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a. REPORT
Exploratory Study to Determine the Ignition Properties and Combustion
Chemistry of Explosives Using Shock Tube Methods
14. ABSTRACT
16. SECURITY CLASSIFICATION OF:
We investigated the potential of a new experimental method for combustion studies of solid nano-particle energetic materials.
This new method is based on the recent development in our laboratory of an aerosol shock tube and its combined use with
laser extinction (for characterization of particle size and loading) and absorption diagnostics (for characterization of vapor
species). We accomplished three main objectives in this study: 1) we demonstrated the ability to load significant amounts of
solid materials into our aerosol carrier and deliver this aerosol into our shock tube; 2) we demonstrated laser-based diagnosticmeasurements of several key aspects of the ignition process of solid/liquid fuel systems; and 3) we characterized the effect of
U
1. REPORT DATE (DD-MM-YYYY)
4. TITLE AND SUBTITLE
01-02-2008
13. SUPPLEMENTARY NOTES
The views, opinions and/or findings contained in this report are those of the author(s) and should not contrued as an official Department
of the Army position, policy or decision, unless so designated by other documentation.
12. DISTRIBUTION AVAILIBILITY STATEMENT
Approved for Public Release; Distribution Unlimited
9. SPONSORING/MONITORING AGENCY NAME(S) AND
ADDRESS(ES)
6. AUTHORS
7. PERFORMING ORGANIZATION NAMES AND ADDRESSES
U.S. Army Research Office
P.O. Box 12211
Research Triangle Park, NC 27709-2211
15. SUBJECT TERMS
Aerosol Shock Tube, nano-aluminum, ignition delay times
D. F. Davidson, R. K. Hanson
Stanford University
Office of Sponsored Research
Board of Trustees of the Leland Stanford Junior University
Stanford, CA 94305 -
REPORT DOCUMENTATION PAGE
b. ABSTRACT
U U
c. THIS PAGE
2. REPORT TYPE
Final Report
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5c. PROGRAM ELEMENT NUMBER
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5a. CONTRACT NUMBER
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NUMBER(S)
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ARO
8. PERFORMING ORGANIZATION REPORT
NUMBER
19a. NAME OF RESPONSIBLE PERSON
19b. TELEPHONE NUMBER
Ronald Hanson
650-723-6850
3. DATES COVERED (From - To)
1-Apr-2007
Standard Form 298 (Rev 8/98)
Prescribed by ANSI Std. Z39.18
- 31-Dec-2007
8/2/2019 Fuel Combustion Study Using Nano Particles
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Exploratory Study to Determine the Ignition Properties and Combustion Chemistry of Explosives Using Shock Tube
Methods
Report Title
ABSTRACT
We investigated the potential of a new experimental method for combustion studies of solid nano-particle energetic materials. This new
method is based on the recent development in our laboratory of an aerosol shock tube and its combined use with laser extinction (for
characterization of particle size and loading) and absorption diagnostics (for characterization of vapor species). We accomplished three main
objectives in this study: 1) we demonstrated the ability to load significant amounts of solid materials into our aerosol carrier and deliver this
aerosol into our shock tube; 2) we demonstrated laser-based diagnostic measurements of several key aspects of the ignition process of
solid/liquid fuel systems; and 3) we characterized the effect of the addition of aluminum nano-particles on n-dodecane ignition under
conditions previously not studied.
(a) Papers published in peer-reviewed journals (N/A for none)
List of papers submitted or published that acknowledge ARO support during this reporting
period. List the papers, including journal references, in the following categories:
(b) Papers published in non-peer-reviewed journals or in conference proceedings (N/A for none)
0.00Number of Papers published in peer-reviewed journals:
Number of Papers published in non peer-reviewed journals:
(c) Presentations
0.00
Number of Presentations: 0.00
Non Peer-Reviewed Conference Proceeding publications (other than abstracts):
Number of Non Peer-Reviewed Conference Proceeding publications (other than abstracts): 0
Peer-Reviewed Conference Proceeding publications (other than abstracts):
D. E. Jackson, D. F. Davidson, R. K. Hanson, Application of an Aerosol Shock Tube for the Study of Nano-Energetic Material
Decomposition Processes, abstract submitted for Fundamental Combustion Processes Session of 44th AIAA/ASME/SAE/ASEE Joint
Propulsion Conference and Exhibit, 2007.
