Aug 31, 1999 - electric fields). However, particle interaction effects are expected .... studies of liquid fuel drop arrays have been conducted ... to create a "model aerosol" consisting of relatively large (100-300 .... the igniter wire was coated with a thin layer of a zirconia- ...... for the constant 1%=106 m3/mol-s and activation.
INTERACTION
OF BURNING
METAL
PARTICLES
Final Report Contract No. NAS3-96017
Period NASA
Contracting
Covered:
Officer's
1 July 1996 - 31 August
Technical
Representative:
Prepared Edward
AeroChem
L. Dreizin
Research
(Principal
Laboratory,
Investigator),
August
NASA-Glenn Cleveland,
to Research OH 44135
Center
Friedman,
Code
6711
by:
Charles
H. Berman,
Titan Research and Technology, P.O. Box 2229 Princeton,
Submitted
Robert
1999
NJ 08543-2229
31, 1999
and Veto
The Titan
K. Hoffmann
Corporation
1. Introduction ................................................................. 2. ConstantPressureCombustionof Aerosolof CoarseMagnesiumParticlesin Microgravity . 3 2.1.Introduction ......................................................... 3 2.2.Experimental........................................................ 5 2.3.Results............................................................. 7 2.4.Discussion......................................................... 14 2.5. Summary 2.6. References 2.7. Figures
.......................................................... .........................................................
19 19
............................................................
3. Further Experiments 3.1. Introduction
22
on Magnesium Aerosol Combustion ........................................................
in Microgravity
..............
40 41
3.2. Experimental ....................................................... 3.3. Results and Discussion ...............................................
42 42
3.4. Concluding __.). References
47 48
3.6. Figures 4. Magnesium
Remarks ................................................. .........................................................
............................................................
Aerosol
Figures
Combustion
Modeling
49
......................................
58
...............................................................
61
5. Combustion of Aerosolized Zirconium And Titanium Particles 5.1. Fine Zirconium Powders .............................................. 5.2. Coarse
Powders
5.3. References 5.4. Figures
of Zirconium
and Titanium
in Microgravity
..............................
.........................................................
64 64 67 69
............................................................
6. High Temperature Phases in Ternary Zr-o-n Systems 6.1. Introduction ........................................................
..........
70 ...............................
81 81
6.2. Experimental ....................................................... 6.3. Results and Discussion ...............................................
81 82
6.4. References
83
6.5. Figures 7. New Technology 8. Summary
......................................................... ............................................................ ...........................................................
and Future
9. Acknowledgments
Work
...................................................
..........................................................
85 87 87 88
1. INTRODUCTION Combustionprocessesin two-phasesystems,such as sprays,dust clouds,and various aerosols,areof interestfor numerousapplicationsin propellants,explosives,andincendiaries.In addition,similarprocesses needto becharacterized andunderstoodfor anumberof fire suppression applications. However,experimentaldatacharacterizingcombustionin two-phasesystemsand. specifically,describingeffectsof multiparticleinteractionon the flame propagation,arelimited. This, primarily, is dueto difficulties in organizinganexperimentthatwouldenablearesearcherto establisha flame in a two-phasesystemand, at the sametime. observebehaviorof individual particles. One crucial problemis that in two-phasesystemsin which flame propagationcan be establishedthe sizeof the particlesis small andthey are hardto distinguishoptically. Another problemis associatedwith strongbuoyantflowsinducedin acloudwhenaflamestartstopropagate. Thesebuoyantflows entrainparticlesandmaskparticle motion inducedby'diffusiophoreticand thermophoreticflows andother possibleparticle interactionmechanisms(e.g., induced electric fields).
However,
flame
particle
propagation
interaction
mechanism,
the temperature
that will remain
aerosolized
their
behavior
behind,
techniques
ahead,
routinely
A new experimental with Mg,
setup
combustion
different
groups,
Most
conducted aerosols
a typical
were conducted
in a burning
flame
studies.
built,
and tested. NASA
and modify
particle
burner",
has been
metals
Mg, and typical
exploited
used in more Experiments
interesting
and used real-time
optical
was addressed.
has been
selected
so that
using
2.2 s drop tower.
of new' and The
gravity)
aerosols
This setup
observed. pressure
at normal
can be observed
Glenn
and a number
"vapor-phase
in the
system.
This approach
metal
utilizing
at constant
products,
two-phase
as they' would
of coarse
were
changes
systems is camed out in the microgravity flows. In addition, large particles can be
camera and a regular speed video camera filter assemblies. Combustion products
phenomena represent
two
"surface
burners",
diagnostics
included
equipped with microscope lenses and were collected and analyzed after the
experiments. of the results
of this effort
journals.
Verbatim
chapters
2, 3, and
6. Chapter
results
designed,
experiments were
reviewed propagation
combustion
combustion
and cause
of combustion
the propagating
particle
in these
namely,,
Zr and Ti. Experiments
within
has been
Zr, and Ti aerosols
microgravity
and
of microgravity
a high speed movie various interference
developing
('i.e., will not fall down
microgravity
characterizing metal
gradients
used in single
in which
than one hundred
to be significant
in which combustion of two-phase one to avoid production of buoyant
used,
in this program,
are expected
affect the size and morphology
and concentration
Experiments environment allow
effects
in magnesium
of microgravity
copies
4 briefly
aerosol
experiments
have
been
reported
of the peer-reviewed describes
in microgravity.
in conference publications
a developed Chapter
with Zr and Ti particles.
proceedings
follow
numerical 5 describes
below model
currently,
and peeras the report of the
flame
unpublished
2. CONSTANT PARTICLES Reference:
PRESSURE
COMBUSTION
OF AEROSOL
OF COARSE
MAGNESIL.qM
IN MICROGRAVITY Combustion
and Flame
118:262-280
The combustion
mechanisms
of clouds
(1999)
ABSTRACT
microgravity
environment
was used to create
large (100-300
lam diameter),
initially
flames,
of individual
panicles,
motion
simultaneously. Various
The experiments
image
the high-speed addressed.
analysis movie
zone into the unburnt flame
speed
flame
rate of less than 0.1 m/s. zone decreased to the cold entrained
gas that
Mg particle contained
was in the range
reported
pushed
ahead
to that
investigation.
Unburnt
pressure
reservoir
ballast
zones
due to oxygen
opposite
at the NASA
aerosol
could
Lewis
particle
be observed
Research
Center.
structure
at constant
and combustion
A
of relatively
of individual
on the flame
combustion
of 0,15-0,30
from
pressure
zones
metal
typical
was of the
particles
zones.
