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
圖10-15 燃油霧化的各個(gè)階段
91．與蒸發(fā)式噴嘴(第4章)不同，霧化噴嘴已發(fā)展成了5個(gè)不同的品種：即單油路噴嘴(Simplex)，可調(diào)進(jìn)口(Lubbock)噴嘴，雙油路噴嘴(Duplex或Duple)，溢流式和空氣霧化式噴嘴。
92．單油路噴嘴示于圖10-16，它首先在早期的噴氣發(fā)動(dòng)機(jī)上使用。它有一個(gè)內(nèi)腔，使燃油產(chǎn)生旋渦，還有個(gè)固定面積的霧化孔。這種燃油噴嘴，在較高的燃油流量，即在較高的燃油壓力時(shí)，能提供良好的霧化質(zhì)量。但是，在低的發(fā)動(dòng)機(jī)轉(zhuǎn)速以及尤其在高空狀態(tài)下，由于要求的油壓
93．目前看，可凋進(jìn)口燃油噴嘴(圖10-17)只有歷史價(jià)值，它采用了彈簧加載的活塞來控制旋渦室的進(jìn)口面積。在低的燃油流量下，活塞的移動(dòng)將該進(jìn)口部分地打開；在高流量下，進(jìn)口被完全打開。用這一方法，基本上克服了平方律壓力關(guān)系問題，在很寬的燃油流量范圍內(nèi)保持了良好的霧化。但是設(shè)計(jì)上存在固有的困難，如成套噴嘴的匹配，臟物顆粒使滑動(dòng)活塞卡滯等。這種類型的噴嘴最終被雙油路噴嘴所取代。
較低，這種噴嘴就很不適合。其原因是這種單油路噴嘴本質(zhì)上是種按“平方律”設(shè)計(jì)的噴嘴；即，燃油流過噴嘴的流量與噴嘴前后的壓力降的平方根成正比。這就是說，如果有效霧化的最小壓力是30磅／平方英寸，那么提供最大流量所需的壓力將大約為3000磅／平方英寸。在那個(gè)年代的燃油泵承受不了如此高的壓力，因而在克服平方律效應(yīng)的過程中便發(fā)展了可調(diào)噴口的噴嘴。
圖10-16 一種單油路燃油噴嘴(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sliding piston due to dirt particles were, however, difficulties inherent in the design, and this type was eventually superseded by the Duplex and the Duple fuel spray nozzles.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．雙油路噴嘴要求有一初級(jí)和一主燃油油路，有兩個(gè)獨(dú)立的孔，一個(gè)孔比另一個(gè)孔小很多。較小的孔處理低燃油流量，較大的孔隨著燃油壓力的增加供應(yīng)較高的燃油流量。這種噴嘴采用了一個(gè)增壓活門，將燃油分配到不同的油路(圖10-18)。當(dāng)燃油流量及壓力增加時(shí)，增壓活門移動(dòng)，逐漸使燃油進(jìn)入主油路和主油孔。這就使燃油由兩條油路合成一股，與單油路噴嘴相比，在相同的最大燃油壓力下用這種方法后雙油路噴嘴能夠在較寬的流量范圍內(nèi)
實(shí)現(xiàn)有效霧化。而且在高空條件下如果要求低燃油流量時(shí)，也可獲得有效的霧化。在組合式加速和轉(zhuǎn)速控制系統(tǒng)中(第51段)，向噴嘴的供油由燃油流量調(diào)節(jié)器分配。
95.溢流式燃油噴嘴可以說成是一個(gè)單油路噴嘴加上一條從旋渦室引出的通道，此通道將溢出的燃油引開。按照這種結(jié)構(gòu)，就可以在所有時(shí)間以高壓向旋禍?zhǔn)夜┯汀．?dāng)高度或發(fā)動(dòng)機(jī)轉(zhuǎn)速要求燃油減少時(shí)，更多的燃油就會(huì)從旋渦室溢出，只留較少部分流過霧化孔。溢流噴嘴總是使用比較高的壓力說明，即使在高空遇到的極低的燃油流量下，仍有足夠的旋渦保證燃油恒定和有效的霧化。
漩渦室
油濾
燃油壓力
壓氣機(jī)供氣
防止孔口積碳
的空氣流
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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