use of methanol as a transportation fuel - mefco2 · 2017-05-04 · use large amounts of methanol...
TRANSCRIPT
Use of Methanol as a Transportation Fuel
Prepared for:
The Methanol Institute4100 North Fairfax Drive
Suite 740
Arlington, VA 22203
November 2007
Prepared by:
Richard L. Bechtold
Marc B. Goodman
Thomas A. Timbario
Alliance Technical Services Inc.10816 Town Center Blvd., #232
Dunkirk, MD 20754
Table of ConTenTsNovember 2007
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Table of Contents
I. ExecutiveSummary..................................................................1II. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3III. MethanolBlendRegulation...........................................................4
A. UnitedStates ....................................................................41. EPAWaiversGrantedandOxygenateAllowancesas“SubstantiallySimilar”. . . . . . . . .42. EPADenials/RevocationsofWaiversatHighAlcohol/OxygenLevels. . . . . . . . . . . . . . .63. UseofMethanolinU.S.Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
B. UseofMethanolBlendsintheEuropeanUnion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8IV. MethanolUseinFlexibleFuelVehicles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9V. MethanolBlendPhysicalandChemicalPropertyImpacts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
A. VaporPressure.................................................................12
B. WaterTolerance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
C. MaterialsCompatibility .........................................................14
D. OxygenContent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
E. OctaneValue...................................................................18
VI. MethanolBlendVehicleOperationalImpacts...........................................19A. Cold-Start .....................................................................19
B. Driveability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
C. Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
D. FuelEconomy ..................................................................21
VII. EmissionsImpacts ..................................................................22A. PrimaryRegulatedExhaustEmissions.............................................22
B. CarbonDioxideEmissions .......................................................24
C. Toxics .........................................................................25
D. EvaporativeEmissions...........................................................25
E. “Well-to-Wheel”GreenhouseGases ...............................................26
VIII.InfrastructureImpacts ..............................................................29A. Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
B. Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
C. ServiceStations.................................................................30
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IX. MethanolUseinDieselHeavy-DutyVehicles...........................................33A. UseofMethanolinBlendswithDieselFuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
B. UseofMethanolinEmulsionswithDieselFuel .....................................33
C. UseofMethanolthroughFumigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
D. UseofMethanolinDualInjectionEngines.........................................34
E. UseofMethanolwithIgnitionImprovers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
F. UseofMethanolinDieselEnginesusingCompressionIgnition.......................35
X. Non-RoadEnginesandVehicles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36A. SmallEngines ..................................................................36
B. LargeEngines ..................................................................36
AppendixA.PropertiesandCharacteristicsofImportanceforFuelSpecifications. . . . . . . . . . . . . . .38A. PropertiesofConcernforLowLevelMethanolBlends ...............................38
B. PropertiesofConcernforHighLevelMethanolFuels(e.g.,M85)......................41
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
I. exeCUTIve sUMMaRyNovember 2007
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I. Executive Summary
Thecapabilityofmethanoltoreplacepetroleumfuelshasbeenknownforalongtime.Nowasthefutureavailabilityofcrudeoilisincreasinglycalledintoquestion,methanolisreceivingrenewedinterestsinceitcanbereadilymadefromremotenaturalgasandfromtheworld’sextensivecoalandbiomassresources.Muchworkwasdonepreviouslyaroundtheworldtoidentifytheproperwaystodesignandmodifyvehiclestousemethanoleitherasaneatfuelorinblendswithgasoline.Extensivefleettestswerealsoconducted,withthemajorityoccurringintheU.S.wheremethanolvehiclesweresoldcommerciallyintheearly1990s.Thisreportpresentsseveralsignificantfindingsfromthatworkandexperience.
Methanolhasalonghistoryofuseinracingvehicleswhereitisvaluedbothforitspowerproducingpropertiesanditssafetyaspects(methanolishardertoignite,createslessradiantheat,andburnswithoutproducingblacksmoke).Methanoluseinnon-racingvehicleshasbeenmuchlesssuccessful.TherewassignificantinterestinusingmethanolasagasolineblendingcomponentforitsoctanevalueandemissionscharacteristicsintheU.S.whenleadwasphasedoutofgasolineandmorestringentemissionstandardswereestablished.Severalmethanol/cosolventblendswereapprovedforusebuttheoxygenatemethyltertiarybutylether(whichusedmethanolinitsmanufacture)waspreferred.Duringthe1980sandthroughmuchofthe1990s,mostgasolineinWesternEuropecontainedasmallpercentofmethanol,usually2-3%,alongwithacosolventalcohol.GasolinesusedinEuropeanUnioncountriesareallowedtohave3%methanol,butitisbeingchallengedbyethanol(allowedupto5%nowwithaproposaltogoupto10%)whichisvaluedforitslowgreenhousegases.Today,Chinaistheleaderinusingmethanolasatransportationfuelwherebetween3and5milliontonswereusedlastyear.
Usingmethanolasagasolineblendingcomponentrepresentsthemostexpeditiouswaytouselargeamountsofmethanolasatransportationfuel.Methanoladditionincreasesoctanevalueandwillcausedecreasesinhydrocarbon,toxic,andcarbonmonoxideemissions.Mostmodernfuelsystemswithfeedbackcontrolshouldbeabletoaccommodatelow-levelmethanolblends(upto10%)withoutdifficulty,thoughexceptionsarepossible.Usinglow-levelmethanolblendsdoesrequiregoodhouse-keepingpracticesintransport,storage,anddispensing,toassurethatwateradditionisminimizedtopreventphaseseparation.Addingmethanoltogasolineincreasesvaporpressurewhichcouldleadtoincreasesinevaporativeemissionsduringwarmweather.Additionofacosolvent(typicallyhigheralcohols)amelioratesboththeseissuesandadjustmentofthegasolinespecificationscaneliminatetheincreaseinvaporpressure.Carefultailoringofthegasolineusedtomakemethanolblendscanmaximizethebenefitsofmethanoladditionandincreasegasolinerefiningefficiency.
Intheearly1980s,therewasconsiderableinterestinusingmethanolasafuelforbothpetroleumdisplacementandairqualityreasons.Toachievethequickestdisplacementandlargestimpactonairquality,itwasdesiredtousemethanolneatornear-neatasatransportationfuel.IntheU.S.,fleetdemonstrationsofmethanolvehicleswereverysuccessfulgiventhevehicles’lowemissions,20%increaseinpower,and15%increaseinenergyefficiency.However,thedecreaseinvehiclerange(thefueltankcouldnotbeexpandedsufficientlytocounteractthedecreaseinmethanolheatingvalue)andthesparsenumberofmethanolrefuelingfacilitiescausedmethanolvehicledriversgreatanxiety.Thisdirectlyledtothedevelopmentofmethanolflexiblefuelvehicles(FFVs)whichcouldusemethanolorgasolineinthesametankthroughtheuseofanalcoholfuel
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sensorthatmeasuredthemethanolcontentofthefuelgoingtotheengine.Thisfreeddriversfromworryingaboutrunningoutoffuelwhilethedevelopmentofmethanolinfrastructurecaughtupwithdemand.TheobjectivewastointroducelargenumbersofmethanolFFVs,buildabroadfuelinginfrastructurenetwork,thentransitionbacktodedicatedmethanolvehicles.FFVsperformedthesameorbetterthantheirgasolinecounterpartswiththesamemassemissions,thoughthiswasalsoaplussincemethanolemissionswereshowntobelessreactive.FleettestsofFFVsoccurredaroundtheworldwiththemostintheU.S.FFVspeakedin1997intheU.S.atjustover21,000withapproximately15,000oftheseinCaliforniawhichalsohadover100refuelingstations.
RelativelyfewchangesareneededtoturnavehicleintoamethanolFFV,andtheincrementalcostislessthanthecostofmostoptionalequipmentoncarstoday.ThereisadrawbacktomethanolFFVs–inordertoaccommodategasoline,theenginecannotbemodifiedtoachievethepowergainsandefficiencyimprovementspossiblewhenonlyusingmethanolasafuelexceptthroughtheadditionofamajorchangesuchasvariablecompressionratio.TuningmethanolFFVstofavormethanolovergasolinewillallowsomeofthesebenefitstoberealized.
InparallelwithFFVdevelopmentintheU.S.,wasthedevelopmentofamethanolfuelspecificationwhatwouldallowvehiclestoachievecold-startandimprovethevisibilityofmethanolflames.Theendresultwasablendof85%methanolwith15%gasolineknownasM85.TheASTMintheU.S.maintainsthespecificationforM85whichhasbeenrecentlyupdated(2007).
Thephysicalandchemicalpropertiesofmethanolmakeitverywell-suitedforuseasaspark-ignitionenginefuel,butitsabilitytocombustwithoutformingsoot(duetothelackofcarbon-to-carbonbonds)hasattracteddieselenginedesignerstofindwaysofusingitaswell.Manywaysofusingmethanolindieselengineshavebeenresearchedincludinguseinblends,emulsions,fumigation,withtheadditionofignitionimprovers,indualinjectionengines,andinenginesmodifiedtoachievedirectcompressionignitionofmethanol.Notethatofthesemethods,onlyuseofignitionimproversandcompressionignitionresultedinenginesthatdisplacedalldieselfueluse,thoughcompletedisplacementwasnotviewedasarequirementsincetheemissionsbenefitsofmethanolweretypicallygreaterthanthepercentdieselfuelitreplaced.Dieselenginescouldalsobeconvertedtosparkignition,butthischangeessentiallymakesthemOttoCycleengines.Lookingforward,homogeneouschargecompressionignition(HCCI)systemsoffertheopportunitytodesignbothheavy-dutyandlight-dutyenginesforcompressionignitionofmethanolandmethanol/dimethyletherblendswithverylowemissionsandhighefficiency.
Thetechnologyforbulkstorageofmethanoliswell-established.Methanolfuelscanbeaccommodatedatretailservicestationsassumingthepropertank,piping,anddispenserisused.Newdry-break,spill-freedispensingnozzlesalleviatesafetyandhumancontactconcernsaboutrefillingmethanolvehicles.
Greenhousegases(GHGs)frommethanolmadefromcoalwillincreaserelativetousinggasolineunlesscarbondioxidesequestrationisimplemented.MethanolmadefromnaturalgaswillhavesimilarGHGsasgasoline.MethanolmadefrombiomassshouldhavesignificantlylowerGHGs.
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II. Introduction
Thecapabilityofmethanoltoreplacepetroleumfuelshasbeenknownforalongtime.Theeasewithwhichcrudeoilcanbeextractedandmadeintofuelhaslongmadepetroleum-basedgasolineanddieselfuelthepreferredchoicesfortransportationvehicles.Nowthatthefutureavailabilityofcrudeoilisinquestion,methanolisreceivingrenewedinterestsinceitcanbereadilymadefromremotenaturalgas,numerousbiomassresources,andfromtheworld’sextensivecoalresources.Methanolisanexcellentfuelforinternalcombustionvehicles,andfuelcellvehiclesusingeitherprotonexchangemembranefuelcellsthatoperateonhydrogenordirectmethanolfuelcells.
Likehydrogen,methanolcanalsobeusedasanenergycarrierwiththeadvantageofbeingaliquidfuelwithhighenergydensityandprovensafety.AsenvisionedintheMethanolEconomy®,methanolismadefromcarbondioxideviacatalyticreductionwithhydrogenorbyelectrochemicalreductionwithwater[1].Thecarbondioxidewouldinitiallycomedirectlyfromfossil-fuelpowerplantsandchemicalplantsandeventuallyfromtheatmosphereitself.Methanolproducedefficientlyfromatmosphericcarbondioxideandhydrogenfromwatercanprovideenergyforfueluseandcouldbetherawmaterialfromwhichsynthetichydrocarbonsandchemicalsaremade.
Methanolhasalonghistoryofuseinracingvehicleswhereitisvaluedbothforitspowerproducingpropertiesanditssafetyaspectsrelativetogasoline:itishardertoignite,itburnsmoreslowly,itemitsnoblacksmokeandemitslowerradiantenergy,whichmakessurroundingmaterialslesslikelytocatchfire.InterestinusingmethanolasablendingcomponentintheU.S.wasintensewhentheoctaneenhancerleadwaslegislatedoutofexistence.ItreceivedadditionalinterestwithpassageoftheCleanAirActAmendmentsof1990,whichenvisagedvehiclesdesignedtorunonmethanol,eitherneatorasM85(ablendof85%methanolwith15%gasoline),tomeetvariousspecialprogramsforalternativefuelvehicles.TheautomakerswereverysuccessfulatengineeringvehiclestouseM85.Thesevehiclesperformedthesameorbetterthantheirgasolinecounterpartswiththesamemassemissions,thoughthiswasalsoaplussincemethanolemissionswereshowntobelessreactive.FleettestsofM85vehiclesoccurredaroundtheworldwiththemostintheU.S.M85vehiclespeakedin1997intheU.S.atjustover21,000[2]withapproximately15,000oftheseinCaliforniawhichalsohadover100refuelingstations.ButautomakersandrefinersquicklyshowedthattheycouldmeettheseemissionstandardswithreformulatedgasolineandstatesconvincedtheU.S.EnvironmentalProtectionAgency(EPA)toletthemopt-outofthealternativefuelvehicleprograms.Inaddition,bythemid-1990s,competitionfromotheralternativefuels,notablyethanolandnaturalgas,dampenedsomeoftheimpetustoimplementmethanol.EthanolrepresentedthegreatestcompetitorsincethesametechnologytomakeM85vehiclesworkedequallywelltomakevehiclesusing85%ethanol(E85).Ethanol’staxcredit,longhistoryofuseinblends,andstronglobbyingsupportfromagriculturalinterestseventuallydisplacedM85intheU.S.Today,thereareover4millionE85vehiclesintheU.S.,thoughonlyabout150,000ofthemuseE85regularly[2].TheonlyroleformethanolcurrentlyasatransportationfuelintheU.S.isasacomponenttomakebiodiesel,whereitisreactedtoformmethylesters.Chinaiscurrentlythelargestuserofmethanolfortransportationvehiclesintheworld.
Interestisagainhightousemethanolasatransportationfuel,particularlyinregionsoftheworldwherethereisanabundanceofreadilyavailablefeedstocks(coal,naturalgas,biomass)fromwhichmethanolcanbeproduced.Muchworkwasdoneinmanycountriespreviouslytoidentifytheproperwaystomodifyvehiclestousemethanoleitherasaneatfuelorinblendswithgasoline.Thisreportpresentsmanyofthemostsignificantfindingsfromthatwork.
