M15.11 Fuel Systems Flashcards
What are the two sub systems of the engine fuel system?
. Fuel distribution
. Fuel control
What are the 3 tasks of the fuel distribution ?
. Safely supply fuel from aircraft to the combustion chamber
. Pressurise the fuel so it can be vaporised for combustion
. Heat the fuel, fuel flow to the fuel nozzles so it’s not blocked by ice
What does the primary fuel system do?
Stores fuel (tank)
Where is the secondary fuel system?
On the engine
What is the journey that fuel takes through the engine??
- From Fuel tank
- Through low pressure fuel shut off valve to
- Main fuel supply line
- Low pressure pump
- Oil cooler
- Fuel filter
- High pressure fuel pump (with pressure relief valve)
- Fuel control unit
- On some engines - servo fuel heater
- Fuel control unit
- To fuel manifold
- Fuel nozzles
Why are oil coolers built into the hp fuel pump??
It reduces the need for lots of external pipelines
What does the LP fuel pump do??
. Increases fuel pressure from the tanks up to 175PSI
. Supplies fuel across oil cooler and filter to hp fuel pump
At max engine speed what does the HP fuel pump do??
. Increases fuel pressure to 900PSI
What stage does the over pressure relief valve open??
1250PSI
The fuel pump always does what?
Supplies more fuel than is needed for combustion
What is the bypass fuel used for?
. To cool the IDG oil cooler
Where is the fuel control unit mounted??
. The engine fuel pump on the accessory gearbox
On most turbofan engines the fuel control unit is?
A hydro mechanical component
How does a hydro mechanical fuel control unit work?
. Controls functions by fluid pressures and mechanical components
What are the two different fuel control unit??
. Speed governed fuel control unit
. Constant thrust control units
What aircraft are speed governed fuel control units used on?
. On older aircraft
What aircraft are constant thrust fuel control units found on??
. Modern turbofan engines
What is the thrust lever signal normally?
A mechanical deflection of a small power lever at the fuel control unit
What do hydro mechanical fuel control units use ?
. Hydraulic, mechanical and pneumatic signals
What 4 signals does a fuel control unit need?
. Throttle demand signal
. Speed feedback signal
. Temperature signals
. Pressure signals
The Fuel control unit is split into what two sections?
. Fuel metering section
. Computing section
What can computing section further be split into?
. Governing section
. Limiting section
What are the 3 main tasks if the fuel control unit??
. Fuel metering
. Power control
. Engine protection
What is the purpose of the metering section??
. Makes sure that all necessary fuel get to the fuel nozzles and all the fuel that is not needed for combustion, returns to fuel pump
What does a governing section do?
. Makes sure selected power is controlled
What does limiting section do?
. Monitors governing section and makes sure the engine always operates within safe limits
What does FADEC stand for??
. Full authority digital engine control
What is the purpose of FADEC??
. Has full authority over engine control functions
What is the heart of the FADEC system??
The digital computer
What is the 2nd main component of the FADEC system??
. The fuel metering unit (FMU)
Why does the FMU and HMU nit have a letter C at the end??
Because it cannot control
— just recurve orders from ECU to move fuel metering valves
Engines that have FADEC systems don’t have what?
Hydro mechanical fuel control unit (HMU)
Where is the electronic control unit located?
On fan stator case of the engine
Where does the power supply for FADEC come from??
. Aircraft or
. Small permanent magnet alternator on engine accessory gearbox
What does the ECU also need?
A feedback signal about the opening condition of the fuel metering valve
What does the engine interface unit do?
. Transmits the data between FADEC system to the aircraft
