The Case for Dieselcleanefficientfast cars.docx
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TheCaseforDieselcleanefficientfastcars
TheCaseforDiesel:
Clean,Efficient,FastCars(HybridsBeware!
)
Thedarkhorseoffossilfuelshascleanedupitsact,allowingautomakerstocreatecarsfortheU.S.thatareultraefficientandhigh-performance.Herecomesthe75-mpgrevolution.
MergingwithnorthboundtrafficonInterstate75justoutsideAuburnHills,Mich.,Ipunchtheaccelerator,quicklyswingleftintothepassinglaneandpullforcefullyaheadofthecarsaroundme.Inanyotherride,onanyothergraymorning,it'dbejustanotherInterstatemoment.Butthisrushhour,I'mbehindthewheelofapreproduction2009VolkswagenJetta,whichispoweredbya2.0-literturbo-charged,direct-injecteddieselenginethat,evenasIleavethespeedlimitintatters,isaveragingnearly50mpg.Equallyimportant,what'scomingoutofthetailpipeisnodirtierthantheemissionsfromthe35-mpgeconoboxesIcannowseeinmyrearviewmirror.Speed,fuelefficiencyandminimalemissions?
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.
Engine:
3.0-litertwin-turboinlineSix
TargetReleaseDate:
2008
BMWplanstoreleasethis3.0-literin5and6Seriesmodelsin2008aswell.Itreportedlygetsmorethan35mpg
Engine:
2.9-literTDIV6
TargetReleaseDate:
2009
LookforcleandieselalsointheBuickEnclave,GMCAcadiaandGMlight-dutypickups,around2010.
FORDF-150PICKUP
HONDAACCORDSEDAN
SATURNAURASEDAN
Engine:
4.4-literV8
TargetReleaseDate:
2009
DerivedfromtheEuro-spec3.6-litercurrentlyusedinLandRovers,whichgetaround31mpgonthehighway
Engine:
2.2-literi-DTEC
TargetReleaseDate:
2009
TheBritishversiongets51.4mpgincombinedcity/highwaydriving.ThehybridCivicgets50mpg.
Engine:
Tobedetermined
TargetReleaseDate:
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-ppmstandÂardinstitutedin1993.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),whichminimizescarbonmonoxideandhydroÂcarbons.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