AGK Engines - Gas Turbine Fuel System Flashcards
Role of the fuel system is to…
Provide correct quantity of fuel at correct pressure under all conditions
~Alt
~Airspeed
~Air temp
~Engine temp
~Engine speed
~Thrust settings
Everything is automatic, apart from thrust
What is fuel delivery dependant on?
Core Rotation Speed (N2)
Your looking at N1, but the fuel system is looking at N2 so it can produce the power you want the N1 to be at
How is fuel delivered onto the engine?
Boost pumps in the main tanks
~30-50psi fuel pressure in the LP (Booster) system
~50psi in central tank so it drains first
~115V AC single phase electric pumps
Where does the fuel go before it reaches the HP system, ready for metering
Goes through a fuel heater and filter
Three different types of HP systems include…
Hydromechanical Unit - uses Fuel Control Unit (FCU) to regulate fuel to the fuel nozzles
Hydromechanical Mechanical Engine Controller (MEC) - an electronic version of FCU
FADEC - uses Electronic Engine Controller (EEC) and Fuel Metering Unit (FMU)
Hydromechanical systems are considered obsolete in modern engines
Hydromechancial (FCU)
Utilises a swashplate pump as a HP source and as speed changes, swash angle changes which causes varied fuel flow
Air/Fuel ratio kept correct to keep engine working in line
As pilots demand more thrust, a governor within FCU commanded more fuel to be injected
Subsequently EGT increases which is sensed by FCU in a closed loop control system
Engine speed would increase to reflect changes
What does the FCU sense?
Thrust lever angle
Air temp and pressure
Rapid acceleration changes
Engine speed
EGT
Compressor delivery pressure (P3)
Power Management Control System
Control a multi spool engine where FCU system can only efficiently deal with a single spool engine
Allows fine control of N2 in order to meet thrust demands and N1 rotation
Some systems refer to Mechanical Engine Control Unit (MECU) the systems are broadly the same
Sensing is achieved using signals converted in voltages
FADEC stands for
The Full Authority Digital Engine Control
What does FADEC compromise of?
Electronic Engine Controller (EEC)
1 FADEC system per engine
2 Channels (2 Separate Computers) (changes channel on each start)
~Each with their own power supply
~Both channels check input/output
signals for validity and errors
Is FADEC highly redundant?
Allows a high degree of reducnacy as the likelihood of total failure is remote
When signals are processed in FADEC where are they delivered to?
Fuel Metering Unit (FMU) situated with the HP fuel system
FADEC performs the following…
Delivery of fuel to the Engine Fuel Nozzles
Maintain fuel pressure under all engine RPM’s
Shut-off fuel when commanded
Engine Overspeed Protection
Controlling Compressor Airflow (Bleed valves)
Reverse Thrust
Active Clearance Control (ACC)
Ensuring Manifold Fuel draining during shut-down
FADEC based fuel system diagram
FADEC reduced functionality
Single channel - no loss of function (uses other channel)
Dual channel - Loss of engine control, but last demanded engine setting is still available (EPR or N1)
~Loss of associated engine instruments
Power supply loss - FADEC has a dedicated alternator, failure will lead to duel channel failure
Signal loss - loss of an input signal may nor have a huge impact but signal losses will cause associated displayed parameters to be lost
Jet fuel
Jet Kerosene or AVTUR (Aviation Turbine Fuel)
Specific gravity of 0.62 or 0.88
Most common : JetA , JetA-1(uses additives)
JetA - used in US
JetA-1 - used in the rest of the world
~Both have a flashpoint not less than +38°C
~JetA has a waxing point of -40°C
~JetA-1 has a waxing point of -47°C
What does Jet fuel contain?
Fuel System Icing Inhibitor (FSII)
Anti Static additives
Oxidation and corrosion inhibitors
Jet B uses and characteristics
Used in cold climates
JetB or AVTAG (Aviation Turbine Gasoline) is known as a wide cut fuel: this means its a blend
~70% Gasoline
~30% Kerosene
~Low flashpoint and high volatility
JetB banned under EU-OPS for commercial operations due to safety and environmental concerns
Fuel Waxing
Exremtly low temps, kerosene begins to change state (wax)
Fully waxed, it resembles Vaseline and will clog components
Therefore crucial to maintain fuel temps in extended cruises
How to prevent waxing
Recirculating fuel, cooling the IDG and placing hydraulic lines within fuel tanks are methods of heating fuel and maintaining suitable temps
Fuel temp can be monitored don the flight deck and raise warnings/cautions when necessary
Additionally, water present in the fuel will form slush way above the waxing point
~Fuel heater is now placed before the
filters to prevent fuel starvation
