1、Lesson Three Text Diesel engine construction (II)Prof. Song Zhou New Words and Expressions in Text recess 凹槽，凹座，凹入處 dowel 銷釘 pin 銷子 caulk 斂(鉚)縫，嵌塞 topmost 最上部 narrow 狹窄的 diagonal 對角的，斜的 overlap 重疊，搭接 joint 接合，接頭 distributor 分配器 slightly 輕微地 round 圓的，使成圓形 film (油)膜 period 期間 opposite 在對面，與相對 diameter

2、 直徑 annular 環形的 ensure 保證，擔保 assembly 組件，組裝 component 部件 journal 軸頸 shoe 滑靴，滑塊 horizontally 水平地 adequate 足夠的，充分的 admit 允許進入，導入 duct 管道 scraper 刮子，刮油器 shim 墊片，調整片 thickness 厚度 adjustment 調整，調節 clearance 間隙 appropriate 適當的 channel 通道 crankpin 曲柄銷 forge 鍛造 shrink 紅套 displace 錯位，變位 carrier ring 承磨環 buil

3、d-in 內裝的，機內的，固定 top-bolt 錐體螺栓 white metal 白合金 telescope pipe 伸縮管，拉管 fitted bolt 拂配螺栓A piston consists of a lower partpiston skirt(活塞裙活塞裙) of cast iron and an upper part or crown(活塞頭活塞頭) made of a special heat-resistant steel. They are bolted together and fixed to the piston rod. 1.Pistons and Piston

4、 rodsPiston crownPiston skirtPiston rodPiston ringThe position of the piston parts in relation to each other is secured by means of machine-turned recesses(凹槽凹槽) and a dowel pin(定定位銷位銷) in the crown.Each piston is provided with five or six piston rings fitted in chromium plated grooves in the crown.

5、 The two or three topmost rings are narrow rings having diagonal cuts(斜切口式斜切口式), while the next two are broad and are provided with overlapping end joints.The lowest ring is an oil distributor ring. Diagonal cuts Overlapping end jointAll the rings are slightly rounded on their external top and botto

6、m edges to keep the oil film on the cylinder liner during the running-in period(跑合期、磨合跑合期、磨合期期) for new piston rings. External topExternal bottomIn order to control thermal stresses, thin-wall intensively cooled pistons(薄壁強制冷卻式薄壁強制冷卻式活塞活塞) are used for some types of modern engines. In this case, the

7、 piston has an internal insert in the piston crown, which serves only to direct the cooling liquid flow and, thereby, to intensify the conventional cocktail shaker(振振蕩冷卻蕩冷卻) effect.The piston rods are bored from the top flange to a point opposite the center of the crosshead(十字十字頭頭). Through this bor

8、e, a long pipe is inserted which goes nearly to the bottom of the bore. PipeThe outside diameter of the pipe is less than the diameter of the bore, the result being that an annular space is formed between the piston rod and the pipe.Annular spaceThe lower end of each piston rod is reduced in diamete

9、r to fit a bore in the crosshead, this being secured to the piston rod by a nut. The piston rods are provided with dowel pins to ensure the c o r re c t a s s e m b l y o f t h e components.Piston rodCrossheadOn each of the two journals of the crosshead, crosshead shoes(十十字頭滑板字頭滑板) are mounted which

10、 are guided in the built-in crosshead guides(十字頭導板十字頭導板) of the engine frame. CrossheadCrosshead shoeEngine frameCrosshead guideThe position of the crosshead shoes on the crosshead is determined by dowel pins. The guide shoes are secured to the crosshead by means of tap-bolts(錐體螺釘錐體螺釘).The crosshead

11、 shoes are white metal lined(白合金襯里白合金襯里), grooves being cut horizontally in the face of the white metal to ensure an adequate supply of lubricating oil.The crosshead is short and rigid and the bearings are so constructed that the bearing pressure between the journal and bearing is distributed evenly

12、 over the entire length of the bearing. In order to improve the working conditions of the bearings, the bearing pressure is made smaller and the peripheral speed (is made) higher in later designs.The pistons are cooled by oil supplied from the forced lubrication system. The cooling oil is admitted t

13、hrough the pipe, from which the oil is led to the cooling spaces of the piston through telescopic pipes(伸縮管伸縮管) or articulated pipe(鉸接管鉸接管), and round the internal pipes of the piston rods.The cooling oil is conducted from the piston through the internal pipes of the piston rods and the ducts in the

14、 crossheads, as well as the slotted pipes from which the oil is led to “control boxes” with sight glasses(觀察鏡觀察鏡) on the engine.Sealing between the crankcase and scavenging air boxes is achieved by means of the piston rod stuffing boxes, located in the bottom of the scavenging air boxes. Each stuffi

15、ng is provided with two sealing rings and three scraper rings. The sealing rings, which are mounted uppermost are in four parts and pressed together around the piston rods by means of coil springs(盤簧盤簧).Connecting Rod and Main Bearings The crosshead and crankpin bearings (曲柄銷軸承曲柄銷軸承) are made of cas

