Chapter 9 Lubrication PDF

Chapter 9: Lubrication Ref: The Jet Engine (Rolls Royce 1996) Introduction  Facts on Lubrication System  Requirement of Lubrication System  Types of Oil System  Operation of Oil System  Components of Oil System  Important Facts on Oil System  Re...

Chapter 9: Lubrication Ref: The Jet Engine (Rolls Royce 1996) Introduction  Facts on Lubrication System  Requirement of Lubrication System  Types of Oil System  Operation of Oil System  Components of Oil System  Important Facts on Oil System  Recap 2 Introduction Lubrication System  The lubrication system is required to provide lubrication and cooling for all gears, bearings and splines.  It must also be capable of collecting foreign matter which, if left in an oil tank / bearing housing / gearbox.  Additionally, the oil must protect the lubricated components which are manufactured from non-corrosion resistant materials.  The oil must accomplish these tasks without significant deterioration. 3 Purpose of Turbine Engine Lubrication  Lubrication of Mating Parts – reduction of friction and wear  Cleaning of moving parts – metal particles formed during wear and tear should be removed to prevent further damages  Cooling of hot parts – heat can cause degradation of material properties & may cause seizure of parts  Oil damping – to reduce vibration 4 Requirements of Aviation Lubricants  Low volatility to reduce evaporation at high altitude  Anti-forming characteristics to give positive lubrication  High flash point  Wide temperature range  Excellent film strength qualities of cohesion and adhesion  High viscosity index meaning the oil will tend to retain its viscosity when heated within the operating temperature 5 Types of Oil System 6 Wet Sump Lubrication System 7 Wet Sump Lubrication System  Wet sump system is the oldest design and is rarely seen in modern engines  The oil is contained integrally in an engine sump  The parts to be lubricated are immersed partially or fully in a bath of oil 8 Dry Sump Lubrication System 9 Dry Sump Lubrication System  Most modern turbine engines of the axial flow configuration uses Dry Sump Lubrication System  Dry Sump Lubrication Subsystem consists of Pressure, Scavenge and Breather vent  Oil is supplied to the lubricating parts by pressure pump and is returned back to the tank by scavenge pumps. 10 A 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 will return 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. 11 Operation of Oil System 12 Overall View of Full Flow Lubricating System 13 Operation of a Full Flow Lubricating System Operation (Supply): 1. The oil flows from the tank down to the pressure stage in the lubrication and scavenge oil pump. 2. The oil pump pressurizes the oil and sends it to the main oil filter. 3. If the oil pressure before the filter is greater than set pressure, some of the oil goes through a pressure relief valve and is returned to the oil tank. 4. From the main oil filter, the oil is sent to the engine air/oil heat exchanger, 5. Then the oil goes to the fuel oil cooler. 6. At the top of the fuel oil cooler, a manifold distributes the oil. 7. Then the manifold sends oil through the last chance strainers/filters, and to the bearing compartments and gearboxes. 14 Operation of a Full Flow Lubricating System Operation (Scavenge Line): 1. The oil is removed from the bearing compartments and gearboxes by the scavenge oil pumps. 2. Before oil reaches to the Scavenge pump, Magnetic Chip Detector will help to remove ferrous metal chips/powder from the bearings (if any) 3. After scavenge pump, oil will travel to the Electric Magnetic Chip Detector and the Oil Temperature Sensor before oil return to the Oil Tank 15 Operation of a Full Flow Lubricating System Operation (Breather Line): 1. Oil mist is removed from the breather air by the deoiler (centrifugal breather). 2. From the deoiler, oil goes to the Tank and breather air is vented overboard. 3. While Oil mist at the LP Turbine will be flushed out from the Exhaust. 16 Components of Oil System 17 Components for a Typical Oil System 1. Oil Tank 2. Pressure & Scavenge Pumps 3. Pressure Relief Valves 4. Fuel Oil Heat Exchanger / Oil Cooler 5. Air Oil Heat Exchanger 6. Deoiler / Centrifugal Breather 7. Magnetic Chip Detectors 8. Filters 18 1. Oil Tank *T900 Training Notes 19 1. Oil Tank  The oil tank is usually mounted on the engine and is normally a separate unit although it may also be an integral part of the external gearbox.  It must have 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. 20 2. Oil Pump Assembly *T900 Training Notes 21 2. Oil Pump  The oil pumps are vital to the efficient operation of the engine.  Failure of the pumps will necessitate a rapid shutdown of the engine.  For this reason, the oil pump drive-shafts do not incorporate a weak shear neck because they 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. 22 2. Gear Type Pump  Gear pumps consist of a pair of intermeshing steel gears which 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. 23 2. Gear Type Pump 24 2. Other Types of Pump - Vane type pump 25 3. Pressure Relief Valve System 26 3. Pressure Relief Valve System  In the Pressure Relief Valve system the oil flow to the bearing chambers is controlled by limiting the pressure in the feed line to a given design value  This is accomplished by the use of a spring loaded valve which allows oil to be directly returned to the oil tank, or pressure pump inlet, when the design value is exceeded. 27 4. Fuel-cooled Oil Cooler 28 4. Fuel-cooled Oil Cooler  A large number of tubes convey the fuel through the matrix, the oil being directed by the baffle plates in a series of passes across the tubes.  Heat is transferred from the oil to the fuel, thus lowering the oil temperature. 29 5. Air/Oil Heat Exchanger 30 5. 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 31 6. Centrifugal Breather *T900 Training Notes 32 7. Magnetic Chip Detector 33 7. Magnetic Chip Detector  Magnetic plugs, or chip detectors, 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 and are retained in self-sealing valve housings.  Upon examination they can provide a warning of impending failure of bearings and splines 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. 34 8. Filter 35 8. Filter  To 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 fitted at the outlet of the oil tank or 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 which retains 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. 36 8. Thread-type Oil Filter (fine)  Thread-type filters are often fitted as a ’last chance’ filter immediately upstream of the oil jets. 37 8. Electronic Cleaning Of A Cleanable Filter 38 8. Electronic Cleaning Of A Cleanable Filter  Traditional of hand cleaning using solvent is still commonly used and acceptable.  The machine above is a ultra sound cleaning device for cleaning of filter. Several rounds are needed to clean the systems.  It is normal to find particles of metal on the filter surfaces. However, 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. 39 Important Facts on Oil System 40 Important Facts on Oil System  Modern gas turbine engines utilize synthetic oil for lubrication. Ex. 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 41 Recap  The requirement of lubrication  The 4 principles / purposes of engine lubrication  Description about the difference between Wet sump and Dry Sump engine  Draw out the Hot Oil Tank Full Flow Lubrication System  Explain the functionality of all major components that are in the diagram  The important facts of an oil system; especially on critical facts that cause the engine to shut-down 42