Aircraft Engine Lubrication Systems

As the gas turbine engines have limited number of moving components their lubrication requirements are much simpler to meet. This is because the oil does not lubricate any parts that are directly heated by combustion (i.e Combustion chambers, Turbine Blades/Vanes...etc) 

However, for a sustained and prolonged operation, the engine requires ample supply of lubricating oil at all the bearings, gears and driving splines. This supply should be a continuous flow of clean filtered oil and an appropriate temperature, pressure and viscosity, throughout the engine operation.
Main goals of  engine lubricating oils are to:

•         Lubricate
•         Cool/ carry away the heat
•         Prevent corrosion
•         Resist oxidation at high temperatures
•         Possess suitable viscosity at all operating temperatures

Gas turbine engines uses specially formulated low viscosity synthetic oil that does not originate from mineral oil. military specification MIL-PRF-7808 commonly referred as Type I jet oil and MIL-PRF-23699 commonly referred as Type II Jet oil are some examples of such synthetic aviation oils. It is essential that only those oils specified by the engine manufacturer are used. 
 
The ultimate decision of which oil to be used is decided by the operation characteristics and the loads of the engine including the bearing temperatures. Often the selection of the appropriate type of oil is a results of multiple engine tests and lab analysis of the oil. There are wide range of components being used in the lubrication system and basic overview is given in the below diagram. More details of each components will be discussed in later posts.

Following video is created to provide overview of the lubrication system : 

 
 

Aircraft Engine Oil Tanks

Engine Oil tanks are the main focal point in the aircraft lubrication system. As the name implies, its main function is to provide storage for the lubrication and thermal control oil being used in the engine and its components. Oil tanks are also used for providing the additional space required for expanding fluids due to temperature rise during its operation cycles. Engine Oil tanks are usually attached to the frontal portion of the engine often called Fan cases.

Oil tanks have few major sub-assemblies which include:  

1. Filling port and an overflow port – For Filling / Top-up purposes
2. Sight gage- To check fluid levels visually
3. Oil-out / Supply port equipped with a strainer – To supply Oil to the inlet of the lubrication pump
4. Drain plug – To drain the tank for emptying
5. Oil-in / Return port – To connect return line from the scavenge circuit
6. De-aerator /  air separator – To separate any trapped air from returning oil
7. Tank vent port – To provide pressure equalizing vents
8. Oil level transmitter – An electronic measuring system for remote indications
9. Internal walls – To strengthen the oil tank structure and also to reduce oil sloshing during operation cycles.