16、t steel and each consist of an upper and a lower part secured to the connecting rod by means of fitted bolts(拂配螺栓拂配螺栓), the nut of which are secured.The bearings have white metal bearing surfaces provided with lubrication grooves for the necessary supply of lubricating and cooling oil. Shims(墊片墊片,調整

17、片調整片) of different thickness are inserted between the shells to enable adjustment of the bearing clearances (approx. 0.20-0.30mm).The main bearings, which support the crankshaft, each consist of two shells of cast steel with white metal bearing surfaces having lubricating grooves of an appropriate s

18、hape. The shells are secured by means of bearing caps and studs, the necessary clearance (approx. 0.30mm) being provided by means of shims of different thickness.All bearings are lubricated from the force-feed lubrication system of the engine, the oil being supplied partly through pipes to each main

19、 bearing cap and partly to the crosshead, from where the lubricating oil flows through channels to the crankpin bearings.3. CrankshaftFlywheel飛輪曲柄銷Crankpin曲柄臂Crank throw(web)Main bearing journal主軸頸The crankshafts are built up types(組合式組合式). For semi-built type(半組合式半組合式), the forged main bearing jour

20、nals are shrunk(紅紅套套) into cast steel crank throws with a crank journal and two crank throws as one unit. In the fully built type(全組合式全組合式), the crank throws are shrunk on to main journals and crank journals. The crank throws are displaced from each other to obtain the same number of degrees between

21、 the different crank throws. The crankpin journals are provided with large bores for balancing purpose.Reading MaterialM.A.N. Marine diesel engineThe latest large bore two stroke M.A.N. engine is the KSZ 90/160B series in cylinder numbers from 6 to 12 and developing 2,700 K.W. (3,672H.P.)/cyl.The en

22、gine operates at 122 rev/min. with an M.E.P.(mean effective pressure平均有效壓力平均有效壓力) of 13 bar and a mean piston speed of 6.5m/sec.The bedplate is of fabricated design and consists of two I-shaped longitudinal girders with transverse members into which the cast steel bearing housings are welded. The th

23、rust bearing casing is incorporated into the bedplate. Columns(機架機架) have been replaced by frames constructed of box shaped longitudinal girders. The fabricated top and bottom sections run the full length of the engine and are mounted on the bedplate. Such an engine frame helps to stiffen the engine

24、 and so protect t h e b e a r i n g s f r o m t h e d e f o r m a t i o n f o r c e s transmitted(傳遞傳遞) via the ships double bottom. The cast iron guideways(導板導板) for the crosshead are attached to the top section and seal off the crankcase.The cylinder jackets are individual castings(鑄件鑄件) bolted to

25、gether to form one continuous member. The one-piece cylinder liners are fitted into the jackets from the top and a cast steel strong back is fitted in way of the combustion space to help absorb gas forces.*The scavenge process is the M.A.N. loop system(回流掃氣系回流掃氣系統統) and the scavenge and exhaust port

26、s are arranged in two tiers and are carried far around the liner. The vertical lands between the ports are cooled by water passing through cast in tubes and thence to passages arranged around the liner above the exhaust ports. Each cylinder cover is in two parts, the lower section is of special thin

27、 walled forged steel permitting the area in way of the c o m b u s t i o n g a s e s t o b e intensively cooled whilst absorbing thermal stressesand this is held in position by an upper supporting unit of cast iron, which transmits the gas forces to the cylinder jackets via long studs. The joint fac

28、e between the cylinder cover and the liner is arranged as far away from the combustion process as possible. The gas loads on the engine structure are constrained(約束約束) by means of hydraulically(液壓液壓的的) preloaded tie rods which connect the bedplate, frame sections and cylinder jackets into a single u

29、nit. The crankshaft is of the semi built type, with the journal being shrunk into the forged or cast steel crank throws. With the exception of the six-cylinder engine, it(crankshaft) is in two parts joined by fitted bolts. The coupling flange(聯接法蘭聯接法蘭) for attachment to the propeller shaft also acco

30、mmodates the turning gear(盤車機盤車機) and is integrally forged with the crankshaft.The aft end section also incorporates a thrust collar(推力推力環環). The drive for the camshaft gear train is taken from a spur gear(正齒輪正齒輪) which for a six cylinder engine is at the coupling end and for 7 to 12 cylinder engine

31、s the drive is located in the middle of the engine.The piston crown is of forged steel and is designed for intensive cooling, the central supporting body is of cast steel and is mainly subjected to compressive stress. The two components are bolted together and connected to the piston rod. A single p

32、iece piston skirt fitted with bronze(青銅青銅) rings guides the piston in the cylinder liner. The piston ring grooves for a standard engine are flame hardened(淬火，硬化淬火，硬化) against wear. The crosshead pin bearings are white metal lined shells lubricated by means of high-pressure pumps. T h e p i s t o n f

33、 o r c e s a r e transmitted over the entire length of the crosshead pin then to the connecting rod via the lower half single bearing shell. The principle of hydrostatic lubrication （液體靜壓潤滑）（液體靜壓潤滑）has been applied to the crosshead using high-pressure lubricators.This is achieved by means of high pr

