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Module 15 - Engines > M15.09 Lubricants and fuels > Flashcards

M15.09 Lubricants and fuels Flashcards

1
Q

What lead to the development of a range of low viscosity oils, replacing older straight mineral oils?

A

The operational requirements for low temperature starting, either on the
ground or at altitude (re-lights), led to the evolution of a range of oils with
viscosities far lower than those of typical aircraft engine oils of the time

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2
Q

Why was it important to replace mineral oils?

A

As gas turbines operated with higher thrust, compression ratios, mineral oil was found to lack stability, gained excessive volatility and thermal degrediation at higher temperatures

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3
Q

Explain ester based type 1 oils

A

Due to this, ester based synthetic oils were developed with properties suitable
for gas turbine lubricants. Unfortunately, the oil produced had a viscosity of
approximately 3 centistokes (3 mm2/s at 100°C). This was an insufficient load
carrying capability for high gear loads, so thickeners were added to raise the
viscosity to about 7.5 centistokes (7.5 mm2/s at 100°C).
These oils were known as Type 1 and had to rely on additives, and in later
improvements, on multi-component additive packages, to raise their
performance. This was particularly necessary to increase resistance to
oxidation and thermal degradation, important properties which govern long
term engine cleanliness

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4
Q

Why were type 2 oils created?

A

With the almost continuous increases in engine size and power output, a
demand developed in the USA for oils possessing improved thermal stability
and high load carrying ability, with some sacrifice in low temperature
performance, Due to this, a Type II 5 mm2/s oil was developed

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5
Q

What are the 4 main tasks of engine oil?

A

Cooling, Lubricating, Cleaning, corrosion protection

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6
Q

How does the oil cool materials?

A

The heat from the metal in contact with the oil is transferred to the oil and carried away

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7
Q

What are the two groups of engine oils?

A

Mineral and synthetic

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8
Q

What are the three types of synthetic oils?

A

TYPES 1 2 3

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9
Q

What are the advantages of synthetic oils?

A

The advantages of synthetic oils are that they have better viscosity, better
thermal stability and a high pressure resistance

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10
Q

What are the disadvantages of synthetic oil?

A

One disadvantage of synthetic oils is that they have a high price.
They are also harmful to the skin, but the most critical disadvantage of
synthetic oils is that they cannot be mixed with synthetic oils from other
manufacturers, even if they are of the same type

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11
Q

What is the viscosity index?

A

The effect temperature has on the viscosity of the oil. A higher number
indicates a viscosity least affected by a change in temperature

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12
Q

What is viscosity?

A

The viscosity is the most important characteristic of engine oil. It is the internal
resistance of a fluid against deformation

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13
Q

What is the pour point?

A

The pour point is the lowest temperature that oil will visibly move in a
31.75 mm test tube held horizontally for 5 seconds

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14
Q

What is the pour point of type 2 oils?

A

Type 2 oils for jet engines have a pour point of -57°C

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15
Q

What is the flash point?

A

The flash point is the lowest temperature that the oil will give off enough
vapour to flash when a flame is applied.
The flash point of engine oils should be as high as possible to avoid fire in the
oil system

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16
Q

What is the flash point of type 2 engine oil?

A

250 degrees c

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17
Q

What is the pressure reistance?

A

This film resists the loads on the bearing and prevents contact between the moving surfaces.
If the loads are higher than the pressure resistance capability of the oil, the
metal bearing surfaces come into contact and heavy material wear occurs

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18
Q

What is the oxidation resistance?

A

Oxidation is the reaction between oil and oxygen. When the oil reacts with
oxygen it gets thicker and increases its viscosity.
The oil starts to react with oxygen when the oil temperature increases above a
certain level.
Therefore the oxidation resistance is an important characteristic of oil
because it increases the durability of the oil

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19
Q

What is the temperature that type 2 oils are resistant to oxidation up too?

A

220 degrees c

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20
Q

Explain oil thermal stability

A

The term thermal stability describes the oil resistance to decomposition of the
oil compounds at high temperatures. The oil molecules are made of several
individual compounds.
At high temperatures these molecules can break apart and the chemical
composition and the lubrication capability of the oil changes.
This decomposition usually occurs at very high temperatures, far above
the normal operating temperatures of the engine oil.

