The Case for Dieselcleanefficientfast cars.docx

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