of doing this, as described in Part 2, but in all instances the resultant reaction or thrust exerted on the engine is proportional to the mass or weight of air expelled by the engine and to the velocity change imparted to it. In other words, the same thrust can be provided either by giving a large mass of air a little extra velocity or a small mass of air a large extra
圖1-5 依靠噴水嘴的反作用力旋轉(zhuǎn)的花園灑水器
velocity. In practice the former is preferred, since by lowering the jet velocity relative to the atmosphere a 噴氣推進(jìn)方式
higher propulsive efficiency is obtained.
METHODS OF JET PROPULSION
10.
The types of jet engine, whether ram jet, pulse jet, rocket, gas turbine, turbo/ram jet or turbo-rocket, differ only in the way in which the 'thrust provider', or engine, supplies and converts the energy into power for flight.
11.
The ram jet engine (fig. 1-6) is an athodyd, or 'aero-thermodynamic-duct to give it its full name. It has no major rotating parts and consists of a duct with a divergent entry and a convergent or
燃油噴嘴 燃燒室
圖1-6 沖壓式噴氣發(fā)動(dòng)機(jī)
Fig. 1-6 A ram Jet engine.
convergent-divergent exit. When forward motion is imparted to it from an external source, air is forced into the air intake where it loses velocity or kinetic energy and increases its pressure energy as it passes through the diverging duct. The total energy is then increased by the combustion of fuel, and the expanding gases accelerate to atmosphere through the outlet duct. A ram jet is often the power plant for missiles and .target vehicles; but is unsuitable as an aircraft power plant "because it requires forward motion imparting to it before any thrust is produced.
12. The pulse jet engine (fig. 1-7) uses the principle of intermittent combustion and unlike the ram jet it can be run at a static condition. The engine is formed by an aerodynamic duct similar to the ram jet but, due to the higher pressures involved, it is of more robust construction. The duct inlet has a series of inlet 'valves' that are spring-loaded into the open position. Air drawn through the open valves passes into the combustion chamber and is heated by the burning of fuel injected into the chamber. The resulting expansion causes a rise in pressure, forcing
13.雖然火箭發(fā)動(dòng)機(jī)（圖1-8）也是噴氣發(fā)動(dòng)機(jī)，但它們有最大區(qū)別。即，火箭發(fā)動(dòng)機(jī)不用大氣作為推進(jìn)流體，而用它攜帶的液態(tài)燃料或化學(xué)分解而成的燃料與氧氣劑的燃燒來產(chǎn)生它自己的推進(jìn)流體，從而能在地球大氣層外工作。因此，它只適用于工作時(shí)間很短的情況。
Basic mechanics
充氣 (節(jié)氣活門打開）
15. The mechanical arrangement of the gas turbine engine is simple, for it consists of only two main rotating parts, a compressor (Part 3) and a turbine (Part 5), and one or a number of combustion chambers (Part 4). The mechanical arrangement of various gas turbine engines is shown in fig. 1 -9. This simplicity, however, does not apply to all aspects of the engine, for as described in subsequent Parts the thermo and aerodynamic problems are somewhat complex. They result from the high operating tem-peratures of the combustion chamber and turbine, the effects of varying flows across the compressor 點(diǎn)火 (節(jié)氣活門關(guān)閉)
節(jié)氣活門
燃燒室
供油
進(jìn)氣道
噴管和推進(jìn)噴口
the valves to close, and the expanding gases are
then ejected rearwards. A depression created by the
exhausting gases allows the valves to open and
repeat the cycle. Pulse jets have been designed for
helicopter rotor propulsion and some dispense with
inlet valves by careful design of the ducting to control
the changing pressures of the resonating cycle. The
pulse jet is unsuitable as an aircraft power plant
because it has a high fuel consumption and is unable
to equal the performance of the modern gas turbine
engine.
15．燃?xì)鉁u輪發(fā)動(dòng)機(jī)的機(jī)械布局很簡(jiǎn)單，因?yàn)樗话瑑蓚�(gè)主要旋轉(zhuǎn)部分，即壓氣機(jī)(第3章)和渦輪(第5章)。及一個(gè)或者若干個(gè)燃燒室(第4章)。各種燃?xì)鉁u輪發(fā)動(dòng)機(jī)的機(jī)械布局示于圖1-9。然而，并非這種發(fā)動(dòng)機(jī)的所有方面都具有這種簡(jiǎn)單性，因
為正象以后幾章敘述的那樣，熱力和氣動(dòng)力問題是比較復(fù)雜的。這些問題是由燃燒室和渦輪的高工作溫度、通過壓氣機(jī)和渦輪葉片而不斷變化著的氣流的影響，以及排出燃?xì)獠⑿纬赏七M(jìn)噴氣流的排氣系
統(tǒng)的設(shè)計(jì)工作造成的。
13.
Although a rocket engine (fig. 1-8) is a jet
engine, it has one major difference in that it does not
use atmospheric air as the propulsive fluid stream.
Instead, it produces its own propelling fluid by the
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