(d) Manuscripts
Number of Peer-Reviewed Conference Proceeding publications (other than abstracts): 0
Number of Manuscripts: 1.00
8/2/2019 Fuel Combustion Study Using Nano Particles
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Number of Inventions:
Graduate Students
PERCENT_SUPPORTEDNAME
David Jackson 0.25
Daniel Haylett 0.10
0.35FTE Equivalent:
2Total Number:
Names of Post Doctorates
PERCENT_SUPPORTEDNAME
FTE Equivalent:
Total Number:
Names of Faculty Supported
National Academy MemberPERCENT_SUPPORTEDNAME
Ronald Hanson 0.02 Yes
0.02FTE Equivalent:
1Total Number:
Names of Under Graduate students supported
PERCENT_SUPPORTEDNAME
FTE Equivalent:
Total Number:
The number of undergraduates funded by this agreement who graduated during this period with a degree in
science, mathematics, engineering, or technology fields:
The number of undergraduates funded by your agreement who graduated during this period and will continue
to pursue a graduate or Ph.D. degree in science, mathematics, engineering, or technology fields:
Number of graduating undergraduates who achieved a 3.5 GPA to 4.0 (4.0 max scale):
Number of graduating undergraduates funded by a DoD funded Center of Excellence grant for
Education, Research and Engineering:
The number of undergraduates funded by your agreement who graduated during this period and intend to
work for the Department of Defense
The number of undergraduates funded by your agreement who graduated during this period and will receive
scholarships or fellowships for further studies in science, mathematics, engineering or technology fields:
0.00
0.00
0.00
0.00
0.00
0.00
......
......
......
......
......
......
Student MetricsThis section only applies to graduating undergraduates supported by this agreement in this reporting period
The number of undergraduates funded by this agreement who graduated during this period: 0.00......
Names of Personnel receiving masters degrees
NAME
Total Number:
8/2/2019 Fuel Combustion Study Using Nano Particles
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Names of personnel receiving PHDs
NAME
Total Number:
Names of other research staff
PERCENT_SUPPORTEDNAME
David Davidson 0.10No0.10FTE Equivalent:
1Total Number:
Sub Contractors (DD882)
Inventions (DD882)
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REPORT DOCUMENTATION PAGEForm Approved
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1. AGENCY USE ONLY ( Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED4. TITLE AND SUBTITLE 5. FUNDING NUMBERS6. AUTHOR(S)7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONREPORT NUMBER 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)
U. S. Army Research OfficeP.O. Box 12211
Research Triangle Park, NC 27709-2211
10. SPONSORING / MONITORING
AGENCY REPORT NUMBER
11. SUPPLEMENTARY NOTES
The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an officialDepartment of the Army position, policy or decision, unless so designated by other documentation.
12 a. DISTRIBUTION / AVAILABILITY STATEMENT
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UL
NSN 7540-01-280-5500 Standard Form 298 (Rev.2-89)Prescribed by ANSI Std. 239-18298-102
Enclosure 1
1/31/2008 Final 4/1/2007-12/31/2007
Exploratory Study to Determine the Ignition Properties and CombustionChemistry of Explosives Using Shock Tube Methods
D. F. Davidson, R. K. Hanson
W911NF-07-1-0123
Stanford University, Office of Sponsored Research320 Panama Street, Stanford CA, 94305
We investigated the potential of a new experimental method for combustion studies of solid nano-particle energetic materials. Thisnew method is based on the recent development in our laboratory of an aerosol shock tube and its combined use with laserextinction (for characterization of particle size and loading) and absorption diagnostics (for characterization of vapor species). Weaccomplished three main objectives in this study: 1) we demonstrated the ability to load significant amounts of solid materials intoour aerosol carrier and deliver this aerosol into our shock tube; 2) we demonstrated laser-based diagnostic measurements of severalkey aspects of the ignition process of solid/liquid fuel systems; and 3) we characterized the effect of the addition of aluminumnano-particles on n-dodecane ignition under conditions previously not studied.
