触，燃油会被点燃，引起气缸内压力迅速升高，驱动活塞在膨胀行程向下移动。As the piston reaches the bottom of the cylinder for the second time the exhaust valve is opened and during the upward and fourth stroke the hot spent gases are expelled through it.随着活塞第二次达到在气缸内的最低点，排气阀被打开，热的废气通过活塞上行从排气阀被排出。
If the charge of air entering the cylinder during the induction stroke is drawn in by the piston movement only without being assisted in any way, then the engine is said to be naturally aspirated.假如在吸气行程中进入气缸的增压空气只通过活塞的上下移动被吸入，而没有辅助机械，那么这就是自然吸气柴油机。
The power of any diesel engine is determined by the amount of fuel that can be burnt in each cylinder per cycle and the speed at which it can be run. 任何柴油机的功率都是通过每个循环喷入气缸燃烧的燃油量和它的运转速度决定。The rotational speed is limited by the forces arising from the inertia of the moving parts.而旋转速度受到运动部件的惯性力限制。 In the case of a naturally aspirated engine the amount of fuel that can be burnt is limited by the mass of air drawn into the cylinder during the induction stroke. 对于自然吸气柴油机来说，参与燃烧的燃油量受到吸气行程中吸入到气缸空气量的限制。Diesel fuel requires about 14.5 times its own mass of air for complete combustion. 柴油大约需要其自身质量的14.5倍空气量才能实现完全燃烧。The time available for combustion in the diesel cycle is very short; if only the chemically correct amount of air were provided, the fuel would not have time to burn completely and, in practice, almost twice this quantity is found to be necessary.在柴油机循环中，燃烧持续的时间非常短暂；假如只有化学反应的空气量，那么燃油就没有时间进行完全燃烧，在实际循环当中，两倍的空气量是必须的。 The cylinder can be charged with a greater mass of air by supplying it under pressure. The air is pressurized in a compressor, sometimes termed a blower, and fed to the induction manifold of the engine. The process is called pressure charging or supercharging.气缸可以在一定压力下充入大量空气。空气在压气机（有时称为鼓风机）中被压缩，然后供给到柴油机的进气总管。这个过程被称为增压。
In some special cases the compressor is driven mechanically from the engine crankshaft. 在有些特殊的装置中，压气机的机械驱动通过柴油机曲轴来实现。More usually, some of the energy present in the exhaust gas is utilized by passing it through a turbine which is directly coupled to a centrifugal compressor. The compressor and turbine together form a free running unit, separate from the engine, known as a turbocharger.更为常见的是利用排气的部分能量，让其通过涡轮机，而涡轮机直接和离心式的压气机连接，这样压气机和涡轮机组合成一个和柴油机分离开来的自由运转机构，这个装置称为涡轮增压器。
The pressure of the air in the inlet manifold to the cylinders of a turbocharged engine is termed the boost pressure.涡轮增压柴油机气缸的进气总管压力被称为增压压力。 In engines having a high boost pressure the air leaving the compressor is hot and it is beneficial and sometime, necessary to cool it as this assists in increasing the mass of air filling the cylinders and in keeping the internal parts of the engine cool. The air is cooled by passing it through an intercooler. 在高增压柴油机中，离开压气机的高温空气对柴油机来说是有利的，但有时必需的冷却有助于提高进入到气缸的空气量，有助于冷却柴油机的内部元件。增压空气的冷却可以通过空气冷却器实现。The quantity of air provided by turbocharger is so great that the amount of fuel that can be burnt in each cylinder per cycle (and hence the power) is not limited on this account but by the temperature which the exhaust valves, cylinder heads and pistons can withstand.由于涡轮增压器的空气进气量太大，所以每个循环下气缸的烧油量（输出功率）
是没有界限的，但是会受到排气阀，气缸头和活塞的承受温度限制。
TWO STROKE CYCLE DIESEL ENGINES 二冲程柴油机
Two stroke cycle diesel engines take several forms. 二冲程柴油机有多种结构。
One form has a valve in the cylinder head through which the exhaust gases leave the cylinder and ports around the lower part of the cylinder through which the air enters.一种结构是在气缸头上安装排气阀，在气缸下部加工一圈环绕的空气进气口。
At the bottom dead centre the exhaust valve and the inlet ports are both open at the same time. The pressure of the air in the inlet manifold is arranged to be higher than the pressure in the exhaust manifold so that on entering the cylinder it sweeps out the exhaust gases and fills the cylinder with a fresh charge. This process of displacing the spent gases in the cylinder by the incoming air is termed scavenging.在下止点，排气阀和进气阀同时开启。进气总管的空气压力大于排气总管的压力，这样就可以清扫废气，让气缸充满新鲜空气。这种新气替换气缸内废气的过程称为扫气。
