轮机英语课件1说课讲解.ppt

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1、Harbin Engineering University轮机英语课件1Harbin Engineering University rotate 旋转，回转 medium 中间的，介质 alternator 交流发电机 in turn 依次，轮流变成 turn into 变成 event 事件，过程 stroke 冲程，行程 separate(from)分离，分开 exhaust 排出，耗尽；排气 combine(with)结合，联合 inlet 进口，入口 scavenge 扫除；吹除 blow 吹，鼓风 residual 剩余的，残留的 value 价值，数值 injector 喷射器，喷

2、油器 continue 继续(进行)revolution 转 theoretically 理论上地 inefficient 效率低的，无效的2007-11-1Harbin Engineering University advantage 优势，优点，长处 application 应用 propulsion 推进(装置)cause 引起；原因 force 迫使 crankshaft 曲铀 propeller 螺旋桨，推进器 cycle 循环 consist(of)由组成 fix 固定 sequence 顺序，系列 bottom dead centre(BDC)下止点 top dead centr

3、e(TDC)上止点 on board ship 在船上 r/min 转分 reduction gear box 减速齿轮箱2007-11-1Harbin Engineering University*The diesel engine is a type of internal combustion engine which ignites(点点燃燃)the fuel by injecting(喷喷射射)it into hot,high pressure air in a combustion chamber(燃燃烧烧室室).2007-11-1Harbin Engineering Univer

4、sityThe marine diesel engine is a type of diesel engine used on ships.The principle of its operation is as follows:2007-11-1Harbin Engineering UniversityA charge of fresh air is drawn or pumped into the engine cylinder(气气 缸缸)and then compressed by the moving piston(活活 塞塞)to very high pressure.2007-1

5、1-1Harbin Engineering UniversityWhen the air is compressed,its temperature rises so that it ignites the fine spray(喷喷雾雾、油油雾雾)of fuel injected into the cylinder.2007-11-1Harbin Engineering UniversityThe burning of the fuel adds more heat to the air charge,causing it to expand and force the engine pis

6、ton to do work on the crankshaft which in turn drives the ships propeller(螺旋桨螺旋桨).2007-11-1Harbin Engineering UniversityExhaust valveInlet valveFuel injectorCylinderPistonPiston ringConnecting rodFour-stroke diesel engineCombustion chamberPiston pincrankshaftCrank web2007-11-1Harbin Engineering Univ

7、ersityFuel injectorFuel injectorExhaust valve扫气口扫气口Scavenge portExhaust portTwo-strokeEngineCross scavenge systemUniflow scavenge systemPiston rodConnecting rodPiston pinCrosshead2007-11-1Harbin Engineering UniversityThe operation between two fuel injections is called a working cycle,which consists

8、of a fixed sequence of events.2007-11-1Harbin Engineering UniversityThis cycle may be achieved either in four strokes(冲冲程程、行程行程)or two.2007-11-1Harbin Engineering UniversityIn a four-stroke diesel engine,the cycle requires four separate strokes of the piston,i.e.suction(吸吸气气),compression(压压缩缩),expan

9、sion(膨膨胀胀)and exhaust(排气排气).*Note:i.e.(拉拉=id est)即；就是即；就是2007-11-1Harbin Engineering UniversityIf we combine the suction and exhaust operations with the compression and expansion strokes,the four-stroke engine will be turned into a two-stroke one,as is shown in Figures 1-a)d).2007-11-1Harbin Enginee

10、ring UniversityScavenge(a)Compression(b)Injection(c)Exhaust(d)ScavengeportExhaustportFuel injectorCylinderPistonConnecting rodCrank2007-11-1Harbin Engineering UniversityThe two-stroke cycle begins with the piston coming up from the bottom of its stroke,i.e.bottom dead center(BDC),with the air inlet

