15.9 Flashcards
(99 cards)
Why are mineral oils bad?
Lack stability, thermal degradation and excessive volatility
What bad about mineral oils sucessor, Esther based synthetic oils?
Low viscosity so insufficient load carrying capability
How was the problem of Esther based synthetic oils overcome?
By adding additives
What are Type 1 oils?
Low viscosity so required additives
What are second generation oils?
Oils that were based on hindered Esthers (Improvement of thermal stability and load carrying)
What are third generation oils?
Oils that have thermal stability?
What are the main tasks of oil on modern jet engine?
Cleaning
Corrosion resistance
Cooling
Lubrication
What does the oil do with the carried particles it cleans off of a surface?
Passes it through a filter
Two groups of engine oils?
Synthetic
Mineral
What are the thee types of synthetic oils?
Type 1 - Old aircraft
Type 2 - Modern aircraft
Type 3 - Special aircraft (Higher stability and viscosity at higher temperatures)
Advantages of synthetic oils?
Better viscosity, high pressure resistance, and better thermal stability
Disadvantage of synthetic oils?
They are expensive
What is viscosity index?
Effect temperature has on the viscosity on the oil. (The higher the number the least effected by change)
What is viscosity?
a fluids internal resistance against deformation
What does the viscosity of oil depend on?
High at low temp
Low at high temp
What is the pour point?
The lowest temperature the oil will visibly move
Type 2 oils have a pour point of what degree?
-57 degrees
What is a flash point?
The lowest temperature in which the oil will give off enough vapour to flash when a flame is applied
What should the flashpoint be in an engine?
High
Type 2 oils have what degree of flash point?
Above 250 degrees
What is pressure resistance?
Capability of an oil film between two components
What is oxidation resistance?
The reaction between oil and oxygen
What happens when oil reacts with oxygen?
It gets thicker and therefore the velocity increases
When does oil start to react with oxygen?
When certain temp increases above a certain level. It increases the durability