Patent GB-892857-A (GB)
Title: Improved gas turbine engine fuel system
Inventor: JUBB ALBERT
IPC: F02C7/22
Filed: 1960-01-18
Abstract: 892,857. Gas turbine engine fuel systems. ROLLS-ROYCE Ltd. Jan. 17, 1961 [Jan. 18, 1960], No. 1758/60. Addition to 850,477. Class 110 (3). The invention as set forth in Claim 1 of the parent Speci fication is modified either in that further means are pro vided for ensuring that the outlet pressure of the said compressor does not exceed a predetermined value, or in that the means for varying the size of the metering orifice comprises means compensating for the effects of the temperature of the fuel passing through the fuel system, or in that further means are provided such means being responsive to the speed of a turbine shaft of the engine for reducing the fuel supply to the burner when the said speed exceeds a predetermined value. The system shown embodies the three further features. Fuel is supplied from a tank through duct 110 to a backing pump 111, the fuel then passing to an oil cooler 113 and thence to a fuel heater 120 where it is heated by hot air from the engine. The fuel then passes through a filter 128, through a flowmeter 129 and thence via duct 130 to the swash-plate type fuel pump 131, the outlet duct of which is indicated at 145. The angle of the swash-plate 132 is varied by means of a piston 143 mounted on a rod 135 which is pivotally connected to the swash-plate, the left-hand side of the piston being subjected to the delivery pressure of the pump while the right-hand side of the piston is subjected by means of duet 147 to the pressure of the fuel being supplied to the main burners 150. The piston 143 is also loaded to the left by means of springs 139, 140 which act on the spring-plate 136, the weaker spring 140 being adjustable by a device 141. The pistonrod 135 has a bore 142 therethrough whereby the opposite ends of the rod are pressurebalanced. A pressure-relief valve 152 is provided at the pump outlet. The fuel passes from the pump through the duct 145 into the casing of the combined acceleration and speed control unit 154. This unit comprises a shaft 155 driven by the engine, the shaft driving by means of gearing 157, a planet carrier 156 which carries compound planet gears 158, 159, the gear 158 engaging a fixed sun gear 160 also an annulus gear 161 provided internally of a governor housing 162. The gear 159 engages with a sun gear 163 which is mounted on a shaft 164, the gear 159 being elongated to permit axial movement of the gear 163 and shaft 164. The acceleration control governor comprises flyweights 165 which act on the collar 167 on the shaft 164. The shaft 164 is secured to a sleeve 168 which has ports 172 therein through which fuel may flow to the main burner passage 170. The sleeve 168 also has ports 169 through which fuel may flow to the pilot burner passage 171 at all positions of the sleeve. The shaft 164 is drivingly connected to a rod 173 which in turn is drivingly connected to a sleeve 175, the sleeve being mounted for rotational movement in a bearing 176 which also transmits axial movement to the sleeve which movement is communicated from a pair of diametrically-disposed acceleration control capsules 177 which are mounted within a common chamber 178. Each capsule 177 is divided into two compartments 179, 180, the compartment 179 being evacuated and the compartment 180 being open by means of duct 181 to pressure P 1 <SP>1</SP>, which is the delivery pressure of the low pressure compressor, the pressure P 1 <SP>1</SP>, being functionally related to the pressure P 1  of the intake to the low pressure compressor. The duct 183 is supplied with air at pressure P 2  which is the delivery pressure of the high-pressure compressor, theair passing from duct 183 through a restriction 184 into the chamber 185 from which it passes through duct 186 into the chamber 178. A diverging passage 187 also communicates with the chamber 185, the upstream end of the passage constituting a restriction, and the passage communicates at its downstream end with the duct 181, or alternatively with atmosphere. A duct 188 also communicates with the chamber 185, the duct leading to a device 189 which is adapted to ensure that the pressure within the chamber 178 does not exceed a predetermined value. The device 189 comprises a lever 190 which is pivoted at 191 and is formed at its other end with a valve 192 which co-operates with a valve seat 193 formed at the end of the duct 188, the air escaping through the valve 192, 193 passing to atmosphere through outlet 194. The lever is acted on in a valve-closing direction by springs 196, 196<SP>1</SP>. The lever 190 carries an arm 197 which is disposed within a capsule 198, the interior of which is open to atmosphere via the port 194. The lever is urged in a valve closing direction by means of a spring 200 which bears on a plate 199 mounted on the capsule. The capsule is disposed within a chamber 203 to which air at pressure P 2  is supplied via duct 204, the