Module 15.11 Fuel systems Flashcards
Quantity of fuel supplied must be automatically adjust for what?
Changes in ambient temperature or pressure
What are the 3 GTE fuel control systems?
- Hydromechanical
- Hydromechanical/electronic
- FADEC
If fuel flow increases too, rapidly an over rich mixture can occur, this can cause what?
- Rich blowout
- Compressor stall
In the dual mode of the hydromechanically/electronic metering system, fuel flow is set by what?
Servo motors
Input + output are electronic
The fuel metering system must be able to do what?
Increase and decrease power
To provide the correct fuel for the engine, hydromechanical fuel controls have what two sections?
Computing and metering
A pure hydromechanical control system has no what? and is driven by what?
- Electronic interface
— accessory gearbox
What is the function of the engine fuel system?
- Pressurise the fuel
- Meter the fuel flow
- Deliver atomised fuel to the combustion chamber
Fuel flow is controlled by what in hydromechanic control?
Hydromechanical fuel control assembly
The Hydromechanical fuel control assembly contains what two parts?
- Fuel shut off section
- Fuel metering section
The total engine fuel and control system contains what components?
- Vane fuel pump
- Filter bypass valve
What is the mechanical indication of bypass valve opening?
Pin extended
What does the EFCU stand for?
Electronic Fuel Control Unit
What does the Electronic Engine Control system consist of? (Hydromechanical)
- Hydromechanical fuel control
- EFCU
- Aircraft mounted power lever angle (PLA) potentiometer
What are the engine generator control signals? (Hydromechanical)
- Fan spool speed
- Gas generator spool speed
- Inner turbine temperature
- Fan discharge temperature
- Compressor discharge pressure
Where is the EFCU mounted?
Airframe
What does the PLA potentiometer transmit?
Electric signal of throttle lever position to the EFCU
The FADEC system uses electronic sensors to provide what?
Information to the EEC (electronic engine control)
What does the EEC do with the FADEC information?
Calculates amount of fuel flow by adjusting the fuel metering valve
What can be said about the two electronic channels in the EEC?
- Physically separate
- Cooled by convection
What provides the throttle lever position to the EEC in the FADEC system?
Throttle lever angle resolver
What does the cross talk logic do?
Compares data from channel A and B
What does the primary EEC channel control?
All the output drivers
Where is the fuel metering unit mounted in the FADEC system?
Front face of the gearbox and to the front of the fuel pump
The EEC provides position feedback for engine compartments by using what?
- RVDT
- LVDT
- Thermocouples
What does the programming plug do in FADEC?
Selects the proper software in the EEC for the engine thrust rating
What is the primary and secondary fuel system?
Primary - Stores fuel
Secondary - Supplies fuel to engine
A non-constant displacement pump (Centrifugal) is used at inlet of the EDP (engine driven pump) to provide what?
Provide positive flow to the second stage of the pump (HP pump)
How is the fuel pump lubricated?
Fuel passing through the pump
Where is the LP filter?
Before the pump
Where is the HP filter?
After the pump
What are the 3 most common types of filter?
- Micron filter
- Wafer screen filter
- Plain screen mesh filter
What filter has the best filtering action?
Micron filter, 10-25 microns
What is the most common filter?
200 mesh and 35 mesh micron filters
GTE fuel systems are very susceptible to what?
Ice in the fuel filters
What does the fuel manifold do?
Distributes the fuel to the individual fuel nozzles
What manifold are most common on GTE’s?
Single-fuel
Where is leaked fuel caught by the shroud drained to?
Engine drain mast
What are the methods of leak protection?
- Shrouded connection
- Double sealed connection
On older aircraft they have how many supply lines and manifolds?
Two
What does the secondary manifold supply fuel to?
Secondary fuel nozzles
What are the two nozzle types?
- Simplex
- Duplex
Duplex nozzles require what?
A duplex (dual) manifold
How can nozzles be mounted?
Internally or externally
What is the drawback of simplex nozzles?
Only good atomisation in a small fuel flow range
Using simplex, what is required for good atomisation across a wide fuel range?
- One set with a small discharge orifice (start to idle)
- Secondary set with large discharge orifice (idle to max)
(Old technology)
Duplex nozzles combine what?
Two nozzles in one component
Why is a check valve used in the fuel nozzle?
Prevent carbon formation
Fuel that is not required returns to the fuel pump via what line?
Bypass return line
Where is the fuel flow indicator located?
In between the Fuel control unit and the nozzles
Fuel to the LP pump is what psi?
40 psi
Fuel after the LP pump is what psi?
175 psi
Fuel after the HP pump is what psi?
1250 psi
Why is bypass return fuel mixed with LP pump outlet fuel in the recirculating valve before entering the engine?
To cool it down
