Lesson Eighteen
Marine Engines
Marine engine is an engine that propels a water-born vessel,Even in small craft the marine engine must have the following characteristics,reliability,light weight,compactness,fuel economy,low maintenance,long life,relative simplicity for operating personnel,ability to reverse,and ability to operate steadily at low or cruising speed,The relative importance of these characteristics varies with the service performed by the vessel,but reliability is of prime importance.
Steam engines
Steam,used to drive the earliest powered vessels,is still a common type of propulsion for large ships,The diesel engine has gained wide acceptance in foreign merchant ships,but in the United States,the majority of seagoing vessels use steam propulsion.
Reciprocating steam engines Early engines commonly used steam flowing in series through as many as four cylinders whose pistons had the same stroke but were of increasing diameters,This system provided for an expansion or increase in steam volume which accompanied the decrease in pressure to the exhaust under a vacuum,The modern,multicylinder,uniflow marine steam engine,with complete expansion in each cylinder,shows better steam economy,Because it has the same diameter for all cylinders (two to six in number),it is preferable from a manufacturing viewpoint,Equal power is developed by each cylinder; units of four cylinders or more have good torque and balance characteristics,A steam rate of 10 lb/hp/hr (1.7 kg/MJ) with 275 psi (1.90 Mpa) at 240°F （116°C）super heat is attainted,Uniflow engines as large as 5000 hp (3.7MW) have been used on shipboard,Normally,steam engines are double-acting; that is,steam acts on each side of the pistons,With superheated steam,piston-cylinder lubrication must be provided,Pure feed-water is required by modern,high-capacity boilers; thus,an effective oil filter is installed where the condensate must be returned to the boiler.
Steam turbines The marine steam turbine has the advantages of direct rotary motion,little or no rubbing contact of pressure-confining surfaces,and ability to use effectively both highly super heated steam and steam at low pressure,that is,at a high vacuum where specific volumes of over 400 ft3/lb are reached.
For good efficiency of steam turbines,high rotative speeds are required,This requirement led to the introduction of the reduction geared turbine and turboelectric drive,These system give efficient turbine speeds and efficient propeller rmp,With geared turbine,for example,turbine rotor speeds range from 3000 to 10,000 rmp,while propeller rmp is reduced to the 80 to 400 range.
Steam is generally supplied to the turbine at 850 psi (5.9MPa) and 950°F (510°C) by pair of oilfired marine water-tube boiler,and the exhaust from the turbine is usually at 1.5 in,lig(5.1kPa) absolute,Forced draft fans and other auxiliaries are usually motor-driven,except for the main feed pimps which are usually driven by an auxiliary turbine,Electric power is provided by a separate turbogenerator.
In low-powered geared turbines,steam completes its expansion in one rotor and casing,Such a design has been used in geared turbines of up to 8000 shaft horsepower (ship) or a shaft power of 6 MW,However,series flow through two or even three casings is preferable in most steam turbines,This arrangement provides more flexibility in turbine design,allowing for different and optimum revolutions for high-and low-pressure rotors,Also,in a seagoing vessel in case of casualty to one turbine or its high-speed pinion,the vessel usually can make port with the remaining turbine in operation,
A steam turbine is made up of fixed blades,usually called nazzles,and rotating blades,A stage is generally one stationary row and one moving row,Impulse staging has all the steam pressure drop taking place in the fixed blades,The moving row then absorbs the kinetic energy produced,Reaction staging results when some of the assume drop occurs in the moving blades,the degree of reaction depending on the design.
Modern marine practice favors impulse staging in the high-pressure end of the turbine because of the steam progresses toward the low-pressure end where the value is much greater the reaction stage is more efficient,The arrangement has a cross compound system with a high-pressure unit of 7 to 10stages and a low-pressure unit of 6to 8 stages,each driving a pinion of a reduction gear.
A turbine is capable of operation in only one direction,In order to provide reverse power,a second turbine is installed on the shaft of the low-pressure ahead turbine,The astern turbine is usually not more than three moving rows of blades,but it may be only two,It produces about 40% of the normal ahead horsepower,Since this unit is turning backward in normal ahead operation,it is located in the low-pressure end of the low-pressure turbine,The steam at this point has a very low density,and hence the astern turbine has a low windage loss.
The propeller is reversed by closing the steam value to the ahead turbine and opening the value to the astern turbine.
