Hanson Stanford Flame Workshop 2012

8/13/2019 Hanson Stanford Flame Workshop 2012

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MeasurementsofElementaryRateConstants,

IgnitionDelaysandSpeciesHistoriesinShockTubes

R.K.Hanson,D.F.Davidson

StanfordUniversity

1st InternationalWorkshoponFlameChemistry

July2829,2012

ShockTube/LaserApproach

AdvancesinMethodology

ElementaryReactionRateStudies

MultiSpeciesTimeHistories


2/36

StanfordShock

Tubes

2

Kinetics

Shock

Tube2

(30atm)

Kinetics

Shock

Tube1(30atm)

Aerosol

Shock

Tube

(10atm)

High

Pressure

Shock

Tube

(500atm)


3/36

NewConstrainedReactionVolume(CRV)Facility

2Configurations

3

CRV1

GasPhase

Experiments

to100atm

CRV2

Aerosol

Experiments

to100atm

Constrained

ReactionVolume

Sliding

Valve

Aerosol

GenerationTank


4/36

StanfordLaser

Diagnostics

4

Ultrafast

lasersusedto

extendUVtuningrange

(2009)

Firstuseof

tunable

dyelasers

inshocktubes

(1982)

Newlasers

allowsimple

accesstomidIR(200710)

Ultraviolet

CH3 216nm

NO

225nm

O2 227nm

HO2 230nm

OH 306nm

NH 336nm

Visible

CN 388nm

CH

431nm

NCO 440nm

NO2 472nm

NH2 597nm

HCO 614nm

Infrared

H2O 2.5m

CO2 2.7m

CH4 3.4m

CH2O 3.4m

CO 4.6m

NO 5.2m

C2H4 10.5m


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LaserAbsorptionYieldsHighSensitivityRepresentativeDetectionLimits:PolyatomicMolecules

Polyatomicmolecules@1500K:2200ppm

1000 1500 2000 2500 3000

0.01

0.1

1

10

100

1000

CH2OCO2

CH3

C2H4

DetectionLimit[pp

m]

Temperature [K]

1atm,15cm,1MHz

H2O

NH2

5


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subppm

sensitivityfor

OH,CH,CN

LaserAbsorptionYieldsHighSensitivityRepresentativeDetectionLimits:DiatomicMolecules

Diatomicmolecules@1500K:

subppmdetectivitiy forUVabsorbers

ppmdetectivity forIRabsorbers

1000 1500 2000 2500 3000

0.01

0.1

1

10

100

1000

CO

OH

DetectionLimit[pp

m]

Temperature [K]

1atm,15cm,1MHz

CH

CN

6


7/36

AdvancesinShockTube

Methodology

1. Improveduniformitywithdriverinserts

2. Longertesttimeswithtailoredgas

mixtures&extendeddriver

3. Reactivegasmodeling:

problemandsolutions

7


8/36

ImprovementinReflectedShockTemperatureUniformity

UsingDriver

Inserts

Conventional shocktube

operationcanprovide

nearidealuniformflows

for13ms

But,boundarylayersand

attenuation inducedP/dt

anddT/dt atlongertimes

8

dP/dt = 3%/ms

dT/dt = 1.2%/ms


9/36


UsingDriver

Inserts

Driverinsertsmodifyflowtoachieve

uniformTandPatlongtesttimes

P5T5

These effectsreduce

ignitiondelaytimes

relativetoConstantPcase

Solution:DriverInserts

VRS

9

dP/dt = 3%/ms

dT/dt = 1.2%/ms


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UsingDriverInserts

Result: dP/dt = 0priortoignition

ProperignforcomparisonwithConstantPsimulations

P5T5VRS

10


11/36

LongerTestTimesAchievablewith

TailoredGasMixtures&ExtendedDriverSectionsConventionalshocktubeoperation:~13mstesttime

NooverlapwithRCMoperation~10150mstesttime

10

0.4 0.8 1.2 1.61E-3

0.01

0.1

1

10

100

1000

TestTime,

Ignition

Time

[ms]

1000/T [1/K]

2500K 1000K 625K

Unmodified

Stanford ST

n-Dodecane/Air

10atm

0.4 0.8 1.2 1.61E-3

0.01

0.1

1

10

100

1000

TestTime,

Ignition

Time

[ms]

1000/T [1/K]

2500K 1000K 625K

Unmodified

Stanford ST

RCM

n-Dodecane/Air

10atm

=1

11


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0.4 0.8 1.2 1.61E-3

0.01

0.1

1

10

100

1000

Tes

tTime,

Ignition

Time

[ms]

1000/T [1/K]

