Lesson 2 How Does a Marine Diesel Engine Work

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1、Lesson2HowDoesaMarineDieselEngineWork第2课船用柴油机是如何工作的1.Thedieselengineisatypeofinternalcombustionenginewhichignitesthefuelbyinjectingitintohot,highpressureairinacombustionchamber.Themarinedieselengineisatypeofdieselengineusedonships.Theprincipleofitsoperationisasfollows:1.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

2、发火。船用柴油机是一种在船上使用的柴油机。其工作原理如下：2.Achargeoffreshairisdrawnorpumpedintotheenginecylinderandthencompressedbythemovingpistontoveryhighpressure.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。3.Whentheairiscompressed,itstemperaturerisessothatitignitesthefinesprayoffuelinjectedintothecylinder.Theburningofthefueladdsmore

3、heattotheaircharge,causingittoexpendandforcetheenginepistontodoworkonthecrankshaftwhichinturndrivestheship'spropeller.空气被压缩时,温度升高,便点燃喷入气缸的油雾。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。4.Theoperationbetweentwoinjectionsiscalledacycle,whichconsistsofafixedsequenceofevents.Thiscyclemaybeachievedeither

4、infourstrokesortwo.Inafour-strokedieselengine,thecyclerequiresfourseparatestrokesofthepiston,i.e.suction,compression,expansionandexhaust.Asitsnameimpliesatwo-strokecycletakesplaceintwoconsecutivestrokesoftheenginepiston,oronerevolutionofthecrankshaft.Thuseachoperationinthecycleisrepeatedduringeve

5、ryrevolutionoftheengine.Thetwostrokesofthecyclemaybetermed:Compressionstrokeandpowerorexpansionstroke.4.两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。这个循环可在二行程或四行程内完成。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。正如其名称所指，二冲程工作循环内发动机活塞完成两个连续冲程，或曲轴转一周。因此，每个循环的运行随着发动机每转一周而重复。这种循环的两个冲程可称为压缩冲程和动力或膨胀冲程。5.Itsoperationisasfoll

6、ows(seeFig.2-1):5.其工作原理如下(见图2-1):1)Thecrankshaftisrevolvingclockwiseandthepistonismovingupthecylinder,compressingthechargeofair.Becauseenergyisbeingtransferredintotheair,itspressureandtemperatureincrease.Bythetimethepistonisapproachingthetopofthecylinder(knownastopdeadcenterorTDC)thepressureisove

7、r100barandthetemperatureover500℃.1)曲轴顺时针旋转，活塞沿气缸向上运动，压缩充入的空气。由于能量被转移到空气中，其压力和温度都增高。当活塞接近气缸顶部(称为上止点或TDG)时，压力达到100bar以上，温度超过500℃。2)JustbeforeTDCfuelisinjectedintothecylinderbythefuelinjector.Thefuelis“atomized”intotinydr