Patent GB-735643-A (GB)
Title: Improvements in or relating to fuel systems for gas-turbine engines
Inventor: DAVIES DAVID OMRI
IPC: F02C7/22
Filed: 1952-06-17
Abstract: 735,643. Gas turbine plant. ROLLS-ROYCE, Ltd. June 5, 1953 [June 17, 1952], No. 15279/52. Addition to 651,599. Class 110 (3). [Also in Group XXIX] In a gas turbine engine fuel system as claimed in the parent Specification, means are provided to vary the ratio of the load dependent on the compressor delivery pressure to the corresponding value of the compressor delivery pressure, which means comprises a conduit leading from the compressor delivery to a point of lower pressure associated with the compressor containing two restricting means arranged in series, adjustable means to vary the ratio of the pressure in the conduit between the two restricting means to the compressor delivery pressure and a second conduit connecting the conduit between the two restricting means to the pressure responsive means of the fuel system. A point of lower pressure associated with the compressor is stated to mean the atmosphere or the inlet or an intermediate stage of the compressor. The invention is described with reference to the fuel system shown in Fig. 4 of Specification 651,599, part of which is shown in Fig. 1 and which comprises a half-ball element 115 controlling the bleed flow from a servo mechanism for adjusting the stroke of the plungers of a multi-plunger fuel pump. The element 115 is carried by a lever 114 which is operated by a rocking lever 175 carried by a flexible diaphragm 174. The lever 175 is subject to the load of a spring 190, a load due to a diaphragm 185 responsive to the pressure drop across a linear flow valve in the fuel supply line and a load due to the diaphragm 179 which is dependent upon the instantaneous compressor delivery pressure. The arrangement is such that the maximum value of the fuel flow to the engine at each instant is dependent upon the instantaneous value of the compressor delivery pressure and increases as the delivery pressure increases. To prevent over-fuelling it is necessary to limit the rate of fuel flow at low rotational speeds during acceleration to a lower value in relation to the compressor delivery. pressure than at high rotational speeds. This is effected by bleeding air from the delivery of the compressor and passing it through a conduit 78a containing a pair of flow restrictors 78b, 78c and a flow control valve 78d, and connecting a point in the conduit 78a between the restrictors to the chamber 179a. The valve 78d is controlled by servomechanism 78f in accordance with engine rotational speed so that at low speeds the valve 78d is fully open, at intermediate speeds it is gradually closed and at high speeds is fully closed. As the valve 78d closes the ratio of the pressure in the conduit 78a between the restrictors 78b, 78c to the compressor delivery pressure increases. In a modification the valve 78d is replaced by a needle valve which cooperates with the flow restrictor 78c. The needle valve may be given a particular shape to vary the required ratio during its movement. In a further modification, the valve 78d is actuated by a solenoid 78k, Fig. 3, energized by a switch 78j which is closed by a speedresponsive device at a predetermined speed. The speed-responsive device may comprise a diaphragm 78l movable against a spring 78m by being subject to the pressure drop across an orifice 78n fed with liquid by an engine driven fixed-capacity positive displacement pump 78p. The adjusting means may be controlled in accordance with the compressor compression ratio or corrected rotational speed N/#T where N is the rotational speed and T the inlet temperature to the compressor instead of by speed. Specifications 666,290, 704,849, 704,850, 713,436 also are referred to.