pressure P 2  acting on the spring plate 199 in a direction tending to open the valve 192. The pressure in the pipe 188 and therefore that in the chamber 178 cannot exceed a predetermined value therefore. Since the capsule compartments 180 are supplied with air at a pressure which is a function of P 1  and since the chamber 178 is supplied with air at a pressure which is a function of P 2 , the capsules will effect axial adjustment of the sleeve 175 in direct proportion to P 1 F (P 2 /P 1 ). The sleeve 175 is also mounted within sleeves 206, 207 which are spaced apart axially to afford an annular gap 208, the sleeve 207 being fixed but the sleeve 206 being axially movable by a top speed control governor 209 whereby the width of the gap 208 is variable. The governor housing 210 is driven from the governor housing 162 by means of gears mounted on a shaft 215. The sleeve 206 is pivotally mounted at 216 to a lever 217 which is mounted on a fixed pivot 218, the lever 217 having an arm 219 carrying a spring plate 220, a spring 221 extending between the plate 220 and the fixed member 222. The member 222 supports a sleeve 223 within which is slidably mounted a rod 224 which incorporates temperature compensating tubes 225 which are provided to compensate for the effects of the temperature of the fuel passing through the system. One end of the rod 224 engages against the spring plate 220 while the other end engages against one end of a curved lever 226 which is pivoted at 227. A roller 229 carried by the pilot's throttle lever 230 engages against a roller 228 mounted on the lever 226. The roller 229 is engaged by a roller 231 carried by a lever 232 which is acted on by a spring 233 which acts to load the spring 221. Adjustment of the pilot's throttle lever 230 therefore adjusts the loading of the spring 221 and therefore adjusts the speed at which the governor 209 moves the sleeve 206 in a direction to close the annular gap 208. Movement of the lever 217 is limited by means of stops 235, 236. The sleeve 175 is formed with a number of slots 237 of triangular or other shape whose crosssection varies axially, the slots 237 co-operating with the annular gap 208 to afford a main or metering orifice, the size of which will vary upon movement of the sleeves 175, 206 by the capsules 177 and governor 209. Fuel which has passed into the control unit through the duct 145 passes through the metering orifice 208, 237 into the interior of the sleeve 175 and thence flows to the outlet passages 170, 171. The passage 171 leads to a chamber 238 into which extends a sleeve 175<SP>1</SP> of the same diameter as sleeve 175, the two sleeves being coupled together by means of a coupling 175<SP>11</SP>; the connection 171 ensures that the sleeve 175 is pressure-balanced axially. The fuel passes from the chamber 238 through a duct 240 which leads via a shut-off cock 241 and an emergency fuel cut-off valve 242 to a pilot burner manifold 243 from which fuel flows to the pilot burners 244. The main burner passage 170 leads to an emergency governor 245 and thence to the shutoff cock 241 and emergency cut-off valve 242 to the main burner manifold 149 and so to the main burners 150. The emergency governor 245 comprises flyweights 247 which tend to move the sleeve 248 to the right against the loading of the springs 249, 249<SP>1</SP>. The sleeve 248 has ports 250, 251 which co-operate with the annular chambers 252, 253, fuel from the passage 170 flowing to the chamber 252 and thence through the sleeve 248 to the chamber 253. The fuel then flows to the duct 148 and so to the duct 148<SP>1</SP>; the duct 147 from which fuel passes to act on the right-hand side of the pump control piston 143 also connects with the duct 148. If the speed of the L.P. shaft of the engine exceeds a predetermined value, the sleeve 248 will be moved to the right, so closing the port 250 and reducing fuel flow to the main burners. The shut-off cock 241 comprises a sleeve 254 which is movable axially by means of a pinion 260 which is rotatable by a manually-operated lever 262. When in the position shown, the sleeve allows main fuel to flow from the duct 148 to duet 148<SP>1</SP> and pilot fuel to flow from pipe 240 via the reduced diameter portion 259 of the sleeve to the duct 240<SP>1</SP>. When moved to the left, however, the sleeve 254 closes off the duct 148 and also closes off the duct 240<SP>1</SP>. Fuel supplied through the pipe 240 will now pass to the pipe 264 and so back to the inlet side of the backing pump 111. The emergency fuel cutoff valve 242 comprises a valve member 265 which controls flow through the ducts 148<SP>1</SP>, 240<SP>1</SP>, the valve member being loaded in the valveclosing direction by spring 266 but being normally held in the open position by means of a rupturable diaphragm 267. The valve member is connected by means of a cable 268 to a screw-and-nut device whereby if the L.P. shaft of the engine breaks at any point between the turbine and compressor, the nut moves along the scr