M15.11 Fuel Systems Flashcards
What is the primary function of the fuel system in a gas turbine engine?
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.
What happens if the quantity of fuel supplied is excessive?
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.
What are the three categories of gas turbine engine fuel control systems?
- Hydromechanical
- Hydromechanical/electronic
- Full Authority Digital Engine Control (FADEC)
What is a hydromechanical fuel control system?
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.
What is the function of the Electronic Engine Control (EEC) in FADEC systems?
To calculate the amount of fuel flow by adjusting the fuel metering valve
The EEC uses electronic sensors for engine parameter information.
What are the key components of the engine fuel control system?
- Vane fuel pump assembly
- Filter bypass valve
- Hydromechanical fuel control assembly
What is the role of the fuel flow transmitter?
To measure the actual fuel flow and transmit signals to the flight deck for fuel flow indication.
What is the purpose of the low-pressure fuel pump in the fuel distribution system?
To increase the fuel pressure from the tanks up to approximately 175 psi.
What type of fuel pump typically provides positive flow to the second stage of the engine-driven pump?
Non-constant displacement (centrifugal pump).
What types of filters are commonly used in fuel systems?
- Micron filter
- Wafer screen filter
- Plain screen mesh filter
What is the function of heat exchangers in gas turbine engine fuel systems?
To prevent the formation of ice in the fuel filters.
True or False: The FADEC system includes a hydromechanical fuel control backup system.
False.
Fill in the blank: The fuel metering unit (FMU) is mounted on the front face of the _______.
gearbox.
What is the purpose of the fuel manifold?
To distribute the fuel to the individual fuel nozzles on the combustion chamber.
What is the primary component of the FADEC engine fuel control system?
The Electronic Engine Control (EEC).
What is a rich blowout?
A condition when there is insufficient oxygen in the air supply to support combustion due to excessive fuel.
What is the purpose of the filter bypass valve?
To allow fuel to bypass the fuel filter when the pressure drop across the fuel filter is excessive.
What does the EFCU stand for?
Engine Fuel Control Unit.
What is the function of the fuel control unit?
To meter the fuel that is needed for combustion and to supply and shut-off fuel to the fuel nozzles.
What does the throttle lever angle resolver do?
Supplies the EEC with a signal in proportion to the thrust lever position.
What is the maximum fuel pressure that the high-pressure pump can achieve?
Approximately 900 psi.
What are shrouded connections used for?
To catch fluid leaks and carry them away to the engine drain mast.
What is the role of the EEC’s crosstalk logic?
To compare data from channels A and B to determine the best channel to control output drivers.
Fill in the blank: The _______ type of filter is rated in microns and has the greatest filtering action.
micron.
What is the purpose of the high-pressure fuel filter?
To protect the fuel control from contaminants coming from the low-pressure pump.
What is the relationship between the fuel nozzles and the combustion chamber?
Fuel nozzles inject fuel into the combustion area in a highly atomised spray pattern.
What is the purpose of shrouds in fluid lines of an aircraft engine?
To catch fluid leaks and carry them away to the engine drain mast
Shrouds are used in critical areas to prevent fluid from leaking onto hot surfaces.
What are the two methods used to protect fluid line connections against leaks?
- Shrouded connections
- Double sealed connections
Shrouded connections help to catch leaks, while double sealed connections aim to prevent them.
What is the function of the O-ring inside the shroud?
To prevent leakage from the coupling nut onto the hot combustion case
O-rings are essential for maintaining safety in engine operations.
How do older aircraft engines differ in their fuel supply systems?
They use two fuel supply lines and two fuel manifolds instead of one
This design helps in redundancy for fuel supply.
What are the two types of fuel nozzles used in aircraft engines?
- Simplex
- Duplex
These nozzles differ in their design and functionality.
What is a key requirement for duplex fuel nozzles?
They usually require a dual manifold and a pressurising valve or flow divider
This setup allows for the division of primary and secondary fuel flow.
What are the two methods of mounting fuel nozzles?
- External mounting
- Internal mounting
Each method has its advantages regarding maintenance and accessibility.
Why is even fuel distribution important in the burner section of an engine?
It is important for efficient combustion
Uneven fuel distribution can lead to performance issues.
What is a disadvantage of the simplex nozzle?
It can only give good atomisation in a small fuel flow range
This limits its effectiveness during different phases of engine operation.
What are the two sets of simplex nozzles used for?
- One set for engine start-up to idle speed (primary fuel nozzles)
- A second set for acceleration to maximum power (secondary fuel nozzles)
This design allows for better atomisation across varying fuel flow requirements.
What do modern engines typically use instead of separate simplex nozzles?
Duplex nozzles that combine two nozzles in one component
This simplifies the fuel delivery system.
What is the role of the check valve in the fuel nozzle?
To prevent fuel from entering the combustion chamber by gravity when fuel pressure decreases
This mechanism helps to avoid unwanted fuel combustion.