15Aerosol Shock Tube, nano-aluminum, ignition delay times
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FinalTechnicalReport
ShortTermInnovativeResearchProgram
AROGrant(STIR) W911NF0710123
ExploratoryStudytoDeterminetheIgnitionProperties
andCombustionChemistryofExplosives
UsingShockTubeMethods
Prepared
for:
DEPARTMENTOFTHEARMY
Dr.RalphAnthenienJr.,ProgramManager
FortheperiodApril1,2007December31,2007
Submittedby:
D.F.DavidsonandR.K.Hanson(PI)
MechanicalEngineering
Department
StanfordUniversity,Stanford,CA94305
January31,2008
HIGH TEMPERATURE GASDYNAMICS LABORATORYMechanical Engineering Department
Stanford University, Stanford CA 94305
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ContentsAbstract............................................................................................................................... 3Project
Description ............................................................................................................. 4
Introduction .................................................................................................................... 4AnInnovativeSolution:AerosolShockTube.................................................................. 4ResearchGoals................................................................................................................ 5
ExperimentalDescription ................................................................................................... 6AerosolGeneration......................................................................................................... 6LaserDiagnosticsMeasurements ................................................................................... 8BaselineIgnitionMeasurementswithNeatnDodecane............................................... 8EffectofNanoAluminumonnDodecaneIgnition ...................................................... 10IgnitionDelayTimeMeasurements.............................................................................. 12
Discussionof
Results
and
Conclusions ............................................................................. 13PotentialApplicationsofTheAerosolShockTubeMethod ............................................. 13
CurrentPublicationsBaseonThisStudy .......................................................................... 14References ........................................................................................................................ 14
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STIR:ExploratoryStudytoDeterminetheIgnitionPropertiesandCombustionChemistryofExplosivesUsingShockTubeMethods
D.F.Davidson,R.K.Hanson
MechanicalEngineeringDepartment
StanfordUniversity,Stanford,CA,94305
AbstractWeinvestigatedthepotentialofanewexperimentalmethodforcombustionstudiesof
solid nanoparticle energetic materials. This new method is based on the recent
developmentinourlaboratoryofanaerosolshocktubeanditscombinedusewithlaser
extinction(forcharacterizationofparticlesizeand loading)andabsorptiondiagnostics
(forcharacterizationofvaporspecies). Weaccomplishedthreemainobjectives inthis
study:1)wedemonstratedtheabilitytoloadsignificantamountsofsolidmaterialsinto
ouraerosol carrieranddeliver this aerosol intoour shock tube;2)wedemonstrated
laserbased
diagnostic
measurements
of
several
key
aspects
of
the
ignition
process
of
solid/liquidfuelsystems;and3)wecharacterizedtheeffectoftheadditionofaluminum
nanoparticlesonndodecaneignitionunderconditionspreviouslynotstudied.
These resultsprovide theDoDwith ademonstrationofanewmethod to investigate
solid/liquid fuelorexplosivemixtures, inparticular the influenceofnanoparticleson
combustion processes. We believe that this technique can be used for the study of
nanoparticleadditivestoliquidfuelsortononreactivecarrierliquids,aswellasforgel
like materials that can be converted into aerosol using ultrasonic spray nozzle
technology. Ourapproachpermitstheapplicationofanarrayofadvancedstateofthe
artlaser
diagnostic
systems,
developed
originally
for
gas
phase
chemistry
studies,
to
research problems of solid fuels. This present exploratory research program has
successfully demonstrated that these shock tube methods can be used to obtain
criticallyneeded informationaboutrapidlythermalizedexplosives. Wethusanticipate
thatouraerosolshocktubewillprovetobeanimportanttoolinfutureDoDresearchon
advancedpropellants,includinggelledandnanopropellants.
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ProjectDescriptionIntroduction
Amajorprobleminunderstandingthemechanismscontrollingtheexplosionsof
energeticmaterialsisthatthereiscurrentlynooptimalwayofprobingthedetailsofthe
firstdecompositionstepsofthetransitionfromsolidtogaseousphaseinthesesystems,
particularlyunderextremeconditions. Anaccurateassessmentofthenascentspecies
enteringthegasphaseduringthistransitionwouldprovideimportantkinetictargetsfor
constrainingandrefiningtheparticlecombustionmodels[1]. Thesetypesoftransient
species measurements have proven to be very difficult, though some progress along
these lineshasbeenmadeusing STMBMSmethods (simultaneous thermogravimetric
modulated beam mass spectrometry) by Rich Behrens and coworkers at Sandia
National Laboratories in the 1990s [2]. In those experiments the authors identified
major decomposition pathways for some explosive materials when the solids were
heated slowly. However, other methods which probe the dynamics of the interface
betweenthe
solid
and
the
gaseous
phase
are
needed,
particularly
those
that
can
operateundertheextremeconditionsoftemperatureandpressureandtherapidtime
framesfoundduringactualexplosions.
AnInnovativeSolution:AerosolShockTube
Webelievethatthesephenomenacanbestudiedusingshocktubemethodscombined
withlaserdiagnosticmethods. Weproposedtoexploretheuseofarecentlydeveloped
aerosolshocktubeandanexistingarrayof laserextinctionandabsorptiondiagnostics
forstudiesofsolid/liquidmaterials, inparticularnanoparticles/fuelmixtures,and the
transition from solid to gaseous phase in explosives. This new shock tube facility at
Stanforduses
aerosols
to
handle
liquid
and,
now
potentially,
solid
fuels
[3].
