The Case for Dieselcleanefficientfast carsWord文件下载.docx
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Thesearen'
tcharacteristicsusuallyassociatedwithdiesel-poweredvehicles.Buttheywillbe.
MostAmericanshaveabadimpressionofdieselcars.Wethinkofthemasloud,hardtostartandfoul-smelling.Wesneeratthemforlackingtheget-up-and-gooftheirgasoline-poweredcousins.Andwedislikethemfortheirperceivedenvironmentalsins,chieflythepollutingbrewofsulfurandnitrogencompoundsthattheyemitintotheatmosphere.Allthosecomplaintswerefairagenerationago,whenthetwinenergycrisesofthe1970spropelleddieselsintonationalpopularityandkeptthemthereforadecade.Backthen,manydriversignoreddiesel'
sfaults,orwereunawareofthem,becausedieselcarsran30percentfartheronagallonoffuelthansimilargasoline-poweredcars.Itfeltsavvytobuyadiesel,evendaring.Thenfuelpricesdroppedinthemid-1980s,anddriversabandonedtheirclattering,odoriferousfuelsippers.Theywentbacktogasoline.
Today,dieselpowertrainsareonthemapagain,forbothcarmanufacturersandefficiency-mindeddrivers.Thetechnologycouldbeheretostay,eveniffuelprices(improbably)decline.Thenewcarsrunaswellastheirgasoline-poweredcompetitors.Andasfortheemissionsproblemsofthepast--well,thedirtybirdoffossilfuelsisn'
tsodirtyanymore.
TheComingDieselInvasion
AUDIA4SEDAN
BMW3SERIESSEDAN
CADILLACCTSSEDAN
Engine:
3.0-literV6
TargetReleaseDate:
2008
This240-hpturbochargeddirect-injectedenginewillalsobeavailableinthefull-sizeAudiQ7sportutility.
3.0-litertwin-turboinlineSix
BMWplanstoreleasethis3.0-literin5and6Seriesmodelsin2008aswell.Itreportedlygetsmorethan35mpg
2.9-literTDIV6
2009
LookforcleandieselalsointheBuickEnclave,GMCAcadiaandGMlight-dutypickups,around2010.
FORDF-150PICKUP
HONDAACCORDSEDAN
SATURNAURASEDAN
4.4-literV8
DerivedfromtheEuro-spec3.6-litercurrentlyusedinLandRovers,whichgetaround31mpgonthehighway
2.2-literi-DTEC
TheBritishversiongets51.4mpgincombinedcity/highwaydriving.ThehybridCivicgets50mpg.
Tobedetermined
2010
TheAura'
sEurotwin,theOpelVectra,getsmoreTDIoptionsin'
09,whichwilltransfertothemodelcominghere.
TheSulfurSolution
"
Ifyoutoldme10yearsagothatI'
dbeputting`clean'
and`diesel'
inthesamesentence,I'
dhavesaidyouwereoutofyourmind,"
saysMargoOge,directoroftheOfficeofTransportationandAirQualityattheEnvironmentalProtectionAgency.However,inresponsetoEPAmandatesthatwentintoeffectinlate2006,oilrefineriesarenowproducingwhat'
scalledultra-low-sulfurdiesel(ULSD).Bydefinition,this"
cleandiesel"
hassulfurconcentrationsofnomorethan15partspermillion(ppm).That'
s98.5percentcleanerthanthesludgethatcoursedthroughthefueldeliverysystemsinthosedisco-erarides,and97percentlesssulfurthanwasallowedundera500-ppmstandÂ
ardinstitutedin1993.Thecutinsulfurmeansthatlesssulfurdioxidegoesintotheatmosphere,whereitcancombinewithwatertoproducesulfuricacid--andthus,acidrain.Therearefurtherbeneficialeffectsofthesulfur-lightfuel,onesthatcouldmaketheadventofcleandieselasenvironmentallymomentousastheintroductionofunleadedgasolinein1974.
Sulfurclogsemission-controldevicesindiesel-poweredcarsthesamewayleadimpededcatalyticconvertersingasolinesystems,"
Ogesays."
Removingtheleadfromgasolineenabledengineerstodevelopanewgenerationofemission-controltechnologiesthathelpedreducenoxiousexhaustemissionsby98to99percent."
Carmakershavealreadystartedbuildingexhaust-scrubbingsystemsforenginesthatburnULSD--sothatnotjustsulfurbutarogue'
sgalleryofotherpollutantsarekeptoutoftheair.Thoughtheydifferindesign,thesystemssharesomebasiccomponents.InaMercedes-BenzBlueTecsystem,forexample,exhaustfromtheengineisfirstfilteredthroughadevicethatlowerscarbonmonoxideandhydrocarbonlevels.Thenitrunsthroughanapparatusthatremovessootandotherparticulates.Finally,theremainingexhaustgasissprayedwithaurea-basedsubstancethathelpsconvertharmfulnitrogenoxides--NOxistheshorthandforthisgroupofcompounds--intoharmlessnitrogengasandwatervapor.AccordingtoMercedes-Benz,thesystemreducesthetotaloutputofharmfulemissionsby80to90percent.Theprocesseveneliminatesdiesel'
sbadodor.