Also,
collective
propagation;
were observed
to the combustion
and the width significant
particles
particle
the
nature
to re-ignite chamber
of the combustion
motion
efficiently
number
eventually
of this
lag relative
however,
the particle
propagated,
at a slower
velocity
were,
Thus,
as the flame
with the microgravity
zone propagated
caused
The
and combustion
flame
returned
inertia
flame.
increased
deficiency.
of the
zone increased
Particle
of the
m/s, consistent
The combustion
The width of the pre-heat
and combustion
quenching
direction
in this research.
consisting
process
information
pre-heat
in the literature.
the flame propagation. was
combustion
to extract
structure
aerosol"
The development
aerosol
records.
by the hot gas in the pre-heat
in the pre-heat flame
during
particles.
and overall
are addressed
model
The pre-heat and combustion zones were identified by differences in of the emitted radiation. The velocity of propagation of the pre-heat
mixture
measurements
motionless
were employed
and video
volatile type aerosol flames. intensity and spectral content
particles
used the 2.2 s Drop Tower
procedures
The observed
of metal a "stationary
density
resulting
was observed motion
when fresh
needs
in
in the further
air from the constant
as it cooled.
2.1. INTRODUCTION Multiple multiple
panicle/droplet
particle
flame
flames
interaction
are ubiquitous
processes
in practical
are of great
combustion
practical
systems,
importance.
strong current interest experimental combustion
in interactive combustion phenomena. Numerous studies of liquid fuel drop arrays have been conducted
interaction
results
[1]. [2,3]
effects.
Recent
in this field were recently
experiments
with two adjacent
new
of flame
revealed
interactions,
Major
which
aspects
can either increase
liquid
interaction or decrease
droplets
burning
processes, burning
and the combustion stage. Interaction of solid fuel flames and for relatively low temperature flames [4-6]. Although interacting metal
summarized such
This explains
the
theoretical to determine
and the
in a comprehensive
under
microgravity
as "positive"
rates depending has been
and thus the
review conditions
and
"negative"
on the droplet
separation
studied
only for bulk samples
metals are widely utilized in solid propellants and in explosives involving multiple particles, no direct experimental studies of the burning metal particle interactions
andtheir effecton flamepropagationhavebeenreported.Apparently,this is dueto experimental difficulties associatedwith studying metal aerosolcombustionbehavior while simultaneously analyzingtheprocessesoccurringwith individual panicles.Individual particlebehaviorcannotbe opticallyresolvedin aburningmetalcloudbecauseonly,veryfine (1-10tamparticlesizerange)and relativelyheavily loadedmetalaerosolscan beignited andburned. Thus,only grossparameters describingcloudcombustionarerecoveredfrom aerosolcombustionexperiments.Thestructureof themetalaerosolflameis notusuallyexpectedtobehomogeneous, insteadit is anticipatedtoconsist of multiplesingleparticleflamesubstructures, i.e.,Nusselttypeof aerosolflame [7]. This structure, however,hasneverbeenexperimentally, identifiedfor metalaerosols.Therelationshipof thegeneral cloudflamestructureandcombustionscenariowith thespecificfeaturesof combustion of individual particles
could
individual
be better understood
particle
simultaneously metal
behavior
observed.
particles
because
Microgravity relatively
large
studied
using
particles
combustion.
densities
rather
Clouds
can be readily
many processes
which
non-metal
particles,
processes
are efficient
and temperature
those
participate
in further
composition are efficiently [16,17]. practical
formed
produced
during
presents
caused
[9-13]).
combustion
Both
(the transitions to non-uniform
combustion
the first
surface species
temperatures
experimental
and
results
of microgravity "model aerosols": in the microgravity environment.
size
4
fine metal
particle
fuel
number
investigation
are
in clouds Among
of
such
temperatures
[7,8] and
from heterogeneous
to vapor
the occurrence
products layer
charged
ionization
and
internal particles potentials
for the performance
of an investigation relatively
combustion
and the particle
for low metal
of
and intermediates,
during
and electrically
can be crucial
classified,
that there
sprays.
combustion,
combustion
the particle
affect particle interactions metal combustion.
during
of an actual
suggests
[14], are produced
[ 15]. Ionized
the
histories,
but do not occur
or in liquid
phase
originating
experimental
combustion
combustion
Different
condensed
features
by the high combustion
combustion
reactions.
at high metal
processes utilizing
This paper parameters aerosolized
multi-step
aerosol
can be
temperature
and with different detailed
of
particles.
particle
temperatures,
symmetric
jumps
as a nanoscale
are modified
These devices
during
spherically
allows
consisting
in a cloud
to the forces
many
metal
metal
metal
heat transfer
be
of large
In microgravity,
trajectories,
type particles which
aerosol"
experiments.
particle
will simulate
of burning
affect
could
aerosol
of such particles
combustion
metal
at lower
mechanism
and from
rnicroexplosions, including
burn
radiative
in the reaction combustion
aerosol"
of individual
significantly which
a "model
will be due exclusively
in microgravity,
understanding
to create
development,
by the interaction
characteristics
and burn a stable
Combustion
particle
with different
created
caused
Our current
changes
flame
combustion
to produce
so that both the
settling.
particles.
their motion
individual
were used in experiments,
cloud
opportunity,
in single
etc., in this "model
of the processes
phase
lam diameter)
Therefore,
transport,
common
it is impossible
a unique
developed
will not settle,
aerosol
the
size particles
of rapid gravitational
(100-300
smoke
and
However,
provides
methods
combustion.
if larger
of the combustion large
metal
particles
of
2.2. EXPERIMENTAL A. Objective
and approach
The
objective
of the experiments
is to create
a stationary
model
aerosol
of relatively
particles to stud), the development of individual particle flames, motion of individual overall aerosol combustion process. The experiment consists of the following steps: a)
aerosolizing under ignition
c)
simultaneous
of the aerosol
burning
experiments
ports,
schematic
utilizing
of both the entire
of the experimental
the 2.2 s Drop Tower
using acoustic
on top of the acoustic diameter,
combustion reservoir,
environment
heat source,
combustion
during
chamber
in turn,
The chamber's
exciter
and the behavior
back
Center,
to a large,
A metal to retain
mesh
to the approximately
line from the reservoir
rubber
membrane
exciter.
