Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go...
Transcript of Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go...
High Pressure Turbulent Flame Initiation (Ignition) and Propagation at
Large Reynolds Number
Shenqyang(Steven)ShyNa/onalCentralUniversity,TaoyuanCity,Taiwan
1st International Workshop on Near Limit Flames Boston University, Boston, USA
July 29 – July 30, 2017
CH4,φ =0.95atm
u′/SL≈ 8 Field of view 12 x 12 cm2
Field of view: 12*12 cm2
NoGo:(1)Nobreakdown(nospark);(2)Spark→ Smallkernel→ Quench; (3) Spark→ Kernel→Smallflame→ Quench
Go:successfuligniIon
(1) Spark(2) Shockwave (a few µs) (3)Flamekernel(hundreds µs) → Expanding flame
MinimumIgniIonEnergy(50%)
HighPressureTurbulentPremixedCombus8on
2/31
Outline of the Talk
(1) Give a brief review on Minimum Ignition Energy (MIE) Transition of turbulent spark ignition up to 5 atm over a wide range of u′/SL [Shy et al. PCI 36 (2016) 1785-1791].
(2) Discuss an unexpected result: “Turbulent facilitated ignition (TFI) through differential diffusion discovered by Law and co-workers [PRL 113 (2014) 024503].
(3) TFI only occurs for Le >> 1 flame and is restricted at rather small spark gap which is much smaller than the quenching distance [Shy et al. CnF 185 (2017) 1-3].
(4) Propagation will not discuss here (ICDERS, TF 1, Tue) 3/31
1.1 m inside diameter > 2 m in length
dmin inside cruciform
bomb is ~ 30 cm
Apparatus:3DCruciformBomb
Near-isotropicturbulenceregion(15x15x15cm3)
Dual-Chamber Design with Optical Access 4/31
ManyparameterscaninfluencesparkigniIon(MinimumIgniIonEnergy,MIE):(1)electricalbreakdowncharacteris/csi.e.typeofdischarge,dischargedvoltage/current,pulsedura8on8me;(2)electrodecharacteris/csi.e.material,geometry,size,gap;(3)flowcharacteris/csi.e.typeofflow,turbulentvelocity/lengthscales,pressure,temperature;(4)mixturecharacteris/csi.e.equivalencera8o,phaseoffuel.ForaccuratereproducIonofasparkigniIonexperiment,theseaforesaidparametersaswellasthedischargedEigareneeded.
5/31
• Independence on electrode geometry
• td = 100 µs • 3 domains • p , Vd
Effect of increasing pressure on spark discharge energy
2.6mm
2.0mm
dgap
2.0mm
6/31 CnF160(2103)1755-1766
From CarIgnition Coil
SparkPearson
Current Probe
V1(t) V2(t)I(t)
To Oscilloscope
I(t)V1(t)V2(t)
I(t)2 kV/div1 ms/div
Volta
ge (k
V)Cu
rren
t (m
A)
V1(t)
I(t)
t1t2
V2(t)
Time (ms)
2
0
4
6
120
80
40
0 1 2 3 4 5 6 7
40 mA/div1 ms/div
mJ.dt)t(I)]t(V)t(tt V[Eig 5612
2
11 =−= ∫
HowaccuratecanwemeasureEig?
CarIgniIonEnergyEigMeasurement
Ground
Peaks,OscillaIonsonV(t)&I(t),largeuncertainIes
=0
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1 1.5 2 2.5 31
2
3
4
5
6
7
Pressure, p (atm)1 2 3 4 51
2
3
4
5
6
7
8
MIEL ~ p-0 .8
MIE
L(mJ)
-1.3
dgap ( m)m
dgapMIEL~
(a) (b)
Glass disk
dgap = 3 mm
1.58 mm
Lewis & von Elbe[1]
0
dgap
2 mm
CH4 =0.6( )
Present
CH4 =0.6( )
dgap= 1 mm
2 mm
Previous
(a) MIEL↓ noticeably w/ dgap from 1 to 3 mm. (b) MIEL~δRZ3(Zeldovich)~(αRZ/SL)3~p-0.9(αRZ~ρ-1~
p-1;SL~p-0.7)
1atm
8/31
A typical voltage and current waveforms directly measured across the electrodes for calculating Eig. Yes, we can measure Eig accurately provided
that we must know: Precise pulse duration time, discharge voltage & current.