A
schematic
representationoftheoperationofthisaerosolshocktubeisshowninFig.1.
ReflectedShock Wave
T5, P5
IncidentShock Wave
EvaporatedAerosol Mixture T2, P2
Shock Tube Filled with Spatially-Uniform Aerosol Test Gas Mixture
Aerosol Mixture Evaporated Behind Incident Shock Wave
Test Gas Mixture Compressed to Reflected Shock Conditions
HeliumDriver
Aerosol Test GasDriven Mixture
T1, P1
Fig.1.Schematicofaerosolshocktubetechnique.
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Theaerosolshockworksbyallowingtheintroductionofnebulizergeneratedmistintoa
shocktube inaspatiallyuniformlymanner. Anyfluidorfluid/particlesuspensionthat
canbeconvertedintoamistbyanebulizercanbeusedasareactant. (Thisreactantfills
theshocktubeattheinitialtemperatureandpressure,i.e.T1,andP1. Ashockwaveis
generated intheshocktubebyrupturingadiaphragm inthedriversectionwithhigh
pressurehelium
gas
and
this
incident
shock
wave
propagates
down
the
shock
tube.
Dropletsformedbythenebulizercompletelyevaporatebehindtheincidentshockwave
at theelevatedconditions (T2,P2)and theevaporated fluid (vapor) rapidlydiffuses to
formauniformdistribution. Thereflectedshockwave(fromtheendwall)thenpasses
backthroughthetestmixture,compressingandheatingittothetargetedtemperature
andpressureconditions forcombustion(T5,P5). Opticalaccesstotheviewingsection
permitstheprobingoftheheatedtestgasmixturewithlaserdiagnosticsandallowsthe
measurement of species concentration time histories for species, such as OH, CH3,
benzyl,NO2,H2O,andothers,duringthecompleteignitionprocess.
ResearchGoals
Whatisofdirectandimmediateinteresttothestudyofsolidexplosiveschemistryisthe
applicationoftheaerosolshocktubetechniquetostudytheeffectofnanoparticleson
fuel mixtures. Only limited quantitative chemical kinetic data are available on the
influence of nanoparticles on kerosenetype fuels; most previous studies have been
concernedwithlargeraluminumparticles(microntomillimetersize).
Bazynetal. [4] investigatedtheburningofnanoaluminumparticles inshock tubes in
CO2/N2andO2/N2. Theycharacterized theburningtimeasa functionof temperature
andpressureandfoundthatnanoaluminumreactedatlowertemperaturesthan10um
particlesundersimilarconditions. At8atmandattemperatureslowerthan1400K,80
nmaluminum
particles
exhibited
light
emission
characteristic
of
burning
for
over
500
s.
Muelleretal.[5]investigatedaluminum/RP1slurrieswith60%byweightaluminumby
feedingtheslurryintoanonpremixedmethaneflame. Theyobservedrigidslurryshells
toformwhosecompositionwasafunctionofdiameter.
WongandTurns[6]investigatedaluminum/JP10slurrydropletsofdiameter500to110
microns(with4micronAlparticles)whichweresuspendedonmicrofibers. Theslurry
dropletswere largeenough that their ignitionmodel included several steps including
burnoff of the JP10, agglomeration/heating of the remaining aluminum, and finally
ignitionofthealuminumparticle. Ignitiontimeswereoftheorderof0.4seconds600
micronslurrydropletsinCO/10%O2/N2flamesat1800K.
Belonietal.[7]investigateddecanebasedslurrieswithmetallicadditives. Theyuseda
lifted laminarflameslurryburnerandstudiedAl,Al0.7Li0.3and2B+Tipowders. TheAl
particleswere15micronsindiameter. Theyobservedthatthealuminumparticlesdid
notburnintheflames.
In this study we have investigated the influence of aluminum nanoparticles on the
ignitiondelaytimesofasinglecomponentkerosene/jetfuelsurrogatendodecane. This
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6
was accomplished in three steps. 1) Wedemonstrated the ability to load significant
amounts of solid materials into our aerosol carrier and deliver this aerosol into our
shock tube;2)wedemonstrated laserbaseddiagnosticmeasurementsof severalkey
aspectsoftheignitionprocessofsolid/liquidfuelsystems;and3)wecharacterizedthe
effectoftheadditionofaluminumnanoparticlesonndodecaneignitiondelaytimes.