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III. Methanol Blend Regulation
Whileithaslongbeenknownbyenginedesignersthatmethanolcouldbeusedasaninternalcombustionenginefuel,itwasnotuntilemissionsandoildependencyconcernswereraisedintheUnitedStatesthatmethanolwasrecognizedmorewidelyasapotentialtransportationvehiclefuel.In1970,RobertaNicholsandco-workersattheAerospaceCorporationpublishedareportidentifyingtheemissionsbenefitsofmethanolasatransportationfuel[3].Laterin1970,amethanol-fueledvehiclewasenteredbyHenryAdelmanofStanfordintheCleanAirCarRace.Hisvehicle(anAMCGremlin)placedfirstintheliquidfuelclassforoverallperformancewhilemeetingthe1975emissionstandards,despiteveryfewenginemodifications.Thisdemonstrationofthecapabilitiesofmethanolpiquedinterestinitsuse.Then,in1971,theEPAannouncedaproposedrule-makingtophaseoutuseofleadingasoline.Thisgaveinterestinmethanolanotherboostbecauseofmethanol’shighoctanerating.TheEPAfollowedtheinterestinmethanolcloselyandin1973commissionedbothExxon(nowExxonMobil)andtheInstituteofGasTechnology(nowtheGasTechnologyInstitute)toconductresource-through-end-usestudiesofalternativefuelstopetroleumforhighwaytransportation.Bothofthesestudiesratedmethanolveryhighlyforitsabilitytouseexistinginfrastructure,foritsnon-petroleumresourcebase,foritslowemissions,andbecauseitcouldbeusedininternalcombustionengineswithoutdrasticmodifications.Theninthefallof1973,theAraboilembargoofcrudeoilsalestotheU.S.greatlyescalatedtheinterestinalternativefuels,ofwhichmethanolwasprominent.FollowingisthehistoryandstatusofmethanolregulationasafuelintheU.S.andEurope.
A. United StAteS
TheCleanAirActamendmentsof1977includedthecreationofsection211(f),whichprohibitstheintroductionintocommerceofanyfuelorfueladditivethatisnotsubstantiallysimilartofuelsusedinvehiclecertification.TheEPAmayissueawaiveroftheprohibitionifapartydemonstratesthatthefuel/additivewillnotcauseorcontributetothefailureofanyemissionscontroldeviceorsystem.
1. EPA WAIVERS GRANTED AND OxyGENATE ALLOWANCES AS “SUBSTANTIALLy SIMILAR”
ThefirstwaiverrequestforanoxygenatedcompoundreceivedbyEPAwassubmittedbyGasPlusandtheIllinoisDepartmentofAgricultureinJune1978for“Gasohol”,ablendof90%gasolineand10%ethanol.Thewaiverapplicationcontainednoactualdataonethanol/gasolineblends.Instead,itincludeddataonmethanol/cosolventblendsandonmethyltertiarybutylether(MTBE),whichwasarguedtoshowexpectedemissionsimpactsfromethanolaswell.TherewasalsoareferencetosomeemissionstestsconductedbythestateofNebraskaon26vehicles,apparentlywithgasoline/ethanolblends,whichwerenotidentifiedandnodataweregiven,butastatementsaidthatthetestsshowedhigherNOxandsomewhatlowerCOandHCemissions[4].
Becauseofthelackofdata,EPAwasunabletograntthewaiverapplication.ButEPAalsodeclinedtodenythewaiverapplicationand,underthetermsofsec.211(f)(4),applicationsaredeemedgrantedafter180daysiftheyhavenotyetbeendenied.OnApril6,1979,EPAissuedaFederalRegisternoticeconfirmingthattheapplicationhadbeendeemedgrantedbyexpirationofthe180-dayperiod[5].
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TheGasoholwaiverapplicationincludednospecificationsdefininguseofthewaiver.BecauseEPAissuednonoticegrantingthewaiver,italsofailedtoimposeanyspecifications.ThisledtoaneedtosubsequentlyissueinterpretationofthewaiverinApril1982clarifyingthatblendsoflessthan10%couldalsobeused[6].Althoughitisnotspecifiedanywhere,EPAhasalsointerpretedthesepercentagelimitstoapplybyvolumeratherthanbyweightormole.
The10%limitonethanolwasgenerallybelievedtotranslatetoapproximately3.5-3.7%oxygeninthegasolinebyweightbasedonsampleanalysis.
In1979,EPAissuedwaiversforupto7%tertiarybutylalcohol(TBA)[7],forupto7%MTBE[8],andforupto5.5%ofacombinationofmethanolwithTBAinequalparts[9].Thesewaiversallowedabout2%oxygenbyweightinthefuelblend.
InOctober1980EPApromulgateditsfirstrealInterpretiveRuledefiningwhatfuelsandadditiveswereconsideredsubstantiallysimilartocertificationfuels[10].(Priortothis,itconsideredonlythoseidenticaltofuelsandadditivesusedincertificationtobe“substantiallysimilar”or“sub-sim.”)Ittreatedaliphaticethersandalcoholsotherthanmethanolassub-siminvolumescontributing2%orlessoxygenbyweight.
InJuly1981,EPAissuedarevisedInterpretiveRulefurtherdefining“sub-sim.”Itallowedforuseofupto2.75%methanolwithanequalvolumeofTBA(orhigheralcohols),aspreviouslyprovidedbywaiver,essentiallyconfirmingthatallowancesmadeinwaiversareapplicabletoallmarketers,notmerelytheapplicant[11].EPAwasaskedinthisrulemakingtoincreasetheoxygenlimitto3.7%,equivalenttothatofGasohol,butEPAdeclinedtodosobasedonobservedNOxincreases,keepingthesub-simoxygenlimitat2%[12].
InNovember1981,EPAgrantedawaiverforuseofARCO’s“Oxinol,”allowingupto4.75%methanolwithanequalamountofTBA,whichprovidesapproximately3.5-3.7%oxygen[13].Thisoxygenlevelbecametheeffectivelimitthereafter.EPAgrantedwaiverstoDupontCorporation(1985)[14]andTexasMethanolCorporation(1988)[15]allowingmethanol/cosolventcombinationsupto3.7%oxygenandincludingethanolasacosolventalcohol,inadditiontohigheralcoholsalreadyallowed.
EPAalsograntedawaiverforupto15%MTBEin1988,whichprovidesapproximately2.7%oxygen[16].Thiswaiverwasrequestedandgrantedatlessthantheoxygenlimitallowedforalcoholsbecauseofthehighvolumeoftheoxygenateitself.Becauseoxygenateshavevariousproperties,distillationimpacts,etc.thataresignificantlydifferentfromgasolinehydrocarbons,15%wasseenastheacceptablelimitforoxygenates,independentoftheoxygencontribution.
In1991,onapetitionfromtheOxygenatedFuelsAssociation,EPArevisedtheInterpretiveRuleonsub-simtoallowformixturesofMTBE(orETBE)andaliphaticalcoholsotherthanmethanoluptothe2.7%oxygenlimitingasoline[17].(Thiscorrespondstothe15%MTBElimit.The2.7%oxygenfromETBEwouldallowabout19%ETBEbutitwasnotexpectedthatthishighcostoxygenatewouldbeusedatsuchalevel.)
InworkshopsrelatingtoimplementationofthefederalReformulatedGasoline(RFG)programestablishedbytheCleanAirActAmendmentsof1990,EPAwasinformedthatwiththe(lowerdensity)fuelsanticipatedasRFG,10%ethanolwouldprovideapproximately4%oxygenbyweight,whereasEPA’smodelonlyextendedupto3.7%oxygen.EPAconfirmedthatuseof10%ethanol
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wouldbeallowedinRFGevenwiththeoxygenatsomewhatabove3.7%(nooxygenlimithavingbeenestablishedfor10%ethanolblends).
Itshouldbenotedthatthemethanolblendwaiversapprovedremainineffecttoday,thoughthepromulgationofadditionalregulatoryrequirementsforgasolineadditivesmeansthatsomeadditionaltestingwouldbeneededbeforetheycouldbemarketedbylargecompanies.
2. EPA DENIALS/REVOCATIONS OF WAIVERS AT HIGH ALCOHOL/OxyGEN LEVELS
InMarch1980,EPAdeniedawaiverapplicationfromBekerIndustriesforupto15%methanol[18].Thedenialwasbasedlargelyontheabsenceofadequatedata.(Infact,nodatahadbeensubmittedonmethanolwithoutcosolventadditives.)ButEPAalsonotedthatthedatasubmittedathighalcohollevelssuggestedthattherecouldbeproblems,includingincreasesinemissionsanddeteriorateddriveability,resultingfromthehigheroxygenlevels.
InAugust1980,EPAdeniedawaiverapplicationfromConservationConsultantsofNewEnglandfor5%ethanolwith5%methanol(oxygencontent4.4%)[19].Theapplicationhadalsorequestedwaiversfor(1)10%methanolwith5%ethanoland(2)8%methanolwith2%ethanol,buttheserequestshadbeenwithdrawnbytheapplicant[20].Thedenialwasbasedonabsenceofdata,butEPAnotedproblemsanticipatedwithexhaustemissions,evaporativeemissions,driveability,andmaterialscompatibility.
InOctober1981,EPAgrantedawaivertoAnafuelUnlimitedforamixtureofupto12%methanolwith6%butanolsandaproprietaryinhibitor[21].Thewaiverwasgrantedunderextremeduress–pressurefromtheWhiteHouseandsomesenators.Thiswouldhaveprovidedaround7%oxygeninthefuel.Subsequenttesting,however,showedthatthetestdatasubmitteddidnotreflectthealcoholpackageinthatvolumeandtheMotorVehicleManufacturers’Association(MVMA)filedbothacourtchallengeandapetitionforEPAreconsideration.EPAproposedtorevokethewaiverbyreconsideration(1984)[22]buttheD.C.CircuitCourtruledthatwaiverswerenotsubjecttosuchreconsiderationbeyonda30dayperiodprovidedinsec.211(f)(4)[23].TheD.C.CircuitCourtsubsequentlyruledinfavorofMVMA’ssuit,however,vacatingtheoriginalgrantingofthewaiversuchthatEPA’sevaluationofitwouldresumewithoutthetainteddata[24].EPAdeniedandfinallyrevokedthewaiverin1986[25].Inthemeantime,AmericanMethylCorp.,successortoAnafuel,hadappliedforanotherwaiverwithavariationoftheformulaata5%oxygenlevel.EPAdeniedthatrequestinNovember1983[26].
In1987,inessentiallythesametimeperiodthattheTexasMethanolCorporation’swaiverapplicationwaspending,EPAwasaskedbyAMLaboratories,Inc.tograntawaiverforuseofupto5%methanolwith5%ethanol,foranoxygencontributionof4.4%,similartothatwhichithaddeniedin1981toConservationConsultants.TheapplicationattachedareportofamajorCanadiantestprogramthatincludedsuch5%/5%blendsandinwhichthedriveabilitydemeritswerearguednottobeexcessive.Theautomakersfiercelyopposedtheapplication,arguingthatotherexistingdataclearlyshoweddriveabilitytobedegradedunacceptablyatlevelsabovearound3.7%.Forthefirsttime,oppositionwasnotlimitedtoU.S.automakersbutincludedopposingsubmissionsfromToyota,aswell.InJanuary1988,EPAissueditsFederalRegisternoticeanddecisiondocumentdenyingthewaiver[27].
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3. USE OF METHANOL IN U.S. FUELS
Inthemid-1980sARCOundertooktheonlyseriouseffortatmarketingmethanolblendsintheU.S.,usingitsOxinolmixtureofmethanolandTBA.ItusedtheOxinolinsomeofitsowngasolineandalsomarketedittoindependentrefinersandblenders.ManyofthoseindependentcustomerssubsequentlydiscontinuedpurchaseoftheOxinol,however,citingreportsfromcustomersofphaseseparationand/ordamagetoelastomersandotherrealorperceivedproblems.ARCOdiscontinueditsmarketingofOxinolsometimearound1986.EPA’sfinalregulationonfuelvolatilityinMarchof1989,whichallowedaonepsidifferentialforethanolblendsbutnotformethanol/cosolventblends,putthemethanolblendsatanadditionalmajordisadvantageandprobablyrepresentedtheirdeath-knellintheU.S.EPA’sRFGandconventionalgasolineanti-dumpingprogram,basedonmodelswhichfavoredevenlowervolatility,madethisbarrierevengreater.Inaddition,EPA’sComplexModelforRFG,useofwhichbecamemandatoryasofJanuary1,1998,didnotincludeparametersrepresentingblendingofmethanoleitherforvolatileorganiccompoundreductioncreditorforcalculationofaldehydeemissionstomeetthetoxicsemissionsstandards.Inorderformethanol/cosolventblendstobeusedinRFG,themodelwouldhavetobe“augmented,”whichwouldrequiresubstantialandexpensiveemissionstestingwithawidevarietyoffuelblendsandvehicles.
Whilethemethanol/cosolventblendsfailedtocatchonintheU.S.,theuseofMTBEprovidedapathformethanoltobeusedingasoline.Bythelate1980s,MTBEproductionhadsurpassedformaldehydeproductionasthegreatestsingleuseofmethanolworldwide.PassageoftheCleanAirActAmendmentsof1990,withtheRFGprogramandtheOxyfuelsprogram,gavefurtherbooststoMTBE.TheRFGprogramrequired2.0%oxygeninRFGduringwarmweathermonthsinthemostseriousozonenon-attainmentareas,whiletheOxyfuelsprogramrequired2.7%oxygeninmanycarbonmonoxide(CO)nonattainmentareasduringcoldmonths.MTBEbecametheoxygenateofchoiceinRFGandwasalsousedtosomeextentinOxyfuelsregions.Astheseprogramswerebeingimplemented,demandformethanoloutstrippedsupplyintheU.S.bysomuchthatmethanolpricesreachedlevelsof$1.85/gallon.
TheCleanAirActAmendmentsof1990envisagedthattherewouldbeamovetowardvehiclesdesignedtorunonmethanol,eitherneatorasM85,tomeetvariousspecialprogramsforalternativefuelvehicles(AFVs),includingtheCleanFuelFleet(CFF)ProgramandtheCaliforniaPilotTestProgram[28].ButautomakersandrefinersquicklyshowedthattheycouldmeettheemissionstandardswithRFGandstates,havingdeterminedthatsuchprogramswerenotcost-effectivewaysofreducingpollutants,convincedEPAtoletthemoptoutoftheCFFprogram.FrustratedwiththelackofprogressinuseofAFVs,CongressenactedlimitedfleetAFVacquisitionrequirementsintheEnergyPolicyActof1992(EPAct92),whichalsocontemplatedmethanolvehicleuse.ButinitialimplementationofthisprogramcoincidedwiththerunawaymethanoldemandforMTBEusewithintheRFGprogramandassociatedrunawaypricessomethanolvehicleswerelargelyignoredintheseAFVprogramsthathadbeendesignedwiththeminmind.