(filter)
pressure
is installed
Before
the combustion A sketch are 102x110x45 of 60x60x inserts. igniter
the end of the microgravity
chamber
is flushed
11 L acoustic
(to scale) mm.
of the combustion
However,
19 mm, is restricted Aerosol
wire
magnesium
is ignited
mounted particle
cloud
based paste that forms The typical
shape
view of a high-speed the camera experiments
in order
using
exciter
exciter
of the chamber heated
chamber.
combustion,
of the flame
To
the igniter
solid coating front that would
camera
both solenoid
(30x21
is shown
to make the flame
an electrically the
a refractory movie
chamber
in the middle
inside
experiment,
with an inert gas to quench
wire
capable
chamber. vessel
form
in the
valves
The
housing
is also about
a
1 m long.
a normallychamber to
are activated
in Fig. 2.2. The chamber optically
transparent,
by two transparent the
effect
was coated of withstanding
in microgravity
ram) are also shown
via 0.93
build-up
and
the reaction.
(30 W DC power)
minimize
which
The chamber
in the line between
in the combustion
to the acoustic
an
three gas-
11.3 L (3 gal) reservoir
to prevent
the particles
in which
windows,
from an acoustic
served
in Fig. 2.1.
0.5 liter chamber
floor is a silicone
reservoir
is presented
An additional miniature inert gas tank is connected to the combustion chamber through closed solenoid valve. A second solenoid valve is installed in a vent from the reservoir atmosphere.
of single
and built for the microgravity
with two Lexan®
transmitted
and connected The
the experiments.
is connected
Research
is an approximately'
oscillations
and the reservoir
The 0.93 cm diameter
Lewis
designed
and is equipped
1 m long tubing.
chamber
the combustion
apparatus
feedthroughs.
the powder
cm (3/8")
aerosol
apparatus
at NASA
It is built of aluminum
and two electrical
is mounted
in an oxygen-containing
a local high energy' density
part of the experimental
aerosolizes
panicles
Hardware
is created.
speaker.
using
observations
A simplified
aerosol
metal
particles.
Experimental
The central
diameter
and
microgravity,
b)
B.
100-300/am
large
panicles,
dimensions
a narrower
zone
13 mm thick Lexan®
100 tam diameter of tungsten
tungsten
oxidation
on
with a thin layer of a zirconiatemperatures experiments
in Fig. 2.2.
up to 2200°C. and the field of
The location
at which
has been focused, was varied from experiment to experiment (for example, in some a portion of ignition wire was included in the corner of the field of view), however the
sizeof thefield of viewremainedessentiallyunchanged.Thehigh-speedimagesconstrictedwithin this field of view (asshownin Fig. 2.2)havebeenusedto examinethe flamestructureandparticle motion,asdiscussed below. Becauseonlya smallportionof theflamewaswithin this field of view, thecurvatureandthechangesin theflameshapeoccurringduringtheexperimenthavenot affected noticeablytherecordedhigh-speedimagesof theflame. Thefield of viewof theregularspeedvideo cameranormallyincludedtheentire60x60 mm arearestrictedby the Lexan®inserts. Electroniccomponents mountedontheexperimentalrig includeanaudiogenerator,anaudio amplifier,a 12V DCdry cellbattery,andaregulatedpowersupplyfor heatingtheignition fusewire. In addition,the apparatusincludesa custom-builttriggeringcircuit. The diagnosticsusedin theexperimentsincludeda video cameraanda high-speedmovie camera.The videocamerawasusedto obtainanoverallpictureof the flame. To betterunderstand processesoccurringin the flamefront it wasdesirableto separateflameradiationbandsgenerated by theMgO andMg vaporsfromthe blackbodyradiation. In orderto do that,anadditionaloptical systemconsistingof two slightlytilted relativetoeachothermirrorsandtwo interferencefilters was installedin front of the video camerain certaintests. The two images,takenthrougha different interferencefilter each,werespatiallyseparated andrecordedin eachvideo-frame.In thatwayit was possibleto separateanddirectlycomparetwo radiationpatternsthatweremeasuredat exactlythe sametime. Interferencefilters for 500 and520nm wereusedto separatethe Mg andMgO vapor phaseradiationbands,respectively[18]. Thehigh speedmoviecamerawasusedto resolvedetailed particle trajectoriesandthe developmentof individual particle flamesusing both dark field and brightfield settings.In thedarkfield setting,theflamewasthesolesourceof light, andwith abright field setting,a tungstenlight bulb wasusedto illuminate the background,so thatparticles were visible independentof the flameluminosity. Preliminarynormal gravity testswereperformedto evaluatethe aerosolparticle number densityasafunctionofthefloor vibrationfrequency.Thenumberdensityoftheaerosolizedparticles wasevaluatedbasedon the measuredattenuationof 670nm laserradiation. A laserdiodeanda photodiodewith filter weremountedona linearslideoutsidethecombustionchamber;theycould be movedtogetherto different vertical andhorizontalpositions,andcould be removedprior to ignition to providea clearview for the video-camera. C.
Microgravity When
results
experiment a microgravity
in aerosolizing
oscillations
sequence test starts,
particles
of the chamber
in the combustion
floor is above
vibrations to aerosolize particles. so that the velocities of particles velocity (rl=l.8-104
of an airborne kJ(m-s)
particle for room
100 - 300 it.tm size range,
the acoustic
exciter
is turned
chamber.
Since
150 Hz, an interval
on for a 0.4 s interval
the frequency
of 0.4 s provides
that
of the acoustic
at least 60 complete
After the acoustic exciter is turned off, a time delay is provided decrease due to aerodynamic drag. The relaxation time, t, for the
9 " is t=(_pr)/(9rl)
temperature
the relaxation
[19], where
P is the particle
air), and r is particle time is in the range
radius.
of 0.05-0.48
density,
1"1is gas viscosity
For the Mg particles s. In the experiments,
in the the
ignition delayvariedfrom 0.2 to 0.3 s thatwassufficientfor decelerationof mostof the panicles. After the delay,the tungstenwire is rapidly heated(it reachesa temperatureabove 1000°Cin less than 50 ms, asmeasuredoptically) andthe aerosolignites. The entireaerosolcombustionevent usuallyoccurswithin 0.5-0.8s. After a time delayof 1.9smeasuredfrom thebeginningof the test, the solenoidvalvesareactivatedto flush thecombustionchamberwith aninert gasandquenchall post-combustionreactions. D. Metal
Powder
Used
Magnesium
was chosen
for the first group
of micro-gravity
experiments
since
it has been
shown previously that even 100-200 p.m size aerosolized magnesium panicles can be easily ignited [20]. Particles used in our experiments were purchased from Aldrich Chemical. The particle size distribution was determined using digitized video-images of particles taken with a camcorder equipped
with close-up
the range
of 100-550
100-320 sieves
lenses.
