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Bearingchambersealingandtheuseofaircra4bleedair
• DrSusanMichaelisPhD,MSc,ATPL• UniversityofS@rling• [email protected]
WhoamI?
PhD(UNSW,2010)-hMp://handle.unsw.edu.au/1959.4/50342MSc:(Cranfield,2016)-hMp://www.susanmichaelis.com/caq.html
Background• Ongoingconcerns-jetengineoilsleakingintocabinairsupply
– Reports-1950’sonwards;widevariety–e.g:toxicity,leakage,effects
– Frequency–Raretofrequent;under-repor@ng– Exposures–occurring(adhocstudies)– Safety–compromised(impairmentinflight)– Increasingac@onsbeingundertaken– Keyissue–Oilleakageseeninavarietyofways
15May1954-WILLIAMJ.VANEVERY-1stLt,USAF
“Atapproximately1530hourson15May1954,Iwasflyingaircra4number52-1436,anRB-57A,inathree(3)planeforma@onfromShawAirForceBase,SouthCarolina.Approximately40minutesa4ertake-offwhileflyingoveranovercastat7000feet,Iexperiencedblurredvision,becamenauseatedandexperiencedconsiderabledizziness.Irecallnostrangeorunpleasantodors,nordidItasteanythingoutoftheordinary.Ididfeeladefinitedrynessofmouthandthroat.Thiscondi@onlastedpossiblyaminuteortwo.AsIbecamemoreawareofthesitua@onornearlytothepassingoutpoint.Irecalldroppingbackfromtheforma@onandopeningtheclearvisionwindowandunhookingtheoxygenmask.Freshairfromthisopenwindowseemedtorelievetheunpleasantcondi@onsIfelt.”Ref:LoomisT,[email protected]:ArmyChemicalCenter,1955.
BureausofairsafetyBleedairsupplycontamina@on• Numerousreports• 22keyrecommenda@onsandfindings• 8bureausofairsafety• Mid1990s–2016• 8countries,2con@nentsRefer:LoraineT.AirAccidentInves@ga@[email protected]@onatInterna@onalAircra4CabinAirConference,ImperialCollegeLondon.19-20September,2017:hMps://www.aircra4cabinair.com/films
AAIBBulle@n:7/2007G-CPET–2006–
Boeing757• Duringthedescent,bothcrewmembersbegantofeel
disorientatedandfoundthattheyhadtoconcentratehardtocarryouttheirnormaldu@es.Atthispointthecommanderbegantofeel‘confused’.
• Theflightcrewexpressedconcernthatneitherhaddetectedtheslowdegrada@onintheirperformanceasthisonlybecamefullyapparenta4ertheyhaddonnedoxygenmasksandbegantorecover.
• Cause:Oilleakfromengineenteringairsupply
Flightsafety-Impairment• BAe146study*:Immediate/STeffects=44%• 15incidentsstudy*:
– Impairment=93%(73%involvedpilots)– 33%-fullorpar@alincapacita@onof2pilots– 87%posi@veoiliden@fica@on
Other–Crewimpairmentrates• CAAMORs:2006-2011-30%• BFU– 27%• Michaelis(PhD,2010)– 32%*MichaelisS,BurdonJ,HowardCV.AerotoxicSyndrome:ANew16.Occupa@onalDisease?PublicHealthPanorama2017;3:141-356.hMp://www.euro.who.int/__data/assets/pdf_file/0019/341533/5_OriginalResearch_AerotoxicSyndrom_ENG.pdf
Health&Science• Exposuretoacomplex(heated)mixtureincludingOPs• Hazardoussubstances:[email protected]/2008;MSDSs/
chemicaldatabases*…• Chroniclowlevelexposure• PrimarypaMerniden@fied-Acuteonchronicexposureswith
diffuseeffects• UFPs(<10-150nm)/OPs&complexmixture–mechanism?*MichaelisS,BurdonJ,HowardCV.AerotoxicSyndrome:ANew16.Occupa@onalDisease?PublicHealthPanorama2017;3:141-356.
