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1、Lesson1HOWDOESAMARINEDIESELENGINEWORK?Thedieselengineisatypeofinternalcombustionenginewhichignitesthefuelbyinjectingitintohot,highpressureairinacombustionchamber.Themarinedieselengineisatypeofdieselengineusedonships.Theprincipleofitsoperationisasfollows:Achargeoffreshairisdrawnorpumpedintotheen
2、ginecylinderandthencompressedbythemovingpistontoveryhighpressure.Whentheairiscompressed,itstemperaturerisessothatitignitesthefinesprayoffuelinjectedintothecylinder.Theburningofthefueladdsmoreheattotheaircharge,causingittoexpandandforcetheenginepistontodoworkonthecrankshaftwhichinturndrivesthesh
3、ip'spropeller.Theoperationbetweentwoinjectionsiscalledacycle,whichconsistsofafixedsequenceofevents.Thiscyclemaybeachievedeitherinfourstrokesortwo.Inafour-strokedieselengine,thecyclerequiresfourseparatestrokesofthepiston,i.e.suction,compression,expansionandexhaust.Ifwecombinethesuctionandexhaust
4、operationswiththecompressionandexpansionstrokes,thefour-strokeenginewillbeturnedintoatwo-strokeone,asisshowninFiguresl(a)-(d).Thetwo-strokecyclebeginswiththepistoncomingupfromthebottomofitsstroke,i.e.bottomdeadcentre(BDT),withtheairinletportsorscavengeportsinthesidesofthecylinderbeingopened(Fig
5、.1(a)).Theexhaustportsareuncoveredalso.Pressurisedfreshairchargesintothecylinder,blowingoutanyresidualexhaustgasesfromthelaststrokethroughtheexhaustports.Asthepistonmovesaboutonefifthofthewayup,itclosestheinletportsandtheexhaustports.Theairisthencompressedasthepistonmovesup(Fig.1(b)).Whenthepis
6、tonreachesthetopofitsstroke,i.e.thetopdeadcenter(TDC),boththepressureandthetemperatureoftheairrisetoveryhighvalues.Thefuelinjectorinjectsafinesprayoffueloilintothehotairandcombustiontakesplace,producingmuchhigherpressureinthegases.Thepistonisforceddownwardasthehighpressuregasesexpand(Fig.1(c))u
7、ntilituncoverstheexhaustports.Theburntgasesbegintoexhaust(Fig.1(d))andthepistoncontinuesdownuntilitopenstheinletports.Thenanothercyclebegins.Inthetwo-strokeengine,eachrevolutionofthecrankshaftmakesonepowerorworkingstroke,whileinth