The camcorder
p.m, however,
more
resolution
was 20 p.m. Panicle
than 80 % of the particles
p.m. For a series of tests particles
were preliminarily
of 150, 180, 250, and 350 p.m opening
diameters
had diameters
size-classified
varied
in
in the range
of
using a set of precision
sizes.
2.3. RESULTS A. Preliminary
Normal
Preliminary to better
evaluate
it was found acoustic
experiments timing
this
dramatically.
range,
the
10%
density
amplitude
vibration
of the total
above
aerosol
was formed
oscillations
rubber
to ignite
used.
silicone
floor
chamber For
rubber
estimated
particles
more
Accordingly,
dropped
the
vibration
15 particle
attenuation
when
frequencies
floor
from
than
light
and
measurements,
study [21], it was estimated
be suspended
floor.
needed
in the combustion
of the
and a theoretical could
rubber
conditions
on the laser light attenuation 150 to 200 Hz were
of the silicone
loaded the
from
of the
amplitude,
particles
3 ram)
Based
ranging
the acceleration
the measured
(approximately
number
to define
tests.
with frequencies
Using
frequency,
were conducted
for microgravity
that the maximum
oscillations
exceeding
about
Gravit3, Experiments
that only diameters
measurements
determined that the magnesium particle number density decreased by a factor of 5 as the height increased from 55 to 80 mm from the chamber floor (the chamber could only be viewed through a window
above
approximately load could
the height
h=40 mm from the floor).
70 mm above
participate
the chamber
in the aerosol
floor,
ignition.
Since
the middle
of the igniter
only a very small fraction
Even
though
in these normal
wire was located
of the total particle gavity
mass
tests the particle
loading was much greater at the chamber floor, it was not anticipated that the flame would propagate downwards, due to buoyancy. It was found that to achieve ignition in these normal gravity experiments,
the total mass of the magnesium
g of magnesium amount height,
would
of oxygen
be needed
when 5 g of powder
level of the middle
to achieve
in the 0.5 L chamber. of igniter
was loaded
particles
loaded
an equivalence
Due
in the combustion
5 g, whereas
ratio of unity (g_=l) based
to the decrease
wire was only 0.075
had to exceed in the particle
chamber,
J1, corresponding
the particle
number
only 0.21 on the total
density
concentration
to approximately
with at the
20 particles
per cubic centimeter,or an inter-particle separationof about 0.37 equivalence greater
ratio (9 (estimated
(close Several
to visualize adhered Later
normal
flame
gravity
on, the multiple
in Fig. 2.2 shows spread
upward
Examination cloud
is illustrated
were conducted to heating
flame developed
ignited
which,
was only 0.34.
However.
revealed
and ignited
and burned
video-images
around
apparently
corresponding
using a high-speed
of the video-recordings prior
by high-speed
how the flame
vertically,
panicles)
The
it became
wire.
experiments
of the igniter-wire particle
process
of the igniter
ignition
propagation.
to the surface
development
for 200 lam diameter
to 0.7) at the bottom
mm.
the tungsten
was the result
that multiple
when
the wire
in the chamber.
presented wire
video camera particles
was heated.
The overall
flame
in Fig. 2.3. The first frame
(indicated
of buoyancy.
by a dotted
Later
line) and
on, as shown
on the
following two frames, the flame width increased at a rate of about - 0.1 m/s and reached up to 35-40 mm for 100-150 ms. The flame width was later observed to decrease and the entire lifetime of the visible
flame
compared
300-350
to the combustion
to the average it about
was around particle
4 times
ms prior
extinguishment.
time of single magnesium
size in the aerosol
shorter
to flame
particles
used) panicle,
than that observed
This
flame
in our experiments.
The
horizontal
width
of the flame
zone,
horizontal direction) vf=dw/dt, were derived zone at a fixed vertical level was measured,
w, and
could
(close
time in air is 80 ms [ 18], i.e.,
Based
panicles
can be
in air. For a 200 jam diameter
the combustion
on this comparison
concluded that not only, ignition and burn-out of a group of single particles wire, but also actual (even though limited) flame propagation into the aerosol experiments. After the flame extinguished, several time to time a cluster of panicles could ignite.
lifetime
still continue
the velocity
it can be
adjacent to the igniter was observed in these to burn, and from
of the flame
front
(in the
from a high-speed video-record. The width of a bright as indicated in Fig. 2.3. As can be seen from Fig. 2.3,
this width was somewhat different at different vertical levels due to curving of the flame zone edges. To choose the vertical level at which the measurements were to be made, the video-record was reviewed
and the level at which
of these earlier
measurements
are shown
for large particle
velocity
plot appear
B. Microgravit Micro__ravity
the curvature in Fig.2.4.
size magnesium
random,
to be minimal,
inferred
flames
oscillations
flame
was identified. velocity
is in the range
[20, 22]. Oscillations were observed
Typical
observed
results reported
in the flame
for all of the experiments.
3, Experiments aerosol
and mass
loadings
that only
0.7 g total
expenments,
The
aerosol
but similar
In the first series of drop-tower
propagation
appeared
were varied mass
in microgravity three
load
unclassified
from 0.65 to 5.4 g (0.21 was
(versus
size-classified
experiments, necessary 5 g needed
powder
lam, d2= 215-+35 Jam, and d_= 300-+50 Jam. were 0.7, 1.1, and 1.6 g.
g would
to achieve in the normal
fractions
(as-received) correspond
repeatable gravity powder
to q0=l).
aerosol experiments).
were used with particle
For each of these
Mg powder
It was found
ignition
and flame
In the following
diameters
fractions,
was used
dl= 165_15
the mass
loadings
Before Some
ignition,
of the
experiment, aerosolized unlike
particles
uniformly
the
aerosolized 3500 p.m.
adhesion that
in the
of the powder
diameter
Based
range
and
field optical
did not move
the equivalence during
Flame
Front
The anticipated
d, density
setting.
during
the
to the chamber
walls
our constant
pressure
burnt
the
9, and the total mass loading,
M,
and N = M/(r_ d39/6),
these
actual
expected
distances
distances
between
on the number
in the video-images,
experiments
experiments most
used,
Based
observed
This initial
gas while
volume
The
and floor.
chamber
]oading.
