劳斯莱斯喷气引擎－中英(87)

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Propelling nozzle
14. The propelling nozzle is of similar material and construction as the jet pipe, to which it is secured as a separate assembly. A two-position propelling nozzle has two movable eyelids that are operated by actuators, or pneumatic rams, to give an open or closed position (para. 4.). A variable-area propelling nozzle has a ring of interlocking flaps that are hinged to the outer casing and may be enclosed by an outer shroud. The flaps are actuated by powered rams to the closed position, and by gas loads to the interme-diate or the open positions; control of the flap position is by a control unit and a pump provides the power to the rams (para. 18).
CONTROL SYSTEM
15.
It is apparent that two functions, fuel flow and propelling nozzle area, must be co-ordinated for sat-isfactory operation of the afterburner system, These functions are related by making the nozzle area dependent upon the fuel flow at the burners or vice-versa. The pilot controls the afterburner fuel flow or the nozzle area in conjunction with a compressor delivery/jet pipe pressure sensing device (a pressure ratio control unit). When the afterburner fuel flow is increased, the nozzle area increases; when the afterburner fuel flow decreases, the nozzle area is reduced. The pressure ratio control unit ensures the pressure ratio across the turbine remains unchanged and that the engine is unaffected by the operation of afterburning, regardless of the nozzle area and fuel flow.

16.
Since large fuel flows are required for afterburn-ing, an additional fuel pump is used. This pump is usually of the centrifugal flow or gear type and is energized automatically when afterburning is selected. The system is fully automatic and incorpo-rates 'fail safe' features in the event of an afterburner malfunction. The interconnection between the control system and afterburner jet pipe is shown diagram-matically in fig. 16-5.

173 17. When afterburning is selected, a signal is relayed to the afterburner fuel control unit. The unit determines the total fuel delivery of the pump and controls the distribution of fuel flow to the burner assembly. Fuel from the burners is ignited, resulting in an increase in jet pipe pressure (P6). This alters the pressure ratio across the turbine (P3/P6), and the exit area of the jet pipe nozzle is automatically increased until the correct PS/PS ratio has been restored. With a further increase in the degree of afterburning, the nozzle area is progressively increased to maintain a satisfactory P3/P6 ratio. Fig. 16-6 illustrates a typical afterburner fuel control system.

17.当选用加力时，信号传输给加力燃烧室燃油控制装置。该装置决定泵的总供油量，并且控制分配给喷嘴组件的燃油流量。喷嘴喷出的燃油点燃后，使喷管压力（P6）增加。这就改变了涡轮前后的压力比（P3/P6），喷管出口面积自动增加一直到正确的P3/P6比恢复。随着加力程度进一步加大，喷口面积也逐步增加以保持一个满意的P3/P6比。图16-6示出了一种典型的加力燃烧室燃油控制系统。

图16-4 典型的加力喷管设备
18. To operate the propelling nozzle against the large 'drag' loads imposed by the gas stream, a pump and either hydraulically or pneumatically operated rams are incorporated in the control system. The system shown in fig. 16-7 uses oil as the
18.操纵推进喷口时要克服燃气流作用的巨大“阻力”载荷，所以在控制系统中装有一个泵和液压或气压驱动的作动筒。图16-7所示的系统使用了滑油周围液压介质，但是有些系统使用燃油作为介质。喷管的移动是通过液压作动筒来实现的液压作动筒由一个滑油泵加压，泵的输出由从压力比控制装置来的操纵杆控制。在要求增加加力程度时，加力燃烧室燃油控制装置使燃油泵输出量相应增加，喷管压力（P6）因此增加，改变了涡轮前后的压力比(P3/P6)。压力比控制装置改变滑油泵的输出量，造成了在喷口鱼鳞片上的液压作动筒载荷与燃气载荷之间不平衡的状况。燃气载荷打开喷口以增加其出口面积，并且当喷口打开时，喷口面积的增加恢复了P3/P6比。压力比控制装置又改变滑油泵的输出量直到液压作动筒载荷及喷口鱼鳞片上的燃气载荷之间恢复平衡。

图16-5 简化的控制系统
Fig. 16-5 Simplified control system.
可变面积
推进喷管
加力燃烧室
推力的增加
 
19．由加力燃烧造成的推力的增加完全取决于燃油在燃烧之前和之后喷管绝对温度的比。例如：忽略由于加力燃烧室装置和燃气流动量变化造成的微小损失，增加的推力可按照下面的方法进行计算。
压力滑油
燃油进口
喷口
滑油泵
滑油进口
凸轮箱
加力燃烧室
燃油控制装置
加力燃烧室燃油
驾驶员操纵杆
压力比控制装置
停车
正常范围
加力燃烧室范围
hydraulic medium, but some systems use fuel. Nozzle movement is achieved by the hydraulic operating rams which are pressurized by an oil pump, pump output being controlled by a linkage from the pressure ratio control unit. When an increase in afterburning is selected, the afterburner fuel control unit schedules an increase in fuel pump output. The jet pipe pressure (P6) increases, altering the pressure ratio across the turbine (P3/P6). The pressure ratio control unit alters oil pump output, causing an out-of-balance condition between the hydraulic ram load and the gas load on the nozzle flaps. The gas load opens the nozzle to increase its exit area and, as the nozzle opens, the increase in nozzle area restores the P3/P6 ratio and the pressure ratio control unit alters oil pump output until balance is restored between the hydraulic rams and the gas loading on the nozzle flaps.
　
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