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NIFE Academics > Engines 7: Fuel Systems > Flashcards

Engines 7: Fuel Systems Flashcards

1
Q

Volatility

A

The measurement of a liquid’s ability to convert to a vaporous state

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2
Q

What is the relationship between temperature and volatility?

A

Directly related; an increase in temperature will result in a increase in volatility

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3
Q

Flashpoint

A

The lowest temperature, of a combustible substance, that would ignite with a momentary application of a flame

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4
Q

What is the relationship between temperature and flashpoint?

A

No relationship; temperature does not change flashpoint

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5
Q

What is the relationship between volatility and flashpoint?

A

Inversely related; as the volatility of a fuel increases, it’s flash point decreases

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6
Q

What are the characteristics of JP-4?

A

High volatility with a low flashpoint (-35°F)

Compared to JP-5:
* Easier engine starting
* Slower acceleration
* Lower operating temperatures
* Higher vapor lock tendency
* Shorter range

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7
Q

What are the characteristics of JP-5?

A

Low volatility with high flashpoint (140°F)
Thermally stable
Safe for storage aboard ships

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8
Q

What are the characteristics of JP-8?

A

Lower flashpoint than JP-5 (100°F)
Better fuel handling and operational safety than JP-4

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9
Q

What are the three military jet fuels?

A

JP-4 (NATO Code F-40)
JP-5 (NATO Code F-44)
JP-8 (NATO Code F-34)

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10
Q

What color is Avgas 100?

A

Green

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11
Q

What is the flashpoint of Avgas 100?

A

-45°F

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12
Q

What color is Avgas 100 LL?

A

Blue

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13
Q

What is the purpose of the fuel system?

A

To supply clean, vapor free fuel at the proper pressure and flow rates to the engine under all operating conditions

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14
Q

What are the major considerations that must be made when designing a fuel system?

A
  • Operations at low atmospheric pressure
  • Piping system complexity
  • Cold weather starting
  • High fuel flow pressure
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15
Q

What is the purpose of the fuel tank?

A

Act as a reservoir for the jet propellant

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16
Q

What is the purpose of the boost pump?

A
  • Ensures an adequate supply of fuel to the engine-driven fuel pump
  • Prevents aeration of the fuel

Located in the wing

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17
Q

What is the purpose of the low pressure fuel filter?

A

To strain impurities from the fuel and absorb water

Very susceptible to clogging due to it being a paper cartridge type filter (because of this, a bypass valve is necessary)

18
Q

What is the purpose of an engine driven pump?

A

A high pressure pump that is supposed to deliver fuel to the FCU

19
Q

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

A

Designed to send metered (measured) fuel to satisfy fuel flow requirements for:

Starting
Acceleration
Deceleration
Steady-state operations

20
Q

What inputs do the FCU consider?

A
  • C = Compressor inlet temperatures
  • R = Compressor RPMs
  • I = Internal turbine temperature
  • P = PCL inputs
21
Q

What are the two operation modes of the FCU?

A

Normal (automatic) Operation
Manual/Emergency Operation

22
Q

Describe the Normal (automatic) Operation mode of the FCU.

A

The FCU automatically governs fuel flow to engines based on inputs

Engines will remain in limits if the FCU is functioning

23
Q

Describe the Manual/Emergency Operation mode of the FCU.

A

The FCU is bypassed; the PCL functions as a throttle and exclusively regulates fuel flow based on its movement

Requires close monitoring so ensure engine limits aren’t exceeded

24
Q

What is the purpose of the fuel flow gauge?

A

Indicates fuel consumption in pounds per hour (PPH)

25
Q

What is the purpose of the Fuel-Oil Cooler/Heat Exchanger?

A

Designed to preheat metered fuel and cool engine lubricant

(Increase volatility and remove ice crystals)

26
Q

What is the purpose of the fuel manifolds?

A

To deliver fuel to the engine burner section through a series of nozzles

27
Q

What is the purpose of the pressurizing and dump valve?

A

Designed to drain the combustion manifold upon engine shutdown and to adjust fuel flow during engine starts

28
Q

What is the position of the pressurizing and dump valve during an engine start?

A

Both the pressurizing and dump valve are closed

Dump valve is sent an electrical signal by the FCU to stay closed during start

29
Q

What is the position of the pressurizing and dump valve during normal engine operation?

A

The pressurizing valve opens (due to the increased fuel pressure) and allows fuel flow into the secondary manifold

The dump valve remains closed

30
Q

What is the position of the pressurizing and dump valve during engine shutdown?

A

The pressurizing valve is closed

The dump valve is opened (due to the drop in fuel pressure) and the manifolds are drained of any fuel

31
Q

How does the afterburner receive fuel?

A

During afterburner operations, the fuel transfer valve opens and fuel goes to the afterburner FCU. At the afterburner FCU, the fuel is measured out and then sent to the spray bars in the exhaust section.

32
Q

What are the three types of rated thrust?

A

Normal Rated Thrust
Military Rated Thrust
Combat Rated Thrust

33
Q

Normal Rated Thrust

A

Thrust produced at max continuous turbine temperature with no time limitation

34
Q

Military Rated Thrust

A

Thrust produced at max turbine temperature for a limited time

Approx. 30mins

35
Q

Combat Rated Thrust

A

Thrust produced with afterburner operation; not based on turbine temperature

36
Q

What does the secondary manifold do?

A

Supplies fuel to the engine when the engine RPMs raises fuel pressure to a predetermined level (usually after engine rpms are stabilized after start)

Used in constant and steady flight operations

37
Q

What takes fuel to the afterburner FCU?

A

Transfer valve

38
Q

What is fuel flow measured in?

A

Pounds per hour (PPH)

39
Q

What is the purpose of the primary manifold?

A

Permits fuel to reach a high degree of pressure which creates a high degree of atomization for starting and altitude idling conditions

This is why the primary manifold tubes are smaller than the secondary manifold tubes

40
Q

What is the purpose of the secondary manifold?

A

Supplies fuel when engine RPMs raises fuel pressure to a predetermined level (usually during constant/steady/normal flight operations)

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