英文课本

英文课本 The working principle of diesel engine The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot,high pressure air in a combustion chamber.The marine diesel engine is a type of diesel engine used on ships.The principle of its operation is as follows: A charge of fresh air is drawn or pumped into the engine cylinder and then compressed by the moving piston to very high pressure. When the air is compressed,its temperature rises so that it ignites the fine spray of fuel injected into the cylinder.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 ship's propeller. The operation between two fuel injections is called a working cycle,which consists of a fixed sequence of events.This cycle may be achieved either in four strokes or two.In a fourstroke diesel engine,the cycle requires four separate strokes of the piston,i.e. suction,compression,expansion and exhaust.If we combine the suction and exhaust operations with the compression and expansion strokes,the fourstroke engine will be turned into a two stroke one,as is shown in Figures101(a)(d). Fig. 101 The principle of the two stroke diesel engine The two-stroke cycle begins with the piston coming up from the bottom of its stroke,i.e. bottom dead centre(BDC),with the air inlet ports or scavenge ports in the sides of the cylinder being opened(Fig.101(a))?.The exhaust ports are uncovered also.Pressurised fresh air charges into the cylinder,blowing out any residual exhaust gases from the last stroke through the exhaust ports. As the piston moves about one fifth of the way up,it closes the inlet ports and the exhaust ports.The air is then compressed as the piston moves up.(Fig.101(b)). When the piston reaches the top of its stroke,i.e. the top dead centre(TDC),both the pressrue and the temperature of the air rise to very high values.The fuel injector injects a fine spray of fuel into the hot air and combustion takes place,producing much higher pressure in the gases. The piston is forced downward as the high pressure gases expand(Fig.101(c))until it uncovers the exhaust ports.The burnt gases begin to exhaust(Fig.101(d))and the piston continues down until it opens the inlet ports.Then another cycle begins. In a four stroke diesel engine,the cylinder cover is fitted with three valves,an air inlet valves,a fuel valve and an exhaust valve,which are operated at the correct moment by the engine by means of cams. The four strokes are called suction,compression,expansion and exhaust,but only the expansion stroke provides the power to drive the ship while the other three require power from the remaining cylinders to perform their various duties. 1st StrokeSuction.The piston is moving downward and the air inlet valve has been opened by the engine while the others remain closed.Air from the engine room is being drawn into the cylinder,and when the piston reaches the bottom of the stroke the cylinder will be full of air and the inlet valve will close. 2nd StrokeCompression.The piston is now being driven upwards,all valves are shut and the air charge is compressed to a pressure of about 3.5 MPa, at which its temperature is 1,200?F. 3rd StrokeExpansion.Just before the beginning of this stroke the fuel valve is opened and oil is sprayed into cylinder in the form of a fine spray.The hot air causes it to burn and this air is further heated by this combustion of the fuel.The fuel valve remains opened for a short period at the beginning of this stroke.The air expands and piston is driven downwards and so supplies power to the crankshaft through the connecting rod. 4th StrokeExhaust.The piston is again travelling upwards and the exhaust valve has been opened,the waste or burnt gases are driven out to the silencer through the exhaust valve. Then the next cycle begins with the drawing of a fresh air charge. In the two-stroke engine,each revolution of the crankshaft makes one power or working stroke,while in the four-stroke engine,it takes two revolutions to make one power stroke.That is why a two-stroke cycle engine will theoretically develop twice the power of a four-stroke engine of the same size.Inefficient scavenging and other losses,however,reduce the power advantage to about 1.8. Each type of engine has its application on board ship.The slow speed(i.e.90 to 120 r/min)main propulsion diesel operates on the two-stroke cycle.At this low speed the engine requires no reduction gearbox between it and propeller.The four-stroke engine(usually rotating at medium speed.between 250 to 750 r/min)is used for alternators and sometimes for main propulsion with a gearbox to provide a propeller speed of between 90 to120 r/min. EXERCISES I. Choose the best answer. 