how does a marine diesel engine workPPT演示课件

,LessonthreeTextHowdoesaMarineDieselengineWork?,2001-03-20,operationdesielengineinternalcombustionengineigniteinjectfuelpressurecylindercombustionchamber,2001-03-20,suctionpistontopdeadcenter/centreinletportbottomdeadcentrecompression/compressinjectorfinesprayoffueloil,2001-03-20,expandexpansioncrankshaftresidualexhaustgasexhaustcyclestrokerevolution,*Thedieselengineisatypeofinternalcombustionenginewhichignites(点燃，点火)thefuelbyinjecting(喷射)itintohot,highpressureairinacombustionchamber(燃烧室).,柴油机是一种内燃机，它是通过往带有高温高压空气的燃烧室喷射燃油进行点火的。,Themarinedieselengineisatypeofdieselengineusedonships.Theprincipleofitsoperationisasfollows:,船用柴油机是一种在船上使用的柴油机。它的工作原理如下：,Achargeoffreshairisdrawnorpumpedintotheenginecylinder(气缸)andthencompressedbythemovingpiston(活塞)toveryhighpressure.,一充量空气被吸入或者泵入汽缸，接着被运动的活塞压缩到高压。,Whentheairiscompressed,itstemperaturerisessothatitignitesthefinespray(喷雾、油雾)offuelinjectedintothecylinder.,当空气被压缩时，其温度升高，结果点燃喷入气缸的燃油喷雾。,Theburningofthefueladdsmoreheattotheaircharge,causingittoexpandandforcetheenginepistontodoworkonthecrankshaftwhichinturndrivestheshipspropeller(螺旋桨).,燃油的燃烧给充气增加了更多的热量，从而导致它膨胀，并且迫使发动机活塞对曲轴做功，曲轴反过来驱动船舶螺旋桨。,Exhaustvalve排气阀,Inletvalve进气阀,燃油喷射器Fuelinjector,Cylinder,Piston,Pistonring,Connectingrod连杆,Four-strokedieselengine,Combustionchamber,Pistonpin活塞销,Crankshaft机轴,曲柄臂Crankweb,Fuelinjector,Fuelinjector,Exhaustvalve,扫气口Scavengeport,Exhaustport,Two-strokeEngine,Crossscavengesystem横流扫气系统,Uniflowscavengesystem直流扫气系统,Pistonrod活塞杆,Connectingrod,Pistonpin,Crosshead十字头,Theoperationbetweentwofuelinjectionsiscalledaworkingcycle,whichconsistsofafixedsequenceofevents.,两次喷射之间的运转被称为一个工作循环，这是由固定顺序的活动组成的。,Thiscyclemaybeachievedeitherinfourstrokes(冲程、行程)ortwo.,这个循环可以由两冲程或四冲程来实现。,Inafour-strokedieselengine,thecyclerequiresfourseparatestrokesofthepiston,i.e.suction(吸气),compression(压缩),expansion(膨胀)andexhaust(排气).,在四冲程柴油机里，一个循环要求活塞有四次独立的冲程，也就是吸气冲程，压缩冲程，膨胀冲程和排气冲程。,Ifwecombinethesuctionandexhaustoperationswiththecompressionandexpansionstrokes,thefour-strokeenginewillbeturnedintoatwo-strokeone,asisshowninFigures1-a)d).,如果我们把吸气和压缩，排气和膨胀冲程连接起来，那么四冲程柴油机将变为两冲程柴油机，如图所示：,Scavenge(a),Compression(b),Injection(c),Exhaust(d),Scavengeport,Exhaustport,Fuelinjector,Cylinder,Piston,Connectingrod,Crank曲柄,Thetwo-strokecyclebeginswiththepistoncomingupfromthebottomofitsstroke,i.e.bottomdeadcenter(BDC),withtheairinletportsorscavengeports(扫气口)inthesidesofthecylinderbeingopened(Fig.1-a).,两冲程柴油机开始是活塞从它的冲程底部，也就是下止点上行，气缸两侧的进气口和扫气口打开。,Theexhaustportsareuncoveredalso.Pressurizedfreshairchargesintothecylinder,blowingoutanyresidualexhaustgasesfromthelaststrokethroughtheexhaustports.,排气口也被打开，受压的新鲜空气充入气缸，从排气口吹出所有最后冲程残余的废气。,Asthepistonmovesaboutonefifthofthewayup,itclosestheinletportsandtheexhaustports.Theairisthencompressedasthepistonmovesup.(Fig.1-b).,当活塞上行五分之一的时候，其关闭进气口和扫气口。那么活塞上行的时候空气就被压缩。,Whenthepistonreachesthetopofitsstroke,i.e.thetopdeadcenter(TDC),boththepressureandthetemperatureoftheairrisetoveryhighvalues.,当活塞到达其冲程顶部，也就是上止点时，空气的压力和温度都达到了很高的值。,Thefuelinjectorinjectsafinesprayoffuelintothehotairandcombustiontakeplace,producingmuchhigherpressureinthegases.,燃油喷射器往高温空气中喷射细雾燃油，燃烧发生，这时气体中产生了更高的压力。