distance
the
were much greater, in the range of 700 inter-particle distances was most likely due
ratio qo in the microgravity
size and mass
between
on the loadings
of 85 to 260 p.m.
in the combustion
by the hot expanding as discussed below.
since of the
varied
equivalence
of be
in the range of 0.25
ratio,
unburnt
density it could
however,
gas was forced
panicles
stayed
did not out of the
in the combustion
Shape
Flame propagation through aerosolized magnesium particles in microgravity experiments significantly from that observed in normal gravity. After the igniter wire was heated, radiating
propagated
zone
through
to be electrically the normal
wire
Alternatively, directions
(flame
front)
the chamber heated
gravity
igniter
filters
to the windows
V = 0.5 L is the chamber
in the chamber.
on panicle
constant
differed
the
using the bright
experiments.
with an average
varied
particles
to 5 depending
General
visualized
particles determined from the video-images The discrepancy of the expected and actual
concluded remain
gravity
as/= (V/N) 'is, where
of panicles panicles
the aerosolized
chamber chamber,
were
to adhere
normal
particles
estimated
is the number
to partial
observed
discussed
distributed
can be roughly
bright
were
particles
and these panicles were excluded from the particle count. It was observed that the (i.e., observed to move) particles were scattered throughout the chamber quite uniformly,
the previously
between
aerosolized
experiments rather
than
the original
radiating
of closely
magnesium
vapor.
and MgO
radiation
spaced When
zone,
bands,
of individual
In most
the flame
away
from
(as those
shown
zone only appeared in these
flames,
video
was recorded
the luminous
zone
front was observed
However, at lower particle loadings, in the middle of the chamber.
shorter
continued in
around
experiments.
propagating
in different
recorded
without
2.5 a,b), one can see both bright spots
whether
or it was
indicative
fronts
front
observed
to widen
microgravity
In the video-images
in Figs.
to decide
particle
flames
the wire igniter
front was never
flame
speed
particle
on, this flame
it as
(Fig. 2.5b).
it hard
Later
even though the flame
split into several
speeds
making
individual
area behind
the luminous
front could different
normal
with no traces cases,
in which
to the igniter.
clark area behind
propagate
flame
parallel
a darker
Such
in front of the camera
and an extensive number
leaving
(Fig. 2.5a).
and with somewhat
installed
was formed
a
the flame filled
uniformly
using interference of the flame
front filters
front appeared
consisted with
of a
burning
separating
Mg
very uniform
(cf. Fig. 2.5c). to travel
through
it was also observed
9
the chamber
that the flame could
until it reached disappear
the wall.
(extinguish)
Structure
of the Flame
Front
Higher spatial resolution with a close focus lens. These different
for different
combustion
zones,
wavelength)
regions
flame images were produced using the high-speed camera images showed that both brightness and the dominating of the flame.
a separation
and green
(540
Assuming
of these zones nm central
that the flame
was attempted
wavelength)
consisted
by comparing
components
equipped color are
of pre-heat
and
the red (650 nm central
of the high-speed
color
video-
images of the flame (obtained by transferring the high-speed movie into the video-format). Green radiation was expected to dominate in the combustion zone due to the strong characteristic radiation bands
at the wavelengths
of 518 and 500 nm for Mg and MgO
pre-heat zone, where particles are expected to be closer to that of a gray-body radiator, The three color components for each (digitized) subtraction
video-image.
Color-Differential images
respectively
[23, 24].
blue, green, (C-D)
and red were digitally
images
from the respective
were then produced
green component
medium
(gray)
intensity
level.
Examples
corresponding C-D image are shown in Fig. 2.6. indeed consistently dominated in the brighter flame red radiation be referred
dominated below
pre-heat
zones
of such
a profile
indicates
were
radiation
as the combustion
were measured is shown
the same.
intensity
is above
The value
and pre-heat
using
intensity
The
was
greater
original
image
general
radiation
intensity
within
Temporal
intensity
when
was
when under
Widths
the
level
the values
radiation
intensity
into gray scale)
is also shown. pre-heat
(gray)
measured
and
and
by a dashed level
was greater
It indicates
zone,
marked
(indicative
profile
will
An example
of the red and green
the background
an intensity
flame
of the combustion
from the C-D images.
body radiation)
throughout
the
and
two parts of the visible
respectively. inferred
the black
the green
video-image
line
intensity
when
than green,
the red and it
of the Mg and MgO for the corresponding
a monotonic
essentially
increase
in the
continuous
radiation
also the particle
velocities,
zone.
Evolution visualization
Time-Differential between
between
images
regular
flame
is shown
that time period,
evolution
were constructed
recorded
appear
(similar
time interval
of an artificial
movie
(first
frames
For this T-D image,
gray.
10
The difference
to the C-D images)
":; for example,
An example
high-speed in Fig. 2.8.
and
digitally
at a known
video-frames.
two sequential
and then digitized), during
of the temporal
(T-D)
two flame images
for a pair of the sequential
did not change
profile
These
background
produced
For reference,
the combustion
For better
as a difference
level
than red.
(transformed
Flame
a difference
intensity
zones, profiles
A reference
to characterize
I r are the and Im_x/2
The C-D images showed that green radiation zone, and they also revealed that a region where
ahead of that zone.
in Fig. 2.7.
(assumed
the background
bands)
format
existed
the gray level on the C-D image
signals
artificial
always
of an original
separated
by the digital
images.
I d ascribed to each pixel in a C-D image was equal to Id=Im_]2+(Ig-Ir), where I_ and intensities measured for the same pixel in green and red component images, respectively, is a constant
In the
to be heated but not burned, the spectrum was expected and thus red radiation was expected to dominate.
of the video-signal,
of the red component
vapors,
T-D image
transformed
as
":=30 ms, produced
to the video-
"_=2.5 ms, and the areas that
in the position
of the flame
front
producedbrightanddarkzonesindicatingthedisplacementof
the leading
the flame,
by the time between
respectively.
yields the velocity dark zones shows of the various description,
zones
of the T-D images for identifying
perpendicular
the minimal
flame
pre-heat
zones
speed video-frames
contrast
in the combustion zone.
while
experiments
of such measurements,
visible
velocity
of the leading this velocity the luminous
The position
of the edge
using regular
a typical
the inferred
combustion
edge
zone
zone
almost
10 mm while
zone
edge of the combustion
using the first edge of
zone.
500 or 520 rim) showed dominated
radiation
The great
from the
of the combustion
for several One example
about velocity,
a value since
of 0.18
m/s. the
mixture.
