1 AME 514 - October 7, 2004 Microgravity combustion Motivation Time scales (Lecture 1) Examples Premixed-gas flames »Flammability limits (Lecture

AME 514 - October 7, 2004AME 514 - October 7, 2004 11

Microgravity combustionMicrogravity combustionMotivationMotivationTime scales (Lecture 1)Time scales (Lecture 1)ExamplesExamples

Premixed-gas flamesPremixed-gas flames» Flammability limits (Lecture 1)Flammability limits (Lecture 1)» Stretched flames (Lecture 1)Stretched flames (Lecture 1)» Flame balls (≈ Lecture 2)Flame balls (≈ Lecture 2)» High Le instabilitiesHigh Le instabilities» ““Cool flames”Cool flames”» Turbulent flames - save for turbulent combustion section…Turbulent flames - save for turbulent combustion section…

Nonpremixed gas jet and counterflow flamesNonpremixed gas jet and counterflow flames Condensed-phase combustionCondensed-phase combustion

» DropletsDroplets» Flame spread over solid fuel bedsFlame spread over solid fuel beds» Particle-laden flamesParticle-laden flames

Reference: Reference: Ronney, P. D., “Understanding Combustion Processes TRonney, P. D., “Understanding Combustion Processes Through Microgravity Research,” Twenty-Seventh Internathrough Microgravity Research,” Twenty-Seventh International Symposium on Combustion, Combustion Institute, ional Symposium on Combustion, Combustion Institute, Pittsburgh, 1998, pp. 2485-2506Pittsburgh, 1998, pp. 2485-2506

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MOTIVATIONMOTIVATIONGravity influences combustion throughGravity influences combustion through

Buoyant convection - large Buoyant convection - large TT Sedimentation in multi-phase systemsSedimentation in multi-phase systems

ApplicationsApplications Spacecraft fire safety - 6 Shuttle pre-fire incidents; Mir nearly Spacecraft fire safety - 6 Shuttle pre-fire incidents; Mir nearly

disastrous fire; ISS and Mars are nextdisastrous fire; ISS and Mars are next Better understanding of combustion at earth gravity for engines, Better understanding of combustion at earth gravity for engines,

burners, fire/explosion hazard management/suppression, ...burners, fire/explosion hazard management/suppression, ...


µg methodsµg methods Drop towers - short duration Drop towers - short duration

(1 - 10 sec) (≈ t(1 - 10 sec) (≈ tradrad), high quality ), high quality

(10(10-5-5ggoo)) Aircraft - longer duration (25 Aircraft - longer duration (25

sec), low quality sec), low quality (10(10-2-2ggoo - 10 - 10-3-3ggoo))

Sounding rockets - still longer Sounding rockets - still longer duration (5 min), fair quality duration (5 min), fair quality (10(10-3-3ggoo - 10 - 10-6-6ggoo))

Orbiting spacecraft - longest Orbiting spacecraft - longest duration (16 days), best duration (16 days), best quality (10quality (10-5-5ggoo - 10 - 10-6-6ggoo))


Time scales - premixed-gas flames (lecture 1)Time scales - premixed-gas flames (lecture 1) Chemical time scaleChemical time scale

ttchemchem ≈ ≈ /S/SLL≈ (≈ (/S/SLL)/S)/SLL≈≈/S/SLL22

= thermal diffusivity [typ. 0.2 cm= thermal diffusivity [typ. 0.2 cm22/s], /s], SSLL = laminar flame speed [typ. 40 cm/s] = laminar flame speed [typ. 40 cm/s]

Conduction time scaleConduction time scale ttcondcond ≈ ≈ TTff/(dT/dt) ≈ d/(dT/dt) ≈ d22/16/16d = tube or burner diameterd = tube or burner diameter

RadiationRadiation time scale time scalettradrad ≈ ≈ TTff/(dT/dt) ≈ T/(dT/dt) ≈ Tff/(/(//CCpp))

Optically thin radiation: Optically thin radiation: = 4 = 4aapp(T(Tff44 – T – T∞∞

44) )

aapp = Planck mean absorption coefficient = Planck mean absorption coefficient

[typically 2 m[typically 2 m-1-1 at 1 atm] at 1 atm] ttradrad ~ P/ ~ P/aapp(T(Tff

44 – T – T∞∞44) ~ P) ~ P00, P = pressure, P = pressure

Buoyant transport time scaleBuoyant transport time scalet ~ d/V; V ≈ (gd(t ~ d/V; V ≈ (gd(//))))1/21/2 ≈ (gd) ≈ (gd)1/21/2

(g = gravity, d = characteristic dimension)(g = gravity, d = characteristic dimension) Inviscid: tInviscid: tinvinv ≈ d/(gd) ≈ d/(gd)1/21/2 ≈ (d/g) ≈ (d/g)1/21/2 (1/t (1/tinvinv ≈ ≈ invinv))

Viscous: d ≈ Viscous: d ≈ /V /V t tvisvis ≈ ( ≈ (/g/g22))1/31/3 ( ( = viscosity [typically 0.2 cm = viscosity [typically 0.2 cm22/s])/s])


Short tutorial on gas radiationShort tutorial on gas radiation Because gases vibrate and rotate only at discrete frequencies, they emit Because gases vibrate and rotate only at discrete frequencies, they emit

and absorb radiation only in narrow bands; this is unlike solid surfaces and absorb radiation only in narrow bands; this is unlike solid surfaces which have essentially an infinite number of degrees of freedom and so can which have essentially an infinite number of degrees of freedom and so can emit/absorb across the whole spectrumemit/absorb across the whole spectrum

Homonuclear diatomic molecules (e.g. OHomonuclear diatomic molecules (e.g. O22, N, N22) cannot radiate) cannot radiate Other diatomic molecules (e.g. CO) radiate weaklyOther diatomic molecules (e.g. CO) radiate weakly Polyatomic gases (e.g. COPolyatomic gases (e.g. CO22, H, H22O) radiate more strongly, but not as strongly O) radiate more strongly, but not as strongly

as particles (e.g. soot)as particles (e.g. soot) The absorption coefficient (a) of gas i is a function of the partial pressure of The absorption coefficient (a) of gas i is a function of the partial pressure of

the gas (Pthe gas (Pii), wavelength (), wavelength () and T (see also lecture 1, slides 71 & 72)) and T (see also lecture 1, slides 71 & 72)

0

1

10

100

1000

100 1000 10000

Wavenumber (cm^-1)

Spectral absorption coefficient

(m^-1 atm^-1)

CO2H2OCODouble-click

plot to open massive spreadsheet


Short tutorial on gas radiationShort tutorial on gas radiation If the length scale (L) of the radiating gas volume is sufficiently small, If the length scale (L) of the radiating gas volume is sufficiently small,

i.e. L < 1/a(i.e. L < 1/a() for all ) for all , then the , then the optically thinoptically thin model applies; absorption model applies; absorption is negligible and the radiant emission is negligible and the radiant emission per unit volumeper unit volume ( () for a gas at ) for a gas at temperature Ttemperature Tgg with environment temperature T with environment temperature T∞∞ is given by is given by

where awhere aPP is the is the Planck mean absorption coefficientPlanck mean absorption coefficient and I and Ibb is the usual is the usual

