Engines 7: Fuel Systems

Question 1

Volatility

Answer 1

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

Question 2

What is the relationship between temperature and volatility?

Answer 2

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

Question 3

Flashpoint

Answer 3

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

Question 4

What is the relationship between temperature and flashpoint?

Answer 4

No relationship; temperature does not change flashpoint

Question 5

What is the relationship between volatility and flashpoint?

Answer 5

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

Question 6

What are the characteristics of JP-4?

Answer 6

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

Question 7

What are the characteristics of JP-5?

Answer 7

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

Question 8

What are the characteristics of JP-8?

Answer 8

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

Question 9

What are the three military jet fuels?

Answer 9

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

Question 10

What color is Avgas 100?

Answer 10

Green

Question 11

What is the flashpoint of Avgas 100?

Answer 11

-45°F

Question 12

What color is Avgas 100 LL?

Answer 12

Blue

Question 13

What is the purpose of the fuel system?

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What is the purpose of the fuel tank?

Answer 15

Act as a reservoir for the jet propellant

Question 16

What is the purpose of the boost pump?

Answer 16

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

Located in the wing

Question 17

What is the purpose of the low pressure fuel filter?

Answer 17

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)

Question 18

What is the purpose of an engine driven pump?

Answer 18

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

Question 19

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

Answer 19

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

Starting
Acceleration
Deceleration
Steady-state operations

Question 20

What inputs do the FCU consider?

Answer 20

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

Question 21

What are the two operation modes of the FCU?

Answer 21

Normal (automatic) Operation
Manual/Emergency Operation

Question 22

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

Answer 22

The FCU automatically governs fuel flow to engines based on inputs

Engines will remain in limits if the FCU is functioning

Question 23

Describe the Manual/Emergency Operation mode of the FCU.

Answer 23

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

Question 24

What is the purpose of the fuel flow gauge?

Answer 24

Indicates fuel consumption in pounds per hour (PPH)

Question 25

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

Answer 25

Designed to preheat metered fuel and cool engine lubricant (Increase volatility and remove ice crystals)

Question 26

What is the purpose of the fuel manifolds?

Answer 26

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

Question 27

What is the purpose of the pressurizing and dump valve?

Answer 27

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

Question 28

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

Answer 28

Both the pressurizing and dump valve are closed ## Footnote Dump valve is sent an electrical signal by the FCU to stay closed during start

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

How does the afterburner receive fuel?

Answer 31

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.

Question 32

What are the three types of rated thrust?

Answer 32

Normal Rated Thrust Military Rated Thrust Combat Rated Thrust

Question 33

Normal Rated Thrust

Answer 33

Thrust produced at max continuous turbine temperature with no time limitation

Question 34

Military Rated Thrust

Answer 34

Thrust produced at max turbine temperature for a limited time ##Footnote Approx. 30mins

Question 35

Combat Rated Thrust

Answer 35

Thrust produced with afterburner operation; not based on turbine temperature

Question 36

What does the secondary manifold do?

Answer 36

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

Question 37

What takes fuel to the afterburner FCU?

Answer 37

Transfer valve

Question 38

What is fuel flow measured in?

Answer 38

Pounds per hour (PPH)

Question 39

What is the purpose of the primary manifold?

Answer 39

Permits fuel to reach a high degree of pressure which creates a high degree of atomization for starting and altitude idling conditions ##Footnote This is why the primary manifold tubes are smaller than the secondary manifold tubes

Question 40

What is the purpose of the secondary manifold?

Answer 40

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