Gas turbine
The gas turbine is a relative newcomer to the marine field,It generally considered of an axial compressor discharging compressed air to a combustion chamber where fuel is burned,adding heat,The produces of combustion at high temperature and pressure then pass through a gas turbine that drives the compressor and load,Generally,the term,gas turbine” is applied to the entire plant,If lower pressure ratios (final pressure leaving the compressor divided by initial pressure entering) are used,a large amount of heat is available in the exhaust gas which may be recovered by heating the compressed air before it enters the combustion chamber,This is done in a regenerator,With higher pressure ratios the expansion through the turbine is so great that the exhaust gas temperature is insufficient to heat the compressed air.
Two distinct types of gas turbines are appearing in the marine field,the aircraft-derived type and the industrial type,The aircraft-derived type uses a jet engine as a gas generator,which discharges to a gas turbine driving the load,This type of plant offers simplicity and light weight but must burn high-quality fuel,The industrial gas turbine is a more rugged machine designed for long life and is capable of using low grades of fuel,properly washed,This plant usually uses a regenerator,The gas turbine offers simplicity,ease of control,and efficiency,but requires special fuel or special treatment of the fuel,Large amounts of air and exhaust gas are used,and as a result uptakes and air supply are a special problem,The aircraft-derived gas turbine seems destined to drive a large number of naval combatant ships,Selections of this type for a new class of naval destroyers has been announced,The industrial type will be used for merchant vessels where its greater weight will be of little disadvantage.
Internal combustion engines
Both diesel and gasoline internal combustion engines are used in marine applications,Many moderate and lowpower marine installations use automotive or locomotive engines designed for variable load and intermittent service,High-power marine propulsion units normally are called on to operate continuously under load,Therefore,the brake horsepower (bhp) rating of units selected for marine service should be conservative,
The gasoline engine is the most common power plant for pleasure craft,It is inexpensive to buy and maintain,Because of its widespread use in automobiles,most parts are readily available,In most areas gasoline costs slightly more than diesel fuel,but the cost differential is usually insufficient to make up the difference between the cost of gasoline and diesel engines,Gasoline presents an explosion and fire hazard,which is its major disadvantage.
Direct-drive diesels For typical commercial freight vessels,direct-drive diesels provide economical service,For good propeller efficiency,the propeller rpm should be under 120±,Such a top limit on engine revolutions results in a large,heavy,bulky,slow-rpm engine,However,the direct-drive diesels have a lower fuel oil consumption than do higher-rpm units,and with suitable fuel treatment they will operate on the better grades of the cheaper fuel oil burned in boilers,
Slow-speed,direct-drive diesels are favored by many European owners and shipbuilders,Turbo-charged,two-cycle,single-acting diesel engines of 50 000 bhp (37MW of brake power) are now available; such engines weigh more than 100 lb/bhp (60kg/kw of brake power),For high horsepower the total machinery weight for diesels is more than the weight of geared turbine machinery,including boilers and auxiliaries.
Moderate-speed diesels Diesel engines of 250-500 rpm are available in two and four cycle,single-acting types,generally with trunk pistons,In some marine applications they are connected directly to the propeller and thus fitted only with reverse gear,However,they are also employed with geared diesel and diesel-electric drive,The weight of such engines runs about 35-70 lb/bhp (21-43 kg/kw of brake power),
High-speed diesels Many high-speed diesel engines of 600 rpm and more (some types originally developed for truck and locomotive service ) are available for marine propulsion,Opposed piston types have been developed; other manufacturers favor a V type to reduce weight,Such engines are of two-and four-cycle types and usually weigh 10-40 lb/bhp (6-24kg/kw of brake power),Because of less efficient scavenging,breaker power,and other factors,their fuel and lubricating oil rates are higher than for large,low-speed diesels.
Except for direct drive in moderate or fairly high-speed craft,marine applications of diesel engines or with diesel-electric drive to provide good propeller efficiency,Because their pistons,valves,and other components are small,standardized,and carried in stock,repairs are readily made,with the result that engines of this type are popular for nonoceangoing services.
Oil consumption and starting Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings,In large engines this contamination is avoided by using piston rod-crosshead construction so that the crankshaft,connecting rods,and crossheads operate in a closed casing separated from the working cylinder,These engines are started and maneuvered by pressure from one or more reservoirs filled with air at about 250 psi (1.7 MPa),To make it feasible to start and readily reverse,two-cycle,single-acting marine engines should have at least four cylinders; four-cycle engines should have five or more cylinders.
