5.加力燃烧的发动机的推力，在没有加力燃烧时,比没有装加力燃烧设备的类似发动机的推力稍微小一些；这是因为在喷管中增加了流体阻力。由于较重的喷管和加力燃烧设备，动力装置的总重量也增加了。
4.对同一种发动机来说，加力燃烧的喷管面积要比正常喷管的面积大以获得速度减低了的气流。为了在各种情况下工作，加力燃烧的喷管装有一个双位或可变面积的喷口(图16-2)。喷口在非加力工作时是关小的，但当选择加力燃烧时，燃气温度增加，喷口打开，使出口面积适合燃气气流容积的增加。这样就避免了喷管压力的增加，喷管的压力增加会影响发动机的性能。这样还能使加力燃烧在发动机转速的广大范围内加以使用。
6.在低涵道比发动机中实现加力燃烧是先将外涵气流和涡轮气流混合，然后喷入加力燃油，并到达稳定器系统，所以燃烧是在混合好的排气流中进行。另一种方法是分别在外涵道气流和涡轮气流中喷入燃油并稳定燃烧，使可用的燃气燃烧并在最后的喷口处达到共同的出口温度。采用这种方法，燃油按计划分别向每股气流喷注，而且，通常在热气流和冷气流中的火焰稳定器之间形成某种形式的相 接，以促进外涵道冷空气流中的燃烧过程。
4.
The area of the afterburning jet pipe is larger than a normal jet pipe would be for the same engine, to obtain a reduced velocity gas stream. To provide for operation under all conditions, an afterburning jet pipe is fitted with either a two-position or a variable-area propelling nozzle (fig. 16-2). The nozzle is closed during non-afterburning operation, but when afterburning is selected the gas temperature increases and the nozzle opens to give an exit area suitable for the resultant increase in the volume of the gas stream. This prevents any increase in pressure occurring in the jet pipe which would affect the functioning of the engine and enables afterburn-ing to be used over a wide range of engine speeds.
5.
The thrust of an afterburning engine, without afterburning in operation, is slightly less than that of a similar engine not fitted with afterburning equipment; this is due to the added restrictions in the jet pipe. The overall weight of the power plant is also increased because of the heavier jet pipe and after-burning equipment.
6.
Afterburning is achieved on low by-pass engines by mixing the by-pass and turbine streams before the afterburner fuel injection and stabilizer system is reached so that the combustion takes place in the
mixed exhaust stream. An alternative method is to inject the fuel and stabilize the flame in the individual by-pass and turbine streams, burning the available gases up to a common exit temperature at the final nozzle. In this method, the fuel injection is scheduled separately to the individual streams and it is normal to provide some form of interconnection between the flame stabilizers in the hot and cold streams to assist the combustion processes in the cold by-pass air.
OPERATION OF AFTERBURNING
7. The gas stream from the engine turbine enters the jet pipe at a velocity of 750 to 1,200 feet per second, but as this velocity is far too high for a stable flame to be maintained, the flow is diffused before it enters the afterburner combustion zone, i.e. the flow velocity is reduced and the pressure is increased. However, as the speed of burning kerosine at normal mixture ratios is only a few feet per second, any fuel lit even in the diffused air stream would be blown away. A form of flame stabilizer (vapour gutter) is, therefore, located downstream of the fuel burners to provide a region in which turbulent eddies are formed to assist combustion and where the local gas velocity is further reduced to a figure at which flame stabi-lization occurs whilst combustion is in operation. 加力燃烧的工作
7.从发动机涡轮出来的燃气流以每秒750-1,200英尺的速度进入喷管。但是由于这种速度太高，无法维持稳定的火焰。所以在气流进入加力燃烧的燃烧区之前，先行扩压，也就是说降低气流速度和增加压力。然而，因为在正常的混合比状态下，燃烧...煤油速度只有每秒几英尺，所以即使在扩压的...气流中，任何点燃的燃油也会被吹灭。因此将火焰稳定器（蒸汽槽）设于燃油喷嘴的下游，提供了一个气流漩涡形成的区域以帮助燃烧，并且在此区域...地燃气速度进一步降低到燃烧在进行时火焰...能稳定。
图16-2 加力喷管与推进喷口举例
Fig. 16-2 Examples of afterburning jet pipes and propelling nozzles.
互锁鱼鳞板
可变面积喷口
驱动套筒
加力燃烧室喷管
喷口作动筒
双位喷口
半圆式调节喷口作动筒
可移动的半圆式调节喷口
加力燃烧室喷管
9.由于燃气流冲涡轮进入喷管时的温度很高，或者人们设想混合物会自发点燃。实际上并非如此，因为尽管冷火焰可在700℃的温度时形成，但是燃烧在800℃一下是不可能进行的。即使在海平面时的发生自发点火的话，那么在大气压低的高空就不可能了。点燃燃烧的火花或火焰必须有相当大的强度才能使点火工作在很高的高空成功。
8.雾化的燃油通过一些喷嘴射到喷管内，这些喷嘴的布局能使燃油均匀地分布在火焰区域。燃烧是靠催化剂点火器引发的，点火器产生的火焰是由于喷射在铂基元件上的燃油空气混合物的化学反应形成的；或利用喷嘴附近的点火电嘴或从发动机燃烧室内生成的火焰热流（图16-3）引燃而成；后一种方法被称之为“热射流”点火。一旦燃烧开始，燃气温度就会升高，燃气通过面积扩大的推进喷管膨胀加速以产生额外的推力。
8. An atomized fuel spray is fed into the jet pipe through a number of burners, which are so arranged as to distribute the fuel evenly over the flame area. Combustion is then initiated by a catalytic igniter, which creates a flame as a result of the chemical reaction of the fuel/air mixture being sprayed on to a platinum-based element, by an igniter plug adjacent to the burner, or by a hot streak of flame that originates in the engine combustion chamber (fig.
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