ENGINE CONTROLS - Unisalento.it

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Università del Salento - FACOLTAFACOLTA’’ DI INGEGNERIA INDUSTRIALE DI INGEGNERIA INDUSTRIALE –– BrindisiBrindisiDipartimento di Ingegneria dell’Innovazione - Lecce

CORSO DI LAUREA SPECIALISTICA IN CORSO DI LAUREA SPECIALISTICA IN IngegneriaIngegneria AerospazialeAerospaziale

PROPULSIONE AEROSPAZIALE IPROPULSIONE AEROSPAZIALE I

ENGINE CONTROLSENGINE CONTROLSApp. O AIAA AIRCRAFT ENGINE DESIGN

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LA DISPENSA ELA DISPENSA E’’ DISPONIBILE SU DISPONIBILE SU http://www.ingindustriale.unisalento.it/didattica/http://www.ingindustriale.unisalento.it/didattica/

Prof. Ing. A. [email protected]

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potential of unstable behavior fan or compressor surge/stall

primary functions of the engine control maintain stable thrust

smooth repeatable performance during transient

stable airflow, pressure, temperature and rotor speed

avoid stall/surge and significant T, p or speed variations

secondary functions startup and shutdown

bleed and power extraction

inlet anti-icing

hot-gas protection

tip clearance control

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difficulty in direct measuring mass flow

thrust must be inferred to relate engine thrust to the

engine operating line on a fan map

mechanical rotor speeds are easily measured the fan rotor speed N1,

corrected for inlet T and p, correlates very well to engine mass flow

a differential pressure measurement correlates very well with fluid velocities

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fan rotor speed N1 and engine pressure ratio EPR correlate to the two most significant variables in the equation of the uninstalled thrust

lines of EPR are roughly parallel to the fan stall line - stability

lines of Tt4 relate to fan inlet corrected airflow and fan pressure ratio –overtemperature protection

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periodically, the engine controls would have to be trimmed for loss of performance trimless control modes

with trimless control modes thrust regulation will be maintained as the engine degrades, but at the expense of increase turbine inlet temperature

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min fan pressure ratio, below which combustion cannot occur

min inlet airflow to sustain continuous operation

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CONTROL LOGIC AND PROCESSING

output command are sent on to the actuators

DIGITAL ELECTRONIC CONTROLLER PLA – power level position – throttle position

coupled with inlet T and p (altitude and Mach n.)

other inputs

OUTPUT – thrust requested – required fan rotor speed and engine pressure ratio

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open-loop and closed-loop control elements

OPEN-LOOP variable geometry stator vanes

compressor bleed flow

CLOSED LOOP fuel flow

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BASIC DYNAMIC

polar moment of inertia of each rotor – dominant effect

volume of the afterburner tailpipe

there is a weak coupling between the tailpipe pressure and fan rotor speed the two closed-loop control

functions can be viewed as independent

the main engine fuel flow will control fan rotor speed

the exhaust nozzle area will control engine pressure ratio

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In control theory, the root locus is the locus of the poles and zeros of a transfer function as the system gain K is varied on some interval. The root locus is a useful tool for analyzing single input single output (SISO) linear dynamic systems. A system is stable if all of its poles are in the left-hand side of the s-plane (for continuous systems) or inside the unit circle of the z-plane (for discrete systems).

In complex analysis, a pole of a meromorphic function is a certain type of singularity that behaves like the singularity 1/zn at z = 0. This means that, in particular, a pole of the function f(z) is a point z = a such that f(z) approaches infinity uniformly as z approaches a.

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rotor inertia determines the dynamic response for a large diameter engine acceleration may take 10 s

for a turbojet 1-2 s

to accelerate the engine quickly, the fuel flow should be raised quickly raising fuel flow too rapidly could cause an engine overtemperature or

stall

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rapid acceleration require the engine to operate transiently very closed to stall line the variable geometry vanes will be positioned to follow a prescribed

schedule

high frequency aerodynamic instabilities – blade flutter

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ADVANCED CONTROL LOGIC

to recapture the loss performance by actively controlling the stall margin MODEL-BASED CONTROL

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detailed non-linear simulation of the engine tracking filter to take comparison between model outputs and sensor

reading to adjust the model parameters

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CONTROL SYSTEM COMPONENTS

ELECTRICAL SUBSYSTEMS

FADEC – full authority digital electronic control redundancy requiements

FUEL DELIVERY SUBSISTEM

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ACTUATION SUBSISTEM

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A FADEC is a system consisting of a digital computer, called an Electronic Engine Control (EEC) or Electronic Control Unit (ECU), and its related accessories that control all aspects of aircraft engine performance. The term FADEC is an acronymfor either Full Authority Digital Engine Control or Full Authority Digital Electronics Control. FADECs have been produced for both piston engines and jet engines, their primary difference due to the different ways of controlling the engines.

