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Lubrication System Introduction

• The lubrication system provides lubrication and cooling for gears, bearings, and splines.
• It collects foreign matter from the oil tank, bearing housing, and gearbox
• The oil protects lubricated components made of non-corrosion resistant materials.
• The oil performs its tasks without significant deterioration.

Purpose of Turbine Engine Lubrication

• Lubrication reduces friction and wear between mating parts.
• Cleans moving parts by removing metal particles formed during wear
• Metal particles formed during wear should be removed to prevent further damage.
• Cools hot parts to prevent degradation of material properties and seizure of parts.
• Oil damping reduces vibration.

Requirements of Aviation Lubricants

• Low volatility is needed to reduce evaporation at high altitude.
• Anti-forming characteristics give positive lubrication.
• High flash point is needed.
• Wide temperature range is needed.
• Excellent film strength qualities of cohesion and adhesion are needed.
• High viscosity index helps the oil retain its viscosity when heated.

Types of Oil Systems

• Wet Sump Lubrication System
• Dry Sump Lubrication System
• Full Flow Type Oil System (Dry Sump)

Wet Sump Lubrication System

• The wet sump system is the oldest design and is rarely seen in modern engines.
• The oil is contained integrally in an engine sump.
• Parts to be lubricated are immersed partially or fully in a bath of oil.

Dry Sump Lubrication System

• Most modern turbine engines of the axial flow configuration use this system.
• The Dry Sump Lubrication Subsystem consists of Pressure, Scavenge and Breather vent
• Oil is supplied to the lubricating parts by pressure pump
• The oil returns back to the tank by scavenge pumps.

Full Flow Type Oil System (Dry Sump)

• The full flow system achieves the desired oil flow rates throughout by dispensing oil based on maximum RPM.
• Excess oil returns through the Pressure Relief Valve to the feeding point of the Supply Pump.
• The pressure pump size is determined by the flow required at maximum engine speed.

Operation of a Full Flow Lubricating System (Supply)

• Oil flows from the tank down to the pressure stage in the lubrication and scavenge oil pump.
• The oil pump pressurizes the oil and sends it to the main oil filter.
• If the oil pressure before the filter is greater than set pressure, some of the oil goes through a pressure relief valve
• The oil returns back to the oil tank.
• From the main oil filter, the oil is sent to the engine air/oil heat exchanger.
• Then the oil goes to the fuel oil cooler.
• At the top of the fuel oil cooler, a manifold distributes the oil.
• Then the manifold sends oil through the last chance strainers/filters, and to the bearing compartments and gearboxes.

Operation of a Full Flow Lubricating System (Scavenge Line)

• Oil is removed from the bearing compartments and gearboxes by the scavenge oil pumps.
• Before oil reaches the Scavenge pump, Magnetic Chip Detector helps remove ferrous metal chips/powder from the bearings.
• After scavenge pump, oil travels to the Electric Magnetic Chip Detector and the Oil Temperature Sensor before returning to the Oil Tank

Operation of a Full Flow Lubricating System (Breather Line)

• Oil mist is removed from the breather air by the deoiler (centrifugal breather).
• From the deoiler, oil goes to the Tank and breather air is vented overboard.
• Oil mist at the LP Turbine will be flushed out from the Exhaust.

Components of a Typical Oil System

• Oil Tank
• Pressure & Scavenge Pumps
• Pressure Relief Valves
• Fuel Oil Heat Exchanger / Oil Cooler
• Air Oil Heat Exchanger
• Deoiler / Centrifugal Breather
• Magnetic Chip Detectors
• Filters

Oil Tank

• The oil tank is usually mounted on the engine and is normally a separate unit
• It may also be an integral part of the external gearbox.
• It has provision to allow the lubrication system to be drained and replenished.
• A sight glass or a dipstick must also be incorporated to allow operator to check the oil level manually.

Oil Pump

• Oil pumps are vital to the efficient operation of the engine.
• Failure of the pumps will necessitate a rapid shutdown of the engine.
• The oil pump drive-shafts do not incorporate a weak shear neck
• The shear neck must continue to supply oil for as long as possible, regardless of damage.
• The Supply pump is normally integrated together with the Scavenge pump in an Oil Pump Assembly.

Gear Type Pump

• Gear pumps consist of a pair of intermeshing steel gears
• The gears are housed in a close fitting aluminum casing.
• When the gears are rotated, oil is drawn into the pump, carried round between the teeth and casing and delivered at the outlet.
• Gear pumps can be used for pressure (feed) pumps and/or scavenge (return) pumps.
• The oil pumps pack is driven by the accessory drive system.

Pressure Relief Valve System

• It controls the oil flow to the bearing chambers
• It limits the pressure in the feed line to a given design value
• This is accomplished by the use of a spring loaded valve
• The spring loaded valve allows oil to be directly returned to the oil tank, or pressure pump inlet, when the design value is exceeded.

Fuel-cooled Oil Cooler

• Transfers heat from the oil to the fuel, thus lowering the oil temperature by passing it through a matrix of tubes
• A large number of tubes convey the fuel through the matrix
• Oil is directed by the baffle plates in a series of passes across the tubes.

Air-cooled Oil Cooler

• The air-cooled oil cooler is similar to the fuel-cooled type in both construction and operation.
• The main difference is that atmospheric/ram air is used as the cooling medium

Centrifugal Breather

• Removes oil from the oil/air mixture

Magnetic Chip Detector

• Are fitted on the scavenge (return) side to collect ferrite debris from each bearing chamber.
• They are basically permanent magnets inserted in the oil flow
• They are retained in self-sealing valve housings.
• Upon examination they can provide a warning of impending failure of bearings and splines
• This can be done without having to remove and inspect the filters.
• They are designed to be removed during maintenance inspection, for condition monitoring purposes without oil loss occurring.

Filter

• Filters prevent foreign matter from continuously circulating around the lubricating system
• A number of filters and strainers are positioned within the system.
• Coarse strainers are usually are fitted at the outlet of the oil tank
• Coarse strainers are fitted immediately prior to the inlet of the oil pumps to prevent debris from damaging the pumps.
• A fine pressure filter is fitted at the pressure pump outlet
• Fine pressure filters retain any small particles which could block the oil feed jets.
• A 'pop up indicator' may be fitted to the filter housing to give a visual warning of a partially blocked filter.
• Thread-type filters are often fitted as a 'last chance' filter immediately upstream of the oil jets.
• Traditional of hand cleaning using solvent is still commonly used and acceptable for filters.
• Ultrasound cleaning devices are also used for cleaning of filters. -Several rounds are often needed to clean the systems.
• It is normal to find particles of metal on the filter surfaces.
• If the level of contamination hits the limits set by the manufacturer, the engine might be facing an impending failure.
• The engine oil could be drained, re-serviced and run for a short period of time to inspect the engine.

Important Facts on Oil System

• Modern gas turbine engines utilize synthetic oil for lubrication.
• Examples of synthetic oil is Mobil jet type II oil, exxon 2380.
• Oil tank is inspected 10 minutes after engine shutdown and usually filled up to the neck .
• Oil quantity may be read on a sight glass or on a gauge in the cockpit or on LED screen engine page.
• Low oil pressure warning is usually red and is a cause for immediate engine shutdown.
• High oil temperature is also a cause for engine shutdown