HowTheyWork:
EmissionReductionSystems
Exhaustleavestheengineandpassesthroughadieseloxidationcatalyst(DOC),whichminimizescarbonmonoxideandhydroÂ
carbons.Itthenpassesthroughaself-cleaningparticulatefilterthattrapsandstoressoot.Aurea-basedsolution,commerciallyknownasAdBlue,isthensprayedintotheexhaustflow.Heatfromtheexhausttransformstheureaintoammonia,whichreactswithnitrogenoxides(NOx)intheSCR,wherethemixisconvertedintoharmlessnitrogengasandwatervapor.
ExhaustfromtheengineflowsthroughacombinationDOC(diminishingtheamountofcarbonmonoxideandhydrocarbons)andaself-cleaningparticulatefilter,whichremovessoot.Fromthere,itentersanewtypeofcatalyticconverterthatabsorbsaportionoftheNOxfromtheexhaustgasandconvertsitintoammoniawithouttheneedforanorganiccatalystlikeAdBlue.ThesystemrecombinesthatammoniawiththeremainingNOx,convertingitintoharmlessnitrogenandwatervapor,justliketheSCRsystem.
The250,000-MileEngine
ULSDfuelandthenewexhaustsystemsreceivemostofdiesel'
saccolades,buttheyaren'
ttheonlyadvancestosettoday'
sdieselsapartfromtheirpredecessors.Advancedelectronicenginecontrolmodulesregulatefunctions,fromfuelinjectiontotiming,morepreciselythanoldmechanicalcontrolsystems,furtherminimizingemissionsandmaximizingfueleconomy.Turbochargerspumpmoreairintotheengines,helpingtoovercomediesel'
sformersluggishnessathigherrpm.Andimprovedengineisolationstrategies,suchastheincorporationofactivemounts,hasquietedtheknockingnoisestypicallyassociatedwithdiesel-poweredvehicles.
Meanwhile,diesel'
scorevirtuesremainunchanged.Thefuelcontainsmoreenergyperunitvolumethangasoline,anddieselenginesoperateathighercompressionratiosthangasolineengines--typically14:
1to25:
1,comparedto8:
1to12:
1.(Thecompressionratioistherelationshipbetweenthevolumeofthecylinderwhenthepistonisatthebottomofitsstrokeandthevolumewhenit'
satthetop.)Thehigherthecompressionratio,themoremechanicalenergyanenginecansqueezefromitsfuel/airmixture.Soeachtimethemixtureinadieselengine'
scylinderignites,thecargetsaslightlybiggerpushthanitwouldinagasolineengine.Thatmeansittakeslessfueltomovethecardowntheroad.Italsomeansthattheenginegeneratesalotofpowerevenwhenitisn'
tcyclingfast--andthat'
sthesourceofthebeefylow-endtorquethesevehiclesarefamousfor.
Thehighcompressionratiosalsoexplainwhydieselenginestendtolastsolong."
Dieselenginesneedtobebuiltstronger,"
explainsTonyMolla,authorofChilton'
sDieselEngineServiceManual."
Thecrankshaftandconnectingrodsarequiteabitheavierthanthoseingasolineengines."
Andbecausedieselhasalowcoefficientoffriction,italsohappenstobeagoodlubricantthatprovidesprotectiontothecylinderwalls.Theresult?
It'
snotunusualtoseedieselenginesstillchuggingalongat250,000miles.
TheEuropeanModel
FansofdieseltechnologyoftenlooklonginglyatEuropetoseehowtheirfavoriteautomotivefuelisfaringinafriendlierenvironment--namely,onewheregasolinecosts$7pergallon.ManyEuropeancountriesprovidetaxbreaksondieselthatmakeitconsistentlycheaperthangas.Morethanhalfofthevehiclessoldonthecontinentaredieselpowered,andthetechnology'
sproponentsliketopointoutthatEurope'
saveragefuelconsumptionis36mpg,comparedtojust22mpgintheUnitedStates.(Tobefair,thatfueleconomynumberispartlyduetothefactthatEuropeansdrivesmallercars,regardlessoftheirpowertrains.)Coulddieselgainasimilarlevelofacceptancehere?
Perhaps.ArecentstudybyJ.D.PowerandAssociatesfoundthatin2007,23percentofU.S.carbuyerswereconsideringacleandieselfortheirnextpurchase,upfrom12percenttheyearbefore.
Ultra-low-sulfurfuelisthekeytocleandiesel.ShellfuelscientistNigelDickensdisplaysthefruitsofthelab.(PhotographbyGettyImages)
Intheshortterm,thosenumberswon'
tbereflectedinnew-car
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