Fuel systems Flashcards
What are the two systems in fuel
Primary & secondary
What’s the primary system used for
Store fuel
Where does secondary system supply fuel to and what does it control
Supply fuel to combustion chamber & control fuel quantity for all operating conditions of engine
What can the secondary fuel system split into
Fuel distribution and fuel control
What are the fuel distribution tasks
Safe supply to combustion chamber
Pressurise fuel so it can be vaporised into combustion chamber
Heat the fuel to prevent ice build up to allow flow
HP Pump pressure
900psi
Overpressure relief
1250psi
What does the LP pump do
Ensures HP pump don’t draw fuel from tanks by suction
Prevents cavitation
What does the metering section do
Returns unused fuel via bypass
How is bypass fuel used
Cool the IDG oil cooler
What type of component is a turbofan engine fuel control unit
Hydro mechanical
How are control functions done in a hydromechanical fuel control unit
Fluid pressures and mechanical components
What fuel control unit is used on modern turbofan engines
Constant trust fuel control units
In a thrust lever signal how does mechanical deflection occur
By rack and pinion transmission or rods and levers
N2 signal
Speed feedback transmitted by mechanical shaft from main fuel pump
N1 signal
Fuel pressure signal from hydromechanical speed sensor
How does fuel control unit receive signals
Via air sense lines
What do pressure sensors in fuel control unit convert
Convert pressure signals into mechanical signals
What 3 signals do hydromechanical fuel control units use
Hydraulic , mechanical and pneumatic signals
What sections is the fuel control unit split into
Fuel metering and computing section
What are the two parts of the computing section
Governing and limiting
Three tasks of fuel control units
Fuel metering
Power control
Engine protection
What does the metering section do
Make se sure necessary fuel gets to the fuel nozzles
And retunes fuel via bypass
What does the governing section
Makes sure selected power is controlled
What does the limiting section do
Make sure engine operates in safe limits
What is the heart of the FADEC system
Digital computer called ECU or EEC
Why do the terms FMU and HMU have no C in the acronym
They aren’t controlling units
FADEC haves a hydromechanical fuel control unit installed true or false
False
What is the FADEC system located
Fan stator case
Where does the power supply for FADEC come from
Aircraft or small permanent magnet alternator
ECU tasks
Fuel metering and engine limit protection
Another ECU task
Full power management & gives optimum thrust control for all operating conditions
What does the engine interface unit do
Transmit data between FADEC and aircraft
Control power supply from aircraft to the ECU
