M15.11 Fuel Systems

Question 1

What is the primary function of the fuel system in a gas turbine engine?

Answer 1

To increase or decrease the power to obtain the required thrust for any operating condition

This is achieved by varying the flow of fuel to the combustion chambers.

Question 2

What happens if the quantity of fuel supplied is excessive?

Answer 2

The limiting temperature of the turbine blades can be exceeded or a compressor stall could occur

This condition is referred to as a rich blowout.

Question 3

What are the three categories of gas turbine engine fuel control systems?

Answer 3

• Hydromechanical
• Hydromechanical/electronic
• Full Authority Digital Engine Control (FADEC)

Question 4

What is a hydromechanical fuel control system?

Answer 4

A system that has no electronic interface for computing or metering fuel flow

It is generally driven by the gas generator gear train of the engine.

Question 5

What is the function of the Electronic Engine Control (EEC) in FADEC systems?

Answer 5

To calculate the amount of fuel flow by adjusting the fuel metering valve

The EEC uses electronic sensors for engine parameter information.

Question 6

What are the key components of the engine fuel control system?

Answer 6

• Vane fuel pump assembly
• Filter bypass valve
• Hydromechanical fuel control assembly

Question 7

What is the role of the fuel flow transmitter?

Answer 7

To measure the actual fuel flow and transmit signals to the flight deck for fuel flow indication.

Question 8

What is the purpose of the low-pressure fuel pump in the fuel distribution system?

Answer 8

To increase the fuel pressure from the tanks up to approximately 175 psi.

Question 9

What type of fuel pump typically provides positive flow to the second stage of the engine-driven pump?

Answer 9

Non-constant displacement (centrifugal pump).

Question 10

What types of filters are commonly used in fuel systems?

Answer 10

• Micron filter
• Wafer screen filter
• Plain screen mesh filter

Question 11

What is the function of heat exchangers in gas turbine engine fuel systems?

Answer 11

To prevent the formation of ice in the fuel filters.

Question 12

True or False: The FADEC system includes a hydromechanical fuel control backup system.

Answer 12

False.

Question 13

Fill in the blank: The fuel metering unit (FMU) is mounted on the front face of the _______.

Answer 13

gearbox.

Question 14

What is the purpose of the fuel manifold?

Answer 14

To distribute the fuel to the individual fuel nozzles on the combustion chamber.

Question 15

What is the primary component of the FADEC engine fuel control system?

Answer 15

The Electronic Engine Control (EEC).

Question 16

What is a rich blowout?

Answer 16

A condition when there is insufficient oxygen in the air supply to support combustion due to excessive fuel.

Question 17

What is the purpose of the filter bypass valve?

Answer 17

To allow fuel to bypass the fuel filter when the pressure drop across the fuel filter is excessive.

Question 18

What does the EFCU stand for?

Answer 18

Engine Fuel Control Unit.

Question 19

What is the function of the fuel control unit?

Answer 19

To meter the fuel that is needed for combustion and to supply and shut-off fuel to the fuel nozzles.

Question 20

What does the throttle lever angle resolver do?

Answer 20

Supplies the EEC with a signal in proportion to the thrust lever position.

Question 21

What is the maximum fuel pressure that the high-pressure pump can achieve?

Answer 21

Approximately 900 psi.

Question 22

What are shrouded connections used for?

Answer 22

To catch fluid leaks and carry them away to the engine drain mast.

Question 23

What is the role of the EEC’s crosstalk logic?

Answer 23

To compare data from channels A and B to determine the best channel to control output drivers.

Question 24

Fill in the blank: The _______ type of filter is rated in microns and has the greatest filtering action.

Answer 24

micron.

Question 25

What is the purpose of the high-pressure fuel filter?

Answer 25

To protect the fuel control from contaminants coming from the low-pressure pump.

Question 26

What is the relationship between the fuel nozzles and the combustion chamber?

Answer 26

Fuel nozzles inject fuel into the combustion area in a highly atomised spray pattern.

Question 27

What is the purpose of shrouds in fluid lines of an aircraft engine?

Answer 27

To catch fluid leaks and carry them away to the engine drain mast ## Footnote Shrouds are used in critical areas to prevent fluid from leaking onto hot surfaces.

Question 28

What are the two methods used to protect fluid line connections against leaks?

Answer 28

* Shrouded connections * Double sealed connections ## Footnote Shrouded connections help to catch leaks, while double sealed connections aim to prevent them.

Question 29

What is the function of the O-ring inside the shroud?

Answer 29

To prevent leakage from the coupling nut onto the hot combustion case ## Footnote O-rings are essential for maintaining safety in engine operations.

Question 30

How do older aircraft engines differ in their fuel supply systems?

Answer 30

They use two fuel supply lines and two fuel manifolds instead of one ## Footnote This design helps in redundancy for fuel supply.

Question 31

What are the two types of fuel nozzles used in aircraft engines?

Answer 31

* Simplex * Duplex ## Footnote These nozzles differ in their design and functionality.

Question 32

What is a key requirement for duplex fuel nozzles?

Answer 32

They usually require a dual manifold and a pressurising valve or flow divider ## Footnote This setup allows for the division of primary and secondary fuel flow.

Question 33

What are the two methods of mounting fuel nozzles?

Answer 33

* External mounting * Internal mounting ## Footnote Each method has its advantages regarding maintenance and accessibility.

Question 34

Why is even fuel distribution important in the burner section of an engine?

Answer 34

It is important for efficient combustion ## Footnote Uneven fuel distribution can lead to performance issues.

Question 35

What is a disadvantage of the simplex nozzle?

Answer 35

It can only give good atomisation in a small fuel flow range ## Footnote This limits its effectiveness during different phases of engine operation.

Question 36

What are the two sets of simplex nozzles used for?

Answer 36

* One set for engine start-up to idle speed (primary fuel nozzles) * A second set for acceleration to maximum power (secondary fuel nozzles) ## Footnote This design allows for better atomisation across varying fuel flow requirements.

Question 37

What do modern engines typically use instead of separate simplex nozzles?

Answer 37

Duplex nozzles that combine two nozzles in one component ## Footnote This simplifies the fuel delivery system.

Question 38

What is the role of the check valve in the fuel nozzle?

Answer 38

To prevent fuel from entering the combustion chamber by gravity when fuel pressure decreases ## Footnote This mechanism helps to avoid unwanted fuel combustion.