15.11 Fuel Systems Flashcards
What is the primary function of the engine fuel system?
To increase or decrease power to obtain the required thrust for any operating condition.
What happens if the quantity of fuel becomes excessive?
It can exceed the limiting temperature of the turbine blades or cause a compressor stall.
What is a rich blowout?
A condition where the mixture is cooled below combustion temperature by excess fuel, causing insufficient oxygen for combustion.
What are the three categories of gas turbine engine fuel control systems?
- Hydromechanical
- Hydromechanical/electronic
- Full Authority Digital Engine Control (FADEC)
What does FADEC stand for?
Full Authority Digital Engine Control.
How does the fuel metering device in a FADEC system operate?
It meters fuel using only outputs from the Electronic Engine Control (EEC).
What is the role of fuel nozzles in the fuel system?
To atomise the fuel for efficient ignition and combustion.
What is the purpose of the hydromechanical fuel control assembly?
To provide the fuel metering function of the Electronic Fuel Control Unit (EFCU).
True or False: Hydromechanical fuel controls are becoming more common in modern engines.
False.
What is the function of the fuel shut-off section in the hydromechanical fuel control assembly?
To allow manual control of fuel flow to the engine.
What does the EEC do in a FADEC system?
It calculates the amount of fuel flow by adjusting the fuel metering valve.
What is the function of the vane fuel pump assembly?
To provide high-pressure fuel to the engine fuel control system.
Fill in the blank: The fuel temperature sensor thermocouple sends information to the __________.
EEC
What does the manual mode solenoid valve do in a hydromechanical/electronic fuel control system?
It enables the mechanical speed governor to function as an all-speed governor.
What is the purpose of the flow divider and drain valve assembly?
To proportion fuel to the engine’s primary and secondary fuel nozzles and drain at engine shutdown.
What is the function of the start fuel enrichment solenoid valve?
To provide additional fuel flow for engine cold starting or altitude restarts.
What is the role of the torque motor in the fuel control system?
To increase or decrease fuel flow in the automatic mode.
What type of memory does the EEC contain?
Both volatile and non-volatile memory.
What does the EFCU control during normal engine operation?
Thrust setting, speed governing, acceleration, and deceleration.
What is the advantage of FADEC systems over traditional controls?
FADEC systems provide more accurate scheduling of fuel by sensing many engine parameters.
What does the crosstalk logic in the EEC do?
Compares data from channels A and B to determine which channel is best for controlling outputs.
What is the significance of the fuel control run cut-off switch?
It controls the high-pressure fuel shut-off valve to start or stop fuel flow.
What is the primary component of the FADEC engine fuel control system?
The Electronic Engine Control (EEC).
What is the function of the minimum pressure and shut-off valve in the fuel metering unit?
To start or stop fuel flow based on signals from the EEC.
Fill in the blank: The EEC receives electronic signals from the flight deck to set engine power or _______.
thrust
What is the function of the off valve in the fuel metering unit?
To start or stop fuel flow
The off valve is crucial for controlling the fuel supply to the engine.
What types of sensors does the EEC use to receive position feedback for engine components?
Rotary differential transformer, linear variable differential transformer, thermocouples
These sensors provide essential engine parameter information.
What does the fuel control run cut-off switch control?
The high-pressure fuel shut-off valve
This valve allows or cuts off fuel flow to the engine.
Where is the fuel temperature sensor thermocouple located?
On the fuel outlet line at the rear of the fuel/oil cooler
This sensor sends temperature information to the EEC.
What are the two main connections shared by both channels of the EEC?
Programming plug, test connectors
These connections are essential for EEC functionality.
What is the purpose of the programming plug in the EEC?
To select the proper software for the thrust rating of the engine
The programming plug ensures the EEC is configured correctly for specific engine performance.
How is the programming plug attached to the engine?
With a lanyard
This attachment method ensures the plug stays with the engine when the EEC is removed.
What are the two subsystems of the engine fuel system?
- Fuel distribution subsystem
- Fuel control subsystem
What are the three main tasks of the engine fuel distribution system?