2500K 1000K 625K

Unmodified

Stanford ST

Modified ST

RCM

n-Dodecane/Air

10atm

Longerdriverlengthandtailoredgasmixtures

canprovidelongertesttimes(>40ms)

2xDriverExtension

ShocktubesnowcanoverlapwithRCMs

=1

LongerTestTimesAchievablewith

TailoredGas

Mixtures

&Extended

Driver

Sections

12


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FirstUseofLongTestTimeFacility:

LowPressurenHeptaneIgnitionintheNTCregime

Testtime=45ms at725K

Enablesfirstlowpressure(~3atm)nheptaneignition

datainNTCregime

Clearevidenceof2stageignition:1=8ms,2=20ms

Nextstep:adddriverinsertsto

removedP/dt &dT/dt

Howdothe3atm data

comparetohighPdata?

13

0 10 20 30 40 500

1

2

3

4

5

62nd Stage

Ignition

OH Emission

Non-Reactive Mix w/o Inserts

RelativePressure

Time [ms]

n-Heptane/21%O2/Ar

=1, 725K, 2.9 atm

Reactive Mix1st Stage

Ignition

Test time = 45 ms


14/36

LowPressure,LowTemperatureStudies:

NewResults

for

nHeptane

inthe

NTC

Regime

Previous1255atm data

New3atm data

Howdomeasurementscomparewithcurrentmodels? 14

1.0 1.2 1.4 1.60.1

1

10

100

55 atm

40 atm

12 atm

1000K 625K833K

IgnitionD

elayTimes

[ms

]

1000/T [1/K]

714K

3 atm

n-Heptane/21%O2/Ar,N2 =1

Stanford

Aachen


15/36

LowPressure,LowTemperatureStudies:

NTCHeptane,

Comparison

with

Model

LLNLC7(2000)modelperformsreasonably wellathighP

FurthertestsneededatlowP

Revealsvalueoflongtesttimeexperiments 15

1.0 1.2 1.4 1.60.1

1

10

100

40 atm

12 atm

1000K 625K833K

IgnitionDelayTimes

[ms

]

1000/T [1/K]

714K

3 atm

n-Heptane/O2/Ar/N2 =1

Solid:

LLNL C7

Model


16/36

ReactiveGasdynamics Modeling:AProblem

Mostcurrentreflectedshockmodelingassumes

ConstantVolumeorConstantPressure

But:

Exothermic energyreleaseduringoxidationor

endothermic coolingduringpyrolysischangesT&P

behindreflectedshocks

notaConstantVorConstantPprocess! Example:HeptaneIgnition

16


17/36

EffectofEnergyReleaseonPProfiles:

nHeptane

Oxidation

Howdoesthiscomparewithmodels?

NotaconstantPprocess!

17

-100 0 100 200 300 400 500 6000

1

2

3

4

5

0.4% Heptane/4.4% O2/Ar, =1

1380K, 2.3 atm

Pressure

[atm

]

Time [us]

ign

0

2

4

MeasuredSidewallP

ConstantP

Model


18/36

EffectofEnergyReleaseonPProfiles:

nHeptane

Oxidation

Howdoesthiscomparewithmodel?

NotaconstantPprocess!

NotaConstantVprocess,evenfor0.4%fuel!

Sohowcanentireprocessbemodeled? 18

-100 0 100 200 300 400 500 6000

1

2

3

4

5

0.4% Heptane/4.4% O2/Ar, =1

1380K, 2.3 atm

Pressure

[atm

]

Time [us]

ign

0

2

4

MeasuredSidewallP

ConstantP

Model

ConstantV

Model


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3ProposedSolutionstoEnableModelingthrough

EntireCombustionEvent

1. Minimizefuelloadingtoreduceexothermically orendothermicallydrivenTandPchangesenabledbyhighsensitivitylaserdiagnostics

2. Modifiedgasdynamics modelingtoaccountforPandTchangeduringcombustionworkinprogress(butcomputationallyintensive:1D,3D)

3. Usenewconstrainedreactionvolumeconcepttominimizepressureperturbations

enablesconstantP(orspecifiedP)modeling

Examples: 1)Useofdilutereactivemixtures2)Useofconstrainedreactionvolume

19


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Example1:BenefitofDiluteMixtures

3PentanoneOxidation

Pressurenearlyconstantthroughoutexperiment

GoodagreementbetweenConstantH,Pmodelandexpt.