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21
Q

What is the temperature that type 2 oils can resist chemical decoposition?

A

340 degrees c

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22
Q

What is oil volatility?

A

The measure of ease in which a liquid is converted into a vaporous state

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23
Q

What is oil acidity?

A

A measure of corrosive tendencies of the oil

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24
Q

What is oil foaming?

A

The measure of the oils ability to resist seperating from entrapped air

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25
Q

What is oil rubber swelling?

A

The measure of the amount of oil to cause a particular rubber compound to swell

26
Q

What is the factors of oxidation and thermal stability in oils?

A

The ability for the oil to resist the formation of hard carbon and sludge at high temperatures

27
Q

What is the factor of corrosivness in oils?

A

The effect the oil has on various metals especially on copper

28
Q

What is the factor of pressure in oils?

A

The ability of the oil to carry load

29
Q

What is the measure of oil coking?

A

The amount of carbon residue within the oil after extream heating

30
Q

What are some additional factors to oils?

A

Additionally, water emulsion, storage stability, compatibility and inter-facial
tension are factors that will affect the oil performance

31
Q

What can be done to oils to allow them to gain desirable features?

A

Chemical additives may be mixed with the oil to impart desirable
characteristics. These additives can include detergents, corrosion
preventatives, dyes, anti-corrosives, antioxidants, foam inhibitors, viscosity
enhancers, pour point depressants and many others, to improve performance
and impart new properties

32
Q

What is the typical composition of jet fuel?

A

A typical fuel will be composed of approximately 16% hydrogen, 84% carbon,
and small amounts of impurities including sulphur, water, nitrogen and other
particulate matter.

33
Q

What are the 4 main types of jet fuel?

A

JET A
JET A1
JET B
JP 5

34
Q

What is the most commonly used fuel in europe?

A

JET A1 (DERD 2494)

35
Q

What is the flash point, freeze point and specific gravity of JET A1?

A

This fuel type is reasonably safe to handle because it has a flash point
minimum of 38°C (100°F), a freeze point maximum of-47°C (-52°F) and a
specific gravity of between 0.775 and 0.840
The American name for this type of fuel is JP 1A

36
Q

What is the jet fuel commonly used in America?

A

Jet A is the most commonly used fuel type for jet engines in America

37
Q

What is the flash point, freeze point and specific gravity of JET A

A

It has the same flash point as Jet A1, but a higher freeze point maximum
(-40°C (-40°F)) and a specific gravity of between 0.775 and 0.83.
In the USA this fuel is called JP 1

38
Q

What is JET B?

A

This fuel is a distillate covering the naphtha and kerosene fractions. It can
be used as an alternative to Jet A1, but because it is more difficult to handle
(higher flammability with a flash point of approximately -20°C (-4°F)), there is
only significant demand in Canada where its better cold weather performance
is important. The freezing point maximum is -58°C (-72.4°F) and a specific
gravity of 0.751 to 0.802.
The military equivalent is JP4, F40 or Avtag. These fuels have the addition of a
corrosion inhibitor and anti-icing additives.
JP4 also meets the requirements of the British Specification DEF STAN 9 1-88
AVTAGIFSII (formerly DERD 2454), where FSII stands for Fuel Systems Icing
Inhibitor. NATO Code F-40

39
Q

What is JP 5?

A

JP 5 is another type of military jet fuel.
It is preferred by the military on aircraft carriers because its very high flash
point of plus 65°C makes it very safe for handling. JP 5 has a relatively low
freezing point of minus 48°C

40
Q

What is a fuels requirements regarding flashpoint?

A

The main requirements of turbine engine fuels are a low freezing point and
a flash point low enough to provide good ignition capabilities but as high as
possible for safe fuel handling.

41
Q

What is a fuels requirements regarding flashpoint?

A

The main requirements of turbine engine fuels are a low freezing point and
a flash point low enough to provide good ignition capabilities but as high as
possible for safe fuel handling.

42
Q

What should the appearance of fuel be?

A

Should be clear, bright and visually free from solid matter and undissolved
water at normal ambient temperature

43
Q

What is the composition of fuels?

