轮机英语lesson-8

HexuemingChinaMaritimePoliceAcademyGasExchangeProcessLesson8HexuemingChinaMaritimePoliceAcademy8.1Newwordsandexpressionsadequate适当的，充分的adjacent邻近的，接近的arrangement布置，安排atmosphere大气；大气的blow鼓风，冲洗blower鼓风机，增压器compressor压缩机density密度，浓度differential微分，压差；差别的，微分的HexuemingChinaMaritimePoliceAcademyelectrically电力地，电动地escape出口；逃逸，溢出essential本质，要点；基本的，重要的pressurize增压，加压process处理；过程removal排除；移动supercharge增压swirl漩涡，涡状形；打漩，使…旋涡运动turbine涡轮，涡轮机HexuemingChinaMaritimePoliceAcademyAbasicpartofthecycleofaninternalcombustionengineisthesupplyoffreshairandremovalofexhaustgases.Thisisthegasexchange.内燃机工作循环的一个基本部分是新鲜空气的进入与废气的排出。这就是换气过程。8.2TextHexuemingChinaMaritimePoliceAcademyScavengingistheremovalofexhaustgasesbyblowinginfreshair.扫气是指用新鲜空气吹出废气。HexuemingChinaMaritimePoliceAcademyChargingisthefillingoftheenginecylinderwithasupplyorchargeoffreshairreadyforcompression.充气是指将新鲜空气充入气缸以备压缩。HexuemingChinaMaritimePoliceAcademyWithsupercharging(增压)alargermassofairissuppliedtothecylinderbyblowingitinunderpressure.至于增压，是在一定压力下把大量空气吹入气缸。HexuemingChinaMaritimePoliceAcademyOlderengineswere‘naturallyaspirated(自然吸气)’—takingfreshaironlyatatmosphericpressure.老式柴油机采用“自然换气”——在大气压下吸入新鲜空气。HexuemingChinaMaritimePoliceAcademyIncreasingthedensityofthechargeairbytheuseofasuitablecompressorbetweentheairintakeandthecylinder,theweightofairinducedperworkingstrokeisincreased.通过在吸气管和气缸之间采用合适的压气机增加充气密度，使进入每个工作冲程的空气重量增加，HexuemingChinaMaritimePoliceAcademyTherebyagreaterweightoffuelcanbeburntwithaconsequentincreaseinthecylinderpoweroutput.因此可燃烧更多的燃油，相应的，每缸输出功率增加。HexuemingChinaMaritimePoliceAcademyThisincreaseinchargeairdensityisaccomplishedonmostmoderndieselenginetypesbyuseofexhaustgasturbocharging,在大多数现代柴油机上，采用废气涡轮增压实现空气密度的增加。HexuemingChinaMaritimePoliceAcademyinwhichaturbinewheeldrivenbyexhaustfromtheengineisrigidlycoupledtoacentrifugaltypeaircompressor.在涡轮增压装置中，一个由柴油机排气驱动的涡轮直接和离心压气机相连。HexuemingChinaMaritimePoliceAcademyBothfour-strokeandtwo-strokecycleenginesmaybepressurecharged.无论是四冲程机还是二冲程机均可增压。HexuemingChinaMaritimePoliceAcademyItshouldbenotedthatsuperchargingisnotsimplyamatterofaddingequipmenttonon-superchargedengines.应当注意，增压对非增压柴油机而言，并非只是设备的增加。HexuemingChinaMaritimePoliceAcademyThesuperchargedenginemustbedesignedtowithstandtheincreasedpressuresandthermalloadswhichresults.增压柴油机必须能经受所增加的压力及所产生的热负荷。HexuemingChinaMaritimePoliceAcademyItisessentialtothescavengingprocessthattheairenteringthecylinderisatahigherpressurethanthegasintheexhaustmanifold.对扫气过程而言，进入气缸的空气压力高于排气总管的压力十分必要。