Oneof
the
key
accomplishments
of
the
present
study
was
to
demonstrate
that
we
can
suspend very finely ground solid energetic material particles (in these experiments
aluminum nanoparticles) in a solvent that acts as a carrier for these particles. This
solventcouldeitherbenonreactive(e.g.water)orpartofthefuelchemistry(inthese
experimentsndodecane). Ineithercase,this liquidwouldcarrytheparticlesfromthe
nebulizerintotheshocktube,andthenevaporatecompletelybehindtheincidentshock.
Whatwouldbe leftwouldbe thenanoparticlesofenergeticmaterials inagasphase
carrier(e.g.airandwatervapororairandgaseousfuelasinthecurrentexperiments),
uniformlydistributedspatiallyandshockheatedtotemperaturesandpressureswhere
we could study the chemistry. Using this method enables experiments that directly
investigatetheearlydecompositionchemistryofthesematerialsanddetectionofthe
initialgasphasedecompositionproducts.
ExperimentalDescriptionThecurrentexperimentswereperformed intheaerosolshocktubefacilityatStanford
University. Thedescriptionofthisworkisinthreesections: theoperationofthespray
nozzle,thelaserdiagnosticscheme,andtheignitiontimemeasurements.
AerosolGeneration
Wefoundthattheadditionofsolidnanoparticlestothe liquidaerosolsolventcarrier
significantly
reduced
the
aerosol
output
of
our
existing
disk
nebulizers.
To
maintain
higher aerosol loading levels, the disk nebulizers were replaced with a SonoTek
Ultrasonicspraynozzle. Aphotographoftheoperatingnozzle isshown inFig.2.This
devicecannebulizesuspensionswithupto40wt.%nanoparticles. Thisnozzleoperates
at 120 kHz and produces aerosol with number mean diameter of approximately 18
microns. ArepresentativesizedistributionisshowninFig.3.
Figure2. Sonotekultrasonicspraynozzleinoperation.
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7
Figure3.Volumesizedistributionplotforandodecaneaerosolproducedusingthe120
kHzSonotekspraynozzleatamassflowrateof200ml/hrandapowerof1.0watt.
TheSonotek
ultrasonic
spray
nozzle
was
installed
in
the
loading
chamber
located
immediatelyadjacenttothetestsectionofouraerosolshocktubefacilityinplaceofthe
disknebulizerassembly. SeeFigs4aand4b.
Figure4a(left).Schematicofsprayjetinstallationwithcoaxialbath(carrier)gas.
Figure4b(right).Photoofsprayjetinstalledonaerosolshocktube.
Thelargeraerosoldroplets(largernumbermeandiameter)producedusingthesprayjet
(thanwith the disk nebulizers) experience faster dropout rates due to gravity. We
characterized thesedropout ratesusing laserextinctionmeasurements (described in
thenext section.) A representative in situ life timemeasurement is shown in Fig.5.Basedonthesemeasurements,weanticipatedthatsuccessfulshockwaveexperiments
wouldrequireveryshort(lessthan10seconds)delaysbetweenfillingandbreakingthe
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8
diaphragm. We thus modified our experimental protocol to enable this type of
operation.
In the future we plan to upgrade this ultrasonic nozzle. Discussions with the
manufactureroftheSonoteknozzle indicate thatahigher frequencymodel (180kHz)
which will have a number mean droplet diameter of 10 microns, may soon become
available.
Theuse
of
this
nozzle
would
improve
the
aerosol
loading
levels,
as
well
as
reducetheamountofsettlinganddropout.
Figure5. Dodecaneaerosolsettlingrate. Miescatteringwasmeasuredusing670nm
diode laser extinction at preshock filling conditions similar to those of typical shock
waveexperiments.
LaserDiagnosticsMeasurements
Figure6showsthelaserdiagnosticsystemsusedintheshockwaveexperiments. Three
lasersystemsareused. Twodiode lasersat660and670nm (referredtoasthenon
resonant lasersystems)areusedtomeasuredropletevaporationandparticle loading.
OneHeNegaslaserat3.39microns(referredtoastheresonantlasersystem)isusedto
measurehydrocarbon (ndodecane in the currentexperiments)absorption. The3.39
micron absorption measurement is also used to measure fuel loading after droplet
evaporationbehindtheincidentshockwaves. Detailsoftheuseoftheselasersystems
toprobeshockwaveexperimentscanbefoundinRef.[3].