1.Marine diesel engine may be divided into two general types, A.onestroke or twostrokeB.twostroke or threestroke C.twostroke or fourstrokeD.threestroke or fourstroke 2. In fourstroke engine,the cycle of events is completed in four strokes of. A.the cylinderB.the pistonC.the crossheadD.the crankshaft 3. Four strokes comprise suction,compressionand exhaust. A.ignitionB.explosionC.powerD.combustion 4. In twostroke diesel engine,the cycle of events is completed in one revolution of. A.crankshaftB.camshaftC.turbine shaftD.main bearing 5. In the twostroke engine,each revolution of the crankshaft makes one power stroke,while in the fourstroke engine,it takesto make one power stroke. A.one revolutionB.two revolutions C.three revolutionsD.four revolutions 6. The diesel engine is. A.a turbine engineB.an internal combustion engine C.a steam engineD.a gas turbine 7. Following the working stroke,theis forced out of the cylinder. A.fresh airB.waste gasC.solutionD.temperature 8. During the suction stroke,the piston is moving . A.upwardsB.inwardsC.downwardsD.outwards 9. When the piston is pushed down, it forces the engine to do work on the crankshaft which in turn drives. A.the turning gearB.the ship's propeller C.the thrust padD.the ship's rudder 10. Since the burning or combustion takes place within the engine itself,the engine is known as. A.a firetube boiler B.an internal combustion engine C.an external combustion engine D.an internal combustion generator 11. Whenis compressed,its temperature rises so that it ignites the fine spray of fuel injected into the cylinder. A.the oilB.the airC.the fresh waterD.the steam 12. The fuel injector injects a fine spray of fuel into the hot air and combustion,producing much higher pressure in the gases. A.has begunB.takes placeC.occursD.happens 13. The slow speed main propulsion diesel usually operates on. A.the four stroke cycleB.the fourstroke cycle C.the two stroke cycleD.the twostroke cycle FUEL OIL SYSTEM The fuel injection system of a marine diesel engine is,in many respects,the heart of an engine.It must meter certain quantities of fuel,deliver the metered fuel at high pressure to the engine cylinder at exactly the correct time,in a precise spray pattern,and at a specified time stop delivery abruptly and completely. In a typical fuel system,fuel oil is transferred to service tank after being passed through an oil separator.Fuel flows from the service tank through a strainer to a fuel supply pump which is normally attached to and driven from the engine.The fuel is discharged from the pump and flows thuough a filter before going to the fuel injection pump. It is customary for the fuel supply pump to have a capacity from three to four times that actually required by the engine.The excess fuel flows through the injection pump housing,cooling the plunger and barrel and insuring that the pump cylinder is completely filled at each stroke.The high pressure fuel is discharged from the injection pump to the fuel valves in each cylinder of the engine through high pressure pipes.Excess fuel flows through leak-off lines from the injection pump and from each fuel valve.The leakoff lines are manifolded to return excess fuel to the service tank. Fuel must be injected into the cylinder at very high pressure so that it will be fully atomized.This pressure depends on the viscosity of the fuel but lies in the range of 35MPa — 70MPa. Fuel oil is injected into cylinder and atomized by the fuel valve,which is practically a needle valve.The needle valve is usually spring-loaded,and it opens when the fuel pressure is about one third of its maximum value with the fuel being injected into the cylinder in fine spray through the orifices in the nozzle. Since marine engines operate over a wide range of speeds and loads,it is desirable to be able to change the fuel injected.The plunger of a fuel injection pump often has a spiral control groove and a control sleeve.By rotating the control sleeve,the position of the control groove relative to the fuel inlet port is changed thus altering the time at which the injection process ends or begins,and therefore the quantity of fuel injected.The engine is also provided with a governor which is connected with the control sleeve.Whenever the running speed goes up or down due to the changes in engine load,the governor can automatically adjust the speed to the set value by reducing or increasing the fuel oil supply. The major objectives of the system are to deliver clean fuel,free of air and water,to the injection pumps.To this end,filter cases are normally installed in locations where they can be easily serviced and the elements can be replaced without introducing dirt and with a minimum of maintenance effort.Adequate and easily accessible drain connections are provided at the lowest part of the fuel service tanks for stripping water or foreign matter which may accumulate. EXERCISES I. Choose the best answer. 