Measurements of Controllable Ignition Energies
9/31
100µs
Spark
LoadingResistor
PearsonCurrent Probe
V1(t) V2(t)I(t)
To OscilloscopeFrom HV M25K& Pulse generator
Goodpulsegenerator&appropriatecircuit
Spark
LoadingResistor
PearsonCurrent Probe
V1(t) V2(t)I(t)
To OscilloscopeFrom HV M25K& Pulse generator
Spark
LoadingResistor
PearsonCurrent ProbeDamping
Resistor
V1(t) V2(t) I(t)
To OscilloscopeFrom HV M25K
& Pulse generator
Time (µs)5 10 15 20 25 30 35
Vol
tage
(kV
)C
urre
nt (A
)
5
0
10
15
0.5
1
5 kV/div5 µs/div
0.5 A/div5 µs/div
I(t)
t1
t2
V1(t)
V2(t)
35 kΩ
V1(t)V2(t)
I(t)I(t)
t2'
mJ.dt)t(I)]t(V)t(tt V[Eig 8732
2
11 =−= ∫
mJ.dt)t(I)]t(V)t('t
t V[Eig 21422
11 =−= ∫
t1
t2
Time (µs)5 10 15 20 25 30 35
Vol
tage
(kV
)C
urre
nt (A
)
5
0
10
15
0.5
1
35 kΩ
100 Ω
V1(t)V2(t)I(t)
I(t)
5 kV/div5 µs/div
0.5 A/div5 µs/div
V1(t)
I(t)
V2(t)
t2'
mJ.dt)t(I)]t(V)t(tt V[Eig 5622
2
11 =−= ∫
mJ.dt)t(I)]t(V)t('t
t V[Eig 27322
11 =−= ∫
10µspulse
Peak
Eliminatepeak
10/31
MIEisasta/s/calproperty,notathresholdvalue.AnoverlappingregionofEigexists
having“Go”or“NoGo”.Tradi/onally,itisknownthatlaminarMIE(MIEL)dataincreasedrasIcallywhendgap<dq,wheredqisacriIcaldgapcalledthequenchingdistancethatmayberelatedtothecriIcalradiusofthedevelopingflamekernel(Rc)forsuccessfulflameiniIaIonintheclassicthermal-diffusiontheory(e.g.,Lewis&vonElbebook;Lawetal.;Juetal.).FlamecriIcalradiusconceptisimportant,butithasa…Problem:SamedischargedEigcannotalwaysproducethesameRcbecauseofelectricalsparkbreakdownperturba<ons. 11/31
Laminarcase:Iso-octane/airmixture(ϕ=0.8)at1atmand373K(100℃)
MIE=Eig@50%
OverlappingRegion
Logis<cRegressionMethod(18~30runs)
12/31
Laminarcase:Eig≈7.7mJ(overlappingregion)Iso-octane/airatφ=0.8,T=373K,p=1atm
Fieldofview:11×11cm2
NoGo Go
13/31
Turbulentcase:Eig≈24mJ(overlappingregion)Iso-octane/airatφ=0.8,T=373K,p=1atm,u′/SL ≈ 5
Fieldofview:11×11cm2
NoGo Go
14/31
Normalized Turbulent Intensities (u'/SL)
MIE T/M
IE L=Γ
10 20 30 40 50
10
20
3040
CH4/Air ( = 0.6)
Γ ~ (u'/SL)4
Γ ~ (u'/SL)0.3
Γ ~ (u'/SL)0.7
Γ ~ (u'/SL)0.7
Γ ~ (u'/SL)10
Γ ~ (u'/SL)3
p = 1
p = 5p = 3
5
MIE Transition
1 mm
2 mm
atmatmatm
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Shy et al. PCI 36 (2017) 1785-1791
(a) 2 ms 6 ms 10 ms
5 mm30×30 mm2
(b) 2 ms 6 ms 10 ms
(a)Laminarcase(Eig≈2.30mJ);(b)turbulentflameletcase(uʹ/SL≈12;Ka≈8>1;Eig≈5.85mJ)
Schlierenimagesatp=5atm:BeforeIgniIonTransiIon
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2 ms
10 ms9 ms8 ms
6 ms4 ms2 ms
65×65 mm2
11 ms 12 ms 14 ms
10 mm A
AAA
A A
APerTITDistributed-likekernelat5atm:uʹ/SL≈40Ka≈40Eig≈42mJIslandforma8onBrokenRZ“A”islandquenching
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Shy et al. PCI 36 (2017) 1785-1791
Shockwave (t0 *)
t1t2 t1t0
Electrodes
u′/SL < (u′/SL)c
t2
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u′/SL > (u′/SL)c
MIEtransi<onoccursatdifferent(u′/SL)c (u′/SL)c≈ 12(1atm),24(3atm),34(5atm)
ηk ηk
smallscaleturbulencediffusivity
u′ηk
reac8onzonethermaldiffusivity
αRZ
PeRZ=u′ηk/αRZ
PeRZ=u′ηk/αRZ
Sparkigni<onseemsself-similar whenusingPe*withpressurecorrecIontominus1/4power.Alldataatdifferentu′ and p are collapsed to a single curve with two different slopes, showing ignition transition.
19/31 IgniIonChemistry?
Γ=MIET/MIEL~Pe*beforetransi8onΓ =MIET/MIEL~Pe*4aPertransi8on
Itseemsthatsparkigni/onisself-similar20/31
KarlovitzandPecletnumberses8matedattheinstantoftheforma8onofsparkkernel(RZ)
Ka=τc/τk;PeRZ=u′ηk/αRZIgni8on transi8on depends on the surface diffusivity ra8obetweensmallscaleturbulenceandchemicalreac8on,nottheir8mera8o.
Is igni'on transi'on a possible universal phenomenon?
21/31
Laser Spark Ignition of Lean Methane/Air Mixtures Using Wind-Tunnel Turbulence by Cardin et al. Combustion and Flame 160 (2013) 1414-1427.