BaselineIgnitionMeasurementswithNeatnDodecane
Representativedatatracesfrombaselineignitionmeasurementswithneatndodecane
usingthenewjetnebulizerareshown inFig.7. The660nmextinctionmeasurement
location is 2 cm from the shock tube endwall; the 670 nm and the 3.39 micron
measurementlocationis5cmfromtheendwall.
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First,examiningthepressuretrace inFig.7,weseethatthere isastep inpressureat
2250swhichcorrespondstothearrivaloftheincidentshockwaveatthelocationof
theKistlerPZTsensor2cm fromtheendwall. Thenextset inpressureat~2340s
corresponds to the arrival of the reflected shockwave returning from the endwall.
Near3000s,thepressurebeginstoriseandatabout3220s,ignitionoccurscausing
thepressure
transducer
to
begin
to
ring.
Figure6. Schematicoflaserdiagnosticsetupforaerosolshocktube.
Next, examining thenonresonant 670nmdiode laser extinction signal and the 3.39
micronlasersignalswhicharebothlocated5cmfromtheshocktubeendwall,wesee
thatwhentheincidentshockwavearrivesatthislocationthepreshockextinction(670
nm)andpreshockextinctionandabsorption(3.39micron)signals(fromthepreshock
ndodecaneaerosolvapor/O2/argonmixture)jumpasaresultofthecompressionand
heatingby
the
incident
shock
wave.
The
3.39
micron
signal
rapidly
achieves
aplateau
level indicativeof complete evaporationof thendodecane,while the670nm signal
decaystozeroconfirmingthecompleteabsenceofdroplets. At2480s,thereflected
shockwavepassesthe5cmlocationandfurthercompressingthendodecanevaporas
indicatedbythestepinthe3.39micronabsorptionsignal;thisshockalsomomentarily
disruptsthe670nmdiodelaserbeamowingtobeamsteering.Near3220s,the3.39
micronsignalgoestozeroasthefuel(ndodecane)isconsumedatignition. Coincident
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with the ignition is a rise in CH* emission which is an indicator of the rapid radical
productionthatoccursduringignition.
Figure7. Representativedatatracesforndodecaneignition. Preshockconditions:T1=
295K,P1=201torr;incidentshockspeed:Vs=757.93m/s,fuelloadingXfuel=0.0021in
21%O2inargon;reflectedshockconditions:T5=1187K,P5=7.1atm,ignitiontime=793
s.
EffectofNanoAluminumonnDodecaneIgnition
Figure8showssimilardatatracesforashocktubeignitionexperimentwith5%or20%
by weight nanoaluminum particles added to the ndodecane aerosol. Several
significant differences are seen between this set of measurements and the neat n
dodecanemeasurements. ThealuminumnanoparticlesweresuppliedbySigmaAldrich
Chemicals: Aluminum nanopowder,99.5%,part#653608. These aluminumparticles
have an average diameter of 100 nm and a thin Al2O3 coating with a core of pure
aluminum.
Pressure:Thepressuretrace(blue) inFig.8showsamuch largerstepandmuchmore
suddenrise
in
pressure
at
ignition.
(The
pressure
signal
actually
goes
off
scale.)
This
is
coincidentwithashorterignitiontime,evenwhennormalizing(usingP1and
1)forthe
differenceinfuelconcentrationandpressureofthetwoexamples. Wehavefoundno
previous direct measurement of the influence of aluminum nanoparticles on the
ignitiontimesofkerosenetypefuels.
NonResonantLasers:Bothnonresonant(tohydrocarbonspecies)lasersignals(660and
670nm)showcontinuedconstantextinctionbehindthe incidentshockwaveafterthe
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complete evaporation of the liquid aerosol carrier, confirming the presence (and
allowingmeasurement)ofthenanopropellantloading. Thiscanbeseeninthe670nm
signal(black)from2180to2350sandinthe660nmsignal(pink)from2180to2250s.
Forboththesetwomeasurementsthereisalsoasignificantstepinextinctionafterthe
arrivalofthereflectedshockwaveat2350sforthe670nmsignalandat2250sfor
the660
nm
signal,
consistent
with
the
increase
in
density
across
this
wave.
Figure 8. Representative ignition experiment using ndodecane with 20% nano
aluminumby
weight.
Initial
conditions:
T1
=296
K,
P1
=223.4
torr;
incident
shock
speed
Vs=781m/s, fuelconcentrationXfuel=0.00550021 in21%O2 inargon;reflectedshock
waveconditions:T5=1197K,P5=9.53atm,ignitiontime=193s.
