Presenting a Technical Report

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Transcript Presenting a Technical Report

Understanding Combustion Processes Through Microgravity Research

Paul D. Ronney

Dept. of Aerospace & Mechanical Engineering University of Southern California Los Angeles, CA 90089-1453 USA http://www-rcf.usc.edu/~ronney

27 Symposium (International) on Combustion, Boulder, CO, August 5, 1998

Supported by NASA-Lewis

Thanks to ...

•

Angel Abbud-Madrid, Tom Avedisian, Yousef Bahadori, John Buckmaster, Mun Choi, Dan Dietrich, Ed Dreizin, Fred Dryer, Said Elgobashi, Gerard Faeth, Osamu Fujita, Guy Joulin, Yiguang Ju, Kaoru Maruta, Moshe Matalon, John Moore, Vedha Nayagam, Takashi Niioka, Sandra Olson, Howard Ross, Kurt Sacksteder, Dennis Stocker, Peter Sunderland, Gregory Sivashinsky, James Tien, Arvind Varma, Karen Weiland, Forman Williams, Ming-Shin Wu University of Southern California - Department of Aerospace and Mechanical Engineering

OUTLINE

• • • • • • •

Motivation Today’s message Time scales Examples

•

Premixed-gas flames

•

Nonpremixed gas flames

•

Condensed-phase combustion Summary Recommendations for future work Perspective on space flight training University of Southern California - Department of Aerospace and Mechanical Engineering

MOTIVATION

• • •

Gravity influences combustion through

•

Buoyant convection

•

Sedimentation in multi-phase systems Many experimental & theoretical studies of µg combustion Applications

•

Spacecraft fire safety



Better understanding of combustion at earth gravity University of Southern California - Department of Aerospace and Mechanical Engineering

TODAY’S MESSAGE

• •

What we have learned from µg research

•

Time scales

• • • • •

Radiative loss – gas-phase & soot Dual limits (high-speed blow-off & low-speed radiative) Spherical flames (flame balls, droplets, ≈ candle flames) Oscillations near extinction Thermophoresis in sooting flames Open issues

•

Reabsorption of emitted radiation

• •

Chemistry of near-limit mixtures Soot formation, accumulation, oxidation, radiation University of Southern California - Department of Aerospace and Mechanical Engineering

• • • •

TIME SCALES FOR PREMIXED-GAS FLAMES

Chemical time (t chem ) (

≈

= thermal diffusivity, S L Buoyant transport time /S L ≈ (

/S L )/S L ≈

/S L 2 = laminar flame speed) ≈ d/V; V ≈ (gd(

)) 1/2 ≈ (gd) 1/2 (g = gravity, d = characteristic dimension)

• •

Inviscid: t inv Viscous: d ≈ ≈ d/(gd) 1/2



t vis Conduction time (t cond ) Radiation time (t

•

Optically thin: rad

) ≈ (d/g) 1/2 ≈ (

/g 2 ) 1/3 ≈ T f /(dT/dt) ≈ T f /(dT/dt) = 4

a p (T f 4 ≈ T – T ∞ 4 ) (

f = viscosity) ≈ d /(

/ 2 /16

C p

) (a p



t = Planck mean absorption coefficient) rad ~ P/

a p (T f 4 – T ∞ 4 ) ~ P 0 , P = pressure University of Southern California - Department of Aerospace and Mechanical Engineering

Time scales (hydrocarbon-air, 1 atm)

T i i i m e s c a l l l e C h e m i i i s t t t r r y ( ( ( t t t c h e m ) ) ) o r r d i i i f f f f f f u s i i i o n ( ( ( t t t d i i i f f f f f f ) ) ) B u o y a n t t t , , , i i i n v i i i s c i i i d ( ( ( t t t i i i n v ) ) ) B u o y a n t t t , , , v i i i s c o u s ( ( ( t t t v i i i s ) ) ) C o n d u c t t t i i i o n ( ( ( t t t c o n d ) ) ) , , , d = 5 c m R a d i i i a t t t i i i o n ( ( ( t t t r r r a d ) ) ) S t t t o i i i c h .

f f f l l l a m e 0 .

