How Is Engine Oil Routed Within Subsystems of Aircraft Engines?

Oct 26, 2023

Engine oil is routed through various internal components for lubrication and cooling.

The oil routing subsystem within jet engines aims to deliver high-pressure clean oil to engine bearings and gears for lubrication and cooling internal components. The efficiency of the accessory drive system depends on the reliability of the oil distribution and scavenge system.

Engine oil is stored in the oil tank, typically attached to the outside of the fan case. The location of the oil tank allows for periodic inspection and top-up of oil as required. An oil quantity transmitter provides the oil tank level to the aircraft cockpit control.

The purpose of the lube and scavenge pump is to pressurize the oil, supply the oil to internal components, and remove the oil. The oil enters the lube and scavenge pump from the oil tank and passes through multiple wash screens to remove large particles.

The oil is pressurized in the pump before passing through a supply filter. The oil is distributed to engine bearings, gears, and crankshafts, through pressurized nozzles for lubrication.

Pressurized oil is also sent to oil pressure sensors and switches. Multiple scavenge elements on the pump allow oil removal from various bearing compartments (sumps). Each scavenge element comprises a filter screen and a specialized magnetic chip detector (MSD). The MSDs trap metal particles carried in the scavenge oil before the oil passes through the main scavenge line.

Contaminants occur in the oil with constant circulation through various components at varying temperatures. While MSDs cannot trap all contamination, those indicate the level of impurities suspended in the oil for when it is time to inspect.

A pressure transmitter installed on the scavenge line sends a differential oil pressure reading to the cockpit control. Additionally, a low oil pressure switch provides a signal to the aircraft indicating and warning control when the oil pressure is low. An oil temperature sensor immersed in the main scavenge line provides engine oil temperature to the aircraft cockpit control.

The oil from the main scavenge line enters the Fuel Oil Heat Exchanger (FOHE), where the oil is cooled while the fuel is heated. The FOHE comprises metal tubes through which the pressurized fuel passes. Hot engine oil runs around the metal tubes, cooling the oil through heat exchange.

It is noteworthy that the metal tubes within the FOHE must be routinely checked to prevent mixing engine oil and pressurized fuel, which could result in smoke or fire in the engine. In hot-tank configurations, the engine oil is routed back to the tank without being cooled.

The cooled oil enters the scavenge oil filter, where the contaminants are removed using a filter element. Oil filters are generally designed such that the incoming oil enters the filter element from the outside, thus leaving any contaminants and debris on the filter face for investigation.

A pressure switch installed on the scavenge oil filter transmits a differential pressure reading to the cockpit control, which is used for filter clog warning indication. The cooled and filtered oil returns back to the oil tank.

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Writer - Omar is an aviation enthusiast who holds a Ph.D. in Aerospace Engineering. With numerous years of technical and research experience under his belt, Omar aims to focus on research-based aviation practices. Apart from work, Omar has a passion for traveling, visiting aviation sites, and plane spotting. Based in Vancouver, Canada