turbulent flames at high reyolds number -...

NSFProjectCBET-1703543 Dr.Song-Charng KongAFOSRProjectFA9550-16-1-0028, Dr.Chiping Li 1

JimDriscoll

AaronSkiba,TimWabel,CamCarter

TurbulentFlamesatHighReyolds Number

a) DistributedCombustion=“NearLimit”b) PilotedBunsen– RegimeDiagram=notveryNearc) JP-8flames- maybehalfway?

2

DistributedTurbulentCombustion ßà Autoignition

Tianfeng Lu,JackieChen,C.K.Law

“Diluted”oxidizer=12%O2,1200K

Airat700K21%O2

Productsat2200K

Fuel

HighSpeedMixing,noflames

Auto-ignition

DistributedCombustion?

H + O2 + M à HO2 + M DME + HO2 à CH3OCH2 +H2O2

3

(a)Distributedcombustion- notfoundforpilotedBunsen

Distributed?

Theory Experiments

notpreheated,notdiluted,methaneonly

TurbulenceIntensityu’/SL

Integralscale Integralscale

NoDistributed

4

DistributedCombustion– howtofindit?

Distributed if:

Highlypreheated- to1200K

HighlydilutedwithproductsN2,CO2 H2O

Temperaturesriseonlyfrom1200Kto1700K

Longresidencetime =recirculation,hotwalls(Medwell,Dally)

Hi-Pilot

DistributedCombustion

PreheatTemp.(K)

ß Dilution=%O2 inreactants21%

5

MichiganDISTRIBU- burner

5m=15feetTupto700K

Highlypreheatedto1200KHighlydiluted–

withN2,CO2 orH2O– to12%O2Usevitiator heater- sodilution

fractioniswellknown

Premixchamber- athighvelocitytopreventflameformation

Longresidencetime,strongmixingHotwalls

O2 injectionN2 injection

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Planfornextyear

1. CompleteMichiganDISTRIBU-burner, achievedistributedcombustion

2. ApplyourPLIFreactionratediagnostics(formaldehyde-OHoverlap,CH)

3. Measureboundariesofdistributedcombustionvs.flamelets

Hi-Pilot

DistributedCombustion

PreheatTemp.(K)

ß Dilution=%O2 inreactants21%

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b)PilotedBunsen=unheated,undilutedflamestructure

ThinWrinkledflamelets(yes)

BroadenedPreheatLayers(yes)

Fractal-like

denselypacked(yes)

Broken(yeswithpoorbacksupport)

Distributed(notunlessaddpreheat,dilution,swirl)

MichiganHi-PilotBurner- methane, notheated,notdiluted

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100m/s

Meanvelocityupto100m/su’/SL upto246Lx/δL upto215ReT =upto100,000

3.“Events”at20kHz:pulseburstlaser- OH+formald +stereoPIV

1.Reactedness structure(temperature)profilesPreheatthickness formald.&RayleighReaction layerthickness CHandoverlapTurbulenceprofiles,b.c.’s

2.MeasuredRegimeBoundaryTurbulentburningvelocity(ST)

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HighReMETHANEDataBase=temperature,preheatzones,reactionzones,turbulence

Temperature(Rayleigh)

CH10kHz

Formaldehyde20kHz

OH20kHz

turbulence(PIV)20kHz

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temperature

Largeblobsofhotproductsconvected upstreambyturbulentdiffusion

similartoDNSofJ.HChen

Reactedness (Temperature)profilesfromRayleigh

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Preheatlayerthickness

from formaldehyde PLIFalso from Rayleigh

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ReactionLayers- fromOverlapandCH

CHPLIFat10kHz

Overlapmethod

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20kHzUnsteadyEvents- simul /stereo-PIV/form.-OH

Preheat (blue), Products (red) Simultaneous Eddies,Velocity

Events:howdolargeeddiescauseDamkohler diffusionofglobsofhotgasesupstreamintoreactants?Forwhateddysize?

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Reactionlayers

CHPLIFat10kHz

Hi-PilotBurner

CamCarter’sLabTonghun Lee’slaseratAFRL

Whatisthemerging rate?pocketformationrate?

extinctionrate?

Whydoesareaneverexceedaboutfivetimes theunwrinkledarea?

