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1、车辆工程专业毕业设计的外文翻译内 燃 机 任何通过燃料在气缸中燃烧，使燃油的化学能转化为机械能，从而获得动力的引擎都成为内燃机。最常见的内燃机有四种：奥托循环式发动机，柴油机，转子发动机和煤气机。根据这四种发动机的优点，把它们应用于不同的工况。奥托循环式发动机，是根据其发明者，德国机械师尼古拉斯.奥格事特.奥托的名字来命名的。是飞机上很常见的一种发动机；而柴油机是由法籍德国工程师Rudolf Christian Karl Diesel命名的。它是一种用柴油作为燃料的先进的发动机。普遍用在电子控机械、战斗机、公共汽车、货车以及一些小车上。奥托式发动机和柴油机的工作方式都是二冲程或者四冲程。奥托式
2、发动机和柴油机的基本构造都是一样的。压缩燃烧室是由一个一段由缸盖另一端由活塞之间的空间所形成。活塞的上下运动使得气缸与活塞间的空间发生大小变化，从而改变压缩空间的大小。活塞与曲轴之间通过连杆相互连接。曲轴将活塞的运动转化成旋转式的运动。多气缸式发动机的曲轴，在每一个气缸处都会多一个称为曲拐的结构部分。这样每个气缸的动力才能很好的传递给曲轴，是曲轴的转动平稳。曲轴上接有飞轮并有平衡坑。这样能够使曲轴运动的惯性最小化，达到平衡的目的。不同的发动机会有一个到二十四个等的气缸。内燃机的燃料供给系统又油箱、油泵、和分油管以及使液体燃料雾化的机构组成。在奥托式发动机上，并不是靠化油器来进行燃油雾化的，而是
3、利用燃油的直接喷入，一直到现在都是如此。在大多数发动机上，燃料都是通过化油器雾化后通过压气机进入进气管道。在部分发动机的排气系统中，也会用到类似的装置来通过利用废气的能量对进气充量进行压缩。燃料平均分配给各个汽缸，而废气则通过排气门排出。进排气门的开闭都是通过凸轮轴的转动从而牵动气门弹簧作用到挺杆，在正确的时间是气门开闭。在上世纪80年代，缸内直喷技术开始用于内燃机领域，从很大程度上代替了传统的燃油与空气相混合的技术。在有直喷装置的发动机上，燃料会通过喷射系统在正确的时刻喷入汽缸或者进气管。这样燃料就会在汽缸里混合，这比化油器混合更充分，污染更小。所有的发动机上，火花塞的位置都必须适宜。比如奥
4、托式发动机的点火系统包括低压电源，即具有变压性质的初级线圈，从而导出直流电。电流会被一个机械式的定时调节器在一秒钟内方向发生多次变化。初级线圈中电流的扰动会产生脉冲，从而会在次级线圈中产生高压电流。这个高压电流会被分电器分配到各个汽缸，件叫做火花，一个安装在汽缸顶部被叫做火花塞的零件。在火花塞末端的两极间有一个间隙，高压电流会击穿这个点火间隙，从而点燃汽缸中的混合气体。由于燃烧室的温度太高，所有的发动机都必须有相应的冷却系统。一些飞机、汽车、和船只上的舷外发动机采用风冷。这些采用风冷的发动机都必须有很多散热片，一边有较大的散热面积，从而很好的带走汽缸的热量。除此之外的还有水冷系统，它是在发动机
5、的汽缸中设有水套来达到冷却的目的。在汽车上，冷却液借助水泵的压力在水套中流动，带走热量。还有一些汽车是利用风冷，海上船只则是用海水作为冷却的介质。与蒸汽机和涡轮机不同，内燃机在发动时并不会产生转矩，并且扭矩的输出必须要靠曲轴的转动才行。汽车发动机的启动要靠一个与曲轴箱啮合的摩擦片，通过摩擦片的分离才能向外输出力矩。小型的发动机有时需要手动的进行多次使离合器的松脱才能发动。有时候在大型发动机上，会有惯性启动装置，或者是借助手工输入力矩知道驱动能量能使曲轴转动。一边带动增压器工作，来增加发动机的功率。一般，惯性启动装置和爆炸性质的装置都是在飞机上采用的。普通的奥托式发动机都是四冲程，也就是说，每一
6、个工作循环中，活塞会有四个行程，两个离缸盖最近，另外两个离缸盖距离最远。在第一个行程时，活塞远离缸盖，同时进气门打开。活塞在这个过程中的运动，使得燃料和空气进入燃烧室混合。接着的行程，就是将混合后的气体压缩到燃烧室里。当活塞上行到最高点时，燃烧室的体积达到最小，火花塞就会点燃混合气体，燃烧产生的膨胀压力会作用在活塞上，使活塞远离缸盖，这就是第三个行程。在最后一个行程中，排气门打开，活塞的上行会对燃烧后的气体进行挤压，是废气排出燃烧室，做好下一循环的准备。发动机的效率会受到很多因素的限制，例如冷却损失以及摩擦损失。通常，发动机的效率是由其压缩比决定的。现在发动机的压缩比一般在8-10之间。更高的
7、压缩比可以达到15，效率的提高也可以通过采用辛烷值较高的燃料来实现。现在，好的发动机的效率在20-25，也就是说，只有这部分能量真正用于产生机械能量。理论上，柴油周期相比奥托循环的区别在于，它的压缩过程是等容、等压的。大多数柴油机都是采用四冲程，但却与奥托式四冲程不一样。首先，在进气时，活塞向下运动，并通过进气门将空气吸进燃烧室。其次，在压缩时，活塞将空气压缩到比先前小很多倍的体积，并在这个过程中使空气的温度达到440（等同于华氏820）。在压缩结束的时候，蒸发的燃油被喷入汽缸，由于汽缸中的气体高温作用而立即燃烧。一些发动机上设有电子喷射辅助系统，在发动机发动直到加热完成期间进行燃油喷射。这样
8、的压缩过程为活塞进行第三个冲程提供强大的动力。第四个冲程跟奥托式四冲程发动机一样，都是排气过程。柴油机的效率，跟一般的奥托式发动机是受同样的因素所影响的，但是稍好于奥托式发动机。事实上，现在发动机中，基本的效率都不会超过40。事实上，柴油机的曲轴转速的100750转每分钟，这等同于奥托式发动机的25005000转每分钟。但是也有一些柴油机的转速达到了2000转每分钟。因为柴油机的压缩比高达14或者15，这使得它们的体积较奥托式大，这个缺点正体现出柴油机的到效率和高燃油经济特性。好的设计一般采用奥托式循环或者二冲程的方式来代替四冲程的方式。因为同样体积的发动机，二冲程的效率是四冲程的两倍。二冲程
9、的有点在于，缩短了燃料压缩的时间，并且减少了燃料的浪费以及用半个冲程完成了四冲程发动机的一个压缩冲程。在最简单的二冲程发动机上，排气门被废气管代替了。在二冲程循环中，燃料和空气的混合气体在活塞在汽缸中下行时进入曲轴箱。紧接着，燃料开始压缩，并在活塞到达上至点是点燃。这是活塞在燃气压力的作用下下行，废弃就会从排气口由汽缸内向外排出去。上世纪50年代，德国机械师菲利克斯.王科尔开发了一种新型的发动机。在这种发动机上，活塞和汽缸被一个在椭圆形燃烧室里旋转的三角转子所代替。混合燃料通过进气口进入，然后分流到有转子表面与端面形成的燃烧室里。混合气体通过转子的旋转得到压缩，最后被火花塞点燃。然后，废弃就会
10、随着转子的运动从排气口排出。循环过程中，转子的旋转一周，会出有三个冲程，而且在转子的正反两面产生压力。正因为转子发动机与柴油机相比，结构紧凑、质量轻，因而在汽车发动机中作用很大。另外，它简单的结构使得生产成本低，冷却系统质量轻，另外它的重心低，使得他的安全性得到了增加。在上世纪70年代初期，一条转子发动机的生产线在日本落成。很多美国的汽车制造商都很看好这个项目。但是，由于转子发动机的低燃料经济性很高污染性，最后没能得到继续的发展。日本的汽车制造商马自达，继续了改善转子发动机燃油经济性的设计和研发。发动机采用火花点火的改进方式，进行分层点火稀薄燃烧，帮助没有使用废气再循环和催化转换器的发动机减小
11、排放量。它的特点在于在一个汽缸中有两个燃烧室，当冲入的混合气体过多是，备用燃烧室就会将多余的混合气体储存起来。火花塞会先点燃多余部分的混合气，在将另一部分点燃。这样最高火焰温度就会比较合适，从而很好的限制NOx化合物的生成量以及CO和HC的排放量。 英文翻译：Internal-Combustion EngineInternal-Combustion Engine, any type of machine that obtains mechanicalenergy directly from the expenditure of the chemical energy of fuel burne
12、d in a combustion chamber that is an integral part of the engine. Four principal types of internal-combustion engines are in general use: the Otto-cycle engine, the diesel engine, the rotary engine, and the gas turbine. For the various types of engines employing the principle of jet propulsion, see
