Gas Turbine Fuel Sys Flashcards
Mec
Mec
Mechanical electrical control
Role of fuel system
~altitude ~airspeed ~air temperature ~eng temperature ~engine speed ~thrust settings
Fuel is dependent of N2 rotation speed
FOHE Is double fault the oil pressure is higher than the fuel to make fuel leak into the oil instead of the opposite.
So oil quantity increases
Shut down the eng if there is a leak
~Booster pumps in the main tanks deliver the fuel at 30/50psi
~115 V AC single phase electric pump
Threee different HP systems are in sue:
~hydromechanical unit uses Fuel control unit (FCU)
~MEC hydromechanical mechanical engine controller uses an electronic version of the (FCU). PMC(power management control)
~FADEC uses an electronic controller (EEC) and a fuel metering unit (FCU)
Low pressure fuel pump High pressure (spur gear ) FADEC
Hydromechanical (FCU)
Utiilised a swashpalte pump as a HP source and as speed changed swash angle changes caused fuel flow to vary
Fcu
Senses ~thrust lever ~air temp and pressure (p0) ~rapid accelarton core rpm ~Enigne speed core rpm ~Exhasut gas temp ~Compressore delivery pressure (P3)
Barometric pressure controlled senses atmosphere pressure changes in order to maintain 15:1 stoichimetric
~Within the FCCU an acceleration control unit (ACU)
~Prevent overfuellling during increase spees
~any signals were first processed by the governeor before passing into the ACU
~once the ACU had corrected the signal the correct fuel quantity was delivers to the fuel nozzles
~the ACU could induce a lag to fuel deliver in order to maintina the working line and compressor stability
~also FCU adjusted fuel flow to maintain the engine within temp (EGT) and rpm limits
Power mangemnt control system
~the PMC sys is bale to ocntorl multiple spool eng where the FCU sys can only deal wiht single spool turbojet
~the PMC allows fine control of N2 in order to meet thrust demands of the pilot and N1 Rotation
~some sys refer to the mechanical engine control unit (MECU) the sys are broadly the same
~sensing is achieced using analogue singlas converted in ovltages
FADEC
Full authority digiatl engine control
~electronic engine controller
~2chanels (2 seprate computers)
~there a two power supplies (fadec genrator and a/c electrical system)
~both channels check input and output signals for validity and errors
~signls and processed and delivered to a fuel metering unit
FADEC performs
~fuel to the engien fuel nozzles
~maintinan fuel pressure under all eng rpms
~shut of fuel when commanded
~eng overspeed protrction
~controlling compressor airflow (bleed valves)
~ensuring manifold fuel draining shut down
Fadec reduced functionality
~single channel failure ,no loss of func
~Dual channel failure ,loss of eng control.
Last demanded eng settings (EPR or N1) available.
Loss of associated eng instruments.
~power supply loss ,fadec has a dedicated alternator ,failure will lead to dual channel failure
~singals loss ,loss of input signals (EGT thermocouple for example) may not have a huge impact but signal losses will cause associated dipslayed pararmeters to be lost
~each eng has a dedicated FADEC so the loss of 1 will allow the reianig eng to operate nonrmaly
Jet fuel
~Refered to as jet kerosene or AVTUR (aviation turibe fuel) ~sg between 0.62/0.88 ~fuell system icing inhibitor (FSII) ~anti static additives ~oxidation and corrosion inhibiotrs ~both have a flshpoint not less than +38C ~jet A has waxing point of -40c ~jet a1 waing point - 47C
Jet B or AVTAG (aviation turbine gasoline) known as wide cut fuel
~70% gasoline
~30% kerosene
~low flashpoint and high volatility
Jet B is banned in EU for commercial operation
Fuel waxing
~recirculating fuel,cooling of the IDG and placing hydraulic line whitin n the fuel tanks
~the fuel heater is now placed before the filter to prefent fuel starvation
