Turbine Engine Fuel Systems Flashcards
Compare and differentiate between AVGAS and turbine engine fuel (including Biojet)
Avtur - high calorific value, low freezing temp, flow across a wide range of temps, fuel assist in lubing, straw coloured and contains kerosene, mixes w water, has wax and bacterial growth. Flashpoint 38ºC and 60ºC, freezing temp as low as -47ºC, 0.8 Specific Gravity
Avgas - blue coloured, doesnt mix, no impurities, 38ºC flashpoint, freezing temp -100ºC, S.G 0.72.
Biofuel - any fuel derives from biomass e.g plant or animal waste.
describe methods of reducing the likelihood of fuelling with the wrong type.
a turbine engine can run on avgas but a reciprocating engine can not run on avtur.
These include, Labeling, hoses, nozzles, and fuel colour as well as that of the tanker. Avtur Nozzles are to small to fit into an avgas powered aircraft.
State the differences between the various types of turbine engine fuel (including Biojet) and identify their common usage names. Different names of Jet A, A1, Jet B
Jet A - freezing point - 40ºC, used in USA since 1950
Jet A1 - JP-5 on aircraft carriers, also known as AVCAT (aviation carrier turbine fuel) doesn’t contain anti-static agents. NATO code: F-44
JP-8 military equivalent of Jet A-1 with addition of corrosion inhibitor and anti-icing additives. Difference is Flashpoint, JP-5 (60ºC) JP-8 (38ºC)
Jet-B - JP-4. Not used except in very cold climates as dangerous to handle. 70% gasoline and 30% kerosene.
Describe the function of the following turbine engine fuel system components—
(a) fuel control unit (hydro pneumatic, hydro mechanical and electro-hydro mechanical)
FCU adjusts the fuel flow to the engine based on computer or pilot input. It takes into account power level position, current engine RPM, inlet air pressure and temp, combustion chamber pressure.
Then meters the correct amount of fuel into the combustion section to get ideal ratio if 15:1.
Either done using hydro-pneumatic, hydro mechanical or electro-hydro mechanical forces.
Describe the function of the following turbine engine fuel system components— fuel filter
Used to filter out any impurities within fuel and prevent blockage from them
Describe the function of the following turbine engine fuel system components— fuel heater
Used to warm the fuel so as to prevent fuel becoming frozen at higher altitudes.
Describe the function of the following turbine engine fuel system components— governors and limiting devices
Ensure that at various points throughout the system that the fuel pressure and/or flow is at the correct value for the localized points in the fuel system.
this ensures that all components operate to within their designed operating band ensuring under/oversupply of fuel to the combustion chamber does not occur.
Describe the function of the following turbine engine fuel system components— main fuel pumps
Ensure fuel system is pressurised to deliver fuel to the FCU at a psi that’ll allow the FCU to divide and meter the fuel as per the engines operating requirements.
State the ideal fuel/air ratio
15:1 15 parts air 1 part fuel
Describe the following properties in relation to turbine engine fuels—
(a) specific gravity
It’s the ratio of a substance to that of water at 4ºC.
Jet A-1 S.G is 0.8.
Describe the following properties in relation to turbine engine fuels—
(b) fire hazard
Flashpoint of jet-a1 is 38ºC, once burning however, jet fuel burns at higher temps then Avgas.
Describe the following properties in relation to turbine engine fuels—
(C) fuel icing
Jet fuel freezing point for jet-A is -40ºC and for jet-a1 its -47ºC, so fuel is kept to be no colder than 37ºC as if it falls water in the fuel may freeze and wax additives may solidify.
the effect of a change in specific gravity with respect to weight of fuel.
It varies with temp and contamination levels. Water becomes less dense as its heated so SG is less and so does avtur. As it cools down the opposite occurs.
Describe the purposes of anti-icing and anti-microbiocidal additives in turbine engine fuels.
anti-icing - fuel system icing inhibitor is a fuel additive that can prevent formation of water ice down to - 40ºC.
Anti-microbial additives - restrict the free water fungus and solid matter to a practical minimum.
State the ground handling requirements and the safety precautions to be observed with the use of turbine engine fuels.
With regard to ground handling, regular quality control, testing of water and microbiological contamination is important, safety gear such as glasses, gloves and antistatic overalls are a must and as with any refueling there must always be a static line bonded to the aircraft prior to fuelling to be sure a static build up does not discharge to the fueller and ignite the aircraft fuel tank.