13、Jet Propulsion; Rocket. The Otto-cycle engine, named after its inventor, the German technician Nikolaus August Otto, is the familiar gasoline engine used in automobiles and airplanes; the diesel engine, named after the French-born German engineer Rudolf Christian Karl Diesel, operates on a different
14、 principle and usually uses oil as a fuel. It is employed in electric-generating and marine-power plants, in trucks and buses, and in some automobiles. Both Otto-cycle and diesel engines are manufactured in two-stroke and four-stroke cycle models.The essential parts of Otto-cycle and diesel engines
15、are the same. The combustion chamber consists of a cylinder, usually fixed, that is closed at one end and in which a close-fitting piston slides. The in-and-out motion of the piston varies the volume of the chamber between the inner face of the piston and the closed end of the cylinder. The outer fa
16、ce of the piston is attached to a crankshaft by a connecting rod. The crankshaft transforms the reciprocating motion of the piston into rotary motion. In multicylindered engines the crankshaft has one offset portion, called a crankpin, for each connecting rod, so that the power from each cylinder is
17、 applied to the crankshaft at the appropriate point in its rotation. Crankshafts have heavy flywheels and counterweights, which by their inertia minimize irregularity in the motion of the shaft. An engine may have from 1 to as many as 28 cylinders.The fuel supply system of an internal-combustion eng
18、ine consists of a tank, a fuel pump, and a device for vaporizing or atomizing the liquid fuel. In Otto-cycle engines this device is either a carburetor or, more recently, a fuel-injection system. In most engines with a carburetor, vaporized fuel is conveyed to the cylinders through a branched pipe c
19、alled the intake manifold and, in many engines, a similar exhaust manifold is provided to carry off the gases produced by combustion. The fuel is admitted to each cylinder and the waste gases exhausted through mechanically operated poppet valves or sleeve valves. The valves are normally held closed
20、by the pressure of springs and are opened at the proper time during the operating cycle by cams on a rotating camshaft that is geared to the crankshaft. By the 1980s more sophisticated fuel-injection systems, also used in diesel engines, had largely replaced this traditional method of supplying the
21、proper mix of air and fuel. In engines with fuel injection, a mechanically or electronically controlled monitoring system injects the appropriate amount of gas directly into the cylinder or inlet valve at the appropriate time. The gas vaporizes as it enters the cylinder. This system is more fuel eff
22、icient than the carburetor and produces less pollution.In all engines some means of igniting the fuel in the cylinder must be provided. For example, the ignition system of Otto-cycle engines described below consists of a source of low-voltage, direct-current electricity that is connected to the prim
23、ary of a transformer called an ignition coil. The current is interrupted many times a second by an automatic switch called the timer. The pulsations of the current in the primary induce a pulsating, high-voltage current in the secondary. The high-voltage current is led to each cylinder in turn by a
24、rotary switch called the distributor. The actual ignition device is the spark plug, an insulated conductor set in the wall or top of each cylinder. At the inner end of the spark plug is a small gap between two wires. The high-voltage current arcs across this gap, yielding the spark that ignites the
25、fuel mixture in the cylinder.Because of the heat of combustion, all engines must be equipped with some type of cooling system. Some aircraft and automobile engines, small stationary engines, and outboard motors for boats are cooled by air. In this system the outside surfaces of the cylinder are shap