Nuclear power
Very successful installations of nuclear power have been made in submarines and a few surface ships,Operation of the first nuclear merchant ship,the Savannah,was successful technically but not commercially,(The operating crew required special training,and it would be difficult to replace with only one commercial nuclear ship in service.)
Mechanical reduction gears
Reduction gearing for diesel and gasoline engines allows the use of a relatively high engine speed and lower,more efficient propeller speed,Speed reduction ratios of 1.8:1 to 4:1 are common,preferably with helical teeth to give better wear and quieter performance,A reverse gear device often is incorporated in lowpower gears for astern operation,Other methods for providing reverse rotation use a direct reversing engine or a controllable-pitch propeller.
One,two,three,or four engines may drive the same gear through individual pinions,The use of a friction,electromagnetic,pneumatic,or hydraulic coupling serves to disconnect any engine,By reversing one or more engines,ready maneuvering,including astern operation,is provided for by the use of the respective coupling.
The high rpm (3000-9000) of modern marine steam turbine and the low revolutions of an effective propeller (as low as 80 rpm) require the use of two-stage gearing,Gear teeth of harder material than the gear,The gear trains are of the double helical,type to avoid heavy axial thrust,Double reduction gears are constructed with flexible couplings between the high-speed train and the low-speed elements.
Mechanical reduction gears are carefully constructed to close tolerances,They have forced lubrication in sprays ahead of the meshing teeth,to the bearings,and to the flexible couplings,Tests have shown that bearings represent at least half the power loss of the entire gear set.
Turboelectric drive
This type of drive,comprising one or more steam turbine generators and ac propulsion motors,is also used for ship propulsion,It was installed in many United States tankers during World War II because of available manufacturing facilities,The synchronous motors are provided with an induction winding for starting and reversing,Relatively large changes in propeller revolutions are made by alteration of the turbogenerator speed.
Motor,generator,exciter,and cooling equipment losses result in several percent lower efficiency than with geared steam turbines,Weights and costs are generally 25-30% higher than for the comparable turbine gear arrangement,Electric drive is not employed unless it offers significant operational or design advantages,These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motor.
Diesel-electric drive
This type of drive,composed of one or more dc diesel generator sets and often a double –armature propulsion motor,is used in tugs,dredges,Coast Guard cutters,and icebreakers,where maneuvering and a wide range in propeller speed are necessary,For slow-speed operating during maneuvering,the engine speed is often reduced and the generator field excitation is altered to provide wide variation in the motor output and propeller speed.
Control arrangements
Bridge or pilothouse control of the ship propulsion unit,without action by the engineer on watch,s used with diesel-electric drive and for small,low-powered,direct-drive,and mechanically geared diesel installations,This is the customary arrangement for tugs and dredges.
Modern practice for large diesel and steamships is to provide pilothouse control of the main engines and no engine-room watch except day workers and when entering and leaving port,Propulsion plant monitoring is usually provided in a central control space,with chart recorders or a data storage system,All levels of automation are now being used,from simple manual surveillance of all systems in a fully manned engine space to a completely unmanned system recording data and monitoring trends to pinpoint possible trouble.
Gonernors
Above the operating rpm,ship propeller torque increases faster than engine or turbine torque,and thus ship propeller drive is inherently stable,Because of the ship’s pitching,the propeller may lift partially out of the water and the engine may tend to race,To allow for this situation,or for propeller shafting failure,American Bureau of Shipping regulations require that a governor be fitted to limit overspeed to 15% above the rated speed.
A common type of governor uses oil pressure developed by small pumps incorporated with the main turbine rotors to activate the governor; low lubricating oil pressure will also shut off the steam supply.
With turboelectric and diesel-electric drive,there is no mechanical connection between the generator set and the propulsion motor and propeller,The operating governor holds generator speed at the set value by throttling turbogenerator steam or the amount of fuel injected in the diesel engine cylinders.