11、ports or scavenge ports(扫扫气气口口)in the sides of the cylinder being opened(Fig.1-a).2007-11-1Harbin Engineering UniversityThe exhaust ports are uncovered also.Pressurized fresh air charges into the cylinder,blowing out any residual exhaust gases from the last stroke through the exhaust ports.2007-11-1

12、Harbin Engineering UniversityAs the piston moves about one fifth of the way up,it closes the inlet ports and the exhaust ports.The air is then compressed as the piston moves up.(Fig.1-b).2007-11-1Harbin Engineering UniversityWhen the piston reaches the top of its stroke,i.e.the top dead center(TDC),

13、both the pressure and the temperature of the air rise to very high values.2007-11-1Harbin Engineering UniversityThe fuel injector injects a fine spray of fuel into the hot air and combustion take place,producing much higher pressure in the gases.2007-11-1Harbin Engineering UniversityThe piston is fo

14、rced(迫迫 使使)downward as the high pressure gases expand until it uncovers the exhaust ports.2007-11-1Harbin Engineering UniversityThe burning gases begin to exhaust(Fig.1-d)and the piston continues down until it opens the inlet ports.Then another cycle begins.2007-11-1Harbin Engineering UniversityIn t

15、he two-stroke engine,each revolution of the crankshaft(曲曲轴轴)makes one power or working stroke,while in the four-stroke engine,it takes two revolutions to make one power stroke.2007-11-1Harbin Engineering UniversityThat is why a two-stroke cycle engine will theoretically develop twice(two times)the p

16、ower of a four-stroke engine of the same size.2007-11-1Harbin Engineering UniversityInefficient scavenging and other losses,however,reduce the power advantage to about 1.8.2007-11-1Harbin Engineering UniversityEach type of engine has its application on board ship.The slow speed(i.e.90 to 120 rev/min

17、)main propulsion diesel operates on the two-stroke cycle.2007-11-1Harbin Engineering UniversityAt this low speed the engine requires no reduction gearbox between it and propeller.2007-11-1Harbin Engineering UniversityThe four-stroke engine(usually rotating at medium speed,between 250 to 750 rev/min)

18、is used for alternators and sometimes for main propulsion with a gearbox to provide a propeller speed of between 90 to 120 rev/min.2007-11-1Harbin Engineering UniversityReading Material Working cyclesA diesel engine may be designed to work on the two-stroke or on the four-stroke cycle:both of these

19、are explained below.2007-11-1Harbin Engineering UniversityThe four-stroke cycleFigure 2 shows diagrammatically the sequence of events throughout the typical four-stroke cycle of two revolutions.2007-11-1Harbin Engineering UniversityIt is usual to draw such diagrams starting at TDC(firing),but the ex

20、planation will start at TDC(scavenge).Top dead center is sometimes referred to as inner dead center(IDC).2007-11-1Harbin Engineering UniversityProceeding clockwise round the diagram,both inlet(or suction)and exhaust valves are initially open.(All modern four-stroke engines have poppet valves(提升阀提升阀)

21、.)2007-11-1Harbin Engineering UniversityIf the engine is naturally aspirated(自自然然吸吸气气),or is a small high-speed type with a centrifugal turbocharger,the period of valve overlap(重重叠叠),i.e.when both valves are open,will be short,and the exhaust valve will close some 10after top dead center(ATDC).2007-

22、11-1Harbin Engineering UniversityTDC（firing)Fuel valve closed(full load)Injection commences10-20BTDCExhaust valve opens120-150ATDCExhaust valve closes 50-60ATDCInlet valve open70-80 BTDCInlet valve close146-155BTDCFig 2四冲程定时图BDC2007-11-1Harbin Engineering UniversityPropulsion engines and the vast ma

23、jority of auxiliary generator engines running at speeds below 1000 rev/min will almost certainly be turbocharged and2007-11-1Harbin Engineering Universitywill be designed to allow a generous throughflow of scavenge air at this point in order to control the turbine blade temperature.2007-11-1Harbin E

