轮机英语课件1

1、Harbin Engineering University 2007-11-1 Lesson one How does a Marine Diesel engine Work? Prof. Song Zhou Harbin Engineering University 2007-11-1 New 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

2、转，进程 charge 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 University 2007-11-1 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 combin

3、e (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，喷油器 continue 继续(进行) revolution 转 theoretically 理论上地 inefficient 效率低的，无效的 Harbin Engineering University 2007-11-1 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 propel

4、ler 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 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 University 2007-11-1 *The diesel engine is a type of internal combustion engine which ignites(点燃点燃) the fuel by in

5、jecting(喷射喷射) it into hot, high pressure air in a combustion chamber(燃烧室燃烧室). Harbin Engineering University 2007-11-1 The marine diesel engine is a type of diesel engine used on ships. The principle of its operation is as follows: Harbin Engineering University 2007-11-1 A charge of fresh air is draw

6、n or pumped into the engine cylinder(气缸气缸) and then compressed by the moving piston(活塞活塞) to very high pressure. Harbin Engineering University 2007-11-1 When 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 Enginee

7、ring University 2007-11-1 The 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 University 2007-11-1 Exhaust valve Inlet valve Fuel injector Cylinder

8、 Piston Piston ring Connecting rod Four-stroke diesel engine Combustion chamber Piston pin crankshaft Crank web Harbin Engineering University 2007-11-1 Fuel injector Fuel injector Exhaust valve 扫气口扫气口 Scavenge port Exhaust port Two-stroke Engine Cross scavenge systemUniflow scavenge system Piston ro

9、d Connecting rod Piston pin Crosshead Harbin Engineering University 2007-11-1 The operation between two fuel injections is called a working cycle, which consists of a fixed sequence of events. Harbin Engineering University 2007-11-1 This cycle may be achieved either in four strokes(冲程、冲程、 行程行程) or t

10、wo. Harbin Engineering University 2007-11-1 In a four-stroke diesel 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 Engineer

11、ing University 2007-11-1 If 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). Harbin Engineering University 2007-11-1 Scavenge (a) Compression (b) Injection (c) Exhaus

12、t (d) Scavenge port Exhaust port Fuel injector CylinderPiston Connecting rod Crank Harbin Engineering University 2007-11-1 The 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 sid

13、es of the cylinder being opened (Fig. 1-a). Harbin Engineering University 2007-11-1 The 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. Harbin Engineering University 2007-11-1 As

14、 the piston moves about one fifth of the way up, it closes the inlet ports and the exhaust 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 University 2007-11-1 When the piston reaches the top of its stroke, i.e. the top dead center (TDC), both th

15、e pressure and the temperature of the air rise to very high values. Harbin Engineering University 2007-11-1 The 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 University 2007-11-1 The piston is fo

16、rced(迫使迫使) downward as the high pressure gases expand until it uncovers the exhaust ports. Harbin Engineering University 2007-11-1 The 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 University 2007

17、-11-1 In the two-stroke engine, each revolution of the crankshaft (曲轴曲轴) makes one power or working stroke, while in the four-stroke engine, it takes two revolutions to make one power stroke. Harbin Engineering University 2007-11-1 That is why a two-stroke cycle engine will theoretically develop twi

18、ce (two times) the power of a four-stroke engine of the same size. Harbin Engineering University 2007-11-1 Inefficient scavenging and other losses, however, reduce the power advantage to about 1.8. Harbin Engineering University 2007-11-1 Each type of engine has its application on board ship. The slo

19、w speed (i.e. 90 to 120 rev/min) main propulsion diesel operates on the two- stroke cycle. Harbin Engineering University 2007-11-1 At this low speed the engine requires no reduction gearbox between it and propeller. Harbin Engineering University 2007-11-1 The four-stroke engine (usually rotating at

20、medium speed, between 250 to 750 rev/min) is used for alternators and sometimes for main propulsion with a gearbox to provide a propeller speed of between 90 to 120 rev/min. Harbin Engineering University 2007-11-1 Reading Material Working cycles A diesel engine may be designed to work on the two- st

21、roke or on the four-stroke cycle: both of these are explained below. Harbin Engineering University 2007-11-1 The four-stroke cycle F 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 Universi

22、ty 2007-11-1 It is usual to draw such diagrams starting at TDC (firing), but the explanation will start at TDC (scavenge ). Top dead center is sometimes referred to as inner dead center (IDC). Harbin Engineering University 2007-11-1 Proceeding clockwise round the diagram, both inlet (or suction) and

