The Jet Engine

Jet engines with which most modern high-speed aircraft are equipped develop thrust on the same principle as the propellers of conventional aero-engines.1In both,the propulsive force is derived from the reaction produced by a stream of air driven rearwards at high velocity. However, in jet-propulsion the air is directed rearwards in a jet from the engine itself. The earliest forms of jet-propulsion, such as the pulse jet utilised in the Flying Bomb, were incapable of functioning at rest, in view of the absence of any means of air-compression. But the introduction of the turbo-jet overcame this problem, since the turbine developed sufficient power to drive a compressor.

喷气发动机

大多数现代高速飞机上装备的喷气发动机产生推力的原理与普通航空发动机的推进器的相同。二者的推进力都来自被高速向后推动的空气流所产生的反作用。不过，在喷气推进器中，空气是通过发动机本身的喷管向后喷射的。最早的喷气推进装置，例如飞弹上使用的脉冲式喷气发动机.由于缺乏空气压缩装置，静止时没有工作能力。但是，采用涡轮喷气发动机之后，这个问题得到了解决，因为涡轮可以产生足够的动力来驱动压气机。

Air enters the engine through a divergent inlet duct, in which its pressure is raised to some extent. It then passes to a compressor, where it is compresscd, and from which it is delivered to the combustion chambers. These are arranged radially round the axis of the turbine, into which the products of combustion pass on leaving the combustion chambers. A proportion of the power developed by these gases is utilised by the turbine to drive the air-compressor, and the residual energy provides the thrust whereby the aircraft is propelled. Due to the expansion of the exhaust gases in the jet-pipe behind the turbine, their exit velocity is very high.

空气通过扩散进气管进入发动机，其压力在进气管中增大到一定程度。然后通到压气机经过压缩之后，再供给各个燃烧室。这些燃烧室是圈绕着涡轮的轴线呈辐射状布置的，燃烧后的气体离开各燃烧室后就进入涡轮中。这些气体所产生的一部分动力，由涡轮用来驱动压气机，其余的能量期提供推力使飞机向前飞行。由于废气在涡轮后边的喷管里膨胀，故其排出速度很高。

In each of the combustion chambers, there is a perforated flame-tube, into which kerosene is sprayed and ignited. Owing to the need to limit temperatures in the combustion chambers, a large volume of excess air is required. The air/fuel ratio necessary to reduce combustion temperatures to an acceptable level is about 60 : 1. However with this ration of fuel to air, the mixture would be difficult to ignite. Therefore only a small proportion of the compressed air is fed into the flame-tube, where it is ignited in a ratio of about 15:1. The remainder enters the flame-tube further down, or mixes with the products of combustion as they leave the tube. "By virtue of this dilution of the hot gases with cooler air, the temperature at which they reach the turbine is reduced to about 850℃.

各燃烧室都有带孔的火焰管，煤油喷进其中并点燃。由于必须限制燃烧室的温度，需要大量过量空气。要把燃烧室的温度降低到允许程度，空气与燃油之比必须为60：1左右。可是，燃油与空气按这种比例组成的混合气很难点燃。所以，只有一小部分压缩空气供给火焰管，形成比例约为15：1的混合气，在此点燃。其余的压缩空气在火焰管内继续前进，或者当燃烧后的气体离开火焰管时与之相混合。由于高温燃气与较冷的空气这样调和，所以当它到达涡轮时，其温度便降到850℃左右。

On entering the turbine, the gases pass through nozzles, by means of which they are directed through a ring of blades. These blades, the shape of which is determined by the need to reduce the torque to a minimum, rotate at high speed.  Because of the tendency of fast-running blades to creep and change their shape, a special high-nickel alloy is used for them. After passing through the turbine, the gas expands down the jet-tube and is ejected into the atmosphere. Owing to the high proportion of unburnt oxygen in this efflux, afterburners are often provided in the jet-pipe, whereby the hot gases are again ignited. This increases their velocity, and provides extra thrust for take-off.

燃气一进入涡轮就通过许多喷咀射到一圈叶片上。这些叶片能高速转动，其形状是按照尽量将转矩减小到最低限度的要求制作的。因为快速转动的叶片容易产生蠕变和变形，故用特种高镰合金来制造，燃气通过涡轮之后，就沿着喷管向后膨胀，喷入大气中。由于在这种喷气流中含有大量未燃烧完的氧气，所以，往往在喷管中装设多个加力燃烧室，利用它们使高温燃气再次点燃，以增加其速度，为起飞提供附加的推进力。

责任编辑：admin