92.
The Simplex spray nozzle shown in fig. 10-16 was first used on early jet engines. It consists of a chamber, which induces a swirl into the fuel, and a fixed-area atomizing orifice. This fuel spray nozzle gave good atomization at the higher fuel flows, that
图10-15 燃油雾化的各个阶段
91．与蒸发式喷嘴(第4章)不同，雾化喷嘴已发展成了5个不同的品种：即单油路喷嘴(Simplex)，可调进口(Lubbock)喷嘴，双油路喷嘴(Duplex或Duple)，溢流式和空气雾化式喷嘴。
92．单油路喷嘴示于图10-16，它首先在早期的喷气发动机上使用。它有一个内腔，使燃油产生旋涡，还有个固定面积的雾化孔。这种燃油喷嘴，在较高的燃油流量，即在较高的燃油压力时，能提供良好的雾化质量。但是，在低的发动机转速以及尤其在高空状态下，由于要求的油压
93．目前看，可凋进口燃油喷嘴(图10-17)只有历史价值，它采用了弹簧加载的活塞来控制旋涡室的进口面积。在低的燃油流量下，活塞的移动将该进口部分地打开；在高流量下，进口被完全打开。用这一方法，基本上克服了平方律压力关系问题，在很宽的燃油流量范围内保持了良好的雾化。但是设计上存在固有的困难，如成套喷嘴的匹配，脏物颗粒使滑动活塞卡滞等。这种类型的喷嘴最终被双油路喷嘴所取代。
较低，这种喷嘴就很不适合。其原因是这种单油路喷嘴本质上是种按“平方律”设计的喷嘴；即，燃油流过喷嘴的流量与喷嘴前后的压力降的平方根成正比。这就是说，如果有效雾化的最小压力是30磅／平方英寸，那么提供最大流量所需的压力将大约为3000磅／平方英寸。在那个年代的燃油泵承受不了如此高的压力，因而在克服平方律效应的过程中便发展了可调喷口的喷嘴。
图10-16 一种单油路燃油喷嘴(Simplex)
Fig. 10-16 A Simplex fuel spray nozzle.
is, at the higher fuel pressures, but was very unsatis-factory at the low pressures required at low engine speeds and especially at high altitudes. The reason for this is that the Simplex was, by the nature of its design, a 'square law' spray nozzle; that is, the flow through the nozzle is proportional to the square root of the pressure drop across it. This meant that if the minimum pressure for effective atomization was 30 lb. per square inch, the pressure needed to give maximum flow would be about 3,000 lb. per square inch. The fuel pumps available at that time were unable to cope with such high pressures so the variable port spray nozzle was developed in an effort to overcome the square law effect.
93. Although now only of historical value, the variable port or Lubbock fuel spray nozzle (fig. 10-17) made use of a spring-loaded piston to control the area of the inlet ports to the swirl chamber. At low fuel flows, the ports were partly uncovered by the movement of the piston; at high flows, they were fully open. By this method, the square law pressure rela-tionship was mainly overcome and good atomization was maintained over a wide range of fuel flows. The matching of sets of spray nozzles and the sticking of the sliding piston due to dirt particles were, however, difficulties inherent in the design, and this type was eventually superseded by the Duplex and the Duple fuel spray nozzles.
94. The Duplex and the Duple spray nozzles require a primary and a main fuel manifold and have two independent orifices, one much smaller than the other. The smaller orifice handles the lower flows and the larger orifice deals with the higher flows as the fuel pressure increases. A pressurizing valve may be employed with this type of spray nozzle to apportion the fuel to the manifolds (fig. 10-18). As the fuel flow 94．双油路喷嘴要求有一初级和一主燃油油路，有两个独立的孔，一个孔比另一个孔小很多。较小的孔处理低燃油流量，较大的孔随着燃油压力的增加供应较高的燃油流量。这种喷嘴采用了一个增压活门，将燃油分配到不同的油路(图10-18)。当燃油流量及压力增加时，增压活门移动，逐渐使燃油进入主油路和主油孔。这就使燃油由两条油路合成一股，与单油路喷嘴相比，在相同的最大燃油压力下用这种方法后双油路喷嘴能够在较宽的流量范围内
实现有效雾化。而且在高空条件下如果要求低燃油流量时，也可获得有效的雾化。在组合式加速和转速控制系统中(第51段)，向喷嘴的供油由燃油流量调节器分配。
95.溢流式燃油喷嘴可以说成是一个单油路喷嘴加上一条从旋涡室引出的通道，此通道将溢出的燃油引开。按照这种结构，就可以在所有时间以高压向旋祸室供油。当高度或发动机转速要求燃油减少时，更多的燃油就会从旋涡室溢出，只留较少部分流过雾化孔。溢流喷嘴总是使用比较高的压力说明，即使在高空遇到的极低的燃油流量下，仍有足够的旋涡保证燃油恒定和有效的雾化。
漩涡室
油滤
燃油压力
压气机供气
防止孔口积碳
的空气流
切向孔
Fuel system
and pressure increases, the pressurizing valve moves to progressively admit fuel to the main manifold and the main orifices. This gives a combined flow down both manifolds. In this way, the Duplex and Duple nozzles are able to give effective atomization over a wider flow range than the Simplex spray nozzle for the same maximum fuel pressure. Also, efficient atomization is obtained at the low flows that may be required at high altitude. In the combined acceleration and speed control system (para. 51), the fuel flow to the spray nozzles is apportioned in the F.F.R.
95.
The spill type fuel spray nozzle can be described as being a Simplex spray nozzle with a passage from the swirl chamber for spilling fuel away. With this arrangement it is possible to supply fuel to the swirl chamber at a high pressure all the time, As the fuel demand decreases with altitude or reduction in engine speed, more fuel is spilled away from the swirl Chamber, leaving less to pass through the atomizing orifice. The spill spray nozzles' constant use of a relatively high pressure means that even at the extremely low fuel flows that occur at high altitude there is adequate swirl to provide constant and efficient atomization of the fuel.
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