ThemarineDieselengine中文翻译.docx

ThemarineDieselengine中文翻译.docx

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ThemarineDieselengine中文翻译

ThemarineDieselengine

Authoredby:

MartinLeduc

Heatenginesaresometimesreferredtoasbeingmotors.Actually,amotorconvertsoneformofenergyintousefulworkwithouttheintentionalproductionofheat,suchasanelectricmotor.Adevicewhichburnsfuelcreatingheattoperformworkisaheatengine.Heatenginescanbeclassifiedasexternalcombustion,suchassteamboiler,orinternalcombustion（IC）.Theycanfurtherbedividedintothesparkignited（SI）engineorthecompressionignitedengine（CI）.Theparticularheatengineweareinterestedaboutwiththiswebpage,istheCompressionIgnitedheatengine.ThisstyleofenginehasbeenmostfamouslyreferredtoastheDieselengine,namedafterit’sinventor,RudolphDiesel.

Thecompressionignitedinternalcombustionenginehastwomaindesigns:

thefourstrokecycle,andthetwostrokecycleengine.Theyarebothverycommonthroughouttheworldbecauseoftheirhighefficiency-comparewithothertypesofheatengines.Theyburnawidevarietyofhydrocarbonfuel,whichisstillcommon.Heavyfueloil,intermediatefueloilandmarinedieseloilarethemostcommonhydrocarbonfuel.Thetwostrokeandfourstroketitlesreferstothemechanicalactionofthemachinery,inparticularthepistonwithinthecylinder,toachievethetheoreticalCarnotheatcycle,asdefinebythelawsofthermodynamics.

Dieselenginesarefurthermoresub-dividedintothreecategories:

slow,mediumandhighspeed.Slowspeedareconsideredtobeupto300rpmsuchasmostbigtwostrokeenginescommonlyfoundonships.Mediumspeedenginesdwellinthe300-900rpmrange.Theyaremostcommononsmallershipsandpowerplantsdriving electricalgeneratorsand/orthepropeller.Highspeedenginesarethemostcommon.Theirhighrevolutionsareidealfordrivingvehiclessuchasbussesandyachts.AllDieseltrucksandvehiclesonourroadsusethisclassofDiesels,havinganrpmover900.

Thetwostrokeengine...

Ittakestwostrokestocompleteapowercycle:

onestrokedown,onestrokeup,resultinginoneturnofthecrankshaft.Asopposetothefourstrokewhichmustseethepistonperformfourstrokesandtwocrankrotations,inordertoachieveonecycle.Thepowerstrokeoccursateverydownstrokewhichwouldleadustobelievethetwostroketobetwiceasefficient.Onlargeplants,thetwostrokeisabout1.8:

1morepowerfulthanafourstrokeengineofsimilarweight.Onsmallerapplication,i.e.abus, thepower/poundgapcloses,andtheeffectivehorsepowerofsimilarsizedengineswillbeaboutthesameforthetwoandfourstroke.

Thetwostrokeismostcommonlyseeninapplicationdemandingalargepoweroutput,suchasshipsandelectricgenerationplants.Intheworldofships,theseenginesarelarge,especiallytall;thisistoaccommodatethelongstrokeenginedesignershavecomeupwithtoincreasetheefficiencyofthepowerstroke.Additionally,thelargephysicalsizeofthesepowerplantstendstoslowthemdown.

Thisslowspeed,around100rpm,hastwobenefitstoanownerofaships.Thefirst,probablythemostimportant,allowstheenginetoburnheavyfueloil（HFO）efficiently.Although,theblack,tarlikesubstancecanbeusedasfuelinboththefourstrokeandtwostrokeengine.Thisfuelismuchcheaper,currentlyaround$150USD/ton,comparedtothe"ordinary"refineddieselfueloil（MDO）,withthecostbeingaround$300USD/ton.

Slowspeed,alsoallowsadirectcouplingofthepropellershafttothecrankshaft,eliminatingtheneedforgearingandsuch.Thereductionofassociatedgearservestoincreasetheirpowertoweightratiowhichusuallyequatestolowercost.Additionally,thetwostrokeengineshavealesscomplicateddesign,namelynointakevalves,thisreducethepossibilityofthingsfailing.Theseattributesgivethetwostrokeengineadvantagesoverthefourstrokes,makingitengineofchoiceforalmostalllargedeepseaships.

