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Module 15 - Gas Turbine Engines > 15.11 - Fuel Systems > Flashcards

15.11 - Fuel Systems Flashcards

1
Q

What do the fuel nozzles do to the liquid fuel?

A

Atomise or vaporise the fuel

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2
Q

What are the three main processes of a fuel control system?

A

Scheduling
Metering
Limiting

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3
Q

What are the fuel to air ratios for:

  • Accelerating
  • Constant power
  • Deceleration
A

Acceleration - 12:1
Constant - 15:1
Deceleration - 18:1

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4
Q

What are the components in the LP fuel system?

A 
EDP
Fuel heater
FCOC
Fuel flowmeter 
LP filter
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5
Q

What is the purpose of the LP fuel pump?

A

It prevents cavitation at the HP fuel pump.

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6
Q

Why is it necessary to heat the fuel up before passing it through the fuel filter?

A

It ensures water in suspension in the fuel doesn’t freeze and causes a blockage in the filter

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7
Q

What is the equation of the flow of a fluid through an orifice (jet)?

A

The area of the orifice multiplied by the square root of the pressure drop across it

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8
Q

What is the purpose of the fuel control unit (FCU)?

A

It maintains the correct air/fuel ratio under any running/flying conditions.

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9
Q

What inputs controls the FCU output?

A 
Engine speed signal
Inlet pressure
Compressor discharge pressure
Burner can pressure
Inlet temperature
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10
Q

What are the four basic groups of fuel system types?

A

Pneumatic-manual
Hydromechanical
Hydromechanical/electronic
Full authority digital engine control (FADEC)

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11
Q

What is the primary purpose of trimming a turbine engine fuel control unit?

A

To obtain maximum thrust output when desired

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12
Q

What is the ASU?

A

Altitude sensing unit

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13
Q

With altitude… what happens to fuel flow to the nozzles?

A

It reduces

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14
Q

How do hydromechanical fuel control units (FCU) vary the fuel flow?

A

By using servo fuel as a hydraulic fluid

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15
Q

Where does FADEC get its air pressure and temperature signal from?

A

The air data computer (ADC)

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16
Q

What is CDP?

A

Compressor discharge pressure

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17
Q

As the temperature of turbine fuel decreases… what happens to its volume?

A

It decreases

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18
Q

How is a turbojet dashpot throttle used?

A

The pilots throttle mechanism is linked to the control valve via a rack and pinion mechanism.

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19
Q

What is an FFR?

A

A fuel flow regulator

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20
Q

What is the purpose of the combustor drain valve?

A

It prevents fuel accumulation in the combustion after a false start.

21
Q

What type of fuel nozzle is used on modern gas turbine engines?

A

Duplex nozzles - air spray nozzles

22
Q

How many fuel supplies are used in a duplex nozzle?

A

2, primary and main.

23
Q

Does a FADEC system have a manual override?

A

No. If there is a total FADEC failure, the engine fails.

24
Q

What is the main advantage of a FADEC system?

A

Highest possible efficiency of the engines.

25
Q

What does the HMU control?

A

VSVs, VBVs and FMV

26
Q

What is the HPSOV?

A

High pressure fuel shut off valve

27
Q

What does the programming plug do?

A

It selects the proper software for the EEC for the thrust rating of the engine.

28
Q

When will the channels of the EEC change?

A

On every engine shut down.

Standby to Active/Active to standby

29
Q

What is the EIMU?

A

Engine interface monitoring unit.

30
Q

What is the PMA?

A

Permanent magnet alternator

31
Q

Where does the EEC get it primary power from?

A

The PMA

32
Q

What directly provides the closure to the fuel supply?

A

The master switch/lever

33
Q

In a kinetic valve, if the knife-edge is fully in…

A

The servo pressure is being bled off

34
Q

After a fuel bag tank replacement, where should you disconnect the system to carry out flow checks?

A

At the engine

35
Q

What happens to a FADEC computer if it loses it’s ADC input?

A

It goes into “soft reversion”

36
Q

What is the main purpose of the boost fuel pumps?

A

Primary purpose is to provide fuel to the engines

37
Q

What is the ADC?

A

The air data computer (Temperature & Pressure)

38
Q

What is the purpose of the “attenuator” fitted between the HP fuel pump and the BPC in a fuel system?

A

It dampens out the pulsations in the fuel delivery to the BPC (barometric pressure capsule).

39
Q

Why is the fuel heater located before the LP fuel filter?

A

It ensures the fuel does not freeze in the fuel filter and block the system

40
Q

When re-light is wanted at altitude in a FADEC engine; how does the pilot select the igniter?

A

The igniter is selected automatically by the FADEC

41
Q

What is the purpose of the BPC? (Barometric Pressure Capsule)

A

It takes P1 pressure (inlet pressure) and adjusts the fuel pressure to the combustion chamber ensuring correct RPM for a given throttle position at all altitudes and air speeds

42
Q

Where is the BPC located within?

A

The altitude sensing unit (ASU) within the FCU.

43
Q

When do the two channels on a FADEC system switch over?

A

On each engine start up

44
Q

With an increase in altitude, what happens to the fuel flow?

A

It decreases to maintain the correct air to fuel ratio

45
Q

What is the purpose of the silver strip on a fuel filter?

A

It indicates a presence of sulphur in the fuel

46
Q

What is used to cool fuel boost pumps?

A

Fuel itself; cooling the bearings inside

47
Q

What does a barometric pressure control unit (BPC) use as it’s sensing control?

A

Intake static air pressure

48
Q

What does the hydro-mechanical governor maintain?

A

RPM irrespective to fuel SG

49
Q

When a throttle is selected to increase power, what happens to the pressure drop across the FCU orifice?

A

It drops and then increases due to the pump outlet increase in pressure

Module 15 - Gas Turbine Engines (22 decks)

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