:

RESEARCHMEMORANDUM”-””COMPARISON OF COMBUSTION RIMCTIVITY OF ETHYLDECABOWNE

FUELS WITH TYPICAL HYDROCARBON FUELS ON BASISOF

SPRAY FIAMMA BILITYLIMITSOF FUEL-RICH MISTSAND

CALCULATED LEAN-LIMIT FLAME TEMPERATURES

FOR FUEL VAPOR-AIR SYSTEMS

By PaulH. Wise andAbraham Lipschitz

LewisFlightPropulsionLaboratoryfl~s$lf!cuffonr-ne.-:lcd(or ch.i~r~d~LI,..~

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‘**~*-..... .. . . . . . . . . . . .. . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . ...*..... .“JGi;:.:2z2.Tb-;TF”*Y=7LNAT;OiiiL ADVISORYCOMMITTEE

FORAERONAUTICSWASHINGTONFebruary27,1957

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HADCADJ ‘57-1578

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IWC(lRME561L2.

NATIONALADVISORYC014KtTTENFOR9-.

AERONAUTICS

RESEARCHMEMORANDUM

COMPAIUSONOFCOMBUSTIONREACTIVJ3?YOF~ FUELSW13CH

T’YTICALHYDROCARBONFUELSONMKCSOFSPRAY~ LIKD!S

OFFUEL-RICHMISTSANDWUUIMWD LEAN-L= FLAME

~ FORFUELVAFOR-AIRSYSTIM

ByPaulH.WiseandAbrahamLlpschitz

SUMMARY

Thesprayflamebi.litylimitsofvarkmshigh-energyfielsandhy-9 drocerbonfuelsweredetermined~erimentalJyinanqpparatuswhich

measuredtheminimumpercentofoxygenbyvolumethatwouldpermittheignitionofa particularfuel.Thefluidsinvestigatedwereethyldeca-

: boranes,sliphatichydrocarbons,olefins,srcmatichydrocarbons,andesters.

Thesprayflammabilitylimitsoftheethyldecaboranefuelsrangefrom2 to5 percentoxygen,-eas thehydrocarbmfuelshavesprayftamabilitylimitsfram12to17percentqgen. Theethyldecabcmnefuelsburnedatlowerfuel-flowratesthanhydrocarbonfuelsofcompsza-blevolatility.

Lean-Mmitflametemperatureswerecalculatedfortheethyldeca-boranefuelsanddecaborane,andthevaluesarecomparedtothecorre-spondingvaluesforsomehydrocarbons.

INTRODUCTION

Thecurrentinterestinmmpoundscontainingboron,hydrogen,andcarbonasaircraftfuelscapableofprovidinggreateroperatingrangehasledtoextensiveinvestigationofthec-stion performanceandphysicalPrq*ies of thesefie~ tich are pertfienttotheirapplicationinaircraft.Somecouibustionstudiesofthesefuelsarediscussedinrefer-.ences1 and2. References3 to6 presentphysicalandchemicalpropertiessuchasthermalstabilityandmechanicalshockstabilityofvariousboron-carbon-hydrogenfuels..

I’MDCADJ’57““l578

2 col!wmEmIAL

.Thisreportdesuibesanemerimntalinvestigation

NACARME56L12

ofthereactiv-

.

ityofthese-fuelswith-en I&measuringthetiimm concentrateionof 8=Y6enrewed fiQ fuel-oqgen-tit~genmisttoperdtignitionofthefuel,

Anapparatusandtechniqueforneasuringtheminimumpercentofoxy-genrequiredforignitionofa fielmistaredescribedinreference7,andtheminimump=centofoxygenthusdetermined,qpressedaspercentofoqygenbyvolumintheoxygen-nitrogengasmixbure,isdefinedeathespr~ flamsibilitylimlt.Thistechniquewasqppliedtofourseqplesof gethyldecaboranefuelsendninehydrocarbonsof varioustypesandvolatil-Ities,andtheresultsarereportedherein.

Thelean-llmitflametemperature(flametemperatureforfuelvapor-airmixtureatflashpetit)wascalculatedfortheethyldemiboranefuelsanddecaborane.Thevaluesarecczuperedtothelean-limitflametemper-aturevaluesforhydro-bons(ref.8)asa meansofestimating theacti-vationenergyoftheethyldec~oranefuelsinrelationtotheactivationenergyforhydrocarbonfielsintheccmibustionreaction.

