劳斯莱斯喷气引擎－中英(86)

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16-3): this latter method is known as 'hot-shot' ignition. Once combustion is initiated, the gas temperature increases and the expanding gases accelerate through the enlarged area propelling nozzle to provide the additional thrust.
9. In view of the high temperature of the gases entering the jet pipe from the turbine, it might be assumed that the mixture would ignite spontaneous-ly. This is not so, for although cool flames form at
10．为了使系统顺利的工作，需要有稳定的火焰，这种火焰在范围宽广的混合物浓度和燃气流量中均将能稳定地燃烧。这种混合物还必须能在所有的飞行条件下容易点燃，并且必须在极少压力损失的情况下维持燃烧。
 
结构
 
喷嘴
 
11．喷嘴系统由几个环形同心输油总管组成。总管用喷管内的支板支撑。燃油通过在支板中的供油管供到输油总管，然后通过燃油总管下游一侧的许多孔，把燃油喷射到几个火焰稳定器之间的火焰区。火焰稳定器为圆头的V型剖面环形圈，安装在燃油喷嘴的下游。另一种系统包括一个附加的分段输油总管，它安装在火焰稳定器中。如图16-4所示的典型的喷嘴和火焰稳定器便是以后一种系统为基础
的。

图16-3 几种加力燃烧的点火方式
Fig. 16-3 Methods of afterburning ignition.

推进喷管
 
14．推进喷管的材料和结构与喷管类似，作为一个独立的装置固定在喷管上。双位置的推进喷管有两个可移动的半圆形调节喷口，由作动筒或气压作动筒操纵。使它处于打开或关闭的位置(第4段)。面积可调的推进喷管有一圈联锁的鱼鳞片，鱼鳞片铰接到外壳上，并用一外罩罩上。鱼鳞片通过有动力的作动筒操纵到关小位置，靠气动载荷吹开到中间或打开位置；鱼鳞片位置的控制是通过控制装置完成的，泵向作动筒提供动力(第18段)。
13．一种类似于喷管材料的环形隔热屏常常被装在喷管内壁中以改善喷嘴后部的冷却。隔热屏由多段组成，用波纹状冷却板连接，形成了单独的一层。隔热屏的后部是一些搭接的耐火“板”，沿圆周铆接(图16-4)。隔热屏也防止燃烧的不稳定性产生过大的噪声和振动，这些过大的噪声和振动也会造成加力燃烧室装置的结构损坏。
控制系统

15．显而易见，为了使加力燃烧室系统达到满意的工作，燃油流量和推进喷管面积这两个功能必须协调一致。这两个功能是根据喷嘴的燃油流量来决定喷口面积而互相关连起来的，反过来也是一样。驾驶员控制加力燃油流量或喷口面积，它们是与压气机出口／喷管压力传感装置(压力比控制装置)连在一起的。当加力燃油流量增加时，喷口面积增加；当加力燃油流量减少，喷口面积也减小。无论喷口面积和燃油流量是多少，压力比控制装置均保证涡轮前后的压力比不变，并且也保证了发动机不受加力工作的影响。

16．由于加力燃烧需要较大的燃油流量，因此常使用额外的油泵。这种泵一般为离心式泵或齿轮式泵，当选用加力燃烧时能够自动供油。该系统为全自动的，在加力燃烧室失效时，具有“故障安全”的特点。控制系统和加力燃烧室喷管之间的相互连接以图解的方式示于图16-5。
temperatures up to 700 deg. C., combustion will not take place below 800 deg. C. If however, the conditions were such that spontaneous ignition could be effected at sea level, it is unlikely that it could be effected at altitude where the atmospheric pressure is low. The spark or flame that initiates combustion must be of such intensity that a light-up can be obtained at considerable altitudes.
10. For smooth functioning of the system, a stable flame that will burn steadily over a wide range of mixture strengths and gas flows is required. The mixture must also be easy to ignite under all conditions of flight and combustion must be maintained with the minimum loss of pressure.
CONSTRUCTION
Burners
11. The burner system consists of several circular concentric fuel manifolds supported by struts inside the jet pipe. Fuel is supplied to the manifolds by feed pipes in the support struts and sprayed into the flame area, between the flame stabilizers, from holes in the downstream edge of the manifolds. The flame stabilizers are blunt nosed V-section annular rings located downstream of the fuel burners. An alternative system includes an additional segmented fuel manifold mounted within the flame stabilizers. The typical burner and flame stabilizer shown in fig. 16-4 is based on the latter system.
Jet pipe
12.
The afterburning jet pipe is made from a heat-resistant nickel alloy and requires more insulation than the normal jet pipe to prevent the heat of combustion being transferred to the aircraft structure. The jet pipe may be of a double skin construction with the outer skin carrying the flight loads and the inner skin the thermal stresses; a flow of cooling air is often induced between the inner and outer skins. Provision is also made to accommodate expansion and contraction, and to prevent gas leaks at the jet pipe joints.

13.
A circular heatshield of similar material to the jet pipe is often fitted to the inner wall of the jet pipe to improve cooling at the rear of the burner section. The heatshield comprises a number of bands, linked by

cooling corrugations, to form a single skin. The rear of the heatshield is a series of overlapping 'tiles' riveted to the surrounding skin (fig. 16-4). The shield also prevents combustion instability from creating excessive noise and vibration, which in turn would cause rapid physical deterioration of the afterburner equipment.
　
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