As the piston rises it cuts off the inlet ports and the exhaust valve is arranged to close at the same time. Compression of the charge of air takes place and fuel is injected into the hot compressed air as top dead centre is approached. Combustion occurs and the piston is driven downwards on the expansion stroke. 随着活塞上行，进气口关闭，同时排气阀也被关闭，开始对空气进行压缩。在活塞接近上止点时，燃油喷入到高温空气当中，发生燃烧，开始膨胀，驱动活塞下行。Towards the end of this stroke the exhaust valve is opened allowing the exhaust gases to escape and the pressure in the cylinder fall below that of the air manifold. Shortly afterwards, as the inlet ports are opened by the downward moving piston, the scavenging air enters and displaces the remaining exhaust gas in preparation for the next cycle.在膨胀行程接近结束时，排气阀打开，开始排气，此时气缸压力降至进气总管压力以下。不久以后，随着下行的活塞打开进气口，扫气空气进入气缸替换剩余的废气，准备进行下一循环。
Another form of two stroke cycle engines is known as the opposed piston type. In operation it is very similar to the type just described, the chief difference being that the exhaust gases leave the cylinder via ports controlled by the upper piston instead of through a valve.二冲程柴油机的另一种结构是对置活塞式柴油机。它和刚才描述的柴油机运转相似，主要的区别在于：废气经过上部活塞控制的气口，而不是气阀离开气缸。
The two pistons may have the same length of stroke or the piston controlling the exhaust ports may have a shorter stroke than the one controlling the inlet ports. 两个活塞有相同的行程长度，或者控制排气口的活塞比控制进气口的活塞行程短。Power is obtained from both pistons and a variety of mechanisms is available to connect them together．做功通过两个活塞运动实现，多种机构用于它们的连接。The two most commonly used are separate crankshafts geared together and side connecting rods for the upper piston operated from extra cranks formed on the single crankshaft. 最为常用的机构是采用独立的曲轴，上部活塞的连杆作用在一个曲轴的额外曲柄上。The piston controlling the exhaust ports is usually given a few degrees lead over the piston controlling the inlet ports in order to allow the cylinder pressure to blow down before the scavenge air enters.活塞控制的排气口开启角度比活塞控制的进气口开启有少许提前，为了是让扫气进入气缸之前，利用气缸压力进行排气。
In the two stroke engines described so far the scavenging is carried out from one end of the cylinder to the other. This is termed uniflow scavenging. 到目前为止描述的二冲程柴油机扫气是从气缸的一端流动到另一端实现，这种方式称为直流扫气。Another arrangement appears
where inlet and exhaust ports are both at the same end of the cylinder. The path taken by the scavenging air leads to the term \cycle engine. The events of the cycle are exactly the same as for the other forms.另一种布置形式是进排气口在气缸的同一端面，这种结构二冲程柴油机的扫气流动轨迹叫做回流扫气，而柴油机的循环过程和其它柴油机相同。 The loop scavenge engine is mechanically simpler than the other types but because one piston controls both inlet and exhaust ports, it is usually necessary to provide light, quick-acting non-return valves in the inlet port to prevent backflow of exhaust gas before the cylinder has blown down to a pressure lower than that in the scavenge air manifold.回流扫气柴油机比其它柴油机机械结构简单，但是因为一个活塞控制进排气口，通常在气缸自身排气压力低于进气总管压力之前，需要在进气口布置一个重量轻，能够快速动作的止回阀来阻止废气逆流。
All two stroke cycle diesel engines require the scavenge air to be at a pressure above that in the exhaust manifold and a scavenge blower is necessary to provide this slightly pressurized air. 所有的二冲程柴油机需要扫气压力大于排气总管压力，所以需要一个扫气风机提供有一定压力的空气。Scavenge blowers may be reciprocating air pumps driven directly from the crankshaft or running gear, or roots blowers or centrifugal compressors driven indirectly from the crankshaft by chain drives or gearing. 扫气风机可能是往复式空气泵，由曲轴或运转机构间接驱动，也可能是鲁式风机或离心风机，通过曲轴的链传动或齿轮机构间接驱动。The volume of air displaced by tile scavenge air blower is a little in excess of the swept volume of the cylinders in order to ensure that scavenging is complete.为了保证扫气彻底，由扫气鼓风机替换的空气体积要稍微大于气缸的总容积。
