86.燃油泵由發動機齒輪系驅動，其輸出量取決于其轉速及柱塞的行程。單臺燃油泵每小時可供油100-200加侖，最大油壓約為2000磅/平方英寸左右。驅動這一油泵可能需要60馬力。
Fig. 10-14 A plunger-type fuel pump.
圖10-l4 一種柱塞式燃油泵
87．燃油泵由一個裝有若干柱塞的轉子組件構成。柱塞的端頭從其孔中向外突出，頂在不旋轉的凸輪盤上。由于凸輪盤的斜度，轉子的運動使各個柱塞作往復運動，由此產生了泵的作用。柱塞的行程由凸輪盤的傾斜角決定。傾斜的度數依據伺服活塞的運動而改變。伺服活塞與凸輪盤機械相連，由彈簧力使之壓到一端，使柱塞選到全行程位置。活塞在彈簧那一側受伺服壓力，另一側受油泵供油壓力；因而伺服活塞前后壓力差的變化會使它發生移動相應地使凸輪盤角度發生變化，進而改變油泵行程。
齒輪式燃油泵
88．齒輪式燃油泵(圖10-12)由發動機驅動，其輸出量與其轉速成正比。向噴嘴供應的燃油流量通過將過量的供油返回到進口來控制。溢流活門感受系統中的控制裝置前后的壓力差，按需要開、關，以增加或減少回油。
燃油噴嘴
89．燃油噴嘴是燃油系統中最終的組件。其基本功能是執行燃油霧化或汽化的任務，以保證燃油快速燃燒。當考慮到來自壓氣機的空氣流的速度以及應當在其中完成燃燒的燃燒系統(第4章)的長度很短，這一過程中的諸多困難是很容易明白的。
90．燃油霧化的早期方法是將其通過一個旋渦室，在此處切向分布的孔或槽通過將壓力能轉變為動能使燃油產生旋渦。在這種情況下，燃油經過出油孔，旋渦消除。使燃油霧化形成了錐形噴油。這被稱之為“壓力噴射霧化”。對于良好的霧化來說，燃油噴嘴中燃油的旋渦程度和壓力是重要因素。噴射的形狀是霧化程度的指標，如圖10-15所示。后來的燃油噴嘴采用了空氣噴霧原理，它使用高速的空氣取代高速的燃油來進行霧化。這種方法可以在低的燃油流量下使燃抽霧化(只要具備足夠的空氣速度)。因此，與壓力噴嘴相比其優點是可以使用輕結構的燃油泵。
Fuel system
square inch. To drive this pump, as much as 60 horsepower may be required.
87. The fuel pump consists of a rotor assembly fitted with several plungers, the ends of which project from their bores and bear on to a non-rotating camplate. Due to the inclination of the camplate, movement of the rotor imparts a reciprocating motion to the plungers, thus producing a pumping action. The stroke of the plungers is determined by the angle of inclination of the camplate. The degree of inclination is varied by the movement of a servo piston that is mechanically linked to the camplate and is biased by springs to give the full stroke position of the plungers. The piston is subjected to servo pressure on the spring side and on the other side to pump delivery pressure; thus variations in the pressure difference across the servo piston cause it to move with corresponding variations of the camplate angle and, therefore, pump stroke.
Gear-type fuel pump
88. The gear-type fuel pump (fig. 10-12) is driven from the engine and its output is directly proportional to its speed. The fuel flow to the spray nozzles is controlled by recirculating excess fuel delivery back to inlet. A spill valve, sensitive to the pressure drop across the controlling units in the system, opens and closes as necessary to increase or decrease the spill.
FUEL SPRAY NOZZLES
89.
The final components of the fuel system are the fuel spray nozzles, which have as their essential function the task of atomizing or vaporizing the fuel to ensure its rapid burning. The difficulties involved in this process can be readily appreciated when one considers the velocity of the air stream from the compressor and the short length of combustion system (Part 4) in which the burning must be completed.
90.
An early method of atomizing the fuel is to pass it through a swirl chamber where tangentially disposed holes or slots imparted swirl to the fuel by converting its pressure energy to kinetic energy. In this state, the fuel is passed through the discharge orifice which removes the swirl motion as the fuel is atomized to form a cone-shaped spray. This is called 'pressure jet atomization'. The rate of swirl and pressure of the fuel at the fuel spray nozzle are important factors in good atomization. The shape of the spray is an indication of the degree of atomization as shown in fig. 10-15. Later fuel spray nozzles utilize the airspray principle which employs
在中等燃油壓力下薄膜在邊緣處破裂形成“喇叭口”的形狀
在低燃油壓力下形成了稱為‘油泡’的連續油膜
high velocity air instead of high velocity fuel to cause atomization. This method allows atomization at low fuel flow rates (provided sufficient air velocity exists) thus providing an advantage over the pressure jet atomizer by allowing fuel pumps of a lighter con-struction to be used.
91.
The atomizing spray nozzle, as distinct from the vaporizing burner (Part 4), has been developed in five fairly distinct types; the Simplex, the variable port (Lubbock), the Duplex or Duple, the spill type and the airspray nozzle.
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