A

Limited acidity and limited amounts of aromatics, olefin, sulphur and
mercaptan sulphur (salts) which produce pollutants, corrosives gums and
odours.
Different fuels have different freezing points depending on their composition

44
Q

What should the volatility of fuel be like?

A

The density of the fuel at 15°C, flash point of the fuel and the initial boiling
point and recovery temperature.
Volatility of fuel is its ability to vaporize. 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

45
Q

What should the fluidity be like for fuels?

A

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 crystallize and the fuel flow slows down. The required freezing point of fuel
for turbine engines should be below minus 40° Celsius.

46
Q

What should the combustion of fuels be like?

A

Calforic Value (minimum of 18 400 BtuJlb (42 800 J/g), luminosity and %
naphthalene (saturated carbons) content

47
Q

What should stbility of fuels be like?

A

Maximum thermal stability (deposits forming at varying temperatures)

48
Q

Explain fuel density?

A

This is the ratio between mass and volume. This ratio changes with the fuel
type and fuel temperature.
Jet A1 and Jet A have the same density of 0.81 kg/ltr at a temperature of 15°C.

49
Q

What are some other requirement’s for fuel?

A

A further requirement of jet engine fuels is that it must be readily available so
that the airlines can get the same fuel type all over the world.
It must also have adequate lubrication capabilities for the moving parts in the
fuel system, and the fuel must have a low tendency to hold water to minimize
water contamination problems.

50
Q

What are the main requirements for fuel in summary?

A

Low Freezing Point
* Flash Point
◦ Low Enough for Ignition
◦ As Low As Possible For Safe Handling
* Low Tendency To Vaporize 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

51
Q

What is the syringe test?

A

Fuel is drawn off into the cartridge through a chemically treated
filter.
If the filter changes colour, the fuel contains water. You then have to wait long
enough for the water to settle down and drain it afterwards

52
Q

What measure of additives are use for mixing with fuels?

A

Parts per million

53
Q

What is the purpose of adding antioxidants to fuel?

A

Anti-oxidants prevent the formation of gum deposits on fuel system
components caused by oxidation of the fuel in storage. It also inhibits the
formation of peroxide compounds in certain jet fuels

54
Q

What is the purpose of adding static dissapators into fuel?

A

Static dissipator additives reduce the hazardous effects of static electricity
generated by movement of fuel through modem high flow-rate fuel transfer
systems.
Static dissipator additives do not reduce the need for bonding to ensure
electrical continuity between metal components (e.g. aircraft and fuelling
equipment) nor do they influence hazards from lightning strikes

55
Q

What is the purpose of adding corrosion inhibitors to fuel?

A

Corrosion inhibitors protect ferrous metals in fuel handling systems, such as
pipelines and fuel storage tanks, from corrosion.
Some corrosion inhibitors also improve the lubricating properties (lubricity) of
certain jet fuels

56
Q

What is the purpose of adding fuel system icing inhibitors to fuel?

A

Also known as anti-icing additives, they reduce the freezing point of water
precipitated from jet fuels due to cooling at high altitudes. They also prevent
the formation of ice crystals which restrict the flow of fuel to the engine.
This type of additive does not affect the freezing point of the fuel itself. Antiicing
additives can also provide some protection against microbiological
growth in jet fuel

57
Q

What is the purpose of adding metal de-activators to fuel?

A

These suppress the catalytic effect which some metals, particularly copper,
have on fuel oxidation.

58
Q

What is the purpose of adding biocide additives to fuel?

A

These are sometimes used to combat microbiological growths in jet fuel, often
by direct addition to aircraft tanks.
Some anti-icing additives appear to possess biocidal properties

59
Q

What is category one tank access?

A

If the tank is a category one, it has a direct access door, but you can’t get in
completely. This means that access is by head and shoulders only

60
Q

What is category two access?

A

A category two tank has a direct access door and is wide enough to gain
access for your complete body

61
Q

What is a category three access?

A

A category three tank has no direct external access door, but there are
internal openings which allow you to get in. They are even wide enough for
rescue if necessary.

Module 15 - Engines (22 decks)

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