Two stroke cycle engines can be turbocharged in the same way as four stroke cycle engines. In most cases a scavenge blower, mechanically driven, is retained to assist the turbocharger. 二冲程柴油机和四冲程柴油机的涡轮增压方式相同。在多数情况下，机械式驱动的扫气风机保持开启协助涡轮增压器工作。The flow of air may all pass through the compressor of the turbocharger and then through the scavenge blower in series, or part of it may pass through the compressor and part through the scavenge blower in parallel. 所有的流动空气都经过涡轮增压器的压气机，然后经过串联的扫气风机，或者是一部分空气经过压气机，另一部分经过和压气机并联的扫气风机。In the latter case the size of the blower required is smaller but it has to be capable of dealing with the full boost pressure ratio. Crosshead type engines sometimes use the undersides of their pistons as scavenge blowers to assist a turbocharged cycle在后一种情况中，所需要的风机尺寸较小，但是必须保证全部的增压比。十字头式柴油机有时使用活塞的底面作为扫气风机，来协助完成涡轮增压循环。
LESSON 3
Engine Construction I 柴油机结构
Traditional Engine Structure 传统柴油机结构
A traditional engine structure arrangement comprises a cylinder block which accommodates the cylinder liners, the block differs in design depending on whether the engine is of in-line or Vee form. The block has spaces to accommodate camshaft drive arrangements (chain or gear), a housing for the camshaft and doors allowing access to the crankcase. The block is a single casting
to ensure rigidity. Cast iron is the usual material. Supporting the cylinder block is the bedplate with its main bearing housings and mounting feet, which connect to the ship's structure. In some cases tie rods are employed to maintain the main bearing housings and engine block in compression. The steel tie rods pass from the upper part of the cylinder block to the lower face of the bedplate below the main bearing housing. Smaller engines often have no tie rods as the structural section thickness is great enough to keep tensile stresses reasonable during peak pressure periods. With a casting there is a minimum section thickness requirement to ensure that the molten metal flows readily to all parts and this thickness is often greater than that dictated by actual stress considerations. Accurate alignment between bedplate and cylinder block is essential to effective stress transmission and engine operation.
传统柴油的结构中包含有一个用来安装汽缸套的汽缸体，发动机是直列式布置还是V型布置就造成了汽缸体设计形式上的差异。机体结构有用来容纳凸轮驱动机构（链条或齿轮）、凸轮轴和进入曲轴箱道门的空间。为了保证刚度，机体结构通常是由铸铁材料铸成一个整体。机座上面安放有汽缸体，其上面带有主轴承座和把机座固定到船体机构上的地脚。有些情况下，用贯穿螺栓以一定压力把主轴承座和汽缸体连接在一起，钢制的贯穿螺栓从汽缸体的上部一直通到机座的下表面（主轴承下部）。小型柴油机没有贯穿螺栓，因为其构件的厚度足够克服由于最高爆发压力所产生的张力。如果是铸铁机体的话，就很少有构件厚度方面的要求，为了保证熔化的铁水能够容易地流到所有的部位，构件的厚度一般要比能承受实际应力的厚度大得多。机座和汽缸体之间正确调整，对于柴油机力的有效传递以及柴油机的正常运转都是非常必要的。
Modern Cast Monoblock Structure 现代整体铸造结构
Engines designed during the 1990s generally employ a cast monoblock form of construction with the cylinder block and bedplate forming a single cast iron structure. This nodular iron casting provides considerable rigidity due to its single-piece design and construction. In some engines additional strengthening can be provided by long tie rods extending from the lower face of the main bearing to the upper part of the structure. Tie rods are also employed between the upper face of the cylinder head and the lower face of the intermediate frame structure to ensure that combustion loads are transmitted from the cylinder head to the engine frame structure. The use of tie rods does not imply a weakness in design and is an effective use of a strengthening mechanism where it is needed. A rigid structure is necessary in order to preserve alignment of all engine parts, particularly the crankshaft and camshaft, and to minimize problems related to vibration of the structure. Some engines (e.g. Wartsila Vasa 38) have the air inlet manifold as an integrated part of the engine block while many water and oil channels are cast-in or machined as part of the engine structure. Such features make for easier maintenance, improved accessibility and a reduction in the number of engine parts.
