通风／冷却空气
15.另一种连续元件传感器具有电容的性质，它有一根管子，管内装有绝缘材料，并有一导体穿中心而过。电压差施加在管子和中心导体之间。当温度增加时，绝缘材料的性能变化，电容值也产生相应的变化，这种电容值得变化就作为火警显示出来。
区域3空气出气口
后防火壁
区域1空气出气口
前防火壁
涡轮机匣冷却总管
减压门
径向传动整流罩
14.无论是热敏电阻还是热电偶探测器均具有十分适合这种应用的特性。热电偶含有两种不同的金属，它们连接在一起形成两个接点。当两个接点间的温差增大时，线路中产生一电动势，这一电动势触发发火警显示器。热敏电阻含有一种半导体材料，这种材料的电阻随温度的增加而变化，且使线路中的电流产生相应的变化。正是这种电流的变化启动报警指示器。热敏电阻可用作一种单点探测器或一种连续元件传感器。
区域1
空气进口
区域3进气槽
区域3进气槽
挂架分流嚣整流罩
图14-2 涡轮风扇发动机的冷却与通风
Fig. 14-2 Cooling and ventilation - turbo-fan engine.
warning displays. The thermistor consists of a semi-temperature increases, with a corresponding change conductor material whose resistance changes as in the current flowing in the circuit. It is this change in
火灾包容
19.发动机起火必须要包容在动力装置内，不能让火蔓延至飞机的其它部分。环绕发动机的整流罩通常是由铝合金制成的，所以当飞机处于静态时，它包不住火。但是在飞行中，整流罩周围的气流提供了充分的冷却空气，使得它们能防火。不受冷却气流影响的防火隔板和整流罩，以及可能起火烧着的某些出口周围的整流罩段，通常是用钢或钛材料制成的。
17.在高马赫数下，急剧升高的温度可能会使热敏电阻或热电偶火灾探测系统工作不良。因此探测器升高或者温升率探测器被证明是最适用的。
18.上述各类探测器的替代物是监视探测器。它们对起火的光辐射产生感应。它们能被制造成敏感度非常之高，以致于仅对煤油起火辐射出的紫外线和红外线产生感应。
the current that operates the warning indicators. A thermistor may be used as a single point detector or as a continuous element sensor.
15.
Another form of continuous element sensor takes the form of a capacitor consisting of a tube containing a dielectric material with a conductor running through the centre. A voltage difference is applied between the tube and the centre conductor. As the temperature increases then the properties of the dielectric change with a corresponding change in the value of capacitance. This change of capacitance is displayed as a fire warning.
16.
The gas filled detector consists of stainless steel tubing filled with gas absorbent material and in the event of a fire or overheat condition the temperature rise will cause the core of the sensing loop to expel the absorbed active gas into the sealed tube causing a rapid increase in pressure. This build up of pressure is sensed by the detector alarm switch. Should the sensing loop become damaged causing a loss of the pressurized gas, an integrity switch will indicate a detection loop fault on the appropriate engine. Fire indication is given by a warning light and bell.
Fire protection
17.
At high Mach numbers, the considerably higher temperature levels may be such as to render the thermistor or thermocouple fire detection system unsatisfactory. Thermal detectors that sense either a temperature rise, or a rate of temperature rise, may therefore prove most suitable.
18.
Alternatives to the above types are surveillance detectors that respond to light radiation from a fire. These may be made so sensitive that they respond only to the ultra-violet and infra-red rays emitted from a kerosine fire.
FIRE CONTAINMENT
19. An engine fire must be contained within the power plant and not be allowed to spread to other parts of the aircraft. The cowlings that surround the engine are usually made of aluminium alloys, which would be unable to contain a fire when the aircraft is static. During flight, however, the airflow around the cowlings provides sufficient cooling to render them fireproof. Fireproof bulkheads and any cowlings that are not affected by a cooling airflow, and sections of cowlings around certain outlets that may act as 'flame-holders', are usually manufactured from steel or titanium.
图14-3 一种连续元件火灾探测系统
22.用于扑灭发动机着火的灭火剂一般是一种氟氯烷(氟利昂)化合物。灭火剂装在增压灭火瓶内且放置在着火危险区之外。当人工操作有关电气线路时，灭火剂从灭火瓶经过系列多孔喷射管或喷嘴喷射到火上(图14-4)。喷射必须足以供应预定浓度的灭火剂，持续时间0.5秒至2秒。通常这种系统是一个可单独喷洒两次的灭火系统。
Fire protection
发动机过热探测
23.涡轮过热不会构成严重的起火危险。但是，探测出过热情况是很重要的，这样可使驾驶员在出现机械或材料损害之前将发动机停车。
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