86.燃油泵由发动机齿轮系驱动，其输出量取决于其转速及柱塞的行程。单台燃油泵每小时可供油100-200加仑，最大油压约为2000磅/平方英寸左右。驱动这一油泵可能需要60马力。
Fig. 10-14 A plunger-type fuel pump.
图10-l4 一种柱塞式燃油泵
87．燃油泵由一个装有若干柱塞的转子组件构成。柱塞的端头从其孔中向外突出，顶在不旋转的凸轮盘上。由于凸轮盘的斜度，转子的运动使各个柱塞作往复运动，由此产生了泵的作用。柱塞的行程由凸轮盘的倾斜角决定。倾斜的度数依据伺服活塞的运动而改变。伺服活塞与凸轮盘机械相连，由弹簧力使之压到一端，使柱塞选到全行程位置。活塞在弹簧那一侧受伺服压力，另一侧受油泵供油压力；因而伺服活塞前后压力差的变化会使它发生移动相应地使凸轮盘角度发生变化，进而改变油泵行程。
齿轮式燃油泵
88．齿轮式燃油泵(图10-12)由发动机驱动，其输出量与其转速成正比。向喷嘴供应的燃油流量通过将过量的供油返回到进口来控制。溢流活门感受系统中的控制装置前后的压力差，按需要开、关，以增加或减少回油。
燃油喷嘴
89．燃油喷嘴是燃油系统中最终的组件。其基本功能是执行燃油雾化或汽化的任务，以保证燃油快速燃烧。当考虑到来自压气机的空气流的速度以及应当在其中完成燃烧的燃烧系统(第4章)的长度很短，这一过程中的诸多困难是很容易明白的。
90．燃油雾化的早期方法是将其通过一个旋涡室，在此处切向分布的孔或槽通过将压力能转变为动能使燃油产生旋涡。在这种情况下，燃油经过出油孔，旋涡消除。使燃油雾化形成了锥形喷油。这被称之为“压力喷射雾化”。对于良好的雾化来说，燃油喷嘴中燃油的旋涡程度和压力是重要因素。喷射的形状是雾化程度的指标，如图10-15所示。后来的燃油喷嘴采用了空气喷雾原理，它使用高速的空气取代高速的燃油来进行雾化。这种方法可以在低的燃油流量下使燃抽雾化(只要具备足够的空气速度)。因此，与压力喷嘴相比其优点是可以使用轻结构的燃油泵。
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
在中等燃油压力下薄膜在边缘处破裂形成“喇叭口”的形状
在低燃油压力下形成了称为‘油泡’的连续油膜
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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