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Transcript of 1 AME 514 - October 7, 2004 Microgravity combustion Motivation Time scales (Lecture 1) Examples ...
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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AME 514 - October 7, 2004AME 514 - October 7, 2004 22
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, ...
AME 514 - October 7, 2004AME 514 - October 7, 2004 33
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))
AME 514 - October 7, 2004AME 514 - October 7, 2004 44
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])
AME 514 - October 7, 2004AME 514 - October 7, 2004 55
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 66
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
∑
AME 514 - October 7, 2004AME 514 - October 7, 2004 77
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 88
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 99
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 1010
““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
AME 514 - October 7, 2004AME 514 - October 7, 2004 1111
““I am not Spock”I am not Spock”
::
::
asas
AME 514 - October 7, 2004AME 514 - October 7, 2004 1212
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 1313
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
⎛
⎝ ⎜
⎞
⎠ ⎟
AME 514 - October 7, 2004AME 514 - October 7, 2004 1414
““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
AME 514 - October 7, 2004AME 514 - October 7, 2004 1515
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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AME 514 - October 7, 2004AME 514 - October 7, 2004 1616
Flame balls - historyFlame balls - history
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
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AME 514 - October 7, 2004AME 514 - October 7, 2004 1717
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 ⇓
AME 514 - October 7, 2004AME 514 - October 7, 2004 1818
Flame balls - historyFlame balls - history
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"
AME 514 - October 7, 2004AME 514 - October 7, 2004 1919
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 2020
Practical importancePractical importance
AME 514 - October 7, 2004AME 514 - October 7, 2004 2121
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)
AME 514 - October 7, 2004AME 514 - October 7, 2004 2222
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 2323
Experimental apparatusExperimental apparatus
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AME 514 - October 7, 2004AME 514 - October 7, 2004 2424
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)
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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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AME 514 - October 7, 2004AME 514 - October 7, 2004 2525
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 2626
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 2727
Flame ball driftFlame ball drift
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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)
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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!!
AME 514 - October 7, 2004AME 514 - October 7, 2004 2929
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3030
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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AME 514 - October 7, 2004AME 514 - October 7, 2004 3131
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???
AME 514 - October 7, 2004AME 514 - October 7, 2004 3232
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3333
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3434
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3535
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)
AME 514 - October 7, 2004AME 514 - October 7, 2004 3636
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3737
Example videos made from individual framesExample videos made from individual frames
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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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3838
Example videos made from individual framesExample videos made from individual frames
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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
AME 514 - October 7, 2004AME 514 - October 7, 2004 3939
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 4040
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 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
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AME 514 - October 7, 2004AME 514 - October 7, 2004 4242
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
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AME 514 - October 7, 2004AME 514 - October 7, 2004 4343
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????
AME 514 - October 7, 2004AME 514 - October 7, 2004 4444
““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
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First 15 minutes only shownFirst 15 minutes only shown
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Crew operationsCrew operations
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Thanks Dave, Ilan, KC and Mike!Thanks Dave, Ilan, KC and Mike!
AME 514 - October 7, 2004AME 514 - October 7, 2004 4747
……and the rest!and the rest!
AME 514 - October 7, 2004AME 514 - October 7, 2004 4848
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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AME 514 - October 7, 2004AME 514 - October 7, 2004 4949
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
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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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( )Temperature Kelvins
+H O2→ +O OH
+H O2+H
2O→HO
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GRI
Peters
Williams
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AME 514 - October 7, 2004AME 514 - October 7, 2004 5151
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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AME 514 - October 7, 2004AME 514 - October 7, 2004 5252
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 5353
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
Thick, Mueller, Soret
Thin, Mueller, Soret
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STS-83/94 experiments
Thick, Mueller, Soret
Thin, Mueller, Soret
AME 514 - October 7, 2004AME 514 - October 7, 2004 5454
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
AME 514 - October 7, 2004AME 514 - October 7, 2004 5555
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))
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High Lewis number flame instabilitiesHigh Lewis number flame instabilities
Earth gravity Earth gravity (end view)(end view)
Microgravity Microgravity (side view)(side view)
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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
AME 514 - October 7, 2004AME 514 - October 7, 2004 5858
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)
AME 514 - October 7, 2004AME 514 - October 7, 2004 5959
Autoignition at µg - experimental apparatusAutoignition at µg - experimental apparatus
R
V
V
VacuumPump
SideCamera
TopCamera
BlowerMotor
PressureTransducer
Solenoid Valve
Computer/Data Acquisition
50cc Cylinder
Premixed Gases
Reactor
TC rake
FURNACE
L
Quartz Window
ManualValve
HeaterElements
AME 514 - October 7, 2004AME 514 - October 7, 2004 6060
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
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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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Autoignition - experimental apparatusAutoignition - experimental apparatus
AME 514 - October 7, 2004AME 514 - October 7, 2004 6262
……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.
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