0 0 0 9 4 s e c 0 .

0 7 1 s e c 0 .

0 1 2 s e c 0 .

9 5 s e c 0 .

1 3 s e c L i i i m i i i t t t f f f l l l a m e 0 .

2 5 s e c 0 .

0 7 1 s e c 0 .

0 1 0 s e c 1 .

4 s e c 0 .

4 1 s e c

•

Conclusions

•

Buoyancy unimportant for near-stoichiometric flames

•

(t inv & t vis >> t chem ) Buoyancy strongly influences near-limit flames at 1g

• • • 

(t inv & t vis < t chem ) Radiation effects unimportant at 1g (t vis << t rad ; t Radiation effects dominate flames with low S L (t rad ≈ t chem ), but only observable at µg inv Radiation > conduction only for d > 3 cm Re ~ Vd/

~ (gd 3 /

2 ) 1/2



<< t rad ) turbulent flow at 1g for d > 10 cm University of Southern California - Department of Aerospace and Mechanical Engineering

µg methods

• • • •

Drop towers - short duration (1 - 10 sec) quality (10 -5 g o ) Aircraft - longer duration (25 sec), low quality (≈ t rad ), high (10 -2 g o - 10 -3 g o ) Sounding rockets - still longer duration (5 min), fair quality (10 -3 g o - 10 -6 g o ) Orbiting spacecraft - longest duration (16 days), best quality (10 -5 g o - 10 -6 g o ) University of Southern California - Department of Aerospace and Mechanical Engineering

Premixed-gas flames – flammability limits

• •

No extinction without losses – no purely kinetic criterion for limits (Giovangigli & Smooke, 1992) Models of limits due to losses - most important prediction: burning velocity at the limit (S L,lim )

•

Upward propagation: rise speed at limit ~ (gd) 1/2

• •

(Levy, 1965); causes stretch extinction (Buckmaster & Mikolaitis, 1982): t chem ~ t inv



S L,lim ~ (g

2 /d) 1/4 Downward propagation – sinking layer of cooling gases near wall outruns and t chem ~ t vis



S “suffocates” flame (Jarosinsky L,lim ≈ 1.3(g

) 1/3

et al.

, 1982) (Krivulin

et al

., 1981, Wang & Ronney, 1993) Heat loss to walls: t chem ~ t cond



S L,lim ≈ 40

/d (Pe lim (Spalding, 1957) = 40) University of Southern California - Department of Aerospace and Mechanical Engineering

Flammability limits – losses - continued…

• • •

Big tube, no gravity – what causes limits?

Radiative loss (Joulin & Clavin, Buckmaster, 1976)

S L

,lim  1 r 

C p

1.2

 L 

f T f

(no reabsorption)

prediction consistent with µg experiments Impact of heat loss ~ Heat loss Heat release ~

T 2 -E/RT



as T



Reabsorption maybe be important when a P -1

•

< d Extends limits & increases S L (Eudier & Joulin, 1988; Abbud-Madrid & Ronney, 1993) – theoretically no limit with

•

graybody absorbers Gases – spectral radiation – 2 mechanisms allow radiation to escape even with reabsorption (Ju

et al.