(From McGraw-Hill,Encyclopedia of Science and Technology”,Vol.8,1982)
Technical Terms
marine engine 船舶发动机
waterborne vessel 船，水上运载器
cruising speed 经济 航速（民船）；巡航速度（军舰）
steam engine 蒸汽机
steam engine 汽轮机
diesel engine 柴油机
reciprocating engine往复式发动机
cylinder 气（汽）缸
double-acting 双作用
piston 活（柱）塞
feed-water 给水
condenser 冷凝器
boiler锅炉，蒸汽发生器
pressure-confining surface 受压面
gearing齿轮装置，传动装置
rotor 转子，电枢
rotating blade旋转叶片
oil-fired燃油的
marine water-tube boiler 船用水管锅炉
forced draft fan 强力通风机
turbogenerator 汽轮发电机
casing 外壳，箱壳
reduction gear 减速齿轮/器
nozzle 喷咀，排气管
stationary 稳定/固定的
impulse stage 冲动级
reaction stage 反动级
kinetic energy 功能
cross compound system 交叉复合系统
parasitic loss 无功/附加损失
windage loss气体阻力损失
gas turbine 燃气轮机
regenerator 回热器
aircraft-derived type 航空派生型
rugged machine 笨重机械
uptake 烟道
destroyer 驱逐舰
internal combustion engine 内燃机
gasoline engine 汽油机
locomotive engine 机车发动机
power plant 动力装置
direct driver diesel 直接驱动的柴油机
turbo-charger 涡轮增压器
two-cycle 二冲程
single-acting 单作用的
moderate-speed diesel 中速柴油机
trunk piston 筒形活塞
diesel-electric drive 柴油机电力传动
opposed piston type 对置活塞型
scavenging 扫气，唤气
crankcase 曲拐箱
contamination 污染
piston ring 活塞环
crankshaft 曲轴
connecting rod 连杆
crosshead 十字头
reverse gear device 容器，储器
nuclear power 核动力
helical teeth 斜齿，螺旋齿
reverse gear device 倒车齿轮（传动）装置
electromagnetic 电磁的
pneumatic 气动的
hydraulic 水力的，液压的
involute 渐开线
gear train 齿轮组/系
meshing teeth 啮合齿
turboelectric drive 汽轮机电力驱动
synchronous motor 同步电动机
induction winding 感应绕组/线圈
exciter 励磁机，激磁器
Coast Guard cutter 美国海岸警卫队快艇
control arrangements 控制装置
governor 调速器，调节器
pilothouse 驾驶室/台
racing 飞车，超速，空旋
throttling 节流
Additional Terms and Expressions
propelling engine 推进发动机
supercharging system 增压系统
cylinder scavenging system 气缸换气系统
fuel system 燃油系统
lubricating system 润滑系统
cooling system 冷却系统
camshaft transmission gear 凸轮轴传动机构
exhaust-gas turbo-charger 废气透平增压器
auxiliary machinery 辅机
marine pump 船用泵
oil separator 分油器，滑油分离机
marine boiler 船用锅炉
refrigerating plant 制冷装置
electric power plant 电站
trouble 故障
centralized monitoring system 巡回检测系统
centralized monitoring system 集中监控系统
Notes to the text
1,If lower press ratios (final pressure leaving the compressor divided by initial pressure entering) are used,a large amount of heat is available in the exhaust gas which may be recovered by heating the compressed air before it enters the combustion chamber
这是一句主从复合句。If lower pressure ratios are used是条件状语从句；主句是a large amount of heat is available in the exhaust gas,而which may be recovered by heating the compressed air是定语从句，修饰a large amount of heat,before it enters the combustion chamber是时间状语从句，修饰前面的heating，而it是指the compressed air.
However,the direct-driver diesels have a lower fuel oil consumption than do higher-rpm units,and with suitable fuel treatment they will operate on the better grades of the cheaper fuel oil burned in boilers.
than do higher-rpm units 是一个比较状语从句。这里的do即表示have a low fuel oil consumption.
burned in boilers 是动词过去分词短语，作后置定语，修饰cheaper fuel oil.
Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings.
复合介词because of后面有两个宾语，一个是the cylinder-piston lubrication，另一个是the contamination of the crankcase oil。that must be provided是定语从句，修饰the cylinder-piston lubrication。with residues blown by the piston rings是说明the crankcase oil污染的原因。
By reversing one or more engines,ready maneuvering,including astern operation,is provided for by the use of the respective coupling.
这是一个简单句。主语为 ready maneuvering，谓语为is provided for,by the use of the respective coupling和by reversing one or more engines是介词短语作行为。方式状语。
5．These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motor.
句中relative to the propeller shaft or propulsion motor是形容词短语，作后置定语，修饰the independence。
All levels of automation are now being used from simple manual surveillance of all systems in a fully manned engine space to a completely unmanned system recording data and monitoring trends to pinpoint possible trouble.
are being used是动词被动态进行式。
recording data和monitoring trends to pinpoint possible trouble均是动词现在分词短语，作定语用，修饰a completely unmanned system。
Marine Engines
Marine engine is an engine that propels a water-born vessel,Even in small craft the marine engine must have the following characteristics,reliability,light weight,compactness,fuel economy,low maintenance,long life,relative simplicity for operating personnel,ability to reverse,and ability to operate steadily at low or cruising speed,The relative importance of these characteristics varies with the service performed by the vessel,but reliability is of prime importance.
