Patent GB-781961-A (GB)
Title: Improvements in or relating to fuel control for turbo power plants
Inventor: BEST STANLEY GORDON
IPC: F02K3/00
Filed: 1953-01-06
Abstract: 781,961. Gas turbine plant. UNITED AIRCRAFT CORPORATION. Jan. 6, 1953, No. 438/53. Class 110 (3). [Also in Group XXIX] A fuel control system for gas turbine power plants comprises a throttle valve 70 arranged between a source of fuel under pressure and the combustion chambers, the opening of the throttle valve being varied in accordance with the product of the movements of two devices one of which operates in accordance with compressor delivery pressure and the other in accordance with turbine speed and being limited by the conjoint effect of two engine operating variables, e.g. turbine speed and compressor inlet temperature. A pipe 74, Fig. 2, leading to the combustion nozzles is supplied through a pipe 66 and the throttle valve 70 by the pumps 50, 52. The pressure drop across the valve 70 is maintained constant by a diaphragmoperated valve 76. The valve 70 is opened against a spring 90 by a servo-piston 150 acting through a knife edge 102, a lever 100 and an adjustable roller 104 on the valve head 92. The servo-piston 150 is controlled by a piston valve 140 operated in accordance with compressor delivery pressure acting within a bellows 120. The bellows 120 acts on the valve 140 through arms 122, 128, rigid with a rod 124 and a lever 130 pivoted on the servo-piston 150. When the compressor pressure reaches a predetermined value further downward movement of the servo-piston and consequent increase of fuel flow is prevented by a fixed member 160<SP>1</SP>, Fig. 3, within the valve 140. In the downward movement of the valve 140, the port 156 is eventually blocked by the land 154 and highpressure fuel cannot reach the top of the servo-piston 150. Still further downward movement connects the top of the piston 150 to drain through ports 156, 158 and the annular channel 160. The roller 104 is adjusted to alter the leverage of the lever 100 and so effect a multiplying action by a main servo-piston 110 acting through a rod 106. The servo-pistons 150, 110 are both of the differential type and are constantly acted on over their smaller areas by the high pressure fuel from the pipe 66 in the chamber 146. The servo-piston 110 is controlled by a piston valve 182 operated by a centrifugal governor 180 driven by the engine and loaded by a spring 204 adjusted by a cam 206 from the pilot's lever 208. The servopiston 110 re-sets the governor valve through a lever 202 and a spring 200. An increase in engine speed results in the roller 104 moving to the left and so reducing the fuel supply. A further piston valve 192 is interposed between the valve 182 and the servo-chamber 198 so that the conduits 188, 196 are normally in communication. This communication is interrupted on operation of the movable element 220 of the valve 192 to the right by a floating lever 222 engaging at its ends the servo-piston 110 and a knife-edge strut 224. The strut is operated by a three-dimensional cam 226 which is formed as a servo-piston working in a chamber 296. The vertical movement of the cam is controlled by a piston valve 294 operated by a governor 290 driven by the engine, the governor being re-set by a spring 310. The rotational movement of the cam 226 is controlled in accordance with the compressor inlet temperature, a bulb 250 exposed to which is in fluid connection with a bellows 252 which operates through rack-and-pinion mechanism 256, a lever 258. A compensating bellows 254 also acts on the lever 258. The lever 258 controls a piston valve 260 the movements of which are followed by a servo-piston 268 which operates through rack-and-pinion mechanism 270 and gears 272, 274 the cam 226. The gear 274 is splined in the top of the cam 226. The cam 226 thus acts to prevent control by the governor valve 182 whenever the combined effect of the compressor inlet temperature and engine speed is sufficient to move the cam to a position in which the valve 192 cuts off the pipe 188 and puts the chamber 198 in communication through a pipe 230 with the high pressure-fuel in the chamber 146. A screw stop 212 limits the closing movement of the throttle. Fig. 4 shows a modified system suitable for a gas turbine driving a variable pitch propeller. In this case the governor 180a functions as an underspeed governor and has a setting lower than the propeller governor so that the propeller blades are against their low pitch stop before the governor 180a is effective. Normal control in this case is effected by a valve 424, between the valve 182 and the maximum limit valve 192. The valve 424 is operated through a floating lever 412 and a roller 414 by a follower member 410 engaging a normal control cam surface on a cam 226a, also having a maximum fuel flow limit cam surface 501 and an overspeed cam surface 502. The lever 412 also engages the servo-piston 110. The roller 414 is adjusted from the pilot's lever 208 through a link 416 and a bell-crank 418. The knife-edge strut 224 operates the maximum limit valve 192 as in the case of Fig. 2. The loading of the governor 180 may be modified in accordance with the ambient air temperature. In this case the fulcrum of the lever 202 is adjusted by a cam movable in response to variations of air temperature. To achieve a temporary re-setting of the governor, the fulcrum of the lever 202 is connected to a dashpot and its upper end is connected to a setting spring and a pre-loading spring. The governor in this case is isochronous. Specifications 781,962; 781,963 and 781,964 [both in Group XXIX], are referred to.