轮机英语课件1

1、Harbin Engineering University2007-11-1Lesson one How does a Marine Diesel engine Work?Prof. Song ZhouHarbin Engineering University2007-11-1New Words and Expressions in Text marine 海运的，船用的 diesel 柴油，柴油机 internal 内部的 combustion 燃烧 ignite 点燃 inject 喷射 chamber 腔，室 principle 原理，原则 operation 工作，操作，运转，进程 c

2、harge 装，充；充填物 fresh 新鲜的，淡(水)的 draw 抽吸 cylinder 气缸 compression 压缩 piston 活塞 fine 细小的，好的 spray 喷雾，(水，油)雾 burn 燃烧Harbin Engineering University2007-11-1 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)

3、 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，喷油器 continue 继续(进行) revolution 转 theoretically 理论上地 inefficient 效率低的，无效的Harbin Engineering University2007-11-1 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

4、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 centre (TDC) 上止点 on board ship 在船上 r/min 转分 reduction gear box 减速齿轮箱Harbin Engineering University2007-11-1*The diesel engine is a type of internal combustion engine which ignites(点燃点燃) the fuel by injecting(喷射喷射)

5、 it into hot, high pressure air in a combustion chamber(燃烧室燃烧室). Harbin Engineering University2007-11-1The marine diesel engine is a type of diesel engine used on ships. The principle of its operation is as follows:Harbin Engineering University2007-11-1A charge of fresh air is drawn or pumped into t

6、he engine cylinder(气缸气缸) and then compressed by the moving piston(活塞活塞) to very high pressure.Harbin Engineering University2007-11-1When the air is compressed, its temperature rises so that it ignites the fine spray(喷雾、喷雾、油雾油雾) of fuel injected into the cylinder.Harbin Engineering University2007-11-

7、1The burning of the fuel adds more heat to the air charge, causing it to expand and force the engine piston to do work on the crankshaft which in turn drives the ships propeller(螺旋桨螺旋桨).Harbin Engineering University2007-11-1Exhaust valveInlet valveFuel injectorCylinderPistonPiston ringConnecting rod

8、Four-stroke diesel engineCombustion chamberPiston pincrankshaftCrank webHarbin Engineering University2007-11-1Fuel injectorFuel injectorExhaust valve扫气口扫气口Scavenge portExhaust portTwo-strokeEngineCross scavenge systemUniflow scavenge systemPiston rodConnecting rodPiston pinCrossheadHarbin Engineerin

9、g University2007-11-1The operation between two fuel injections is called a working cycle, which consists of a fixed sequence of events. Harbin Engineering University2007-11-1This cycle may be achieved either in four strokes(冲程、冲程、行程行程) or two.Harbin Engineering University2007-11-1In a four-stroke di

10、esel engine, the cycle requires four separate strokes of the piston, i . e . s u c t i o n ( 吸 气吸 气 ) , c o m p r e s s i o n ( 压 缩压 缩 ) , e x p a n s i o n ( 膨 胀膨 胀 ) a n d exhaust(排气排气). * Note: i.e. (拉拉=id est)即；就是即；就是Harbin Engineering University2007-11-1If we combine the suction and exhaust ope

11、rations 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). Harbin Engineering University2007-11-1Scavenge(a)Compression(b)Injection(c)Exhaust(d)ScavengeportExhaustportFuel injectorCylinderPistonConnecting rodCrankHa

12、rbin Engineering University2007-11-1The 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 ports or scavenge ports(扫气口扫气口) in the sides of the cylinder being opened (Fig. 1-a). Harbin Engineering University2007-11-1The e

13、xhaust 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. Harbin Engineering University2007-11-1As the piston moves about one fifth of the way up, it closes the inlet ports and the exhaust

14、p o r t s . T h e a i r i s t h e n compressed as the piston moves up. (Fig. 1-b). Harbin Engineering University2007-11-1When the piston reaches the top of its stroke, i.e. the top dead center (TDC), both the pressure and the temperature of the air rise to very high values. Harbin Engineering Univer

15、sity2007-11-1The fuel injector injects a fine spray of fuel into the hot air and combustion take place, producing much higher pressure in the gases. Harbin Engineering University2007-11-1The piston is forced(迫使迫使) downward as the high pressure gases expand until it uncovers the exhaust ports. Harbin

16、 Engineering University2007-11-1The burning gases begin to exhaust (Fig. 1-d) and the piston continues down until it opens the inlet ports. Then another cycle begins.Harbin Engineering University2007-11-1In the two-stroke engine, each revolution of the crankshaft (曲轴曲轴) makes one power or working st

17、roke, while in the four-stroke engine, it takes two revolutions to make one power stroke. Harbin Engineering University2007-11-1That is why a two-stroke cycle engine will theoretically develop twice (two times) the power of a four-stroke engine of the same size.Harbin Engineering University2007-11-1

18、Inefficient scavenging and other losses, however, reduce the power advantage to about 1.8.Harbin Engineering University2007-11-1Each type of engine has its application on board ship. The slow speed (i.e. 90 to 120 rev/min) main propulsion diesel operates on the two-stroke cycle. Harbin Engineering U

19、niversity2007-11-1At this low speed the engine requires no reduction gearbox between it and propeller. Harbin Engineering University2007-11-1The four-stroke engine (usually rotating at medium speed, between 250 to 750 rev/min) is used for alternators and sometimes for main propulsion with a gearbox

20、to provide a propeller speed of between 90 to 120 rev/min. Harbin Engineering University2007-11-1Reading Material Working cyclesA diesel engine may be designed to work on the two-stroke or on the four-stroke cycle: both of these are explained below.Harbin Engineering University2007-11-1The four-stro

