M15.11 Fuel Systems Flashcards
What three groups are gas turbine engine fuel control systems divided into?
Hydromechanical
Hydromechanical/ Electronic
Full authority digital engine control (FADEC)
How does hydromechanical/electronic fuel control work?
A hybrid of the two types
Can function solely as hydromechanical
In dual mode inputs and outputs are electronic
Fuel flow set by servo motors
How is a hydromechanical fuel control driven?
Generally driven by a gas generator train of the engine
What does the total engine fuel and control system consist of?
The vane fuel pump assembly
The filter bypass valve
FADEC has no what type of backup system?
Hydromechanical fuel control
The FADEC system uses what sensors?
Electronic sensors
The FADEC system uses electronic sensors for what?
To provide engine parameters information to the EEC
What does the EEC do with the information from the electronic sensors?
Calculates the amount of fuel flow by adjusting the fuel metering valve.
The fuel metering valve reacts to commands from what?
The EEC
What is the EEC?
Electronic engine control- the computer that controls the operation of the engine
Where is the EEC generally placed?
Placed in an area of the engine nacelle that is cool during operation
Where is the fuel metering unit mounted?
On the front face of the gearbox
What is the difference between the primary fuel system and the secondary fuel system?
Primary- Stores the fuel
Secondary- supplies the fuel to the engine
Main purpose of the secondary fuel system supply?
Supply fuel to combustion chamber
Control the quantity of fuel necessary for the correct operation of the engine
The engine due, system can be split into what two subsystems?
Fuel distribution system
Fuel control system
3 main tasks of fuel distribution system?
Safely supply the fuel from the aircraft fuel system to combustion chamber?
To pressure rise the fuel sufficiently so that it can be vaporised in the combustion chamber
To heat the fuel
Describe the start of the fuel distribution layout?
The fuel system starts directly behind the low pressure fuel shut off valve
The low pressure fuel pump increases the fuel pressure to approx what?
175psi
At maximum engine speed, the high pressure fuel pump increases fuel pressure to what?
900psi
Does the pump always supply more or less fuel needed for combustion?
Always more fuel than is needed
Two types of engine driven pumps?
Constant displacement
Non-constant displacement
What type of pump is usually used at the inlet of the engine driven pump?
A non constant displacement (centrifugal pump)
To provide positive flow to the second stage of the pump
How is the fuel pump lubricated?
Lubricated by the fuel passing through the pump and should never be turned without a fuel flow supplied into the inlet.
3 most common fuel filters?
Micron filter
Wafer screen filter
Plain screen mesh filter
To prevent ice formation in the fuel filters what is required?
Heat exchangers
What is the bleed air and oil type in a heat exchanger?
Air to liquid exchanger
Liquid to liquid heat exchanger
What are used on fluid lines routed through critical areas of the engine to catch fluid leaks?
Shrouds
Two methods to protect the connections of fluid lines against leaks?
Shrouded connections
Double sealed connections
Can shrouded connections prevent leaks?
No, they catch leaks and carry them away by the engine drain system
Two types of fuel nozzles?
Simplex
Duplex
What does a duplex nozzle require?
A dual manifold
Pressuring valve or flow divider and secondary fuel flow
What does a simplex nozzle require?
Single manifold
The fuel nozzles supply the metered fuel into what part of the combustion chamber?
The forward part
To prevent carbon formation what is used in a fuel nozzle?
A check valve
How does the check valve work in the fuel nozzle?
Closes when the fuel pressure in the manifold decreases after the HP fuel shut off valve is closed
What is the function of the check valve used in the fuel nozzle
Prevents the formation of carbon inside the fuel nozzle
What is the dual function of the oil cooler?
The fuel cools the oil of the engine oil system which in turn heats the fuel
