EFI COCKPIT CONTROLS
ENGINE
AIRFRAME
Demonstrator Engine
Twin Lane Digital Controller Block Diagram

 Modeling
 System Identification
 Linear design
 Non Linear – Non Real Time Simulation
 Hardware in the Loop Simulation
 Engine Test
Control System Evolution

ENGINE / SYSTEM
SIMULATION
SYSTEM
IDENTIFICATION
ARX / IT / BJ / CO
Input Output
ENGINE TRANSFER FUNCTION
(Estimated)
ENGINE / SYSTEM
TEST DATA
SYSTEM
IDENTIFICATION
ARX / IT / BJ / CO
Input Output
ENGINE TRANSFER FUNCTION
(Evaluated)
Validation
R(s)
C(s)
= G(s)
System Identification

 Classical design technique.
 Piecewise linearisation at various speeds (80%, 85%, 90%, 94% &
98% NH) and flight conditions:
T1
K
P1
psia
Alt
Km
MNo Condition
240 3.715 11 0.42 ISA+15
288 14.700 0 0.00 ISA
315 12.676 6 0.98 ISA+15
350 13.952 11 1.59 ISA+15
380 28.302 3 1.30 ISA+15
Linear Design

 Each of the following control loop is designed to have
desired response:
• Metering Valve position loop
• NHdot acceleration
• NL speed control
• VG control
• Nozzle control
• Reheat fuel control
• Backup fuel override schedule control
 In addition following control loops are designed at
appropriate conditions:
• NH at idle
• Limiter control loops – NH , P3, P3/P1, T6
Linear Design

Response of NL for Step input in PLA
0 5 10 15 20 25 30
0
0.2
0.4
0.6
0.8
1
1.2
Response of NL for Step input in PLA
Time (sec)
NL

0 5 10 15 20 25 30
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Time (sec)
NH
0 5 10 15 20 25 30
-1
0
1
2
3
4
5
6
7
Time (sec)
P3
0 5 10 15 20 25 30
-2
0
2
4
6
8
10
12
14
16
Time (sec)
T4
0 5 10 15 20 25 30
-2
0
2
4
6
8
10
12
Time (sec)
T6
Response of Engine Parameters for Step Input in PLA
T4
NH
T6
P3

• All the models of the Engine and control system
subsystems
• Controller gains and lead compensation parameters
obtained in the Linear design at various speeds and
flight conditions are scheduled.
• Integrated simulation study carried out for:
1. Small inputs & steady state performance study.
2. Large input slam/chop performance study
3. Study the efficiency of control logics incorporated
4. Assurance of controller stability and transient
capability at all operating points
Non Linear – Non Real time Integrated Simulation

Engine Speed response for PLA slam (Idle to Max dry)

Test Description Standard
Temperature testing – Hot MIL-E-5007 E
Temperature testing – Cold MIL-E-5007 E
Room temperature endurance MIL-E-5007 E
Pressure testing fatigue proof and ultimate pressure test ACJ-E-640 & JAR-E-640
Low lubricity fuel test MIL-E-5007 E
Humidity MIL-STD-810D
Fungus MIL-STD-810D
Salt mist MIL-STD-810D
Sand and dust MIL-STD-810D
Contaminated fuel MIL-E-5007 E
Icing MIL-STD-810D
Explosion proof / explosive atmosphere MIL-STD-810D
Sustained acceleration test MIL-STD-810D
Functional shock MIL-STD-810D
Vibration test MIL-STD-810D
Fire test MIL-E-5007 E
Simulated operational test MIL-E-5007 E
QUALIFICATION TESTS

Intelligent Gas Turbine
Engines
• Intelligent Propulsion Systems lay greater
emphasis on aircraft safety, enhanced
performance and affordability, need to reduce
the environmental impact of aircrafts
• This calls for the increased efficiencies of
components through active control, advanced
diagnostics and prognostics integrated with
intelligent engine control and distributed control
with smart sensors and actuators

Engines[contd]
• Actively Controlled Components will mitigate
challenges related inlet flow distortion and
separation and noise; compressor aerodynamic
losses and surge and stall; combustion
instabilities, uneven temperature distribution,
and pollution emission; turbine aerodynamic
losses and leakages, high cycle fatigue, and
limited airfoil durability, jet noise, emission and
signature

Engines[contd]
• Intelligent Control and Health Monitoring with
advanced model-based control architecture
overcomes the limitations of state-of-the-art engine
control and provides the potential of virtual sensors
• “Tracking filters” are used to adapt the control
parameters to actual conditions and to individual
engines. Currently, health monitoring units are
stand-alone monitoring units. Integration of both
control and monitoring functions is possible
• Adaptive models open up the possibility of adapting the
control logic to maintain desired performance in the
presence of engine degradation

