hanson stanford flame workshop 2012
TRANSCRIPT
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MeasurementsofElementaryRateConstants,
IgnitionDelaysandSpeciesHistoriesinShockTubes
R.K.Hanson,D.F.Davidson
StanfordUniversity
1st InternationalWorkshoponFlameChemistry
July2829,2012
ShockTube/LaserApproach
AdvancesinMethodology
ElementaryReactionRateStudies
MultiSpeciesTimeHistories
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StanfordShock
Tubes
2
Kinetics
Shock
Tube2
(30atm)
Kinetics
Shock
Tube1(30atm)
Aerosol
Shock
Tube
(10atm)
High
Pressure
Shock
Tube
(500atm)
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NewConstrainedReactionVolume(CRV)Facility
2Configurations
3
CRV1
GasPhase
Experiments
to100atm
CRV2
Aerosol
Experiments
to100atm
Constrained
ReactionVolume
Sliding
Valve
Aerosol
GenerationTank
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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
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AdvancesinShockTube
Methodology
1. Improveduniformitywithdriverinserts
2. Longertesttimeswithtailoredgas
mixtures&extendeddriver
3. Reactivegasmodeling:
problemandsolutions
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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
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ImprovementinReflectedShockTemperatureUniformity
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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ImprovementinReflectedShockTemperatureUniformity
UsingDriverInserts
Result: dP/dt = 0priortoignition
ProperignforcomparisonwithConstantPsimulations
P5T5VRS
10
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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
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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
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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
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ReactiveGasdynamics Modeling:AProblem
Mostcurrentreflectedshockmodelingassumes
ConstantVolumeorConstantPressure
But:
Exothermic energyreleaseduringoxidationor
endothermic coolingduringpyrolysischangesT&P
behindreflectedshocks
notaConstantVorConstantPprocess! Example:HeptaneIgnition
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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
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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
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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
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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
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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
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ElementaryReactionRate
Determinations
Goal
Neardirectdeterminationofrateconstantsforspecificreactions
ExamplesOH+ketones:
acetone,2butanone,2&3pentanone
OH+alkanes
OH+butanol isomers
OH+methylesters
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ExperimentalStrategy
fast upon
shock heating
tertbutylhydroperoxide
TBHPusedasapromptOHprecursor
UsefulTrange(850to1350K)
PioneeredbyBott andCohen(1984) AlsousedatArgonne
Fuelinexcess,pseudofirstorderexperiment
24
Acetone
+ +
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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
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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)
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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
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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
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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
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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
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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
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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
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Acknowledgements
ARO,AFOSR,DOE,NSF
Students: Genny Pang,MattCampbell,WeiRen,BrianLam,SijieLi,
SreyashiChakraborty
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