How Diesel Locomotives WorkWord格式文档下载.docx
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How Diesel Locomotives WorkWord格式文档下载.docx
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The3,200-horsepowerenginethatdrivesthemaingenerator
WhyHybrid?
WhyDiesel?
Themainreasonwhydiesellocomotivesarehybridisbecausethiseliminatestheneedforamechanicaltransmission,asfoundincars.Let'
sstartbyunderstandingwhycarshavetransmissions.
Yourcarneedsatransmissionbecauseofthephysicsofthegasolineengine.First,anyenginehasaredline--amaximumrpm(revolutionsperminute)valueabovewhichtheenginecannotgowithoutexploding.Second,ifyouhaveread
HowHorsepowerWorks,thenyouknowthatengineshaveanarrowrpmrangewherehorsepowerand
torque
areattheirmaximum.Forexample,anenginemightproduceitsmaximumhorsepowerbetween5,200and5,500rpm.Thetransmissionallowsthe
gearratiobetweentheengineandthedrivewheelstochangeasthecarspeedsupandslowsdown.Youshiftgearssothattheenginecanstaybelowtheredlineandneartherpmbandofitsbestperformance(maximumpower).
Thefive-orsix-speedtransmissiononmostcarsallowsthemtogo110mph(177kph)orfasterwithanengine-speedrangeof500to6,000rpm.Theengineonourdiesellocomotivehasamuchsmallerspeedrange.Itsidlespeedisaround269rpm,anditsmaximumspeedisonly904rpm.Withaspeedrangelikethis,alocomotivewouldneed20or30
gears
tomakeitupto110mph(177kph).
Agearboxlikethiswouldbehuge(itwouldhavetohandle3,200horsepower),complicatedandinefficient.Itwouldalsohavetoprovidepowertofoursetsofwheels,whichwouldaddtothecomplexity.
Bygoingwitha
hybrid
setup,themaindieselenginecanrunataconstantspeed,turninganelectricalgenerator.Thegeneratorsendselectricalpowertoatractionmotorateachaxle,whichpowersthewheels.Thetractionmotorscanproduceadequatetorqueatanyspeed,fromafullstopto110mph(177kph),withoutneedingtochangegears.
WhyDiesel?
Dieselengines
aremore
efficient
thangasolineengines.Ahugelocomotivelikethisusesanaverageof1.5gallonsofdieselpermile(352Lper100km)whentowingaboutfivepassengercars.Locomotivestowinghundredsoffullyloadedfreightcarsusemanytimesmorefuelthatthis,soevenafiveor10percentdecreaseinefficiencywouldquicklyadduptoasignificantincreaseinfuelcosts.
SteelWheels
Everwonderwhytrainshave
steelwheels,ratherthan
tires
likeacar?
It'
storeduce
rollingfriction.Whenyourcarisdrivingonthefreeway,somethinglike25percentoftheengine'
spowerisbeingusedtopushthetiresdowntheroad.Tiresbendanddeformalotastheyroll,whichusesalotofenergy.
Theamountofenergyusedbythetiresisproportionaltotheweightthatisonthem.Sinceacarisrelativelylight,thisamountofenergyisacceptable(youcanbuylowrolling-resistancetiresforyourcarifyouwanttosavealittlegas).
Sinceatrainweighsthousandsoftimesmorethanacar,therollingresistanceisahugefactorindetermininghowmuchforceittakestopullthetrain.Thesteelwheelsonthetrainrideonatinycontactpatch--thecontactareabetweeneachwheelandthetrackisaboutthesizeofadime.
Byusingsteelwheelsonasteeltrack,theamountofdeformationisminimized,whichreducestherollingresistance.Infact,atrainisaboutthemostefficientwaytomoveheavygoods.
Thedownsideofusingsteelwheelsisthattheydon'
thavemuch
traction.Inthenextsection,we'
lldiscusstheinterestingsolutiontothisproblem.
Traction
Tractionwhengoingaroundturnsisnotanissuebecausetrainwheelshaveflangesthatkeepthemonthetrack.Buttractionwhenbrakingandacceleratingisanissue.
Thislocomotivecangenerate64,000poundsof
thrust.Butinorderforittousethisthrusteffectively,theeightwheelsonthelocomotivehavetobeabletoapplythisthrusttothetrackwithoutslipping.Thelocomotiveusesaneattricktoincreasethetraction.
Infrontofeachwheelisanozzlethatusescompressedairtospraysand,whichisstoredintwotanksonthelocomotive.Thesanddramaticallyincreasesthetractionofthedrivewheels.Thetrainhasanelectronictraction-controlsystemthatautomaticallystartsthesandsprayerswhenthewheelssliporwhentheengineermakesanemergencystop.Thesystemcanalsoreducethepowerofanytractionmotorwhosewheelsareslipping.
