7.這一同樣的反作用原理出現于所有運動形式之中，通常有許多應用方式。噴氣反作用最早的著名例子是公元前120年作為一種玩具生產的赫羅的發動機（圖1-4）這種玩具表明了從若干噴嘴中噴出的水蒸氣的能量能夠把大小相等方向相反的反作用力傳給這些噴嘴本身，從而引起發動機旋轉的道理。
8.類似的旋轉式花園噴灌器（圖1-5）是這一原理更為實用的
一個例子。這種噴灌器借助于作用于噴水嘴的反作用力旋轉。現代滅火設備的高壓噴頭是“噴流反作用”的一個例子。由于水噴流的反作用力，一個救火員經常握不住或控制不了水管。也許，這一原理的最簡單的表演是狂歡節的氣球，當它放出空氣或氣體時，它便沿著與噴氣相反的方向急速飛走。
4. 噴氣發動機（圖1-2）雖然與活塞發動機－螺旋槳組合貌似大相徑庭，但是卻采用了同樣的基本原理來實現推進。正如圖1-3所示，二者純粹是通過將大量氣體向后推而推進它們的飛機。
5.今天，雖然噴氣推進與燃氣渦輪發動機密切相關，但是，也有其它類型的噴氣推進發動機，如沖壓噴氣、脈沖噴氣、火箭、渦輪/沖壓噴氣和渦輪－火箭發動機等。
Basic mechanics
圖1-2 惠特爾型的一種渦輪噴氣發動機
噴管和推進噴口
Fig. 1-2 A Whittle-type turbo-jet engine.
4.
The jet engine (fig. 1-2), although appearing so different from the piston engine-propeller combination, applies the same basic principles to effect propulsion. As shown in fig. 1-3, both propel their aircraft solely by thrusting a large weight of air backwards.
5.
Although today jet propulsion is popularly linked with the gas turbine engine, there are other types of jet propelled engines, such as the ram jet, the pulse jet, the rocket, the turbo/ram jet, and the turbo-rocket.
PRINCIPLES OF JET PROPULSION
6. Jet propulsion is a practical application of Sir Isaac Newton's third law of motion which states that, 'for every force acting on a body there is an opposite and equal reaction'. For aircraft propulsion, the 'body' is atmospheric air that is caused to accelerate as it passes through the engine. The force required to give this acceleration has an equal effect in the opposite direction acting on the apparatus producing the acceleration. A jet engine produces thrust in a similar way to the engine/propeller combination. Both propel the aircraft by thrusting a large weight of air backwards (fig. 1-3), one in the form of a large air slipstream at comparatively low speed and the other in the form of a jet of gas at very high speed.
燃氣室
渦輪
燃油
進氣道
壓氣機
7.
This same principle of reaction occurs in all forms of movement and has been usefully applied in many ways. The earliest known example of jet reaction is that of Hero's engine (fig. 1-4) produced as a toy in 120 B.C. This toy showed how the momentum of steam issuing from a number of jets could impart an equal and opposite reaction to the jets themselves, thus causing the engine to revolve.
8.
The familiar whirling garden sprinkler (fig. 1-5) is a more practical example of this principle, for the mechanism rotates by virtue of the reaction to the water jets. The high pressure jets of modern fire-fighting equipment are an example of 'jet reaction', for often, due to the reaction of the water jet, the hose cannot be held or controlled by one fireman. Perhaps the simplest illustration of this principle is afforded by the carnival balloon which, when the air or gas is released, rushes rapidly away in the direction opposite to the jet.
9.
Jet reaction is definitely an internal phenomenon and does not, as is frequently assumed, result from the pressure of the jet on the atmosphere. In fact, the
9.噴氣反作用絕對是一種內部現象。它不象人們經常想象的那樣說成是由于噴氣流作用在大氣上的壓力所造成的。實際上，噴氣推進發動機，無論火箭、沖壓噴氣、或者渦輪噴氣，都是設計成加速空氣流或者然氣流并將其高速排出的一種裝置。當然，如第2章中描述的那樣，這樣做有不同的方式。
jet propulsion engine, whether rocket, athodyd, or turbo-jet, is a piece of apparatus designed to accelerate a stream of air or gas and to expel it at high velocity. There are, of course, a number of ways
Fig. 1-3 Propeller and jet propulsion.
換言之，給大量空氣附加一個小速度或者給少量空氣一個大速度能提供同樣的推力。實用中，人們喜歡前者，因為降低相對于大氣的噴氣速度能得到更高的推進效率。
圖1-3 螺旋槳和噴氣推進
10.不同類型的噴氣發動機，無論沖壓噴氣、脈沖噴氣、燃氣輪機、渦輪/沖壓噴氣或者渦輪-火箭，其差別僅在于“推力提供者”即發動機供應能量并將能量轉換成發行動力的方式。
11.沖壓噴氣發動機（圖1-6）按其全稱是一種氣動熱力涵道。它沒有任何主要形狀零件，只包含一個擴張形進氣涵道和一個收斂形或者收斂－擴散形出口。當由外部能源強迫其向前運動時，空氣被迫進入進氣道。當它流過這一擴散形涵道時，其速度或動能降低，而壓力能增加。爾后，靠燃油的燃燒來增加其總能量，膨脹的燃氣通過出口涵道加速并排入大氣。沖壓噴氣發動機常作為導彈和靶機的動力裝置，但不適于作為飛機動力裝置，因為在它產生推力前，要求向它施加向前的運動。
Basic mechanics
12.脈沖噴氣發動機（圖1-7）采用間歇燃燒原理。與沖壓噴氣發動機不同，它能在靜止狀態工作。這種發動機是由類似沖壓噴氣發動機的一種空氣動力涵道構成。但是，由于它的壓力較高，其結構比較堅實。進氣涵道有許多進氣“活門”，在彈簧力作用處于打開位置。通過打開的活門吸入的空氣進入燃燒室，并靠燃燒噴入燃燒室中去的燃油得到加熱。由此引起的膨脹使壓力升高，迫使活門關閉，然后膨脹的燃氣向后噴出。排氣造成降壓，使活門開啟。這種過程周而復始。脈沖噴氣發動機已設計成直升機旋翼的推進裝置，有的還通過精心設計涵道來控制共振循環的壓力變化而省去了進氣活門。脈沖噴氣發動機不適于作為飛機動力裝置，因為它的油耗高，又無法達到現代燃氣渦輪發動機的性能。 中國航空網 www.k6050.com 航空翻譯 www.aviation.cn 本文鏈接地址：勞斯萊斯噴氣引擎－中英(3)