,Thepistonisforced(迫使)downwardasthehighpressuregasesexpanduntilituncoverstheexhaustports.,当高压气体膨胀，活塞被迫下行，直到其打开排气口。,Theburninggasesbegintoexhaust(Fig.1-d)andthepistoncontinuesdownuntilitopenstheinletports.Thenanothercyclebegins.,燃烧的气体开始排气，活塞继续下行，直到其打开进气口。接着另外一个循环开始。,Inthetwo-strokeengine,eachrevolutionofthecrankshaft(曲轴)makesonepowerorworkingstroke,whileinthefour-strokeengine,ittakestworevolutionstomakeonepowerstroke.,在两冲程柴油机里，曲轴的每次旋转都做一次功或者一个工作冲程，然而，在四冲程柴油机里，曲轴要旋转两次才做一次功。,Thatiswhyatwo-strokecycleenginewilltheoreticallydeveloptwice(twotimes)thepowerofafour-strokeengineofthesamesize.,那就是为什么两冲程柴油机理论上所做的功两倍于同样大小的四冲程柴油机。,Inefficientscavengingandotherlosses,however,reducethepoweradvantagetoabout1.8.,然而，低效的扫气和其它的一些损失使这个做功优势降低到1.8倍。,Eachtypeofenginehasitsapplicationonboardship.Theslowspeed(i.e.90to120rev/min)mainpropulsiondieseloperatesonthetwo-strokecycle.,每种发动机在船上都有其用途。低速主推进柴油机用二冲程柴油机。,Atthislowspeedtheenginerequiresnoreductiongearboxbetweenitandpropeller.,因为速度低，这种柴油机和螺旋桨之间不需要减速齿轮箱。,Thefour-strokeengine(usuallyrotatingatmediumspeed,between250to750rev/min)isusedforalternatorsandsometimesformainpropulsionwithagearboxtoprovideapropellerspeedofbetween90to120rev/min.,四冲程柴油机（通常中速旋转，每分250-750转）用于发电机，有时也用作主机，带有一个变速箱给螺旋桨提供每分90-120的转速。,ReadingMaterialWorkingcyclesAdieselenginemaybedesignedtoworkonthetwo-strokeoronthefour-strokecycle:bothoftheseareexplainedbelow.,Thefour-strokecycleFigure2showsdiagrammaticallythesequenceofeventsthroughoutthetypicalfour-strokecycleoftworevolutions.,ItisusualtodrawsuchdiagramsstartingatTDC(firing),buttheexplanationwillstartatTDC(scavenge).Topdeadcenterissometimesreferredtoasinnerdeadcenter(IDC).,Proceedingclockwiseroundthediagram,bothinlet(orsuction)andexhaustvalvesareinitiallyopen.(Allmodernfour-strokeengineshavepoppetvalves(提升阀).),Iftheengineisnaturallyaspirated(自然吸气),orisasmallhigh-speedtypewithacentrifugalturbocharger,theperiodofvalveoverlap(重叠),i.e.whenbothvalvesareopen,willbeshort,andtheexhaustvalvewillclosesome10aftertopdeadcenter(ATDC).,TDC（firing),Fuelvalveclosed(fullload),Injectioncommences10-20BTDC,Exhaustvalveopens120-150ATDC,Exhaustvalvecloses50-60ATDC,Inletvalveopen70-80BTDC,Inletvalveclose146-155BTDC,Fig2,四冲程定时图,BDC,Propulsionenginesandthevastmajorityofauxiliarygeneratorenginesrunningatspeedsbelow1000rev/minwillalmostcertainlybeturbochargedand,willbedesignedtoallowagenerousthroughflowofscavengeairatthispointinordertocontroltheturbinebladetemperature.,Inthiscasetheexhaustvalvewillremainopenuntilexhaustvalveclosure(EVC)at50-60ATDC.Asthepistondescendstoouterorbottomdeadcenter(BDC)onthesuctionstroke,itwillinhale(吸入)afreshchargeofair.,Tomaximizethis,balancingthereducedopeningasthevalveseatsagainsttheslightram(进气阀座)orinertiaeffectoftheincomingcharge,theinlet(suction)valvewillnormallybeheldopenuntilabout25-35ABDC(145-155BTDC).,Thiseventiscalledinletvalveclosure(IVC).Thechargeisthencompressedbytherisingpistonuntilithasattainedatemperatureofsome550.,Atabout10-20BTDC(firing),dependingonthetypeandspeedoftheengine,theinjectoradmitsfinelyatomized(雾化的)fuelwhichigniteswithin2-7(dependingontypeagain)and,thefuelburnsoveraperiodof30-50whilethepistonbeginstodescendontheexpansionstroke,thepistonmovementusuallyhelpingtoinduceairmovementtoassistcombustion.,Atabout120-150ATDCtheexhaustvalveopens(EVO),thetimingbeingchosentopromote(促进)averyrapidblow-down(排出)ofthecylindergasestoexhaust.,Thisisdone:(a)topreserve(保留)asmuchenergyasispracticabletodrivetheturbocharger,and(b)toreducethecylinderpressuretoaminimumbyBDCtoreducepumpingworkonthe“exhaust”stroke.,Therisingpistonexpels(排出)theremainingexhaustgasandatabout70-80BTDCtheinletvalveopens(IVO)sothattheinertiaoftheoutflowinggas,plusthepositivepressuredifference,whichusuallyexistsacrossthecylinderbynow,producesathroughflowofairtotheexhausttoscavengethecylinder.,IftheengineisnaturallyaspiratedtheIVOisabout10BTDC.Thecyclenowrepeats.,Thetwo-strokecycleFigure3showsthesequenceofeventsinatypicaltwo-strokecycle,which,asthenameimplies,isaccomplishedinonecompleterevolutionofthecrank.,Exhaustcloses110-150BTDC,Exhaustopens110-120ATDC,Inletopens130-150ATDC,Inletcloses130-150BTDC,TDC,Fuelvalvecloses(fullload),Injectioncommences10-20BTDC,Fig.3,二冲程定时图Thetwo-strokecycle,Two-strokeenginesinvariablyhaveportstoadmitairwhenuncoveredbythedescendingpiston.,Theexhaustmaybeviaportsadjacenttotheairportsandcontrolledbysamepiston(loopscavenge回流扫气)orviapoppetexhaustvalvesattheotherendofthecylinder(uniflowscavenge直流扫气).,StartingatTDCcombustionisalreadyunderthewayandtheexhaustopens(EO)at110-120ATDCtopromotearapidblow-downbeforetheinletopens(IO)about20-30later(130-150ATDC).,Inthiswaytheinertiaoftheexhaustgasesmovingataboutthespeedofsoundiscontrived(设计、设法)toencouragetheincomingairtoflowquicklythroughthecylinderwithaminimumofmixing,becauseanyunexpelled(未排出的）exhaustgasesdetracts(减损，降低)fromtheweightofairentrainedforthenextstroke.,Theexhaustshouldclosebeforetheinletonthecompressionstroketomaximizethecharge,butthegeometryoftheenginemaypreventthisifthetwoeventsarepistoncontrolled.,Itcanbedoneinanenginewithexhaustvalves.,AtalleventstheinletportswillbeclosedasmanydegreesABDCasopenedbeforeit(i.e.again130150BTDC)andtheexhaustinthesameregion.,Injectioncommencesatabout10-20BTDCdependingonspeed,andcombustionlasts30-50aswiththefour-stroke.,1.Morethan50/above50/over5050多2.Lessthan50/under50/below50不到50或50以下Thetemperatureisbelow20.3.50more再加50tenmoredays再10天Pleaseadd50moregramsofsalttothewater.,Jimeiuniversity,4.akilometerormore一公里或一公里多些alongkilometer一公里多alonghour足足一小时adozen一打，dozens几十、几打5.数字+oddtwentyodd/twenty-odd/twentyandodd/20多,Jimeiuniversity,6.fromtwentytothirty/twentytothirty/从20到307.somethirtyfeet/aboutthirtyfeet/thirtyfeetorso/30英尺左右ahundredmoreorless/100上下moreorlesstwentypages/20页左右8.ntime(s)/增加到n倍，n倍于Theoutputhasincreased(by)threetimesascomparedwiththatoflastyear.,Jimeiuniversity,Waterconductsheatabout20timesbetterthanairdoes.8.增加多少量，常用by引出。Thecokeusedhasbeenincreasedby18%ascomparedwithlastyear.Thispipeis2incheslongerthanthatone.,Jimeiuniversity,9.降低多少倍：减少ntimes，译为降低到几分之几，或降低了几分之几。Thenewmotoristentimesaslightastheoldone.新马达的重量是旧马达的十分之一.Theswitchingtimeofthenew-typetransistorisreduced3times.新晶体管的开关时间减缩了三分之二.,Jimeiuniversity,10.减少多少量，常以by引出，为绝对数量。Theprimecostdecreasedby40%.主要成本下降了百分之四十。Thispipeisshorterthanthatoneby3meters.这根管子比那根短3米。,Jimeiuniversity,1、主语如果是用连词and,bothand连接的并列主语，谓语要用复数形式。但是，如果两个词是指同一个人或同一概念时，谓语要用单数形式。如课文：Bothofthese(two-strokeandfo