, 1998)

Absorption spectra of products different from reactants

Spectra broader at high T than low T University of Southern California - Department of Aerospace and Mechanical Engineering

Reabsorption effects on planar premixed flames

Ju, Masuya, Ronney (1998) University of Southern California - Department of Aerospace and Mechanical Engineering

Absorption spectra of H

O & CO

University of Southern California - Department of Aerospace and Mechanical Engineering

Premixed-gas flames - stretched flames

• • • •

Nonuniform flow, unsteady/curved flames: “flame stretch”

S  1

A dA dt

(A = flame area) Strong stretch (

-1 ≈ t chem ) extinguishes flames Moderate stretch strengthens flames for Le < 1

Le  Thermal diffusivity of the bulk mixture ( a ) Mass diffusivity of scarce reactant into the bulk mixture (D)

Spherical expanding flames, Le < 1: stretch allows flames to exist in mixtures below radiative limit until r f curvature benefit too weak

S  1

A dA dt

 1 4 

r f

d dt

 

2  2

r f dr f dt

too large &



Dual limit: radiation at large r f , curvature-induced stretch at small r f (ignition limit) University of Southern California - Department of Aerospace and Mechanical Engineering

Stretched flames - continued

• • • • •

Counterflow configuration (Tohoku group)

• S

= dU/dy – flame located where U = S L Increased stretch pushes flame closer to stagnation plane

•

Decreased volume of radiant products Similar Le effects as curved flames Results

•

Dual limits

• •

Flammability extension even for Le > 1 Multiple solutions (which ones are stable?) Dual limits & Le effects seen in µg experiments, but evidence for multivalued behavior inconclusive University of Southern California - Department of Aerospace and Mechanical Engineering

“FLAME BALLS”

•

Zeldovich, 1944: stationary spherical flames possible since &



2 C = 0 have solutions



2 T for

unbounded

domain in spherical

•

geometry Mass conservation requires U everywhere (no stretch)



0 – only

• 

diffusive transport T ~ 1/r - unlike propagating flame where T ~

-r - dominated by 1/r tail (with r 3 volume effects!) Buckmaster, 1985; Joulin, 1985: adiabatic flame balls are

unstable

University of Southern California - Department of Aerospace and Mechanical Engineering

Flame ball schematic

Temperature T* T o Interior filled with combustion products C ~ 1-1/r Fuel concentration T ~ 1/r Reaction zone Fuel & oxygen diffuse inward Heat & products diffuse outward University of Southern California - Department of Aerospace and Mechanical Engineering

Flame balls - continued

• • • • • •

Ronney (1990): seemingly stable, stationary flame balls accidentally discovered in drop-tower experiment Confirmed in parabolic aircraft flights (Ronney Only seen at µg, low Le, near extinction limits

et al.

, 1993) Space experiments (STS-83 & 94, 1997)

•

Stable for > 500 seconds (!)

• •

Weakest flames ever burned (1 – 2 Watts/ball) Very long evolution time scales ~ (



r * ) 2 /

≈ 100 s Buckmaster, Joulin & collaborators: window of conditions with radiative loss & low Le

stable

Detailed numerical modeling (Yale, USC)

•

Dual limits

• • • 

Unsatisfactory agreement with experiment Results sensitive to H + O 2 + H 2 O



HO 2 Reabsorption effects in H 2 -O 2 -CO 2 & H 2 -O 2 + H -SF 6 2 O mixtures ???

University of Southern California - Department of Aerospace and Mechanical Engineering

Theory of non-adiabatic flame balls

15 Unsta ble to 3-d dis turbanc es 10 Stable Equation of c urve: R -2 ln(R) = Q 5 Unsta ble to 1-d dis turbanc es 0 0 0.05

0.1

Dimensionless heat loss (Q) 0.15

0.2

•

Buckmaster, Jouliln, Ronney (1990) University of Southern California - Department of Aerospace and Mechanical Engineering

Comparison of predicted & measured radii

12 10 Peters & Rogg GRI Yetter Experiments 8 6 4 2 0 3 3.5

4 M ole percent H 4.5

2 in air 5

•

H 2 -air mixtures, 1 atm University of Southern California - Department of Aerospace and Mechanical Engineering

Comparison of predicted & measured S

400 350 300 250 200 150 100 50 0 0 1 Yetter GRI Peters Expt. 2 3 Equivalence ratio 4 5