1. The fuel valves are operated by means of. A.camsB.flywheelC.chainsD.thrust pad 2. It is advantageous to have the fuel valvein way of the nozzle. A.heatedB.cooledC.expandedD.washed 3. The function of the fuel valve is to inject the fuel. A.in a finely atomized sprayB.in a solid state C.in first class condition stateD.in a liquid state 4.is not properly set thus causing either advanced or retarded firing. A.The pistonB.The fuel injection pump C.The cylinder linerD.The oil purifier 5.The fuel pump has the task of delivering fuel to the fuel valve at pressure ranging from. A.0.2 to 0.5MPaB.2 to 5MPa C.20 to 50MPaD.200 to 500MPa 6.A change in the degree of fuel atomization in a diesel cylinder would have the greatest effect on the. A.combustion in the cylinderB.cylinder air turbulence C.fuel spray angleD.fuel injection rate 7.Fuel is not supplied to the corresponding cylinder due to. A.a failure of the motorB.a failure of fresh water generator C.a failure of governorD.a failure of fuel pump 8.are not in proper condition so that too much fuel is supplied to the corresponding cylinder. A.Piston rodsB.Sounding rodsC.Regulating rodsD.Connecting rod 9.The most vital parts of the fuel injection equipment are,fuel valve and actuating gear. A.sea water pumpB.booster pumpC.lower pressure pumpD.high pressure pump 10.The fuel system is used to to the combustion chamber in the cylinder. A.discharge the bilge waterB.transfer the fuel oil C.pump the cylinder oilD.mix water and oil 11.The fuel should be separated before being pumped into. A.the daily service tankB.the settling tank C.the expansion tankD.the doublebottom tank 12.The sequence of fuel injection into the cylinder is determined by. A.the driving gearB.the driven gearC.the timing gearD.the turning gear 13.The viscosity regulator controls in order to provide oil at the correct viscosity for combustion. A.the engine's speedB.the engine's load C.the fuel oil temperatureD.the fuel oil flow 14.Fuel oil is thought to be one of the main factorsthe operation and maintenance of an engine. A.have nothing to do withB.having nothing to do with C.have much to do withD.having much to do with 15.The engine has one or two groups of fuel pumps,depending upon. A.the number of the fuel valves B.the number of cylinder C.the speed of engine D.the power of engine SUPERCHARGING AND SCAVENGING Air supply is very important to the perfect combustion of fuel in the diesel engine.As the air density dertermines the maximum weight of fuel that can be burned per working stroke in the cylinder,it also determines the maximum power that can be developed by the engine?.If the chargeair density is increased by a compressor before it enters the cylinder,a greater amount of fuel can be burned,resulting in an increase of power output.This is the main principle of exhaust turbocharging. In today's practice,the compressor,i.e. a blower,is driven by the heat energy obtained from the engine exhaust gases.The turboblower comprises a gasturbine,driven by the engine exhaust gases and directly coupled to the blower,which draws fresh air from the engineroom and discharges it into the air inlet manifold on the engine?.The power produced in the turbine must be equal to that required by the compressor.The air is pumped into the cylinder through the inlet ports.The turboblower is provided with a filtersilencer. Fig. 12.1 The manner of scanvenging According to the way the energy of the exhaust gases is utilized,pressurecharging can be divided into two main system,namely,the constantpressure system and the pulsesystem. It is usually desirable to fit chargeair coolers to turbocharged twostroke engines.The coolers are located between the turboblowers and the cylinders.As the chargeair density increases,the amount flowing into the cylinders is increased and as the chargeair temperature lowers,the exhaust temperature and the engine thermal loading are reduced.The chargeair cooler is usually of the watercooled design with the sea water circulating in it. As the air passes through the charge air cooler,its temperature may be reduced and moisture condensed,with the condensation in danger of being carried into the engine.So a water separator should be mounted beneath the bottom part of the engine inlet manifold. It is very important that each cylinder should be well scavenging before the charged air is compressed,otherwise this fresh air charge will be fouled by the residual exhaust gases from the last cycle.?Three basic systems are in common use:the cross flow,the loop and the uniflow. In cross scavenging the incoming air is directed upwards,pushing the exhaust gases before it.The exhaust gases then travel down and out of the exhaust ports.Fig121(a) illustrates the process. In loop scavenging the incoming air passes over the piston crown then rises towards the cylinder