Planck functionPlanck function aaPP(T) is tabulated for many gases (next page); in a gas mixture(T) is tabulated for many gases (next page); in a gas mixture Example: lean CHExample: lean CH44-air combustion products at 1 atm-air combustion products at 1 atm

PPH2OH2O ≈ 0.1 atm; P ≈ 0.1 atm; PH2OH2O ≈ 0.05 atm; T ≈ 1500K ≈ 0.05 atm; T ≈ 1500K

1500K: a1500K: aP,H2OP,H2O = 2.2 m = 2.2 m-1-1atmatm-1-1, a, aP,CO2P,CO2 = 12.2 m = 12.2 m-1-1atmatm-1-1, ,

aaPP = 2.2*0.1 + 12.2*0.05 = 0.83 m = 2.2*0.1 + 12.2*0.05 = 0.83 m-1-1

= 4 * 5.67 x 10= 4 * 5.67 x 10-8-8 W/m W/m22KK44 * 1.33 m * 1.33 m-1-1 *[(1500K) *[(1500K)44 - (300K) - (300K)44] ] = 9.51 x 10= 9.51 x 1055 W/m W/m33 = 0.95 W/cm = 0.95 W/cm33

If the gas is not optically thin then the analysis is If the gas is not optically thin then the analysis is muchmuch more more complicated; many models have been developed, e.g. the complicated; many models have been developed, e.g. the Statistical Statistical Narrow BandNarrow Band model (click on spreadsheet on previous slide) model (click on spreadsheet on previous slide)

€

=4σaP Tg4 − T∞

4( ); aP ≡

a(λ )Ibλ dλ 0

∞

∫Ibλ dλ

0

∞

∫=

π

σT 4a(λ )

2hc 2

λ5 ehc / λkT −1( )dλ

0

∞

∫

€

aP ≡ aP ,iPi

i=1

n

∑


Planck mean absorption coefficientPlanck mean absorption coefficient

1

10

100

300 500 700 900 1100 1300 1500

Temperature (K)

SF6

H2O

CO

CO2

CH4

N2O

NH3


Time scales (hydrocarbon-air, 1 atm)Time scales (hydrocarbon-air, 1 atm)

ConclusionsConclusions Buoyancy unimportant for near-stoichiometric flamesBuoyancy unimportant for near-stoichiometric flames

(t(tinv inv & t& tvisvis >> t >> tchemchem)) Buoyancy strongly influences near-limit flames at 1gBuoyancy strongly influences near-limit flames at 1g

(t(tinv inv & t& tvisvis < t < tchemchem)) RadiationRadiation effects unimportant at 1g (t effects unimportant at 1g (tvisvis << t << tradrad; t; tinvinv << t << tradrad)) Radiation effects dominate flames with low SRadiation effects dominate flames with low SLL

(t(tradrad ≈ t ≈ tchemchem), but only observable at µg), but only observable at µg Small tSmall tradrad (a few seconds) - drop towers useful (a few seconds) - drop towers useful Radiation > conduction only for d > 3 cmRadiation > conduction only for d > 3 cm Re ~ Vd/Re ~ Vd/ ~ (gd ~ (gd33//22))1/21/2 turbulent flow at 1g for d > 10 cm turbulent flow at 1g for d > 10 cm

TTTiiimmmeee ssscccaaallleee SSStttoooiiiccchhh... ffflllaaammmeee LLLiiimmmiiittt ffflllaaammmeee

CCChhheeemmmiiissstttrrryyy (((tttccchhheeemmm)))ooorrr dddiiiffffffuuusssiiiooonnn (((tttdddiii ffffff)))

000...000000000999444 ssseeeccc 000...222555 ssseeeccc

BBBuuuoooyyyaaannnttt,,, iiinnnvvviiisssccciiiddd (((ttt iiinnnvvv))) 000...000777111 ssseeeccc 000...000777111 ssseeecccBBBuuuoooyyyaaannnttt,,, vvviiissscccooouuusss (((tttvvviiisss))) 000...000111222 ssseeeccc 000...000111000 ssseeecccCCCooonnnddduuuccctttiiiooonnn (((tttcccooonnnddd))),,, ddd === 555 cccmmm 000...999555 ssseeeccc 111...444 ssseeecccRRRaaadddiiiaaatttiiiooonnn (((tttrrraaaddd))) 000...111333 ssseeeccc 000...444111 ssseeeccc


Premixed-gas flames – flammability limitsPremixed-gas flames – flammability limits Too lean or too rich mixtures won’t burnToo lean or too rich mixtures won’t burn

- - flammability limitsflammability limits No limits without No limits without losseslosses – no purely chemical criterion – no purely chemical criterion Models of limits due to losses - most important prediction: Models of limits due to losses - most important prediction:

burning velocity burning velocity at the limitat the limit (S (SL,limL,lim)) Heat loss to walls: tHeat loss to walls: tchemchem ~ t ~ tcondcond S SL,limL,lim ≈ 40 ≈ 40/d (Pe/d (Pelimlim = 40) = 40) Upward propagation: rise speed at limit ~ (gd)Upward propagation: rise speed at limit ~ (gd)1/21/2; causes ; causes

stretch extinctionstretch extinction Downward propagation – sinking layer of cooling gases near Downward propagation – sinking layer of cooling gases near

wall outruns & “suffocates” flame wall outruns & “suffocates” flame Microgravity, big tube: radiation-induced limitsMicrogravity, big tube: radiation-induced limits

» ……but watch out for reabsorption effectsbut watch out for reabsorption effects» Stretched flames: multiple extinction limitsStretched flames: multiple extinction limits» Spherical expanding flames: SEFsSpherical expanding flames: SEFs


““FLAME BALLS”FLAME BALLS”Zeldovich, 1944: stationary Zeldovich, 1944: stationary

spherical flames possible: spherical flames possible: 22T & T & 22C = 0 have solutions for C = 0 have solutions for unboundedunbounded domain in spherical domain in spherical geometry - T ~ Cgeometry - T ~ C11 + C + C22/r - bounded /r - bounded as r as r ∞ ∞

Not possible for Not possible for Cylinder (T ~ CCylinder (T ~ C11 + C + C22ln(r))ln(r)) Plane (T ~ CPlane (T ~ C11+C+C22r)r)

Mass conservation requires UMass conservation requires U0 0 everywhere (everywhere (no convectionno convection) – only ) – only diffusivediffusive transport transport


““I am not Spock”I am not Spock”

::

::

asas


I prefer…I prefer…

::

::

asas

Reactants

T = Ti

(0)

Products

T = Te

(0)

Adiabatic

end walls

Well-stirred

reactor

T = Te

(1)

