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M15 > M15.11 Fuel Systems > Flashcards

M15.11 Fuel Systems Flashcards

1
Q

What are the two sub systems of the engine fuel system?

A

. Fuel distribution
. Fuel control

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2
Q

What are the 3 tasks of the fuel distribution ?

A

. Safely supply fuel from aircraft to the combustion chamber
. Pressurise the fuel so it can be vaporised for combustion
. Heat the fuel, fuel flow to the fuel nozzles so it’s not blocked by ice

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3
Q

What does the primary fuel system do?

A

Stores fuel (tank)

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4
Q

Where is the secondary fuel system?

A

On the engine

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5
Q

What is the journey that fuel takes through the engine??

A
  1. From Fuel tank
  2. Through low pressure fuel shut off valve to
  3. Main fuel supply line
  4. Low pressure pump
  5. Oil cooler
  6. Fuel filter
  7. High pressure fuel pump (with pressure relief valve)
  8. Fuel control unit
  9. On some engines - servo fuel heater
  10. Fuel control unit
  11. To fuel manifold
  12. Fuel nozzles
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6
Q

Why are oil coolers built into the hp fuel pump??

A

It reduces the need for lots of external pipelines

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7
Q

What does the LP fuel pump do??

A

. Increases fuel pressure from the tanks up to 175PSI
. Supplies fuel across oil cooler and filter to hp fuel pump

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8
Q

At max engine speed what does the HP fuel pump do??

A

. Increases fuel pressure to 900PSI

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9
Q

What stage does the over pressure relief valve open??

A

1250PSI

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10
Q

The fuel pump always does what?

A

Supplies more fuel than is needed for combustion

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11
Q

What is the bypass fuel used for?

A

. To cool the IDG oil cooler

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12
Q

Where is the fuel control unit mounted??

A

. The engine fuel pump on the accessory gearbox

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13
Q

On most turbofan engines the fuel control unit is?

A

A hydro mechanical component

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14
Q

How does a hydro mechanical fuel control unit work?

A

. Controls functions by fluid pressures and mechanical components

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15
Q

What are the two different fuel control unit??

A

. Speed governed fuel control unit
. Constant thrust control units

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16
Q

What aircraft are speed governed fuel control units used on?

A

. On older aircraft

17
Q

What aircraft are constant thrust fuel control units found on??

A

. Modern turbofan engines

18
Q

What is the thrust lever signal normally?

A

A mechanical deflection of a small power lever at the fuel control unit

19
Q

What do hydro mechanical fuel control units use ?

A

. Hydraulic, mechanical and pneumatic signals

20
Q

What 4 signals does a fuel control unit need?

A

. Throttle demand signal
. Speed feedback signal
. Temperature signals
. Pressure signals

21
Q

The Fuel control unit is split into what two sections?

A

. Fuel metering section
. Computing section

22
Q

What can computing section further be split into?

A

. Governing section
. Limiting section

23
Q

What are the 3 main tasks if the fuel control unit??

A

. Fuel metering
. Power control
. Engine protection

24
Q

What is the purpose of the metering section??

A

. Makes sure that all necessary fuel get to the fuel nozzles and all the fuel that is not needed for combustion, returns to fuel pump

25
Q

What does a governing section do?

A

. Makes sure selected power is controlled

26
Q

What does limiting section do?

A

. Monitors governing section and makes sure the engine always operates within safe limits

27
Q

What does FADEC stand for??

A

. Full authority digital engine control

28
Q

What is the purpose of FADEC??

A

. Has full authority over engine control functions

29
Q

What is the heart of the FADEC system??

A

The digital computer

30
Q

What is the 2nd main component of the FADEC system??

A

. The fuel metering unit (FMU)

31
Q

Why does the FMU and HMU nit have a letter C at the end??

A

Because it cannot control
— just recurve orders from ECU to move fuel metering valves

32
Q

Engines that have FADEC systems don’t have what?

A

Hydro mechanical fuel control unit (HMU)

33
Q

Where is the electronic control unit located?

A

On fan stator case of the engine

34
Q

Where does the power supply for FADEC come from??

A

. Aircraft or
. Small permanent magnet alternator on engine accessory gearbox

35
Q

What does the ECU also need?

A

A feedback signal about the opening condition of the fuel metering valve

36
Q

What does the engine interface unit do?

A

. Transmits the data between FADEC system to the aircraft

M15 (10 decks)

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