Themostprominentbuildersoflarge,slowspeed,twostrokeengineareSulzerofSwitzerland,producerofthefirstbigtwostrokedesign,andBurmeister&Wain（B&W）ofDenmark,thepioneersoftheengine’sapplicationtoshipdesign.Othermanufactureralsoproducethesetypesofengine,suchasKawasaki（Japan）,Hyundai（Korea）andFincantieriNaval（Italy）tonameafew.MostshipbuilderbuildtheSulzerorB&Wenginesunderlicense.Totheland-lubber,thebiggestbuilderoftwostrokeengineistheDetroitDieselCorporation,nowownedbyDaimlerChrysler."GeeMees",astheyarecommonlyknown,canbefoundextensivelyintransitbusses,firetrucksandmanymilitaryapplications.EMD,anotherdivisionofGeneralMotors,alsobuildstwostrokeenginewhichareverycommonontheNorthAmericancoastandinlocomotives.Twostrokeenginehaveawidevarietyofpoweroutputfromthe353DetroitDieselwithanoutputoflessthan75kWtoaSulzerRT-flex96Cproducinga80,080kWorabout109,000bhpfromfourteencylindersturningat102rpm,nottobeoutdoneMANB&WhascomeoutwiththeK108ME-C.Thisthingsisun-precedentbig!

LiketheSulzer,itsa14cylinder,butthebore,theareaofthetopofthepiston,is108cm,that'soverameterwide.Itcanproduceamindnumbing97,300kW,over130,000hp,turningapropellerofalmost30feetwideat94rpm.Boththeseenginesaredeveloptopowerthelatestandlargestcontainerships,expectedtocarry10,000to12,000teu,orabout6000tractortrailertrucks. 

Thecomponents...

Theheartofthetwostrokeenginecomprisesofacylinderlinerwithinletportsabout2/3ofthedistancefromthetopoftheliner.Thecylinderhead,alsoknowascylindercover,containtheexhaustvalve's）（picturedabove）.Thepistonwithinthecylinderisconnectedtothecrankshaftbytheconnectingrod.Onthelargerengines,thepoweristransmittedtoacrossheadassemblyfirst.Thecrossheadslideupanddownwiththepistonandtransmitpowerfromittotheconnectingrodandcrankshaft. 

Thetwostrokeengineisnotanaturallyaspiratedengine.Itdependsapositivechargeofairtofillandscavengethecylinder.Thisisprovidedbyablowerwhichchargestheairbox.Theblowercanbemechanicallydriven,suchasontheGeeMeesorelectricmotordrivenonthebiggerengines.Mostenginesnowadaysaresupercharged（turbocharger）aswell.

Thechainreaction...

Describingtheactionofthepistonwithinthecylindergenerallystartwiththepistoninthebottomdeadcenterposition（BDC）,attheendofitstraveldownwardbeforeit’stravelupwards.Withthepiston,havingcoveredtheintakeports,travelsupwards,compressingthetrappedairfromitsoriginalvolumetoafractionofit,generallyanywherefrom17:

1to23:

1（gasenginesareabout9:

1）toabout42bars（~600psi）.Theair’svolumereductioncrushestheairmoleculetogetherandasaresulttheybuildupheat.

Slightlybeforetopdeadcenter（TDC）,around10degrees,injectionofatomizedfuelbegins,itburns,ignitedbythehightemperaturefromtotheairbeingcompressed.Injectionlastabout30degrees,thisvariesdependingonload.Thefuelcontinuestoburnandexpandswhichincreasesthepressureandtemperaturewithinthecylinder.Around15degreesafterTDC,combustioniscompleteandmaximumpressureisreachedwithinthecylinder,thisstageiscommonlycalledPmax.Pmaxisanywherebetween180barsto195bars（~2500-2800psi）;thisiswhyDieselengineconstructionissorobust,itistowithstandthispressure.

Twostrokeenginetimingdiagram

Saidtwostrokeengineisatimingdiagram

1-2fuelinjector,2-3powerstroke,3-5exhaustphase,4-6intakephase,6-1compressionstroke

Thepressureforceactsupontheareaofthepistoncrown,pushingitdown.Thisdownwardforceistransmittedtothecrankshaftbytheconnectingrod,transformingitintoarotationalforce.About45degreesbeforeBDCandjustpriortouncoveringtheinletportsnearthebottomofthecylinder,theexhaustvalveopen,releasingthepressureinthecylinder.Theexhaustgasesatthisstageareabout600degrees.

Thecontinueddownwardtravelofthepistonuncoverstheinletports,wherepositivelychargedair,30-70kPa（3-4psi）,providesascavengingeffecttodriveexhaustgasesoutthroughtheexhaustvalve.Thisactionnotonlyclearsthecylinderofspentgasesbutalsocoolsthecylinder.Around35degreesafterBDCtheexhaustvalvecloses,andat50degreesafterBDCtheinletportsarecovered（closed）.

Withtheinletportsbeingcoveredbytheupwardtravelingpiston,thecompressionstrokebeginsagainwithafreshchargeofair.Thusthetwostrokeearnsit’sname,onedownwards（powerstroke）andtheupwardstroke（compressionstroke）completeonecycle.

Theaboveprocessisbestillustratedbythefollowingdiagram