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Module 15 > 15.11 > Flashcards

15.11 Flashcards

1
Q

The fuel quantity changes with what?

A

Ambient pressure and temperature

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2
Q

What can happen if the quantity of the fuel is excessive?

A

Rich blow out (turbine temp is exceeded) and stalling.

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3
Q

When does a rich blow out happen? (2 things)

A

The amount of oxygen in the air supply isn’t good enough.
Or if the mixture is cooled below the temperature for combustion by excessive fuel.

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4
Q

When must energy/fuel be transferred to the turbine more than necessary?

A

When rapid acceleration occurs

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5
Q

When does an over rich condition occur?

A

If there is too much fuel

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6
Q

What can an over rich condition cause? (2 things)

A

A rich blow out
Compressor stall

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7
Q

What is the hydromechanical/electronic fuel control?

A

A hybrid of the two fuel systems

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8
Q

What does the dual mode in hydromechanical/electronic allow?

A

The inputs and outputs to be electronic

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9
Q

What is the best affect if the hydromechanical/electronic system fails electronically?

A

It still has mechanical linkages

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10
Q

What allows the inputs and outputs in a hydromechanical/electronic fuel system to control fuel rate?

A

Servo valves

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11
Q

Even though hydromechanical/electronic uses servo to control the inputs, what does FADEC use fir the same function?

A

Electronic sensors

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12
Q

What do the inputs from the sensor of the computing sections of FADEC rely on?

A

ECC which metres the fuel flow

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13
Q

Despite the different types of fuel control systems, what is the overall goal for the fuel systems?

A

To have enough fuel for the power of the engine

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14
Q

What are the two sections of el control?

A

Metering and computing

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15
Q

What fuel system has no electronic interface?

A

Mechanical

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16
Q

What is the hydromechanical fuel control system controlled by?

A

The gas generator gear train (Gearbox as its the only thing in the engine that will drive the mechanical pumps)

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17
Q

Disadvantage of hydromechanical fuel control system?

A

It Is less accurate

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18
Q

What directs the fuel flow in a hydromechanical/electronic fuel system?

A

The EEC

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19
Q

Where is the ECC located in the hydromechanical/electronic fuel system?

A

Remote of the engine

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20
Q

3 functions of the engine fuel systems?

A

To pressurise,
metre fuel flow
Send atomised fuel to the combustion section of the engine (for combustion and cooling)

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21
Q

What provides high pressure fuel to the fuel control system?

A

The vane fuel pump

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22
Q

What type of pump is the vane fuel pump?

A

Fixed displacement

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23
Q

What does the filter bypass valve allow for in the fuel pump?

A

Fuel to bypass the filter if it’s blocked (Pressure drops)

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24
Q

What two things happen when a blockage occurs?

A

Differential pressure indicator says theres a block
A pin extends from the fuel filter bowl

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25
Q

In the electrical aspect of the hydromechanical/electronic fuel system. what does the EEC consist of?

A

PLA Potentiometre

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26
Q

Where is the PLA potentionmetre mounted?

A

On the aircraft on the throttle quadrant

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27
Q

Where are control signals sent to for interpretation?

A

EFCU (throttle levers will be pushed to a certain position, then this position will be collected to the potentionmetre which is included in the EEC and from here will be sent to the EFCU which receives the control signals to then metre fuel flow because it uses the position of the thorttlke to assume the required fuel)

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28
Q

When the EFCU decides a power change is needed (more fuel) what modulates the differential pressure at the head sensor?

A

Torque motor

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29
Q

Where is the EFCU located?

A

Remotely on the airframe

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30
Q

What does the FADEC use to provide information to the EEC?

A

Electronic sensors

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31
Q

What gives commands to the fuel metering valve in FADEC?

A

EEC

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32
Q

What does the fuel metering valve measure?

A

Fuel flow

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33
Q

What fuel systems do turbofan high bypass engines use?

A

FADEC

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34
Q

What is the EEC?

A

A computer that controls the operation of the engine

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35
Q

How many channels does an EEC contain?

A

2 (A and B)

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36
Q

How is the EEC cooled?

A

By convection

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37
Q

Where is the EEC stored?

A

Engine nacelle

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38
Q

What supplies the EEC in FADEC with the proportion of the thrust lever position?

A

Thrust lever angle resolver

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39
Q

What does the crosstalk in EEC’S decide?

A

Which channel s best to use for control of output

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40
Q

Does the EEC have volatile or non volatile memory?

A

Both

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40
Q

What does the primary channel control?

A

ALL output drivers

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41
Q

Where is the FMU mounted?

A

On the front face of the gearbox attatched to fuel pump

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42
Q

What starts/stops fuel?

A

Shut off valve

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43
Q

In a FADEC system what provides feedback?

A

LVDT, RVDT and thermocouples (mounted on the fuel outlet line of the rear oil cooler and sends information to the EEC)

44
Q

What does the programming plug do?

A

Selects proper software in the EEC for thrust rating

45
Q

When removing an EEC where does the programming plug stay?

A

On the engine fan case via a lanyard

46
Q

What 2 subsystems can fuel be split into?

A

Distribution and control

46
Q

Fuel distrbution has what three tasks?

A

Pressurise the fuel
Supply fuel to combustion chamber
Heat the fuel (no ice in nozzles)

47
Q

Where does the fuel system usually start?

A

Behind LP fuel shut off valve

47
Q

What does the LP fuel shut off valve do?

A

It feeds the fuel into the fuel main supply line

47
Q

What component comes after the LP fuel shut off valve?

A

The LP pump

48
Q

What comes after the LP pump?