Area = AR

x = 0x = 1

Wall temperature = Tw

(x) = (Tw,e

(x) + Tw

(x))/2

Surface temperature = Tw,e

(x)

Surface temperature = Tw,i

(x)

Heat transfer coefficient to wall = h1

Gas temperature = Te

(x)

Gas temperature = Te

(x)

Heat transfer coefficient to wall = h1

Heat loss coefficient to ambient = h2

Heat loss coefficient to ambient = h2

Wall thickness τ

Channelheightd

Channelheightd


Steady (?!?) flame ball solutionsSteady (?!?) flame ball solutions If reaction is confined to a thin zone near r = RIf reaction is confined to a thin zone near r = RZZ (large (large ))

This is a This is a flame ballflame ball solution - note for Le < > 1, T solution - note for Le < > 1, T** > < T > < Tadad; for Le = 1, ; for Le = 1,

TT** = T = Tadad and R and RZZ = = Generally unstableGenerally unstable

R < RR < RZZ: shrinks and extinguishes: shrinks and extinguishes R > RR > RZZ: expands and develops into steady flame: expands and develops into steady flame RRZZ related to requirement for initiation of steady flame related to requirement for initiation of steady flame

… … but stable for a few carefully (or accidentally) chosen mixtures but stable for a few carefully (or accidentally) chosen mixtures as we will discuss…as we will discuss…

€

R > Rz : θ =1−ε

Le

Rz

R+ ε; Y =1− Rz

R

R < Rz : θ = θ * = constant; Y = 0

€

θ* ≡T*

Tad

= ε +1−ε

Le or T* = T∞ +

Tad − T∞

Le

€

Rz =δ

Leexp

β

2

1

θ *−1

⎛

⎝ ⎜

⎞

⎠ ⎟

⎛

⎝ ⎜

⎞

⎠ ⎟;δ =

α

SL

;SL =2εLeα oA

βexp

−β

2

⎛

⎝ ⎜

⎞

⎠ ⎟


““FLAME BALLS”FLAME BALLS”

T ~ 1/r - unlike propagating flame where T ~ T ~ 1/r - unlike propagating flame where T ~ ee-r-r - - dominated by 1/r tail (with rdominated by 1/r tail (with r33 volume effects!) volume effects!)

Flame ball: a tiny dog wagged by an enormous tailFlame ball: a tiny dog wagged by an enormous tail

Temperature

Fuel concentration

T ~ 1/r

Reaction zone

Interior filledwith combustion

products

Fuel & oxygen diffuse inward

Heat & products

diffuse outward

C ~ 1-1/r

T*

T∞

0

0.2

0.4

0.6

0.8

1

1.2

0.1 1 10 100Radius / Radius of flame

Propagating flame(/r

f=1/10)

Flame ball


Flame balls - historyFlame balls - history

Zeldovich, 1944; Joulin, 1985; Buckmaster, 1985: adiabatic Zeldovich, 1944; Joulin, 1985; Buckmaster, 1985: adiabatic flame balls are flame balls are unstableunstable

Ronney (1990): seemingly Ronney (1990): seemingly stablestable, , stationarystationary flame balls flame balls accidentallyaccidentally discovered in very lean H discovered in very lean H22-air mixtures in drop--air mixtures in drop-tower experiment tower experiment

Farther from limit - expanding cellular flamesFarther from limit - expanding cellular flames

Far from limitFar from limit Close to limitClose to limit

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Only seen in mixtures having very low Lewis numberOnly seen in mixtures having very low Lewis number

Results confirmed in parabolic aircraft flights (Ronney Results confirmed in parabolic aircraft flights (Ronney et et al.al., 1994) but g-jitter problematic, 1994) but g-jitter problematic

KC135 µg aircraft testKC135 µg aircraft test




Flame balls - historyFlame balls - historyBuckmaster, Joulin, Ronney (1990, 1991): window of Buckmaster, Joulin, Ronney (1990, 1991): window of stable stable

conditions with radiative loss, near-limit & low Lewis numberconditions with radiative loss, near-limit & low Lewis number

Radiative loss (important for near limit mixtures) needed, Radiative loss (important for near limit mixtures) needed, otherwise no “penalty” for ball growing larger (loss ~ rotherwise no “penalty” for ball growing larger (loss ~ r33, , generation ~ rgeneration ~ r11), larger = weaker), larger = weaker

Low Le needed, otherwise no “benefit” to flame curvatureLow Le needed, otherwise no “benefit” to flame curvature2 solutions2 solutions

Small flame balls nearly adiabatic (small volume), always Small flame balls nearly adiabatic (small volume), always unstableunstable

Large flame balls stable, but if too large then unstable to 3D Large flame balls stable, but if too large then unstable to 3D (cellular) instability(cellular) instability

Impact of heat loss ~

Heat loss

Heat release

~

T

2

e

-E/RT

⇑ as T ⇓



Predictions consistent with experimental observationsPredictions consistent with experimental observations

0 0.05 0.1 0.15 0.20

5

10

15

Dimensionless heat loss (Q)

Unstable to 3-d disturbances

Equation of curve:

R-2ln(R) = Q

Unstable to 1-ddisturbances

Stable

"Hot dwarfs"

"Cold giants"


Flame balls - practical importanceFlame balls - practical importance Improved understanding of lean combustionImproved understanding of lean combustion

Benefit of lean combustion to efficiency & emissionBenefit of lean combustion to efficiency & emission Lean mixtures - misfire & rough operationLean mixtures - misfire & rough operation Need better models of weak combustion - determine ultimate Need better models of weak combustion - determine ultimate

limits of lean operationlimits of lean operation Current HCurrent H22- O- O22 chemical models inadequate chemical models inadequate HH22-O-O22 essential building block of hydrocarbon-air chemistry essential building block of hydrocarbon-air chemistry

Spacecraft fire safety - flame balls exist in mixtures outside Spacecraft fire safety - flame balls exist in mixtures outside one-g extinction limitsone-g extinction limits

Stationary spherical flame - simplest interaction of chemistry Stationary spherical flame - simplest interaction of chemistry & transport - test combustion models& transport - test combustion models Motivated > 30 theoretical papers to dateMotivated > 30 theoretical papers to date


Practical importancePractical importance


Implementation of space experimentImplementation of space experimentSee Ronney See Ronney et al.et al., 1998, 1998Need space experiment - long Need space experiment - long

duration, high quality µgduration, high quality µgStructure Of Flame Balls At Low Structure Of Flame Balls At Low

Lewis-number (SOFBALL)Lewis-number (SOFBALL)Space Shuttle missions MSL-1 (April Space Shuttle missions MSL-1 (April

4 - 8, 1997) & MSL-1R (July 1 - 16, 4 - 8, 1997) & MSL-1R (July 1 - 16, 1997)1997)

Combustion Module-1 (CM-1) facilityCombustion Module-1 (CM-1) facilityTest strategy - 4 mixture typesTest strategy - 4 mixture types