Oscillations
in time for several filter.
Figure zone
in the combustion
to those observed pattern
2.10 and zone
for the velocity
of the flame propagation
of Figs. 2.9 and 2.10 shows This conclusion
for sequential
in Fig.
it indicates
edge of the combustion
similar
zone.
measured
lam) is shown
was also monitored
is further
C-D images.
that the
confirmed
An example
of such
increase (from 7-8 to 15-18 ram) in the preand pre-heat zones were within the camera of the leading zone
5 mm, indicating
11
were
a 500 nm interference
The oscillating
The displacement about
fluctuates
The comparison
constructed
zone
to the video-format.
zone propagates.
edge of the combustion
zone moved
better. both the
Therefore,
only evolution
of the leading
than the pre-heat
profiles
50 ms).
the leading
images,
the
and the dark zone observed
into the unburnt
through
profiles is shown in Fig. 2.11. It shows a substantial heat zone width during the time when both combustion field of view (approximately
zone
propagates
zone (Fig. 2.9).
slower
be observed
of the leading
1 g, 180 btm
20
0.20
w
UJ
O
tlJ
121 LIJ
IX,
O z
_J ki.
15
0.15
121 W _J
0.10
0
50
100
150
TIME, Fig. 2.9. Temporal
variations
200
10 250
ms
of the propagation
velocity of the leading edge
of the pre-heat zone and the flame width infrerred from the recored high-speed movie. The time "0" corresponds entered the camera field of view
30
to the moment the flame
(J_
pg-rng-r13
PDW
20 E
)
0.10 /
_o.os t-
_.
_'g °.°6E- c/ _
_'
0.04
/_
]10
/
oo2dX¢, [_ 0
o.oo__ ,_-0.02 W
i 100
0
I 200
I 300 TIME,
Fig. 2.10.
Temporal zone
variations
and distance
of the propagation this edge traveled
The time "0" corresponds
-
I 400
0 600
ms
velocity inferred
to the moment
I 500
flame
of the leading
edge of the combustion
from the recorded entered
31
the camera
high-speed
movie
field of view
run
2(_ frame
gCi, I00
profiles
TIME PRE-HEAT ZONE
100 ms
i.U .A :! l
COMBUSTION
O ZONE
•
>i(/) Z iii l
PRE-HEATZONE
Z iii
150 ms COMBUSTION ZONE
(J
0
5
10
15 LENGTH,
p
I
I
20
25
30
mm
Fig. 2.11. Intensity profiles measured for two C-D images visualizing structure of a magnesium
aerosol microgavity
32
35
the
flame at different moments
TIME, 50
0 75
100
,
ms
150
I
200
I
250
300
I
O
I
=m ol
eee"
E E d
70650
llJ
Q_
E "0 e= X
60 E E
E O e'O
Combustion
zone
leading
0
55 0
0
|
45-
[]
0
50i-
edge
[]
[]
0
e-
g_
e-
._
=m
40() []
O
35[, ] 1
[]
_
Combustion
zone
edge
S
I
I
F
I
I
I
I
2
3
4
5
6
7
8
9
FRAME Fig. 2.12.
trailing
Sequential
positions
zone in the magnesium r%malar speed
of the leading aerosol
video-record
33
and trailing
microgravity
profiles,
run Mg 27,
edges of the combustion flame determined
using
j253
_M gF,#,20
(57[:-200)
250 PREHEAT ZONE
200
op,,_
..4
a
150
100
oo
2: COMBUSTION
[.-
ZONE
POSTFLAME ZONE
2:50 i----I
I
0
I
50
0
f
100
I
150 TIME,
I
200
300
250
ms _'a tiffs3&33_
177) PDW
100
o,,,_
80
0.9 s)
cooled
air entered
the partially
the combustion burnt
aerosol
chamber
the entire pressure
as soon as the flame
in the combustion
chamber.
radiation Two optically tilted
mirrors
profiles
measured
showed,
consistently
dominated within
used, could
velocities
significantly
propagation
after propagation over a length of 20 - 30 mm rather than propagated through chamber, as the flames ignited after shorter delay times. Because the constant
extinguished.
using
particle
on flame
particles.
extinguished combustion
Flame
particles
have been essential would
speed
into the heat transfer
(t < 0.6 s) were
therefore, when
could gravity
of particle of particles
filtered and
along
the same
were simultaneously
as described
observations exists
An example
ahead
equation
using color of the flame
of the two intensity
is shown in Fig. 3.3. When comparing the intensities emissivity difference between the two wavelengths Planck's
above.
line in each of the two filtered
body radiation
flame zone.
of the flame filters,
with the previous
by the black
the brighter
images
interference
for the black body emission,
acquired images
differential whereas profiles
44
of the radiation
of the magnesium images
MgO radiation illustrating
flame
[2], that a zone dominates
this observation
of the two profiles, a correction for black body used should be taken into consideration. Using
the ratio of the radiations
and _2 is
in each video frame
Comparisons
at the two wavelengths
)_
where c.=1.436cm-K, andT is temperature.For )_z=510
nm and
approximately
from
radiation
from
signal
1.6 to 1.1 as the temperature
filtered
a 500 nm filter
through
increases
a 510 nm filter should
at low temperatures
noticeably
and that difference
should
_.,=500
1000
nm,
to 2500
the ratio K.
varies
Therefore,
exceed
the signal
filtered
become
almost
negligible
a
through as the
temperature increases. That agrees with the higher signal measured through the 510 nm filter ahead of the flame front (cf. Fig.3.3). In the combustion zone, the intensity measured for the 500 nm radiation radiation.
significantly exceeds that for the 510 nm radiation, indicative of the strong MgO band A combustion zone dominated by 500 nm radiation was observed to form in all the
microgravity MgO
combustion
products
Product
A dense
development
of a vapor phase
flame
in which
the
Size Distribution
cloud
produced
collection
indicating
were produced.