Modelsuccessfullyincludestemperaturechange

0 500 1000 15000

50

100

150

OHMoleFraction[ppm]

Time [s]

Const. H PModel

OH Data

0 500 1000 1500

0.0

0.5

1.0

1.5

2.0

Pressure[atm]

Time [s]

400 ppm 3-Pentanone/O2/Ar

1486 K, 1.52 atm, =1

LowFuelLoadingExperiment

20

OHMoleFraction

TfinalTInitial=45K


21/36

Example2:ConstrainedReactionVolumeApproach

HydrogenIgnitionat950K

Largereactionvolumegiveslargeenergyrelease P& T

CRVgivesreducedenergyrelease nearconstantP

ConventionalShockTube

21

ConstrainedReactionVolume

Helium TestMixture

PreShock

PostShock

PreShock

PostShock

Helium NonReactiveMix TM

LargeRegionof

Energy Release

SmallRegionof

EnergyRelease

Reflected

ShockWave


22/36

ConventionalSTexhibitslargepressurechange!

CRVpressurenearlyconstantthroughoutexperiment!

Allowskineticsmodelingthroughignitionandcombustion!

ConventionalShockTube

22

ConstrainedReactionVolume

0 1 2 3 4 5

0

2

4

6

8

Pressure

4%H2-2%O

2-Ar

Normal Filling979K, 3.44 atm

Pressure

[atm]

Time [ms]

Emission

0 1 2 3 4 5

0

2

4

6

8

Pressure

4% H2-2%O

2-Ar

CRV = 4 cm956K, 3.397 atm

Pressure

[atm]

Time [ms]

Emission

Ignition

Example2:ConstrainedReactionVolumeApproach

HydrogenIgnitionat950K


23/36

ElementaryReactionRate

Determinations

Goal

Neardirectdeterminationofrateconstantsforspecificreactions

ExamplesOH+ketones:

acetone,2butanone,2&3pentanone

OH+alkanes

OH+butanol isomers

OH+methylesters

23


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ExperimentalStrategy

fast upon

shock heating

tertbutylhydroperoxide

TBHPusedasapromptOHprecursor

UsefulTrange(850to1350K)

PioneeredbyBott andCohen(1984) AlsousedatArgonne

Fuelinexcess,pseudofirstorderexperiment

24

Acetone

+ +


25/36

Representative3Pentanone+OHData:

1188Kand1.94atm

0 50 100

0

5

10

15

20

OHM

oleFraction[ppm]

Time [s]

Current Study

1.23x1013

cm3mol

-1s

-1

211 ppm 3-Pentanone / Ar

17 ppm TBHP

1188 K, 1.94 atm

0 50 100-4

-3

-2

-1

0

1

OH

Sensitivity

Time [s]

3-Pent+OH=Products

CH3+OH=CH

2*+H

2O

C2H

5=C

2H

4+H

Highqualitydataallowshighprecisioncomparisonwithmodel

Sensitivityanalysisconfirmspseudofirstorderbehavior

Neardirectdeterminationofreactionrateconstant!25


26/36

Resultsfor3Pentanone+OH Products

Nootherhightemperaturedataavailable

NUImodel(Serinyel etal.)inexcellentagreement

0.7 0.8 0.9 1.0 1.1 1.21E12

1E13

1E14

833K1429K 909K1000K1111K

Current Study

Serinyel et al. - NUI Galway (2010)

k[cm

3m

ol-1

s-1]

1000/T [1/K]

3-Pentanone + OH = Products

1250K

26

0.7 0.8 0.9 1.0 1.1 1.21E12

1E13

1E14

833K1429K 909K1000K1111K

Current Study

k

[cm

3m

ol-1

s-1]

1000/T [1/K]

3-Pentanone + OH = Products

1250K

+/20%


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Summary:OH+KetonesProducts

HowdodatacomparewithStructuralActivityRelationship(SAR)model?

Dataagreewithin25%withSARestimatedrateconstants

Similarmeasurementsperformedwithmethylesters 27

0.7 0.8 0.9 1.0 1.1 1.21E12

1E13

833K909K1000K1111K1250K

Acetone

2-Butanone3-Pentanone

2-Pentanone

kKetone+OH

[cm

3m

ol-1

s-1]

1000/T [1/K]

Ketone + OH = Products

1429K

Lines: Modified SAR (SAR x 0.75)


28/36

Summary:OH+Methyl Esters Products

Dataagreewithin25%withSARestimatedrateconstants

Currentwork: OH+aldehydes,alcohols

28

0.7 0.8 0.9 1.0 1.1 1.2

1E12

1E13

833K909K1000K1111K1250K

MButanoate

MPropanoate

MFormate

MAcetate

Lines: Modified SAR (SAR x 0.75)

kMethylEs

ter+OH

[cm

3m

ol-1 s

-1]

1000/T [1/K]

Methyl Ester + OH = Products

1429K


29/36

MultiSpeciesTimeHistories

Motivation

Multispecies

provide

greater

constraint

onmechanismrefinement/evaluation

RecentWork

Ketones:Acetone,Butanone,3Pentanone

Alcohols:1,2,tert,&isoButanol

Alkanes:nHexadecane

Esters:MethylFormate,MA,MP,MB,EP

29


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MultiSpeciesApproach:3PentanonePyrolysis

3Pent =3.39m CH3 =216nm

C2H4 =10.5mCO =4.6m

0 100 200

0

100

200

300

0.1% 3-Pentanone / Ar.

1346 K, 1.67 atm

CH

3MoleFraction[ppm]

Time [s]

0 500 1000 1500

0.0

0.5

1.0

1.5

2.0

1343 K, 1.60 atm

C2H

4MoleFraction[%]

Time [s]

1% 3-Pentanone / Ar

0 500 10000.0

0.4

0.8

1.2 1% 3-Pentanone / Ar

3-PentanoneMoleFraction[%]

Time [s]

1323 K, 1.32 atm

0 500 1000

0

1000

2000

3000

1325 K, 1.60 atm

C

O

MoleFraction[ppm]

Time [s]

0.25% 3-Pentanone / Ar

30ExcellentSNR,

high

sensitivity

data


31/36

ComparisonwithSerinyel etal.(2010)GalwayNUI

3Pent CH3

C2H4CO

0 100 200

0

100

200

300

0.1% 3-Pentanone / ArSerinyel et al.

1346 K, 1.67 atm

CH

3MoleFraction[ppm]

Time [s]

0 500 1000 1500

0.0

0.5

1.0

1.5

2.0

1343 K, 1.60 atm

C2

H4

MoleFraction[%]

Time [s]

1% 3-Pentanone / Ar

0 500 10000.0

0.4

0.8

1.2 1% 3-Pentanone / ArSerinyel et al.

3-PentanoneMoleFraction[%]

Time [s]

1323 K, 1.32 atm

0 500 1000

0

1000

2000

3000

1325 K, 1.60 atm

C

O

MoleFraction[ppm]

Time [s]

0.25% 3-Pentanone / ArSerinyel et al.

TwoDifferences:1)3Pdecompositionrate; 2)CO/C2H

4yields

31


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3PDataEnablesRevisionofDecompositionRate

3Pdatashow strongsensitivitiestok1+k2

3PentanoneSensitivity

Revisedktotal3.5xSerinyel etal.rate

COyieldsstillnotcorrect!

ArrheniusPlot:

3Pent

Products

0.7 0.8 0.91

10

100

1000

10000

100000

1111K1250K

ktotal

[1/s]

1000/T [1/K]

3-Pentanone = Products

1.6 atm

Serinyel et al. (2010)

1429K

32

2Channels


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COYieldResolvedthroughUseofOAtomBalance

Modelunderpredicts COandoverpredicts methylketene

Why? Methylketenedecompositionpathwaymissinginmechanism

IntroduceCH3CHCO C2H4+CO(assumekthesameasketenedecomp.)33

3PandCOdatayieldtotalOatoms Oatomconcentrationat1.5ms

LaserAbsorption

3Pentanone:

CO:

Sum:

23%

69%

Simulation(withnewk1+k2)

3Pentanone:

CO:

CH3CHCO:

Sum: 93%

23%

43%

27%

92%

0 500 1000 1500

0.0

0.2

0.4

0.6

0.8

1.0

MoleFraction[%]

Time [s]

1% 3-Pentanone / Ar

1248 K, 1.6 atm

3-PentanoneCO


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RevisedModelImproves3PSimulations

CH3

CO

0 500 1000

0

1000

2000

3000

1325 K, 1.60 atm

COM

oleFraction[ppm]

Time [s]

0.25% 3-Pentanone / Ar.

1215 K, 1.68 atm

1403 K, 1.57 atm

1272 K, 1.64 atm

FinalModificationstoSerinyel etal.

3PentanoneMechanism

Reviseddecompositionrate:

3pentanone products

Additionalreaction:methylketene C2H4+CO

34

C2H4

Goodagreementwith3P,CH3,CO,andLowTC2H4timehistories


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OngoingWork

Diagnostics development & spectroscopy:

aldehydes (CH2O, CH3CHO)

alkyl radicals (C2H5)

methyl esters (methyl formate)

Alkenes (C3H6, C4H8)

Continued improvement of shock tube methods: constrained reaction volume

Direct measurement of elementary reactions:

OH + oxygenates (aldehydes, ethers, alcohols)

decomposition of oxygenates

CH3, HO2 reactions with HC

35


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Acknowledgements

ARO,AFOSR,DOE,NSF

Students: Genny Pang,MattCampbell,WeiRen,BrianLam,SijieLi,

SreyashiChakraborty

36

Hanson Stanford Flame Workshop 2012

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