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ChinaMaritimePoliceAcademyHexuemingLessonTwoHowdoesaMarineDieselengineWork?ChinaMaritimePoliceAcademyHexueming2.1Newwordsandexpressions1.marinea.海洋的，海运的，船用的2.internala.内部的（反）external外部的3.chargev.n.充入，注入（电，气）4.cylindern.圆柱体，气缸5.pistonn.活塞6.stroken.冲程thepowerstroke动力冲程theworkingstroke工作冲程ChinaMaritimePoliceAcademyHexueming7.separate(from)a.分离的，分隔开的，独立的v.分离，分隔8.combine(with)v.合并，联合9.crankshaftn.曲轴thecrank曲柄，曲拐crankarm曲柄臂10.propellern.螺旋桨theship’spropeller11.consist(of)vi.由组成12.fixv.固定修理决定ChinaMaritimePoliceAcademyHexueming*Thedieselengineisatypeofinternalcombustionenginewhichignites(点燃)thefuelbyinjecting(喷射)itintohot,highpressureairinacombustionchamber(燃烧室).柴油机是一种内燃机，通过把燃油喷入高温高压的燃烧室而发火。2.2TextChinaMaritimePoliceAcademyHexuemingThemarinedieselengineisatypeofdieselengineusedonships.Theprincipleofitsoperationisasfollows:船用柴油机是一种在船上使用的柴油机。其工作原理如下：ChinaMaritimePoliceAcademyHexuemingAchargeoffreshairisdrawnorpumpedintotheenginecylinder(气缸)andthencompressedbythemovingpiston(活塞)toveryhighpressure.一定量的新鲜空气被吸入或泵入气缸并被运动的活塞压缩至很高的压力。ChinaMaritimePoliceAcademyHexuemingWhentheairiscompressed,itstemperaturerisessothatitignitesthefinespray(喷雾、油雾)offuelinjectedintothecylinder.空气被压缩时，温度升高，便点燃喷入气缸的油雾。ChinaMaritimePoliceAcademyHexuemingTheburningofthefueladdsmoreheattotheaircharge,causingittoexpandandforcetheenginepistontodoworkonthecrankshaftwhichinturndrivestheship’spropeller(螺旋桨).燃油的燃烧对缸内空气的加热，使空气膨胀并迫使发动机活塞对曲轴做功，随之驱动螺旋桨。ChinaMaritimePoliceAcademyHexuemingExhaustvalveInletvalveFuelinjectorCylinderPistonPistonringConnectingrodFour-strokedieselengineCombustionchamberPistonpincrankshaftCrankwebChinaMaritimePoliceAcademyHexuemingFuelinjectorFuelinjectorExhaustvalve扫气口ScavengeportExhaustportTwo-strokeEngineCrossscavengesystemUniflowscavengesystemPistonrodConnectingrodPistonpinCrossheadChinaMaritimePoliceAcademyHexuemingTheoperationbetweentwofuelinjectionsiscalledaworkingcycle,whichconsistsofafixedsequenceofevents.两次喷油期间的运转过程叫一个工作循环。它由一些程序固定的过程组成。ChinaMaritimePoliceAcademyHexuemingThiscyclemaybeachievedeitherinfourstrokes(冲程、行程)ortwo.这个循环可在二行程或四行程内完成。ChinaMaritimePoliceAcademyHexuemingInafour-strokedieselengine,thecyclerequiresfourseparatestrokesofthepiston,i.e.suction(吸气),compression(压缩),expansion(膨胀)andexhaust(排气).四冲程柴油机的工作循环需要四个独立的活塞行程，即吸气、压缩、膨胀和排气。ChinaMaritimePoliceAcademyHexuemingIfwecombinethesuctionandexhaustoperationswiththecompressionandexpansionstrokes,thefour-strokeenginewillbeturnedintoatwo-strokeone,asisshowninFigures2-1(a)—(d).