Byearlyinthisdecade,detectionofMTBEingroundwaterinvariouslocationsraisedconcernsthatledanumberofstatestobanuseofMTBE,anditsusefelloffsharplyasaresult,largelythroughsubstitutionofethanol.Then,theEnergyPolicyActof2005(EPAct05)eliminatedtheoxygenrequirementforRFGwhileimposinga“RenewableFuelStandard,”essentiallyarequirementforuseofincreasingvolumesofethanolbyrefiners.AbsenttheRFGoxygenrequirement,refiners’concernsaboutliabilityforleaksofMTBEhavepromptedallmajorU.S.refinerstoceaseblendingofMTBEandithasvirtuallydisappearedfromU.S.gasolinesupplysinceMay2006.
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel III. MeTHanol blend RegUlaTIon
8
WiththeeliminationofMTBE,theonlysignificantuseofmethanolinU.S.fuelsupplyisitsuseinproductionofmethylesterbiodiesel.AlthoughthisaccountsforalmostallU.S.biodiesel,dieseluseintheU.S.isfarlowerthangasolineuseandonlyasmallpartofU.S.dieselfuelincludesbiodiesel,mostlyatthe20%blendlevelorless.Therefore,thebiodieselusedoesnotcompensateforthelossofMTBEasasourceofmethanoldemand.
B. USe of MethAnol BlendS in the eUropeAn Union
MethanolfuelblendswereintroducedintheFederalRepublicofGermanyin1968withuseof2%methanol/2%TBAblends,reachinggeneralusearound1977.TheGermangovernmentsetalimitof3%methanol.Duringthe1980sandthroughmuchofthe1990s,mostgasolineinEuropecontainedasmallpercentofmethanol,usually2-3%,alongwithacosolventalcohol.A“commondirective”oftheEuropeanEconomicCommunity(EEC,apredecessortotheEuropeanUnion-EU)authorizedalcoholblendingingasolinestartingin1988,includingalowlevelthatmembercountrieswererequiredtoallowandahigherlevelthatcouldbeallowedbymembercountrieswithlabelingonpumps.Franceauthorizedsuchhigherlevelblends,buttheiruseapparentlydidnotbecomewidespread.InSweden,whereoxygenateswereallowedupto3wt%oxygen,methanolwasalsoallowedupto2%[29].ThecurrentEUstandard,EN228,aslastrevisedin2004,allowsupto3%methanoltobeused,witharequirementforacosolvent(“stabilizingagent”).InJanuaryof2007,theEuropeanCommissionproposedanewfuelstandardthatwouldrequireallfuelsmarketedinEuropetomeetastandardforgreenhousegasemissions,whichwouldincludeareductioningreenhousegas(GHG)emissionsby1%peryearfrom2011through2020,withtheintentthatthesereductionsbemetlargelythroughincreasingthebiofuelscontentofthefuel.Theproposalstatesthatanewgasolinestandardwillbepromulgatedthatwillallowupto10%ethanoltoaccommodatetheGHGemissionsreductions,comparedtothecurrentstandardthatallowsonly5%ethanol.
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Use of MeTHanol as a TRansPoRTaTIon fUel
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IV. Methanol Use in Flexible Fuel Vehicles
Intheearly1980s,therewasconsiderableinterestinusingmethanolasafuelforbothpetroleumdisplacementandairqualityreasons.Toachievethequickestdisplacementandlargestimpactonairquality,itwasdesiredtousemethanolneatornear-neatasatransportationfuel.ForddevelopedaversionoftheirEscortin1981thatranon90%methanolanda10%hydrocarbonblendspecificallytailoredtogivereliablecoldstarts[30].FortyofthesemethanolEscortswereputintofleetuseinLosAngelesandtheir20%increaseinpowerand15%increaseinenergyefficiencymadethemverypopularincomparisontothegasolineversions.TheseinitialvehiclesweresosuccessfulthatLosAngelesaskedformoreandin1983Forddeliveredanadditional501.However,therefuelinginfrastructurewasnotexpandedsufficientlyandthedecreaseddrivingrange(approximately230milesversus300forgasoline)becameanissue.Thisexperiencedirectlyledtothedevelopmentofmethanolflexiblefuelvehicles(FFVs)whichcouldusemethanolorgasolineinthesametankthroughtheuseofanalcoholfuelsensorthatmeasuredthemethanolcontentofthefuelgoingtotheengineandadjustedthefuelflowrateandsparkadvanceaccordingly.Thisfreeddriversfromworryingaboutrunningoutoffuelwhilethedevelopmentofmethanolinfrastructurecaughtupwithdemand.TheobjectivewastointroducelargenumbersofmethanolFFVs,buildabroadfuelinginfrastructurenetwork,thentransitionbacktodedicatedmethanolvehicles.FigureIV.1showsthedifferencesinamethanolFFVfromthestandardgasolineversionfromwhichitwasderived.
AsFigureIV.1shows,relativelyfewchangesareneededtoturnavehicleintoanFFV.Analcoholfuelsensorisusedtomonitorthefuelmixtureandsignaltheon-boardcomputertoadjustfuelflowandsparktiming(currentmodelethanolFFVshaveeliminatedthesensor–performingthattaskwithsoftware).Largerfuelinjectorsareusedtocompensateforthemethanol’slowerenergycontenttoassurethatthesameamountofmaximumenginepowerisproduced.
fIgURe Iv.1 Changes in FFvs Compared to Straight Gasoline models
1996 TAURUS 3.0L FFV
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel Iv. MeTHanol Use In flexIble fUel veHICles
10
Becausemethanoliscorrosiveandwillattackcertainmetals(suchasaluminumandmagnesium)andelastomers(includingrubberandpolyurethane),electrolessnickelplatedorstainlesssteelfueltanksandstainlesssteelorTeflon®-linedfuellinesareemployed,andmethanol-compatibleelastomersareusedinallfuel-wettedparts.Ananti-siphondeviceisinstalledinthefillerneckandanenlargedcarboncanisterisinstalledtocontainevaporativeemissionswhenco-minglingoccursinthefueltank,i.e.,whenthefuelinthetankcontains5-20%methanolwiththeremaindergasoline.
Therewasacompromise,however,inthemethanolFFVs–inordertoaccommodategasoline,theenginewasnotmodifiedtoachievethepowergainsandefficiencyimprovementsdemonstratedbyFordintheirfirstmethanolEscorts.Nonetheless,FFVswereperceivedasthe“missinglink”inthetransitiontomethanol.
WhenFFVswerefirstsold,theincrementalretailpricewasaround$350.ThemanufacturersneverrevealedtheincrementalcostofmakingFFVsnorfullydefinedwhatchangestheymade.Today,aftermillionsofethanolFFVshavebeensold,thesituationhasnotchanged,butestimatesoftheincrementalcostarenowbetween$50-100.MethanolFFVsbuiltinlargevolumewouldbeexpectedtohaveasimilarincrementalcost,thoughperhapsslightlyhigherifmoreexpensivefuelsystemmaterialsarerequiredrelativetoethanol,andwhethermethanolFFVscandowithoutafuelsensorasethanolFFVshavelearnedtodo.
InparallelwithFFVdevelopment,wasdevelopmentofamethanolfuelspecificationwhatwouldallowvehiclestoachievecold-startandimprovethevisibilityofmethanolflames.Theendresultwasablendof85%methanolwith15%gasolineknownasM85.WhileFordshowedonly10%hydrocarbonswereneeded,theextra5%allowedtypicalspecificationgasolinetobeusedwhichwasabundant,ofcourse,butmoreimportantly,inexpensive.
In1988,theCaliforniaEnergyCommissionestablishedtheCaliforniaFuelMethanolReservetoincreasetheavailabilityofmethanolfuelacrossthestate.Theagencyalsoenteredintovoluntary10-yearleaseagreementswithARCO,Chevron,Exxon,Mobil,ShellandTexacofortheinstallationofmethanolundergroundstoragetanksandfuelingpumpsat60publicretailstations.Thestateandlocalagencieswouldhelpbuildanother45privatefleetaccessiblefuelingstationsacrossthestate.Fromthemid-1980stothelate1990s,over15,000methanolFFVswereoperatingonCalifornia’sstreetsandfreeways,alongwithhundredsofmethanol-fueledtransitandschoolbuses.Attheheightoftheprogramin1993,over12milliongallonsofmethanolwasusedasatransportationfuelinthestate.
WhilemostautomakersbuiltanddemonstratedFFVs,onlyfourmethanolFFVmodelsmovedfromprototypedemonstrationstocommercialavailability.TheyweretheFordTaurusFFV(1993-1998modelyears);ChryslerDodgeSpirit/PlymouthAcclaim(1993-1994modelyears);ChryslerConcorde/Intrepid(1994-1995);andtheGeneralMotorsLumina(1991-1993modelyears).Thesemid-sizedsedanswerethelargestsellingfleetvehiclesonthemarket,andfleetsarewherethevastmajorityofmethanolFFVsweresold.Bythe1996modelyear,theFordTaurusFFVwastheonlymethanol-fueledvehicleonthemarket,andittoowouldbediscontinuedafterthe1998modelyear.Bythistimemanyoftheoriginal10-yearleaseagreementswiththemajoroilcompaniestooperatemethanolpumpsattheirretailstationshadexpired,andthemethanolpumpslargelyturnedovertopumpinggasoline.
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Californiawasnottheonlystatetodemonstratetheuseofmethanol-fueledvehicles.Methanolfuelingstationswerebuiltin15statesbetweenthemid-1980sandmid-1990s.TheNewYorkStateThruwayAuthorityfundedtheinstallationofabove-groundmethanolstationsatrestareasalongtheentirestate-widerouteoftheNewYorkThruway,fromtheTappanZeeBridgetoNiagaraFallstoserveafleetofmethanolFFVs.
Fromthesedemonstrationefforts,itwaslearnedthattherearenotechnicalbarrierstobuildingmethanol-fueledvehicles.Itwasalsolearnedthatmethanolcanbeeasily,safelyandeconomicallystoredanddispensed.Thecosttoinstallamethanolfueledundergroundstoragetankanddispenserisaround$60,000andmostinstallationscanbecompletedin60days.ImplementationofmethanolFFVsandmethanolinfrastructurecouldproceedrapidly,especiallyconsideringtheexperiencegainedwithethanolFFVsandtheethanolinfrastructure.
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V. Methanol Blend Physical and Chemical Property Impacts
Addingmethanoltogasolinecausesbothphysicalandchemicalpropertychanges,primarilyanincreaseinvaporpressureandchangeddistillationandmaterialscompatibilitycharacteristics.Thesechangesinphysicalandchemicalpropertiescanhaveadverseeffectsonvehicleoperationandemissions.Thissectionlooksatthesechangesandidentifiessomewaysthechangescanbemanaged.
A. VApor preSSUre
WhiletheReid1vaporpressure(RVP)ofmethanolisonly4.6psi(32kPa),comparedtogasolinethatistypicallyintherangeof7-9psi(48-63kPa),addingmethanoltogasolinecausesanincreaseinvaporpressure.Thisisbecausemethanolcombineswithcertainlowmolecularweighthydrocarbonstoformazeotropes.Azeotropeshavelowerboilingpointsthanthehydrocarbonsfromwhichtheyaremade,resultinginanincreaseinvaporgenerationatlowertemperatures.FigureV.1illustratesthisphenomenonwhichhasbeendocumentedwidelybyseveralresearchers[31,32]
FigureV.1showsthattheeffectofmethanolongasolinevaporpressurepeakswithadditionofaround10%methanolbyvolume,anddecreaseswithlargeradditions,decreasinginanalmostlinearfashionto4.6psiat100%methanol.(However,theincreaseinvaporpressurevariesslightly
1ReidvaporpressurereferstoaspecificASTMtest(D323)conductedat100°F.
Volume % oxygenate in gasoline
Ble
nd R
VP, p
si
0 5 10 15 20
13
12
11
10
9
8
Methanol/TBA(1:1)
Ethanol
Methanol
MTBETBA
fIgURe v.1 The effect of Alcohol Addition to Gasoline rvP (Source: ref. 32)
v. MeTHanol blend PHysICal and CHeMICal PRoPeRTy IMPaCTsNovember 2007
Use of MeTHanol as a TRansPoRTaTIon fUel
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witheachblendofgasoline.)WhatisparticularlysignificantwhenaddingmethanoltogasolineistheveryrapidriseinRVP–thevastmajorityoftheincreaseoccursbythetime2-3%methanolisadded.ThislargeincreaseinRVPcreatesverylargeincreasesinvaporgenerated,whichoftenoverwhelmthefuelevaporativesystemandresultinsignificantlyincreasedevaporativeemissions.CosolventscanmoderatetheincreaseinvaporpressuresomewhatasillustratedinFigureV.1fora50/50blendofmethanolandTBA,butthemosteffectiveremedyistodecreasetheRVPofthebasegasoline.Whenusedwithcosolvents,theRVPpeakoccursataround5%alcoholcontent.
FigureV.2showstheeffectmethanolandotheralcoholshaveonthedistillationcurveofgasolinewhenaddedatthe15wt%level.Methanol(labeledC1inFigureV.2)showsthelargestdistillationcurvedistortionwhichiscausedbythemethanolanditsazeotropesboilingofffirst.Afterabout60%distilled,almostallthemethanolisvaporizedandthedistillationcurverevertsbacktobenearlythesameasforstraightgasoline.
B. WAter tolerAnce
Whilemethanolissolubleingasoline,thepresenceofwatermaycausephaseseparation(waterandmethanolseparateoutofsolution).Whetherphaseseparationoccursdependsontheamountofwaterandthetemperature–highwatercontentandlowtemperaturesfavorphaseseparation.Methanolistheworstalcoholinregardtophaseseparation,whichisoneofthereasonsthathighermolecularweightalcoholshavebeenfrequentlyrecommendedascosolventsformethanol/gasolineblends.Cosolventsamelioratephaseseparation,vaporpressureincrease,andmaterialscompabilityproblems.TheEPAhasrequiredcosolventsforallmethanolblendwaiversforthesethreereasons.ForhighmethanolcontentfuelssuchasM85,phaseseparationisnotaproblembecauseofthelargecapacityofmethanoltoabsorbwater.
FigureV.3showsthewatertoleranceofagasolinewithvariousconcentrationsofmethanol.Thisfigurevividlyillustrateshowmethanoladditionquicklycausesthetemperatureatwhichphaseseparationoccurstorise.Forexample,10wt%methanolwillseparatewhentheblendiscooledtoatemperatureofonly15°F(-9°C).At15wt%methanolthephaseseparationtemperaturerisestojustbelowfreezing.