Steam engines
Steam,used to drive the earliest powered vessels,is still a common type of propulsion for large ships,The diesel engine has gained wide acceptance in foreign merchant ships,but in the United States,the majority of seagoing vessels use steam propulsion.
Reciprocating steam engines Early engines commonly used steam flowing in series through as many as four cylinders whose pistons had the same stroke but were of increasing diameters,This system provided for an expansion or increase in steam volume which accompanied the decrease in pressure to the exhaust under a vacuum,The modern,multicylinder,uniflow marine steam engine,with complete expansion in each cylinder,shows better steam economy,Because it has the same diameter for all cylinders (two to six in number),it is preferable from a manufacturing viewpoint,Equal power is developed by each cylinder; units of four cylinders or more have good torque and balance characteristics,A steam rate of 10 lb/hp/hr (1.7 kg/MJ) with 275 psi (1.90 Mpa) at 240°F （116°C）super heat is attainted,Uniflow engines as large as 5000 hp (3.7MW) have been used on shipboard,Normally,steam engines are double-acting; that is,steam acts on each side of the pistons,With superheated steam,piston-cylinder lubrication must be provided,Pure feed-water is required by modern,high-capacity boilers; thus,an effective oil filter is installed where the condensate must be returned to the boiler.
Steam turbines The marine steam turbine has the advantages of direct rotary motion,little or no rubbing contact of pressure-confining surfaces,and ability to use effectively both highly super heated steam and steam at low pressure,that is,at a high vacuum where specific volumes of over 400 ft3/lb are reached.
For good efficiency of steam turbines,high rotative speeds are required,This requirement led to the introduction of the reduction geared turbine and turboelectric drive,These system give efficient turbine speeds and efficient propeller rmp,With geared turbine,for example,turbine rotor speeds range from 3000 to 10,000 rmp,while propeller rmp is reduced to the 80 to 400 range.
Steam is generally supplied to the turbine at 850 psi (5.9MPa) and 950°F (510°C) by pair of oilfired marine water-tube boiler,and the exhaust from the turbine is usually at 1.5 in,lig(5.1kPa) absolute,Forced draft fans and other auxiliaries are usually motor-driven,except for the main feed pimps which are usually driven by an auxiliary turbine,Electric power is provided by a separate turbogenerator.
In low-powered geared turbines,steam completes its expansion in one rotor and casing,Such a design has been used in geared turbines of up to 8000 shaft horsepower (ship) or a shaft power of 6 MW,However,series flow through two or even three casings is preferable in most steam turbines,This arrangement provides more flexibility in turbine design,allowing for different and optimum revolutions for high-and low-pressure rotors,Also,in a seagoing vessel in case of casualty to one turbine or its high-speed pinion,the vessel usually can make port with the remaining turbine in operation,
A steam turbine is made up of fixed blades,usually called nazzles,and rotating blades,A stage is generally one stationary row and one moving row,Impulse staging has all the steam pressure drop taking place in the fixed blades,The moving row then absorbs the kinetic energy produced,Reaction staging results when some of the assume drop occurs in the moving blades,the degree of reaction depending on the design.
Modern marine practice favors impulse staging in the high-pressure end of the turbine because of the steam progresses toward the low-pressure end where the value is much greater the reaction stage is more efficient,The arrangement has a cross compound system with a high-pressure unit of 7 to 10stages and a low-pressure unit of 6to 8 stages,each driving a pinion of a reduction gear.
A turbine is capable of operation in only one direction,In order to provide reverse power,a second turbine is installed on the shaft of the low-pressure ahead turbine,The astern turbine is usually not more than three moving rows of blades,but it may be only two,It produces about 40% of the normal ahead horsepower,Since this unit is turning backward in normal ahead operation,it is located in the low-pressure end of the low-pressure turbine,The steam at this point has a very low density,and hence the astern turbine has a low windage loss.
The propeller is reversed by closing the steam value to the ahead turbine and opening the value to the astern turbine.