21、ke cycleF i g u r e 2 s h o w s d i a g r a m m a t i c a l l y t h e sequence of events throughout the typical four-stroke cycle of two revolutions. Harbin Engineering University2007-11-1It is usual to draw such diagrams starting at TDC (firing), but the explanation will start at TDC (scavenge ). T

22、op dead center is sometimes referred to as inner dead center (IDC).Harbin Engineering University2007-11-1Proceeding 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).)Harbin Engineering University20

23、07-11-1I f t h e e n g i n e i s n a t u r a l l y aspirated(自然吸气自然吸气), or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap(重叠重叠), i.e. when both valves are open, will be short, and the exhaust valve will close some 10after top dead center (ATDC). Harbin Engine

24、ering University2007-11-1TDC（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BDCHarbin Engineering University2007-11-1Propulsion engines and the vast majority o

25、f auxiliary generator engines running at speeds below 1000 rev/min will a l m o s t c e r t a i n l y b e turbocharged andHarbin Engineering University2007-11-1will be designed to allow a generous throughflow of scavenge air at this point in order to control the turbine blade temperature.Harbin Engi

26、neering University2007-11-1In 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. Harbin Engineering University2007-11-1To maximize

27、this, balancing the reduced opening as the valve seats against the slight ram(进气进气阀座阀座) or inertia effect of the incoming charge, the inlet (suction) valve will normally be held open until about 25- 35 ABDC (145-155BTDC). Harbin Engineering University2007-11-1This event is called inlet valve closure

28、 (IVC). The charge is then compressed by the rising piston until it has attained a temperature of some 550. Harbin Engineering University2007-11-1At about 10-20BTDC(firing), depending on the type and speed of the engine, the injector admits finely atomized(雾化的雾化的) fuel which ignites within 2-7(depen

29、ding on type again) andHarbin Engineering University2007-11-1the 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 m o v e m e n t t o a s s i s t combustion.Harbin Engineering University2007-11-1At about 12

30、0-150ATDC the exhaust valve opens (EVO), the timing being chosen to promote(促进促进) a very rapid blow-down(排出排出) of the cylinder gases to exhaust. Harbin Engineering University2007-11-1T h i s i s d o n e : ( a ) t o preserve(保留保留) as much energy as is practicable to drive the turbocharger, and (b) to

31、 reduce the cylinder pressure to a minimum by BDC to reduce pumping work on the “exhaust” stroke.Harbin Engineering University2007-11-1The rising piston expels(排出排出) the remaining exhaust gas and at about 70-80 BTDC the inlet valve opens (IVO) so that the inertia of the outflowing gas, Harbin Engine

32、ering University2007-11-1plus the positive pressure difference, which usually exists across the cylinder by now, produces a through flow of air to the exhaust to scavenge the cylinder.Harbin Engineering University2007-11-1If the engine is naturally aspirated the IVO is about 10BTDC. The cycle now re

33、peats. Harbin Engineering University2007-11-1The two-stroke cycleFigure 3 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. Harbin Engineering University2007-11-1Exhaust closes110-150BTDCExhaust opens110-1

34、20ATDCInlet opens130-150ATDCInlet closes130-150BTDCTDCFuel valve closes (full load )Injection commences10-20BTDCFig.3二冲程定时图The two-stroke cycleHarbin Engineering University2007-11-1Two-stroke engines invariably have ports to admit air when uncovered by the descending piston.Harbin Engineering Univer

35、sity2007-11-1The exhaust may be via ports adjacent to the air ports and controlled by same piston (loop scavenge回流扫气回流扫气) or via poppet exhaust valves at the other end of the cylinder (uniflow scavenge直流扫气直流扫气). Harbin Engineering University2007-11-1Starting at TDC combustion is already under the wa

36、y and the exhaust opens (EO) at 110-120ATDC to promote a rapid blow-down before the inlet opens (IO) about 20-30later (130-150ATDC). Harbin Engineering University2007-11-1In this way the inertia of the exhaust gasesmoving at about the speed of soundis contrived(设计、设法设计、设法) to encourage the incoming

37、air to flow quickly through the cylinder with a minimum of mixing, Harbin Engineering University2007-11-1because any unexpelled (未排未排出 的 ）出 的 ） e x h a u s t g a s e s detracts(减损，降低减损，降低) from the weight of air entrained for the next stroke. Harbin Engineering University2007-11-1The exhaust should

38、close before the inlet on the compression stroke to maximize the charge, but the geometry of the engine may prevent this if the two events are piston controlled. Harbin Engineering University2007-11-1It can be done in an engine with exhaust valves. Harbin Engineering University2007-11-1At all events

39、 the inlet ports will be closed as many degrees ABDC as opened before it (i.e.again 130150 BTDC) and the exhaust in the same region. Harbin Engineering University2007-11-1Injection commences at about 10-20BTDC depending on speed, and combustion lasts 30-50as with the four-stroke. Harbin Engineering

40、University2007-11-11. 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 below 20.3. 50 more 再加50 ten more days 再10天 Please add 50 more grams of salt to the water.Harbin Engineering University2007-11-14. a kilometer or more 一公里或一公里多些 a long kilo

41、meter 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Harbin Engineering University2007-11-16. 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

42、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.Harbin Engineering University2007-11-1Water 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 wi

43、th last year.This pipe is 2 inches longer than that one.Harbin Engineering University2007-11-19. 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 light 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.Harbin Engineering University2007-11-110. 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 me