•

H 2 -air mixtures, 1 atm University of Southern California - Department of Aerospace and Mechanical Engineering

Evidence of reabsorption effects in flame balls

16 12 Predic tions (without CO 2 radiation) 8 4 Experiments Predic tions (with CO 2 radiation) 0 2 4 6 8 10 Mole % H 2 12 14 16

H

-O

-CO

mixtures (H

:O

= 1:2)

University of Southern California - Department of Aerospace and Mechanical Engineering

EXAMPLES - NONPREMIXED GAS FLAMES

• • •

Counterflow flames

•

Nonpremixed flames – less freedom of movement – flame

•

must lie where stoichiometric flux ratio maintained Radiating gas volume ~ flame thickness ~ (

) 1/2 Computations & µg experiments – simple C-shaped dual limit response Conductive loss to burners at low

? (

min ) -1 ≈ t cond University of Southern California - Department of Aerospace and Mechanical Engineering

Nonpremixed-gas flames - gas-jet flames

• • •

Flame height (L f ) and residence time (t jet ) determined by equating diffusion time (d 2 /D) to convection time (L f /U) Mass conservation: U(0)d(0) 2 ~ U(L f )d(L f ) 2 (round jet); U(0)d(0) ~ U(L f )d(L f ) (slot jet) Buoyant flow: U(L f ) ~ (gL f ) 1/2 ; nonbuoyant: U(L f ) = U(0) G e o m e t t t r r r y

R o u n d j j j e t t t R o u n d j j j e t t t S l l l o t t t j j j e t t t S l l l o t t t j j j e t t t

F l l l o w

M o m e n t t t u m B u o y a n t t t M o m e n t t t u m B u o y a n t t t

L f f f

U o d o 2 / / / D U o d o 2 / / / D U o d o 2 / / / D ( ( ( U o 4 d o 4 / / / D 2 g ) ) ) 1 / / / 3

t t t j j j e t t t

d o 2 / / / D ( ( ( U o d o 2 / / / g D ) ) ) 1 / / / 2 d o 2 / / / D ( ( ( U o 2 d o 2 / / / g 2 D ) ) ) 1 / / / 3

University of Southern California - Department of Aerospace and Mechanical Engineering

• • • •

Gas-jet flames - results

L f ≈ same at 1g or µg for round jet (what about slot jet?) t jet



larger at µg than 1g for round jet Larger µg flame width ~ (Dt jet ) 1/2 - greater difference at low



Re due to axial diffusion & buoyancy effects Greater radiative loss fraction at µg (≈ 50% vs. 8%) Turbulent flames: D ~ u’L I ; u’ ~ U o ; L I

• 

~ d o L f ~ d o (independent of Re) Differences between 1g & µg seen even at high Re buoyancy effects depend on entire plume Soot formation

•

Typically greater at µg due to larger t jet

•

- outweighs lower T Smoke points seen at µg - WHY???

t jet ~ U o 1/2 for buoyant flames BUT...

t jet independent of U o for nonbuoyant flames !

Axial diffusion effects negligible at Re > 50

•

Thermophoresis effects - concentrates soot in annulus University of Southern California - Department of Aerospace and Mechanical Engineering

Flame lengths at 1g and µg

100

Sund erlan d et al. (1g) Sund erlan d et al. (µg, 1 a tm) Sund erlan d et al. (µg, 0.5 atm ) Sund erlan d et al. (µg, 0.2 5 atm) Coch ran a nd Mas ica (µg) Baha dori et a l. (µ g) Baha dori & Stocke r (µg)

10 1 1 10 100 Reynolds number (Re) 1000

Sunderland

et al.

(1998) - CH

/air

University of Southern California - Department of Aerospace and Mechanical Engineering

Flame widths at 1g and µg

10 1 10

Sunderland et al. (1g) Sunderland et al. (µg, 1 atm) Sunderland et al. (µg, 0.5 at m) Sunderland et al. (µg, 0.25 atm) Cochran and Mas ic a Bahadori et al.