23、 exhaust valves are initially open. (All modern four-stroke engines have poppet valves (提升阀提升阀).) Harbin Engineering University 2007-11-1 I 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),

24、 i.e. when both valves are open, will be short, and the exhaust valve will close some 10after top dead center (ATDC). Harbin Engineering University 2007-11-1 TDC（firing) Fuel valve closed(full load) Injection commences 10-20BTDC Exhaust valve opens 120-150ATDC Exhaust valve closes 50- 60ATDC Inlet v

25、alve open 70-80 BTDC Inlet valve close 146-155BTDC Fig 2 四冲程定时图 BDC Harbin Engineering University 2007-11-1 Propulsion engines and the vast majority of 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 and Harbin Engineering Universi

26、ty 2007-11-1 will be designed to allow a generous throughflow of scavenge air at this point in order to control the turbine blade temperature. Harbin Engineering University 2007-11-1 In this case the exhaust valve will remain open until exhaust valve closure (EVC) at 50- 60ATDC. As the piston descen

27、ds 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 University 2007-11-1 To maximize 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

28、 (suction) valve will normally be held open until about 25- 35 ABDC (145-155BTDC). Harbin Engineering University 2007-11-1 This event is called inlet valve closure (IVC). The charge is then compressed by the rising piston until it has attained a temperature of some 550. Harbin Engineering University

29、 2007-11-1 At 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(depending on type again) and Harbin Engineering University 2007-11-1 the fuel burns over a period of 30-50while the piston begins to descend

30、 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 University 2007-11-1 At about 120-150ATDC 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 ga

31、ses to exhaust. Harbin Engineering University 2007-11-1 T 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 reduce the cylinder pressure to a minimum by BDC to reduce pumping work on the “exhaust” stroke. Harbin Engineering University

32、 2007-11-1 The 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 Engineering University 2007-11-1 plus the positive pressure difference, which usually exists across the cylinder by now, produces

33、a through flow of air to the exhaust to scavenge the cylinder. Harbin Engineering University 2007-11-1 If the engine is naturally aspirated the IVO is about 10BTDC. The cycle now repeats. Harbin Engineering University 2007-11-1 The two-stroke cycle Figure 3 shows the sequence of events in a typical

34、two-stroke cycle, which, as the name implies, is accomplished in one complete revolution of the crank. Harbin Engineering University 2007-11-1 Exhaust closes 110-150BTDC Exhaust opens 110-120ATDC Inlet opens 130-150ATDC Inlet closes 130-150BTDC TDC Fuel valve closes (full load ) Injection commences

35、10-20BTDC Fig.3 二冲程定时图The two-stroke cycle Harbin Engineering University 2007-11-1 Two-stroke engines invariably have ports to admit air when uncovered by the descending piston. Harbin Engineering University 2007-11-1 The exhaust may be via ports adjacent to the air ports and controlled by same pist

36、on (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 University 2007-11-1 Starting at TDC combustion is already under the way and the exhaust opens (EO) at 110- 120ATDC to promote a rapid blow-down before the inlet op

37、ens (IO) about 20- 30later (130-150ATDC). Harbin Engineering University 2007-11-1 In 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 air to flow quickly through the cylinder with a minimum of mixing, Harbin Engineering Uni

38、versity 2007-11-1 because 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 University 2007-11-1 The exhaust should close before the inlet on the compression stroke to maximize the charge, but the geo

39、metry of the engine may prevent this if the two events are piston controlled. Harbin Engineering University 2007-11-1 It can be done in an engine with exhaust valves. Harbin Engineering University 2007-11-1 At all events the inlet ports will be closed as many degrees ABDC as opened before it (i.e. a

40、gain 130150 BTDC) and the exhaust in the same region. Harbin Engineering University 2007-11-1 Injection commences at about 10-20BTDC depending on speed, and combustion lasts 30-50as with the four-stroke. Harbin Engineering University 2007-11-1 1. More than 50 / above 50 / over 50 50多 2. Less than 50

41、 / 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 University 2007-11-1 4. 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

42、 odd / twenty-odd / twenty and odd / 20多 Harbin Engineering University 2007-11-1 6. from twenty to thirty / twenty to thirty / 从20 到30 7. 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 ou

43、tput has increased (by) three times as compared with that of last year. Harbin Engineering University 2007-11-1 Water 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. H

44、arbin Engineering University 2007-11-1 9. 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 as the 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 University 2007-11-1 10. 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。 Har