ANDAmmAmJs

Fuels

Theethyldecaboranefuelswerecommercialseqplessu~liedbytheBureauofAeronautics,DepartmentoftheNavy,aspartofProjectZip.ThecompositionsandsanepropertiesoftheethyldecdboranefuelswepresentedIntableI. Thehydrocarbons(tableI)werepreparedandpuri-fiedbytheJU(MorprocuredfromtheBuresnofStandards.Theethyl-acetatewasa comnercialsample.

Appsrattm . ,.

TheapparatususedinthisproJectLssimilartothatdescribedinreference7. Itconsistsofa horizontalconbustlonchember(fig.1)openattaneendandfittedwitha high-energysparkgap toignitethefuelmist.Theclosedendofthecombu8tlonchsnibersupporteda therm.coupletomeasurethetemperatureriseinthecoibustlonchsaiberandtheatomiztngnozzle(fig.2)forintroducingthefuelmist.Oxygenandnitrogenweremeteredtoa mixingchaniberfromwhichthisoxidant-gasmixtureflowedtothefuelatomizer(fig.5)whichintroducedthefuel-oxygen-nitrogenmisttotheconibustlonchdber.Theaxidant.gaamixturewassupplledtotheatomizerata pressureof18to28poundspersqp~einchgagewitha totalgasflowof9 tololitersperminuteatstandardtemperatureandpressure.Thefuelwasmeteredtotheatomizerby driv-ingtheplungerofa hypodermicsyringewitha constant-speedelectric

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caNFIRmTm

—,

NMA RME56L12 coNFIDmlTIAL 3. a

motor.Fuel-flawratesof2.6,4.7,or15.0millilitersperminute● couldbeobtainedby seL?ctingthepropersizesyringe.Themist

movedatdbout5.7to5.8centimeterspersecondinthecouibustlonch?miber.

Stainlesssteelwasusedfortheconibustioncheniberbecauseitwase~ectedtowithstand,betterthenbrass,thecmibinedcorrosiveeffectsoftheso13dproductsofconhstlonandthefrequentwashingtoremovetheseproducts.

Theignitionsystemwasa cotiinationofa high-voltagelow-energya-csparkoperatingat120sparkspersecondanda low-voltagehigh-energycontinuousd-cspark(similartoref. 9). A reasor&leestimatefortherateofenergydissipationatthesparkgapwouldbe 300joulespersecond.

q

B Thesyringewasfilledwiththefueltobetested.ThewaU tem-h peratureofthecofiusthncbiberwasbroughtto24°&.5°Cbytheflow

ofwaterintheJacket,andthepressureregulatorsweread$zstedattheoxygensndnitrogencylinderstogivethedesiredoxygen-nitrogenmix-

. ture.Thegaswasallowedtorunthroughthechauiberforabout45sec-ondsbeforethefielflowwasstarted.ThefuelflowwasInitiatedbystartingthemotortodrivetheplungerofthesyringeandopeningthefuelneedlevalveoftheatomizingnozzletothefullopenposition.Fivesecondsaftercommencingtheoperationoftheatomizingnozzle,thearcwasstartedandallowedtoburnforabout5 seconds.Anincreaseintemperatureofabout15°to20°C asindicatedbythethermocouplewastakenasa positivetestforignition.Afterthetest,thechamberwasthoroughlycleaned,andtheelectrodeswereremoved,cleaned,filed,andrespaced.

RESUUPSANDDISCUSSION

Thespr~flammabilitylimitsofseveral.ethyldecaboranefuelsweredeterminedbymasuringthemininwmpercentofoxygenrequiredforigni-tionofflowingfuel-~en-nitrogenmists.Thelean-ldmitflemetemper-aturesforthreessmplesofethyldecaboraneandforde=boranewerecal-culatedforthefuel-alrmixtureattheflashpointofthesefiels.ThedataandresultsarepresentedintablesIIandIII.Sprayflammsbilityltmitsarepresentedasa range,generallyof 2 percent.Thisrange. representsthereproducibilityoftheexperimentalresults.

.

ccmmENTm

HADC/UIJ’57-1578

4 NACAM E56L12C(m?mm.

~w FlemablMtyIdmits

Thesprayflammabilitylimitsshowa markeddifferencebetweenthe8

ethyldeceboraneendtheI@rocarbonfuels.Atequivalentfuel-flowrates(2.6~min) threeethylde-oranefuelsrequireonly2to5 percentoxy.genforIgnition,whereaseighthydrocarbonsendethylacetateregptiefrom11toashighas17percentmgen.

