Module 15.11 Fuel Systems Flashcards
Where does the fuel system start?
Directly behind the low-pressure fuel shut-off valve.
What does the LP fuel shut-off valve do?
Feeds fuel into the main fuel supply line.
Where does the supply line run?
From the wing to the engine accessory gearbox.
What is the dual function of the oil cooler?
Cold fuel cools the oil which in turns heats the fuel.
Where does fuel go after exiting the supply line?
The low pressure fuel pump.
Where does fuel go after the low pressure fuel pump?
To the oil cooler.
What temperature does the oil cooler heat the fuel to?
Above the freezing point of water.
What is located after the oil cooler?
A fuel filter.
What component is after the fuel filter?
High pressure pump
What does the high pressure fuel pump do?
Increases the fuel pressure to the level required for correct fuel vaporisation in the engine combustion chamber.
What valve accompanies the high pressure pump?
A pressure relief valve.
Where does fuel go to after the high pressure fuel pump?
Fuel Control Unit (FCU)
What does the fuel control unit do?
Meters the fuel that is needed for combustion.
What two valves does the Fuel Control Unit (FCU) consist of?
Fuel Metering Valve
High pressure shut-off valve
What is responsible for the supply and shut-off of fuel to the fuel nozzles at the combustion chamber?
The Fuel Control Unit.
Where does fuel go after leaving the Fuel Control Unit?
Fuel flow transmitter.
What does the fuel flow transmitter do?
Measures the actual fuel flow and transmits signals to the flight deck for the fuel flow and fuel used indication.
After leaving the fuel flow transmitter, where does fuel go?
To the engine fuel manifold
What does the engine fuel manifold do?
Distributes the fuel to the individual fuel nozzles on the combustion chamber.
What does the low pressure pump increase the fuels pressure to?
175 psi
At maximum engine speed, what does the high-pressure fuel pump increase the fuel pressure to?
900 psi
What does the high pressure relief valve do and where is it located?
Prevents damage to the fuel system components.
Located with the HP fuel pump.
Does the high pressure pump supply more of less fuel that is needed for combustion?
More
What is done to the fuel that’s not needed after the metering stage?
It returns to the fuel pump via the bypass return line.
What are the two types of engine-driven fuel pump?
Constant displacement
Non-constant displacement
What is used at the inlet of the engine-driven pump to provide positive flow to the second stage of the pump?
A non-constant displacement (centrifugal pump).
What lubricates the fuel pump?
Fuel passing through the pump
Why are heat exchangers needed?
To stop water from freezing in the fuel when it reaches 0°C or below in the tank.
What two sources of heat can the heat exchangers use?
Engine bleed air or engine oil
What is an air-to-liquid heat exchanger?
A heat exchanger that uses engine bleed air to heat the fuel.
What is a liquid-to-liquid heat exchanger?
A heat exchanger that uses engine oil to heat the fuel.
What type of fuel manifold is found on modern gas turbine engines?
Single-fuel manifolds.
What are the two types of fuel nozzles?
Simplex
Duplex
What type of manifold does a duplex fuel nozzle need?
Dual manifold
What type of manifold does a simplex fuel nozzle need?
Single manifold
What type of fuel nozzle do modern engines use?
Simplex
Other than a dual manifold, what else do duplex fuel nozzles need?
A pressurising valve or flow divider for dividing primary and secondary (main) fuel flow
What are the three engine fuel control system categories?
Hydromechanical
Hydromechanical/electronic
Full Authority Digital Engine Control (FADEC)
What is the function of fuel control systems?
To schedule the fuel flow to match the power requested by the flight crew.
What is a hydromechanical fuel control system?
A system that has no electronic interface assisting in computing or metering the fuel flow.
What is a hydromechanical/electronic fuel control system?
A system where the fuel pressure, metering and delivery is controlled by the hydromechanical fuel control assembly. An Electronic Engine Control (EEC) adjusts the fuel flow.
What is a Full Authority Digital Engine Control (FADEC) system?
A system that uses electronic sensors to provide engine parameter information to the EEC.
What is the primary component of the FADEC system?
The EEC (Electric Engine Controls).
What does the EEC (Electric Engine Controls) do?
Controls the operation of the engine.
What does the EEC housing consist of?
Two electronic channels (A and B) that are physically separated.
Where is the EEC located?
In an area of the nacelle that is cool during engine operation.
What supplies the EEC with a signal in proportion to the thrust lever position?
The throttle lever angle resolver.
What does the cross talk logic in the EEC do?
Compares data from channels A and B and uses this to find which EEC channel is the best to control the output driver.
What happens if the EEC finds the other (monitoring) channel is better for control of a specific bank?
It changes control of that one bank to the other channel.
What does the EEC have to store performance and maintenance data?
Volatile and non-volatile memory.
Where is the Fuel Metering Unit (FMU) mounted?
On the front face of the gearbox and is attached to the front of the fuel pump.
What two input connections do both channels of the EEC share?
The programming plug and test connectors.
What does the programming plug do?
Selects the proper software in the EEC for the thrust rating of the engine.
When removing the EEC does the programming plug remain with the EEC or the engine?
The engine
What two methods protect the connections of fluids against leaks?
Shrouded connections
Double sealed connections
What are primary fuel nozzles?
A nozzle with small discharge orifices for engine start up.
What are secondary fuel nozzles?
Nozzles with large discharge orifices for acceleration up to max power.
Where is the EFCU mounted?
On the airframe.