Theextinctioninthe660nmsignaldecaysafterthepassageofthereflectedshockwave
untiljustbeforeignitionwhenitrapidlydecays. Similarbehaviorisseeninthe670nm
signal at the 5 cm location, except that the blast wave from the ignition that occurs
upstream(atthe2cm locationandclosertotheendwall)rapidlysweepsbythe5cm
location and causes the rapid decrease in the 670 nm almost immediately after the
ignitioneventatthe2cmlocation. Aftertheignitionevent,bothofthe660and670nm
signalscontinue
to
show
absorption/extinction.
This
absorption/extinction
is
consistent
with absorption features of gaseous aluminum oxides near these wavelengths or
possiblywiththeappearanceofaluminumoxideparticles.
3.39 um Laser: After the passage of the incident shock wave, the 3.39 m laser
experiences both extinction from the aerosol droplets ane bare aluminum nano
particles,andabsorptionfromthendodecanevapor. AcalculationoftheexpectedMie
scattering of 100 nm nanoparticles at 3.39 microns indicates that only about 1%
8/2/2019 Fuel Combustion Study Using Nano Particles
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12
extinctionwillresultfromthenanoparticlesaftertheaerosolhasevaporatedandthus
themeasuredabsorptionafterevaporationiseffectivelydueentirelytofuelvapor.
The3.39micronlasersignal(blue)showsamorerapiddecaybehindthereflectedshock
wave than is seen in the neat ndodecane experiment, possibly owing to the
involvementofthealuminumnanoparticleswiththendodecaneoxidationchemistry.
Afterignition,
there
is
no
apparent
absorption,
consistent
with
acomplete
consumption
ofhydrocarbonspeciesandnotabsorptionbyaluminumoxides.
Emission:Thisrapiddecay inthe660nmsignalatthe2cm location iscoincidentwith
the strong rise seen in the 431 nm emission signal (green). This emission extends
throughthe ignitioneventwithaFWHMofapproximately80s. Noemissionpeak is
seenintheexperimentwithnoaluminumnanoparticles.
IgnitionDelayTimeMeasurements
Figure9showsasummaryoftheignitiondelaytimemeasurementsofneatndodecane
and
n
dodecane
with
aluminum
nano
particles.
In
this
figure
previous
measurements
in
ourlaboratoryofndodecaneignitiondelaytimesareshownasstandarddisknebulizer
C12H26[3]. Measurementsofneatndodecaneusingthenewjetnebulizerareshown
as Sonotekjet nebulizer C12H26. Measurements with 5% or 20% added aluminum
nanoparticles(byweight)arealsoidentified.
Figure9. Ignitiondelaytimemeasurementsofndodecaneandndodecane/NanoAl.
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13
At temperatures below 1175 K, there appears to be no significant difference in the
ignition times of ndodecane and ndodecane/nanoAl mixtures. Nano aluminum
shortenstheignitiontimesattemperaturesabove1175K. Thisisparticularlyevident
forthethreedatapointsnear1250Kwherethe ignitiontimesaresignificantlyshorter
than the ignition delay times of the neat ndodecane experiments at the same
temperatures.
DiscussionofResultsandConclusionsThepresentexperimentsextends significantly the rangeofcombustionconditions for
which mixtures of aluminum and kerosenelike fuels have been studied. Several
observationscanbemadeincomparisonwithpreviouswork.
Bazynetal.observedslowburning inpurealuminumnanoparticles(burningtimesof
greater than 500s at temperatures below 1400 K). Based on the same criteria of
burningtimesusedbyBazynetal. (emissionmeasurements)wefindburningtimesof
lessthan100snear1200Kinourndodecane/nanoaluminumignitionexperiments.
WongandTurnsobservedlongignitiontimes(oforder0.1to1second)forlargeslurry
droplets (oforder1000microns). The slurries investigated in thepresent studyhave
initialdropletdiametersoforder1020micronswith100nmaluminumnanoparticles.
Our laser absorption and extinction measurements indicate that these droplets fully
evaporate in timesoforder100sbehind incidentshockwavesandwhenheated to
~1200K,ignitedin100s.
The combustion regime studied in the current experiments is different than that
previously studied. Mueller et al., Beloni et al., and Wong and Turns studied larger
dropletsinflamegeometrieswheretheignitionprocessisacombinationofevaporation,
agglomeration,particle
heating
and
particle
flame
kinetics.