0 20 40 60 80 100
500
400
300
200
100
0
No alcoholMethanolEthanoln-Propanoli-Butanol
B.P. - C1
DISTILLATED RECOVERED, volume percent
15% of Various Alcohols in Gasoline
B.P. - C2
B.P. - C3
B.P. - C4
DIS
TILL
ATIO
N T
EMPE
RAT
UR
E, °F
fIgURe v.2 The effect of Alcohol Addition to Gasoline Distillation (Source: ref. 31)
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Cosolventscanhaveadramaticeffectonthewatertoleranceofgasolineblendedwithmethanol.FigureV.4showstheimpactthatadding5wt%alcoholcosolventscanhaveonthewatertoleranceofa10wt%blendofmethanolingasoline.ThehigheralcoholsofFigureV.4significantlyimprovethewatertoleranceofmethanolblends.
Thecompositionofthegasolinecanalsohavealargeimpactonmethanolsolubility.Gasolineswithhigharomaticcontentwilldissolvemoremethanolthangasolineswithhighparaffiniccontent.TableV.1showsthelargeimpactgasolinecompositioncanhaveonmethanolsolubility.
c. MAteriAlS coMpAtiBility
Automotivefuelsystemscontainawiderangeofelastomeric2andmetalliccomponents.Theelastomersareusedprimarilyassealsandfuellinesbutvehiclemanufacturershaverecentlybeenmovingtofuellinesthatarenon-metallicallthewayfromthefueltanktotheenginefuelsystem,whichgreatlyincreasestheamountofwettedareabetweentheelastomersandthefuel.Manyfueltanksarenownon-metallicaswellforreasonsofcostandabilitytobemoldedintocomplexshapesthatmaximizevolumeintightvehicleconfines.2Elastomerisagenerictermthatincludesallsoftpartsinafuelsystemincludingrubbers,plastics,nylons,fluorosilicones,urethanes,etc.
PHA
SE S
EPA
RAT
ION
TEM
PER
ATU
RE,
°F
0.04 0.08 0.12 0.16 0.20 0.24WATER, weight percent
90
80
70
60
50
40
30
20
10
0
Methanol
30%
20%15%10%5%
3%
CLO
UD
PO
INT
TEM
PER
ATU
RE,
°F
0 .1 .2 .3 .4 .5 .6 .7
WATER, weight percent
80
70
60
50
40
30
20
10
0
-10
-20
Plus
eth
anol
Plus
2 -
prop
anol
Plus
1 -
prop
anol
Base
fuel Pl
us m
etha
nol
Plus
ben
zene
fIgURe v.3 The Water Tolerance of methanol Added to Gasoline (Source: ref. 31)
fIgURe v.4 The Impact of Cosolvents on the Water Tolerance of a 10 wt% blend of methanol in Gasoline (Source: ref. 31)
v. MeTHanol blend PHysICal and CHeMICal PRoPeRTy IMPaCTsNovember 2007
Use of MeTHanol as a TRansPoRTaTIon fUel
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Elastomersmustnotcrack,leak,orbecomepermeabletofuel;iftheydo,vehiclesafetyisimpairedand/orevaporativeemissionsincreaseswilloccur.Noelastomeriscompletelyunaffectedbyexposuretofuel,withchangesoccurringinvolume(swell),tensilestrength,andelongation.Theadditionofmethanoltogasolinecauseschangesinelastomersthataredifficulttopredict.FigureV.5illustratestestingdoneonvariousgenericelastomersusedinfuelsystems(measuringswell)usingtwogasolines,neatethanol,andablendofthebasegasolineand10%methanol[32].Ingeneral,neatmethanolcausedlessswellingoftheelastomersthantheblendof10%methanolingasoline,andinmostcases,the50%aromaticgasolinecausedmoreswellingthan10%methanol.Onlythefluorocarbonshowedmoreswellinginmethanolandthe10%blendthanineitherofthegasolinestested.
Table v.1 methanol Solubility based on Gasoline Composition (Source: ref. 32)
Aromatics in Gasoline, Volume percent
Methanol Solubility, Volume percent
-10° to 0°f 32° to 37°f
16 2-3 5-10
28 5-10 15-20
31 5-10 >50
42 >50 >50
Gasoline composition Minimum temperature at which 10% Methanol
will dissolve, °fSaturates Aromatics olefins
100 - - 80
65 21 14 44
43 2 55 20
20 78 2 4
0
50
100
150
200
250
30% AromaticGasoline (A)
50% AromaticGasoline
Neat Methanol 10% Methanol,90% Gasoline A
Elas
tom
erSw
ell(
%)
FluorocarbonPolyester UrethaneFluorosiliconeButadiene-acrylonitrilePolyacrylateChlorosulfonatedPolyethyleneEthylene-propylene-dieneterpolymerNatural Rubber
fIgURe v.5 elastomer Swell from exposure to Gasoline, methanol, and a 10% methanol blend (Source: ref. 32)
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FiguresV.6andV.7showadditionaltestdatacomplementarytotheresultsinFigureV.5forpolyesterurethaneandfluorocarbonovertheentirerangeofmethanolblendsfrom0to100%[33].Thesedatashowthatelastomerschangecontinuouslywithpercentmethanolcontent,withthegreatestchangeoftenoccurringwithanintermediateblend.Afieldtrialof4%and15%methanolingasolineinNorwayreportedswellingofsomefuellines,thoughtheamountwasnotquantified[34].InasimilarfieldtrialofM15inNewZealand,problemswithfuellineswereobservedalongwithotherfuelsystemelastomersincludingcarburetorneedlevalveseats,fueltanklevelfloats,andfuelpumpdiaphragms[35].TheproblemsreportedintheNewZealandfleettestwerejudgedtoberelativelyminorandwereeasilycorrectedbyreplacementwithnewparts.Withoutacontrolfleet,itisnotknownwhethertheseproblemsrepresentedasignificantchangeornot.
Thesedatasuggestthattheimpactofmethanolonelastomermaterialsisrelativelybenigncomparedtohigharomaticgasolines.However,thesetestsweredoneusingnewelastomersandrelativelypurefuels.Aselastomersageinservice,theyarelessamenabletochange.Thereareseveralinstancesoffieldproblemscausedbychangesinfuelproperties.Forexample,thechangetoultra-lowsulfurdieselfuelcausednumerousfuelsystemleaksbecausetheelastomerswereadverselyaffectedbyarelativelysmallchangeinfuelproperties.Newversionsofthesameelastomersworked,illustratingtheimpactagingcanhaveonfuelsystemelastomers.Otherconfoundingfactorsinclude
* MPa = Mega-Pascals
Alcohol (vol%)0 10 20 30 40 50 60 70 80 90 100
1109070503010
0-10
Volu
me
Chan
ge (%
) Alcohol (vol%)0 10 20 30 40 50 60 70 80 90 100
16141210
86420
Tens
ile S
treng
th (M
Pa*)
Alcohol (vol%)0 10 20 30 40 50 60 70 80 90 100
200150100
500El
onga
tion
(%)
MethanolEthanol
fIgURe v.7 Fluorocarbon Compatibility with ethanol and methanol blends (Gasoline A from Figure v.5; Source: ref. 33)
* MPa = Mega-PascalsAlcohol (vol%)
0 10 20 30 40 50 60 70 80 90 100
70605040302010
0Volu
me
Cha
nge
(%)
Alcohol (vol%)0 10 20 30 40 50 60 70 80 90 100
2016
8840
Tens
ile S
treng
th (M
Pa*) Alcohol (vol%)
0 10 20 30 40 50 60 70 80 90 100
500400300200100
0Elon
gatio
n (%
)
MethanolEthanol
fIgURe v.6 Polyester Urethane Compatibility with ethanol and methanol blends (Gasoline A from Figure v.5; Source: ref. 33)
v. MeTHanol blend PHysICal and CHeMICal PRoPeRTy IMPaCTsNovember 2007
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theshapeoftheelastomerandwhetheritisattachedtoametalthatmightbeattackedbymethanol.Complex-shapedelastomersmayreactdifferentlythantheuniformelastomershapesusedfortesting.
Methanolfuelsofalltypescanbeextremelyaggressivetowardmagnesiumand,iftheycontaindissolvedorseparatedwater,towardaluminum,also[36].Steelandotherferrousmetalsareusuallyonlyslightlyaffectedunlesstheblendhasaseparatedwaterphase,inwhichcasesomepittingmayoccur.Additiveshavebeenfoundtobeeffectiveinreducingthecorrosiveeffectsofmethanolingasoline(blendsofupto10%)oncopper,castiron,steel,andaluminum[37].Corrosioninside4-strokeenginescanbecontrolledthroughtheuseofproperlyformulatedengineoils[38].
Methanolblendfuelsoftencausematerialdeteriorationproblemswithnonmetalsusuallyinproportiontotheamountofmethanolintheblend.Methanol-richfuelshavebeenshowntocauseshrinkage,hardening,swellingorsofteningofcorkgasketmaterial,leather,Viton,andpolyurethane[36].Buna-N,Delrinacetal,high-densitypolyethylene,polypropylene,andNylon6/6showedgoodresistancetotheseeffectsinthesamestudy.Apotentiallyseriousproblemmayoccurinthereactiontomethanolfuelsdisplayedbypolyester-bondedfiberglasslaminateatsomewhatelevatedtemperatures(approximately118°F[47.8°C]).Softening,swelling,blistering,andsignsofdelaminationwereobservedinthispopularfuelstoragetankandtankliningmaterial[36].Reactionsatroomtemperatures(approximately73°F[22.8°C])werelesssevere,butstillnoticeable.Notethattheseissuesonlyrefertovehiclesdesignedforgasolinefuelonly.VehiclesdesignedforM85haveelastomerscompatiblewithmethanol.
d. oxyGen content
Gasolinesanddieselfuelproducedfromcrudeoilarecomposedentirelyofcompoundsthatarecomposedalmostentirelyofcarbonandhydrogenwithverysmallamountsofnitrogenandsulfur.Incontrast,methanolis50%oxygenwiththeremainderbeingcarbonandhydrogen.Asaresult,methanolneedslessairforcompletecombustionsincetheoxygeninitscompositiondisplacestheneedforoxygenintheair.Thestoichiometricair/fuelratioformethanol(weightbasis)is6.45(massairtomassmethanol)comparedtoabout14.7forgasoline.FigureV.8showstheimpactthishasonblendsofgasolineandmethanol.Asmethanolisaddedtogasoline,theoxygencontentoftheblendgoesup,but,sincetheoxygendoesnotcontributetoheatingvalue,thevolumeoffuelneededtogeneratethesamepowerincreases.(Thisdiscussionassumesthattheefficiencyoftheenginedoesnotchangewiththeamountofmethanol,whichisreasonableforfixedcompressionratioengines.)Thus,ablendof10%methanolingasolinerequiresapproximately105%ofthevolumeofstraightgasolinetomakethesameamountofpower.Ifanenginewerecapableofoperatingon100%methanol,itwouldrequiretwiceasmuchfuelvolumecomparedtoanenginerunningonstraightgasoline.
Theprecedingdiscussionassumestheengineisdesignedforgasolinebutisusingmethanolblendswithgasoline.Enginesoptimizedforuseofmethanolblendswheremethanolisthepredominatecomponent,suchas85%methanol(M85),canbemademoreefficientthroughuseofhighercompressionratiosandotherengineadjustmentsoptimizedtomethanol.Inaddition,anengineoptimizedforhighmethanolblendscanhavehigherspecificpoweroutput,creatingtheopportunitytoreduceenginedisplacementforagivenapplication.Withbothanengineoptimizedformethanolandreducedenginedisplacement,significantincreasesinenergyefficiencyarepossiblerelativetogasolineengines.
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel v. MeTHanol blend PHysICal and CHeMICal PRoPeRTy IMPaCTs
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e. octAne VAlUe
Methanolhasgoodoctanepropertiescomparedtogasoline.Witharesearchoctanevalueof108.6andamodifiedmotoroctanevalue3of88.6,methanolhassufficientoctanetoallowenginesoptimizedformethanoltohavehighcompressionratioswiththeattendantbenefitsofimprovedpowerandefficiency.Whenusedinblends,thehighoctanevalueofmethanolcanbeusedtoreducetherefiningseverityoftheassociatedgasolineblendstock,allowingincreasesinrefineryoutputandefficiency.
3Thestandardmotoroctanetestmustbemodifiedtoincludefuelheaterstoenablemethanoltobetested.
fIgURe v.8 oxygen Content and Fuel volume ratio for Gasoline/methanol blends
1.0
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VI. Methanol Blend Vehicle Operational Impacts
Becausemethanolblendshavealowerheatingvaluethanstraightgasoline,thevehicle’sfuelsystemmustbecapableofsupplyinganincreaseintotalfuelvolumeatalloperatingconditionstomaintainvehiclepower,driveability4,andcold-startperformance.Theamountofincreasedependsontheamountofmethanolintheblend,asillustratedinFigureV.8.Vehicleswithfeedbackfuelsystemsthatuseanoxygensensorintheexhauststreamwillbeabletocompensateuptotheexcessflowratebuiltintothefuelsystembydesign.However,theamountofexcessflowratebuiltintoavehiclefuelsystemvarieswitheachvehiclepowertrainfamilyandmayalsochangewithtime,asfuelpumpperformancedegradesanddepositsbuildupthatconstrictfuelflow.
Mostcurrenttechnologyfuelsystemshavethecapabilitytoadjustfuelflowinresponsetoenvironmentalfactorssuchasaltitude,temperature,humidity,andchangesinfuelpropertiesthataffectstoichiometry,suchashydrocarboncompositionandoxygencontent.Thiscapabilityiscalledadaptivelearningandtakesplaceafterthevehicleiswarmedup5andthefeedbackcontrolsystemisoperating.Theobjectiveofadaptivelearningistofine-tunethesystemtodithertheair/fuelratioaroundthestoichiometricvalueasdeterminedbytheoxygensensorsothatthethree-wayexhaustcatalystwilloperateefficiently.Asmethanolisaddedtogasoline,thestoichiometricair/fuelratiochanges,andthefeedbackcontrolsystemmustadjustaccordingly.
Engineoperatingmodeswhereadaptivelearningisnotineffectincludecold-start,warm-upbeforethefeedbackcontrolsystemisactive,prolongedidle,wide-open-throttleacceleration,andclosedthrottledeceleration.Duringthesemodes,changesinfuelstoichiometricair/fuelratiowillbereflecteddirectlyinvehicleoperationsincetheenginecontrolsystemhasnowayofdetectingthatadifferentfuelisbeingused.