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Function To be a true, 100%, Full Authority Digital Engine Control, there must not be any form of

manual override available. This literally places full authority to the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an Electronic Engine Control or Electronic Control Unit. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene.

FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many others. The inputs are received by the EEC and analyzed up to 70 times per second. Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are computed from this data and applied as appropriate. FADEC also controls engine starting and restarting. The FADEC's basic purpose is to provide optimum engine efficiency for a given flight condition.

FADEC not only provides for efficient engine operation, it also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.

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Safety

With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two or more, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerantengine control.

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Application To perhaps more clearly illustrate the function of a FADEC, explore a typical civilian transport aircraft

flight. The flight crew first enters the data appropriate to the day’s flight in the flight management system or FMS. The FMS takes environmental data such as temperature, wind, runway length, runway condition, cruise altitude etc. and calculates power settings for different phases of flight. For takeoff, the flight crew advances the throttle (which contains no mechanical linkage to the engine) to a takeoff detent or opts for an auto-throttle takeoff if available. The FADECs know the calculated takeoff thrust setting and apply it. The flight crew notes that they have merely sent an electronic signal to the engines, no direct linkage has been moved to open fuel flow. This procedure is the same for climb, cruise, and all phases of flight. The FADECs compute the appropriate thrust settings and apply them. During flight, small changes in operation are constantly being made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but remember, limitations can’t be exceeded. The flight crew has no means of manually overriding the FADECs, so if they make a decision the crew doesn’t like, it will have to be accepted.

FADECs today are employed by almost all current generation jet engines and increasingly in newer piston engines, on fixed-wing aircraft and helicopters.

In piston-engine powered aircraft, the system replaces both magnetos, making obsolete repetitive and costly magneto maintenance, and eliminates carburetor heat, mixture controls and engine priming. By controlling each cylinder of the engine independently for optimum fuel injection and spark timing, the need for the pilot to monitor and control mixture is eliminated. Because imprecise mixture operation can affect engine life, the FADEC has the potential to reduce operating costs and increase engine life for the average General Aviation pilot. Tests have also shown significant fuel savings potential. FADEC paid for itself in reduced operating costs.

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Advantages Better fuel efficiency Automatic engine protection against out-of-tolerance operations Safer as the multiple channel FADEC computer provides redundancy in case of failure Care-free engine handling, with guaranteed thrust settings Ability to use single engine type for wide thrust requirements by just reprogramming the FADECs Provides semi-automatic engine starting Better systems integration with engine and aircraft systems Can provide engine long-term health monitoring and diagnostics Number of external and internal parameters used in the control processes increases by one order of

magnitude Reduces the number of parameters to be monitored by flight crews Due to the high number of parameters monitored, the FADEC makes possible "Fault Tolerant Systems"

(where a system can operate within required reliability and safety limitation with certain fault configurations)

Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically).

Disadvantages Engineering processes used to design, manufacture, install and maintain the sensors which measure and

report flight and engine parameters to the control system itself Software engineering processes used in the design, implementation and testing of the software used in

these safety-critical control systems. This led to the development and use of specialized software such as SCADE.

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Electronic control unit The ECU handles the four successive operations needed for system control, repeated

several times a second: 1/. Gathering data on system operation, sent by sensors via the wiring harnesses. 2/. Filtering this data, which may experience electromagnetic interference at the computer,

and encoding the data in digital form. This operation is handled by data conditioners, which are complex electronic components.

3/. Data processing and analysis by the ECU’s digital core. Special algorithms calculate the commands to be sent to the control devices. The computer is connected to the cockpit, with which it exchanges information via a digital databus.

4/. Formatting of operating commands, and amplifying them if needed to drive the actuators and other control devices.

