15.9 Lubricats And Fuels Flashcards
What are the problems with mineral oils?
Were found to lack stability and suffer from excessive volatility and thermal degradation at higher temperatures that were obtained
Why were ester based oils developed?
Because they have properties suitable for gas turbine engine lubricants
Performance improvements stress the engine oil. For this reason, the original Type II oils are becoming less suitable for use in modern aircraft engines how do you get around this?
This has resulted in the need for engine oils with extremely improved thermal stability. These types of oil are now generally known as third-generation oils
What are the main tasks of oil on modern jet aircraft?
Lubricating, cooling, corrosion protection, cleaning
What are the two types of oils used in an engine?
Synthetic oil and mineral oil
What are the three synthetic oils?
Type 1, type 2, type 3
What is a type 1 synthetic oil and where are they used?
Type 1 oil is a 1st generation synthetic oil, used on some older gas turbine engines
Where are type 2 synthetic oils mostly used?
Type 2 mostly used on modern gas turbine
What are the benefits of type 3 synthetic oils and where are they found?
Type 3 have higher thermal stability, used on military aircraft
What are the advantages of synthetic oils?
Have better viscosity
Better thermal stability
High pressure resistance
What are disadvantages of synthetic oils?
Very expensive
All lubricants for gas turbine engines must exhibit certain physical and performance properties, what are they tested for?
Viscosity Index
Viscosity
Pour point
Flash point
Pressure resistance
Oxidation resistance
Thermal stability
Volatility
Acidity
What is viscosity index?
The effect temperature has on the viscosity of oil, a higher number indicates a viscosity least affected by a change in temperature
What is viscosity?
The internal resistance of a fluid against deformation
Give examples to explain viscosity?
If a metal ball falls into a glass of oil, the ball will take time to reach the bottom
If the ball falls slowly, this shows that the viscosity of the oil is high
If the ball falls quickly, this shows that the viscosity of the oil is low
How does temperature affect viscosity?
It is high at low temperatures and low at high temperatures
What is pour point?
Pour point is the lowest temperature that oil will visibly move in a 31.75mm test tube held horizontally for 5 seconds
What is the pour point for type 2 oils?
Type 2 oils for jet engines have a pour point of -57 °C
What is flash point?
The lowest temperature the oil will give off enough vapour to flash when flame is applied
What is type 2 oils flash point?
Type 2 oils have a flash-point which is higher than 250 °C
What is pressure resistance?
Pressure resistance capability of the oil is an important factor for the oil film between the moving components
What is oxidation resistance?
Oxidation resistance is the reaction between oil and oxygen, when oil reacts with oxygen it gets thicker and increases its viscosity
What is thermal stability?
Describes the oil resistance to the decomposition of the oil compounds at high temperatures
What is volatility?
The measure of the ease with which a liquid is converted into a vapours state
What is acidity?
A measure of the corrosive tendencies of oil
What is oil foaming?
The measure of the resistance of the oil to separate from trapped air
What is rubber swelling?
The amount the oil will cause a particular rubber compound to swell
What is oxidation and thermal stability?
The ability of the oil to resist the formation of hard carbon and sludge at high temperatures
What is corrosiveness?
The effect the oil has on various metals, especially, but not restricted to, copper
What is pressure?
The ability of the oil to carry a load
What is coking?
The amount of carbon residue remaining in the oil after being subjected to extreme heating
What are the four main types of jet fuel used?
Jet A1, Jet A, Jet B, JP 5
Where is jet A1 used?
Most commonly used fuel type for jet engines in Europe
Where is Jet A used?
Most commonly used in America
Where and why is JetB used?
Alternative to jet A1, more flammable with a flash point of approximately -20°C, only used in Canada where cold weather performance is is important
Who uses JP5?
Military
What is JP5 flash and freeze point?
Flash point 68°C low freezing point of -48°C
What are the main fuel requirements?
Main requirements is low freezing point and a flash point low enough to provide good ignition capabilities but as high as possible for safe handling
What should fuel appearance be?
Clear, bright and visually free from solid matter and undissolved water at normal ambient temperature
What should fuel composition be?