HowardCV,MichaelisS,WaMersonA.TheAe@ologyof‘AerotoxicSyndrome’-AToxico-PathologicalViewpoint.OpenAccJofToxicol.2017;1(5):555575HowardCV,JohnsonDW,MortonJ,MichaelisS,SuppleeD,etal.IsaCumula@veExposuretoaBackgroundAerosolofNanopar@clesPartoftheCausalMechanismofAerotoxicSyndrome?JNanomedNanosci2018;JNAN-139JonesB,RothJ,HosniM(2017)[email protected]@[email protected]:2017ASHRAEWinterConferencePapers.KansasStateUniversity,USA.
Oilleakageseenin3mainways1.Rarebearingsealfailure2.Failurecondi@on+opera@onalfactors-Oilspillage,sealwear….3. Designfactor-lowlevelleakageofoilinnormalflight
Aims&Objec@vesAim-assessgapbetweenaircra4cer@fica@onrequirementsforthecleanairincrewandpassengercompartmentsoftransportaircra4usingthebleedairsystemandthetheore@calandprac@[email protected]@ves–Assess(bleedairsystem)1. cleanaircer@fica@onrequirements2. Theore@caldocumentedunderstandingofbleedair
contamina@onofcabin3. Feasibilityofimplementa@onofcleanair
requirements
Methodology
2Interviewgroups:• Regulatorsx2-FAA&EASA• Engineersx12–(aerospacex10&sealsuppliersx2)–Highlyexperienced
Interviewques@ons(Q)– Regulators–Prac@calprocessofcer@fica@on&compliance-X7Q
– Engineers–Professionalviewhowoilleakspastbearingseals–x8Q
Avia@onregula@ons/standards/Guidancematerial-cabinairquality1/2
• CS/FAR25.1309…-EquipmentandSystemsDesign–Airframe(25.1309c-warningsystems)
• CSE510&FAR33.75…–safety
Analysis(engine&APU)àbleedair(Incapacita@on<10-7/ez;impairment<10-5/ez)
• CSE690…–Bleedairpurity-(engines/APU)
• Failurecondi@oneffects
Avia@onregula@ons/standards/guidancematerial-cabinairquality2/2
• CS&FAR25.831a/b-ven@la@onA)Enoughfreshairfordu@es–withoutunduediscomfort/fa@gue(10cfm+)B)Freeofharmfulhazardousconcentra@onsofgasesorvapors-(CO,CO2,O3)+++?
• AMC21.A.3B(b)–Unsafecondi@on–Impairment/discomfort–Incr
frequency• (EU)Reg2015/1018-Repor@ng:e.g:Contaminatedairincockpitorcabin
whichcouldendangeraircra4/occupants/fumes/leakingliquid….
Oil/airsystem• Oilsystemprovidesoilunderhighpressure:
• Lubrica@on,cooling,sealing…..• e.g:mainsha4bearingsinbearingchambers(con@nuoussupply
&removalofoil)• Secondary(core/bleed)airfromcompressor–manyfunc@onsincl.
• Coolingengine/accessorycomponents• Bearingchamberandoilcooling/sealing• Controlturbine@pclearances• Cabinpressurisa6on/ven6la6on
• Amountofsecondaryairusedishighlycontrolled&minimized–ReduceSFCpenal@es-OilandAirSealsarerequiredtodothis.