如果把吸气和排气行程与压缩和膨胀行程结合起来，四冲程柴油机就变成了二冲程柴油机。如图2-1(a)～(d)所示。ChinaMaritimePoliceAcademyHexuemingScavenge(a)Compression(b)Injection(c)Exhaust(d)ScavengeportExhaustportFuelinjectorCylinderPistonConnectingrodCrankFig2-1ChinaMaritimePoliceAcademyHexuemingThetwo-strokecyclebeginswiththepistoncomingupfromthebottomofitsstroke,i.e.bottomdeadcenter(BDC),withtheairinletportsorscavengeports(扫气口)inthesidesofthecylinderbeingopened(Fig.2-1a)).Theexhaustportsareuncoveredalso.二冲程循环从活塞离开其行程底部，即下止点(BDC)向上运行开始，气缸侧面的进气口即扫气口是打开的(图2-1(a))，排气口也是打开的。ChinaMaritimePoliceAcademyHexuemingPressurizedfreshairchargesintothecylinder,blowingoutanyresidualexhaustgasesfromthelaststrokethroughtheexhaustports.经压缩的新鲜空气充入气缸，通过排气口将上一行程的残余废气吹出。ChinaMaritimePoliceAcademyHexuemingAsthepistonmovesaboutonefifthofthewayup,itclosestheinletportsandtheexhaustports.Theairisthencompressedasthepistonmovesup.(Fig.2-1(b)).当活塞上行至其行程的1／5时，关闭进、排气口，随后空气在活塞上行中被压缩(图2-1(b))。ChinaMaritimePoliceAcademyHexuemingWhenthepistonreachesthetopofitsstroke,i.e.thetopdeadcenter(TDC),boththepressureandthetemperatureoftheairrisetoveryhighvalues.当活塞上行到行程顶部，即上止点(TDC)时空气的压力和温度都升高到很高的数值。ChinaMaritimePoliceAcademyHexuemingThefuelinjectorinjectsafinesprayoffuelintothehotairandcombustiontakeplace,producingmuchhigherpressureinthegases.(此时)喷油器把很细的油雾喷入炽热的空气中，燃烧开始，从而产生更高的压力。ChinaMaritimePoliceAcademyHexuemingThepistonisforced(迫使)downwardasthehighpressuregasesexpand(Fig.2-1(c)).untilituncoverstheexhaustports.随着高压气体的膨胀，活塞被推动下行(图2-1(c))，直到它打开排气口.ChinaMaritimePoliceAcademyHexuemingTheburninggasesbegintoexhaust(Fig.2-1(d))andthepistoncontinuesdownuntilitopenstheinletports.Thenanothercyclebegins.废气开始排出(图2-1(d))，活塞继续下行直到它打开进气口，另一个循环开始。ChinaMaritimePoliceAcademyHexuemingInthetwo-strokeengine,eachrevolutionofthecrankshaft(曲轴)makesonepowerorworkingstroke,whileinthefour-strokeengine,ittakestworevolutionstomakeonepowerstroke.在二冲程柴油机中，曲轴转一转产生一个动力冲程，即做功行程，而在四冲程柴油机中，曲轴转两转才产生一个动力行程。ChinaMaritimePoliceAcademyHexuemingThatiswhyatwo-strokecycleenginewilltheoreticallydeveloptwice(twotimes)thepowerofafour-strokeengineofthesamesize.这就是为什么从理论上说，二冲程柴油机能产生相同尺寸的四冲程柴油机的2倍功率.ChinaMaritimePoliceAcademyHexuemingInefficientscavengingandotherlosses,however,reducethepoweradvantagetoabout1.8.然而，扫气不充分和其他损失使功率势降低到大约1.8倍。ChinaMaritimePoliceAcademyHexuemingEachtypeofenginehasitsapplicationonboardship.Theslowspeed(i.e.90to120rev/min)mainpropulsiondieseloperatesonthetwo-strokecycle.在船上，每种柴油机都有它的作用。低速(即90～120r／min)主推进机柴油机以二冲程工作。ChinaMaritimePoliceAcademyHexuemingAtthislowspeedtheenginerequiresnoreductiongearboxbetweenitandprope