100 Reynolds number (Re) 1000

Sunderland

et al.

(1998) - CH

/air

University of Southern California - Department of Aerospace and Mechanical Engineering

Turbulent flame lengths at 1g and µg

500 400 Microgravity 300 200 Blow-off limits Earth gravity 100 0 0 1000 2000 3000 4000 5000 Jet Reynolds number 6000 7000 8000

Bahadori

et al.

(1997) - C

H

/air

University of Southern California - Department of Aerospace and Mechanical Engineering

Sooting gas jet flames at 1g and µg

1g µg n-butane in air, 10mm diameter jet, Re = 42 Fujita

et al.

, 1997 University of Southern California - Department of Aerospace and Mechanical Engineering

EXAMPLES - Condensed-phase - droplets

• • •

Spherically-symmetric model (Godsave, Spalding 1953)

•

Steady burning possible - similar to flame balls (large radii: transport diffusion-dominated)

•

Mass burning rate = (π/4)

d d d K; K = (8



d C P ) ln(1+B)

•

Flame diameter d f = d d ln(1+B) / ln(1+f)

•

1st Regressing droplet: d do 2 - d d (t) 2 = Kt if quasi-steady µg experiment - Kumagai (1957) - K(µg) < K(1g) Dual-limit behavior

•

Residence-time limited (small d d ): t drop

•

Heat loss (large d d ): t drop ≥ t rad

•

Radiative limit at large d d confirmed by = d f 2 /

≤ t chem µg experiments University of Southern California - Department of Aerospace and Mechanical Engineering

Droplet combustion - continued

•

Large droplets not quasi-steady

•

Extinction occurs at sufficiently large d d , but d d decreases during burn - quasi-steady extinction not observable

• •

K & d f /d d not constant - depend on d do & time Large time scale for diffusion of radiative products to far-

• •

field & O 2 from far-field Soot accumulation dependent on d do Absorption of H 2 O from products by fuel University of Southern California - Department of Aerospace and Mechanical Engineering

Soot formation in µg droplet combustion

0 sec 0.2 sec 0.3 sec 0.4 sec 0.5 sec 0.6 sec 0.7 sec 0.8 sec n-heptane in air (Lee

et al.

, 1998) University of Southern California - Department of Aerospace and Mechanical Engineering

Condensed-phase combustion - candle flames

• •

Similar to quasi-steady droplet but near-field not spherical Space experiments (Dietrich

• • • •

et al.

, 1994, 1997) Nearly hemispherical at µg Steady for many minutes - probably > d f 2 /

Eventual extinguishment - probably due to O 2 depletion Oscillations before extinguishment, except for small d f

Near-limit oscillations of spherical flames? (Matalon)

Edge-flame instability? (Buckmaster)

Some evidence in droplets also (Nayagam

et al., 1998

) University of Southern California - Department of Aerospace and Mechanical Engineering

Candle flames at 1g and µg

1g µg Dietrich, Ross, Tien (1994) University of Southern California - Department of Aerospace and Mechanical Engineering

Condensed-phase combustion - flame spread

•

deRis (1968); Delichatsios (1986): flame spread rate (S f ) with opposing flow U, infinite-rate kinetics (mixing limited)

 

g f



s C p



s T f T v

 

T v T



(thin fuel) - independent of P and U

• •

S f



r

C P



s C p



T f



T v

 

T v T

  

2 (thick fuel) - S f ~ P 1 U 1 Diffusive transport time scale (t diff ) ≈

/U ≈

/U 2 Heat loss parameter H ~ t diff /t rad

• • • •

S f At lower at µg, S f µg: U = S f << U(1g) lower at lower P



/U 2 t rad ~ P -1 U -2 higher H Infinite-rate kinetics limit not achieved at 21% O 2 Dual-limit behavior

Residence-time limited (large U): t diff

» »

Heat loss (small U): t diff Confirmed by thin-fuel ≥ t rad ≤ t chem µg experiments (Olson !

et al.