- Safely supply the fuel to the combustion chamber
- Pressurise the fuel for vaporisation
- Heat the fuel to prevent ice build-up
What is the main purpose of the secondary fuel system?
To supply fuel to the engine combustion chamber and control the quantity of fuel for correct engine operation.
What component feeds fuel into the main fuel supply line?
Low-pressure fuel shut-off valve
What does the low-pressure fuel pump do?
Increases the fuel pressure that comes from the fuel tank boost pumps.
What is the dual function of the oil cooler in the fuel system?
- Cools the engine oil
- Heats the fuel to prevent ice build-up
What is the role of the high-pressure fuel pump?
Increases fuel pressure to the level required for correct vaporisation in the combustion chamber.
What does the fuel control unit do?
Meters the fuel needed for combustion and controls the supply and shut-off of fuel to the fuel nozzles.
Fill in the blank: The _______ measures the actual fuel flow and transmits signals to the flight deck.
fuel flow transmitter
Where are all components of the fuel distribution system located?
In the area of the accessory gearbox on the engine.
What is the function of the pressure relief valve in the high-pressure fuel pump?
Protects components in the high-pressure fuel system against overpressure.
True or False: The low-pressure fuel pump prevents cavitation at the inlet of the high-pressure fuel pump.
True
What types of fuel filters are commonly used?
- Micron filter
- Wafer screen filter
- Plain screen mesh filter
What is the purpose of the micron filter?
Removes foreign matter measuring from 10-25 microns.
What is the main function of heat exchangers in gas turbine engine fuel systems?
To prevent the formation of ice in the fuel filters.
What types of heat exchangers are used in fuel systems?
- Air-to-liquid exchanger
- Liquid-to-liquid heat exchanger
What is the primary function of fuel spray nozzles?
Inject fuel into the combustion area in a highly atomised spray pattern.
What is a fuel manifold?
Distributes fuel to the individual fuel nozzles on the combustion chamber.
What are the two types of fuel nozzles commonly used?
- Simplex
- Duplex
What is the disadvantage of the simplex nozzle?
Can only provide good atomisation in a small fuel flow range.
What type of nozzle combines the functions of primary and secondary nozzles?
Duplex nozzle
What is the main function of the fuel nozzle in terms of atomisation?
Change solid fuel flow into a mist of microscopic fuel droplets.
What type of nozzles do modern engines typically use?
Duplex nozzle
Duplex nozzles combine the functions of primary and secondary flow nozzles into one component.
What are the two components of a dual-flow nozzle?
Two discharge orifices and two internal fuel supply lines
The primary orifice is smaller and located at the center, while the larger secondary orifice is arranged around it.
What controls the secondary fuel flow in a duplex nozzle?
A spring-loaded pressurising valve
This valve is also known as the flow divider valve and is typically an internal component of the fuel nozzle.
What happens to the flow divider valve as engine speed increases?
It opens
The valve closes when the engine speed decreases.
What role does airflow play in fuel nozzles?
It cools the nozzle and removes residual fuel
Airflow enters the combustion chamber through slots and holes in the nozzle tip.
What is the purpose of the check valve in the fuel nozzle?
To prevent fuel from entering the combustion chamber by gravity
The check valve closes when fuel pressure in the fuel manifold decreases.
How does the air-spray nozzle achieve atomisation?
By using a high velocity of air
This method allows for good atomisation even at low fuel flows.
What feature of the air-spray nozzle aids in fuel atomisation?
A large inner airflow that rotates after passing through the inner swirler
This airflow meets the fuel at the nozzle tip, turning it into small droplets.
What does the outer airflow do in an air-spray nozzle?
It passes through an outer swirler
This airflow further enhances the atomisation of fuel.
Is the air-spray nozzle a single-flow or dual-flow nozzle?
Single-flow nozzle
It can supply sufficient fuel for all engine operating conditions.
What prevents carbon formation at the tip of the air-spray nozzle?
Bypassing airflow
Similar to the fuel spray nozzle, this airflow cools the nozzle.