Dodecane,whichiscmqpa.%bleinvolatilitytotheethyldecaboraneftzels,reqtirednotonlymore o~gen butSJ.SOa muchMgh= fuel-flowrate forignitionInthisapparatus.Dc&canerequired12to14percent~6en -d a fielfl~ of~ ti~litersperml.nute,moret- 5 timesthefuelflowfortheethyldecdboranefuels.Aliphaticnormalhydro.carbonshigherinmolecularweightthsmA-nonanewouldnotigniteendburninthisqpparatusatfuel-flawratesof2.6or4.7millilitersperminute.Inallofthepositivetestsforbothhydrocarbonandethyldeca-borenefueb,cdbustionoccurredina fuel-richcondition.

Onesaqleofethyldecaboranefuel,56Z2,failedtoIgniteInthis6YStem,d.- cncygenConcentmtlonsashighas15percentandfuel– -flowsof2.6and4.7millilitersperminutewereused.A possibleex-planationmaybethehigherviscosityofthissampleandtheresultlng ●

poorersprayddstrlbutlonInccuqparisontothefuelswhichignitedsuc-cessfully.Theviscositiesoftheethyldemiboranefuelsaregiveninthefolloulngtable:

Fuel Kinematicviscosityat25°C,centistokes

56Z213.9(Uhpubllsheddata(Callery))55zl 6.1(Unpublisheddata(OlinMthleson))55Z7 6.01(Unpublisheddata(OllnMthieson)55Z6 6.4(Unptillsheddata)

Theviscosityof56Z2istwicethatofthethreeotherfuelssuqples.The

!!j

highviscositymeyhavehinderedtheatomizationof56Z2bythest~lenozzleusedinthese~eriments.

Comparisonsoftheflashpoints,spontaneousignition temperatures,andsprayflammabilityMmItsoftheethyldecaboranefuelsasa classwiththehydrocarbonfuelsmeasuredinthisinvestigationrevealnotrendsotherthantheMfferenceofthesprayflammabilitylimits.Thisdifferenceindicatesthattheethyldecdboranefuelsaremuchmorereac-ttveIntheccmibustionreactionthanl@rocarbone.

.

Lean-LimitFlameTemperatures ...

Thelean-limitflamet~turee fortheethyldecaboranefuels.

(5521}5527,and5526)anddecaboranewerecalculatedaccordingtothe

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NAM F/ME56L1.2 CONFIDENTIAL 5.

method ofreference10. Thefuelvapor-airmixture,calculatedfromthe* vaporpressureofthefuelsattherespectiveflashpoints(ref.11)~

wasusedasthemixturecompositionfortheleen-limltflame.Thekaluesofthelean-limitflametemperatureareincludedIntdbleIIIalongwiththoseforbenzeneandheptanefromref=ence8.

Reference8 statesthattheactivationenergyoftherate-determiningreactionina lean-limitflemeisproportionaltothelesn-limitflametmrature. Thelean-limitflametemperaturevsluesfordecdborane(696°K)andforthethreessmplesofethyldecaborane(725°,790°,snd879°K)areroughlyone-halfthevaluesforbenzene(1715°K)ed heptane(1980°K),whicharetypicalofthevaluesfor22hydrocarbonstnrtier-ence8. Itseemsreasonabletoassumethattheactivationen=giesoftheethyldec~orane fuels are elso about one-half the activationener@esofthehydrocarbons.A luwervalueofactivationenergyfortheethyl-decaboranefuelsagreeswiththeIncreasedconibustionreactivityandde-creasedsprayflammabilityllmitwhichhavebeenfound~erimntall.y.

SUMMARYOFRE8UILE● Theexperimentaldeterminationoftheminhmmpercentofoxygen(ex-

pressedasvohnepercentofthe-dant-gasmixtures)requtiedforigni-tion offlowing(5.7to5.8c#sec)fuel-oxygen-nitrogenmists,whena.fixedamountofelectricalenergyissuppliedintheformofa sperkdis-chargeinthemist,gavethefollowingresults:

1.Threesezqplesofethyldecaborenefuelsre@red 2 to5 percentoxygenby volume.

2.EighthydrocarbonsrequiredXlto17percent-en forthesamefuel-flowrateasfortheethylde-boranefuels.