, 1990)

Most robust U ≈ 10 cm/s - less than 1g buoyant flow!

University of Southern California - Department of Aerospace and Mechanical Engineering

Flame spread - continued

• •

Radiation not all lost if ambient atmosphere absorbs; Honda & Ronney, 1998:

•

O 2 -N 2 , O 2 -He, O 2 -Ar: S f (1g) > S f (µg) due to radiative loss

•

O 2 -CO 2 , O 2 -SF 6 : S f (1g) < S f (µg) due to reabsorption

•

International Space Station uses CO 2 fire extinguishers!

Thick fuels

•

Steady S f not possible at µg since S f ~ U; instead S f decreases until extinction (Altenkirch

et al.

, 1996)

•

~ t -1/2 , Possible 3-d effects

» » d

thermal ~

/S f ,

O2 ~ D O2 /S f With radiative loss:

O2 >

>> sample width (6.3 mm) thermal - could narrower sample burn faster due to lateral O 2 influx?

University of Southern California - Department of Aerospace and Mechanical Engineering

Flame spread 1g vs. µg, optically-thin vs. thick

30% O 2 in N 2 , 1g 42% O 2 in SF 6 , 1g 30% O 2 in N 2 , µg 42% O 2 in SF 6 , µg University of Southern California - Department of Aerospace and Mechanical Engineering

Flame spread rates in reabsorbing atmospheres

2.5

2 1g (CO µg (CO 1g (SF µg (SF 2 ) 2 ) 6 ) 6 ) 1.5

1 0.5

0 20 25 30 35 40 O 2 concentration (mole % ) 45 50 Honda & Ronney, 1998 University of Southern California - Department of Aerospace and Mechanical Engineering

Smoldering flame spread over thin fuels at µg

•

Olson

et al.

• • •

1998 - space experiments Strong forced flow - smooth fronts, similar to 1g Weak or no forced flow - fingering fronts Similar behavior seen at 1g in narrow channels & low U but not wider channels & high U (Zik & Moses, 1998)

•

Radiative or conductive loss: gas-phase heat transfer lost; heat transport through solid phase; O occur through gas phase 2 transport can only

•

Two Lewis numbers?

High U: heat transport in gas phase; Le eff



0: heat transport through solid; Le eff

gas /D O2 =

solid /D O2 ≈ 1 << 1 Would explain cells at low U & high heat loss - diffusive thermal instability University of Southern California - Department of Aerospace and Mechanical Engineering

Fingering smolder spread at µg



Air, 6.5 cm/s Olson

et al.,

1998 University of Southern California - Department of Aerospace and Mechanical Engineering

Flame spread over liquid fuel pools

• •

Similar to thick-fuel flame spread over solids with small T v , with flow in condensed-phase Steady & pulsating spread

•

Pulsating spread never observed experimentally at µg, but predicted computationally at µg

•

Importance of thermal expansion in pulsating spread absent from computation when expansion neglected

•

Why is S f (1g, U = 30 cm/s) fast, pulsating but S f cm/s) slower & steady???

(1g, U = 30 University of Southern California - Department of Aerospace and Mechanical Engineering

Summary

•

What we have learned from µg research

•

Time scales

when buoyancy, radiation, etc. is important

•

Radiative loss – gas-phase & soot

causes many of the observed effects on burning rates & extinction conditions

• •

Dual limits (high-speed blow-off & low-speed radiative)

seen for practically all types of flames studied to date

Spherical flames (flame balls, droplets, ≈ candle flames)

long time scales, large domains of influence, radiative loss

•

Oscillations near extinction

Common, not yet fully understood

•

Thermophoresis in sooting flames

Affects net heat release, soot oxidation, radiative loss

University of Southern California - Department of Aerospace and Mechanical Engineering

Recommendations for future work

•

Radiative reabsorption effects

•

Apparently seen in particle-seeded premixed-gas flames,

• •

flame balls, thin-fuel flame spread Easier to study at µg - no interference from turbulence Relevant to IC engines, large furnaces, EGR, flue-gas

•

recirculation May occur in other µg flames,

e.g.

