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M15 > FUEL SYSTEMS > Flashcards

FUEL SYSTEMS Flashcards

1
Q

Where is the fuel control unit of an engine usually mounted?

A

To the engine fuel pump on the accessory gearbox.

On turbofan engines, usually hydromechanical component

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2
Q

In a hydromechanical fuel control unit what are all control functions done by?

A

Fluid pressures and mechanical components.

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3
Q

What are the 2 different types of fuel control unit?

A

Speed governed fuel control unit (older engines)

Constant thrust fuel control unit (modern engines)

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4
Q

What do speed governed fuel control units mainly use for steady state fuel metering?

A

N2 demand signal and N2 speed feedback signal.

Constant thrust fuel control, additional thrust feedback signals such as N1 speed, ambient pressure and temp signals

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5
Q

What do temperature signals like CIT or fan inlet temperature convert the air temperatures to in a fuel control unit?

A

Fuel pressure signals.

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6
Q

What do hydromechanical fuel control units use for operation?

A

Hydraulically, Pneumatically and mechanically

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7
Q

What 2 parts can the fuel control unit be split into?

A

Fuel metering section

Computing section

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8
Q

What can the computing section of the fuel control system be further divided into?

A

Governing section

Limiting section

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9
Q

What does the fuel metering system do in a fuel control unit?

A

Ensures necessary fuel gets to the fuel nozzles and all fuel not needed for combustion returns to the fuel pump.

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10
Q

What does the governing section of the fuel control unit do?

A

Makes sure that the selected power is controlled.

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11
Q

What is the limiting section for in a fuel control unit?

A

ensures the engine always operates within safe limits.

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12
Q

What does FADEC stand for?

A

Full Authority Digital Engine Control.

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13
Q

What is the digital computer in FADEC system normally called?

A

ECU or EEC.

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14
Q

What is a FADEC made up of?

A

EEC or ECU

FMU (fuel metering unit)

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15
Q

Where are the electronic control units and FMU located?

A

Fan stator case of the engine.

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16
Q

What can a small permanent magnet alternator on the accessory gearbox provide for FADEC?

A

A power supply.

17
Q

What are engine interface units (EIU) for?

A

Transmit the data between the FADEC system and the aircraft.

Control power supply from aircraft to ECU.

18
Q

What can the engine fuel system be separated into?

A
  • fuel distribution subsystem

- fuel control system

19
Q

What 3 main tasks does the fuel distribution system have?

A
  • safely supply fuel to combustor
  • pressurise fuel
  • heat the fuel
20
Q

What does the low pressure fuel pump do?

A

Increases the pressure that comes from the tank boost pumps

21
Q

What two functions does the oil cooler have?

A

Cold fuel cools the engine lubrication system

Puts fuel above freezing so it doesn’t block the fuel filter

22
Q

Where is the filter located in comparison to the oil cooler?

A

Downstream.

Ensures that ice cannot block the filter as fuel is warmed above freezing point

23
Q

What is a high pressure fuel pump?

A

Increases fuel pressure so it’s able to vaporise in the combustion chamber

24
Q

What is the purpose of the fuel control unit?

A

Meters the fuel which is needed for combustion. Also responsible for supply and shut off.

25
Q

The fuel control unit needs high pressure fuel to be used as servo pressure for internal mechanisms. To avoid ice build up, what can be added?

A

An additional servo fuel heater.

26
Q

What does a fuel flow transmitter measure?

A

Measure the actual flow of fuel and transmits to cockpit

27
Q

What is the fuel manifold?

A

Distributes fuel to individual fuel nozzles on the combustion chamber.

28
Q

What is the advantage of having an oil cooler downstream of the high pressure pump?

A

Requires less external fuel lines because the low and high pressure pumps are in one housing but the Danger of fuel leaks is greater in a low pressure system

29
Q

What PSI does the low pressure fuel pump increase the fuel pressure to before supplying fuel to the high pressure stage?

A

175psi

30
Q

Why is it necessary for the low pressure fuel pump to pressurise before the high pressure stage?

A

So the HP does not have to draw via suction and prevents cavitation at the inlet.

31
Q

At max engine speed, what does the high pressure pump increase the fuel pressure to?

A

900psi

32
Q

On the high pressure pump, when will the overpressure relief open?

A

When the system reaches 1250psi

Some fuel is released back to the inlet port of the high pressure pump

33
Q

How much fuel will the pump supply in comparison to the amount that is needed?

A

Always supplies more than needed.

Fuel that isn’t needed returns via the bypass return line

34
Q

Fuel that is passed down the bypass line can be used to cool what?

A

The IDG oil cooler

35
Q

In low engine power conditions, bypass fuel is returned to the tank. How is it ensured that fuel is not too hot when re-entering?

A

Cold fuel from the LP stage is added to the hot bypass fuel

M15 (18 decks)

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