工作循环
2．燃气涡轮发动机的工作循环类似于4冲程活塞发动机。然而，在燃气涡轮发动机中，燃烧在等压下进行，而在活塞发动机中，燃烧时体积不变。这两种发动机循环(图2-1)表明每一种循环里都有进气、压缩、燃烧和排气。这些过程在活塞发动机中是间歇性的，而在燃气涡轮中是连续进行的。活塞发动机只有一个冲程用于产生功率，其余冲程用于工作流体的充填、压缩和排放。相反，涡轮发动机取消了三个“不做功”冲程，因而能在更短时间内燃烧更多的燃油；所以，就一给定尺寸的发动机而言，它产生更大的功率输出。
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.由于涡轮发动机的连续作用和燃烧室不是一个封闭空间这一事实，在燃烧过程中，空气压力不象在活塞发动机中那样上升，而其体积却要增加。这种过程称之为等压加热。在这些状态下，没有峰值压力或波动压力要承受。而活塞发动机的峰值压力超过1000磅／平方英寸。就是这些峰值压力使活塞发动机必须采用结构笨重的气缸和高辛烷值燃油。相反，低辛烷值燃油和轻结构的燃烧室用于涡轮发动机。
4．图2-2用最简单的形式表示了燃气涡轮发动机运行的工作循环。也即在压力-体积图上画出来的循环。点A表示大气压下的空气，它沿AB线得到压缩。从B到C靠引入燃油并在等压下燃烧向空气加热，因而空气的体积增加很多。燃烧室(第4章)中的压力损失用B和C间的压降表示。从C到
D表示燃烧产生的燃气通过涡轮和喷管膨胀并且排入大气。在循环的这 一部分，膨胀燃气中的部分能量靠涡轮转变成机械功率；其余的能量，在它排入大气时提供推进喷气流。
排气
间歇的
排气
燃烧
空气／燃油进入 压缩
进气道
压缩
连续的
燃烧
Working cycle and airflow
工作循环和气流
燃烧(增加热能)
图2-1涡轮喷气发动机和活塞发动机工作循环比较
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 压力
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. 膨胀(通过涡轮和喷管)
压缩(增加压力能)
外部空气
容积
图2-2 压力体积图上的工作循环
5.因为涡轮喷气发动机是热力发动机，燃烧温度愈高，燃气膨胀得愈多。然而，燃烧温度必须不超过涡轮部件的设计和材料所适合的涡轮燃气进口温度值。
6．在涡轮部件中使用气冷工作叶片允许更高的燃气温度，从而得到更高的热效率。
工作循环和气流
Working cycle and airflow
the turbine; the remainder, on its discharge to THE RELATIONS BETWEEN PRESSURE, 压力、体积和温度间的关系
atmosphere, provides a propulsive jet. VOLUME AND TEMPERATURE
7.在涡轮发动机的工作循环过程中，空气流或“工作介质”接受并放出热量，从而引起其压力、体积和温度变化。这些变化在其发生时密切相关，因为它们遵循在波伊尔和查里斯组合定律中所阐述的一项共同的原理。简言之，它意指，工作循环各阶段中空气的压力和体积之乘积与这些阶段中空气的绝对温度成正比。不论用什么方式来改变空气的状态，这一关系都能适用。例如，无论是通过燃烧或者压缩来加入能量，或者通过涡轮来抽取能量，热能的变化总是与加入到燃气或者从燃气中抽取的功成正比。
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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