1 atm H1 atm H22-air (Le ≈ 0.3)-air (Le ≈ 0.3) 1 atm H1 atm H22-O-O22-CO-CO22 (Le ≈ 0.2) (Le ≈ 0.2) 1 atm H1 atm H22-O-O22-SF-SF66 (Le ≈ 0.06) (Le ≈ 0.06) 3 atm H3 atm H22-O-O22-SF-SF66 (Le ≈ 0.06) (Le ≈ 0.06)


Experimental apparatusExperimental apparatusCombustion vessel - cylinder, 32 cm i.d. x 32 cm lengthCombustion vessel - cylinder, 32 cm i.d. x 32 cm length15 individual premixed gas bottles15 individual premixed gas bottles Ignition system - spark with variable gap & energyIgnition system - spark with variable gap & energy Imaging - 2 views, intensified videoImaging - 2 views, intensified videoTemperature - fine-wire thermocouples, 6 locationsTemperature - fine-wire thermocouples, 6 locationsRadiometers (4), chamber pressure, acceleration (3 axes)Radiometers (4), chamber pressure, acceleration (3 axes)Gas chromatographGas chromatograph


Experimental apparatusExperimental apparatus

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Flame balls in spaceFlame balls in space STS-83 & STS-94, 1997STS-83 & STS-94, 1997 Stable for > 500 seconds (!)Stable for > 500 seconds (!) Very long evolution time scales ~ Very long evolution time scales ~

((rr**))22// ≈ 100 s ≈ 100 s Weakest flames ever burned (1 – 2 Weakest flames ever burned (1 – 2

Watts/ball) (birthday candle ≈ 50 Watts/ball) (birthday candle ≈ 50 Watts)Watts)





4.0% H4.0% H22-air, 223 sec elapsed time-air, 223 sec elapsed time

4.9% H4.9% H22- 9.8% O- 9.8% O22 - 85.3% CO - 85.3% CO22, 500 sec, 500 sec 6.6% H6.6% H22- 13.2% O- 13.2% O22 - 79.2% SF - 79.2% SF66, 500 sec, 500 sec

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Surprise #1 - steadiness of flame ballsSurprise #1 - steadiness of flame ballsFlame balls survived much longer than expected without drifting into chamber wallsFlame balls survived much longer than expected without drifting into chamber wallsAircraft µg data indicated drift velocity (V) ≈ (grAircraft µg data indicated drift velocity (V) ≈ (gr**))1/21/2

Gr = O(10Gr = O(1033) - V ≈ (gr) - V ≈ (gr**))1/21/2 - like - like inviscidinviscid bubble rise bubble rise In space, flame balls should drift into chamber walls after ≈ 10 min at 1 µgIn space, flame balls should drift into chamber walls after ≈ 10 min at 1 µg

Space experiments: Gr = O(10Space experiments: Gr = O(10-1-1) - creeping flow - apparently need to use ) - creeping flow - apparently need to use viscousviscous relation: relation:

Similar to recent prediction (Joulin Similar to recent prediction (Joulin et al., 1999et al., 1999)) Much lower drift speeds with viscous formula - possibly Much lower drift speeds with viscous formula - possibly hourshours before flame balls would drift into walls before flame balls would drift into walls We get too soon old and too late smart…We get too soon old and too late smart…

Also - fuel consumption rates (1 - 2 Watts/ball) could allow several Also - fuel consumption rates (1 - 2 Watts/ball) could allow several hourshours of burn time of burn time

V=13gr*

2

νρbρo

−1⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

μo+μb

μo +1.5μb

⇒ V≈2.4gr*

2

ν


Surprise #2 - flame ball driftSurprise #2 - flame ball driftFlame balls always drifted apart at a continually Flame balls always drifted apart at a continually

decreasing ratedecreasing rate Flame balls interact by Flame balls interact by

(A) warming each other - attractive(A) warming each other - attractive(B) depleting each other’s fuel - repulsive(B) depleting each other’s fuel - repulsive

Analysis (Buckmaster & Ronney, 1998)Analysis (Buckmaster & Ronney, 1998) AdiabaticAdiabatic flame balls, two effects flame balls, two effects exactly cancelexactly cancel Non-adiabaticNon-adiabatic flame balls, fuel effect wins - thermal effect flame balls, fuel effect wins - thermal effect

disappears at large spacings due to radiative lossdisappears at large spacings due to radiative loss

Higher fuelconcentration

Lower fuelconcentration

Fuel concentrationprofile

Affected ball Adjacent ball

DRIFTDIRECTION


Flame ball driftFlame ball drift



1

10

10 100 1000

Time (seconds)

Space experiments

4.9% H2 - 9.8% O

2 - 85.3% CO

2

MSL-1/STS-833 flame balls

Theory (Buckmaster & Ronney, 1998)


Surprise #3: g-jitter effects on flame ballsSurprise #3: g-jitter effects on flame ballsRadiometer data drastically affected by impulses caused Radiometer data drastically affected by impulses caused

by small VRCS thrusters used to control Orbiter attitudeby small VRCS thrusters used to control Orbiter attitude Temperature data moderately affectedTemperature data moderately affected Vibrations (zero integrated impulse) - no effectVibrations (zero integrated impulse) - no effect

Flame balls & their surrounding hot gas fields are very Flame balls & their surrounding hot gas fields are very sensitive accelerometers!sensitive accelerometers!

Requested & received “free drift” (no thruster firings) Requested & received “free drift” (no thruster firings) during most subsequent tests with superb resultsduring most subsequent tests with superb results

Even in orbiting spacecraft, g is not zero!!Even in orbiting spacecraft, g is not zero!!


G-jitter effects on flame ballsG-jitter effects on flame balls

Without free driftWithout free drift With free driftWith free drift

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-0.1

-0.05

0

0.05

0.1

0.15

-20

0

20

40

60

80

100

15:33:20 15:35:00 15:36:40 15:38:20 15:40:00GMT

Beginning of test

-0.1

-0.05

0

0.05

0.1

0.15

0.2

-20

0

20

40

60

80

0 100 200 300 400 500

Time from ignition (seconds)

VCRS activitiesBeginning of test


G-jitter effects on flame balls - continuedG-jitter effects on flame balls - continuedFlame balls seem to respond more strongly than Flame balls seem to respond more strongly than

ballisticallyballistically to acceleration impulses, I.e. change in ball to acceleration impulses, I.e. change in ball velocity ≈ 2 ∫gvelocity ≈ 2 ∫g dtdt

Consistent with “added mass” effect - maximum Consistent with “added mass” effect - maximum possible acceleration of spherical bubble is 2gpossible acceleration of spherical bubble is 2g

-1

0

1

2

0

1

2

3

4

0 100 200 300 400 500 ( )Time from ignition s

STS-94/MSL-1R, TP 13AR7.0% H

2 - 14.0% O

2 - 79.0% SF

6

3 atm total pressure1 flame ball

Impulse

Flame ball velocity

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Surprise #4: heat release from flame ballsSurprise #4: heat release from flame balls2 missions, 26 burn tests, 1 atm & 3 atm, N2 missions, 26 burn tests, 1 atm & 3 atm, N22, CO, CO22, SF, SF66 diluents, 20x range of thermal diffusivity, 2600x range of Planck mean diluents, 20x range of thermal diffusivity, 2600x range of Planck mean

absorption length, 1 to 9 flame balls, yetabsorption length, 1 to 9 flame balls, yet Every single flame ball, without exception, produced between 1.0 and 1.8 Watts of radiant power !!!!!Every single flame ball, without exception, produced between 1.0 and 1.8 Watts of radiant power !!!!!