24、ngineering UniversityIn this case the exhaust valve will remain open until exhaust valve closure(EVC)at 50-60ATDC.As the piston descends to outer or bottom dead center(BDC)on the suction stroke,it will inhale(吸吸入入)a fresh charge of air.2007-11-1Harbin Engineering UniversityTo maximize this,balancing

25、 the reduced opening as the valve seats against the slight ram(进进气气阀阀座座)or inertia effect of the incoming charge,the inlet(suction)valve will normally be held open until about 25-35 ABDC(145-155BTDC).2007-11-1Harbin Engineering UniversityThis event is called inlet valve closure(IVC).The charge is th

26、en compressed by the rising piston until it has attained a temperature of some 550.2007-11-1Harbin Engineering UniversityAt about 10-20BTDC(firing),depending on the type and speed of the engine,the injector admits finely atomized(雾雾化化的的)fuel which ignites within 2-7(depending on type again)and2007-1

27、1-1Harbin Engineering Universitythe fuel burns over a period of 30-50while the piston begins to descend on the expansion stroke,the piston movement usually helping to induce air movement to assist combustion.2007-11-1Harbin Engineering UniversityAt about 120-150ATDC the exhaust valve opens (EVO),the

28、 timing being chosen to promote(促促进进)a very rapid blow-down(排排 出出)of the cylinder gases to exhaust.2007-11-1Harbin Engineering UniversityThis is done:(a)to preserve(保保留留)as much energy as is practicable to drive the turbocharger,and(b)to reduce the cylinder pressure to a minimum by BDC to reduce pum

29、ping work on the“exhaust”stroke.2007-11-1Harbin Engineering UniversityThe rising piston expels(排排出出)the remaining exhaust gas and at about 70-80 BTDC the inlet valve opens(IVO)so that the inertia of the outflowing gas,2007-11-1Harbin Engineering Universityplus the positive pressure difference,which

30、usually exists across the cylinder by now,produces a through flow of air to the exhaust to scavenge the cylinder.2007-11-1Harbin Engineering UniversityIf the engine is naturally aspirated the IVO is about 10BTDC.The cycle now repeats.2007-11-1Harbin Engineering UniversityThe two-stroke cycleFigure 3

31、 shows the sequence of events in a typical two-stroke cycle,which,as the name implies,is accomplished in one complete revolution of the crank.2007-11-1Harbin Engineering UniversityExhaust closes110-150BTDCExhaust opens110-120ATDCInlet opens130-150ATDCInlet closes130-150BTDCTDCFuel valve closes(full

32、load)Injection commences10-20BTDCFig.3二冲程定时图The two-stroke cycle2007-11-1Harbin Engineering UniversityTwo-stroke engines invariably have ports to admit air when uncovered by the descending piston.2007-11-1Harbin Engineering UniversityThe exhaust may be via ports adjacent to the air ports and control

33、led by same piston(loop scavenge回回流流扫扫气气)or via poppet exhaust valves at the other end of the cylinder(uniflow scavenge直流扫气直流扫气).2007-11-1Harbin Engineering UniversityStarting at TDC combustion is already under the way and the exhaust opens(EO)at 110-120ATDC to promote a rapid blow-down before the i

34、nlet opens(IO)about 20-30later(130-150ATDC).2007-11-1Harbin Engineering UniversityIn this way the inertia of the exhaust gasesmoving at about the speed of soundis contrived(设设 计计、设设 法法)to encourage the incoming air to flow quickly through the cylinder with a minimum of mixing,2007-11-1Harbin Enginee

35、ring Universitybecause any unexpelled(未未排排出出的的）exhaust gases detracts(减减损损，降降低低)from the weight of air entrained for the next stroke.2007-11-1Harbin Engineering UniversityThe exhaust should close before the inlet on the compression stroke to maximize the charge,but the geometry of the engine may pre

36、vent this if the two events are piston controlled.2007-11-1Harbin Engineering UniversityIt can be done in an engine with exhaust valves.2007-11-1Harbin Engineering UniversityAt all events the inlet ports will be closed as many degrees ABDC as opened before it(i.e.again 130150 BTDC)and the exhaust in