Gas turbine
The gas turbine is a relative newcomer to the marine field,It generally considered of an axial compressor discharging compressed air to a combustion chamber where fuel is burned,adding heat,The produces of combustion at high temperature and pressure then pass through a gas turbine that drives the compressor and load,Generally,the term,gas turbine” is applied to the entire plant,If lower pressure ratios (final pressure leaving the compressor divided by initial pressure entering) are used,a large amount of heat is available in the exhaust gas which may be recovered by heating the compressed air before it enters the combustion chamber,This is done in a regenerator,With higher pressure ratios the expansion through the turbine is so great that the exhaust gas temperature is insufficient to heat the compressed air.
Two distinct types of gas turbines are appearing in the marine field,the aircraft-derived type and the industrial type,The aircraft-derived type uses a jet engine as a gas generator,which discharges to a gas turbine driving the load,This type of plant offers simplicity and light weight but must burn high-quality fuel,The industrial gas turbine is a more rugged machine designed for long life and is capable of using low grades of fuel,properly washed,This plant usually uses a regenerator,The gas turbine offers simplicity,ease of control,and efficiency,but requires special fuel or special treatment of the fuel,Large amounts of air and exhaust gas are used,and as a result uptakes and air supply are a special problem,The aircraft-derived gas turbine seems destined to drive a large number of naval combatant ships,Selections of this type for a new class of naval destroyers has been announced,The industrial type will be used for merchant vessels where its greater weight will be of little disadvantage.
Internal combustion engines
Both diesel and gasoline internal combustion engines are used in marine applications,Many moderate and lowpower marine installations use automotive or locomotive engines designed for variable load and intermittent service,High-power marine propulsion units normally are called on to operate continuously under load,Therefore,the brake horsepower (bhp) rating of units selected for marine service should be conservative,
The gasoline engine is the most common power plant for pleasure craft,It is inexpensive to buy and maintain,Because of its widespread use in automobiles,most parts are readily available,In most areas gasoline costs slightly more than diesel fuel,but the cost differential is usually insufficient to make up the difference between the cost of gasoline and diesel engines,Gasoline presents an explosion and fire hazard,which is its major disadvantage.
Direct-drive diesels For typical commercial freight vessels,direct-drive diesels provide economical service,For good propeller efficiency,the propeller rpm should be under 120±,Such a top limit on engine revolutions results in a large,heavy,bulky,slow-rpm engine,However,the direct-drive diesels have a lower fuel oil consumption than do higher-rpm units,and with suitable fuel treatment they will operate on the better grades of the cheaper fuel oil burned in boilers,
Slow-speed,direct-drive diesels are favored by many European owners and shipbuilders,Turbo-charged,two-cycle,single-acting diesel engines of 50 000 bhp (37MW of brake power) are now available; such engines weigh more than 100 lb/bhp (60kg/kw of brake power),For high horsepower the total machinery weight for diesels is more than the weight of geared turbine machinery,including boilers and auxiliaries.
Moderate-speed diesels Diesel engines of 250-500 rpm are available in two and four cycle,single-acting types,generally with trunk pistons,In some marine applications they are connected directly to the propeller and thus fitted only with reverse gear,However,they are also employed with geared diesel and diesel-electric drive,The weight of such engines runs about 35-70 lb/bhp (21-43 kg/kw of brake power),
High-speed diesels Many high-speed diesel engines of 600 rpm and more (some types originally developed for truck and locomotive service ) are available for marine propulsion,Opposed piston types have been developed; other manufacturers favor a V type to reduce weight,Such engines are of two-and four-cycle types and usually weigh 10-40 lb/bhp (6-24kg/kw of brake power),Because of less efficient scavenging,breaker power,and other factors,their fuel and lubricating oil rates are higher than for large,low-speed diesels.
Except for direct drive in moderate or fairly high-speed craft,marine applications of diesel engines or with diesel-electric drive to provide good propeller efficiency,Because their pistons,valves,and other components are small,standardized,and carried in stock,repairs are readily made,with the result that engines of this type are popular for nonoceangoing services.
Oil consumption and starting Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings,In large engines this contamination is avoided by using piston rod-crosshead construction so that the crankshaft,connecting rods,and crossheads operate in a closed casing separated from the working cylinder,These engines are started and maneuvered by pressure from one or more reservoirs filled with air at about 250 psi (1.7 MPa),To make it feasible to start and readily reverse,two-cycle,single-acting marine engines should have at least four cylinders; four-cycle engines should have five or more cylinders.
Nuclear power
Very successful installations of nuclear power have been made in submarines and a few surface ships,Operation of the first nuclear merchant ship,the Savannah,was successful technically but not commercially,(The operating crew required special training,and it would be difficult to replace with only one commercial nuclear ship in service.)
