71.当加速到较高的压力比P4／P1时，油门控制孔增大。减小了的压力允许压力比控制膜盒收缩，因
Fuel system
increases and the capsule moves the metering altitude is increased. This maintains the thrust 72．飞机高度的变化要求燃油流量发生变化，以满足发动机推力和飞机爬升的要求。正常情况下，高度增加会降低压力P1和P4，因此会打开压力比控制活门并使燃油流量调节器膜盒膨胀，以减小可调节流孔的面积，进而减少供油。但是，为了满足发动机推力和飞机爬升的要求，需要随着高度的增加增大P4／P1。这个功能是由微调活门和一个感受压力P1的膜盒来实现。当压力P1减小时，微调活门移过P1控制孔，以减小控制压力。该压力由控制膜盒感测，靠作用在压力比控制活门上的压力，控制膜盒能随着高度的增加延缓可调节流孔的关闭过程。这样在保持油门处于固定位置的情况下，满足了推力的要求。
sleeve to increase the V.M.O. area. The effect of requirement with the throttle at a fixed position.
opening the V.M.O. is to reduce the pressure difference and this is sensed by the pressure drop governor, which opens the pressure drop control orifice. The reduced system pressure difference is immediately sensed by the pressure drop spill valve, which moves towards the closed position and conse-quently increases the fuel output. The increased fuel flow accelerates the engine with a subsequent increase in pressure ratio (P4/P1). When the required pressure ratio is reached, the pressure ratio control valve opens and the F.F.R. capsule chamber pressure reduces. The capsule assembly expands, moving the V.M.O. sleeve to reduce the orifice area. The resultant increased pressure difference is sensed by the pressure drop control governor, which adjusts the pressure drop control orifice to a point at which the pressure drop spill valve gives a fuel output consistent with steady running requirements.
70.
During a rapid acceleration, the degree of overselling is mechanically controlled by the acceler-ation stop, which limits the movement of the pressure ratio control valve. A similar stop prevents the fuel supply from being completely cut off during a rapid deceleration.
71.
When accelerating to a higher P4/P1 ratio, the throttle control orifice is increased. The reduced pressure allows the pressure ratio control capsule to contract so that the valve contacts the acceleration stop. F.F.R. capsule chamber pressure increases and the capsule moves to increase the V.M.O. area. This action continues until the required P4/P1 ratio is reached. The increased P4 pressure allows the pressure ratio control capsule to re-expand and the valve to return to the steady running position.
72.
A change in altitude of the aircraft requires a variation in fuel flow to match the engine thrust and aircraft climb requirement. The normal effect of an altitude increase is to decrease the P1 and P4 pressures, thus opening the pressure ratio control valve and allowing the F.F.R. capsule to expand to reduce the V.M.O. area and, in consequence, the fuel flow. However, to match the engine thrust and aircraft climb requirement it is necessary to increase the P4/P1 ratio with increasing altitude. This is done by a trimmer valve and a capsule that is subjected to P1 pressure. As P1 pressure decreases, the trimmer valve moves across the P1 controlled orifice to reduce the control pressure. This is sensed by the control capsule, which, by acting on the pressure ratio control valve, slows the closure of the V.M.O. as
73.
To prevent the maximum L.P. compressor r.p.m. and engine gas temperature from being exceeded, a valve, known as the auxiliary throttling valve, is fitted in the outlet from the fuel pump, Under steady running conditions, the valve is held open by spring force, When limiting conditions are reached, the fuel flow is reduced in response to speed and temperature signals from the engine. The signals are amplified and passed to a rotary actuator that reduces the area of a variable restrictor. The effect of this is to increase the fuel pressure, which partially closes the throttling valve. H.P. fuel pressure acting on the face of the pressure drop spill valve is increased and the spill valve opens to reduce the fuel flow to the spray nozzles.
74.
H.P. shaft speed is also governed by the auxiliary throttling valve. Should other controlling devices fail and pump speed increases, the fuel pressure closes the throttling valve and opens the pressure drop spill valve to reduce the fuel flow.
75.
With the throttle closed, idling condition is determined by controlling the amount of air being vented through the idling adjuster and the ground idling solenoid valve, With both bleeds in operation, satisfactory flight idling for the air off-takes is ensured. By closing the solenoid valve a lower power condition for ground idling is obtained.
76.
This fuel system, like the combined acceleration and speed control system, has no pressurizing valve to divide the flow from the fuel pump into main and primary flows.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：劳斯莱斯喷气引擎－中英(56)