26、ed in a series of radiating fins with a large area of metal to radiate heat from the cylinder. Other engines are water-cooled and have their cylinders enclosed in an external water jacket. In automobiles, water is circulated through the jacket by means of a water pump and cooled by passing through t
27、he finned coils of a radiator. Some automobile engines are also air-cooled, and in marine engines sea water is used for cooling.Unlike steam engines and turbines, internal-combustion engines develop no torque when starting, and therefore provision must be made for turning the crankshaft so that the
28、cycle of operation can begin. Automobile engines are normally started by means of an electric motor or starter that is geared to the crankshaft with a clutch that automatically disengages the motor after the engine has started. Small engines are sometimes started manually by turning the crankshaft w
29、ith a crank or by pulling a rope wound several times around the flywheel. Methods of starting large engines include the inertia starter, which consists of a flywheel that is rotated by hand or by means of an electric motor until its kinetic energy is sufficient to turn the crankshaft, and the explos
30、ive starter, which employs the explosion of a blank cartridge to drive a turbine wheel that is coupled to the engine. The inertia and explosive starters are chiefly used to start airplane engines.The ordinary Otto-cycle engine is a four-stroke engine; that is, in a complete power cycle, its pistons
31、make four strokes, two toward the head (closed head) of the cylinder and two away from the head. During the first stroke of the cycle, the piston moves away from the cylinder head while simultaneously the intake valve is opened. The motion of the piston during this stroke sucks a quantity of a fuel
32、and air mixture into the combustion chamber. During the next stroke, the piston moves toward the cylinder head and compresses the fuel mixture in the combustion chamber. At the moment when the piston reaches the end of this stroke and the volume of the combustion chamber is at a minimum, the fuel mi
33、xture is ignited by the spark plug and burns, expanding and exerting a pressure on the piston, which is then driven away from the cylinder head in the third stroke. During the final stroke, the exhaust valve is opened and the piston moves toward the cylinder head, driving the exhaust gases out of th
34、e combustion chamber and leaving the cylinder ready to repeat the cycle.The efficiency of a modern Otto-cycle engine is limited by a number of factors, including losses by cooling and by friction. In general, the efficiency of such engines is determined by the compression ratio of the engine. The co
35、mpression ratio (the ratio between the maximum and minimum volumes of the combustion chamber) is usually about 8 to 1 or 10 to 1 in most modern Otto-cycle engines. Higher compression ratios, up to about 15 to 1, with a resulting increase of efficiency, are possible with the use of high-octane antikn
36、ock fuels. The efficiencies of good modern Otto-cycle engines range between 20 and 25 percentin other words, only this percentage of the heat energy of the fuel is transformed into mechanical energyTheoretically, the diesel cycle differs from the Otto cycle in that combustion takes place at constant
37、 volume rather than at constant pressure. Most diesels are also four-stroke engines but they operate differently than the four-stroke Otto-cycle engines. The first, or suction, stroke draws air, but no fuel, into the combustion chamber through an intake valve. On the second, or compression, stroke t
