15.11 Flashcards
How do you increase and decrease power needed for the required thrust output
Varying flow of fuel to the combustion chamber
What is rich blowout
When quantity of fuel becomes excessive limiting the temperature of blades exceeded
When does rich blowout occur
Not enough oxygen in air supply to support combustion
Excess fuel cools mixture to below combustion temperature
What is the function of fuel control systems
Match fuel flow to power requested by flight crew
Fuel control sections
Computing and metering
What does EEC stand for
Electronic engine control
How does the fadec system work
No hydromechanical fuel control back up system
How does the fadec system provide information
Electronic sensors to give engine parameter information to the EEC
What does the EEC do
Computer that controls the operation of the engine
What is the EEC placed
In part of the engine nacelle that is cool
How many channels does the EEC have
2 , A and B
What memory does the EEC have
Volitile and non-volitile to store performance and maintenance data
Where is the fuel metering unit located
Mounted on the front face of the gearbox
What does primary fuel system do
Store fuel
What does secondary fuel system do
Supplies fuel to the engine
What are the 2 parts of the fuel system
Distribution and control
3 tasks of fuel distribution system
Supply fuel from fuel system to combustion chamber
Pressurise fuel so it vapourises in the combustion chamber
Heat the fuel
How much does the low pressure fuel pump increase pressure to
175psi
How much does the high pressure pump increase fuel pressure to
900 psi
What are engine driven fuel pumps divided into
Constant displacement
Non-constant displacement
What is a centrifugal pump
Non-constant displacement pump
What is the boost stage of the engine driven pump
Where the output of the centrifugal is varied
How is the fuel pump lubricated
Passing fuel through it
Never turn the pump on without a fuel flow supplied to the inlet
Where is a low pressure filter
Between supply tanks and engine fuel system to protect engine driven fuel pumps
Where is the high pressure filter
Between fuel pump and fuel control to protect fuel control from contaminants brought by low pressure pump
3 types of filters used
Micron
Wafer screen
Plain screen mesh
What filter has the greatest filtering action
Micron
Porous cellulose can remove FOD up to 10-25 microns
What’s the most widely used filter
200 mesh
35 mesh micron filters
Used in fuel pumps and fuel controls
What does the wafer type filer have
Replaceable element made of layers of screen disks
What are mesh filters made of
Mesh steel wire
What does the heat exchanger use to heat up fuel to stop water freezing
Engine bleed air or engine oil
How do we protect connections in fluid lines against leaks
Shrouded connections
Double sealed connections
What does a shrouded connection do
Doesn’t prevent a leak but catches leaks and carries them away by the engine drain system
How many manifold does a simplex nozzle need
One
How many manifolds does a duplex nozzle need
Dual manifold and pressuring valve or flow divider to divide primary and secondary main fuel flow
What is external mounting
where a mounting pad is provided to attach nozzle to case or inlet air elbow
What is internal mounting
At the liner dome the chamber cover is removed for replacement or maintenance of the nozzle
What are primary fuel nozzles
Set of simple nozzles used for engine start up to idle speed
What are secondary fuel nozzles
Second set of simplex nozzles used acceleration to maximum power
What’s a duplex nozzle
Dual flow nozzles which combine the 2 simplex nozzles in one
Why is a check valve used
Prevent carbon formation
When does the check valve close
Fuel pressure in the manifold decreases after the hp fuel shut off valve is closed
Why is it important for the check valve to close
So no fuel enters the combustion chamber from the manifold by gravity
What does crosstalk logic do
Compares data from channels A and B