head.The exhaust gases are forced before the air passing down and out of exhaust ports located just above the inlet ports.The process is shown in fig121(b). With uniflow scavenging the incoming air enters at the lower end of the cylinder and leaves at the top.The output at the top of the cylinder may be ports or a large valve.The process is shown in Fig121(c). Each of the system has various advantages and disadvantages.Cross scavenging requires the fitting of a piston skirt to prevent air or exhaust gas escape when the piston is at the top of the stroke.Loop scavenge arrangements have low temperature air and high temperature exhaust gas passing through adjacent ports,causing temperature differential problems for the liner material.Uniflow is the most efficient scavenging system but requires either an opposed piston arrangement or an exhaust valve in the cylinder head.All these systems have the ports angled to swirl the incoming air and direct it in the appropriate path. EXERCISES I. Choose the best answer. 1.When exhaust ports and scavenging ports are arranged on the same side ,the exhaust ports arethan the scavenging ports. A.slightly higherB.slightly lowerC.much higherD.much lower 2.means that both exhaust ports and scavenging ports are arranged on the same side. A.Uniflow scavengingB.Cross scavenging C.Loop scavengingD.Straight scavenging 3.The scavenging ports communicate with. A.the turbochargerB.the scavenging air receiver C.the blowerD.air receiver 4.When the scavenging ports are uncovered,rushes into the cylinder. A.exhaust gasB.scavenging airC.burned gasD.atmosphere 5.The exhaust ports connect with . A.the compressed air pipeB.the sea water pipe C.the piping systemD.the exhaust manifold 6. is stored in the scavenging air receiver A.Lowpressure airB.Highpressure air C.Compressed airD.Exhaust gas 7.is important to the perfect combustion of fuel oil in the diesel engine. A.Air supplyB.Gas supplyC.Water supplyD.Store supply. 8.A number of different scavenging methods in slow speed twostroke engines. A.are in useB.is usedC.are usingD.has been used 9.Modern engines exhaust gas driven turbochargers to supply pressurised fresh air for scavenging and supercharging. A.make use ofB.have made the use of C.by means ofD.make advantage of 10.All three systems have the ports to swirl the incoming air and direct it in the appropriate path. A.angledB.foundedC.being angledD.being rounded 11.Uniflow is the most efficient scavenging system but requires an opposed piston arrangement an exhaust valve in the cylinder head. A.neither/norB.both/alsoC.either/orD.not only/but also 12.Charging is the filling of the engine cylinder with a supply or charge of fresh air compression. A.to needB.ready forC.want toD.going to be COOLING SYSTEM The cooling of lowspeed marine diesel engine is a consideration of great importance.Engine cooling is important for several reasons.The strength of engine materials decreases with higher temperature,therefore,cooling is necessary to regulate the temperature to a level that will ensure the material strength required? .The viscosity of lube oil is sensitive to temperature,and at elevated temperatures the lube oil will break down with a resulting loss of lubricating properties.Additionally,cooling of the scavenging air is necessary because highly dense air required for degrees of supercharging. Water is the cooling medium commonly used on board ships.There are usually two kinds of cooling water,fresh water and sea water.At higher temperature levels,sea water has unsatisfactory corrosive and hardness properties,consequently,it is only usable at lower temperature level,e.g., to cool lube oil coolers,air coolers.Fresh water,with a low hardness and a corrosionpreventive additive,is used at the higher temperature levels.Engine jackets are always cooled with fresh water.The fresh water is in turn cooled by means of a sea waterfresh water heat exchanger,the freshwater cooler, Two separate cooling water systems are normally provided,one for the circulation of the fresh water and the other for the circulation of the sea water.The fresh water cooling system is a closed cooling system,in which the fresh water first passes the freshwater cooler,where it is cooled by sea water,and then is circulated through the cooling water jackets of the main engine by fresh water pump to cool cylinder liners,cylinder heads and exhaust valves?.At the highest position of the system an expansion tank has been provided to take up the difference in the water volume due to changes of temperature.The thermostatically controlled 3way valve,which is connected to the inlet of the freshwater cooler by means of a bypass pipe,has usually been installed at the outlet of the freshwater cooler to mix cooled and uncooled fresh water in such proportions that the