38、he air is compressed to a small fraction of its former volume and is heated to approximately 440C (approximately 820F) by this compression. At the end of the compression stroke, vaporized fuel is injected into the combustion chamber and burns instantly because of the high temperature of the air in t
39、he chamber. Some diesels have auxiliary electrical ignition systems to ignite the fuel when the engine starts and until it warms up. This combustion drives the piston back on the third, or power, stroke of the cycle. The fourth stroke, as in the Otto-cycle engine, is an exhaust stroke. The efficienc
40、y of the diesel engine, which is in general governed by the same factors that control the efficiency of Otto-cycle engines, is inherently greater than that of any Otto-cycle engine and in actual engines today is slightly more than 40 percent. Diesels are, in general, slow-speed engines with cranksha
41、ft speeds of 100 to 750 revolutions per minute (rpm) as compared to 2500 to 5000 rpm for typical Otto-cycle engines. Some types of diesel, however, have speeds up to 2000 rpm. Because diesels use compression ratios of 14 or more to 1, they are generally more heavily built than Otto-cycle engines, bu
42、t this disadvantage is counterbalanced by their greater efficiency and the fact that they can be operated on less expensive fuel oils. By suitable design it is possible to operate an Otto-cycle or diesel as a two-stroke or two-cycle engine with a power stroke every other stroke of the piston instead
43、 of once every four strokes. The power of a two-stroke engine is usually double that of a four-stroke engine of comparable size.The general principle of the two-stroke engine is to shorten the periods in which fuel is introduced to the combustion chamber and in which the spent gases are exhausted to
44、 a small fraction of the duration of a stroke instead of allowing each of these operations to occupy a full stroke. In the simplest type of two-stroke engine, the poppet valves are replaced by sleeve valves or ports (openings in the cylinderwall that are uncovered by the piston at the end of its out
45、ward travel). In the two-stroke cycle, the fuel mixture or air is introduced through the intake port when the piston is fully withdrawn from the cylinder. The compression stroke follows, and the charge is ignited when the piston reaches the end of this stroke. The piston then moves outward on the po
46、wer stroke, uncovering the exhaust port and permitting the gases to escape from the combustion chamber.In the 1950s the German engineer Felix Wankel developed an internal-combustion engine of a radically new design, in which the piston and cylinder were replaced by a three-cornered rotor turning in
47、a roughly oval chamber. The fuel-air mixture is drawn in through an intake port and trapped between one face of the turning rotor and the wall of the oval chamber. The turning of the rotor compresses the mixture, which is ignited by a spark plug. The exhaust gases are then expelled through an exhaus
48、t port through the action of the turning rotor. The cycle takes place alternately at each face of the rotor, giving three power strokes for each turn of the rotor. Because of the Wankel engines compact size and consequent lesser weight as compared with the piston engine, it appeared to be an importa
49、nt option for automobiles. In addition, its mechanical simplicity provided low manufacturing costs, its cooling requirements were low, and its low center of gravity made it safer to drive. A line of Wankel-engine cars was produced in Japan in the early 1970s, and several United States automobile manufacturers researched the idea as well. However, production of the Wankel engine was discontinued as a result of its poor fuel economy and its high pollutant emissions. Mazda, a Japanese car manufact