Combustion
smoke,
experiments
of the
of airborne
smoke
usually
in a vapor
powder
from
the
was observed
phase
flame
chamber
in the chamber
was not
floor.
after each experiment.
analyzed
Powders
and
collected
simply from
This
vented
prior
the chamber
to
after
combustion experiments were examined using an optical microscope. Feret diameter defined as the diameter of a circle having the same area as the object and computed as d_(4"area/rc) °5, was determined produce
for each particle particle
classified
size
distributions.
using sieves
Fig. 3.4. Even as compared coating
Combustion
Product
burns
particles
Surface
surface
dispersive
3.5 and close-ups and 60, in which (long
delays),
clean surfaces calibration collected Particles observed comparable surfaces
surface
delays
used
with
likely
are shown (virgin)
showed
layer
quenched that
to that detected of the particles
delay
attached
different
in single
in
size do not
and porous
used
delays
oxide
after
This
layers MgO
previously
surface particle
contained
particles
layer
EDS analyses MgO.
in
chosen
for the
1.05 and 0.95 particles
s
have
using standardless Surfaces
were
of particles
markedly
different.
of 0.4 and 0.1 s, respectively, is similar
to the oxide
experiments
amounts
on the surface
runs 56 and 57, in which 45
[1, 2]),
combustion high
contents
after runs 53, 56, 57,
magnesium
were used,
particles.
are shown in Fig.
samples
collected
delays
metal
oxygen
particles
"Virgin"
(Fig. 3.6a).
ignition
and burnt
Five particle
of stoichiometric
magnesium
surface
in the small
collected
particle
qualitatively
and particles
were used.
consist
(Fig. 3.6 b,d).
these
(size-
are shown
for the burnt powder
due to a thick
magnesium
in Fig. 3.6.
particles
respectively, particles
in which
a fibrous
the burnt
of unburnt
to compare
after both runs #53 and 60 with the ignition
on particles
particles
Compositions
of various
of 0.4 s (a typical
that these white
after experiments
Mg
and used to
powders
size is observed
morphology
views
with small size, white particles
collected
measurements
was
General
and 0.1 s (a short delay),
showed
are coated
the surface
were unburnt
ignition
unburnt
phase,
particle
and Elemental
0EDS)
samples.
of the particle
SEM and EDS analyses
in the vapor larger
This shift is most
Morphology
spectroscopy
layers of different
of both
ImageTool)
(see below).
An SEM was used to compare Electron
actively
magnesium.
on burnt
(UTHSCSA
distributions
a slight shift towards
to the original
produced
size
software
sizes of 180 and 250 jam), and the burnt
magnesium
Instead,
analyzing
The
with nominal
though
show a decrease.
with image
of oxygen,
of virgin
long delays
coating
[5].
EDS
generally
magnesium.
The
of 1.05 and 0.95
s,
respectively,wereused,wereindistinguishablefromthesurfacesoftheunburntparticles.However, EDS showedsignificant oxygen presencein surfacelayers (the depth of the electron beam penetrationis about2-3 gm) for mostof theseparticles(seeTable 1). Surfacemorphology'and oxygencontentdetectedfor particlescollectedafterruns56 and57 areverydifferent from anyof thequenchedsinglemagnesiumparticlesamplesanalyzedin an earlierresearch[5]. The internalelementalcompositionswereanalyzedusingEPMA for threecross-sectioned combustionproductsamples.Thesewerethesamecombustionproductsamplesfor which surface elementalanalyseswereconductedusingEDS"samples53,56, and60for whichtheignitiondelay, s in microgravity experimentswere 0.4, 1.05, and 0.1 s, respectively.EPMA oxygen content measurementswere calibratedusing a commercial MgO standardsample by C.M. Taylor. Magnesium
content
Chemical)
measurements
magnesium
observations
were calibrated
particles
of the particle
employed
surfaces,
quenched after runs 53 (see example after run 56 (in which a long ignition
using
in our
a thick
oxide
cross-sections
experiments. layer
was
of the 99 % pure
Consistent present
with
(Aldrich
the previous
on the surfaces
of particles
in Fig. 3.7 a and b) and 60, but not on the particles collected delay was used, see Fig. 3.8). The cross-sections revealed the
highly porous structure of the oxide layer as shown in Fig. 3.7 b. The particle interiors were metallic and, according to our analyses, contained essentially pure magnesium for most of samples 53 and 60.
Local
regions
with detectable
oxygen
maximum measured oxygen contents were measured in most of the particles used in the microgravity higher
oxygen
particles
content
from EDS,
be distinguished Table I. Sample
experiment
propagation
were
was observed
with the high oxygen/magnesium 1. Note,
that several
Mg were also observed
Summary of electron micro Time delay used in microgravity
the particles
also observed,
the
are shown in Table 1. Significantly higher oxygen contents from the sample 56, for which the longest ignition delay was
in Table
from the unburnt
inside
and a slow flame
is consistent
also shown
content
_robe analyses Maximum
test to
suppress particle motion, s
peak
oxygen-free
(cf. Fig. 3.2).
ratios particles
found
This
for these
that could
not
in this sample.
of magnesium combustion Oxide layer (yes/no)
oxygen content measured in
products Surface oxygen/magnesium peak
ratio (EDS)
cross-section (WDS), atomic %*
MgO
-
-
0.42
Mg Run 60
0.1
0.47
No Yes
0.05 0.42
Run 53
0.4
0.49
Yes
0.30
Run 57
0.95
-
No'"
0.20""
Run 56
1.05
3.26
No
0.20
Oxygen
detection
limit is approximately
"*Several
particles
coated
with
oxide
0.3 atomic were
detected.
% These
particles
were
not used
for surface
oxygen/magnesium peak ratio measurements. Combustion Products Bulk Compositions Combustion
products
of magnesium
collected 46
after
the microgavity
experiments
were
analyzedusing XRD. Four samplescollectedafter runs 53, 56, 57, and60 wereused(the same samplesthat wereselectedfor SEMandEPMA analyses).For reference,XRD spectrafor coarse magnesiumpowdersusedin our experimentswerealsocollected. Silicon powderwasusedasan internalstandardin theseanalyses.ThemeasuredXRD spectraareshownin Fig. 3.9. XRD spectra for runs53 and60 showedbothmagnesiumandmagnesiumoxidepeaks.This resultsupportsthe electronmicroscopyanalysesin whichoxidelayersweredetectedonsurfacesof particlesrecovered aftertheseruns. Asshownin Fig.3.9,onlymagnesiumpeaksappearedin theXRD spectrafor runs 56and57,for whichlongerignition delayswereusedandmeasuredflamevelocitieswerealsovery low. Thesensitivityof thesemeasurements for MgOis about1%. Theabsenceof oxidein products collectedafterrunswith longignitiondelaysdeterminedfrom XRD analysesis,also,consistentwith theelectronmicroscopyresultsthatshowedno oxide layersonparticlescollectedafterruns56 and 57 ("lonc," delays). 3.4.