temperature of outlet water from the main engine is maintained at 80??.To prevent air accumulation in the system,a venting tank also has been inserted in the pipelines.The sea water is circulated in an open system,in which it is drawn up from the sea by the sea water pump,then the water flows through the lube oil cooler,whereafter it is divided into two separate branches:one through the adjustable valve directly to main engine air coolers and the other to the camshaft lube oil cooler and the freshwater cooler.The sea water from the abovementioned two branches is later mixed again,and then it is discharged overboard.This system has normally been provided with a 3way regulating valve before the overboard valve.It is used to adjust the temperature at the inlet of sea water pump.If the temperature drops below a set value,the regulating valve will open for the return flow to the sea water pump suction piping. Between the seawater and freshwater systems there are blankoff connecting pipes.These connections can be used in case of freshwater system failure,thus allowing the main engine to be cooled with sea water.The freshwater cooling system can also make it possible to use the cooling water from the auxiliary engines to preheat the main engine before starting. Oil is sometimes used as the coolant because of its advantage that it does not cause corrosion to metals compared with water.The common example is the cooling of pistons.Owing to the high temperature at which they operate,there is a hazard of hightemperature corrosion,at the same time the high operating temperature of the piston results in a considerable thermal expansion and can create adverse conditions for the piston rings?.Since water leakage within the engine can cause corrosion ,oil is usually used as the coolant to cool the piston in replace of the water. EXERCISES I. Choose the best answer. 1. The cooling system is provided with two relative systems,i.e. A. freshwater system and lube oil system B. freshwater system and sea water system C. freshwater system and fuel oil system D. seawater system and lube oil system 2. It is necessary the various components of the machinery so that the engine can work properly. A.to constantly coolB.to constantly heat C.to constantly burnD.to constantly paint 3. The cooling system also makes it possible to warm up the main engine by means of the cooling water from . A.the condenserB.the turbocharger C.the auxiliary engineD.the boiler 4. The practice of the present day is to circulate the fresh water in a . A.opened systemB.semiclosed system C.closed systemD.semiopened system 5.The piston cooling system may employ similar components,except that is used instead of a head tank. A.a sump tankB.a feed wellC.a double bottom tankD.a drain tank 6. the corrosion problem are reduced in a centrol cooling system. A. With no equipment in contact with sea water B. With less equipment in contact with fresh water C. With more equipment in contact with sea water D. With less equipment in contact with sea water 7.Cooling enables the engine metals their mechanical properties. A.to retainB.to remainC.to maintenanceD.to have 8.A separate piston cooling system is used any contamination from piston cooling glands to the piston cooling system ones. A.to helpB.to limitC.to protectD.to remove 9.It is necessary to cool the various components of the machinery so that the engine can work properly. A.continuouslyB.regularlyC.constantlyD.period 10.Cooling of engines is achieved . A.by blowing charge air B.by circulating with salt water C.by circulating with refrigerant D.by circulating with fresh water 11.A heater in the circuit facilitates warming of the engine prior to by circulating hot water. A.startingB.stoppingC.to startD.to stop 12.A separate piston cooling system is used to limit any contamination piston cooling glands the piston cooling system only. A.between/toB.either/orC.from/toD.not only/but also LUBRICATING SYSTEM We all know that when two hard metal surfaces rub against each other,friction is caused and part of the mechanical energy would be lost.Should this friction be great,the metal surfaces would be easily worn out?.For exmple,owing to engine knocking,the pistons or bearings may run hot,seize or even break down. Friction,therefore,is an important cause of wear.The way to reduce friction is to build up a film of lubricant between any two surfaces that rub against each other.The viscosity of the lubricant should be sufficient to hold the film together,even under the weight of the max.load,while,on the other hand,it should allow the lubricant to flow easily. In the diesel engine there are two kinds of luboil supply that inside the cylinders and that in the bearings.The oil quantity for lubricating the cylinders must be proportioned while that for bearing