Nowlet'
scheckoutthelayoutofthelocomotive.
TheLayout:
MainEngineandGenerator
Nearlyeveryinchofthe54-ft(16.2-m)locomotiveistightlypackedwithequipment.
Mouseoverthepartlabelstoseewhereeachislocatedonthedieselengine.
MainEngineandGenerator
Thegianttwo-stroke,
turbocharged
V-12andelectricalgeneratorprovidethehugeamountofpowerneededtopullheavyloadsathighspeeds.Theenginealoneweighsover30,000pounds(13,608kg),andthegeneratorweighs17,700pounds(8,029kg).We'
lltalkmoreabouttheengineandgeneratorlater.
Theviewfromthecabofthelocomotive
CabandTrucks
Mouseoverthepartlabelstoseewhereeachislocatedonthedieselengine.
Cab
Thecabofthelocomotiveridesonitsownsuspensionsystem,whichhelpsisolatetheengineerfrombumps.Theseatshaveasuspensionsystemaswell.
Insidethecabtherearetwoseats:
onefortheengineerandoneforthefireman.Theengineerhaseasyaccesstoallofthelocomotive'
scontrols;
thefiremanhasjustaradioandabrakecontrol.Alsoinsidethecar,rightinthenoseofthelocomotive,isa
toilet.
Trucks
Thetrucksarethecompleteassemblyoftwoaxleswithwheels,tractionmotors,gearing,suspensionandbrakes.We'
lldiscussthesecomponentslater.
Power,FuelandBatteries
Head-endPowerUnit
The
head-endpowerunit
consistsofanotherbigdieselengine,thistimeafour-stroke,twin-turbochargedCaterpillarV-12.Theengineitselfismorepowerfulthantheengineinalmostanysemi-truck.Itdrivesageneratorthatprovides480-volt,3-phaseACpowerfortherestofthetrain.Thisengineandgeneratorprovideover560kWofelectricalpowertotherestofthetrain,tobeusedbytheelectricairconditioners,lightsandkitchenfacilities.Byusingacompletelyseparateengineandgeneratorforthesesystems,thetraincankeepthepassengerscomfortableevenifthemainenginefails.Italsodecreasestheloadonthemainengine.
FuelTank
Thishugetankintheunderbellyofthelocomotiveholds
2,200gallons
(8,328L)ofdieselfuel.Thefueltankiscompartmentalized,soifanycompartmentisdamagedorstartstoleak,pumpscanremovethefuelfromthatcompartment.
Batteries
Thelocomotiveoperatesonanominal64-voltelectricalsystem.Thelocomotivehaseight8-volt
batteries,eachweighingover300pounds(136kg).Thesebatteriesprovidethepowerneededtostarttheengine(ithasahugestartermotor),aswellastoruntheelectronicsinthelocomotive.Oncethemainengineisrunning,analternatorsuppliespowertotheelectronicsandthebatteries.
Let'
stakeamoredetailedlookatsomeofthemainsystemsonthelocomotive.
TheEngineandGenerator
ThemainengineinthislocomotiveisaGeneralMotorsEMD710seriesengine.The"
710"
meansthateachcylinderinthisturbocharged,two-stroke,dieselV-12hasadisplacementof710cubicinches(11.6L).That'
smorethandoublethesizeofmostofthebiggestgasolineV-8carengines--andwe'
reonlytalkingaboutoneofthe12cylindersinthis3,200-hpengine.
Sowhy
two-stroke?
Eventhoughthisengineishuge,ifitoperatedonthefour-strokedieselcycle,likemostsmaller
dieselengines
do,itwouldonlymakeabouthalfthepower.Thisisbecausewiththetwo-strokecycle,therearetwiceasmanycombustionevents(whichproducethepower)perrevolution.Itturnsoutthatthedieseltwo-stokeengineisreallymuchmoreelegantandefficientthanthetwo-strokegasolineengine.See
HowDieselTwo-StrokeEnginesWork
formoredetails.
Youmightbethinking,ifthisengineisabout24timesthesizeofabigV-8carengine,andusesatwo-strokeinsteadofafour-strokecycle,whydoesitonlymakeabout10timesthepower?
Thereasonisthatthisengineisdesignedtoproduce3,200hpcontinuously,anditlastsfordecades.Ifyoucontinuouslyrantheengineinyourcaratfullpower,you'
dbeluckyifitlastedaweek.
Herearesomeofthespecificationsofthisengine:
∙Numberofcylinders:
12
∙Compressionratio:
16:
1
∙Displacementpercylinder:
11.6L(710in3)
∙Cylinderbore:
230mm(9.2inches)
∙Cylinderstroke:
279mm(11.1inches)
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