BearingcompartmentsealingOilSealFunc6ons-BearingCompartments
• Preventoilleakageout(fires/fumesincabin/lossofaerodynamicperf’)• Preventmoisture&dirtin• ControlofairleakageinàImproveperformance• Reduceoilconsump@on• Operateunderposi@ve&reversepressures
Pressurisedairfromthecompressorisusedtopreventoilleakingthroughbearingseals&tocool/ven@latebearingsumps
Philosophy:UsepressurisedairtomaintainbearingcompartmentatalowerpressurethansurroundingsàInwardflow/preventoutwardleak
1950s:Highawarenessofoilcontamina@onofthebleedairbutdesiretoreducecostsofextracompressor–Bleedairacceptedassimilarqualitytooutsideair2maintypesofsealsused:Labyrinth&mechanical
• Alldynamicsealsaredesignedtoleak• Howmuchtheyleakdependsonmanyfactors/hydrodynamiceffects
• Styleofseal&balancera@oortoothpaMern• Lubrica@ngregime• Opera@ngcondi@ons(speed/temperatures/pressures)• Componentcondi@on/wearlife/distor@on
( )
( )21ln6
213
RR
PPhmµ
ρπ −=
h m clL2
sRTVrel
relMγ
=
Simplifiedleakageformulae
Factorsaffec@ngseals• Howsealsoperate
Factorsaffec@ngseals
TheJetEngine,RollsRoyce
• Noncontac@ngclearancetypeseal• Operateswith@ghtclearances(200-400nm)• Controlsleakageofairorliquidover
restric@onsreducespressureoverseal• Fluidcanflowineitherdirec@ondepending
onpressure/momentum/design
clL2
• Performancedeteriorateswith@me,wear,changesinopera@ngcondi@ons
• ‘Rubs’canhaveimmediatedetrimentalimpactonleakageasclearancesincrease
• Variousbenefits-lowcost/simple
• Labyrinthseal
Factorsaffec@ngseals
h Increases In Speed Viscosity Waviness Roughness = Increased Gap
PVlimits
• Mechanicalface(carbon)sealHydrodynamiceffects
Distor6oneffects
• Microsealfacesepara@ontypically10to40micro-inches(0.25–1.0µm),solowleakage
• Pressureandtemperaturedistor@oncanimpacttheparallelismofthesealfacesandreduceorincreaseleakage
• Surfaceroughness1to10micro-inchesRA(0.025to0.25micrometresCLAcaninfluencefluidfilmcondi@on
• Performancelesslikelytodeteriorateswith@me,wear,orchangesinopera@ngcondi@onsasdesignscano4encompensateduringwearlife
• MaterialscanusuallyrecoverfromintermiMentcontact,butnotcon@nuousdryrunning
• Morecomplexandexpensive
00.5
11.5
22.5
3
0 100 200 300 400 500PV, psi ft/min
wea
r, m
ils
Ni-Resist Ceramic TC
CastIron/Ceramic/WC
Hydro Mechanical Thermal
Fluid / Gas Film
Sealing gap characteristics
Components
Seal / housing component
characteristics
Heat transfer
Thermal distortion
Gap temp.
Total gap
profile
Fluid / Gas
viscosity
Frictional heat
Hydrodynamic / pressure
distributions
Hydrostatic pressure
distribution
Pressure distortion
Hydraulic balance /
separation
Thermal Hydro-mechanical Other
Factorsaffec@ngseals• Sealleakageconcepts
Commonassump@ons–Oilleakage1/2
1. Higherpressureingaspaththaninsidebearingchamber–Keepsoilinbearingchamber
2. Sealsonlyleakwhenfailureoccurs3. Reversepressurestobeavoided–prevents
leakage
Commonassump@ons–Oilleakage2/2
HoweverA) Oilmayflowwith&againstposi@vepressuregradientwith
bothtypesofsealsB) Posi@vepressuregradientdifficulttoaMainatnearambient
pressures(usedinsealingbearingchambers)C) Reversepressuresoverseals-Allowoiltoflowinopp
direc@on–Bothsealtypes• Labyrinths-clearance• Mechanicalfaceseal-faceopensup• Alldynamicsealswillleak,withsealsdesignedtolimit
leakage/‘emissionratherthanleakage’
Engineersresearch1/31.Oilleakage–Internal&externalengineleakage/Intocore&bleedair2.Leakagepastseals:• Sealsdesign:
• notabsolutedesign-sealsleak• Pressuredifferen@als• Thermal&axialradial(mechanical)changesinenginestructures• Leakageaffectedbyenginespeed&power• Designparametersdon’taccountforallcondi@ons
• Sealwear/installa@on/maintenance…..3.Phaseofflightaffectsleakage:Changesinengineperformance(pressuredifferen@als/mechanicalstructurechanges);lowpowerse|ngs….
