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Lesson 8

Text Lubrication system

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Duties of a lubricant

The successful operation of any engine or machine and its trouble fretrouble free life(e life( 无故障使用寿命无故障使用寿命 )) depends on effective lubrication which involves the formation and maintenance of a lubricating oil film between the moving parts.

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The marine diesel engine is no exception and considerable thought has gone into the problem of the lubrication of its many parts with their widely varying operating conditions.

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In addition to providing lubricating films, oils used in marine diesel engines have to remove heat from oil cooled pistons, neutralizneutralizee(( 中和中和 )) acidic products of combustion,

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cleanse hot moving parts of carbonaceous deposits, resist oxi oxidation(dation( 氧化氧化 )) and wash away wear detritus(wear detritus( 磨屑磨屑 )).

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The development of oils has kekept pace with(pt pace with( 与…同步与…同步 )) the increasing demands made by the steady rise in powers produced by modern marine diesels.

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The selection of an oil from the commercially available range depends to a great extent on the operating conditions, the design of the engine and the type of fuel to be burned.

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Large marine diesel engines of crosshead construction generally have two systems of lubrication:

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a total loss system(a total loss system( 全损系统全损系统 )) feeding the cylinders and a circulating system lubricating the running gear and cooling the pistons.

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CYLINDER LUBRICATION

Temperatures in the cylinder are naturally high, though only the cylinder combustion space and piston crown are subjected to actual flame temperatures.

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The piston rings exert a varying pressure on the liner walls under conditions involving rapidly changing speed and reversal of direction of motion.

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Oil is supplied to the cylinder liner wall and the piston rings by means of mechanical lubricators giving a carefully controlled oil feed, through injectors or quiquills(lls( 注油针注油针 )),

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and in some designs it is timed so that the oil impinges(impinges( 射到射到 )) only on the piston ring beltpiston ring belt, thus ensuring the most efficient lubrication.

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Cylinder liner Piston

Piston ringQuillJimei university

belt

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Injector

Hydraulic motor

Camshaft

Gear pump

Lubrication oil

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The films of oil between the rings and the liner and between the rings and the grooves in the piston are not only essential for lubrication but also play an important part in achieving a gas seal.

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In carrying out these duties the oil is exposed to contamination by products of combustion.

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Some of these are acidic, particularly if residual fuelsresidual fuels are being used and can cause corrosive conditions which promote heavy rates of wear.

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Also, lacquer(lacquer( 漆膜漆膜 )) and carbonaceous deposits form in the ring belt which interfere with the correct operation of the rings.

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To counteract these undesirable effects cylinder oils usually contain additives formulated(formulated( 配配制制 )) to impart(impart( 给予给予 )) a high degree of alkalinity(alkalinity( 碱性碱性 )) and dedetergency(tergency( 去垢能力去垢能力 )).

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The alkalinity neutralizes the acid conditions and the detergency cleanses the rings and grooves.

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CRANKCASE LUBRICATION

Operating conditions in the crank chamber are very different from those in the cylinder and it is the need for the oil to perform its functions over a very long period, which determines the properties required in the lubricant.

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The following features are essential for crank chamber oils:

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1. They must have good lubricating properties and be able to resist rupture(rupture( 破裂破裂 )) of the film separating the moving parts in order to ensure minimum friction losses.

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2. They must be able to remove heat from a bearing and to do so the viscosity should be high enough at operating temperatures to assist film maintenance.

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3. They must be capable of removing heat from oil cooled pistons and in doing so must have the highest possible degree of resistance to oxidation and other effects of heat.

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The use of a poor quality oil can lead to rapid deteriorationdeterioration(( 变质、恶化变质、恶化 )) of its properties with the resultant formation of deposits in the piston crown

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which in turn results in a considerable reduction in heat transfer with subsequent overheating and thermal cracking.

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The cooling oil is usually supplied to the pistons by means of telescopic pipes、 articulated particulated pipe (ipe ( 铰接管铰接管 )) connected to the crossheads and passages in the piston rods.

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To ensure a constant supply of clean and temperature controlled oil to the engine requires the provision of a great deal of auxiliary equipment such as pumps, filters, centrifuges, coolers, drain and storage tanks etc.

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READING MATERIALA. LUBRICATION

The lubrication system of an engine provides a supply of lubricating oil to the various moving parts in an engine.

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Its main function is to enable the formation of a film of oil between the moving parts, which reduces friction and wear. The lubricating oil is also used as a cleanercleaner and in some engines as a coolant.

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Lubricating oil for an engine is stored in the bottom of the crankcase, known as the sump, or in a drain tank(drain tank( 循环油柜循环油柜 )) located beneath the engine.

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The oil is drawn from this tank through a strainer, one of a pair of pumps, into one of a pair of fine filters.

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It is then passed through a cooler before entering the engine and being distributed to the various branch pipes.

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The branch pipe for a particular cylinder may feed the main bearing, for instance.

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Some of this oil will pass along a drilled passage in the crankshaft to the　 connecting rod bottom end bearing and then up a drilled passage in the connecting rod to the gudgeon pingudgeon pin(( 十字头销十字头销 )) or crosshead bearing.

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An alarm at the end of the distribution pipe ensures that adequate pressure is maintained by the pump.

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Pumps and fine filters are arranged in duplicate with one as standby. The fine filters will be arranged so that one can be cleaned while the other is operating.

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After use in the engine the lubricating oil drains back to the sump or drain tank for re--use. A level gauge gives a local read-outread-out of the drains tank contents.

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A centrifuge is arranged for cleaning the lubricating oil in the system and clean oil can be provided from a storage tank.

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The oil cooler is circulated by sea water, which is at a lower pressure than the oil. As a result any leak in the cooler will mean a loss of oil and not contamination of the oil by sea water.

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CYLINDER LUBRICATION

Large slow speed engines are provided with a separated lubrication system for the cylinder liners.

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Oil is injected between the liner and the piston by mechanical lubricators which supply their individual cylinder.

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A special type of oil is used which is not recovered. In addition to lubricating, it assists in forming a gas seal and contains additives which clean the cylinder liner.

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A. DIFFICULTY WITH THE CYLINDER LUBRICATING SYSTEM

Possible causes may be:(a) The non-return valve for the lubricating stud is defective.(b) The cylinder lubricator or its drive is defective.

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(c) Lubricating oil pipes or pipe connections are defective.(d) Lubricating oil pipes, or cylinder lubricating studs, are defective.(e) The cylinder lubricators need replenishing.(f) There is air in the piping.