工作循環(huán)
2．燃?xì)鉁u輪發(fā)動(dòng)機(jī)的工作循環(huán)類似于4沖程活塞發(fā)動(dòng)機(jī)。然而，在燃?xì)鉁u輪發(fā)動(dòng)機(jī)中，燃燒在等壓下進(jìn)行，而在活塞發(fā)動(dòng)機(jī)中，燃燒時(shí)體積不變。這兩種發(fā)動(dòng)機(jī)循環(huán)(圖2-1)表明每一種循環(huán)里都有進(jìn)氣、壓縮、燃燒和排氣。這些過程在活塞發(fā)動(dòng)機(jī)中是間歇性的，而在燃?xì)鉁u輪中是連續(xù)進(jìn)行的�；钊l(fā)動(dòng)機(jī)只有一個(gè)沖程用于產(chǎn)生功率，其余沖程用于工作流體的充填、壓縮和排放。相反，渦輪發(fā)動(dòng)機(jī)取消了三個(gè)“不做功”沖程，因而能在更短時(shí)間內(nèi)燃燒更多的燃油；所以，就一給定尺寸的發(fā)動(dòng)機(jī)而言，它產(chǎn)生更大的功率輸出。
3. Due to the continuous action of the turbine engine and the fact that the combustion chamber is not an enclosed space, the pressure of the air does not rise, like that of the piston engine, during combustion but its volume does increase. This process is known as heating at constant pressure. Under these conditions there are no peak or fluctuating pressures to be withstood, as is the case with the piston engine with its peak pressures in excess of 1,000 lb. per sq. in. It is these peak pressures which make it necessary for the piston engine to employ cylinders of heavy construction and
3.由于渦輪發(fā)動(dòng)機(jī)的連續(xù)作用和燃燒室不是一個(gè)封閉空間這一事實(shí)，在燃燒過程中，空氣壓力不象在活塞發(fā)動(dòng)機(jī)中那樣上升，而其體積卻要增加。這種過程稱之為等壓加熱。在這些狀態(tài)下，沒有峰值壓力或波動(dòng)壓力要承受。而活塞發(fā)動(dòng)機(jī)的峰值壓力超過1000磅／平方英寸。就是這些峰值壓力使活塞發(fā)動(dòng)機(jī)必須采用結(jié)構(gòu)笨重的氣缸和高辛烷值燃油。相反，低辛烷值燃油和輕結(jié)構(gòu)的燃燒室用于渦輪發(fā)動(dòng)機(jī)。
4．圖2-2用最簡單的形式表示了燃?xì)鉁u輪發(fā)動(dòng)機(jī)運(yùn)行的工作循環(huán)。也即在壓力-體積圖上畫出來的循環(huán)。點(diǎn)A表示大氣壓下的空氣，它沿AB線得到壓縮。從B到C靠引入燃油并在等壓下燃燒向空氣加熱，因而空氣的體積增加很多。燃燒室(第4章)中的壓力損失用B和C間的壓降表示。從C到
D表示燃燒產(chǎn)生的燃?xì)馔ㄟ^渦輪和噴管膨脹并且排入大氣。在循環(huán)的這 一部分，膨脹燃?xì)庵械牟糠帜芰靠繙u輪轉(zhuǎn)變成機(jī)械功率；其余的能量，在它排入大氣時(shí)提供推進(jìn)噴氣流。
排氣
間歇的
排氣
燃燒
空氣／燃油進(jìn)入 壓縮
進(jìn)氣道
壓縮
連續(xù)的
燃燒
Working cycle and airflow
工作循環(huán)和氣流
燃燒(增加熱能)
圖2-1渦輪噴氣發(fā)動(dòng)機(jī)和活塞發(fā)動(dòng)機(jī)工作循環(huán)比較
Fig. 2-1 A comparison between the working cycle of a turbo-jet engine and a piston engine.
to use high octane fuels, in contrast to the low octane fuels and the light fabricated combustion chambers 壓力
used on the turbine engine.
4. The working cycle upon which the gas turbine engine functions is, in its simplest form, represented by the cycle shown on the pressure volume diagram in fig. 2-2. Point A represents air at atmospheric pressure that is compressed along the line AB. From B to C heat is added to the air by introducing and burning fuel at constant pressure, thereby consider-ably increasing the volume of air. Pressure losses in the combustion chambers (Part 4) are indicated by the drop between B and C. From C to D the gases resulting from combustion expand through the turbine and jet pipe back to atmosphere. During this part of the cycle, some of the energy in the Fig. 2-2 The working cycle on a pressure-expanding gases is turned into mechanical power by volume diagram. 膨脹(通過渦輪和噴管)
壓縮(增加壓力能)
外部空氣
容積
圖2-2 壓力體積圖上的工作循環(huán)
5.因?yàn)闇u輪噴氣發(fā)動(dòng)機(jī)是熱力發(fā)動(dòng)機(jī)，燃燒溫度愈高，燃?xì)馀蛎浀糜�。然而，燃燒溫度必須不超過渦輪部件的設(shè)計(jì)和材料所適合的渦輪燃?xì)膺M(jìn)口溫度值。
6．在渦輪部件中使用氣冷工作葉片允許更高的燃?xì)鉁囟�，從而得到更高的熱效率�?/p>
工作循環(huán)和氣流
Working cycle and airflow
the turbine; the remainder, on its discharge to THE RELATIONS BETWEEN PRESSURE, 壓力、體積和溫度間的關(guān)系
atmosphere, provides a propulsive jet. VOLUME AND TEMPERATURE
7.在渦輪發(fā)動(dòng)機(jī)的工作循環(huán)過程中，空氣流或“工作介質(zhì)”接受并放出熱量，從而引起其壓力、體積和溫度變化。這些變化在其發(fā)生時(shí)密切相關(guān)，因?yàn)樗鼈冏裱诓ㄒ翣柡筒槔锼菇M合定律中所闡述的一項(xiàng)共同的原理。簡言之，它意指，工作循環(huán)各階段中空氣的壓力和體積之乘積與這些階段中空氣的絕對溫度成正比。不論用什么方式來改變空氣的狀態(tài)，這一關(guān)系都能適用。例如，無論是通過燃燒或者壓縮來加入能量，或者通過渦輪來抽取能量，熱能的變化總是與加入到燃?xì)饣蛘邚娜細(xì)庵谐槿〉墓Τ烧取?br />
5.
Because the turbo-jet engine is a heat engine, the higher the temperature of combustion the greater is the expansion of the gases. The combustion temperature, however, must not exceed a value that gives a turbine gas entry temperature suitable for the design and materials of the turbine assembly.
6.
The use of air-cooled blades in the turbine assembly permits a higher gas temperature and a consequently higher thermal efficiency.
7. During the working cycle of the turbine engine, the airflow or 'working fluid' receives and gives up heat, so producing changes in its pressure, volume and temperature. These changes as they occur are closely related, for they follow a common principle that is embodied in a combination of the laws of Boyle and Charles. Briefly, this means that the product of the pressure and the volume of the air at the various stages in the working cycle is proportion-al to the absolute temperature of the air at those
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