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Concept of Engine Control (2)

Engine can be controlled by controlling:

Fuel flowto vary demanded engine speeds, to handle the

engine without damages

Air flowto operate the engine efficiently throughout the aircraft

flight envelope and with adequate safety margins Exhaust gas flowburning the exhaust gases and varying the

nozzle area to provide additional thrust

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Types of aircraft engine (1)

Turbojet

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Types of aircraft engine (2)

Turboprop

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Types of aircraft engine (3)

Turbofan

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Types of aircraft engine (4)

Turboshaft

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Environment within gas

turbine

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Operational Limits

Structural limits

Maximum fan and core speeds: N1 (rotational speed of LPC) and

N2 (rotational speed of HPC)both in rpm

Maximum turbine blade temperature

Safety limits: Adequate stall margincompressor and fan

Lean burner blow outminimum fuel

Operational limit:

Maximum turbine inlet temperature To provide long life for the engine

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Why important?

Maximum fuel limit protects against surge/stall (flow

instability), over-temperature, over-speed, and over-pressure

Minimum fuel limit protects against combustor blow-out

(flame failure occurs at high altitude operation)

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Fuel Flow control (1)

Power or thrust can be controlled by regulating the fuel flow

into the combustor

When higher thrust is required, throttle is opened and fuel

pressure to the burner increases due to higher fuel flow.

Increases in fuel pressure increase gas temperature which inturn increase the acceleration of the gases through the

turbine to give a higher engine speed, greater air flow which

resulting in increase in thrust.

Changes in altitude, air temperature, and aircraft speedchange the density of the air at the engine intake and the

mass of air flowing through the engine.

To maintain conditions demanded by pilot, fuel control unit

(FCU) or fuel management unit (FMU) is used

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FCU/FMU

Hydro-mechanical device mounted on the engine

Contain valves to direct fuel and to restrict fuel flow

Contain pneumatic capsules to modify flows according to

prevailing atmospheric conditions Contain dashpot/spring/damper combinations to control

acceleration and deceleration rates

Fuel Flow control (2)

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Engine control system

parameters (1) Active control process which involves engine sensors, control

units and actuators

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Engine control system

parameters (2) Sensors located within gas turbine engine to perform controlling

function

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Engine control system

parameters (3)

Signals Sensors

Throttle position Transducer - connected directly to the throttle

level (either by electrical signaling or connected

to the end of control rods for mechanical

operation)

Air data (altitude and

airspeed)

Using air data computer (ADC) or flight control

system air data sensors

Total temperature Using temperature probe mounted at the engine

face, intakes or on aircraft structure

Engine speed Using pulse probes

function to have magneticfield interrupted by moving metallic parts of the

engine or gear box

Engine temperature Using thermocouples- arrange as a ring of parallel

connected thermocouples to obtain mean gas

temperature

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Engine control system

parameters (4)Signal Sensors

Pressure ratio Diaphragm operated device

Two high accuracy pressure sensors and electronics

Nozzle position Position sensors located to the nozzle actuation

mechanism

Fuel flow Turbine flow meter installed in fuel pipework

Fuel control unit (FCU)

Fuel flow control Solenoid, torque motor or stepper motor

Air flow control Inlet Guide Vanes (IGV) or bleed valves located between

engine stages

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Modern Civil Aircraft Engine

Control Full Authority Digital Engine Control System (FADEC)

Mounted on fan casing

Monitor and control:

N1 and N2

Temperature and pressure Exhaust gas temperature (EGT)

Oil temperature

Turbine High pressure (HPT) and turbine low pressure (LPT) cooling

loops

Engine start Fuel control