Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Resource Group Mod 15 2024 > 15.11 Fuel Systems > Flashcards

15.11 Fuel Systems Flashcards

1
Q

How is power increased or decreased in the engine?

A

By varying the amount of fuel flow to the combustion chamber.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a ‘Rich blowout’?

A

Excess fuel cools the air-fuel mixture below combustion temperature.

The amount of oxygen in the air supply is insufficient to support combustion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What’s the 3 main functions of an engine fuel system?

A
  • Pressurise the fuel.
  • Meter the fuel flow.
  • Deliver atomised fuel flow to the combustion chamber.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the three main types of fuel control system?

A
  • Hydromechanical.
  • Hydromechanical/electronic.
  • FADEC.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What’s the main fact about a ‘Pure hydromechanical system’?

A

It has no electronic interface in assisting the computing and metering of fuel.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What’s true about the accuracy of the fuel metering function in a pure hydromechanical system?

A

It’s not as accurate as an electronic system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the two main sections of a fuel control system?

A
  • Computing section.
  • Metering section.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What be can added to a hydromechanical unit to improve fuel flow metering?

A

An electronic system.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What’s the 3 advantages of adding an electronic system to a hydromechanical unit?

A
  • Can receive more inputs.
  • Is more accurate.
  • The hydromechanical section can then act as a backup if the electronic system fails.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is an EEC?

A

Electronic engine control.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does a hydromechanical/electronic system consist of?

A

A hydromechancal unit, and a remotely located EEC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two modes of a Hydromechanical/electronic system?

A
  • Automatic mode.
  • Manual mode.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is automatic mode in a Hydromechanical/electronic system?

A

The EEC is in control of fuel flow metering.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is manual mode in a Hydromechanical/electronic system?

A

The hydromechanical unit takes over control of fuel flow metering.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In normal operation, what does the Engine Fuel Control Unit control? (4)

A
  • Thrust setting.
  • Speed governing.
  • Acceleration.
  • Deceleration.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What happens if the electronic unit fails, in a Hydromechanical/electronic system?

A

Manual mode is activated and allows the engine to operated at a reduced power under full control of the hydromechanical unit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Is the solenoid energised or de-energised, when in automatic mode?

A

The solenoid is energised.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What type of filter is the fuel supplied to the unit through?

A

A 200 micron inlet filter screen.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What determines the position of the metering valve, in terms of a specific ratio?

A

Fuel flow (wf) / Compressor discharge pressure (P3).

(wf/P3 ratio).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does a fixed wf/P3 ratio give, in terms of thrust?

A

A minimum of 90% thrust, up to 30000ft, surge-free.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What drains the fuel nozzles and manifold after engine shutdown?

A

Drain valve assy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Where is the Engine Fuel Control Unit usually located?

A

Remotely located and airframe mounted.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How is the interface between the remotely located EFCU and the engine/aircraft, achieved?

A

Branched wiring harness.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does FADEC stand for?

A

Full Authority Digital Engine Control.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Does the FADEC system have a hydromechanical backup?

A

Nope.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the primary component of the FADEC system?

A

The EEC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

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

A

Electronic sensors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

How does the EEC calculate fuel flow for the metering valve, in a FADEC system?

A

The EEC uses the signals received from the FADEC’s electronic sensors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

How does the metering valve know how to control the fuel flow, in a FADEC system?

A

It reacts to the commands received from the EEC’s calculations.

(The EEC makes its calculations based on information from the FADEC’s sensors).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the construction of the EEC’s channels?

A

It has a two channel system (A and B) that are physically independent from eachother.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What does one channel of the EEC’s two channel system, consist of?

A

It’s an independent computer that can completely control engine operation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

How do the EEcs channels communicate to eachother?

A

Via crosstalking.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What does the crosstalking logic do?

A

Compares the data from the two channels, to determine which data is best to control the output driver for the torque motor, or the solenoid bank.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What does the primary channel control?

