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.

噴氣發(fā)動機

大多數(shù)現(xiàn)代高速飛機上裝備的噴氣發(fā)動機產(chǎn)生推力的原理與普通航空發(fā)動機的推進器的相同。二者的推進力都來自被高速向后推動的空氣流所產(chǎn)生的反作用。不過，在噴氣推進器中，空氣是通過發(fā)動機本身的噴管向后噴射的。最早的噴氣推進裝置，例如飛彈上使用的脈沖式噴氣發(fā)動機.由于缺乏空氣壓縮裝置，靜止時沒有工作能力。但是，采用渦輪噴氣發(fā)動機之后，這個問題得到了解決，因為渦輪可以產(chǎn)生足夠的動力來驅(qū)動壓氣機。

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.

空氣通過擴散進氣管進入發(fā)動機，其壓力在進氣管中增大到一定程度。然后通到壓氣機經(jīng)過壓縮之后，再供給各個燃燒室。這些燃燒室是圈繞著渦輪的軸線呈輻射狀布置的，燃燒后的氣體離開各燃燒室后就進入渦輪中。這些氣體所產(chǎn)生的一部分動力，由渦輪用來驅(qū)動壓氣機，其余的能量期提供推力使飛機向前飛行。由于廢氣在渦輪后邊的噴管里膨脹，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℃.

各燃燒室都有帶孔的火焰管，煤油噴進其中并點燃。由于必須限制燃燒室的溫度，需要大量過量空氣。要把燃燒室的溫度降低到允許程度，空氣與燃油之比必須為60：1左右?？墒?，燃油與空氣按這種比例組成的混合氣很難點燃。所以，只有一小部分壓縮空氣供給火焰管，形成比例約為15：1的混合氣，在此點燃。其余的壓縮空氣在火焰管內(nèi)繼續(xù)前進，或者當(dāng)燃燒后的氣體離開火焰管時與之相混合。由于高溫燃氣與較冷的空氣這樣調(diào)和，所以當(dāng)它到達渦輪時，其溫度便降到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.

燃氣一進入渦輪就通過許多噴咀射到一圈葉片上。這些葉片能高速轉(zhuǎn)動，其形狀是按照盡量將轉(zhuǎn)矩減小到最低限度的要求制作的。因為快速轉(zhuǎn)動的葉片容易產(chǎn)生蠕變和變形，故用特種高鐮合金來制造，燃氣通過渦輪之后，就沿著噴管向后膨脹，噴入大氣中。由于在這種噴氣流中含有大量未燃燒完的氧氣，所以，往往在噴管中裝設(shè)多個加力燃燒室，利用它們使高溫燃氣再次點燃，以增加其速度，為起飛提供附加的推進力。

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