3.Dodecane,whichiscomparableinvolatilitytotheethyldeca-boranefuels,requireda fuel-flowrate5 timesgreaterthan theethyl-decaboranefuelsaswellas12to14percentoxygenforignition.

4.OnessmpleofethyldecaboranefuelfailedtoQnltewitho~genconcentrationsasM@ e815percentandfuelfluwssomewhathigherthenthoseusedfortheotherethyldecaboranefuelsInthisprogram.

5.Calculatedlean-limitflemetemperaturesfortheethyldecaboranefuelsareqpproxbnatelyone-half the valuesforI@roc=bonfuelswMchsuggeststhattheconibustionactivationenergies=8 alsoaboutone-half

. theactivationenergiesofhydrocarbonfuels.

. LewisI?llghtRopuhionLaboratoryNattonelAdvisoryCozmnitteeforAeronautics

Cleveland,Ohio,Deceuiber12,1956

CONI?JDENTIAL

6

1.

2.

3.

4.

5.

6.

7.

8.

9.

coNFmIAL NAcARME56LI.2.

*

Olson,WalterJ.~ Breitwieser$Roland,- Gibbons~LouisC.: A Re-viewofNACAResearchThrough1854onBoronCcqmUndeasFuelsforJetAircraft(ProjectZip).NACARME55~l,1957.

Breitwies=,Roland,andUseller}JemeEI1?.:PtiormenceofPenta-borane,Pent~orane- JP-4FuelMixtures,andT&imethylborateAzeo-tropeFuelina N1-ScaleTurbojetEngine.NACARME56G19,1956.

McDonald,GlenE.: ThermalDecompositionofEthylpent~orsneinGasPhase.NACARME56D26,1.956.

i!j

McDonald,G.E.: ThermalStsbiQtyofIECaboraneandofa CcnmmrclalEthylDecaborane(HEF-3)IntheRangeof202°to252°C. NACARME56124,1956.

Sobieniak,M.G.,and!lhomaa}DelbertD.:”TheMechanicalShockSensi-tivityof~opylpenteborane(9).MCC-1023+CR-173,OlinMathiesonChem.Corp.,Dec.30,1955,(ContractNOa(s)52-1023-C,D@. Navy,Bur.Aero.) —

●

Tannetitmum,Stanley:A l&eliminaryInvestigationoftheThermalDe-._ositicm ofE%hyldecaborane.MCC-1023-TR-14O,Res.Dept.,OlinMathlesonChem.Corp.,Jan.1956.(ContractNOa(s)52-1023-C,Dept. -Navy,Bur.Aero.) — .-

Sullivan,M. V.~Wolfe,J.K.~ andZtsmm,W.A.: Flammabilityof theH@Ier BoilingLiquidsandTheirMists.. Ind. a@ E@. Chem.~ vol.39,no. 12,Dec.1947,~. 1607-1614.

Fenn,JohnB.: LeanFlanmuibilityLimitandMinimmSp~k IgnitionEnergy. Ind. andEng. Chem.,vol.43,no.12,Dec.1951,pp.2865-

—

2868.” .-

BrockmanjEmnk G.,andEochgesang,F.P.: ElectricalIgnitionofthespectrographicArc● Ind.andEng.Chem,,Analcd.,vol.14,no.10,Ott.1942,p.796.

10.Hall,EldonW.,andWeber,RichardJ.: TablesandChaZ%SforThermo-dy%micCal&lationeIn-kolvingAirandFuelsCou&inhgBoron,Cerbon,Hydrogen,andOxygen.NACARME56B27,1.956.

11.Rmanski,Barbara:Self-IgnitionTemperaturesandFlashPointsofSomeIUgh-EnergyFuels.NACARME56C16a,1956.

12.Rossinl,FrederickD.,etal.: SelectedVeluesofPropertiesofHy-arocsrbons. Circular461,Nat. Bur. Standards,NOV.1947.

.:..

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NACARME56LI.2 CONFIDENTIAL

13.Doss,M.P.: ~iti (hXlstantSOfthe~tiCipa,l~ocarbons.. Fourthed.,TheTexasCo.,1943.

14.Jackson,JosephL.: SpontaneousIgnitionTemp~atures. Conmercis,lFluidsand~ Hydrocarbons.tidoand~. Chin.,vOl.43,no.12,Dec.1951,pp.2869-2870.

7

15.Feldman,Julian;Myles,Mary,Wander,Irving,andOr&in,Milton:EvaluationofVacuumRectificationColums~UseofBinaryTestMixtures.Ind.andEng.Chem.,vol.41,no.5,May1949,~.1032-1036.