Engineersresearch2/34.Mechanicalandlabyrinthsealsbothleakforvaryingreasons:• Leakageisinevitable-design• Labyrinth-relymoreonpressurediff• Mechanical(carbon)–Lubrica@onbetweensurfaces=leakage• oversealfaces/Moresubjecttowear&temperaturecri@cal• Leakageoccursbothwith&againstthepressuredrop-both5.Oilleakage®ulatorycompliance:• Nopublishedlimitsforoilcontamina@on• Noac@onrequiredifleakageunderpermissibleoilconsump@on
Engineersresearch3/36.Oilleakage:• Oilleavingintendedareas-Vapor/drip….(emissionsignored)• Abovepermissibleoilconsump@onlimits
7.Repor6ngoilleakage:• Under-repor@ngisoccurring• Oil‘toppingoff’isanormalprocedure
8.Mi6ga6ngoilleakstobegivenhigherpriority–solu@onsexist
Regulatorsresearch1/21.Engine/APUcer6fica6onprocess• Nospecificprocesstofollow/Mustdemonstratecompliance
2.Bleedairqualitycompliance:CS–E510/FAR33.75(safetyanalysis)• Hazardousengineeffects(Toxicproducts[e.g.:oil]in‘cabin’bleedair)incapacita@onofcrew/pax-extremelyremote<=10-7-10-9/ez
• Bleedairpuritytes@ng:CSE690/CSAPU320• Nospecificguidancegiven
3.Substancesreviewed&limits–toxinsinbleedair? • Nonespecified/concentra@onsufficienttoincapacitate-FAA• SAEARP4418A–EASA(recommendedprac@ce)
Regulatorsresearch2/24.Airframecer6fica6onprocess:CS/FAR25.831• Airdoesnotneedtobepris@ne-FAA• Enoughfreshairtoavoiddiscomfort/fa@gue• LevelsprovidedforCO,CO2,O3only• Recentcer@fica@on/sourcesofdata(FAA):NRC,ASHRAE,AECMA-STAN(cancelled),NIOSH,CDC,Harvardpublichealthetc….
Discussion:oilcontamina@onofthebleedairsupply
1. Regula6ons/standards&guidancematerialrelatedtoCAQ-exist2. Theore6calunderstanding:
• General-avia@onindustry–Raresealleakage/withinlimits• Specialistaero/sealsexperts–Commonlyusedbearingcompartment
sealsallowlower-leveloilleakageoversealsinnormalflight
3. Feasibilityofimplementa6onofstandardswithbleedairsystem• Low-leveloilleakageoversealsarepartofnormalsystemfunc@on
usingpressurisedoilbearingseals.
Conclusions1/5
Thereisagapbetweencer0fica0onrequirementsforprovisionofcleanairinaircra9crewandpassenger
Compartmentsusingthebleedairsystem.
Conclusions3/5
Design1. Lowleveloilleakageoverthebearingsealsintothebleedair:
• Expectednormalcondi6on-variousphasesofflight2.Cer6fica6onreq’snotbeingmet(despiteappearancetheyare)
• Literature/aero&sealexpertsresearch• Oilleakagepastsealsassociatedwithimpaired/degradedperformanceoccursmorefrequentlythan‘major’effects(remote/improbable)<10-5-10-9/eg….
• Oilleakage(impairment)-Guidancematerial• Probableorabove>=10-5/eg….• Unsafecondi6on
Conclusions5/6
Compliance:• Inadequatelyundertakenatcer@fica@on• Nodetec@onsystemstomonitorairinflight• Requirementsnotspecificenoughtoensureoccupantswillremainfreeofadverseeffects
Preventa6vecontrolmeasures:• Low-leveloilemissionsnottakenintoaccount• Designsbasedonsteady-statecondi@ons• Nodetec@onsorfiltra@onsystems• Rigorouscontrolslacking
Conclusions6/6
Retrospec6vely:• Previouscer@fica@onrequirementsnotspecificenoughtopreventoilleakageintoairsupply
Exper6se&communica6on:• Highlyspecialistarea&inadequatecommunica@onbetweenpar@estoensurecompliance&airworthiness
Recommenda@ons1/2• Reviewstandards,guidancematerial
• Preventa@vemeasures:Normal&abnormalopera@ons
• Oilleakagenottobelinkedexclusivelytorarefailurecondi@ons/maintenanceirregulari@es
• Frequency–Explainedbydesignfactor• Retrospec@vecer@fica@onforbleedairquality• Futureaircra4-bleedfreedesigns• Fargreaterpriorityprioritytoregulatorycomplianceincludinglow-levelemissionsinflight
• Warningsystemsintroduced&
Recommenda@ons2/2
• Sealdesignersbroughtintodesignprocessfarearlier&partoftheprocess
• Moreadvancedseal/enginedesigns
THANKYOUtoallhere&EUsealingAssocFURTHERINFORMATIONAVAILABLE:CAQPAGE:susanmichaelis.comMSc:[email protected]@rlingMichaelisAvia@onConsul@ng
MScaward(Cranfield2017)CourseDirectorsbestMScstudentaward