lubrication should be applied in such an amount as to be sufficient to carry away the heat caused by the friction at the bearings?.And the oil used for bearing lubrication can be put into reuse again. Each of the engine cylinders is lubricated from a lubricator,driven by the engine's camshaft.Each lubricator consists in a receiver,in which are assembled in units a mumber of small pumps,each supplying oil to its point of lubrication in the liner?.The pump plungers which are driven from the camshaft draw lubricating on from the receiver and deliver it into the inside surface of the cylinder. The strokes of the plungers in a lubricator,may be adjusted individually or simultaneously.the latter case taking place during manoeuvres.Care should also be taken that the lubricators do not run empty as the plungers might then run hot and seize.The working oil level should therefore always be seen in the control glasses. All bearings of the driving gear,the thrust bearing,the camshaft bearings and the bearings of the governor driver are connected with a pressure oil system,known as the forced feed system by which an oil film is maintained on the surfaces.Oil is drawn from a sump,usually located in the bedplate of the engine,by an electrically driven oil pump or by a lubricating oil pump connected to the engine,and delivered through filters and oil coolers to the bearings?.As the pressure in the driving gear is acting in a downward action,a special pressure lubrication is provided for the crosshead bearings. After feeding all the bearings,the oil drops into the crankcase and drains away to the sump for recirculation. The lubrication of the turboblower is carried out by a separate system with trubine oil. It should also be noted that only the best lubricants be used.Most of them contain additives counteracting oxidation and neutralizing the acids formed in the course of lubrication. EXERCISES I. Choose the best answer. 1. The successful operation of any engine or machine and depend on effective lubricating. A.their no trouble periodB.their freely trouble period C.its free trouble lifeD.its trouble free life 2. The lubricating oil is pumped from the drain tank very often with in the suction line. A.a filterB.a strainerC.a magnetic filterD.a fine strainer 3. The lubricating system for the cylinder walls is different from the bearing in that the oil for the former one is supplied in while that for the latter one is . A.sufficient quantity/measured B.measured quantity/sufficient C.excessive quantity/sufficient D.the less quantity the better/the more the better 4. The film of oil between the rings and the liner is not only essential for the lubrication but also achieving a gas seal. A.play a great part ofB.run a role in C.plays an important part inD.acts an important part at 5. Additives protective layers on metals surfaces guarding them against corrosion. A.damageB.formC.dissolveD.contaminate 6. The film of oil between the rings and the liner is not only essential for the lubrication but also plays an important part in achieving. A.an oil sealB.removing heat C.a gas sealD.cooling the piston 7. The removal offrom lubricating oil will reduce engine wear and possible breakdown. A.contaminating waterB.contaminated additives C.contaminated fuelD.contaminating impurities 8. The selection of a lubricating oil depends to a great extent on the operating condition of. A.the type of coolantB.the design of the engine C.the type of fuel to be burnedD.B and C 9. providing lubricating films,oil used in marine diesel engines have to remove heat from oil cooled piston. A.Except forB.BesideC.ExceptD.In addition to 10.of the lubricant should be sufficient to hold the film together but should allow the lubricant to flow easily. A.The specific gravityB.The viscosity C.The acid valueD.The water content 11. The lube oil in the bearing is drawn from,usually located in the bedplate. A.a tankB.a sumpC.a vesselD.a bottle 12.The lubrication of the turboblower is carried out by a separate system with. A.turbine oilB.cylinder oilC.gear oilD.engine oil 13.Since the same oil is used both for bearing lubrication and for cooling the piston,it is importantat regular intervals. A.to filter the oilB.to discharge the oil C.to burn the oilD.to pump out the oil 14.Each of the engine cylinder is lubricated from a lubricator,driven by the engine. A.crankshaftB.main shaftC.tail shaftD.camshaft STARTING CONTROL SYSTEM The engine is started with compressed air at a pressure of 3×106 Pa a maximum.The compressed air is stored in special containers with a prescribed minimum holding capacity.The individual cylinders receive compressed air through the starting valves in the same sequence as the cranks are staggered.Opening and closing the starting valves is pneumatically controlled.During starting