This
ignition
process
in
the
current study, we believe, is that of a dry aluminum nanoparticle in a high
temperaturegasphasebathofndodecane/21%oxygen/balanceargon,similartothat
ofBazynetal.butinanhydrocarbonfuelenvironment.
Usingtheaerosolshocktubemethod,thechemicalkineticsofnanoparticlesinreactive
fuel mixtures can be investigated without interference from other physicalchemical
processes. Thisisdonebyseparatelyevaporatingtheaerosoldropletsandthenheating
themtoignitiontemperatures.Thisavoidstheoverlapofevaporationphenomenaand
particleagglomerationprocessesthatcanoccurwithlargerdroplets. Severalexamples
oftheseexperimentsaredescribedinthenextsection.
PotentialApplicationsoftheAerosolShockTubeMethodThemainthrustofthisinitialeffortwastoestablishfeasibilityofusingtheaerosolshock
tube to study solid energetic materials. With this demonstrated, there are several
immediate and obvious problems currently of interest to the energetic materials
communitythatwebelievemeritinvestigation.
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14
1) RDX decomposition pathways and rates. Large uncertainties exist in the
decomposition chemistry of RDX [8]. Measurements of NO2 concentration time
histories(usinglaserabsorptionat472nm)couldprovideneededaccuratequantitative
measurementsofthedecompositionofRDXandrelatedcompounds.
2)Rapid testingofmixturesofenergeticmaterialsand reactive solvents. Ithas long
beenknown
that
the
decomposition
rate
of
energetic
materials
can
be
influenced
by
the addition of various agents. A comparison of the magnitudes of the effect on
decompositionrateofanenergeticmaterialbyvarioussolvents,bothreactiveandnon
reactive,canbemade inastraightforwardmannerusingtheaerosol loadingmethod.
Informationfromthesestudiesmayguidethedevelopmentofnewenergeticmaterials.
3) Relationship of ignition delay time to material properties. Ignition delay time
measurementsmayprovideasimpleindicatorofenergeticmaterialproperties[9]. An
initialsurveyoftheignitiondelaytimesofseveralestablishedenergeticmaterialswould
allowthisrelationshiptobestudied.
4)Extension
of
the
method
to
investigate
gel
propellant
components.
While
we
have
notyetdevelopedamethodtoconvertfullygelledpropellantmixturesintoaerosolsfor
shock tube loading, it should be immediately possible to study the combustion
propertiesofgelpropellantcomponentsdissolvedinsolventsorslurries.
CurrentPublicationsBaseonThisStudyD.E.Jackson,D.F.Davidson,R.K.Hanson,ApplicationofanAerosolShockTubeforthe
Study of NanoEnergetic Material Decomposition Processes, abstract submitted for
Fundamental Combustion Processes Session of 44th
AIAA/ASME/SAE/ASEE Joint
PropulsionConferenceandExhibit,2007.
References[1] T. R. Botcher, C. A. Wight, Explosive Thermal Decomposition of RDX, Journal of
PhysicalChemistry98:54415444(1994).
[2]R.Behrens,ThermalDecompositionofEnergeticMaterials:TemporalBehaviorsof
the Rates of Formation of the Gaseous Pyrolysis Products for CondensedPhase
Decomposition of Oxtahydrotetranitrotetraocine, Journal of Physical Chemistry 94:
67066718(1990).
[3]D.F.Davidson,D.C.Haylett,R.K.Hanson,DevelopmentofanAerosolShockTube
forKineticStudiesofLowVaporPressureFuels,CombustionandFlame,inpress.
[4]
T.
Bazyn,
H.
Krier,
N.
Glumac,
Combustion
or
Nanoaluminum
at
Elevated
Pressure
andTemperatureBehindReflectedShockWaves,CombustionandFlame145:703713
(2006).
[5] D. C. Mueller, S. R. Turns, Some Aspects of Secondary Atomization of
Aluminum/HydrocarbonSlurryPropellants,JournalofPropulsionandPower9:345351
(1993).
[6]S.C.Wong,S.R.Turns, IgnitionofAluminumSlurryDroplets,Combustion,Science
andTechnology52:221242(1987).
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15
[7] E. Beloni, V. K. Hoffman, E. L. Dreizin, Combustion of DecaneBased Slurries with
MetallicFuelAdditives,45th
AIAAAerospaceScienceMeetingandExhibitJanuary2007
RenoNV.
[8] M. M. Kuklja, Chemical Decomposition of Solid Cyclotrimethylene Trmitramine,
ComputationalNanoscience,ISBN0970827539(2001).
[9]W.
Anderson,
ARL,
personal
communication
2007.