毕业论文中英语短片
2020-03-02 19:07:23 来源：范文大全收藏下载本文
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1、MAN MARINE DIESEL ENGINE MAN
The latest large bore two storke MAN, engine is the KSZ 90/163B series in cylinder number from 6 to 12 and developing2,700kW(3,672HP)/cyl.The engine operates at 122r/min, with an M.E.P of 13bar and a mean piston speed of 6.5m/s.
The bedplate is of fabricated design and consists of weo I-shaped longitudinal girders with transverse menbers into which the cast steel bearing housings are welded.The thrust bearing casting is incorporated into the bedplate.
Columns have been replaced by frames constructed of box shaped longitudinal girders.Thew fabricated top and bottom sections run the full length of the engine and are mounted on the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 and so protect the bearings from the deformation forces transmitted via the ship\'s double bottom.The cast iron guideways for the crohead are attached to the top section and seal off the crankcase.
The cylinder jackets are individual castings bolted together 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 proce is the MAN loop system and the scavenge and wxhaust ports are arranged in two tiers and are carried far around the liner.The vertical lands between the ports are cooled by water paing hrough cast in tubes and hence to paages arranged around the liner above the exhaust ports.
Each cylinder cover is in two parts, the lower section is of special thin walled forged steel permitting the area in way of the combustion gases to be intensively cooled whilst absorbing thermal strees and 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 face between the cylinder cover and the liner is arranged as far from the combustion proce as poible.The gas loads on the engine structure are constrained by means of hydraulic preloaded tie rods which connect the bedplate, frame sections and cylinder jackets into a single unit.
The crankshaft is of the semi-built tybe, with the journal being shrunk into the forged or cast steel crank throws.With the exception of the six-cylinder engine, it is in two arts joined by fitted bolts.The coupling flange for attachment to the propeller shaft also accommodates the turning gear and is integrally forged with the crankshaft.The aft end section also incorporates a thrust collar.The drive for the camshaft gear train is taken from a spur gear which for a six cylinder engine is the couping end and for 7 to 12 sylinder engines 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 suvjected to compreive stre.The two components are bolted together and connected to the piston rod.A single piece piston skirt fitted with bronze rings guides the piston in the cylinder liner.The piston ring grooves for a standard engine are flame hardened against wear.The crohead pin bearings are whte metal lined shells lubricated by means of highpreure pumps.The piston forces are transmitted over the entire length of the crohead pin then to the connecting rod via the lower half single bearing shell.The principle of hydrostatic lubrication has been applied to the crohead using high-preure lubricators.This is achieved by means of high preure rod,high preure oil is delivered to the ower part of the crohead bearing, the pumps pre oil film is maintained 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 preure of the exhaust gas is used to drive the turbochargers.During running up and in the lower partial load range the turbochargers are aisted by electrically driven auxiliary blowers connected before the compreors of the main blowers.In the upper power range the auxiliary blowers are disconnected.Diffusers are fitted in the exhaust system and facilitate charge removal and scavenging in each cylinder.The diffuser also prevents preure pulses from one cylinder interfering with another during operation.
2、MAN-B&W MC ENGINE MAN-B&W MC
MAN-B&W K90 MC-C engine is a large crohead tybe two-stroke engine with a broe of 900mm, a 2,300mm stroke and an operating speed of 104r/min.It is constructed with between six and twelve cylinders.
Developed as one of the extensive range of the manufacturer\'s 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 in mean effective preure(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 \'A\' frames are aembled into a frame box which contains the crankcase, the crohead 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, both of which are water-cooled.
Long pre-streed tie bolts are fitted between the top of the frame and the 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 is shaped internally to accommodate most of the combustion space.Cylinder luvricating oil is injected at one level in the liner.Pistons have a chrome-molybdenum alloy steel crown with hard chrome-surfaced ring grooves in which four compreion rings are fitted.In this particular model a protective layer of Inconel is welded to part of the crown surface to prevent high temperature corrosion.The piston is oil cooled, oil being supplied by a telescopic gland to the crohead and then through the piston rod.It is returned from the crohead to a slotted pipe in the crankcase.A short cast iron skirt is added.The crown 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 ata the top of a cylindrical crohead which is of large diameter and incorporates a full-length bottom half-bearing shell.Floating guide shoes are attached at each end.
The crankshaft may be either semi-built up or of welded construcion, with large journals and pins.All crankcase hearings are of white metal.Main bearings have thick shells, crankpin( bottom end ) and crohead(top end) bearing have thin-wall shells.White metal is used for the guide surfaces.The exhaust valves are operated hydraulically under oil preure from cam-timed actuated pistons.They have air compreed springs which allows them to be rotated by vanes.The valve spindles are usually manufactured by the hot isostatic preure(HIP) method, a compound Nimonic and austenitic steel part construction.Valve housing is cooling at its seat and spindle guide bush but its upper duct is uncooled to avoid low temperature corrosion.Fuel pumps are cam driven and timed by the plunger helix.An adjustable barrel allows variable ignition timing to maintain combustion efficiency at low speed and can be adjusted to match the ignition quality of fuels.Pump timing is changed for astern operation by a link connected at the cam roller guide which is activated by compreed air.Each pump supplies three identical fuel injectors for the
corresponding unit.Injectors are uncooled but they circulate hot fuel oil directly white their needle valves are in the closed position.
The engine operates with a constant preure system, with uncooled turbochargers.Two auxiliary blowers are fitted to operate at low charge air preure or at low
engine revolutions.A number of waste heat recovery and power take-off systems can be operated under running conditions.
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