在20实际90年代，柴油机设计开始运用整体铸造结构，把汽缸体和机座一起铸造成一个铸铁构件。由于设计和构造上的整体性，使得球墨铸铁件非常的坚固。一些柴油机还利用长贯穿螺栓从主轴承的下表面通到构件的上部为整个机体进行额外加强。贯穿螺栓也用在汽缸头的上表面和机架的下表面之间，以保证把燃烧负荷从汽缸盖传到机架上。使用贯穿螺栓并不是意味着设计上存在缺陷，而是在需要的地方有效地利用加强机构。一个刚性结构应该保证主机各部件，尤其是曲轴和凸轮轴的精确位置，将结构的振动问题降到最低。一些机型（如：Wartsila Vasa 38）将进气总管与机体集成在一起，而水和油的通道则采用铸造或车削后，做为机体结构的部件。这样设计特性简化了维修保养，提高了可达性，降低了主机部件的数量。
With monoblock structures, a sub-frame is required to act as the engine sump. This sub-frame, which bolts directly to the lower face of the engine structure, takes no load and can be manufactured from welded plate. Lubricating oil suction pipes and strainers are arranged within the sump.
对于整体结构来说，下部结构被用作柴油机的油底壳。油底壳用螺栓直接连接到主机整体结构的下表面上，不承受负荷，可用金属板焊接制成。润滑油的吸入口和过滤器都安装在油底壳中。
Main Bearings 主轴承
Main bearing support housings are cast as part of traditional bedplate arrangements, and these combine adequate rigidity for the crankshaft with relative ease of bearing adjustment.
主轴承座作为传统机座的一部分也是铸铁的，轴承座和机座具有足够的刚度，这样轴承的调整就相对容易
Bearing replacement requires lifting the bearing cap, which is held from above with studs and nuts.
轴承更换的时候需要卸下轴承盖，轴承盖是从上部用螺栓螺母固定的。
Although this type of arrangement can, in theory, be incorporated within a monoblock engine structure, it is not used. An underslung main bearing support system is preferred. Nodular cast-iron bearing caps are held from below by means of two hydraulically tensioned studs.
尽管理论上可把这种设计的轴承盖与整体式机体结构做成一体，但实际中并不这样做。一般首选悬挂式的主轴承支撑系统，球墨铸铁轴承盖利用两个液压张紧螺栓从下面固定。
These bearing caps are guided laterally into the engine block at the top and bottom and the hydraulic jacks are often permanently fitted to allow for ease of maintenance. Hydraulically tensioned horizontal side studs support the main bearing caps and with the vertical studs and lateral guide arrangements provide a very rigid main bearing support for the crankshaft.
主轴承盖可从上部和下部横向导入机体结构，为了方便维护保养经常安装固定式的液压千斤顶。水平布置得液压张紧螺栓支撑主轴承盖，再加上垂直螺栓和侧向楔形块，就给曲轴的轴承提供了一个很大刚性的支撑。
Main bearings for medium speed engines currently in use are of the thin shell type. 中速机普遍使用薄瓦性的主轴承。Similar bearing shells are employed for bottom end bearings.底部轴承也利用相似的轴瓦 。This type of bearing essentially consists of a thin steel backing shell with a layer, or layers, of bearing material cast, flashed or deposited on the rubbing surface. 这种类型的轴瓦基本上是在薄钢衬壳内部的粗糙的表面上浇注或沉淀一层或多层的轴承材料。 This type of bearing is prefinished and does not require scraping to fit; indeed no scraping is possible due to the thin layer of bearing material present. 这种类型的轴承只需要表面抛光，不需要过多处理，实际上由于轴承材料层很薄没有必要进行刮擦等处理。Over the years bearing materials have changed to meet the operating conditions. 多年来为了满足工作条件，轴承材料进行了不断地改进。Early arrangements simply had a layer of white metal on the steel backing shell but this gave way to the multi-layer bearing with a layer of lead-bronze or copper between the steel and white metal in order to improve adhesion. 早期的轴瓦只是简单的在薄钢衬壳内部浇注一层白合金，但是这种制作方法为多层轴瓦提供了借鉴，多层轴瓦是在薄钢衬壳和白合金之间又加了一层铅青铜或者黄铜来提高金属间的粘着力。This layer also provided an emergency bearing surface. 添加的这一层也提供了一个应急轴承面。The use of overlay material provides a degree of protection against corrosion, while a thin layer of nickel prevents the lead in the overlay from