Aircraft Engine Lubrication Unit ( Lubrication Pump)

Lubrication unit Or simply said the Lubrication pump system is the main driving force behind the pressurized lubricants in a jet engine. Its main function is to provide oil under the required pressure for lubrication of the engine components and spool bearings, then perform the scavenging (returning) of the oil after lubrication process then finally to directs it to the oil tank via the oil/fuel heat exchanger.

In order to pressurize and to maintain positive displacement flow, it uses a series of pumps which are driven by a single shaft. Often the pump is a Gerortor pump (Click on to read on Gerotor pump construction) which is driven by a single shaft. Number of pumps in the shaft depends on the number of supply and scavenge systems available.  

Lubrication units has its main supply inlet from the Main Oil Tank , one or more Supply lines and one or more scavenge lines for returning oil. It also has various tapping for temperature and pressure measuring sensors. (See below)

The return lines are equipped with scavenge filter screens/mesh to remove any debris from entering the pump system. Each scavenge line is often provided with oil condition monitoring magnetic chip detectors. Magnetic chip detectors works by attracting metal substances to its tip and provide good indications on possible failures in the system ( based on metal analysis). It also aid in reducing  the amount of powdery metallic debris in oil system by attracting the metallic substances.(See below)

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 :