Events- measurethemergingrateathighRe

CHlayers

MeasuredflameletMergingrate(M)

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PredictedRegimeBoundaries

DistributedReactions

Motivation:

Whenaremodelsvalid?

Thinflamelet modelThickenedflamelet modelDistributedreactionmodel

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Flamelets notdistributed abovepredicted“distributed” boundary

1.0

10.0

100.0

1000.0

Lx,0 /δf

u0’/SL

ThinFlamelets(Gulder)

PresentHi-Pilot data=notdistributed

LaminarWrinkledflames

Dunn,BarlowAlden=notdistributed Predicted

“Distributed”Boundary

à isnotvalidfortheseexpts.

1.0

10.0

100.0

1000.0

Lx,0 /δf

u0’/SL

Solidsymbols=MeasuredBroadenedPreheat,ThinReaction layers

Opensymbols=measured


PresentHi-Pilot data

Laminar

Dunn,BarlowAldendata

MeasuredRegimeDiagram- broadeningboundary

PredictedbroadeningBoundarydoesnotagreewmeasurements

MeasuredbroadeningboundaryDT =u’Lx =180D*

CONCLUSIONSforMETHANEfuel

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1. FirstHiRedatabase- flamestructurein“Extreme” turbulenceu’/SL =240,ReT =100,000- completedimagesoftemperature,OH,formaldehyde, CH,velocity“intense” range=ReT =5,000=Dunn-Barlow,Alden(Lund)

3.MeasuredRegimeDiagram– forpilotedbunsen flamesonly

2. Broadenedpreheat,thinreactionlayersareobservedDistributedorbrokennotobservedforthisexpt.

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Broadenedpreheatlayersmeasuredtooccurwhen

DT =u’Lx =180D*

TwoboundariesonthepredictedBorghi donotmatchtheMeasuredRegimeDiagram

Brokenreactionlayersnotobserved inpresentwork- forKarlovitz numberuptofivetimesthepredictedvalue

Dunn,Masri seesomebrokenatKa =tentimespredicted

à Flamelets occurovermuchwiderrangethanpredicted

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Disclaimer- westudyTWOoutofSEVENpossiblegeometries

2.GasTurbineLPPCombustorlowmeanvelocitylargeresidence time

“DISTRIBU-burner”distributed,flameletsandextinction ?

1.Afterburnerlargemeanvelocitysmallresidencetimenotsheardominated

“High-Pilot’PilotedBunsenburnerfavorsflamelets andhardtoextinguish

Othergeometries:

3.Premixedjetflame:issheardominated

4. Bluffbody

5.Counter-flowflames

6.Sphericalflame

7.Wellstirredreactors

JP-8Flames- inprogress

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100m/s vaporized JP-8

heating tape

fine sprayDelevan atomizerliquid JP-8

5m=15feetTupto700K

JP-8premixedReT =20,000

ChemistryinHighReJP-8Flames

Pyrolysiszone

Preheatzone?

PrimaryReactionZone

WhystudyJP-8chemistryinturbulentflames?

à Onlyturbulentflames(athighRe)providerealistic

residence times =timeforfluidelementtocrossthreelayers

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Step1:PLIFofpreheatedJP-8flamesatMichigan

Fluorescenceintensity

266 nmlaserline460nm540nmwavelength

GritschONERA

Fluorescenceintensity

266 nmlaserline460nm540nm

tolueneC7H8

Sick(Michigan)

naphthalenetri-methylC10H8 benzene

PLIFofformaldehyde,OHPLIFofJP-8components:naphthalene,toluene,tri-methylbenzene

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STEP2:LineCARS- ofJimGord atAFRL

preheat

pyrolysis

primary reactions

Pumpsheet

Probesheet

Profilesof14speciesinavaporizedJP-8flame-

canitbedone?

