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JID:PROCI[mNS;August23,2020;9:25]
ProceedingsoftheCombustionInstitute000(2020)1–10
Experimentalflatflamestudyofmonoterpenes:Insights
intothecombustionkineticsofα-pinene,β-pinene,and
myrcene
a,∗bac
ThomasBierkandt,MartinHoener,NinaGaiser,NilsHansen,
ab
MarkusKöhler,TinaKasper
aInstituteofCombustionTechnology,GermanAerospaceCenter(DLR),Pfaffenwaldring38-40,70569Stuttgart,Germany
bMassSpectrometryinReactiveFlows,IVG,UniversityofDuisburg-Essen,47057Duisburg,Germany
cCombustionResearchFacility,SandiaNationalLaboratories,Livermore,CA94550,USA
Received7November2019;accepted7June2020
Availableonlinexxx
Abstract
Pinenesandpinenedimershavesimilarenergydensitiestopetroleum-basedfuelsandareregardedas
,butinformationontheircombustionkinet-
,flatpremixedflamesoftheC10H16monoterpenesα-pinene,β-pinene,
andmyrcenewereinvestigatedbysynchrotron-basedphotoionizationmolecular-beammassspectrometry
(PI-MBMS)attheAdvancedLightSource(ALS).Thistechniqueallowsisomer-resolvedidentificationand
-samplingmolecular-beam
ofitsknownformationduringβ--
compositionstepsofthefuelsprovideimportantinformationforthedevelopmentoffuturechemicalki-
theunimolecularcleavageofthecarbon-
decompositionsbyβ-scissiontostablecombustionintermediatessuchasisoprene(C5H8),1,2,3-butatriene
(C4H4)orallene(aC3H4)-
carbonsintheβ-pineneflameareclosertothemyrceneflamethantotheα-
andthedirectidentificationofmyrcenebyitsphotoionizationefficiencyspectrumduringβ-pinenecombus-
tionindicatethatβ-
speciessuchasphenylacetylene(C8H6),styrene(C8H8),xylenes(C8H10),andindene(C9H8)couldbeclearly
identifiedandhavehigherconcentrationsintheα-,ahighersootingtendencycan
ofthethreemonoterpenesα-pinene,β-pinene,andmyrcenegiveinsightsintotheircombustionkinetics.
©.
Keywords:Monoterpene;Pinene;Biofuel;Photoionization;Molecular-beammassspectrometry
∗Correspondingauthor.
E-mailaddress:thomas.******@().
/
1540-7489©.
Pleasecitethisarticleas:,.,Experimentalflatflamestudyofmonoterpenes:
Insightsintothecombustionkineticsofα-pinene,β-pinene,andmyrcene,ProceedingsoftheCombustionInstitute,
/
ARTICLEINPRESS
JID:PROCI[mNS;August23,2020;9:25]
,./ProceedingsoftheCombustionInstitutexxx(xxxx)xxx
-pinene/benzene/air
Overthepast25years,theglobalproductionenergies[10]andlaminarburningspeeds[11]are
ofbiofuelsasanalternativetofossilfuelsforthealsoavailableforα-pinene/
transportsectorhascontinuouslyincreased[1]-pineneis
theyenableareductionofCO2emissionsandothersuitableforgasolineengines,butobservedsoot
aviationfuels,.,ahighenergydensityandaandEUROVfuelstandards[12].
lowfreezingpoint[2],typicallyrestrictthedirectEarlypyrolysisstudiesofpinenesshowedthat
useofconventionalbiofuelsasanalternativetobothα-pineneandβ-pineneisomerizetodifferent
petroleum--C10H16speciesincludingtheacyclicmonoterpenes
ciallyavailablebiojetfuels,.,hydroprocessedes-alloocimenefromα-pineneandmyrcenefromβ-
tersandfattyacids(HEFA)orfarnesane,aresuit-pinene[13,14].Burwellpublishedamechanismex-
ableasdrop-incomponentsforJetA-1usedinplainingtheformationoftheobservedisomeriza-
civilaviation,whilealternativestopetroleum-basedtionproductsduringthepyrolysisofpinenesviadi-
fuelswithevenhigherenergydensitiesforpower-radicaltransitionstates[14].Recentstudiesonthe
intensiveaircraft,rockets,-pineneproduces
Forsuchapplications,thepinenedimers,whichmainlyalloocimeneandlimoneneandβ-pinene
haveasimilarenergydensitytothetacticalfuelmainlylimonene,myrcene,and-limoneneviadi-
JP-10,couldbeapromisingalternative[3,4].Hy-radicaltransitionstates[15,16].Figure1shows
drogenatedpinenedimers(C20H34)weresynthe-thestructuralformulasofC10H16isomersformed
sizedinhighyieldbydimerizationofβ-pineneandduringpyrolysisofpinenesbyopeningthefour-
subsequenthydrogenationoverPtO2duringchem--
icalcatalysis[3].Highestyieldsofmorethan90%cyclicterpenesareformedbyhydrogenshiftreac-
werereachedwithNafionascatalystandareactiontionfromthebiradicals,whileformationofthe
timeofsixhoursat100°Candatmosphericpres-acyclicterpenesneedsC–Cbondscissionandin-
sure[3].-tramolecularradicalrecombination[15].Foral-
drogenatedterpenedimersaspotentialhighenergyloocimene,fastisomerizationfromtheacyclicβ-
densityfuelsfromα-pinene,twootherterpenes,ocimeneisassumed[16].