The ECU also features a built-in test function, and supports maintenance of the system it controls.

The ECU is a single line replaceable unit (LCU), combining performance, reliability, simplicity and low purchase cost.

To develop an ECU demands broad-based expertise, covering: A design that combines dependability and dynamic performance.

Design of boards and subassemblies (acquisition chain and digital core). Development of real-time software and complex electronic components. Integration in a demanding environment. Qualification and production engineering.

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Digital Engine Control The Full Authority Digital Engine Control, better known as a FADEC, is one of the largest ECUs on an aircraft. It is a

microprocessor-based unit. The FADEC continuously processes and analyzes key engine parameters (up to 70 times a second), to make sure the

engine operates at maximum potential. It manages the startup phase (which takes only about 40 seconds on the latest models), and then the entire operating envelope, from idle to full throttle.

Hispano-Suiza has developed three generations of FADEC systems for high-power commercial aircraft engines (in conjunction with BAE Systems). The latest member of this family is the FADEC 3, designed, produced and supported through FADEC International, a joint venture of Hispano-Suiza and BAE Systems.

The FADEC 3 is not only lighter than its predecessor, but has 10 times the computing power. This means it can incorporate new functions, especially maintenance and diagnostics, to better satisfy engine-makers’ current and future needs. The FADEC 3 uses a larger share of off-the-shelf electronic components, has fewer connectors, and more input/outputs to handle more sensors and actuators. Last but not least, it can be used on several different types of engines, based on a common core of up to 80% of the system.

Starting in the late 1980s, the FADEC 1, 2 and 2+ have been used on the CFM56 (-5 and -7), CF6-80 and GE90. The FADEC 3 has now been chosen for the GE90-115B - today’s most powerful engine at 115,000 pounds of thrust-

powerplant of the Boeing 777-300ER and 777-200LR. It is now being applied to five other engine programs :

GP7200, one of the engines selected for the Airbus A380, built by the Engine Alliance joint venture between General Electric and Pratt & Whitney.

CFM56-7B, by CFMI, an equal joint venture of General Electric and Snecma, for the Boeing 737 Next Generation family. General Electric CF6-80C2L1F to re-engine the C-5 Galaxy. Europrop International (EPI) TP400-D6 turboprop for the Airbus A400M; EPI is a joint venture of ITP,MTU Aero Engines,

Rolls-Royce and Snecma. General Electric GEnx for the Boeing 787 and the Airbus A350.

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Thrust reverser actuation system

ETRAS ® is the first electrical system of this type, enabling designers to eliminate all hydraulic circuits in this critical area of the engine.

It comprises: A computer and an electronic power amplifier, capable of driving 25 kW actuators.

Electromechanical actuators. Sensors.

Developed in partnership with Honeywell, ETRAS ® uses some of the most innovative technologies developed through the Power Optimized Aircraft (POA) european research program. The POA program aims to replace hydraulic and pneumatic equipment by electrical equipment, in order to reduce size, weight and risks and increase maintainability.

From the outset, the two partners integrated the requirements of operators, aircraft manufacturers and nacelle suppliers, to make sure the product would be mature from its service entry.

ETRAS ® was selected by Aircelle, a SAFRAN group company that is in charge of the design and production of thrust reversers for the two engines offered on the Airbus A380 super-jumbo, the Rolls-Royce Trent 902 and the Engine Alliance GP7200.

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Reduction gearboxes

Hispano-Suiza has design capability for reduction gearboxes on high-power, high-speed turbine engines. Reduction gearboxes are used on both helicopters and turboprop airplanes.

For example, Hispano-Suiza developed the reduction gearbox for the CTS 800 engine made by LHTEC (originally Rolls-Royce and Allison), intended for the Lynx helicopter, and now powering the Westland Super Lynx. Weighing in at 50 kilos, this gearbox transmits about 1,500 kW of power, lowering the engine speed from 24,000 rpm to 6,000 rpm, considered the optimum speed for this class of helicopter.

Hispano-Suiza also makes some parts of the reduction gearbox for the Tyne turboprop engine, which powers the Transall military transport and the Atlantic maritime patrol aircraft. A coaxial, two-stage gearbox, it handles 4,400 kW of power - about 6,000 horsepower - and is an elegant combination of compact design and power.

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