16. Lange,l?orbertAdolph:_ook of~~stry, Sev-enthed.,MOokPubl.,Inc.,1849,p.41.

17. Ftzrukawa, George T.,andPark,IUtaP.: HeatC~city,HeatsofFusionandV~orization,andVapor=essureofDacaborane(B@14).NBSRep.3612,U.S.Dspt.Commerce,Nat.~. Standards,July25,1954.

.

8 confidential NACARME56L12.

TABLEI.- coMPosmm ANDPRoPERm OFFUELS

Ftlel ~

a Sanrplenuniber

55Zl

55Z8

56Z2

BenzeneI’oluenep-Xylene~-Eexaneg-E@mneI-Octane~-llonane~Dodecanel.-HexeneRhylacetate

ComposIt ion

Monoethyl-decdmranej 95percentpure

Wnoethyl-decdmrane,99

Aercentpure

2 Monoethyl-decaboreae,l/3diethyldeca-borane

MtxedethylderlvatIvesofdecaboraneandpentaborane

9S+molepercent

Commercial

lollingtointat‘%n?&g

’283

%!20

%242

----

%0.1’110.6%8.3%8.7d98.4d125.6dl~.88215mg*3.5h77

Flashpoint)o~

%59

b73

b45

C65

‘-IL%0----‘-Me-2e13b33b78---h-b

SpontaneousignitIontemperature,

Oc

b123

%23

C147

f592f568’565f261f247f24(=Jfzzb----f272h486

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%alculatedboiliugpoint.Fueldeconrpose~belowboilingpointat760mm.

bRef.11.unpublishedNACAdata.%ef. 12.‘?Ref.13.fRefo14.%&. 15.%&. 16. —

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MA RME56L12 coNFmENTIAL.

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TABLEII.-SPRAYFLAMMABIIZTYIZMITS(E’FUEIS

Fuelnameor Fuelln$ec- l?uel-oxygenratio sprayflamnla-sampkumbertiunrate,MolarWeightPercentbiltty limit,

ml/tin stolchl-percentmetric oxygenin

geestreamHigh-energyfuele

55Z1 2.6 ‘ 1.0304.83 1445 2 -455Z7 2.6 .7823.66 mo 3 -555Z8 2.6 .8934.22 U?60 3 -456Z2 2.6 No Ignitionw

4.7 to15percentoxygen

Otherthanhigh-energyfueleBenzene 2.6 0.5001.22 375 14.-16

4.7 .7141.74 535 >MToluene 2.6 .4161.20 375 l%ls

4.7 .5551.60 500 17-Wp-xylene 2.6 ●333 1.10 350 14-M;-Eexane 2.6 .4251.14 11-13

4.7 .4171.li? 396 19&Heptane 2.6 .312 .976 343 14-15

4.7 .4761.49 523 16-18@ctane 2.6 ●244 .868 305 15-17n-Wnane 2.6 .2701.08 379 12-14

4.7 .4441.78 . 623 13-15@odecane ls.o 1.1.506.10 2130 12-14l-Hexene 2.6 .3841.01 346 B-3.5

4.7 .5401.42 486 17-18Ethylacetate 2.6 .5881.62 295 11-I.2

4.7 .7692.11 365 15-17

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caNFIDENTIAL

10 CONFIDENTIAL

T/i61WIII.- IZMM-IJMITFLAMETEMPERA-S

C!AUUIWZDFCIRCOMK)SITIONATFLASHPOINT

LFuel

Benzeneg-HeptaneDecaborsne

I 55ZI.I 55Z7

I 5528

Flashpoint,Oc

a-n

2%8+3%5

%ef..l3.bCalculatedfrominref.12.

%ef. 8.‘Ref.11.‘Catiuktedfr~inref.17.

Vaporpres-sureatflashpoint,mmHg

%0.45%0.02el.19f1●19fl.73

4

Fuel-airratioWeight

--------------0.00558.00666.00936.008411

Percentstoichi.metric

----------6.966.6012.0810.95

NACAI/ME56H2

Iean-llmttflametem-perature,

%

C1715c1880696725879790

vapor-pressure- temperatureequations

vqpor-pressure- temperatureequation

fCalculatedfromvapr-pressure- temperature;quationEavailableaaunp~lisheddata.

gun- lisheddata.

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m.gum 1. - Cdbwtitm Ckumber .

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