the fuel charge should be reduced to position 3.5 or so.As soon as the cylinders fire,the starting valves cease to open. The starting manoeuvre is initiated by means of the starting lever on the control stand.The starting control system is interlocked with the reversing control against incorrect manoeuvre by two starting lever bloking devices working in different ways.One blocking device is actuated by the telegraph lever and is purely mechanical in operation.The other is controlled by the two reversing servomotors and works mechanicalhydraulically. The pipe system of the starting control equipment consists of the main startingair system and the pilotair system.The automatic startingair stop valve together with the nonreturm valve is arranged between the air containers and the engine.In accordance with the safety regulation the startingair pipe on the engine is equipped with safety valves,which are set to below off at a pressure of 3×106 Pa. The individual supply pipes air fitted with flame traps which ,however,cause a somewhat higher loss of startingair pressure. For starting,the starting lever,which is normally held in its resting position by a spring,is moved to position“starting”. This can only be effected if the blocking device of the starting lever releases the latter.Operating the starting lever also raises the startingair pilot valve,so that the compressed air passes from the startingair container through the pilot valve into the pilotair line,provided that the blocking device of the truning gear allows the air to pass through?. The pilot air is then distributed and passes to both the actuating valve of the automatic starting air stop valve and the startingair control slide valves.The latter are forced down on to the starting cam with their rollers by the pressure of the pilot air,while the actuating valve is raised by the pressure of the pilot air,causing the automatic startingair stop valve to open?. Now the distribution duct for the startingair control slide valves receives pressure also,so that the valves put the two controlair pipes,the opening and the closing pipe,to each starting valve under pressure alternatively,in accordance with the operation of the cam?. Since at the same time the main starting air has passed through the distribution pipe as far as the starting valves in the cylinder cover,all conditions necessary for starting are fulfilled.Now the starting valves are alternatively opened and closed by the controlair pipes in the desired sequence.The starting air acts on the pistons and causes the engine to turn over.As soon as the engine fires,the starting lever is released and moved back to its resting position on account of the spring. EXERCISES I. Choose the best answer. 1. Once all cylinders are firing regularlyis shut off. A.the starting airB.the charge air C.the fuel oilD.the cooling water 2.is usually driven by the engine camshaft and supplies pilot air to the cylinder air start valve. A.An air receiverB. An operating valve C.An automatic valveD. An air distributor 3.A heater in the circuit facilitates warming of the engine priors toby circulating hot water. A.startingB.stoppingC.to startD.to stop 4.in what position the engine stop there will always be at least one of the cylinders with its starting air valve open to admit compressed air to start the engine. A.BecauseB.Owing toC.ForD.No matter 5.Diesel engines are started by supplyinginto the cylinders in the appropriate sequence for the required direction. A.fuel oilB.diesel oil C.compressed airD.jacket water 6.Whenis operated a supply of pilot air enables the remote valve to open. A.the distributorB.the cylinder air start valve C.the turning gearD.the air start lever 7.Before starting the engine the air bottle should be. A.pumpedB.loadedC.chargedD.released 8.In the event of the cylinder starting valve leakagewould pass into the air pipes and ignite the oil deposited. A.cooling waterB.vapor from the boiler C.starting airD.hot gases 9.The starting air system usually hasto prevent starting if anything is not in order. A.drain cocksB.vent valvesC.counteractsD.interlocks 10.During the inspection the starting air valves should be closedthe engine from turning. A.to increaseB.to speed upC.to preventD.to reduce 11.Before a marine diesel engine is started the cylinders and pistons must be. A. cooled to appropriate temperature B. warmed up gradually to appropriate temperature C. opened up and renewed D. ground and polished 12.We should not start the engine unless the turning gear is. A.onB.disengagedC.boltedD.unscrewed 13.We use the compressed air fromto start the main engine. A.air receiverB.scavenging air receiver C.air strainerD.air duct 14.The engine is started withsupplied from the air bottle. A.pressurized oilB.pressurized water C.compressed airD.waste gas