A. cold-StArt
Methanolhasseveralcharacteristicsthatincreasethedifficultyofcold-startininternalcombustionengines.Themostimportantoftheseisthehighflashpointofmethanolcomparedtogasoline.Methanol’sflashpointis52°F(11°C)comparedtogasoline,whichhasatypicalflashpointof-43°F(-45°C).Thusanengineconfiguredtousemethanolinsteadofgasolinewillnotstartbelow52°Fwithoutexternalstartingaids.
Anotherlargedifferenceisthatmethanolrequiresabout3.5timesmoreenergyperunitmasstovaporizeitcomparedwithgasoline.Factoringintheneedfortwiceasmuchmethanolasgasolinetoproducethesamepower,thedifferenceisafactorof7.Thefactthatmethanolisahomogeneousliquidwithasingleboilingpointcombinedwiththeneedformuchmoreenergytovaporizeitresultsinmuchlessvaporgenerationattypicalstartingtemperaturesthangasoline,whichhassomehydrocarbonsthatvaporizeatlowtemperatures.
4 Driveabilityisameasureofvehicleoperationalproblemssuchasstallingorsurgingduringwarm-up,unstableidle,unevenacceleration,non-linearthrottleresponse,occurrenceofvaporlock,etc.Gooddriveabilityisanabsenceofoperationalproblems.5Being“warmed-up”generallymeansthreecriteriahavebeenmetforvehicleswithcatalystemissioncontrolsystems:1)theoxygensensortemperatureisaround600°F,2)thecoolanttemperatureisaround150°F,and3)apredeterminedamountoftimehaselapsedfromthetimetheenginehasstarted(fromafewsecondsto1-2minutes).
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel vI. MeTHanol blend veHICle oPeRaTIonal IMPaCTs
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Whenmethanolisblendedingasoline,itadverselyaffectscold-startcapabilityinanumberofsimilarways.Whilemethanoldepressesthelowerenddistillationofthegasolineintowhichitisblended,thevaporthatisgeneratedhasdisproportionatelymoremethanolinitmakingthevaporleanerthanthatfromstraightgasoline.Thehigherlatentheatofvaporizationofmethanolmakesthevaporgeneratedmoredifficulttoheatup,resultinginlowertemperaturesduringstartingevents.Ablendof5%methanolingasolineneeds14%moreenergytovaporizecompletely[32],withmostofthatdifferenceaccountedforbefore50%distilled,asillustratedinFigureV.2.Moreover,ifthegasolinehashaditsfrontendvolatilityadjustedtocompensatefortheazeotropingeffectwhenmethanolisadded,thelowboilinghydrocarbonsthatprovidemuchofthevaporforcold-weatherstarting,suchasbutane,willhavebeenreduced,causingfurtherdetrimenttocold-startingcapability.
InOtto-cyclesparkignitionengines,morefuelisintroducedduringcold-startthanisnecessaryforcompletecombustionsothatsufficientfuelvaporisgeneratedtogetintotheflammablerange.Intestingconductedwithgasolineat-22°F(-30°C),itwasfoundthattheamountofgasolineneededtoachievecold-startwaseighttimesthestoichiometricvalue.Withablendof10%methanolhavingthesameRVPasthegasoline,itwasfoundthatfuelneededtobeaddedattherateof14timesthe
stoichiometricvalue[32].Despitetheadverseimpactsaddingmethanolcanhavetocold-startperformance,fleettestsoflow-levelmethanolblendsdidnotreportstatisticallysignificantchangesincold-startperformance.
B. driVeABility
Ownersofmodernvehiclesexpectnearlyflawlessoperationintermsofdriveability,whichincludesnostallingorsurgingduringwarm-up,idleataconstantspeed,smoothaccelerationwithoutstumblesorsags,linearthrottleresponse,andabsenceofvaporlock.Asexplainedpreviously,addingmethanoltogasolinecausestheenginetooperateleaner,especiallyduringcold-startandwarm-up,whendriveabilitydefectsaremostlikely.TestingbyGeneralMotorshasshownthataddingmethanoltogasolineisequivalenttooperatingwithaleanercalibrationusinggasolineintermsofcausingdriveabilitydemerits(seeFigureVI.1).Recenttestsofexistinggasolinevehiclesusingupto30%ethanolwithoutdriveabilityproblemssuggeststhatcurrentvehiclesthathavefeedbackemissioncontrolsystemshavethecapabilitytocompensateforlow-levelmethanolblendsandshouldnothavedegradeddriveability.
fIgURe vI.1 Adding methanol to Gasoline is equivalent to Leaner Gasoline Calibration in Terms of Driveability (Source: ref. 32)
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c. AccelerAtion
Whenadriverevaluatesacceleration,itisoftennotjusthowquicklythevehiclewillaccelerate,butthequalityofthatacceleration(i.e.,linearthrottleresponse,nosurgesorstumbles,etc.).Ifthevehicleisnotfullywarmedup,methanolblendscancausethevehicletoexhibitsloweraccelerationandthedriveabilityproblemsjustidentified.Whenthevehicleisfullywarmedup,thedrivermaynotnoticeanychangeifthefuelsystemcompensatesforthemethanoladditionthroughthefeedbackcontrolsystem.However,ifthevehiclespendsasignificantamountoftimeatfull-throttle,accelerationmaybeimpacteddependingonthefull-throttlecalibrationusinggasoline.Forexample,testsofearlycarburetedvehiclesinBrazilcalibratedtouse20%ethanolfoundthataccelerationwasbetterusing20%ethanolthanstraightgasoline[39].Thereasonwasthatthecalibrationwastoorichformaximumaccelerationwhenusingstraightgasoline,whileusing20%ethanolmadethestoichiometryclosertothebestvalueformaximumpower.Allthingsequal,useofmethanolresultsinfasteraccelerationbecauseitshigheroctaneandlatentheatofvaporizationallowformoresparkadvancethangasoline.Enginesoptimizedformethanolcaneasilybemorepowerfulthansimilardisplacementgasolineengines,withtheresultbeingfasteracceleration.
d. fUel econoMy
AsshowninFigureV.8,addingmethanoltogasolinereducestheheatingcontentperunitvolumeoffuel.Controlleddynamometertestshaveshownthataddingmethanoltogasolinereducesfueleconomy(seeFigureVI.2)[40].However,whenthechangeinenergycontentwastakenintoaccount,therewasnochange,indicatingthattheengineefficiencywasnotaffected.(Notethat30%methanolwasthemaximumblendthisvehiclecouldaccommodatewithoutdriveabilityproblems.Cold-startingusing30%methanolwasnottested.)Vehicleusersexperienceawiderangeoffueleconomiesdependingonweatherandonhowthevehicleisused,andmaynotbeabletodistinguishtheimpactsoflow-levelmethanolblends.
0 5 10 15 20 25 30% Methanol Blend
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November 2007Use of MeTHanol as a TRansPoRTaTIon fUel vII. eMIssIons IMPaCTs
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VII. Emissions Impacts
A. priMAry reGUlAted exhAUSt eMiSSionS
Methanolhassomeinherentemissionadvantagesovergasolinewhencombustedininternalcombustionengines.EmissionsofCOareafunctionofcombustionstoichiometryandwillnotbesignificantlydifferentfromgasolinecombustionasthesamestoichiometry[33].Likewise,HCemissionswillbesimilarinmagnitudecomparedtogasoline,butunburnedmethanolhassignificantlylowerreactivityasanozoneprecursorintheatmospherecomparedwithmostgasolineHCs.Thisadvantageisoffsetsomewhatbyincreasedformaldehydeemissionsfrommethanolcombustion,butmoderncatalystsystemsareveryeffectiveatreducingformaldehydeemissions,resultinginanetbenefitformethanolovergasoline.FigureVII.1showsgeneralengine-outemissiontrendsforCOandHCswithstoichiometryformethanolcombustion.
EmissionsofNOxaretypicallylowerthanthosefromgasolinewhenmethanoliscombustedundersimilarengineconditions(seeFigureVII.2).Thisisdueprimarilytothelowerpeakflametemperatureofmethanol,andsecondarily,tothehighlatentheatofmethanol,whichreducespre-ignitiontemperatures.Whenoperatinganengineatconstantcompressionratio,substituting100%methanolforgasolinehasbeenshowntoreduceNOxemissionsby30%[40,41].Thisadvantageissignificantlynegatediftheenginecompressionratioisincreasedand/orotherenginechangesaremadetomaximizethespecificpowerpotentialofmethanol.ResearchbyVolkswagenshowedthatincreasingthecompressionratioto13:1totakeadvantageofmethanol’shigheroctaneincreasedengine-outNOxemissionstothesamelevelasforgasolineatacompressionratioof8:1[42].However,withmodernthree-waycatalystsystems,theinherentadvantageoflowerengine-outNOxemissionsisnotasignificantadvantage.
Recentdevelopmentofthehomogeneouschargecompressionignition(HCCI)combustionsystemholdspromiseforinternalcombustionenginesusingneatmethanolasfuel.WhenmethanolisusedinHCCI
NOx EMISSIONS
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sion
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vII. eMIssIons IMPaCTsNovember 2007
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engines,emissionsofNOxcandecreasetonear-zero[43].HCCIengineshavethepotentialtoreplacebothgasolineanddieselengines.
Blendsofmethanolandgasolineaffectvehicleemissionsaccordingtotheamountofoxygenintroducedintotheblendfromthemethanol.FigureVII.3showsgeneraltrendsandconfidenceintervalsfortestsofmanyvehiclesusingarangeofmethanolblends(includingco-solvents)[44].Thesearetailpipeemissionsfromtypicalemissioncontrolsystemsforvehiclesofthatera(early1980s),whichincludedanoxidationcatalyst.Theadditionofoxygenthroughmethanolanditsco-solventscausesthefuelstoichiometrytomoveleanerwiththeresultthatCOandHCsarereducedwithNOxincreasingslightly.TheseresultswerecorroboratedbytheCoordinatingResearchCouncilintestsperformedfortheU.S.DepartmentofEnergy[45].
TheU.S.EnvironmentalProtectionAgency(EPA)testedsixin-usepassengercarschosentohavefuelandemissionsystemsrepresentativeofpopularonesinusein1995,usingblendsofupto40%ethanolingasoline[46].Thevehicleswere1990and1992models,allequippedwithfuelinjectionandthree-waycatalystfeedbackemissioncontrolsystems.Thegasolineusedwasrepresentativeofasummer-timegasolineandtheethanolwassplash-blended(i.e.,thehydrocarbonportionwasnottailoredforethanolblending).AlltheemissionstestswereconductedonachassisdynamometerusingtheFederalTestProcedure.Whilethesetestswereconductedusingethanol,theyarerepresentativeofmethanolblendsupto28%basedonthesameoxygencontent,whichistheprimarydriverincriteriaemissionschanges.(Therewasnoindicationwhetherthesevehicleswouldhaveacceptabledriveabilityatthehigherblendlevelstested.)
WhilethemagnitudeoftheemissionchangesvariedamongthesixvehiclesEPAtested,theyallshowedthetrendsillustratedinFigureVII.3.Basedonalinearregressionoftheresults,EPAfoundthatthesevehiclesonaverageshoweda45%reductioninCOemissionsat14%oxygenintheblend(theequivalentof40%ethanolor28%methanol).ForHCs,thereductionwas32%whileNOxincreased64%.Thus,whilethesevehicleswereatleasttenyearsnewerthantheonestestedtodevelopthedataofFigureVII.3,thesametrendspersisted,nodoubtduetothefactthatmostemissionsfromvehicleswithmoderncatalyticemissioncontrolsystemsoccurduringopen-loopoperation,e.g.,cold-start,warm-up,andwide-open-throttleacceleration.Itshouldbenoted,however,thatthesevehicleshaddiminishedresponsetofueloxygencontentcomparedwiththedataofFigureVII.3,thoughstillsignificant.
Amorerecentstudyusinglate-modelvehiclesfueledwith20%ethanol(7%oxygen)wasconductedbyOrbitalEngineCompany
fIgURe vII.3 emission Trends for blends of methanol in Gasoline (Source: ref. 44)
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November 2007Use of MeTHanol as a TRansPoRTaTIon fUel vII. eMIssIons IMPaCTs
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forEnvironmentAustralia[47].Theytestedfive2001modelyearvehicles,withallofthemhavingelectronicfuelinjectionandthree-waycatalystemissioncontrolsystems.ThesevehicleswerechosentoberepresentativeofthefleetinAustralia,buttheyhavethesamefuelandemissioncontrolsystemsastheircounterpartsinotherpartsoftheworld,exceptforperhapsdifferentcalibrations.
TheemissionsofthesevehiclesweretestedusingtheU.S.FederalTestProcedure,thesameasEPAusedinitstestprogram.Orbitalfoundthatonaverage,HCemissionsdecreasedby30%,COemissionsdecreasedby29%,andNOxincreasedby48%whenusing20%ethanol.TheseresultsaresimilarindirectionbutlargerthanwhatEPAhadfound(i.e.,16%decreaseintotalHCs,22%decreaseinCO,and32%increaseinNOxat7%oxygen).OnedifferencebetweenthesetwogroupsofvehiclesisthattheOrbitalvehicleswerepurchasednewandwereoperated4,000milesbeforeemissionstestingwasconducted,whilethevehiclestestedbyEPAwerein-usevehicles(theirindividualmileageaccumulationswerenotlisted).Itshouldalsobenotedthatpercentchangeinemissionsisbeingcomparedamongthesethreegroupsofvehicles,notabsoluteemissionslevels,whichweredifferentforallthevehiclestested.
Thesechangesinemissionsareindicativeoftheinabilityofthefuelsystemstocompensatecompletelyunderallcircumstancesfortheoxygenadditionfromtheethanol.Onepotentiallong-termimpactoftheoxygenadditionismorerapiddeteriorationofthecatalyst.Orbitalmeasuredcatalysttemperaturesthatwerehigherduringwide-open-throttleusing20%ethanolcomparedtostraightgasolineineveryvehicleduetotheinabilityofthefuelsystemtomaintainthedesiredstoichiometry.Elevatedcatalysttemperaturesduringwide-open-throttlecausemorerapidcatalystdeteriorationandincreasesinallemissionsasthecatalystdegrades.ThisisinfactwhatOrbitalfoundafterdrivingitsvehiclesfor80,000km(50,000miles)andretestingemissions[48].OnlytwoofthefivevehiclesshoweddecreasedHCandCOemissionsat50,000miles,whileallthevehiclesshoweddecreasesinHCsusing20%ethanolduringtestingat4,000miles.FouroutoffivevehiclesshowedanincreaseinNOxat50,000milesusing20%ethanol,whichisthesameresultaswasobtainedduringthe4,000miletestingexceptthatthevehiclesshowingthedecreasewerenotthesameat4,000and50,000miles.Orbitalinvestigatedthevehiclewiththemostemissionsdeteriorationandfoundthatthecatalysthadalargedecreaseinconversionefficiency,withhighercatalystoperatingtemperaturesbeingthemostlikelyreason.Thisvehiclehadalowpower-to-weightratioandthereforeoperatedathighengineloadsforagreaterpercentageofthetime,whichaccelerateditscatalystdeteriorationduetohigherexhausttemperatures.Theeffectontheothervehicleswassimilarbutmoregradual.
ThesetestprogramssuggestthatusingintermediatetohighlevelmethanolblendsinvehiclesnotdesignedforthemcanreduceCOandHCemissionsintheshortterm,butcauseincreasesinallemissionsoverthelongtermifthecatalystismorerapidlydegraded.
B. cArBon dioxide eMiSSionS
Thepredominatecompoundfromthecombustionofmethanoliscarbondioxide,asfromgasoline.Forthesameamountofenergy,methanolwillproduce94%asmuchcarbondioxideasgasoline.Enginesthathavebeenoptimizedformethanolwithincreasedefficiencywillhavelowercarbondioxideemissions.TheGreenhousegases,RegulatedEmissions,andEnergyuseinTransportationmodel(GREET)maintainedbyArgonneNationalLaboratoryshowscarbondioxideemissionsforflexible-fuelvehiclesusing85%methanol(M85)tohavecarbondioxideemissionsthat
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are96%thoseofasimilarvehicleusinggasoline[49].Thisincreaserelativetoneatmethanolisdueprimarilytothe15%gasolineinM85.GREETalsoincludesa“neat”methanolvehiclethathasbeenoptimizedforM90.This“neat”methanolvehiclehascarbondioxideemissionswhichare89%thoseofasimilargasolinevehicle.ThedecreaserelativetotheM85vehicleisdueprimarilytothebuilt-inassumptioninGREETthatthe“neat”methanolvehicleis7%morefuelefficientthanthesimilargasolinevehicle.Methanolvehicleswithenginesoptimizedformethanolcouldachieveevengreaterfuelsavingswithcorrespondingdecreasesincarbondioxideemissions.
c. toxicS
Whenmethanoliscombusted,theHCemissionsarecomposedprimarilyofunburnedmethanolandaldehydes,withformaldehydebeingdominant.Testinghasshownthatneatmethanolwillproduceabouttwicethelevelofaldehydesasgasoline[50](seeFigureVII.4forgeneraltrendsinaldehydeemissionsfrombothmethanolandgasoline).Testsofneatmethanolvehicleshaveshownthatformaldehydeisthepredominanttoxicemissionfrommethanolcombustion[51].Aldehydeemissionsareeffectivelycontrolledbyuseofacatalyticconverter.
Gasolineproducesadditionaltoxicssuchas1,3-butadiene,benzene,hexane,toluene,andxylene,whicharisefromvarioushydrocarbons.Whenmethanolisaddedtogasoline,productionofthesetoxicsiscorrespondinglyreduced.Inaddition,ifthemethanoladditioncausesaleanshiftinstoichiometry,theoveralldecreaseinHCemissionsassociatedwiththatshiftdecreasestoxicemissionsinproportion.
d. eVAporAtiVe eMiSSionS
Neatmethanolproduceslowerlevelsofvaporcomparedtogasolinebecauseofitshigherboilingpointcomparedtotheinitialboilingpointofgasoline.EarlyworkbyUnionOilCompanyfoundthatmethanolvapordegradedtheabilityofautomotivecharcoalcanisterstoadsorbvaporscomparedtogasoline[36].However,theM85vehiclesproducedandusedintheU.S.metthesameevaporativeemissionstandardsascomparablegasolinevehiclesandlong-termdeteriorationofthecharcoalwasnotreportedasaproblem.
ALDEHYDE EMISSIONS
Methanol
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Lean 1.0 Rich
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Figure vII.4 Aldehyde emission Trends for methanol and Gasoline (Source: ref. 33)
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel vII. eMIssIons IMPaCTs
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AsexplainedinSectionV,addingmethanoltogasolinewillgreatlyincreasetheamountofvaporgeneratedalongthelowerhalfofthegasolinedistillationcurve.Sincevehicleevaporativesystemsaresizedforgasoline,addingmethanoltogasolinethathasnotbeenmodifiedtoreduceitsfrontendvolatility(0to50%distilled)willalmostcertainlyresultinsaturationofthecanisterand,consequently,veryhighevaporativeemissions.Inresponsetorequestsforuseofmethanol/gasolineblendsintheU.S.,theEPAdevelopedamodifiedevaporativeindextocapturethechangemethanolcausestogasolinefrontendvolatility.Methanol/gasolineblendsthatmeetthemodifiedevaporativeindexshouldnotcauseincreasesinevaporativeemissions.InoneofEPA’srulingsonamethanol/gasolinewaiverrequest,theycommentedthatproperlyformulatedblendswillnotdecreasetheabilityofthecarboncanisterstoadsorbvapors[52].ForevaporativeemissionscertificationofM85vehicles,EPArequirestestsusingM85,straightgasoline,andtheblendofthetwowiththehighestvaporpressure[53].
Asfuelsystemshavemovedawayfromsteeltanksandlinestoplastic,permeationemissionsfrommethanolandmethanolblendsislikely.(Permeationistheevaporationoffuelthroughelastomericmaterialsusedinthefuelsystem,butprimarilyfromthelinesandtanks.)IntheU.S.,testinghasbeendonetomeasurethepermeationemissionsofethanolblendsingasoline.Itwasfoundthattheethanolinethanolblendstendedtobepreferentiallyabsorbedintotheplasticfuellinesandtanks,andthenevaporatedawayfromthesurface[54].Sincetheimpactofmethanolonelastomersissimilartothatofethanol,andinsomecasesworse,itislikelythatmethanolblendswillcausepermeationemissionsaswell.Permeationemissionscanbepreventedbypropermaterialselectionanddesignchanges.Forexample,treatmentsforplastictankshavebeendeveloped(florinationandsulfonation)toreducepermeationlosses.Multi-layerfueltanksthatcontainacontinuouslayerofareducedpermeationcomponentinthemiddlehavealsobeendeveloped.Whilethetechniquestoreducepermeationundoubtedlycostmorethanplainplastictanks,theyarethesametechniquesusedtoreducepermeationemissionsfromgasolinevehiclesdesignedtomeetthemoststringentevaporativeemissionsstandards,i.e.,thePZEV(partialzero-emissionvehicle)standardinCalifornia.Asmorestringentevaporativeemissionstandardsbecomemoreprevalent,thecostdifferentialformethanolvehicleswithsuchfuelsystemswillbecomeinsignificant.
e. “Well-to-Wheel” GreenhoUSe GASeS
Whilemethanolcombustiondoesnotresultinsignificantlydifferentemissionsofcarbondioxidecomparedwithgasoline,thesituationchangeswhentheentireresource-extraction-through-end-usepathisconsidered.ThistypeofassessmentoftheGHGsfromtransportationvehiclesisknownas“well-to-wheels”.Inthiscase,itisassumedthatthemethanolisusedininternalcombustionenginevehiclesspecificallydesignedformethanol,whichtakeadvantageofmethanol’spropertiestoincreaseefficiency.
TheGREETmodelwasusedpredominatelyforthisanalysis[49].GREETonlyincludespreliminarynumbersformethanolfromcoalandmethanolfrombiomass.Anindependentestimateofthewell-to-wheelsGHGsofmethanolfromcoalwasmadeforthisanalysis.
Thefollowingmethanolproductionresourceswereincluded:
NaturalgasCoal
−−
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CoalwithsequestrationofcarbondioxideBiomass
Thenaturalgascaseisincludedasabenchmarkforcomparisonsincenaturalgasisthepredominateresourcecurrentlyusedtoproducemethanol.However,itshouldbeunderstoodthatthisnaturalgascaseisspecifictoNorthAmerica–methanolmadefromnaturalgaselsewhereorunderspecificcircumstancescouldhavehigherorlowerGHGs.ThecoalcasesarealsospecifictoNorthAmericaandassumeuseofbituminouscoal(propertiestakenfromGREET).Twolevelsofsequestrationareincluded:75%efficiencyreflectiveofcurrenttechnologyand90%efficiencywhichistheU.S.DepartmentofEnergygoalfor2012[55].Methanolfrombiomassisassumedtousewoodastheresourcewithgasificationtechnology.
Themethanolinternalcombustionenginevehiclesareassumedtobe7%moreefficientthantheirgasolinecounterparts[49].Thereasonsincludehigheroctanevalue,lowercombustiontemperature,andmoreefficientcombustion.
FigureVII.5showstheresults.Methanol(MeOH)fromnaturalgasisprojectedtoproducejustslightlylessGHGsthangasoline–thisisdueprimarilytotheassumptionthatmethanolvehiclesare7%moreefficient.WiththerangeofGHGemissionspossiblefrombothgasolineproductionandmethanolproductionfromnaturalgas,itismostlikelythatthisdifferenceisnotsignificant.MethanolfromcoalwithoutsequestrationproducesalmosttwicetheGHGsofgasoline–aresultthatisnotunexpectedgiventhehighcarboncontentandlowhydrogencontentofcoal.Methanolmadefromcoalwithtoday’slevelofcarbonsequestrationefficiencyshowsverysimilarGHGemissionscomparedtogasoline–improvementincarbonsequestrationcouldlowerGHGsabout15%further.Finally,methanolfrombiomasshasanetGHGcreditbecauseallthe
−−
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MeOH fromCoal
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fIgURe vII.5 methanol “Well-to-Wheel” GHGs from various resources
November 2007Use of MeTHanol as a TRansPoRTaTIon fUel vII. eMIssIons IMPaCTs
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carbonusedtomakeitisrenewable(i.e.,thecarbonemittedissequesteredbackintothegroundbyregenerationofthefeedstock)
Thecoalcaseshereassumeplantsthatonlymakemethanol.Plantsthatcombinemethanolproductionwithelectricitygenerationhavethepotentialtoproducemethanolmoreefficientlythanstand-aloneplants.TheefficiencyofproducingmethanolusingtheAirProductsLPMEOHTMmethanolproductiontechnologyhasbeenestimatedtobe71%,comparedwiththe55%assumedhereforstand-aloneplants[56].MethanolproducedinthesefacilitieswouldhavecorrespondinglylowerGHGs.
vIII. InfRasTRUCTURe IMPaCTs November 2007
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VIII. Infrastructure Impacts
Methanolismadeinnumerousplacesaroundtheworldandisoftentransportedviaoceantankertovariouscountriesthatconsumeit.Thissectionfocusesonthedistribution,storageandretaildispensingofmethanolwithincountriesforuseintransportationvehicles.
A. diStriBUtion
Methanolistypicallyshippedviarailroadtankcar,barge,andtrucktanker,dependingonvolumeanddistance[57].IntheU.S.,onlyaverysmallamountofmethanolissentthroughpipelines,andonlyoververyshortdistances[58].Pipelinetransportisthemostcost-effectivelong-termmethodfortransportingfuelsbecauseofthevolumesanddistancesinvolved.Manycountrieshavepipelinesforthetransportofpetroleumproducts,butusingthesepipelinestotransportmethanolfacesseveralhurdles.Duringtheintroductionofmethanol,methanolmovementwouldinitiallyrepresentasmallminorityofalltheliquidfuelbeingtransportedviapipeline.Intermittenttransportofmethanolinpetroleumpipelinesfacestheproblemsofpotentialinterfaceminglingandtheneedforadditionalstoragesuitedformethanol.Wherepetroleumproductsaretakenoutofthepipeline,thecut-pointisdesignedtoprotecttheproductthatwouldbemostunacceptablydegraded,whileleavingasmuchoftheinterfaceinaproductthatwouldnotbedegraded,ifpossible.Forexample,methanolcouldpossiblybeshippedneat,wrappedwithdifferentclassesofgasolineateachend.Theinterfacecouldstaywiththemethanol,thusprovidingsomeofthegasolinethatwouldotherwisebeblendedtoproduce,forexample,M85.Theproliferationofdifferentproductsforpipelinestowrap,however,makessucharrangementsincreasinglycomplicated.Ifmethanolhadtobewrappedwithproductsotherthangasoline,suchcuttingwouldbeunacceptable.Inthosecases,muchoftheinterface–the“transmix”–wouldhavetoberemovedandreprocessed,possiblybyasmallregionaltransmixseparatorbutinsomecasesitwouldhavetobeshippedbacktoarefinery.Suchseparationswillbemuchmoredifficultwithinterfacescomposedofmethanolandpetroleumfuel.
Inaddition,themethanolwillremoveanyexistingwaterandpetroleumresiduesinthepipeline,furtherdegradingthequalityoftheinterfacevolume.
Onetechniquetominimizeinterfacevolumeisthroughtheuseofadevicethatphysicallyseparatesbatcheswithinapipeline,commonlycalleda“pig.”Theuseofpigsmaynotsolvethewateruptakeanddepositremovalproblem,however,anditisunknownhowfrequentlyitispracticaltosendpigsthroughtheline(pipelinesgenerallyonlygoinonedirection–thepigswouldhavetobetransportedbacktotheplaceoftheirinsertion).Theseissuesandotherswillneedtobeexploredbeforeitwillbeknownwhethershipmentofmethanolthroughexistingpetroleumpipelineswillbepractical.
Someexistingpipelinesmaybedivertedtodedicatedmethanoluse.Oncethesepipelinesarecleaned,theywillnothavetheproblemsassociatedwithintermittentuseinpetroleumpipelinesjustdiscussed,andwaterpick-upandresidueremovalshouldnotbeproblems.Evenso,potentialmaterialcompatibilityissueswithexistingpipelinesrequireresearch,andtheavailabilityofstoragetankssuitabletostoremethanolremainsaquestionwhenusingexistingpetroleumpipelinesfordedicatedmethanoltransport.
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B. StorAGe
Bulkstorageofmethanolshouldbedoneinappropriatelydesignedhorizontalorverticalstoragetanks.Tolimitmoistureinfiltration,aconservationventwithaflamearrestorisrecommended,ornitrogenblanketing.Propergroundingisessential,givenmethanol’slowconductivity.