A

Oil cooler

49
Q

What is the dual function of the oil cooler?
What come after?

A

Cools the oil and heats the fuel
HP fuel pump

50
Q

What occurs in the HP fuel pump?
What comes after?

A

Fuel is pressurised to level required for vapourisation in combustion chamber
FCU

51
Q

What 2 things does the fuel control unit do?
What comes after?

A

Metres the fuel needed for combustion
Responsible for supply/shut off of fue to fuel nozzles
FFT

52
Q

What does the fuel flow transmitter do?

A

Measures fuel flow and indicates to flight deck

53
Q

What happens after the fuel flow transmitter?

A

The fuel is directed to the engine fuel manifold

54
Q

What does the engine fuel manifold do?

A

Distributes to individual nozzles

55
Q

What PSI does the low pressure fuel pump pressurise to?

A

175 psi

56
Q

What does LP pump distribute to?

A

Oil cooler, fuel filter and HP pump

57
Q

When is high pressure fuel pump used?

A

When engine at max speed

58
Q

What PSI is the HP pump pressurising to?

A

900

59
Q

What does the overpressure relief valve do in the HP compressor?

A

Prevent damage to fuel systems

60
Q

Fuel from HP pump flows where?

A

to the metering section of FCU

61
Q

How much does the pump, pump fuel for combustion?

A

More than enough (incase of rapid acceleration)

62
Q

Un needed fuel goes where?

A

Back to the fuel pump via the fuel bypass return line

63
Q

What lets only metered fuel enter the nozzles?

A

The metering section

64
Q

Two types of pressurised pumps?

A

Constant displacement
Non Constant displacement

65
Q

What decides which pump is used?

A

Where they are in the engine fuel system

65
Q

Where is a non constant displacement (Centrifugal) used?

A

At the inlet of a pump to provide positive pressure

66
Q

What is the centrifugal pump (non constant displacement) referred to as?

A

Boost stage pump

67
Q

How are fuel pumps lubricated?

A

By passing fuel so must never be run dry

68
Q

What psi do the LP pumps increase the system pressure to?

A

175

69
Q

Where does the LP pump fuel flow to?

A

The oil cooler and the fuel filter after being pumped through HP pump

70
Q

What psi do the HP pump increase system pressure to?

A

900psi

71
Q

What does the HP pump have that the LP pump doesnt?

A

An overpressure relief valve to prevent damage to the systems

72
Q

Where is a LP filter positioned?

A

In between supply tank and engine fuel system to protect engine driven pumps

73
Q

Where is the HP filter installed?

A

Between the fuel pump and fuel control unit to protect from any contaminants arising from LP pump.

74
Q

What filter has the greatest filtering action?

A

Microns

75
Q

Porous cellulose material used in construction of cartridges is can remove what size micron?

A

10-25

76
Q

What is required for filters with minute openings? (Microns)

A

Bypass valve (clogging)

77
Q

What mesh filters are most widely used?

A

200 and 35 mesh microns

78
Q

What are micron filters made up of?

A

Mesh steel wire

79
Q

What prevents the formation of ice in fuel systems?

A

Heat exchangers

80
Q

What is the source of heat for heat exchangers?

A

Bleed air or engine oil

81
Q

How do fuel nozzles ensure that the combustion is done evenly?

A

It sprays in a highly atomised spray pattern

82
Q

What does the fuel manifold do?

A

Distribute fuel to the nozzle

82
Q

What does keeping the flame within the liners and in the centre prevent?

A

Hot spots

83
Q

Where is a single fuel manifold found?

A

Modern gas turbine engine

83
Q

What does the single fuel manifold surround?

A

The combustion case

84
Q

Two method of protecting connections from leaks?

A

Shrouded connections
Double sealed connection

84
Q

What is on the fuel lines to catch any fluid leaks? And where are the leaks sent?

A

Shrouds and they are sent to the drain mast.

85
Q

What do shrouded connections do and don’t do?

A

They don’t prevent leaks but they catch and carry them away via the engine drain system

86
Q

What prevents leaks from the coupling connector nut getting onto the combustion case?

A

O-ring

87
Q

On older aircraft how many lines and manifolds were used?

A

2

88
Q

Two types of fuel nozzles?

A

Simplex (Single valve)

Duplex (Double manifold and pressurising valve/divider to seperate secondary and primary)

89
Q

Where is a fuel nozzle mounted externally?

A

Via a mounting pad on the CASE or the INLET AIR ELBOW

90
Q

Where are fuel nozzles mounted internally?

A

On the Liner dome (remove chamber cover for maintenance)

91
Q

Where is fuel suppled in the combustion chamber?

A

Forward part

92
Q

What is a disadvantage of simplex fuel nozzles?

A

Covers a small range as discharge orifice is small. Good for ignition only, not reaching take off power

93
Q

What can you use to cover a good fuel range?

A

Two sets of simplex nozzles

94
Q

What are primary fuel nozzles used for (In two sets of simplex nozzles)?

A

Small discharge orifice so start up, to idle

95
Q

What are secondary fuel nozzles used for (In two sets of simplex nozzles)?

A

Acceleration to maximum power

96
Q

Modern aircraft use duplex nozzles. What are they?

A

Dual flow nozzles in one

97
Q

What prevents carbon formation?

A

A check valve in the fuel nozzle

98
Q

When does the check valve close?

A

When the HP fuel shut off valve is closed (pressure decrease)

99
Q

What does the check valve ensure?

A

That no fuel flows to the combustion chamber from manifold by gravity.

100
Q

What is the dual function of the oil cooler?

A

Oil heats the fuel and the fuel cools the oil

Module 15 (18 decks)

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