A

All of the output drivers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What two types of memory does the EEC have?

A
  • Volatile.
  • Non-volatile.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What are the two thrust control modes for the EEC?

A
  • Normal mode.
  • Alternate mode.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What controls thrust in EEC normal mode?

A

The thrust is set by the EPR (Engine Pressure Ratio).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What controls alternate thrust in EEC alternate?

A

The thrust is set by N1.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What does the programming plug in the EEC do?

A

Selects the correct software in the EEC for the thrust rating of the engine.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What happens to the programming plug if the EEC is removed?

A

It remains with the engine, its attached to the fan case with a lanyard.

41
Q

What is the primary fuel system?

A

It stores the fuel.

42
Q

What is the secondary fuel system?

A

Supplies the fuel to the engine.

43
Q

What are the two main purposes of the secondary fuel system?

A
  • Supply fuel to the combustion chamber.
  • Control quantity of fuel necessary for correct engine operation.
44
Q

What two sub-systems is the engine fuel control system split into?

A
  • Distribution System.
  • Control system.
45
Q

What are the 3 main tasks of the distribution system?

A
  • Safely supply fuel to the combustion chamber.
  • Pressurise fuel for vaporisation.
  • Heat the fuel.
46
Q

What’s the first component in the fuel distribution system?

A

Low pressure fuel pump.

47
Q

What is the purpose of the LP fuel pump?

A

Receives fuel from the tanks and increases fuel pressure to 175psi. Prevents cavitation at the HP pump.

48
Q

What does the fuel flow through, before it reaches the HP pump?

A

Through the oil cooler (to heat the fuel) and the inlet filter.

49
Q

The fuel then reaches the HP Pump. What happens here?

A

Fuel pressure is increased to 900psi at max engine speed.

50
Q

What other component does the HP pump have, to protect against overpressure?

A

A pressure relief valve that opens at 1250psi.

51
Q

What does the HP pump supply then fuel to?

A

The metering valve.

52
Q

What is true about the quantity of fuel that is supplied to the metering section from the HP pump?

A

It always supplies a greater quantity of fuel to the metering section, than is actually required.

53
Q

What happens in the metering section with regards to how the fuel is metered?

A

The metering section only supplies the metered fuel to the fuel nozzles.

The un-metered (excess) fuel flows back to the pump via the bypass return line.

54
Q

What is the purpose of the un-metered fuel?

A

The un-metered fuel is used to cool the IDG oil, on its way back to the LP pump.

55
Q

In low-power conditions, where is the un-metered fuel from the metering section sent to?

A

Back to the fuel tanks, via the fuel recirculation valve.

56
Q

What’s the purpose of sending un-metered fuel through the fuel recirculation valve, in low power conditions?

A

It uses colder fuel to help cool the hot un-metered fuel before it flows back into the fuel tank.

This is because the hot fuel could cause the LP pump to overheat.

57
Q

What type of fuel pump is normally used at the inlet of the engine driven pump?

A

Non-constant displacement fuel pump.

58
Q

What type of fuel pump is normally used at the main stage of the engine driven fuel pump?

A

Positive displacement pump.

59
Q

How are fuel pumps lubricated?

A

By the flow of fuel passing through them.

60
Q

When should you never operate a fuel pump?

A

If there is no fuel supply to it. It will burn out very quickly.

61
Q

Where are low pressure filters usually installed?

A

Between the supply tanks and the engine fuel system, to protect the EDP.

62
Q

Where are high pressure filters usually installed?

A

Between the fuel pump and fuel control system, to protect the system from contaminants from the LP pump.

63
Q

What are the 3 most common types of fuel filter?

A
  • Micron filter.
  • Wafer screen filter.
  • Plain screen mesh filter.
64
Q

What is the most commonly used type of filter?

A

Micron filter, because it has the greatest filtering action.

65
Q

What size particles can a micron filter, filter out?

A

10-25 microns.

66
Q

What’s the disadvantage or micron filters, and how is it overcome?

