Turbine engine fuel and metering systems Flashcards
What are the different types of jet fuel and which is the most common?
Jet A most common
Jet A1
Jet B
Why does jet fuel cause more problems that avgas?
Jet fuel has a higher viscosity than avgas and holds contaminants better
What is an FCU and what is its function?
Fuel Control Unit is to schedule the fuel flow to match the power required by the pilot
What are basic types of fuel control units?
Hydromechanical
Hydromechanical/electronic
Full Authority Digital Engine (or Electronics) Control (FADEC)
What are the two sections on a hydromechanical FCU?
Computing and metering
What is the computing section of an FCU?
It determines the correct amount of fuel flow
What is the metering section of a FCU?
Delivers the fuel to the engine fuel system through cams and servo valves
How does a hydromechanical/electronic FCU work?
The system uses a remotely located EEC to adjust the fuel flow
How does the FADEC FCU work?
A system of electronic sensors that feed engine parameter information into the EEC
What type of adjustments are allowed on an FCU?
Only external commonly called trimming the engine
What are the two trimming adjustments?
Idle RPM
Maximum RPM
What FCU require trimming?
Hydromechanical or supervisory
In which direction should the aircraft be facing while trimming the engines?
Into the wind for a specific target RPM or EPR
How is target RPM or EPR determined?
Using charts based on temp and barometric pressure
Where does the fuel pump receive fuel?
The fuel pump
Which stage of the boost pump pressurized the fuel and sends it to the fuel/oil cooler?
The low pressure boost state.
What happens in the high pressure main stage?
It increases the fuel pressure and sends it to the fuel metering unit
What is the fuel filter located?
After every pump
What is a Delta P?
Differential pressure switch that gives a warning to the crew if the fuel filter is blocked
What are different types of fuel filters?
Wafer screens
Steel mesh
Cellulose fiber
Why do turbine powered aircraft require fuel heaters?
They operate in cold ambient air that can cause ice crystals to form and clog the filter
What are the two types of fuel heaters?
Air to fuel-air from the engines compressor
Oil to fuel-hot oil from the lubricating system
What are the two distinct fuel system pump categories?
Constant displacement
Variable displacement
What is a positive displacement pump?
The gear that supplies a fixed quantity of fuel to the engine for every revolution of the pump gears
What is the function of fuel nozzles?
To inject fuel into the combustion area in a highly atomized, precisely patterned spray so that burning is completed evenly, in the shortest possible time
What are the two types of fuel nozzles?
Simplex
Duplex
What is the advantage of a duplex over a simplex fuel nozzle?
Provides better atomization at starting and idling speeds
What is a flow divider?
Creates primary and secondary fuel supples