WHY???WHY???


Changes from SOFBALL-1 to SOFBALL-2Changes from SOFBALL-1 to SOFBALL-2STS-107 - Columbia’s last flightSTS-107 - Columbia’s last flightSpaceHab vs. SpaceLab moduleSpaceHab vs. SpaceLab moduleHigher energy ignition system - Higher energy ignition system -

ignite weaker mixtures nearer ignite weaker mixtures nearer flammability limitflammability limit

Much longer test timesMuch longer test times 3- 1500 sec3- 1500 sec 6 - 3000 sec6 - 3000 sec 2 - 4500 sec2 - 4500 sec 3 - 6000 sec3 - 6000 sec 1 - 10000 sec1 - 10000 sec

Free drift provided for usable Free drift provided for usable radiometer dataradiometer data


Changes from SOFBALL-1 - continuedChanges from SOFBALL-1 - continuedHigh pressure HHigh pressure H22-air - different chemistry-air - different chemistryCHCH44-O-O22-SF-SF66 test points - different chemistry test points - different chemistryHH22-O-O22-CO-CO22-He test points - higher Lewis number (but -He test points - higher Lewis number (but

still < 1) - more likely to exhibit oscillating flame ballsstill < 1) - more likely to exhibit oscillating flame balls3rd intensified camera with narrower field of view - 3rd intensified camera with narrower field of view -

improved resolution of flame ball imagingimproved resolution of flame ball imagingExtensive ground commanding capabilities added - Extensive ground commanding capabilities added -

reduce crew time scheduling issuesreduce crew time scheduling issues


Summary of resultsSummary of results• CM-2 /SOFBALL hardware performed almost flawlesslyCM-2 /SOFBALL hardware performed almost flawlessly• Free drift: microgravity levels were excellent (average Free drift: microgravity levels were excellent (average

accelerations less than 1 micro-g for most tests)accelerations less than 1 micro-g for most tests)• 37 combustion tests37 combustion tests• 15 different mixtures15 different mixtures• 56 flame balls, of which 33 were named by the crew56 flame balls, of which 33 were named by the crew• 6 1/4 hours total burn time for all flames6 1/4 hours total burn time for all flames• Despite the loss of Columbia, much data was obtained via Despite the loss of Columbia, much data was obtained via

downlink during missiondownlink during mission• ≈ ≈ 90% of thermocouple, radiometer & chamber pressure90% of thermocouple, radiometer & chamber pressure• ≈ ≈ 90% of gas chromatograph data90% of gas chromatograph data• ≈ ≈ 65% (24/37) of runs has some digital video frames (not always 65% (24/37) of runs has some digital video frames (not always

a complete record to the end of the test) - video data need to a complete record to the end of the test) - video data need to locate flame balls in 3D for interpretation of thermocouple and locate flame balls in 3D for interpretation of thermocouple and radiometer dataradiometer data


AccomplishmentsAccomplishments• Weakest flames ever burned, either in space or on the ground Weakest flames ever burned, either in space or on the ground

(≈ 0.5 Watts) (Birthday candle ≈ 50 watts)(≈ 0.5 Watts) (Birthday candle ≈ 50 watts)• Leanest flames ever burned, either in space or on the ground Leanest flames ever burned, either in space or on the ground

(3.2 % H(3.2 % H22 in air; equivalence ratio 0.078) (leanest mixture that in air; equivalence ratio 0.078) (leanest mixture that

will burn in your car engine: equivalence ratio ≈ 0.7)will burn in your car engine: equivalence ratio ≈ 0.7)• Longest-lived flame ever burned in space (81 minutes)Longest-lived flame ever burned in space (81 minutes)


Test objectives based on SOFBALL-1 resultsTest objectives based on SOFBALL-1 resultsCan flame balls last much longer than the 500 sec Can flame balls last much longer than the 500 sec

maximum test time on SOFBALL-1 if free drift (no thruster maximum test time on SOFBALL-1 if free drift (no thruster firings) can be maintained for the entire test?firings) can be maintained for the entire test? Answer: not usually - some type of flame ball motion, not Answer: not usually - some type of flame ball motion, not

related to microgravity disturbances, causes flame balls to related to microgravity disturbances, causes flame balls to drift to walls within ≈ 1500 secondsdrift to walls within ≈ 1500 seconds - - but there was an but there was an exceptionexception

We have no idea what caused this motion - working We have no idea what caused this motion - working hypothesis is a radiation-induced migration of flame ballhypothesis is a radiation-induced migration of flame ball

The shorter-than-expected test times meant enough time for The shorter-than-expected test times meant enough time for multiple reburns of each mixture within the flight timelinemultiple reburns of each mixture within the flight timeline


Example videos made from individual framesExample videos made from individual frames

QuickTime™ and aCinepak decompressorare needed to see this picture. QuickTime™ and aCinepak decompressorare needed to see this picture.

Test point 14a (3.45% HTest point 14a (3.45% H22

in air, 3 atm), 1200 sec in air, 3 atm), 1200 sec total burn timetotal burn time

Test point 6c (6.2% HTest point 6c (6.2% H22 - 12.4% - 12.4%

OO22 - balance SF - balance SF66, 3 atm), 1500 , 3 atm), 1500

sec total burn timesec total burn time


Example videos made from individual framesExample videos made from individual frames


Wide field of view cameraWide field of view camera Narrow field of view camera Narrow field of view camera

Test point 9a (3.32% HTest point 9a (3.32% H22 in air, 1 atm), in air, 1 atm),

470 sec total burn time470 sec total burn time


Hypothesized mechanism of flame ball driftHypothesized mechanism of flame ball drift Reabsorption of emitted radiation is a probably significant Reabsorption of emitted radiation is a probably significant

factor for all flame balls (discussed later…)factor for all flame balls (discussed later…) For most gases, opacity decreases as T increasesFor most gases, opacity decreases as T increases A small increase in T in some radial direction will lead to more A small increase in T in some radial direction will lead to more

radiative transfer (longer absorption length) in that directionradiative transfer (longer absorption length) in that direction Previous work (Buckmaster and Ronney, 1998) shows that Previous work (Buckmaster and Ronney, 1998) shows that

flame balls will drift up temperature gradientsflame balls will drift up temperature gradients This drift will decrease/increase the convection-diffusion zone This drift will decrease/increase the convection-diffusion zone

thickness in the upstream/downstream direction, thereby thickness in the upstream/downstream direction, thereby amplifying this gradient and encouraging driftamplifying this gradient and encouraging drift