Limited acidity and limited amounts of aromatics, olefin, sulphur and mercaptan sulphur (salts) produce pollutants, corrosive gums and odours
What is volatility?
The volatility of fuel is its ability to vaporise. A highly volatile fuel is very desirable for engine starts in cold weather and in flight, and fuel with low volatility is desired to eliminate vapour lock and to reduce fuel losses by evaporation
What is fluidity?
Maximum freezing point temperature in °C and the maximum viscosity at ‑20 °C. The freezing point is the temperature at which some elements of the fuel start to crystallise and the fuel flow slows down
What is combustion?
Calorific Value
What is stability?
Maximum thermal stability (deposits forming at varying temperatures)
What is conductivity?
Minimum and maximum electrical conductivity.
What is the fuel density?
This is the ratio between mass and volume. This ratio changes with the fuel type and fuel temperature
What are the main requirements for turbine engine fuel?
Low Freezing Point
Flash Point - low enough for ignition and as low as possible for safe handling
Low Tendency to Vaporise in High Altitudes
Widely Available
Low Tendency to Carry Water
High Volatility Desirable for Engine Starts
Available all Over the World
Adequate Lubrication Capabilities
Low Tendency to Hold Water
What does water water encourage in fuel tanks?
Ice build up if fuel cools below 0°c it supports corrosion in the fuel tanks
Where are anti-ice additives applied?
Can be added to bulk fuel and also directly into the fuel tank during refuelling
Where does microbial contamination form in fuel ?
Due to prescience of water in fuel and water that is dissolved into the fuel
What additive also stops microbial contamination?
Anti ice additives
What are the most commonly used additives?
- anti oxidants
- static dissipator additives
- corrosion inhibitors
What do antioxidants do?
Prevent the formation of gun deposits on fuel system caused by oxidation
What do you static dissipater additives do?
Reduce the hazardous effects of static electricity generated by movement of fuel
What do metal deactivators do?
Suppress the catalytic effect that some metals have on oxidation.
What is provided on MSDS ?
Information on limits of exposure to a chemical
As oil should never be invested, what should never be done?
You should never siphon by mouth
What should be done if oil gets in your eyes?
Flush with fresh water
What can spilt oils do to paint and how should they be dealt with?
Oil can blister, discolour and remove paint. When is built. It should be wiped with a petroleum solvent following a spillage.
What should be done when storing synthetic oils?
They are not stable in storage, so they should be protected from extremities of temperatures
Why should open synthetic oil cans not be used ?
They can absorb moisture from the atmosphere rendering it unusable
What safety precautions should be followed when handling of storing jet fuels?
-Static electrical charges accumulate rapidly with high fuel flow rates, high specific gravity and wider boiling range fuels. Flow rates must be restricted to specific minimums, as determined by the diameter of the hose. Bonding and earthing (grounding) are essential.
-As jet fuel tends to soften asphalt and does not readily evaporate, spillages should be avoided.
-Small amounts of spillage may be removed with commercial absorbing agents. Larger spills will need to be washed away with plenty of water, ensuring it does not enter drainage systems.
-Jet fuel should not be used for cleaning purposes.
-Inhalation of fuel vapours and skin contact should be avoided. Inhalation may cause nausea, headaches and dizziness. If affected, move to an area with fresh air.
-If fuel comes in contact with the skin, the area should be washed thoroughly with soap and water as it is a skin irritant. Prolonged or repeated contact may cause skin irritation (dermatitis). Where skin rashes or other irritations persist seek medical advice. If fuel enters the eyes flush with plenty of clean water for up to 10 minutes and seek medical advice.
-If ingested, do not induce vomiting. Drink 250 ml (1/2 pint) of water and obtain medical attention immediately.
-Contaminated clothing should be removed and laundered as soon as possible.
How should a fuel leak be taken care of ?
-stop the leak
-add binding agent to the fuel spillage
What sort of tools should be used in fuel tanks?
Explosion proof tools
What are some sources of unwanted ignition when referring?
-Electrical switching
-HF transmission
-Weather radar operation
-Metal parts, such as tools, being struck together
-Electric static discharge
Why should special clothing be used when entering a fuel tank?
Made of cotton, which will not create static charges, this is done to avoid creating a spark