MIETransi/on
22/31
ConcludingRemarksandAPuzzle(1) Itseemsthatigni8ontransi8oncouldbeauniversal
phenomenon,becausebothelectrode&lasersparksfoundsimilarITphenomenonregardlessofdifferentigni8onsystems&differentflowconfigura8onsused.
(2) Sparkigni8onmaybeself-similar,whichischaracterizedbyasparkkernelsurfacediffusionra8obetweensmallscaleturbulenceandchemicalreac8on.
(3) Contrarily,Lawandco-workers(PRL2014)foundthatturbulencecanfacilitateigni8onforLe>>1flames.
Why???23/31
24/31
TFI:Lawandco-workersdiscoveredthatturbulencecanfacilitateigni/onthroughdifferen/aldiffusionwhentheeffec/veLewisnumber(Le)ofmixturesissufficientlygreaterthanunity,whereapairofthincan/leverelectrodesof0.25-mmindiameterwithsmallelectrodegaps(dgap≤0.8mm)wasappliedinnear-isotropicturbulencegeneratedbyafan-sIrredburner. Flame speed versus flame radius for (a) lean H2/air at ϕ = 0.18 and (b) rich H2/air at ϕ = 5.1, at different ignition voltages and turbulent levels (Phys. Rev. Lett 113 (2014) 024503).
Ques/on:IstheaforesaidTFIforLe>>1
dependentondgap?
EffectofsparkgaponTFI?
Approach:UsingthesamerichandleanH2/airmixturesandelectrodesasthatusedbyLawandco-workersinourcruciformbombtogetherwiththewell-establishedigniIonsystemallowsmeasuringEighereofhighaccuracyand/orminimumigniIonenergy(MIE)asafuncIonofdgapatbothquiescence(uʹ=0)andintenseturbulence(uʹ=5.4m/s)condiIons,whichrevealsthesubtledetailofsparkigniIonphenomena.
GoNo GoProbability95% Confidence
x
H2 (φ = 5.1)uʹ = 0dgap = 2 mm
Prob
abili
ty o
f Ign
ition
Spark Energy (mJ)
0.10 ms
Go
This figure shows a typical case for the statistical determination of MIE ≡ Eig(50%) using the logistic regression method, where the hydrogen/air mixture at φ = 5.1 with Le ≈ 2.3 is applied in quiescence.
Laminarcase:Eig≈10.2mJ(overlappingregion)Hydrogen/airatφ=5.1,T=298K,p=1atm.
Fieldofview:11×11cm2
NoGo Go
NoGo Go
Turbulentcase:Eig≈9.3mJ(overlappingregion)Hydrogen/airatφ=5.1,T=298K,p=1atm,uʹ=5.4m/s
Fieldofview:11×11cm2
Min
imum
Igni
tion
Ene
rgy,
Eig
(50%
) (m
J)
Min
imum
Igni
tion
Ene
rgy,
Eig
(50%
) (m
J)
Distance between Electrodes, dgap (mm)
Laminar uʹ = 0
Turbulentuʹ = 5.4 m/s
H2/Air
2.0 mm Sharp end
14.0
1.11 1.06 1.42
0.52
17.3 36.8
Turbulent Facilitated Ignition (TFI)
255.5 mJ
φ = 0.18
φ = 5.1
φ = 0.18 & 5.1
dgap
0 0.5 1.0 1.5 2.0
100
101
102
100
101
102
1 2 3 4 5 6
0
10
20
30
40
50
60
Min
imum
Igni
tion
Ene
rgy,
Eig
(50%
) (m
J)
Distance between Electrodes, dgap (mm)
100% ignitabilityat 0.2 mJ
61.5 mJ
11.0
0.80
26.0
9.20 6.303.05
50.6
41.0 Laminaruʹ = 0
Turbulent uʹ = 5.4 m/s
H2/Air (φ = 5.1)
dgap
0.25 mm Flat end
KeyResults:EffectofSparkGaponTFI[Shyetal.CnF185(2017)1-3]
Turbulencecanfacilitateigni/onthroughdifferen/aldiffusionforLe>>1mixture,butsuchpeculiarphenomenonisrestrictedatsmalldgap.
Ref:Z.Chen,M.P.Burke,Y.Ju,Onthecri<calflameradiusandminimumigni<onenergyforsphericalflameini<a<on,Proc.Combust.Inst.33(2011)1219-1226.
Changeofthecri<calflameradiusRcandtheflameballradiusRzwiththeLewisnumber.
• Regime I (Le < 1.0): Rc = Rz < δF• RegimeII(1<Le<Le*):Rc = Rz > δF• RegimeIII(Le>Le*):δF < Rc < Rz
Weusethenumericalfindingofcri/calflameradiusRcasafunc/onofLefoundbyJu&co-workerstoexplaintheseresults.Pleaseseearecentbriefcommunica/on[CnF185(2017)1-3].
Thank you for your attention!
Thisresearchiscon<nouslysupportedbyMinistryofScienceandTechnology(MOST),Taiwan
Taipei 101 Taiwan
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