Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go...

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High Pressure Turbulent Flame Initiation (Ignition) and Propagation at Large Reynolds Number Shenqyang (Steven) Shy Na/onal Central University, Taoyuan City, Taiwan 1 st International Workshop on Near Limit Flames Boston University, Boston, USA July 29 – July 30, 2017

Transcript of Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go...

Page 1: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

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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

Page 3: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

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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

Page 5: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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.

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Page 6: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

•  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

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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

7/31

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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

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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

Page 10: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 11: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 12: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Laminarcase:Iso-octane/airmixture(ϕ=0.8)at1atmand373K(100℃)

MIE=Eig@50%

OverlappingRegion

Logis<cRegressionMethod(18~30runs)

12/31

Page 13: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Laminarcase:Eig≈7.7mJ(overlappingregion)Iso-octane/airatφ=0.8,T=373K,p=1atm

Fieldofview:11×11cm2

NoGo Go

13/31

Page 14: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Turbulentcase:Eig≈24mJ(overlappingregion)Iso-octane/airatφ=0.8,T=373K,p=1atm,u′/SL ≈ 5

Fieldofview:11×11cm2

NoGo Go

14/31

Page 15: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 16: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

(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

16/31

Page 17: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 18: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 19: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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?

Page 20: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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.

Page 21: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Is igni'on transi'on a possible universal phenomenon?

21/31

Page 22: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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

Page 23: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

ConcludingRemarksandAPuzzle(1)  Itseemsthatigni8ontransi8oncouldbeauniversal

phenomenon,becausebothelectrode&lasersparksfoundsimilarITphenomenonregardlessofdifferentigni8onsystems&differentflowconfigura8onsused.

(2) Sparkigni8onmaybeself-similar,whichischaracterizedbyasparkkernelsurfacediffusionra8obetweensmallscaleturbulenceandchemicalreac8on.

(3) Contrarily,Lawandco-workers(PRL2014)foundthatturbulencecanfacilitateigni8onforLe>>1flames.

Why???23/31

Page 24: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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).

Page 25: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Ques/on:IstheaforesaidTFIforLe>>1

dependentondgap?

EffectofsparkgaponTFI?

Page 26: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Approach:UsingthesamerichandleanH2/airmixturesandelectrodesasthatusedbyLawandco-workersinourcruciformbombtogetherwiththewell-establishedigniIonsystemallowsmeasuringEighereofhighaccuracyand/orminimumigniIonenergy(MIE)asafuncIonofdgapatbothquiescence(uʹ=0)andintenseturbulence(uʹ=5.4m/s)condiIons,whichrevealsthesubtledetailofsparkigniIonphenomena.

Page 27: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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.

Page 28: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Laminarcase:Eig≈10.2mJ(overlappingregion)Hydrogen/airatφ=5.1,T=298K,p=1atm.

Fieldofview:11×11cm2

NoGo Go

Page 29: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

NoGo Go

Turbulentcase:Eig≈9.3mJ(overlappingregion)Hydrogen/airatφ=5.1,T=298K,p=1atm,uʹ=5.4m/s

Fieldofview:11×11cm2

Page 30: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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.

Page 31: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

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].

Page 32: Shenqyang (Steven) Shy Na/onal Central University, Taoyuan ...yju/1st-near-limit-flames...Go No Go Probability 95% Confidence x H 2 (φ = 5.1) uʹ = 0 Probability of Ignition d gap

Thank you for your attention!

Thisresearchiscon<nouslysupportedbyMinistryofScienceandTechnology(MOST),Taiwan

Taipei 101 Taiwan

31/31