15.11 Fuel System Flashcards
Fuel systems must be able to respond to rapid acceleration demands. But if fuel flow increases too rapidly what can happen?
Rich blowout or compressor stall.
What are the 3 types of fuel controller systems?
Hydro mechanical.
Hydro mechanical/electronic.
FADEC.
What does FADEC fuel control system use?
Electronic sensors.
What are the 2 sections of the hydro mechanical fuel control system?
Computing and metering.
Does hydro mechanical fuel control system have an electronic interface?
No
What are the negatives of the hydro mechanical fuel control system?
Very complicated.
Fuel metering is not as accurate as electronic type.
What does a hydro mechanical/electronic fuel control system use?
Remotely located Electronic Engine Control (EEC)
What are the 3 functions of the engine fuel system?
Pressurise fuel.
Meter fuel.
Deliver atomised fuel.
What are the 2 sections of a hydro mechanical/electronic fuel control asssmbly?
Fuel shut off.
Fuel metering.
What is the purpose of the vane fuel pump assembly in a hydro mechanical/electronic system?
To provide high pressure fuel.
What does the filter bypass have to provide excessive differential pressure?
An integral differential pressure indicator.
What provide the fuel metering function of the EFCU in a hydro mechanical/electronic system?
Hydraulically Metering Unit.
What does the hydro mechanical/electronic EEC system consist off?
Hydro mechanical fuel control/ HMU.
EFCU
Power Lever Angle (PLA) potentiometer.
What transmits electronic signals to the EFCU in a hydro mechanical/electronic system?
PLA potentiometer.
Where is the EFCU located?
Remotely located mounted on the aircraft.
What does the EEC do in a FADEC fuel control system?
Calculates the amount of fuel by adjusting the Fuel Metering Valve.
In a FADEC system, the EEC houses 2 electronic channels ( A + B ). What can be said about them?
Separated internally.
Cooled by convection.
What supplies EEC in the FADEC system?
Throttle Lever Angle resolver.
In a FADEC system, how do the 2 electronic channels compare their data?
Crosstalk logic.
What system has a Fuel Metering Unit( FMU)?
FADEC system only.
Where is the FMU mounted?
Mounted on gearbox front face, and attached to fuel pump front.
In a FADEC system, How does the EEC receive position feedback?
RVDT.
LVDT.
Thermocouples.
What is the difference between the primary and secondary fuel system?
Primary= stored fuel.
Secondary = supplies fuel.
What is the pressure of fuel at the LP fuel valve?
40 psi.
What is the pressure of fuel at the LP fuel pump?
175psi.
The LP fuel pump increases pressure.
What can the oil cooler also be known as ?
Fuel heater.
What can be said about the Fuel Control Unit?
It gets more fuel than necessary to be ready for acceleration.
What returns excess fuel from the FCU?
Bypass return line.
What is the pressure of fuel after the Pressure Relief Valve?
900 psi.
What does the Fuel Recirculation Valve do?
It mixes cold fuel from tank with hot fuel then returns it to the tank
What does the Fuel Flow Transmitter do?
Measures fuel flow.
What is the purpose of a servo fuel heater?
Secondary heating if ice is still present in fuel.
Why must the Engine Driven fuel pump be capable of maximum flow?
For satisfactory nozzle spray and accurate fuel regulation.
What are the 2 types of EDPs?
Constant displacement.
Non- constant displacement/ centrifugal.
How is the fuel pump lubricated?
By fuel passing through the pump.
Where is the LP filter located?
Between supply tank and engine fuel system.
(Before LP pump)
Where is the HP filter located?
Between the fuel pump and fuel control.
(After HP pump)
What are the 3 types of filters?
Micron,
Wafer screen,
Plain screen.
What filter offers the greatest filtering action?
Micron filter.
10-25 microns.
What is the most used filter?
200 and 35 mesh micron filter.
On what engines are single fuel manifolds used?
Modern GTE.
What is the purpose of shrouds?
To catch fuel leaks and drain them to the engine drain mast.
What are the 2 methods to protect fluid line connections?
Shrouded lines.
Double sealed lines.
How many lines and manifolds do old GTEs have?
2 fuel supply lines and 2 manifolds.
What manifolds do duplex and simplex nozzles require?
Duplex= dual.
Simplex= single.
What’s the negative of simplex nozzles?
Only give good atomisation in a small fuel flow range.
When 2 sets of simplex nozzles are used, what’s the difference between the 2?
Primary = small discharge orifice for engine start up.
Secondary = larger discharge orifice for acceleration up to max power.
What does the check valve prevent as well as backflow?
Carbon formation
How does a dual flow nozzle differ from 2 single flow nozzle?
It combines 2 nozzles into 1 component instead of 2.