Forstorageatretailservicestations,theundergroundtankispreferred.Undergroundstoragehasseveraladvantages:thefuelstaysatarelativelyconstantcooltemperature;theabove-groundspaceismaximizedforvehiclerefueling;andrefillingfromtankertruckscanbedoneusinggravityratherthanapump.Tanksformethanolcanbemadefromstainlesssteel,carbonsteel,ormethanol-compatiblefiberglass.IntheU.S.,methanoltanksplacedundergroundmusthavesecondarycontainmentbecausemethanolisclassifiedasahazardouschemical.Secondarycontainmentincludes:
Double-walledtanksPlacingthetankinaconcretevaultLiningtheexcavationareasurroundingthetankwithnaturalorsyntheticlinersthatcannotbepenetratedbymethanol
Forundergroundmethanoltanksatservicestations,conservationventswithflamearrestorsaretypicaltopreventwaterabsorptionratherthannitrogenblanketing.Conservationventsareusuallyconfiguredtoallowventingtooccuronlywhenthepressureinthetankexceeds7-21kPa(1-3psi),andwhenthevacuuminthetankexceeds5-10cm(2-4inches)ofwater[59].Thisisespeciallyimportantwhenstoringneatmethanolsincethevaporspaceinthetankwillbeflammable,unlikestorageofgasolineorM85wherethevaporspacewillbetoorichtobeflammable.
Existingundergroundpetroleumtanksmustbethoroughlycleanedbeforestoringmethanoltoremoveallwaterandsediment.Someundergroundstoragetanksuselinerswhichmustbemethanol-compatible.
Inadditiontomoistureinfiltrationfromtheair,wateroftengetsintoundergroundstoragetanksfrominadequatesealsontherefillingmanholes.Effortsshouldbemadetopreventwaterinfiltrationfromthesurfaceabovesincethiswateroftenincludesimpuritiessuchassodiumandchlorideionsthatgreatlyincreasethecorrosivenessofmethanol
c. SerVice StAtionS
Servicestationsmustbecapableofmovingmethanolfromtheundergroundstoragetanktothedispenserandintothevehicle[60].Mostundergroundstoragetanksusesubmersiblepumps,whichmusthavematerialscompatiblewithmethanol.Asthemethanolispumpedfromtheundergroundtank,ittravelsthroughpipingtothedispenser(seeFigureVIII.1).Liketanks,pipingformethanolcanbemadefromstainlesssteel,carbonsteelormethanol-compatiblefiberglass.IntheU.S.,pipingcomesunderthesamerulesasundergroundtanks,i.e.,double-walledpipingorsecondarycontainmentisrequired.
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Forthreadedpipeconnections,Teflon®tapeorpasteispreferredforusewithmethanol.Pipedopeintendedforusewithgasolinewillbedissolvedbymethanol,creatingleaks.Boltedconnectionsmustusegasketscompatiblewithmethanol.
Dispensersdesignedforpetroleumfuelstypicallyusesteel,castiron,aluminum,brass,bronze,andstainlesssteel.Ofthese,onlythesteelsandcastironarecompatiblewithmethanol.Inaddition,dispensersuseseveralgasketsandelastomerswhichareunlikelytobemethanol-compatible.Dispensermanufacturershavedevelopedunitscompatiblewithmethanol;thesemustbeusedtopreventmalfunctionandfirehazardsfromleaks.
Mostdispensersincludefilters,bothspin-onandthosewithreplaceableelements.Themostdurablefiltersincludenylonfilterelementsandmethanol-compatibleadhesives.Becausemethanolisveryaggressivetomanymetalsandbecausetheproductsofcorrosioncancauseproblemsinmethanolvehiclefuelsystems,itisrecommendedthatmethanolfilterelementporesbe3µmmeandiameter,insteadofthe10µmmeandiametertypicalofthoseforgasoline[59].
Filterelementswithsmallmeandiameterporesaremoresusceptibletobuild-upofstaticelectricity.Thisisparticularlyaproblemformethanolbecauseofitslowconductivity.Inseverecases,thedischargeofstaticelectricityfromthefilterelementtothehousingcancauserapiderosionofthehousingfromtheinside,eventuallycausingaholetoappear.Changingthefilterbeforeback-pressurebuildssignificantlywillminimizebuild-upofstaticelectricity.
Whenusedformethanol,dispensinghosesdesignedforgasolinewillrapidlydegradeandputdebrisintothevehicle,whichwill,inturn,clogitsfuelfilter.Evenmethanol-compatibledispensinghoseshavebeenfoundtoreleaseplasticizersandshouldbesoakedfor24hoursinmethanoltoremovethembeforeinstallation[59].Break-awayfittingsarerecommendedformostdispenserapplicationsandneedtobemethanol-compatible.
Conventionalnozzlesdesignedformethanolareavailable,butabettersolutionisthe“dry-break”or“spill-free”nozzle.Thespill-freenozzle(seeFiguresVIII.2andVIII.3)wasdeveloped
fIgURe vIII.1 methanol refueling Station Schematic (Source: ref. 60)
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bytheMethanolFuelCellAlliance,anindustryconsortiumledbyBASF,BP,DaimlerChrysler,Methanex,Statoil,andBallard[61].Fiberopticcommunicationsarebuiltintothenozzleandthevehiclefuelreceptacletoensureproperfuelingwithoutanelectronicinterface.Useofsuchanozzleeliminatesspillsandconcernaboutfiresafetyandhumancontactwithmethanol[62].
fIgURe vIII.3 The Identic Spill-Free methanol refueling Nozzle In Use (Source: ref. 62)
fIgURe vIII.2 The Identic Spill-Free methanol refueling Nozzle In Use (Source: ref. 61)
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Ix. Methanol Use in Diesel Heavy-Duty Vehicles
Thephysicalandchemicalpropertiesofmethanolmakeitverywell-suitedforuseasaspark-ignitionenginefuel,butitsabilitytocombustwithoutformingsoot(duetothelackofcarbon-to-carbonbonds)hasattracteddieselenginedesignerstofindwaysofusingitaswell.Manywaysofusingmethanolindieselengineshavebeenresearchedincludinguseinblends,emulsions,fumigation,withtheadditionofignitionimprovers,indualinjectionengines,andinenginesmodifiedtoachievedirectcompressionignitionofmethanol[63].Notethatofthesemethods,onlyuseofignitionimproversandcompressionignitionresultedinenginesthatdisplacedalldieselfueluse,thoughcompletedisplacementwasnotviewedasarequirementsincetheemissionsbenefitsofmethanolweretypicallygreaterthanthepercentdieselfuelitreplaced.Dieselenginescouldalsobeconvertedtosparkignition,butthischangeessentiallychangesthemtobeOttoCycleengines.Numerousfleettestsofheavy-dutyvehicleswithmethanolengineshavebeenconducted[64,65,66,67].
A. USe of MethAnol in BlendS With dieSel fUel
Methanolhasverylimitedsolubilityindieselfuel(onlyafewpercent)andwasnotconsideredseriouslyasameansofusingitindieselengines.Otheroxygenateshavebeenseriouslyconsideredforblendingintodieselfuel[68].
B. USe of MethAnol in eMUlSionS With dieSel fUel
Theverylimitedsolubilityofmethanolindieselfuelledtoextensiveresearchtofindwaysofusingmethanolthroughemulsions[63,69].Throughtheuseofemulsions,itwasfoundpossibletoaddlargeamountsofmethanoltodieselfuel(testsusing10-30%werecommon).Thedisadvantagesfoundtomethanolemulsionsincludedthefollowing:
Roughlyanequalamountofemulsifierwasneededasmethanol,makingthefuelexpensive.Theadditionofmethanolquicklydegradedthecetanenumberoftheemulsion,necessitatingengineinjectiontimingchangesoradditionofanignitionimproveradditive.Emulsionsbecomequiteviscousatlowtemperaturesandtendtoseparateinthepresenceofwater.Emulsionstendtocorrodefuelinjectionsystemcomponentsandcauseelastomercompatibilityproblems.Sincethevolumetricheatingvalueofemulsionsisreducedrelativetodieselfuel,adjustmentstoincreasefuelflowmaybenecessarytomaintainfullpower.
Forthesereasons,noemulsionsofmethanolanddieselfuelhavebeencommercializedtodate.
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c. USe of MethAnol throUGh fUMiGAtion
Fumigationisamethodtointroducealcoholintoadieselenginebycarburetionorvaporizationintheintakemanifoldwithsubsequentignitionbydieselfuelinjection.Thisrequiresadditionofacarburetor,fuelinjectionsystem,orvaporizeralongwithaseparatefueltank,lines,andcontrolsforthemethanol.Methanoldeliverymustbelimitedatallloadstopreventmisfireandatintermediateandhighloadstopreventengineknock.Inthemidloadrange,upto50%ofthefuelenergycanbederivedfrommethanol,whileatlowerengineloads,upto80%dieselfuelenergysubstitutionhasbeendemonstrated[63].Thetypicaloverallreplacementvaluehasbeenmuchlower,however.Thecontrolrequirementofanenginetoachieveitsmaximumdieselfueldisplacementvalueincreasesthecomplexityoftheenginecontrolsystem.Anadvantageofafumigationsystemisthatswitchingfromfumigationtostraightdieselfueloperationmaybepossible–clearlyadesirableoptionifmethanolsuppliesareintermittent.
Turbochargedenginespresentdifficultiesformethanolfumigation.Ingeneral,itiseasiertointroducethemethanolbeforetheturbocharger,butmethanolisdifficulttovaporizetotallybecauseofitshighlatentheat,andliquidimpingementonthecompressorwheelwillcausedamagerapidly.Introductionofthemethanoldownstreamofthecompressoralleviatesthisproblembutmakesinstallationmoredifficult.
Overall,fumigationisbestsuitedtoretrofitapplicationswhereitcanhavebeneficialeffectsonemissions[70].
d. USe of MethAnol in dUAl injection enGineS
Indualinjectionengines,asecondinjectionsystemisaddedjustformethanol.Theoriginalinjectionsysteminjectsjustenoughdieselfueltoignitethemethanol.Dualinjectionenginesareveryeffectiveatusinglargeamountsofmethanol–displacementsof90%atfull-loadand50%atidleandlow-loadhavebeenachievedbynumerousresearchers[63].Enginesconfiguredthiswayhaveshownessentiallythesameefficiencyastheirdieselfuelcounterparts,withtheemissionsadvantagesofmethanol(i.e.,lowerNOxandparticulates).Dualinjectionenginesneverachievedcommercialization,nodoubtduetotheirincreasedcost(asecondfuelsystem)andtheinconvenienceofhavingtwofuelsystemsonboard.
e. USe of MethAnol With iGnition iMproVerS
Ignitionimprovers(alsoreferredtoascetaneimprovers)promiseanattractivemeanstoallowtheuseofmethanolindieselengines.Theadditionofignitionimproverstomethanolcangiveitthesameignitabilitycharacteristicsasdieselfuel.Thisallowstheuseofmethanolinunmodifieddieselengines,avoidingcomplicatedandcostlyenginemodifications(thoughthefuelinjectionsystemwillhavetobemodifiedforincreasedflowcapacityandforcompatibi1itywithmethanol).A1so,itcoulda1lowthesameenginetousemethanolanddieselfuela1ternativelyastheoperatorseesfit.
Whilenoignition-improvedmethanolhasbeenusedotherthaninfleetdemonstrations,ignition-improvedethanolhasbeenusedasafuelindieselenginesinBrazilsinceMercedes-BenzdoBrasilinitiatedatestprojectusingbusesin1979.Theinitialexperiencewasfavorableandin198322-tonand32-tonclasstruckswithenginesconvertedtouseignition-improvedethanolwereintroducedforsalebyMercedes-BenzdoBrasil.(Conversionkitsforexistingtruckswerea1somade
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availab1e.)Asof1986,about1,700trucksusingignition-improvedethanol(newandconverted)wereinoperationinBrazil[63].
Sincemostignition-improvershavenitrogenintheircomposition,concernwasexpressedthatthisnitrogenwouldcontributetoNOxemissions.ExtensivetestingshowedthatonlyasmallfractionofthisnitrogenendedupasNOxandoverall,NOxemissionsdecreasedbasedprimarilyontheemissioncharacteristicsofmethanol[63].
Overall,ignition-improvedmethanolrepresentsawaytousemethanolinexistingandnewdieselenginesalbeitwithsuitablemodificationstoaddressmaterialscompatibilityissues.Thecostoftheignitionimproverisalsoafactorinwhetherignition-improvedmethanolrepresentsaviablefuel.Inthisregard,dimethyletherhasshownpromise[71].
f. USe of MethAnol in dieSel enGineS USinG coMpreSSion iGnition
Severalresearchersdemonstratedthatdieselenginescouldachievecompressionignitionofmethanolwiththeassistanceofglowplugsor“hotspots”inthecombustionchamber.TheDetroitDieselCorporationusedthisconcepttobuildacompressionignitionversionoftheirpopular2-strokedieselenginethatwasusedinhundredsoftransitbusesintheU.S.andinotherheavy-dutyvehicleapplications[72].Thisengineachievedcompressionignitionofmethanolatlowloadsbyglowplugheating,andathighloadsbyretaininglargeamountsofburnedgaseswhichheatedtheincomingmethanolsoitwouldreachignitionundercompression.TheseengineshadverylowNOxemissionsandtheonlyparticulateemissionstheyemittedwherefromconsumedlubricatingoil.Whiletheseenginesarenolongerinuseandhavebeenreplacedbynewer-design4-strokeengines(nomethanolversions),theyillustratethecapabilitytodesignenginesforcompressionignitionofmethanol.Caterpillardevelopedamethanolversionoftheir33064-strokedieselengineusingglowplugstoachieveignition[73]andNavistardevelopedamethanolversionofitsDT-4664-strokedieselenginealsousingglowplugs[74].
Lookingforward,homogeneouschargecompressionignitionofferstheopportunitytodesignheavy-dutyenginesforcompressionignitionofmethanolwithverylowemissionsandhighefficiency[43].
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x. Non-Road Engines and Vehicles
A. SMAll enGineS
Millionsofsmallenginesareutilizeddailyinlawnmowers,chainsaws,leafblowers,etc.Mostatthesmallestendofthemarketaretwo-strokedesign,whilesomeofthelargerenginesinthiscategoryarefour-stroke.Thevastmajorityaresingle-cylinderwithsimplefuelsystemsconsistingofatank,shut-offvalveandverysimplecarburetor.Becausethiscategoryofenginesisverypricecompetitive,materialsarechosenonthebasisofcostandarenotengineeredtowithstandthesamelevelofmisusethatautomotivefuelsystemcomponentsareengineeredfor.
Thesesmallenginesaretypicallycalibratedtooperateonthe“rich”sideofstoichiometricforreasonsofstableoperation,easystarting,anddurability.Assuch,theseenginescantypicallyaccommodatefairlylargepercentagesofmethanolingasolinewithoutadverseimpactsonoperation.Intestsofasingle-cylinder(123ccdisplacement)gensetengine,itwasfoundtooperatewithoutanyadverseimpactsusing30%methanolingasoline[75].Thiswasdueprimarilytothefactthatthisenginewasstilloperatingrichofstoichiometricusing30%methanolingasolineatzeroengineload.Atfull-load,30%methanolingasolinereducedtheCOemissionsfrom8.7%downto4.8%.Similarly,HCemissionswerereducedfrom730to495ppm.NOxemissionswerenotmeasured,butattheserichstoichiometries,itislikelythattheywereverylowinallcases.Aldehydeemissionswerenotmeasured,butitwouldbeexpectedthatformaldehydeemissionswouldincreasesignificantlyfromthecombustionofmethanol.