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ChemistryinHighReJP-8Flames– jointMichigan–AFRL

pyrolysis zone imaged with JP-8 PLIF

preheat region imaged withformaldehyde PLIF

high T reaction zone imaged with OH PLIF

CARS line imaging of temperature, species

methane H2Xi OH

JP-8 components formaldehyde

tolueneXi OH

x x

CO

acetylene

CO2

ethylene

Fluorescence: 5 species (Michigan) CARS: 9 species (Gord, Meyer) 27

Chemistrydatareduction

Eachlasershot(someat10Hz,someatkHz)

a) Profileofonespeciesandtemperature(CARSorLIFlineimaging)

JP-8Xi

x, mm

T

b)Simultaneous2-DPLIFimagesofpyrolysislayer,preheat,reactionlayertomeasureresidencetime=thickness/normalvelocity

Forresidencetime=0.1ms

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29

END

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Events:extinctionwithpoorbacksupport

reactants(black)

noCH=extinction

10kHzCH-OHsimultaneously

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Compare“Events”toDNSofJackieChen,JohnBell

“areaincrease”events:

vortexpassage,flamestretch,extinction,

rollup,merging

“Damkohler diffusion”events

globsofhotgasesconvecting,broadeningthepreheatlayer

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TurbulentBurningVelocity(ST)

previousdataofGulder

lowturbulence=linearvariationofSTextremeturbulence=squarerootdependence

Truemeasuredburningvelocity

Wrinkledarea/timeaveragedarea

AthighReynoldsnumber,wasDamkohlerpredictioncorrect?YES

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“Measurements toDetermine RegimesofPremixedFlames inExtremeTurbulence”,T.Wabel, A.Skiba,J.Temme,J.F.Driscoll

“TurbulentBurningVelocityMeasurements: ExtendedtoExtremeLevelsofTurbulence”T.Wabel,A.Skiba,J.F.Driscoll

“Reaction layervisualization:acomparisonoftwoPLIFtechniquesandadvantagesofkHz-imaging”Skiba,T.Wabel,C.D.Carter,S.Hammack,J.Temme,T.H.Lee,J.F.Driscoll

+twopaperssubmittedforJournalpublication

Formoredetails:seeourrecentpapers

36th Comb.Symp.Seoul:

34

1. Events:Merging,extinction,broadening

4. RegimeofContinuousThickenedFlamelets - is largerthanpredictedbyPetersPredicted“Brokenregime”boundary- isnot consistentwithourdata

5. Wemeasuredtheboundary wherepreheatlayersarebroadenedDT >180D*

6. TurbulentburningvelocityatextremeturbulenceagreeswithDamkohler trends

7. PLIFofJP-8,toluene,formaldehyde,OH– carefulselectionofwavelengthsneeded

Conclusions - whathappensatextreme levelsofturbulence?

2.Preheatlayers- becomesverybroadened,Reaction layers– remainthin

3.Stratifiedflamesbecomebrokenanddistributed (butnon-stratifieddonot)

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20-40kHzPulseBurstLaserand10kHzLaser

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Flamelets arenotbroken abovethepredicted“Broken”boundary

1.0

10.0

100.0

1000.0

Lx,0 /δf

u0’/SLPredicted“Broken”boundary



Presentdata


Dunndata

37

1.0

10.0

100.0

1000.0

Lx,0 /δf

u0’/SL

Solidsymbols=MeasuredBroadenedPreheat,ThinReaction



Presentdata

DT =180D*


MeasuredRegimeDiagram- broadeningboundary

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Goal#3MeasuredRegimes- twomeasuredboundariesdonotagree

Flamelets occurovermuchwiderrangethanwaspredicted

Broadeningofreactionlayersà whenKaPexceedsfivetimespredictedvalue

BroadeningofpreheatLayersà whenDT /D*=180whereDT =u’Lx

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InteractionswithDrs.CamCarter,JimGord AFRL

1. AFRL:KilohertzCHmoviesinHi-Pilot (completed)

2. AFRL:KHzsimultaneousCH-OHinHi-Pilot(completed)

3. ComparedCHtoOverlapmethods (completed)

4.Michigan:SetupJP-8Hi-Pilotflame (completed)

5. AFRLandMichigan:PIVvelocityfield (thiscomingyear)

6. AFRL:RunHi-PilotonJP-8forLineCARS (thiscomingyear)

Michigan:measuredburningvelocities,preheatandoverlap(reaction)layers(completed)

Profilesof14speciesinavaporizedJP-8flame-

canitbedone?

40

Extinctionevents- leadtobrokenreactions

CHreactionlayer=thinbrightblueline

OHproducts=broadlightblue

Brokenreactions

darkblue=stratifiedproducts

reactants

Brokenreactions

darkblue=stratifiedproducts

reactants

CH-OHmethodofCamCarter

turbulent flames at high reyolds number -...

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