Bearingchambersealingandtheuseofaircra4bleedair

•  DrSusanMichaelisPhD,MSc,ATPL•  UniversityofS@rling•  susan@susanmichaelis.com

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

1952/53–J57Engine

•  Bleedair•  Synthe@cjetoils

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,KropS.MLSRNo.61-CabinAirContamina@onInRB-57AAircra4.Maryland:ArmyChemicalCenter,1955.

BureausofairsafetyBleedairsupplycontamina@on•  Numerousreports•  22keyrecommenda@onsandfindings•  8bureausofairsafety•  Mid1990s–2016•  8countries,2con@nentsRefer:LoraineT.AirAccidentInves@ga@onFindingsandRecommenda@ons.Presenta@onatInterna@onalAircra4CabinAirConference,ImperialCollegeLondon.19-20September,2017:hMps://www.aircra4cabinair.com/films

Interna@onalac@ons

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:EUClassifica@onreg.1272/2008;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)Thenatureofpar@culatesinair34.cra4bleedairresul@ngfromoilcontamina@on.LV-17-C046.In:2017ASHRAEWinterConferencePapers.KansasStateUniversity,USA.

Oilleakageseenin3mainways1.Rarebearingsealfailure2.Failurecondi@on+opera@onalfactors-Oilspillage,sealwear….3.  Designfactor-lowlevelleakageofoilinnormalflight

Aims&Objec@vesAim-assessgapbetweenaircra4cer@fica@onrequirementsforthecleanairincrewandpassengercompartmentsoftransportaircra4usingthebleedairsystemandthetheore@calandprac@calimplementa@onoftherequirements.Objec@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

OilBearingchamber

ExxonMovil(2016)-JetEngineOilSystem-PartOneAndTwo,ExxonMobilAvia@onTechTopics.

•  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•  Labyrinthseal

TheJetEngine,RollsRoyce2005

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• Mechanicalface(carbon)seal

TheJetEngine,RollsRoyce2005

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&regulatorycompliance:•  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

Conclusions4/5

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

Faildangerous!

Sealshaveconsequences

THANKYOUtoallhere&EUsealingAssocFURTHERINFORMATIONAVAILABLE:CAQPAGE:susanmichaelis.comMSc:point4susan@susanmichaelis.comUniversityofS@rlingMichaelisAvia@onConsul@ng

MScaward(Cranfield2017)CourseDirectorsbestMScstudentaward