15.9 - Lubricants & Fuels

Question 1

List five requirements of aviation gas turbine lubricants:

Answer 1

• Low volatility; to reduce evaporation at high altitude
• Anti-foaming characteristics; to give positive lubrication
• Anti-lacquering characteristics; prevents sludging
• High flash point; resistance to giving off inflammable vapour
• High viscosity index; to retain viscosity at high temperatures
• Wide temperature rnage; -50^C to +200^C
• Good film strength; molecules stick together under load
• Low pour point; lowest temperature at which oil will gravity flow

Question 2

List five requirements of aviation gas turbine fuels:

Answer 2

• Pumpability: Should flow easily under all conditions
• Lightability: Should promote easy light up on ground or in flight
• High calorific value: The amount of heat energy per unit weight
• Good lubricity: Should prevent wear in fuel system components
• High flash point
• Minimal corrosive effect: Must not attack fuel system or turbine

Question 3

Define viscosity.

Answer 3

The measure of a fluid’s resistance to flow. An example of a fluid with high viscosity is honey while water possesses low viscosity.

Question 4

Define what a synthetic oil is.

Answer 4

Oil made by chemical synthesis of a mineral, animal, or vegetable base. Synthetic oils have appropriate additives that give them such characteristics as low volatility, low pour point, high viscosity index, good lubricating qualities, low coke and lacquer formation, and low foaming.

Question 5

List the 2 most common types of lubricant

(in terms of viscosity and engine type)

Answer 5

Low viscosity synthetic oils - Modern gas turbine engines

Slightly higher viscosity oil - Turbo-prop engines

Question 6

What is meant by the viscosity of oil?

Answer 6

Viscosity is a fluid’s resistance to flow.

Question 7

What is the pour point of an oil?

Answer 7

Pour point = lowest temperature at which oil will gravity flow

60^C (low pour point ??)

Question 8

Which has a higher freezing point Jet A1 or Jet A

Answer 8

Jet A1 fuel has a lower freezing point then Jet A fuel

Question 9

What contaminants can be found in fuel?

Answer 9

• Dissolved Water = like humidity in air, not a problem
• Free water = entrained water and present in tiny droplets and is visible. very bad
• Microbiocidal agents (fungi, bacteria)

Question 10

When is water most likely to enter a fuel?

Answer 10

When it is warmer

Kerosene is hygroscopic

Meaning it has the property of dissolving atmospheric moisture into itself.

The warmer it is, the more moisture the fuel can absorb and the colder it is it will precipitate back out into a liquid

Question 11

How can water be detected in fuel?

Answer 11

Draw a sample of fuel from the re-fueller into a sample jar for checking

If acceptable water level, no colour change

if water contents is over limits, the element capsule will turn toaward a blue colouration (reject fuel)