Mineav, Kagan, Joulin, Sivashinsky (CTM, 2000) propose a Mineav, Kagan, Joulin, Sivashinsky (CTM, 2000) propose a mechanism for self-drift but predictions suggest it exists only mechanism for self-drift but predictions suggest it exists only for flame balls larger than 3D stability limitfor flame balls larger than 3D stability limit


Test objectives based on SOFBALL-1 resultsTest objectives based on SOFBALL-1 resultsCan oscillating flame balls be observed in long-Can oscillating flame balls be observed in long-

duration, free-drift conditions?duration, free-drift conditions? Answer: Probably - but need to check to see if flame ball Answer: Probably - but need to check to see if flame ball

motion rather than inherent oscillations of stationary motion rather than inherent oscillations of stationary flame ball caused radiometer data to show oscillationsflame ball caused radiometer data to show oscillations

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Test point 7D


Test objectives based on SOFBALL-1 resultsTest objectives based on SOFBALL-1 resultsAre higher Lewis number flame balls (e.g. HAre higher Lewis number flame balls (e.g. H22-O-O22-He-CO-He-CO22, ,

Le ≈ 0.8) more likely to oscillate, as predicted Le ≈ 0.8) more likely to oscillate, as predicted theoretically?theoretically? Answer: No. These flames were extremely stable.Answer: No. These flames were extremely stable.

Test point 11C: 8% HTest point 11C: 8% H22 - 16% O - 16% O22 - 7.6% CO - 7.6% CO22 - 68.4% He - 68.4% He

QuickTime™ and aCinepak decompressorare needed to see this picture.

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Test objectives based on SOFBALL-1 resultsTest objectives based on SOFBALL-1 resultsDo the flame balls in methane fuel (CHDo the flame balls in methane fuel (CH44-O-O22-SF-SF66 ) behave ) behave

differently from those in hydrogen fuel (e.g. Hdifferently from those in hydrogen fuel (e.g. H22-O-O22--

SFSF66) ?) ? Answer: Yes! They frequently drifted in corkscrew Answer: Yes! They frequently drifted in corkscrew

patterns! patterns! We have no idea why.We have no idea why.

9.9% CH9.9% CH44 - 19.8% O - 19.8% O22 - 70.3% SF - 70.3% SF66

QuickTime™ and aCinepak decompressorare needed to see this picture.


Parting commentsParting comments• When the Gods want to punish you they answer your prayers. When the Gods want to punish you they answer your prayers.

It will take us a long time to analyze & data mine all of the It will take us a long time to analyze & data mine all of the data obtained on STS-107 (due to extensive downlinking data obtained on STS-107 (due to extensive downlinking during the mission)during the mission)

• Flame balls live by the old stage performer motto – “leave ‘em Flame balls live by the old stage performer motto – “leave ‘em wanting more…” Several tests were expected to last > 1 hour, wanting more…” Several tests were expected to last > 1 hour, but none did because of the mysterious drift, UNTIL…but none did because of the mysterious drift, UNTIL…

• ……the very last test: 9 flame balls formed initially and the very last test: 9 flame balls formed initially and extinguished one by one until only one (Kelly”) remained. extinguished one by one until only one (Kelly”) remained. Unexpectedly, Kelly survived 81 minutes, seemingly immune Unexpectedly, Kelly survived 81 minutes, seemingly immune to drift, until it was intentionally extinguished due to to drift, until it was intentionally extinguished due to operational limitations (it was still burning at the time).operational limitations (it was still burning at the time).

• BUT WHY DIDN’T KELLY DRIFT????BUT WHY DIDN’T KELLY DRIFT????


““Orbit 2” flame balls (lead flame ball: Kelly)Orbit 2” flame balls (lead flame ball: Kelly)7.5% H7.5% H2 2 - 15% O- 15% O2 2 - 77.5% SF- 77.5% SF66, 3 atm, 3 atm

Camera 1 viewCamera 1 view Camera 2 (orthogonal) viewCamera 2 (orthogonal) view


First 15 minutes only shownFirst 15 minutes only shown


Crew operationsCrew operations

QuickTime™ and aSorenson Video decompressorare needed to see this picture.


Thanks Dave, Ilan, KC and Mike!Thanks Dave, Ilan, KC and Mike!


……and the rest!and the rest!


Comparison of predicted & measured radiiComparison of predicted & measured radii

HH22-air mixtures, 1 atm-air mixtures, 1 atm

Computational model (Wu Computational model (Wu et al.et al., 1998, 1999), 1998, 1999) 1-d, spherical, unsteady code (Rogg)1-d, spherical, unsteady code (Rogg) Detailed chemistry, transport, radiationDetailed chemistry, transport, radiation Isothermal, fixed composition at outer boundaryIsothermal, fixed composition at outer boundary Study evolution over time to steady state or extinctionStudy evolution over time to steady state or extinction

Unsatisfactory agreement with experiment - even with chemical Unsatisfactory agreement with experiment - even with chemical models that correctly predict planar Hmodels that correctly predict planar H22-air burning velocities!-air burning velocities!

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Comparison of predicted & measured radiiComparison of predicted & measured radiiResults sensitive to H + OResults sensitive to H + O22 + H + H22O O HO HO22 + H + H22O - not important for planar flames away from limitsO - not important for planar flames away from limitsAlso depend strongly on rate of H + OAlso depend strongly on rate of H + O22 OH + O, but everybody agrees on this rate! OH + O, but everybody agrees on this rate!

SSr*r* = (Z = (Zreactionreaction/r*)(∂r*/∂Z/r*)(∂r*/∂Zreactionreaction), S), SHRHR = (Z = (Zreactionreaction/HR)(∂HR/∂Z/HR)(∂HR/∂Zreactionreaction))

r* = flame ball radius; HR = heat release rate (Watts)r* = flame ball radius; HR = heat release rate (Watts)

Elementary step Sr* SHR

H + O2 + H2O→ HO2+H2O -0.394 -0.316H +O2→ OH +O 0.324 0.251

H2+OH→ H2 O +H 0.154 0.137H +HO2→ OH +OH 0.118 0.089H +O2+N2→ HO2+N2 -0.115 -0.092

OH +HO2→ O2+H2O -0.088 -0.067H2+O→ OH +H 0.072 0.054

OH +OH→ H2 O +O 0.025 0.027H +O2+O2→ HO2+O2 -0.016 -0.013H +HO2→ O2+H2 -0.014 -0.011O +HO2→ OH +O2 -0.012 -0.009


Chemical rate discrepanciesChemical rate discrepancies

Competition between branching & recombination depends not Competition between branching & recombination depends not only on [M] ~ P, but also Chaperon efficiencies, esp. Honly on [M] ~ P, but also Chaperon efficiencies, esp. H22OO

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Reabsorption effects in flame ballsReabsorption effects in flame balls LLplanckplanck,CO,CO22 ≈ 3.5 cm at 300K; L ≈ 3.5 cm at 300K; Lplanckplanck, SF, SF66 ≈ 0.26 cm at 300K - ≈ 0.26 cm at 300K -

reabsorption effects important!reabsorption effects important!Decreases heat loss, widens flammability limitsDecreases heat loss, widens flammability limitsAgreement much better when COAgreement much better when CO22 & SF & SF66 radiation ignored! radiation ignored!