Mechanical reduction gears
Reduction gearing for diesel and gasoline engines allows the use of a relatively high engine speed and lower,more efficient propeller speed,Speed reduction ratios of 1.8:1 to 4:1 are common,preferably with helical teeth to give better wear and quieter performance,A reverse gear device often is incorporated in lowpower gears for astern operation,Other methods for providing reverse rotation use a direct reversing engine or a controllable-pitch propeller.
One,two,three,or four engines may drive the same gear through individual pinions,The use of a friction,electromagnetic,pneumatic,or hydraulic coupling serves to disconnect any engine,By reversing one or more engines,ready maneuvering,including astern operation,is provided for by the use of the respective coupling.
The high rpm (3000-9000) of modern marine steam turbine and the low revolutions of an effective propeller (as low as 80 rpm) require the use of two-stage gearing,Gear teeth of harder material than the gear,The gear trains are of the double helical,type to avoid heavy axial thrust,Double reduction gears are constructed with flexible couplings between the high-speed train and the low-speed elements.
Mechanical reduction gears are carefully constructed to close tolerances,They have forced lubrication in sprays ahead of the meshing teeth,to the bearings,and to the flexible couplings,Tests have shown that bearings represent at least half the power loss of the entire gear set.
Turboelectric drive
This type of drive,comprising one or more steam turbine generators and ac propulsion motors,is also used for ship propulsion,It was installed in many United States tankers during World War II because of available manufacturing facilities,The synchronous motors are provided with an induction winding for starting and reversing,Relatively large changes in propeller revolutions are made by alteration of the turbogenerator speed.
Motor,generator,exciter,and cooling equipment losses result in several percent lower efficiency than with geared steam turbines,Weights and costs are generally 25-30% higher than for the comparable turbine gear arrangement,Electric drive is not employed unless it offers significant operational or design advantages,These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motor.
Diesel-electric drive
This type of drive,composed of one or more dc diesel generator sets and often a double –armature propulsion motor,is used in tugs,dredges,Coast Guard cutters,and icebreakers,where maneuvering and a wide range in propeller speed are necessary,For slow-speed operating during maneuvering,the engine speed is often reduced and the generator field excitation is altered to provide wide variation in the motor output and propeller speed.
Control arrangements
Bridge or pilothouse control of the ship propulsion unit,without action by the engineer on watch,s used with diesel-electric drive and for small,low-powered,direct-drive,and mechanically geared diesel installations,This is the customary arrangement for tugs and dredges.
Modern practice for large diesel and steamships is to provide pilothouse control of the main engines and no engine-room watch except day workers and when entering and leaving port,Propulsion plant monitoring is usually provided in a central control space,with chart recorders or a data storage system,All levels of automation are now being used,from simple manual surveillance of all systems in a fully manned engine space to a completely unmanned system recording data and monitoring trends to pinpoint possible trouble.
Gonernors
Above the operating rpm,ship propeller torque increases faster than engine or turbine torque,and thus ship propeller drive is inherently stable,Because of the ship’s pitching,the propeller may lift partially out of the water and the engine may tend to race,To allow for this situation,or for propeller shafting failure,American Bureau of Shipping regulations require that a governor be fitted to limit overspeed to 15% above the rated speed.
A common type of governor uses oil pressure developed by small pumps incorporated with the main turbine rotors to activate the governor; low lubricating oil pressure will also shut off the steam supply.
With turboelectric and diesel-electric drive,there is no mechanical connection between the generator set and the propulsion motor and propeller,The operating governor holds generator speed at the set value by throttling turbogenerator steam or the amount of fuel injected in the diesel engine cylinders.