CONCLUDING
REMARKS
Observations pre-heat
and combustion
microgravity, portions
zones
consistent
with
of the video-signal An
effect
observed.
through
propagation
speeds
detailed
Radiation
gas. When
became
using
interference
distinguished
results
based
on the flame the particle
less than predicted
appears
before
filters
have shown
in magnesium
on the comparison
showed
propagation
to the role speeds
through
to interpret
speed
aerosol of the
that the flames
green
and
in microgravity
the moving
were lower
by a simplified
propagating
to be necessary
measurements
phase Mg combustion produced by the vapor spectroscopic
can be optically the earlier
motion
to extinguish
modeling
structure
that this can be attributed
a steady
observed
flame
in red
[2].
of particle
It appears
transfer were
of the luminous
model
[8]. Such slow moving combustion
observations
strong MgO emission
play in the heat
than 0.1 m/s, the observed
the entire
these
particles
has been flame flames
chamber.
More
fully.
for all the flames,
indicative
of vapor
and MgO formation. In addition, a dense smoke (MgO) cloud, usually phase flame, was observed after all experiments. Despite this visible and
similarity
between
the "slow"
and
"fast"
flames,
the surfaces
of the combustion
product particles are markedly different. Powders collected after the experiments in which the flame velocities were low (i.e., those with long time delays) had no MgO layer and were indistinguishable by SEM from these "slow" measurements
particles
powder
by XRD
of the smoke oxide
inefficient
deposition
of the unburnt
collected
show MgO
produced
for the slow flames.
process
A higher dissolved the "slow" flames. Since
In addition,
(Fig. 3.9).
In "fast"
coating
on particles.
in the gas phase flame
It also appears
might not be the primary after the experiments
(Fig. 3.6, 3.8).
measurements
(Figs. 3.6, 3.7, 3.9) clearly
the deposition was
those
flame products
source
with shorter
reasonable of the thick time delays
MgO
was not detected
flames,
It thus seems
on the surface to suggest MgO layer and higher
clear that
of burning
that the oxide found
for
the SEM and XRD particles smoke
on the surfaces
observed
flame
of
speeds.
oxygen content was detected inside the oxide-free particles collected from in these experiments flame extinguished before propagation through the 47
entirechamber,it is suggestedthatthesecombustionproductsrepresentpartially burnedparticles thatwererapidlyquenchedduetoflameextinguishment.Thedifferencebetweentheseparticlesand thosecollected from "fast" flames is, therefore,in the completenessof their combustionand quenchingrate. Thepresenceof thethick oxide layeron thesurfacesandabsenceof oxygenin the interiors of particlescollectedfrom "fast" flamesis consistentwith the combustionmechanism includingthe formationof anMg-O solutioninsideburningparticlesthat saturatesandundergoes a phasechangeproducingthe MgO phase,as was previouslyproposedbasedon single particle combustionexperiments[5]. The absenceof a surfaceoxide layerandthe presenceof dissolved oxygeninsidethe particlescollectedfrom the "slow" flamesindicatethatthephasetransitionhas not occurredfor theseparticles,i.e., that the particles were quenchedbefore the solution has saturated. The resultsof this work indicate that the MgO formationmechanismvia the phase separationfrom Mg-O solutioncould contributemoresignificantlyto the formationof an oxide coatingthanthe MgO depositionfrom thevapor-phaseflame. 3.5.
REFERENCES
,
Dreizin,
,
Cleveland OH 1997, pp. 55-60 Dreizin, E.L., and Hoffman, V.K.,
3.
E.L., NASA
Dreizin,
C.H. Berman,
International ,
Dreizin,
6.
Pearse, NY,
°
o
9.
Baron,
International
Combust.
Combustion
R., and Hirano,
E.L., C.H. Berman R.W.B.,
Fourth
V.K. Hoffmann,
Micro_ravitv
Sun, J.H., Dobashi,
5.
CP 10194,
Flame
Workshop,
T., Combust.
A.G.
Cleveland
Combust.
Workshop,
(1999)
E.L., NASA CP 1999-208917,
Flame
The identification
Combustion
118:262-280
and E.P. Vicenzi
and E.P. Vicenzi
and Gaydon,
Microeravitv
OH
(in press, Flame
1999, pp. 216-218 1999)
(in press,
of molecular
.Fifth
1999)
spectra.
Halsted
Press,
1976 P.A., and Willeke,
K., Gas and Particle
Techniques
and Applications
New
pp. 179-206
York,
(K. Willeke
Motion,
inAerosol
and P.A. Baron,
Van
Nostrand
Principles, Reinhold,
(1993)
Ballal, D.R., Proc. R. Soc. Lond. A 385, pp. 21-51 (1983) Williams, F. A., Combustion Theor3,, Benjamin/Cummings California,
Measurement.
Eds)
1985
48
Publishing
Co., Menlo
Park
3.6.
FIGURES
Time
delay
= O. 1 s 0.4 s
S
10
0 0.0
I 0.1
I 0.2
I 0.3 TIME,
Fig.
3.1.
Magnesium tracking
flame
front
for experiments
the end of the silicone
with
determined different
oscillation
49
0.5
s
positions
floor
I 0.4
time and
using
threshold
delays
between
ignition
del-,.eioclty
4OO
PDW
\ \ \ \
o0
ESTIMATED
300
(Vo=500
E E
mm/s)
k
200
N
-
AVERAGE
FLAME
SPEED
\
O
\
.J
HA >
VELOCITY
k
>_k-O
PARTICLE
100 -
;TIMATED
0 0.0
BURNING
"" "" _ _
__
i
I
r
I
I
0.2
0.4
0.6
0.8
1.0
TIME
Fig.
VELOCITY
3.2. Average function are also
velocity of time
DELAY,
s
of the magnesium delay.
shown
50
1.2
Estimated
flame particle
propagation and
flame
as a velocities
profSO0-
] pDW
300 BURNT
UNBURNT
_41--AEROSOL
AEROSOL--'II_
250
200
__
_00 nm (MgO
band)
10 < "Tignition=2700
K
_
-_
_
---
°5I
I
I
q
r
F
I
C
I
0
100
200
300
400
500
600
700
800
TIME,
ms
Fig. 4.1. Computed
velocities
of unburned
61
gas as a function
of time
900
_PEN END 12 %_CLOSED
END, 1GN1TION
8 6
after ignition 80 ms
240 ms
_00 ms
4 2 0
FLAME
PROPAGATION
2
4
6
DISTANCE,
Fig. 4.2. Computed
8
cm
gas velocity profiles at different times
62
10