(limit of zero absorption length for CO(limit of zero absorption length for CO22 & SF & SF66))Still better with optically thick modelStill better with optically thick model

HH22-O-O22-CO-CO22 mixtures (H mixtures (H22:O:O22 = 1:2) = 1:2)

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Reabsorption effects in flame ballsReabsorption effects in flame balls Need to carefully consider (Wu et al, 2000; Kwon et al, 2004?)Need to carefully consider (Wu et al, 2000; Kwon et al, 2004?)

Chemical model (GRIMech, Mueller et al, …)Chemical model (GRIMech, Mueller et al, …) Radiation model (Optically thin, opaque CORadiation model (Optically thin, opaque CO22, or SNB (thick)) , or SNB (thick)) Transport model including “thermal diffusion” (Soret effect; diffusive Transport model including “thermal diffusion” (Soret effect; diffusive

transport of mass via temperature (not concentration) gradients)transport of mass via temperature (not concentration) gradients)

HH22-air -air

mixturesmixtures


Reabsorption effects in flame ballsReabsorption effects in flame balls Need to carefully consider (Wu et al, 2000; Kwon et al, 2004?)Need to carefully consider (Wu et al, 2000; Kwon et al, 2004?)

Chemical model (GRIMech, Mueller et al, …)Chemical model (GRIMech, Mueller et al, …) Radiation model (Optically thin, opaque CORadiation model (Optically thin, opaque CO22, or SNB (thick)) , or SNB (thick)) Transport model including “thermal diffusion” (Soret effect; diffusive Transport model including “thermal diffusion” (Soret effect; diffusive

transport of mass via temperature (not concentration) gradients)transport of mass via temperature (not concentration) gradients)

HH22-O-O22-CO-CO22 mixtures mixtures

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STS-83/94 experiments

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Thin, Mueller, Soret

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STS-83/94 experiments

Thick, Mueller, Soret

Thin, Mueller, Soret


Summary - flame ballsSummary - flame balls SOFBALL - dominant factors in flame balls:SOFBALL - dominant factors in flame balls:

Far-field (1/r tail, rFar-field (1/r tail, r33 volume effects, r volume effects, r22// time constant) time constant) Radiative heat lossRadiative heat loss Radiative reabsorption effects in CORadiative reabsorption effects in CO22, SF, SF66

Branching vs. recombination of H + OBranching vs. recombination of H + O22 - flame balls like - flame balls like

“Wheatstone bridge” for near-limit chemistry“Wheatstone bridge” for near-limit chemistry General comments about space experimentsGeneral comments about space experiments

Space experiments are Space experiments are notnot just extensions of ground-based µg just extensions of ground-based µg experimentsexperiments

Expect surprises and be adaptableExpect surprises and be adaptable µg investigators quickly spoiled by space experimentsµg investigators quickly spoiled by space experiments

““Data feeding frenzy” during STS-94Data feeding frenzy” during STS-94 Caution when interpreting accelerometer data - frequency Caution when interpreting accelerometer data - frequency

range, averaging, integrated vs. peakrange, averaging, integrated vs. peak


Earth gravity (end view) Earth gravity (end view) Microgravity (side view)Microgravity (side view)

High Lewis number flame instabilitiesHigh Lewis number flame instabilities High Le - theory predicts pulsating & travelling-wave instabilitiesHigh Le - theory predicts pulsating & travelling-wave instabilities Structure depends on g (Booty Structure depends on g (Booty et alet al., 1986)., 1986) Qualitatively consistent with experiments in tubes (Pearlman Qualitatively consistent with experiments in tubes (Pearlman et et

al. 1994, 1997al. 1994, 1997))

QuickTime™ and aMotion JPEG A decompressor



High Lewis number flame instabilitiesHigh Lewis number flame instabilities

Earth gravity Earth gravity (end view)(end view)

Microgravity Microgravity (side view)(side view)


Autoignition & “Cool flames”Autoignition & “Cool flames”Pearlman Pearlman et al.et al., 2000a,b, 2000a,bHomogenous ignition of heated Homogenous ignition of heated

reactants in closed vessel widely reactants in closed vessel widely studied at 1gstudied at 1g

Many phenomena possible - single Many phenomena possible - single explosions, two-stage ignition, explosions, two-stage ignition, multiple “cool flames”, etc.multiple “cool flames”, etc.

Many practical applicationsMany practical applications Classical means to study chemical Classical means to study chemical

kineticskinetics Possible source of TWA 800 explosionPossible source of TWA 800 explosion Precursor to engine knockPrecursor to engine knock Can occur in mixtures outside flammable Can occur in mixtures outside flammable

range for propagating flamesrange for propagating flames


Autoignition & “Cool flames”Autoignition & “Cool flames” Experiments indicate buoyancy affects apparent ignition limit - Experiments indicate buoyancy affects apparent ignition limit -

prevents homogeneous temperatureprevents homogeneous temperature

Effect of Rayleigh number = GrPr on explosion limit (Tyler, 1966)Effect of Rayleigh number = GrPr on explosion limit (Tyler, 1966)


Autoignition at µg - experimental apparatusAutoignition at µg - experimental apparatus

R

V

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Reactor

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ManualValve

HeaterElements


Buoyancy causes ignition at top of vessel rather than centerBuoyancy causes ignition at top of vessel rather than center

50% n-C50% n-C44HH10 10 - 50% O- 50% O22, T = 310, T = 310ooC, P = 4.7psiaC, P = 4.7psia

Earth gravityEarth gravity MicrogravityMicrogravity

Autoignition - resultsAutoignition - results


Buoyancy enhances formation of multiple cool flamesBuoyancy enhances formation of multiple cool flames

Earth gravityEarth gravity MicrogravityMicrogravity

25% n-C25% n-C44HH10 10 - 25% O- 25% O22 - 50% Ar (Le = 1.1) - 50% Ar (Le = 1.1)

T = 310T = 310ooC, PC, Pinitial initial = 3.7psia, 10 cm i.d. spherical Flask= 3.7psia, 10 cm i.d. spherical Flask

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End of Reduced-Gravity

Autoignition - experimental apparatusAutoignition - experimental apparatus


……but high Le enables multiple cool flames even at µgbut high Le enables multiple cool flames even at µg

Ar diluent (Le ≈ 1.1)Ar diluent (Le ≈ 1.1) He diluent (Le ≈ 2.5)He diluent (Le ≈ 2.5)