HexuemingChinaMaritimePoliceAcademyOntwo-strokedieselsanelectricallydrivenauxiliaryblowerisusuallyprovidedbecausetheexhaustgasdriventurbo-blowercannotprovideenoughairatlowenginespeeds.就二冲程柴油机而言，由于废气涡轮增压器在低转速下不能提供足够的空气，通常配备一台电动辅助鼓风机。HexuemingChinaMaritimePoliceAcademyHighpressuresuperchargedenginesuseturbochargersinseries(串联的).Thepressurizedairisusuallycooledtoincreasethechargeairdensity.高增压发动机使用串联(多级)涡轮增压。增压后的空气通过冷却来增加空气的密度。HexuemingChinaMaritimePoliceAcademyTheturbo-blowerorturbo-chargerhasonoppositeendsofasingleshaftanexhaustgasdriventurbineandanaircompressor.Thecompressorandtheturbinearesealedfromeachother.涡轮风机或涡轮增压器是在同一根轴相对的两端装废气涡轮和压气机。压气机和涡轮之间彼此密封。HexuemingChinaMaritimePoliceAcademyShaftTurbineAirSealCompressorPressurizeairExhaustgasFreshairFreshairExhaustgasHexuemingChinaMaritimePoliceAcademyItisessentialthateachcylindershouldbeadequatelyscavengedofgasesbeforeafreshchargeofairiscompressed,在新充的新鲜空气被压缩之前，每个气缸充分地驱除废气十分必要，HexuemingChinaMaritimePoliceAcademyotherwisethisfreshairchargeiscontaminatedbyresidualexhaustgasesfromthepreviouscycle.否则新充新鲜空气将被循环的残余废气污染。HexuemingChinaMaritimePoliceAcademyFurther,thecycletemperaturewillbeunnecessarilyhighiftheairchargeisheatedbymixingwithresidualgasesandbycontactwithhotcylindersandpistons.而且，若新充空气因与废气混合与热的缸壁及活塞接触而被加热，则循环的温度会毫无必要地增加。HexuemingChinaMaritimePoliceAcademyInthefour-strokecycleenginethereisanadequateoverlapbetweentheairinletvalveopeningandtheexhaustvalveclosing.在四冲程柴油机中，从进气阀打开到排气阀关闭，其间有一个适度的重叠。HexuemingChinaMaritimePoliceAcademyTheairflowthroughthecylinderduringtheexhaust/scavengeoverlapperiodhasavaluablecoolingeffect;在重叠期间流过气缸的空气流产生有益的冷却效果。HexuemingChinaMaritimePoliceAcademyithelpstoincreasethevolumetricefficiency(容积效率)andtoensurealowcycletemperatureandalsotoobtainarelativelycoolerexhaustimposedontheturbineblades(叶片).这将有助于增加容积效率，并确保循环温度较低，而且还使作用在涡轮叶片上的废气温度相对较低。HexuemingChinaMaritimePoliceAcademyWithtwo-strokecycleenginesthisoverlapislimitedbytheenginedesigncharacteristics,andsomeslightmixingofexhaustgasesandincomingairdoesoccur.而在二冲程柴油机中，这一重叠受到柴油机设计特点的限制，进排气的轻微混合确实存在。HexuemingChinaMaritimePoliceAcademyAnumberofdifferentscavengingmethodsareinuseinslowspeedtwostrokeengines.低速二冲程柴油机有多种不同的扫气方式。HexuemingChinaMaritimePoliceAcademyIneachthefreshairentersastheinletportisopenedbythedownwardmovementofthepistonandcontinuesuntiltheportisclosedbytheupwardmovingpiston.无论哪一种都是从向下运动的活塞打开进气口开始至向上运动的活塞关闭进气口为止。HexuemingChinaMaritimePoliceAcademyTheflowpathofthescavengeairisdecidedbytheengineportshapeanddesignandtheexhaustarrangements.扫气空气的流动线路取决于柴油机气口的形状设计以及排气布