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Module 15 Richard > 15.11 Fuel Systems > Flashcards

15.11 Fuel Systems Flashcards

1
Q

What is the primary fuel system and what is the secondary fuel system

A

Primary - Fuel storage

Secondary - On the engine

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2
Q

What are the two engine fuel subsystems

A
  • Fuel distribution subsystem

- Fuel Control subsystem

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3
Q

What are the 3 main purposes of the engine fuel distribution subsystem

A
  • Safely supply the combustion chamber
  • Pressurise fuel enough to combust in combustion chamber
  • To heat fuel and prevent ice build up in jet nozzles
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4
Q

Where does the engine fuel distribution system start

A

Directly behind the low pressure fuel shut off valve

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5
Q

What does the main fuel shut off valve supply

A

The main fuel supply line

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6
Q

Where is the low pressure fuel pump located

A

On the auxiliary gearbox

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7
Q

What is the purpose of the low pressure fuel pump

A

Increase the pressure of the fuel coming from the wing tank jet pumps

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8
Q

Where does the fuel go after the low pressure fuel pump

A

The oil cooler

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9
Q

What is the purpose of the oil cooler

A

The cold fuel cools the hot oil of the engine lubrication system and the hot engine oil warm the cold fuel about the melting point of water

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10
Q

What is located downstream of the oil cooler

A

The fuel filter

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11
Q

What component comes after the fuel filter

A

The high pressure fuel pump

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12
Q

What is the purpose of the high pressure fuel pump

A

Increases the pressure of the fuel enough for vaporisation to combust

It is fitted with a pressure relief valve

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13
Q

After the high pressure fuel pump where does the fuel go

A

The fuel control unit

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14
Q

What is the purpose of the fuel control unit

A

Meters the fuel needed for combustion

Responsible for supply and shut off to fuel to the fuel nozzles and combustion chamber

Needs high pressure fuel to operate internal control mechanisms

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15
Q

What do some fuel control units have to ensure there is going to be no ice build up

A

An additional servo fuel heater

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16
Q

When the fuel leaves the fuel control unit where does it flow next

A

The fuel flow transmitter

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17
Q

What is the purpose of the fuel flow transmitter

A

Measures the actual fuel flow and transmits signals to the cockpit for fuel flow and fuel used Indication

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18
Q

Where does the fuel flow after the fuel flow transmitter

A

It is routed to the fuel manifold which distributes the fuel to the individual fuel nozzles on the combustion chamber

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19
Q

What does the low pressure fuel pump increase the pressure of the fuel to

A

Around 175PSI

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20
Q

What is the secondary purpose of the low pressure fuel pump

A

To prevent cavitation at the inlet of the high pressure pump

21
Q

At maximum engine speed the high pressure fuel pump increases the fuel pressure to approx what pressure

A

900 PSI

22
Q

The overpressure relief valve open when the pressure reaches approx?

A

1250PSI

23
Q

Where would the fuel go after the metering unit if it is not needed for combustion

A

It would return to the fuel pump by the bypass return line

24
Q

What is the bypass return line connected to (and to perform what task) from the fuel metering unit

A

On some engines it’s connected to the IDG oil cooler to cool IDG oil

25
Q

On most turbofan engines what type of unit is the fuel control unit

A

A hydromechanical component

26
Q

Where is the fuel control unit usually mounted

A

To the engine fuel pump on the auxiliary gearbox

27
Q

In a hydromechanical unit what are all functions controlled by

A

Fluid pressures and mechanical components

28
Q

What are the two different types of fuel control unit

A
  • Speed governed fuel control unit, which you usually find on older engines
  • Constant thrust fuel controlled units usually use the N2 demand signal and the N2 speed feedback for steady state fuel metering
29
Q

The fuel control unit has many pipes and push pull cables connected to it. What are they needed for

A

Some are needed to transmit throttle demand signal, the temperature signal, the pressure signal and the speed feedback signals for fuel metering and others are needed for the engine compressor

30
Q

Thrust lever is usually a mechanical deflection of a small power lever at the fuel control unit, by what means is this done

A

Rack and pinion transmission or rods and levers

31
Q

How is the N2 speed feedback signal transmitted

A

Via a mechanical drive shaft from the main fuel pump

32
Q

What two major sections can the fuel control unit be split into

A
  • The fuel metering section
  • The computing section
    The computing subsystem can be sub split into:
  • A governing section
  • A limiting section
33
Q

What are the 3 main tasks of the fuel control unit

A
  • Fuel metering
  • Power control
  • Engine protection
34
Q

What does the governing computing section of the computing section do

A

Makes sure the selected power is controlled

35
Q

What does the limiting section of the computing section do

A

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

36
Q

What does FADEC stand for

A

Full Authority Digital Engine Control

37
Q

What is the purpose of the FADEC computer

A

In a FADEC system a digital computer has full authority over the engine control functions. The digital computer is the heart of the FADEC system (Normally called the EEC or ECU)

38
Q

What is the second main component of the FADEC system

A

The Fuel Metering Unit

39
Q

What is the Fuel Metering Unit also known as

A

The Hydromechanical Unit (HMU)

40
Q

What does the FMU control

A

The FMU is not a controller, it only receives orders from the ECU to move the Fuel Metering Valve

41
Q

What type of systems does not have a hydromechanical unit

A

A FADEC system

42
Q

Where is the ECU usually located

A

On the fan stator case of the engine

43
Q

What parameters does the ECU need to operate properly

A

Needs a demand signal from the thrust lever in the cockpit, engine speed and all important air temperatures and air pressures of the engine.

It also needs electrical power for its operation

44
Q

Where does the power for the ECU come from

A

Either from aircraft power or the Permanent Magnet Alternator on the engine

45
Q

What main tasks does the ECU perform apart from fuel metering and engine limit protection

A

Performs full power management and gives optimum thrust control for all operating conditions

46
Q

What subsystems does the ECU control

A
  • The compressor stall protection system
  • The turbine and compressor clearance control system
  • The thrust reverser system
  • The engine starting system
  • The engine Indication system
47
Q

What main components make up a FADEC system

A
  • An ECU
  • A Fuel Metering Unit
  • Many electrical sensors on the engine
  • Many control possibilities for other engine sub systems
48
Q

What are EIUs

A

Engine Interface Units

Transmit data from the FADEC system to the aircraft. They also control the power supply from the aircraft to the ECU

Module 15 Richard (18 decks)

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