37、 the same region.2007-11-1Harbin Engineering UniversityInjection commences at about 10-20BTDC depending on speed,and combustion lasts 30-50as with the four-stroke.2007-11-1Harbin Engineering University1.More than 50/above 50/over 50 50多2.Less than 50/under 50/below 50 不到50 或50 以下 The temperature is

38、below 20.3.50 more 再加50 ten more days 再10天 Please add 50 more grams of salt to the water.2007-11-1Harbin Engineering University4.a kilometer or more 一公里或一公里多些 a long kilometer 一公里多 a long hour 足足一小时 a dozen 一打，dozens 几十、几打5.数字+odd twenty odd/twenty-odd/twenty and odd/20多2007-11-1Harbin Engineering U

39、niversity6.from twenty to thirty/twenty to thirty/从20 到307.some thirty feet/about thirty feet/thirty feet or so/30英尺左右 a hundred more or less/100上下 more or less twenty pages/20页左右8.n time(s)/增加到n倍，n倍于 The output has increased(by)threetimes as compared with that of last year.2007-11-1Harbin Engineeri

40、ng UniversityWater conducts heat about 20 times better than air does.8.增加多少量，常用by引出。The coke used has been increased by 18%as compared with last year.This pipe is 2 inches longer than that one.2007-11-1Harbin Engineering University9.降低多少倍：减少n times，译为降低到几分之几，或降低了几分之几。The new motor is ten times as li

41、ght asthe old one.新马达的重量是旧马达的十分之一.The switching time of the new-type transistor is reduced 3 times.新晶体管的开关时间减缩了三分之二.2007-11-1Harbin Engineering University10.减少多少量，常以by引出，为绝对数量。The prime cost decreased by 40%.主要成本下降了百分之四十。This pipe is shorter than that one by 3 meters.这根管子比那根短3米。2007-11-1Harbin Engin

42、eering University1、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：Both of these(two-stroke and four-stroke cycle)are explained;Both the m/v“Zheng Zhou”and the m/v“Chang Feng”are 25 000tOcean-going cargo ships designed and built entirely by China;2007-11-1Harbin Engineering Uni

43、versity The iron and steel industry is a basic industries.钢铁工业是基础工业。The steward and commissar has/have come.服务员兼政委/服务员和政委已经来了。2007-11-1Harbin Engineering University2、主语如果是用成语连词 as well as 连接的两个名词或代词，谓语要与第一个名词或代词的人称和数一致。如：The young motorman as well as the others has learned to operate the oil separat

44、ors.这位年青机匠，和其他人一样，已经学会操作分油机。2007-11-1Harbin Engineering University3、主语如果是由一个名词或代词和介词 with 与名词、代词组成的介词短语所组成，谓语要与被介词短语所修饰的名词、代词的人称和数一致。例如：The main engine together with other driven machinery is running smoothly.主机和其它被带动的机械（一起）正在平稳地运转。2007-11-1Harbin Engineering University4、主语如果是用连词 or,eitheror,neither

45、nor,not onlybut also 连接的两个名词或代词，谓语要与后一个名词或代词的人称和数一致。例如：Neither aluminum nor copper is easy to corrode.Not only the main engine but also the auxiliary machines have to be checked at intervals.2007-11-1Harbin Engineering University5、主语如果是集体名词或当作一个整体看待的表示时间、距离、重量的名词复数形式，谓语要用单数形式。例如：30 kilograms is the maximum weight for each passenger.每一位旅客携带物品的重量不得超过30千克。2007-11-1Harbin Engineering University6、主语如果是成对使用的名词，谓语要用单数形式。例如：Trial and error is also a source of ourknowledge.试验和失败也是（我们获得）知识的源泉。2007-11-1Harbin Engineering University此课件下载可自行编辑修改，仅供参考！此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢感谢您的支持，我们努力做得更好！谢谢