(From McGraw-Hill,Encyclopedia of Science and Technology”,Vol.8,1982)
Technical Terms
marine engine 船舶发动机
waterborne vessel 船，水上运载器
cruising speed 经济 航速（民船）；巡航速度（军舰）
steam engine 蒸汽机
steam engine 汽轮机
diesel engine 柴油机
reciprocating engine往复式发动机
cylinder 气（汽）缸
double-acting 双作用
piston 活（柱）塞
feed-water 给水
condenser 冷凝器
boiler锅炉，蒸汽发生器
pressure-confining surface 受压面
gearing齿轮装置，传动装置
rotor 转子，电枢
rotating blade旋转叶片
oil-fired燃油的
marine water-tube boiler 船用水管锅炉
forced draft fan 强力通风机
turbogenerator 汽轮发电机
casing 外壳，箱壳
reduction gear 减速齿轮/器
nozzle 喷咀，排气管
stationary 稳定/固定的
impulse stage 冲动级
reaction stage 反动级
kinetic energy 功能
cross compound system 交叉复合系统
parasitic loss 无功/附加损失
windage loss气体阻力损失
gas turbine 燃气轮机
regenerator 回热器
aircraft-derived type 航空派生型
rugged machine 笨重机械
uptake 烟道
destroyer 驱逐舰
internal combustion engine 内燃机
gasoline engine 汽油机
locomotive engine 机车发动机
power plant 动力装置
direct driver diesel 直接驱动的柴油机
turbo-charger 涡轮增压器
two-cycle 二冲程
single-acting 单作用的
moderate-speed diesel 中速柴油机
trunk piston 筒形活塞
diesel-electric drive 柴油机电力传动
opposed piston type 对置活塞型
scavenging 扫气，唤气
crankcase 曲拐箱
contamination 污染
piston ring 活塞环
crankshaft 曲轴
connecting rod 连杆
crosshead 十字头
reverse gear device 容器，储器
nuclear power 核动力
helical teeth 斜齿，螺旋齿
reverse gear device 倒车齿轮（传动）装置
electromagnetic 电磁的
pneumatic 气动的
hydraulic 水力的，液压的
involute 渐开线
gear train 齿轮组/系
meshing teeth 啮合齿
turboelectric drive 汽轮机电力驱动
synchronous motor 同步电动机
induction winding 感应绕组/线圈
exciter 励磁机，激磁器
Coast Guard cutter 美国海岸警卫队快艇
control arrangements 控制装置
governor 调速器，调节器
pilothouse 驾驶室/台
racing 飞车，超速，空旋
throttling 节流
Additional Terms and Expressions
propelling engine 推进发动机
supercharging system 增压系统
cylinder scavenging system 气缸换气系统
fuel system 燃油系统
lubricating system 润滑系统
cooling system 冷却系统
camshaft transmission gear 凸轮轴传动机构
exhaust-gas turbo-charger 废气透平增压器
auxiliary machinery 辅机
marine pump 船用泵
oil separator 分油器，滑油分离机
marine boiler 船用锅炉
refrigerating plant 制冷装置
electric power plant 电站
trouble 故障
centralized monitoring system 巡回检测系统
centralized monitoring system 集中监控系统
Notes to the text
1,If lower press ratios (final pressure leaving the compressor divided by initial pressure entering) are used,a large amount of heat is available in the exhaust gas which may be recovered by heating the compressed air before it enters the combustion chamber
这是一句主从复合句。If lower pressure ratios are used是条件状语从句；主句是a large amount of heat is available in the exhaust gas,而which may be recovered by heating the compressed air是定语从句，修饰a large amount of heat,before it enters the combustion chamber是时间状语从句，修饰前面的heating，而it是指the compressed air.
However,the direct-driver diesels have a lower fuel oil consumption than do higher-rpm units,and with suitable fuel treatment they will operate on the better grades of the cheaper fuel oil burned in boilers.
than do higher-rpm units 是一个比较状语从句。这里的do即表示have a low fuel oil consumption.
burned in boilers 是动词过去分词短语，作后置定语，修饰cheaper fuel oil.
Lubricating oil consumption of diesel engines is high because of the cylinder-piston lubrication that must be provided and the contamination of the crankcase oil with residues blown by the piston rings.
复合介词because of后面有两个宾语，一个是the cylinder-piston lubrication，另一个是the contamination of the crankcase oil。that must be provided是定语从句，修饰the cylinder-piston lubrication。with residues blown by the piston rings是说明the crankcase oil污染的原因。
By reversing one or more engines,ready maneuvering,including astern operation,is provided for by the use of the respective coupling.
这是一个简单句。主语为 ready maneuvering，谓语为is provided for,by the use of the respective coupling和by reversing one or more engines是介词短语作行为。方式状语。
5．These include flexibility of control and the independence of the location of the turbo generator relative to the propeller shaft or propulsion motor.
句中relative to the propeller shaft or propulsion motor是形容词短语，作后置定语，修饰the independence。
All levels of automation are now being used from simple manual surveillance of all systems in a fully manned engine space to a completely unmanned system recording data and monitoring trends to pinpoint possible trouble.
are being used是动词被动态进行式。
recording data和monitoring trends to pinpoint possible trouble均是动词现在分词短语，作定语用，修饰a completely unmanned system。
