5.加力燃燒的發動機的推力，在沒有加力燃燒時,比沒有裝加力燃燒設備的類似發動機的推力稍微小一些；這是因為在噴管中增加了流體阻力。由于較重的噴管和加力燃燒設備，動力裝置的總重量也增加了。
4.對同一種發動機來說，加力燃燒的噴管面積要比正常噴管的面積大以獲得速度減低了的氣流。為了在各種情況下工作，加力燃燒的噴管裝有一個雙位或可變面積的噴口(圖16-2)。噴口在非加力工作時是關小的，但當選擇加力燃燒時，燃氣溫度增加，噴口打開，使出口面積適合燃氣氣流容積的增加。這樣就避免了噴管壓力的增加，噴管的壓力增加會影響發動機的性能。這樣還能使加力燃燒在發動機轉速的廣大范圍內加以使用。
6.在低涵道比發動機中實現加力燃燒是先將外涵氣流和渦輪氣流混合，然后噴入加力燃油，并到達穩定器系統，所以燃燒是在混合好的排氣流中進行。另一種方法是分別在外涵道氣流和渦輪氣流中噴入燃油并穩定燃燒，使可用的燃氣燃燒并在最后的噴口處達到共同的出口溫度。采用這種方法，燃油按計劃分別向每股氣流噴注，而且，通常在熱氣流和冷氣流中的火焰穩定器之間形成某種形式的相 接，以促進外涵道冷空氣流中的燃燒過程。
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. 加力燃燒的工作
7.從發動機渦輪出來的燃氣流以每秒750-1,200英尺的速度進入噴管。但是由于這種速度太高，無法維持穩定的火焰。所以在氣流進入加力燃燒的燃燒區之前，先行擴壓，也就是說降低氣流速度和增加壓力。然而，因為在正常的混合比狀態下，燃燒...煤油速度只有每秒幾英尺，所以即使在擴壓的...氣流中，任何點燃的燃油也會被吹滅。因此將火焰穩定器（蒸汽槽）設于燃油噴嘴的下游，提供了一個氣流漩渦形成的區域以幫助燃燒，并且在此區域...地燃氣速度進一步降低到燃燒在進行時火焰...能穩定。
圖16-2 加力噴管與推進噴口舉例
Fig. 16-2 Examples of afterburning jet pipes and propelling nozzles.
互鎖魚鱗板
可變面積噴口
驅動套筒
加力燃燒室噴管
噴口作動筒
雙位噴口
半圓式調節噴口作動筒
可移動的半圓式調節噴口
加力燃燒室噴管
9.由于燃氣流沖渦輪進入噴管時的溫度很高，或者人們設想混合物會自發點燃。實際上并非如此，因為盡管冷火焰可在700℃的溫度時形成，但是燃燒在800℃一下是不可能進行的。即使在海平面時的發生自發點火的話，那么在大氣壓低的高空就不可能了。點燃燃燒的火花或火焰必須有相當大的強度才能使點火工作在很高的高空成功。
8.霧化的燃油通過一些噴嘴射到噴管內，這些噴嘴的布局能使燃油均勻地分布在火焰區域。燃燒是靠催化劑點火器引發的，點火器產生的火焰是由于噴射在鉑基元件上的燃油空氣混合物的化學反應形成的；或利用噴嘴附近的點火電嘴或從發動機燃燒室內生成的火焰熱流（圖16-3）引燃而成；后一種方法被稱之為“熱射流”點火。一旦燃燒開始，燃氣溫度就會升高，燃氣通過面積擴大的推進噴管膨脹加速以產生額外的推力。
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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