34、essure pumps with two plungers and rods operated by the oscillating(振蕩振蕩) movement of the connecting rod, high pressure oil is delivered to the lower part of the crosshead bearing, the pumps press oil into the bearing when the load on the shell is at its lowest. This ensures that the oil film is mai

35、ntained at all times and on all loads between the journal and the shell. Scavenging of the cylinder liner is on the loop scavenge system and constant pressure of the exhaust gas is used to drive the turbochargers. During running up(起動起動) and in the lower partial load range the turbochargers are assi

36、sted by electrically driven auxiliary blowers connected before the compressors of the main blowers.In the upper power range the a u x i l i a r y b l o w e r s a r e disconnected. Diffusers(擴壓器擴壓器) are fitted in the exhaust system and facilitate charge removal and scavenging in each cylinder. The di

37、ffuser also prevents pressure pulse from one cylinder interfering with another during operation. B. MAN-B&W MC ENGINEMAN-B&W K 90MC-C engine is a large crosshead type two-stroke engine with a bore of 900 mm, a 2,300 mm stroke and an operating speed of 104 r/min. It is constructed with between six an

38、d twelve cylinders. Developed as one of the extensive range of the manufacturers MC engines, it is of the power and speed best suited to large, fast container ships. The increase in running speed is obtained by a slight decrease in engine stroke.High thermal efficiency is maintained by an increase i

39、n mean effective pressure(M.E.P).Construction can be considered generally as typical for the whole range.The engine bedplate is of rigid box form,fabricated from steel plates with main bearing supports of cast steel . Welded Aframes are assembled into a frame box which contains the crankcase, the cr

40、osshead guides and also supports the wheels for the chain drive of the camshaft.A cast iron cylinder frame accommodates the scavenge space between the cylinder jacket and the diaphragm(橫隔板）橫隔板）, both of which are water-cooled. Long pre-stressed tie bolts are fitted between the top of the frame and t

41、he underside of the bedplate girders.The cylinder liner is of alloy cast iron, its upper flange lands on top of the frame and has bore cooling. It is secured by a forged steel cylinder cover which is also bore cooled and shaped internally to accommodate most of the combustion space.Cylinder lubricat

42、ing oil is injected at one level in the liner.P i s t o n h a v e a c h r o m e -molybdenum alloy steel(鉻鉬合鉻鉬合金鋼）金鋼） crown with hard chrome-surfaced(plated)（表面鍍鉻）（表面鍍鉻） ring grooves in which four compression rings are fitted. In this particular model a protective layer of inconel(鉻鎳鉻鎳鐵合金）鐵合金） is wel

43、ded to part of the crown surface to prevent high temperature corrosion.The piston is oil cooled, oil being supplied by a telescopic pipe to the crosshead and then through the piston rod. It is returned from the crosshead to a slotted pipe in the crankcase. A short cast iron skirt is added. The crown

44、 is bolted to the piston rod at an inner support ring.Surface hardening reduces wear on the piston rod at the diaphragm gland. The rod is bolted at the top of a cylindrical crosshead which is of large diameter and incorporates a full-length bottom half-bearing shell. Floating guide shoes are attache

45、d at each end.The crankshaft may be either semi-built up or of welded construction, with large journal and pins. All crankcase bearings are of white metal. Main bearings have thick(wall) shells, crankpin(bottom end)and crosshead(top end ) bearing have thin-wall shells. White metal is used for the gu

46、ide surface.The exhaust valves are operated by hydraulically under oil pressure from cam-timed actuated pistons. They have air compressed springs which allows them to be rotated by vanes. The valve spindles are usually manufactured by the hot isostatic(均均衡的衡的) pressure(HIP) method熱均壓熱均壓法法, a compoun

47、d Nimonic(鎳鉻鈦合鎳鉻鈦合金金) and austenitic(奧氏體的奧氏體的) steel part construction. Valve housing（閥殼）（閥殼） is cooled at its seat and spindle guide bush（導套）（導套） but its upper duct is uncooled to avoid low temperature corrosion.Fuel pumps are cam driven and timed by the plunger helix(螺旋螺旋槽槽). An adjustable barrel(

48、套筒套筒) allows variable ignition timing to maintain combustion efficiency at low speed and can be adjusted to match the ignition quality of fuels. Pumping timing is changed for astern operation by a link connected at the cam roller guide which is activated by compressed air.Each pump supplies three id

49、entical fuel injectors for the corresponding unit. Injectors are uncooled but they circulate hot fuel directly while their needle valves are in the closed position.The engine operates with a constant pressure system, with uncooled turbochargers. Two auxiliary blowers are fitted to operate at low cha

50、rge air pressure or at low engine revolutions. A number of waste heat recovery(余熱回收裝置余熱回收裝置) and power take-off systems(取力系統取力系統) can be operated under running conditions.c. VIBRATION DAMPER減振器減振器The vibration damper serves to reduce the torsional(扭轉扭轉的的)vibration generated by the crankshaft. The damper consists of a ho