A

They are susceptible to clogging.

Overcome by pressure bypass valve.

67
Q

What is the benefit of using a Porous Cellulose material in the filter element?

A

It can also absorb some of the water that may be present in the fuel.

68
Q

What are the most common mesh ratings of filters used in fuel systems?

A

200 mesh and 35 mesh.

69
Q

Which type of filter element is replaceable?

A

Wafer screen type.

70
Q

What two sources of heat can a heat exchanger use to heat the fuel?

A
  • Engine bleed air.
  • Hot oil.
71
Q

What’s the name for a heat exchanger that uses bleed air to heat the fuel?

A

Air-to-liquid exchanger.

72
Q

What’s the name for a heat exchanger that uses hot oil to heat the fuel?

A

Liquid-to-liquid exchanger.

73
Q

What supplies fuel to the fuel manifold?

A

The fuel control unit.

74
Q

What does the fuel manifold supply fuel to?

A

The fuel nozzles.

75
Q

What is the purpose of using shrouds around the fuel manifold?

A

They protect against high pressure fuel leaks in the hot environment of the compressor and combustion case.

76
Q

How do the shrouds protect against fuel leaks?

A

They catch any leaked fuel and carry it to the engine drain system.

77
Q

What do double-sealed connections between the fuel manifold and fuel nozzles, provide?

A

Two layers of protection against fuel leaks between the fuel manifold and nozzles.

78
Q

What creates the inner seal in a double-sealed connection?

A

A pair of O-rings.

79
Q

What creates the outer seal in a double-sealed connection?

A

A conical seal between the manifold and nozzle.

80
Q

What is the main purpose of the fuel nozzles?

A

To atomise the fuel.

81
Q

What are the two types of fuel nozzles?

A
  • Simplex.
  • Duplex.
82
Q

What’s inside a simplex fuel nozzle?

A

A swirl chamber.

83
Q

What’s the disadvantage of a simplex fuel nozzle?

A

Only provides good atomisation in a small fuel-flow range.

84
Q

How is the disadvantage of simplex fuel nozzles overcome?

A

By using two different sets of simplex nozzles. (primary and secondary).

85
Q

What is the function of the primary simplex nozzles?

A

They are used for engine start up to idle speed.

86
Q

What is the function of the secondary simplex fuel nozzles?

A

They are used for acceleration up to full power.

87
Q

Are simplex fuel nozzles normally used on modern GTEs?

A

Nope.

88
Q

What do Duplex fuel nozzles achieve?

A

They combine the two systems of the simplex fuel nozzles, into one.

89
Q

What does each duplex nozzle consist of?

A

Each nozzle has ‘dual-flow’;

  • Two discharge orifices.
  • Two internal supply lines.
90
Q

What is the structure of the primary orifice in a duplex nozzle?

A

It’s smaller and located in the centre of the nozzle.

91
Q

What is the structure of the secondary orifices in a duplex nozzle?

A

They are larger, and they surround the primary orifice.

92
Q

What divides the flow of fuel through the duplex nozzle into the different orifices?

A

Flow divider valve. It’s spring loaded.

93
Q

What happens to the flow divider valve, as engine speed increases?

A

The valve opens to increase fuel pressure.

94
Q

What else do the duplex nozzles do, in relation to airflow and cooling?

A

They pick-up some of the airflow from the combustion chamber, to help cool the nozzle.

Also helps blow-away residual fuel on the nozzle tip after engine shutdown.

95
Q

How do air-spary nozzles atomise fuel?

A

They use high velocity airflow that flows through an inner and outer air swirler.

96
Q

What’s the advantage of air-spray nozzles?

A

They provide good atomisation even at lower engine speeds.

97
Q

What’s the disadvantage of air-spray nozzles?

A

They require a constant high-velocity airflow.

98
Q

What type of flow do air-spray nozzles always provide?

A

Single flow.

Resource Group Mod 15 2024 (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions