M15.11 Flashcards
(55 cards)
What is a rich blow out
If the quantity of fuel becomes excessive the limiting temperature of the turbine blades can be exceeded, or a compressor stall could occur
Gas turbine engine fuel control systems are generally divided into three categories:
- Hydromechanical
- Hydromechanical/electronic
- Full Authority Digital Engine (or Electronics) Control (FADEC)
The hydromechanical/electronic fuel control is a hybrid of the two types of fuel control but can function solely as a hydromechanical control. In the dual mode, inputs and outputs are electronic, and fuel flow is set by
Servo motors
The FADEC-type control gives the electronic controller (computer) what type of control
Full control
What 2 sections do fuel controls have
Computing and metering
Does a hydro mechanical fuel system have any electronic interface in computing or metering fuel flow
A pure hydromechanical fuel control system has no electronic interface assisting in computing or metering the fuel flow. It is generally driven by the gas generator gear train of the engine to sense engine speed
What parameters do hydro mechanical fuel systems sense
compressor discharge pressure, burner pressure, exhaust temperature, and inlet air temperature and pressure
How is fuel metering achieved through a hydro mechanical fuel system
When the computing section determines the correct amount of fuel flow, the metering section through cams and servo valves delivers the appropriate quantity of fuel to the engine fuel system.
Is a hydro mechanical fuel delivery system as accurate as electric
No
Why is the fuel control unit sometimes mounted on the fuel pump
The fuel control unit is sometimes mounted on the vane fuel pump assembly. It provides the power lever connection and the fuel shut-off function. The unit provides mechanical overspeed protection for the gas generator spool during normal (automatic mode) engine operation.
What type of filter is fuel supplied through
A 200 micron inlet screen
Is the fuel manual mode solenoid valve energised or de energised in the automatic mode
The manual mode solenoid valve is energised in the automatic mode.
Fuel sub systems
- Distribution
- Control
LP fuel pump pressure
175psi
HO fuel pump max pressure
900psi at max power
Overpressure relief valve pressure
1250psi
Types of HP fuel pump
- Gear type
- Piston type
Most common type of fuel pump in turbofans
Gear type
Heat exchangers that can be found in the engine fuel system
- Engine oil cooler
- Servo fuel heater
- IDG oil cooler
What prevents fuel leaks in the hot environment of the HPC and combustion case
Fuel lines protected by shrouds
Methods to protect the connections of fluid lines against leaks
- Shrouded connections
- Double sealed connections
Disadvantage of ding,e flow nozzles
Only has good atomisation at a small fuel flow range
How do we overcome the disadvantages of single flow nozzles
- Having a primary and secondary set
- Primary for start and idle
- Secondary for max
How are primary and secondary fuel nozzle usually supplied
Independent fuel manifolds