Engines[contd]
• Distributed Engine Control using high temperature
electronics and open systems communications will
reverse the growing trend of increasing ratio of
control system weight to engine weight and also will
be a major factor in
• Challenges for implementation include need for high
temperature electronics (located on or close to the
sensing element), development of simple, robust
communications (simplifying and reducing the wiring
harness), and power supply for the on-board
distributed electronics

Engines[contd]
• Sensors mainly require higher operational
temperatures. Some progress can be made by
changing the packaging and/or design of the current
sensors, but sensor for locations close to the engine
combustion chamber or afterburner do not exist.
There is also a need for smart sensors, which would
enable future distributed control architecture.
• Actuator requirements are addressed for three
common actuation functions, namely: Micro flow
manipulation; Large-scale flow switching; and
Mechanical manipulation.

I G T Engines-Key Enabling
Technologies
• Increased efficiencies of components through
active control
• Increased overall engine gas-path
performance and extended “on wing” life of
the engine through
• Model-based control and health monitoring
• Reduced weight ratio of control system to
engine through distributed control with smart
sensors.

Technologies[contd]
• Active Component Control that can help to
meet future engine requirements by an
active improvement of the component
characteristics.
• The concept is based on an intelligent
control logic, which senses actual
operating conditions and reacts with
adequate actuator action.

Technologies[contd]
• Active control addresses the design
constraints imposed by unsteady
phenomena like
• Inlet distortion, compressor surge,
combustion instability, flow separations,
vibration and noise, which only occur
during exceptional operating conditions.

Technologies[contd]
• Inlet: Active Inlet Control, Active Noise
Suppression, Active Noise Cancellation
• Compressor: Active Surge Control, Active
Flow Control, Active Clearance Control,
Active Vibration Control
• Combustor: Active Combustion, Instability
Control
• Turbine: Active Clearance Control, Cooling
Air Control, Active Flow Control

Technologies[contd]
• Nozzle: Active Noise Control, Adaptive
Nozzles,
• Thrust Vectoring, Active Core Exhaust
Control,
• Afterburner Stability Control
• Significant efforts in research and
development remain to implement these

Technologies[contd]
• Intelligent Control and Health Monitoring
concepts using advanced model-based
Multi Input Multi Output (MIMO) control
architecture, where all available control
actuators are manipulated in a coordinated
manner.
• Can provide outputs for which sensors are
not available, i.e. virtual sensors.

Technologies[contd]
• Adaptive models adapt the control logic to
maintain desired performance in the presence of
engine degradation or accommodating any
faults in a way such as to maintain optimal
performance
• The Model Predictive Control (MPC) is an
emerging approach, which solves a constrained
optimization problem online to obtain the “best”
control action, based on a tracked engine model,
constraints, and the desired optimization
objective.

Technologies[contd]
• The implementation of distributed engine control
is not without significant challenges, including
needs for high temperature electronics,
development of simple, robust communications,
and power supply for the on-board electronics
• A need for on-board electronics located on or
close to the sensing element or the actuator,
such that network communications can be
enabled and the wiring harness required for
communications between sensors and actuators
and the engine controller can be substantially
reduced.

Technologies[contd]
• The standard GTE Gas Path Sensors are
designed and packaged according to the
specifications driven by the certification reqmts.
• Written by the GTE manufacturers following
guidelines of MIL-STD 810F for tailoring
sensors’s environmental design and test limits to
the conditions that the specific sensor will
experience throughout its service life
• Present sensors with integrated electronics are
limited to environment conditions within –65 C to
+115 C.

Technologies[contd]
• Micro-Electro Mechanical Systems (MEMS) is a
good candidate to address the need for high-
temperature operation and for new types of
sensors, including smart sensor capabilities.
Silicon-on-Insulator (SOI) provides some
advantages (with potential operational
temperatures of 300ºC); the semiconductor SiC
(up to 500 C) and the ceramic material SiCN (up
to 1700 C) are explored for even higher
temperatures.

Technologies[contd]
• Generic actuator requirements for three
common actuation functions :
• Flow manipulation (of the boundary layer by
either mechanical effects or aerodynamic means
with blowing or sucking air);
• Large scale flow switching (valves with
applications to stall/surge control, bleed flows,
cooling flows,other); and
• Mechanical manipulation (intakes, variable guide
vanes and nozzles).

Technologies[contd]
• Emerging technologies for actuation systems
would include:
• Electroactive materials, including piezoelectric
ceramics and Electro Active Polymers (EAPs)
• Shape memory materials
• Magnetic strained materials (providing
magnetostrictive effects)
• Magnetic Shape Memory (MSM) or
Ferromagnetic Shape Memory (FSM) materials
and Microsystems, micromachines and MEMS

Controls of Aero Gas Turbine Engines

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