andturpentinebyselectivedimerizationandsubse-Inthiswork,thefirstquantitativespeciation
quenthydrogenation[4].Thehighviscosityofsuchdatasetofcombustionintermediatesfromflatpre-
terpenedimerspreventstheiruseassinglefuelcom-mixedlow-pressureflameswithα-andβ-pinene
ponent,but50:50blendswithconventionalfuels,,thecombustionof
.,JP-8andJP-10,haveacceptableviscosityevenmyrcene,whichisconsideredasthemainpyroly-
atlowertemperatures[5].Apromisingmethodforsisproductofβ-pinene,-
obtainingpinenesasprecursorsforpinenedimersicalstructuresofthethreeinvestigatedC10H16
fromreadilyaccessiblerawmaterialsisthesynthe-.
sisofpinenesfromconversionofglucosebyengi-
neeredEscherichiacolibacteria[6].Currently,the
yieldislow,.,%
thetechnicallypossibleyield,anditmustincrease
toatleast26%tobeaneconomicalalternativetoThreestoichiometric(=),flatpremixed
JP-10[6].flamesofthethreeC10H16isomers(-)-α-pinene
Pinenes(C10H16)areunsaturated,bicycliccom-(Sigma-Aldrich,≥97%),(-)-β-pinene(Sigma-
,≥97%),andmyrcene(Sigma-Aldrich,
haveasimilarenergydensitytoconventionaldiesel≥95%)wereinvestigatedattheAdvancedLight
[6].Pinenes,alsoknownasmonoterpenes,(2slmAr,
simplestterpenesandconsistoftwoisoprenebuild-,)withacoldgas
,.,α-.
β-pinene,exist,butα-pineneisthemoreabundantFlameswerestabilizedat30mbaronaMcKenna
-
().-beammass
ofpinenesisturpentine,whichismainlyobtainedspectrometryexperimentisdescribedindetailin
bytappingpinesorasaby-productofpapermak-[17]
ing[7].evaluationprocesstoobtainspeciesmolefraction
Previousinvestigationsonthecombustionofprofilesisalsodescribedinthesupplementary
thecombustionpropertiesofα--measuredphotoionizationefficiency(PIE)spectra.
mumignitionenergies[8]andthelaminarburningUncertaintyofcalculatedspeciesmolefractionsis
speedsaswellastheMarksteinlengths[9]wereestimatedtobe15–20%formainspecies,30–50%
Pleasecitethisarticleas:,.,Experimentalflatflamestudyofmonoterpenes:
Insightsintothecombustionkineticsofα-pinene,β-pinene,andmyrcene,ProceedingsoftheCombustionInstitute,
/
ARTICLEINPRESS
JID:PROCI[mNS;August23,2020;9:25]
,./ProceedingsoftheCombustionInstitutexxx(xxxx)xxx3
-andβ-pineneformedbydiradicaltransitionstates.
forintermediatespecieswithmeasuredphotoion-compositionofthegasphasemixturesisidenti-
izationcrosssections(PICS),-
2–,theexhaustgastemperaturesandtheexhaust
unknownPICSwerequantifiedfromscansnotgasconcentrationsofthemajorspeciesshould
sothattheirestimatedPICSfromchemicallyseveralterpenesincludingthethreeinvestigated
Uncertaintiesinflame-samplingMBMSwereHawkinsandEriksen[20].Thevaluesatstan-
furtherdiscussedin[18].-pinene,
weremeasuredintheflameswithatypeRther--pinene,
mocouplecoatedwithSiO2tominimizecatalyticformyrcene[20]andarethereforeclosetoeach
,volumetricheatofcom-
thetemperaturedependenceofthesamplingratebustionofJP-10,practicallyasingle-component
throughthesamplingnozzle[19].Uncertaintyoffuel(exo-tetrahydrodicyclopentadiene)andaniso-
thetemperatureprofilesisexpectedtobe5–10%.merofthethreeinvestigatedterpenes,isabout7%
higherthanforthepinenes[3].
Profilesofthemajorspecies(Ar,H2,H2O,CO,
,O2,andfuel)weredeterminedexperimen-
tallyforthestoichiometricα-pinene,β-pinene,
Understandingofthecombustionchemistryandmyrceneflames(fordata,seesupplementary
ofmonoterpenesbecomesofscientificimportancematerial).Asexpected,themolefractionprofiles
duetotheincreasinginterestinbiomass-derived,areverysimilarforallthreeisomersandmeasured
.
aboutthedecompositionofthethreemonoter-Differencesintheexhaustgasconcentrationsat
penes,.,α-pinene,β-pinene,andmyrcene,and30mmarebelow10%exceptforhydrogen,whose
theformationofcombustionintermediates,flamesmolefractionisverysmallcomparedtothemole
-resolvedfractionofH2O(ratioofabout1:10).Deviations
speciationdatacanalsobeusedasastartingpointinthemolefractionofH2O,whicharewithin
thermalmassflowcontrollers,leadtosignificant
,when
Thethreeinvestigatedfuelshavethesameel-differenceisobservedforthemolefractionprofiles
α
ementalcomposition,.,C10H16,andtheinputofthefuels.-Pinenedegradesatslowerrate
Pleasecitethisarticleas:,.,Experimentalflatflamestudyofmonoterpenes:
Insightsintothecombustionkineticsofα-pinene,β-pinene,andmyrcene,ProceedingsoftheCombustionInstitute,
/
ARTICLEINPRESS
JID:PROCI[mNS;August23,2020;9:25]
,./ProceedingsoftheCombustionInstitutexxx(xxxx)xxx
:α-Pinene(α);Red
symbols:β-Pinene(β);Greensymbols:Myrcene(M).
thanβ-pineneandmyrcene,
completelyconsumedataheightabovetheburnertheallyliccarbon