25% n-C25% n-C44HH10 10 - 25% O- 25% O22 - 50% Ar or He - 50% Ar or He

T = 310T = 310ooC, PC, Pinitial initial = 3.7psia, 10 cm i.d. spherical Flask= 3.7psia, 10 cm i.d. spherical Flask

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ReferencesReferences M.R. Booty, S.B. Margolis and B.J. Matkowsky (1986). "Interaction of pulsating and spinning M.R. Booty, S.B. Margolis and B.J. Matkowsky (1986). "Interaction of pulsating and spinning

waves in nonadiabatic flame propagation," SIAM J. Appl. Math. 47, 1241.waves in nonadiabatic flame propagation," SIAM J. Appl. Math. 47, 1241. Buckmaster, J. D., Weeratunga, S. (1984). The stability and structure of flame-bubbles, Buckmaster, J. D., Weeratunga, S. (1984). The stability and structure of flame-bubbles,

Combust. Sci. TechCombust. Sci. Tech. 35, 287-296.. 35, 287-296. Buckmaster, J. D., Joulin, G., Ronney, P. D. (1990). Effects of heat loss on the structure and Buckmaster, J. D., Joulin, G., Ronney, P. D. (1990). Effects of heat loss on the structure and

stability of flame balls, stability of flame balls, Combust. FlameCombust. Flame 79, 381-392. 79, 381-392. Buckmaster, J. D., Joulin, G., Ronney, P. D. (1991). Structure and stability of non-adiabatic Buckmaster, J. D., Joulin, G., Ronney, P. D. (1991). Structure and stability of non-adiabatic

flame balls: II. Effects of far-field losses,flame balls: II. Effects of far-field losses, Combust. Flame Combust. Flame 84, 411-422. 84, 411-422. Deshaies, B., Joulin, G. (1984). On the initiation of a spherical flame kernel, Deshaies, B., Joulin, G. (1984). On the initiation of a spherical flame kernel, Combust. Sci. Combust. Sci.

TechTech. 37, 99-116.. 37, 99-116. Guy Joulin, Vadim N Kurdyumov and Amable Liñàn (1999). Existence conditions and drift Guy Joulin, Vadim N Kurdyumov and Amable Liñàn (1999). Existence conditions and drift

velocities of adiabatic flame-balls in weak gravity fields, Combust. Theory Modelling 3, 281-velocities of adiabatic flame-balls in weak gravity fields, Combust. Theory Modelling 3, 281-296.296.

Pearlman, H. (1997). Excitability in high-Lewis number premixed gas combustion, Pearlman, H. (1997). Excitability in high-Lewis number premixed gas combustion, Combust. Combust. FlameFlame 109, 382-398. 109, 382-398.

Pearlman, H. (2000a). Low-temperature oxidation reactions and cool flames at earth gravity Pearlman, H. (2000a). Low-temperature oxidation reactions and cool flames at earth gravity and microgravity. and microgravity. Combust. FlameCombust. Flame 121, 390-393. 121, 390-393.

Pearlman, H. (2000b). Cool Flames and Low Temperature Hydrocarbon Oxidation At Pearlman, H. (2000b). Cool Flames and Low Temperature Hydrocarbon Oxidation At Reduced-Gravity - An Experimental Study, submitted.Reduced-Gravity - An Experimental Study, submitted.

Pearlman, H. G., Ronney, P. D. (1994). Near-limit behavior of high Lewis-number premixed Pearlman, H. G., Ronney, P. D. (1994). Near-limit behavior of high Lewis-number premixed flames in tubes at normal and low gravity, flames in tubes at normal and low gravity, Phys. FluidsPhys. Fluids 6, 4009-4018. 6, 4009-4018.

Ronney, P. D. (1990). Near-limit flame structures at low Lewis number, Ronney, P. D. (1990). Near-limit flame structures at low Lewis number, Combust. FlameCombust. Flame 82, 1. 82, 1. Ronney, P. D., Whaling, K. N., Abbud-Madrid, A., Gatto, J. L., Pisowicz, V. L. (1994). Ronney, P. D., Whaling, K. N., Abbud-Madrid, A., Gatto, J. L., Pisowicz, V. L. (1994).

Stationary premixed flames in spherical and cylindrical geometries, Stationary premixed flames in spherical and cylindrical geometries, AIAA J.AIAA J. 32, 569-577. 32, 569-577.


ReferencesReferences Ronney, P. D., Wu, M. S., Weiland, K. J. and Pearlman, H. G. (1998). Structure Of Flame Balls Ronney, P. D., Wu, M. S., Weiland, K. J. and Pearlman, H. G. (1998). Structure Of Flame Balls

At Low Lewis-number (SOFBALL): preliminary results from the STS-83 space flight At Low Lewis-number (SOFBALL): preliminary results from the STS-83 space flight experiments, experiments, AIAA JournalAIAA Journal 36, 1361-1368. 36, 1361-1368.

Tyler, B. J. (1966). An Experimental Investigation of Conductive and Convective Heat Transfer Tyler, B. J. (1966). An Experimental Investigation of Conductive and Convective Heat Transfer during Exothermic Gas Phase Reactions. during Exothermic Gas Phase Reactions. Combust. FlameCombust. Flame 10, 90-91. 10, 90-91.

Wu, M.-S., Liu, J. B., Ronney, P. D. (1998). Numerical simulation of diluent effects on flame Wu, M.-S., Liu, J. B., Ronney, P. D. (1998). Numerical simulation of diluent effects on flame ball structure and dynamics, ball structure and dynamics, Proc. Combust. Inst.Proc. Combust. Inst. 27, 2543-2550. 27, 2543-2550.

Wu, M. S., Ronney, P. D., Colantonio, R., VanZandt, D. (1999). Detailed numerical simulation Wu, M. S., Ronney, P. D., Colantonio, R., VanZandt, D. (1999). Detailed numerical simulation of flame ball structure and dynamics, of flame ball structure and dynamics, Combust. Flame Combust. Flame 116, 387-397.116, 387-397.

Wu, M.-S., Ju, Y. and Ronney, P. D. (2000). Numerical simulation of flame balls with radiative Wu, M.-S., Ju, Y. and Ronney, P. D. (2000). Numerical simulation of flame balls with radiative reabsorption reabsorption effectseffects,” Paper No. 2000-0851, 38,” Paper No. 2000-0851, 38 thth AIAA Aerospace Sciences Meeting, Reno, NV, AIAA Aerospace Sciences Meeting, Reno, NV, January 11-14, 2000.January 11-14, 2000.

Zeldovich, Ya. B. (1944). Zeldovich, Ya. B. (1944). Theory of Combustion and Detonation of GasesTheory of Combustion and Detonation of Gases , Academy of Sciences , Academy of Sciences (USSR), Moscow.(USSR), Moscow.

Documents

1 AME 514 - October 7, 2004 Microgravity combustion Motivation Time scales (Lecture 1) Examples Premixed-gas flames »Flammability limits (Lecture