15.9 - Lubricants and Fuels Flashcards
What are the three main sources of lubricating oils?
Mineral
Synthetic
Vegetable
Why are synthetic oils used in jet engines over mineral oils?
They retain their lubricating properties and are more resistant to oxidation at higher temperatures
What is viscosity of a fluid?
The internal resistance of a fluid to deform under shear stress. It depends on temperature.
What is the pour point?
An oils temperature at which point when it is cooled down, means it cannot flow
What is the flash point?
The lowest temperature at which it becomes an ignitable mixture with air. It’s the liquid temperature at which the vapour is given off
What is the pressure resistance?
A load carrying capability of the oil when it forms a film between two parts. It’s resistance on the loads of the moving surfaces.
What is an oils oxidation resistance?
Ensures the oils resistance and durability.
Oxidised oil becomes thicker and increases viscosity, reducing the lubrication effect.
What is thermal stability of an oil?
The resistance of the oil to decomposition in high temperatures.
What additives can be added to oil?
Extreme pressure
Anti-corrosion
Detergent
Inhibitors
What is a detergent additive used for in engine oil?
They allow the oil to hold sludge or debris in suspension, preventing it from building up within the engine. It will be carried until trapped by filters.
What are inhibitors used for in oil?
Additives used to slow down the formation of oxidation products.
What can water or moisture do to a lubricating system?
- breaks down heavily loaded surfaces
- water and oil forms an emulsion, reducing its lubrication effect
- water breaks down the additives in the oil
- causes excessive frothing, with subsequent loss of oil through the vent systems
What types of fuel do international airliners use?
Jet-A and Jet-A1
What types of fuels are used by military jets?
Jet-B, Turbo fuel 5, JP-4 and JP-5
What are metal de-activators in fuel?
They suppress the catalytic effect which some metals, particularly copper, have on fuel oxidation.
What are biocide additives in fuel?
Reduces the risks of microbiological growths in the fuel systems. Biopic is well known.
What types of tools should be used with fuel systems?
Spark-free
What is a hydrokit used for?
Detecting in dissolved water quantities in turbine fuel
What is the name of the microbiological fungus found in contaminated fuel?
Cladosporium Resinae
What ratio of kerosene and air will burn effectively?
15 parts air to 1 part fuel
What is an oils viscosity index based on?
It rate of change in viscosity with temperature change
What is the resistance to flow of an oil known as?
It’s Viscosity
The combined output from all of the scavenge pumps will be _______ than the pressure pump output.
Greater than the pressure pump output
What is the typical operating PSI in a gas turbine lubricating system?
100psi
How is a gear box breather prevented from leaking oil to the atmosphere?
An impeller and centrifugal force
What is Jet B fuel?
A kerosene based fuel
What is Reid vapour pressure?
It is the pressure exerted by a fuel when heated to 38 degrees C
What happens to the weight of the fuel if the specific gravity is increased?
It increases
To what condition does the fuel flow respond during aircraft acceleration?
The mass airflow through the engine
To read oil pressure direct from the source, what system would you use?
A Bourdon tube
What is an EP lubricant?
Extreme pressure - Used for gear-type pumps where high tooth pressures and high rubbing forces are present
What is DERD 2494?
A kerosene based fuel
What advantage do mineral oils have over vegetable oils in a turbine engine?
They are more chemically stable
What should you do when servicing a felt-type filter?
Remove and replace the filter