Droplet combustion - Stefan flow at surface limits

conductive flux - ln(1+B) term; radiation not affected

  ln  





B R

/    ;



q r d d C P



L V

;  

d C P



Flame spread over thick fuels - could lead to steady spread even at µg in O 2 -CO 2 , O 2 -SF 6

S f

  a

s C P





T v

L  a

   



T f



T v

 

•

Need faster computational models of radiative transport!

University of Southern California - Department of Aerospace and Mechanical Engineering

Predicted droplet burning rates with radiation

5 4 3 2 1 0 B = 3 B = 8.5

2 4 R



q r d d C P /2 6



L v 8 10 K = burning rate constant; R = radiation parameter University of Southern California - Department of Aerospace and Mechanical Engineering

Recommendations for future work - continued

• • •

High-pressure combustion

•

Buoyancy effects (t chem /t vis ) increase with P for weak mixtures

•

Reabsorption effects increase with P

•

Turbulence more problematic

•

Few µg studies - mostly droplets 3-d effects

•

Flame spread - effects of fuel bed width

•

Flame balls - breakup of balls Gas jet flames at µg

• • •

Soot formation what causes smoke points at µg???

Slot jet vs. round-jet Radiative extinction at large d(0)?

University of Southern California - Department of Aerospace and Mechanical Engineering

Recommendations for future work - continued

• •

Spherical diffusion flames - porous sphere experiment

•

Liquid or gaseous fuel

• • • •

Could provide quasi-steady spherical nonpremixed flame Increase fuel mass flow slowly until extinction Difficult experimentally - long times, large chamber Initial results with gaseous fuel - steady-state not reached should use diluted fuel & enriched O 2 d f



smaller t drop “Catalytic flame ball”

•

1d, steady catalytic system

• •

Radius known, T * and Y * unknown Extract overall surface reaction rates

 (

Y s

T s

)  r

s D s r s Y

 



Y s

  /

Y M

;



- increases f, reduces





 

T s T ad



 

     

 s

s r s



 

T s T s

 



  

University of Southern California - Department of Aerospace and Mechanical Engineering

Recommendations for future work - concluded

•

Chemical models

•

Many µg combustion phenomena of interest occur near extinction limits

•

Sensitive to chemical mechanism - branching vs.

•

recombination H + O 2 + M



HO 2 + M identified for further study Could Chaperon efficiency relative to N 2 dependent?

be temperature University of Southern California - Department of Aerospace and Mechanical Engineering

Branching & recombination rate discrepancies

2.5 10 17 Lindstedt H+O 2 +H 2 O



HO 2 +H 2 O H+O 2



O+OH 2 10 17 2 10 11 1.5 10 11 1.5 10 17 1 10 17 Williams Peters GRI 5 10 16 Leeds Yetter 0 600 700 GRI Leeds Williams Yetter Peters Lindstedt 1 10 11 5 10 10 800 900 1000 T emperature (Kelvins) 1100 0 10 1200 0

•

Competition between branching & recombination depends not only on [M] ~ P, but also Chaperon efficiencies, esp. H 2 O University of Southern California - Department of Aerospace and Mechanical Engineering

PERSPECTIVE ON SPACE FLIGHT TRAINING

• • •

2 types of training

•

Orbiter-related

Launch & entry

Living in space

Photography, videography

•

Payload related

Science background

» » »

Procedures and schedules Performing experiments On-orbit repair Not like “The Right Stuff” now - STRAIGHTFORWARD Toughest part - TRAVEL University of Southern California - Department of Aerospace and Mechanical Engineering