TheEngineManufacturersAssociation(EMA)representstheinterestsofsmallenginemanufacturers.Whilemostdonotaddressuseofmethanol,individualmanufacturerguidelinesforusingethanolblendsprovidesomeinsight.Whilesomesmallenginemanufacturersacceptuseofethanolblends,theyrecommendthatthefuelnotbeallowedtostayinthefuelsystemwhiletheengineisnotbeingused.Thisispresumablybecausetheirfuelsystemsarenotcompatiblewithethanolunderconditionsofconstantexposure.Deteriorationofplasticpartssuchaslinesandtanksareprobable,asiscorrosionofthefuelsystemandevenofinternalengineparts–thecrankcaseoftwo-strokeengines,forexample.Corrosioninhibitorshavebeenfoundtobesuccessfulinreducingthecorrosionof2-strokeenginematerialsandwouldhavetobeintroducedasacomponentofthefuel[76].
B. lArGe enGineS
Largenon-roadenginesaretypicallyderivedfromtransportationengines,thoughsomearepurpose-built.Acharacteristictheyallhaveincommonisasimplefuelsystemandnoemissioncontrolsystem(thoughthisischangingintheU.S.,whichisimplementingemissionstandardsfornon-roadengines.)Largenon-roadenginestypicallyarenotset-uptooperateasrichlyastheirsmallercounterparts.Consequently,addingmethanoltotheirfuelwillbenoticedmorereadilyintermsofmoredifficultcold-starts,degradedtransientresponsetorapidthrottlechangesandreducedmaximumpoweroutput.Cloggedfuelfiltersarelikelysoonafterintroductionofmethanolblendssincethemethanolwillremoveanyresiduethathasbuiltupinthefuelsystemovertime.
Changesinemissionsfortheseenginesusingmethanolblendsshouldbesimilartothoseforsmallengines:significantlyreducedCOandHCs,andslightincreasesinNOx.Sincetheseengines
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rarelyhavecatalysts,methanolblendswouldbeexpectedtoincreaseemissionsofformaldehyde,whilehydrocarbontoxicswouldbeexpectedtodecrease,asexplainedinSectionVII.
Usingmethanolblendsinlargenon-roadenginesislikelytocausecorrosionofthefuelsystemcomponentsandincreasedwearoftheengineunlessoilchangesaremademorefrequently.Manyoftheseenginesusecarburetors,whicharemadeofmetalsthatwillcorrode,andhavemanyelastomericandplasticpartsthatwillbedegradedbymethanol.Fuellinesarelikelytoswellandsoften,leadingtoleaksastheydeteriorate.Filterelementstendtoseparatesincetheglueusedinmanufacturehasbeenshowntodissolvewhenexposedtomethanol.
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Appendix A. Properties and Characteristics of Importance for Fuel Specifications
Mostorallmethanolplantsintheworldtodayhavebeendesignedtoproducemethanoltoexactingchemicalgradestandards.Alessstringent“CommercialGradeMethanol”specificationhasalsobeenusedwhereahighlevelofchemicalpurityhasnotbeenrequired.Methanolbelowchemicalgradecanresultfromrunningachemicalmethanolplantbelowdesignstandardsforpurity,fromcontaminationinstorageandtransport,orfromotherprocesses,suchasrecyclingmethanolusedinachemicalprocess,suchasintheproductionofdimethylterephthalate.
Withrenewedinterestinusingmethanolasafuelforinternalcombustionengineandfuelcellvehiclesand/orasablendingcomponentforgasoline,therecouldbeaneedtoconsidertheadoptionofstandardsforsuchusebasedonthepropertiesofmethanolanditseffectonthepropertiesoftheblendedfuels.Suchstandardscouldtakeanumberofforms,includingstandardsforthemethanolitself,standardsformethanol/cosolventmixtures,and/orstandardsforthefinalblendedfuels.Someoftheparametersthatshouldbeconsideredforinclusioninsuchstandardswouldapplytobothneatmethanolfueluse(e.g.M100and/orM85)andlowlevelmethanolblends(e.g.5-10%,includingcosolvents),whileotherparameterswouldprobablybedifferentforhighlevelvs.lowlevelblends.Someofthefuelmethanolparameterscouldinvolvelesspuritythanchemicalgradestandards,butconcernsrelatedtofuelusecouldsuggesttheneedforadditionalparametersnotrelevantwiththeultra-purechemicalstandards.
TheASTMintheU.S.hasdevelopedandmaintainedaspecificationforM85foruseinFFVs[77].CaliforniadevelopedanM85specificationguideline[78]thoughithasbeensupersededbytheASTMspecification.Californiaalsodevelopedaneatmethanolspecificationguidelineformethanolusedinheavy-dutyvehiclesorforblendingofothernear-neatmethanolfuels[79].ThesespecificationsandguidelinesrepresenttheaccumulatedexperienceofusingmethanolasavehiclefuelintheU.S.Thefollowingnarrativeprovidesinsightintotheimportanceofthecomponentsofvariousfuelpropertiesandcharacteristicsthatareaddressedbythespecifications.
A. propertieS of concern for loW leVel MethAnol BlendS
Water ToleranceMethanolhasaveryhighmiscibilitywithwater,whilebothmethanolandwaterhavea
fairlylowsolubilitywithmanyofthehydrocarbonsconstitutinggasoline.Thesolubilityofbothmethanolandwateringasolinedependsonthecompositionofthegasoline,witharomaticshavingthehighestmutualsolubility,followedbyolefins.Therefore,methanolissusceptibletocarrywatercontaminationintogasolineandtoattractadditionalwateronceinavehicle’stank.Withaccumulationofwaterorsignificanttemperaturedrops,thefuelblendispronetoseparateintodistinctphaseswithdistinctwater/methanolandgasolinephases.Ifthisoccursinthetank,theaqueousphasewillfalltothebottom,buttheseparationcouldoccuratotherpointsinthefuelsystemandcouldpotentiallycauseavarietyofproblemsincludingfailuretostartbecausetheengineisstarvedofthevolatilehydrocarbons,knockingbecausethegasolinehaslosttheoctaneofthemethanol(andpossiblyofaromaticspartiallyseparating),filterplugging,andcorrosion,amongothers.
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Avoidanceofphaseseparationandwater-associatedproblemsinvolvesnumerousprecautionsinmarketinganddistributionofmethanolblends.Withregardtofuelcomposition,watertolerancecanbeaddressed(beyondlimitsonthemethanolcontent)throughacombinationofuseofcosolvents(usuallyhigheralcohols),formulationofthegasolineblendstock,andlimitsonwatercontentofthemethanoland/orblendedfuel,suchasatpointofsale.Unfortunately,formulatingtheblendstockforhighwatertolerancegenerallyworksagainstformulatingforemissionscontrol.
ASTMD4814,theU.S.StandardSpecificationforAutomotiveSparkIgnitionFuel,includesaspecificationforwatertolerance,withmaximumphaseseparationtemperatureprovidedforspecificregionsmonth-by-month.Unfortunately,thetestprocedureforthestandard,D6422,hasapparentlyshownpoorrepeatability,andthephaseseparationstandardofD4814maybeeliminatedintheabsenceofareliabletestmethod.Intheabsenceofsuchastandard,alimitonthewatercontentofthemethanolandblendedfuel,alongwithpossiblecosolventrequirements,maybetheonlyavailablecontrolparameters.Specificgravitymightalsobeusedasaproxyforwatercontentofthemethanolbutwillnotindicatethewatertoleranceoftheblendedfuel.
Volatility/DistillationVolatilitypropertiesofgasolines,includinggasoline/alcoholblends,areimportanttoavoid
bothproblemsincold-starting(inadequatevolatility)anddrivabilityproblemssuchasvaporlock,aswellasexcessevaporativeemissions(excessvolatility).Volatilityparameterstypicallyincludevapor/liquidratio,vaporpressure,anddistillationmeasuressuchasrelationshipsbetweentemperaturesandpercentsevaporated.Blendingmethanolwithgasolineatlowlevelstypicallybooststhevaporpressureandcreatesabulgeor“knee”inthedistillationcurve,whichcanbereducedwithuseofcosolvents,butblendstocksmayneedtobespeciallydesignedtoprovideacceptablevolatilitycharacteristics.Merelyreducinglightendstocompensateforthefrontendvolatilityboostmayresultinstartingproblemsandotherdrivabilitydegradation.
CarbonylsCarbonylsareoftenpresentasby-productsofmethanol/higheralcoholproductionand
representtoxicityconcernsinhighconcentrations.
AcetoneConcernshavebeenexpressedregardingacetone,includingconcernsoveruncontrolled
combustionandpossibledamagetovehicles.The“CommercialGrade”methanolspecificationsusedinEPAwaiversalsoincludedanacetonelimit,thoughthatmaynothavederiveddirectlyfromfuelconcernsorexperience.
AcidityLowmolecularweightacidscanbeverycorrosivetometals,particularlyinaqueoussolutions,
whichcouldresultfrommethanol’shighwatermiscibility.Onewayofcontrollingthemwouldbealimitonweightpercentofaceticacid.
AlkalinityExcessalkalinitycouldreflectanexcessofammonia,whichcouldalsobecorrosiveorhave
undesirablecombustionproperties,possiblycontrolledthroughweightpercent.
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pHeLevelsofpHebelow6.5infuelmethanolcanresultinformationoffilmorexcessivewearof
certainengineparts,whilepHelevelsabove9.0canadverselyimpactplasticpumpparts.
NonvolatilesNonvolatilescouldbepresentfromvarioussourcesandcouldresultincloggingoffueland
enginecomponentsorcouldcauseincreasesinexhaustemissionsthroughincompletecombustion.
CopperCopperisknowntobeacatalystoflowtemperatureoxidationofhydrocarbonsandto
contributetoformationofgumsandpolymers.
Corrosion/ConductivityCorrosionisaconcerngenerallyforalcohol/gasolineblends,includingpossiblecorrosionfrom
thealcohols,fromwatercarriedbythealcohols,orfromexcessacidityorammonia.Whiletestmethodsdonotexistforallmetalsusedinvehiclesystems,afewdoexistandshouldbeconsidered,amongthemcopperstripcorrosionandtheNACERustTestadoptedbytheNationalAssociationofCorrosionEngineers.Conductivitycanalsobeusedasanindicatoroftotalions,whichwillserveasacontrolonioniccorrosivity.
AshAshismorelikelytobepresentfromcosolventalcoholsthanfromthemethanolitselfbut
couldalsobeaconcernandshouldbeconsidered.
GumPresenceofgumsinfuelcancauseformationofdepositsthatcouldimpedethefunctioningof
movingpartswithinenginesandfuelsystems,aswellasplugfilters,etc.Alcoholshavebeenknowntodissolvegumsinstorageandtransportvessels,carryingthemintovehiclefuelsystems.Althoughthealcoholsarenotthemselveslikelytoformgums,impuritiesinthealcohols,suchascopper,cancontributetogumformation.Testproceduresexistforpresenceofgums,bothas“existentgums”andas“solventwashedgum,”i.e.,gumpresentafteraheptanewashofthefuel.
SulfurSulfurreducestheeffectivenessofemissionscontrolsystemsandcausesthemtodegrademore
rapidly.Inaddition,itcancauseengineoiltodegrademorerapidlyandcorrodeengineparts.TheU.S.andEuropehaveadoptedstrictlimitsonthesulfurcontentofgasoline,andmethanoladditionshouldnotbeallowedtocausethestandardtobeexceeded.
SulfatesSulfates,particularlyinorganicsulfates,havebeenbelievedtocausedepositsbothinfuel
dispensingpumpsandinvehiclefuelinjectors,withthelatterresultinginenginemisfiringandpoordriveability.Sulfateionsarealsoofconcerninregardtoelectrolyticcorrosion.Considerationshouldbegiventoincludingeitheratotalsulfatespecification,inorganicsulfatespecification,orboth.
aPPendIx aNovember 2007
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Chlorides/ChlorineLowconcentrationsofchlorideionscanbecorrosivetometals.Atestprocedureexistsfor
chlorideion.Chloridesandchlorinegenerallyarealsoofconcernrelatingtocorrosion,formationofdioxinsincombustion,andotherpossibletoxiccombustionproducts,sothatatotalchlorideoraninorganicchlorinetestmightalsobeconsidered.
Purity and AppearanceStandardscanspecifypurityandappearancecharacteristicsasgeneralprecautionsagainst
otherconcernsnotspecificallyidentified.
B. propertieS of concern for hiGh leVel MethAnol fUelS (e.G., M85)
MostoftheparametersofconcernandpossibletypesofspecificationsindicatedabovewillalsobeapplicabletoneatmethanolandM85,sometoagreaterdegreeandsometoalesserdegree.Therearesomedifferences,however,asdescribedbelow.
Volatility/DistillationUnlikewithlowlevelmethanolblends,theprimaryvolatilityconcernwithhighlevelmethanol
fuelsisinadequatevaporpressureforcold-starting,particularlyinlowambienttemperatures.RVPhastraditionallybeenusedtoassurestartingwithhydrocarbonfuelsbuthassometimesbeenfoundinadequateforM85.Althoughthereisnogenerallyacceptedspecification,GeneralMotorsCorporationhasproposeda“ColdStartingPerformanceIndex”thatcorrelatesbetterwithstartingthanRVPdoes.VolatilityanddistillationparametersforM85fuels,aswithlowerlevelblends,aredeterminedprimarilybythecompositionofthehydrocarbonfractionofthefuel.Fordriveabilitygenerally(beyondstartingconcerns),thesamedistillationspecificationsthatapplytoothersparkenginefuelscanbeusedforM85.
Flame LuminosityMethanolburnswithaflamethatisnearlyinvisibleindirectsunlight,whichraisessafety
concernsiffiresweretooccurandgounnoticed.Flameluminositycanbeprovidedbydesignofthehydrocarbonportionofthefuel,withhigherconcentrationsofaromatics,particularlycertainaromatics,providinggreaterluminosity.Considerationshouldbegivenforincludingaflameluminosityspecification.
LubricityMethanolprovideslesslubricitythanhydrocarbonfuels,whichcanresultinincreasedwear
onvariousenginefuelsystemcomponentswithveryhighlevelblends.Lubricityadditivesareonemeansofaddressingthis.Eitherafuellubricitystandardorarequirementforadditivesmeetinganadditivestandardcouldbeused.
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