FUEL comprises of Iso Octane and Heptane
Iso Octane has 100% anti knocking value
Heptane is used to decrease anti knocking value below 100%
TETRA ETHYL LEAD – increases fuel octane rating above 100% Iso Octane
ISO PROPYL ALCOHOL – reduces freezing temperature of the liquid
ETHYLENE GLYCOL MONOETHER – absorbs water vapor present in the liquid
TETRA ETHYL LEAD – increases fuel octane rating above 100% Iso Octane.
Fuel and oil expands on being heated.
Therefore the oil and fuel tanks should never be filled to the top when the temp is expected to rise, otherwise the fuel will expand and come out of the tanks increasing the chances of the fire.
Temperature increases fuel density decreases fuel expands, volume increases.
Temperature decreases density increases fuel contracts, volume decreases.
Amount of H2O vapour held by fuel depends on temperature of fuel. If temperature increases more H2O vapour can be dissolved in fuel.
H2O can be reduced from fuel by reducing temperature of the fuel.
Temperature decreases (cold) Air density increases
Temperature increases (warm) Air density decreases
Therefore, temperature decreases fuel density increases fuel contracts, volume of fuel decreases.
Temperature increases fuel density decreases fuel expands, volume of fuel increases.
Fuel tanks are provided with vents.
If vent gets clogged, the pressure in the tank will decrease & fuel flow decrease and engine may fail.
Fuel tanks have Baffle plates.
Baffle plates prevent surging of the fuel.
Cockpit
CAUTION LIGHTS – YELLOW
WARNING LIGHTS – RED
If temperature increases Specific gravity decreases, if temperature decreases, Specific gravity increases
Therefore Cold fuel is heavier and Warm fuel is lighter.
Temperature increases density decreases, fuel expands, volume of fuel increases.
Temperature decreases density increases, fuel contracts, volume of fuel decreases.
If temperature decreases in night & fuel tanks are not full & airspace above the fuel in fuel tank is large, the fuel tank walls will become cold & the condensation takes place (Water vapor changes into water droplets).
Filling tanks to top prevents or minimizes Condensation.
Filling fuel tanks to full minimizes Condensation.
If tanks are not full the water vapor converts into water droplets & will gather at lowest point in tank (Water is heavier than fuel) & can cause engine roughness or ever engine failure.
If tanks are full in night and temperature increases, density decreases, fuel expands and volume of fuel increases and fuel will overflow the tanks.
Isopropyl Alcohol increases freezing temperature of the fuel.
Ethylene Glycol Monoethyle Ether – absorbs the water particles in vapour form of the fuel.
Vapor lock in the fuel tank is caused by
1) Low pressure of the fuel
2) High temperature of the fuel
3) Highly volatile
4) Swashing of fuel due to the turbulence.
Booster pump provides the flow of fuel & remove vapor locks.
Fuel tanks are pressurized in some fuel tanks (particular Air tanks) to force fuel from them to the engine as main tanks.
Fuel tanks can be pressurized by
1) Pressure is fed from exhaust side of the vacuum pump which is then put to the fuel tank venting system & than sealed.
When Air tanks are used to replenish main tanks they are pressurized at all times. Fuel is transferred out automatically under control of a float valve in each main tank whenever the contents of the main tank falls below a pre-determined level.
The pressure of fuel tank also prevents cavitation of the pumps.
Note – Some fuel tanks are pressurized by ram air system and all fuel tank pressurization systems include the fitting of a relief valve to present over pressuring.
Note – IN the event of Booster pump failure, fuel can still be made to flow through it by the engine driven pump.
Priming the engine is to fill the system with fuel & not pressurizing
When temperature drops water can condense into fuel tanks & settle into the bottom.
To prevent – fill fuel tanks to full after each flight.
AUTOMATIC MIXTURE CONTROL
Two methods –
(1) Throttle lever is set to give not more than the maximum weak mixture boost, therefore ensuring mixture is correctly set.
When engine use this method, care is necessary particularly when flying at or near Full Throttle height, to ensure that rich mixture is not being used inadvertently.
To ensure that weak mixture is in use in these conditions. Throttle should be opened fully & then slowly closed until boost starts to fall, this position will then give the required weak mixture setting.
If at any time the fuel consumption becomes high, a check should be made to see that weak mixture is in fact being used.
(2) The throttle is set at or behind the economical cruise position marked on the quadrant.
Fuel
Higher Flash point – (If temp increases, evaporation in air increases) higher flash point is require so that fuel doesn’t catch fire if there is a smoke in the cabin.
Flash point is when fuel goes is air as a vapor.
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JP-1, Jet Petroleum- Kerosene type of fuel.
It is used in Gas turbine Engine.
It has low freezing temperature point.
High altitude engine starting is poor.
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JP-2, Natural availability in crude petroleum. Its availability is very less (only 5%).
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JP-3
More volatile
Loss of fuel due to evaporation is more.
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JP-4
Flash point is less than JP-1 therefore fire hazards are more.
Natural availability is more (35%)
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JP-5
It has higher flash point to decrease fire hazard.
In India we use JP-1 called ATFK 50
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ATF – is aviation Turbine Fuel.
K– Kerosene
50 – is freezing temperature as – 500 c
At high altitude at higher speeds, the wing tanks get heated therefore fuel gets heated.
TAT– Total air temperature.
TAT– Ram effect temperature due to change + static temperature.
Fungus– occurs due to the Microbiological growth in the fuel.