Patent GB-842861-A (GB)
Title: Control systems for gas turbine power units for aircraft
Inventor: SKELLERN JOHN
IPC: F02C9/28
Filed: 1956-04-13
Abstract: 842,861. Gas turbine plant. NAPIER & SON Ltd., D. March 15, 1957 [April 13, 1956], No. 11388/56. Class 110 (3). [Also in Group XXIX] A control system for a gas turbine power plant comprises a single control lever for adjusting a fuel metering device which is provided with automatic compensating devices responsive to variations in ambient conditions whereby the fuel supply at any given setting of the control lever is in excess of that required to maintain the speed corresponding to the control lever setting, and a speed-sensitive device of which the datum is controlled by the control lever and which is operative to trim the fuel supply in response to the difference between the actual speed and the datum. The apparatus is suitable for controlling the speed of the compressor-turbine in a plant of the kind having a separate power turbine and in which fuel control involving compensation for ambient air pressure and temperature would not necessarily maintain a constant speed owing to the effect of possible variations of power-turbine speed. As shown, fuel delivered by a variable swashplate pump 23 passes through a conduit 30 to the interior of a metering valve assembly and thence through a metering orifice 33 to a conduit 47 leading to the burners 13. The metering valve assembly consists of an outer sleeve 32 provided with the orifice 33 and upper and lower inner sleeves 34, 35 of which the upper is fixed and the lower is adjustable in accordance with compressor inlet temperature by a servo-piston 44 controlled by a valve 42 actuated through a lever 41 by a temperature-responsive Bourdon tube 39. Manual adjustment of the metering orifice is effected by a lever 70 acting through a shaft 61 and lever 72 on the outer sleeve 32, and the pressure drop across the orifice is maintained constant by adjustment of the swashplate of the pump 23 by a servomotor 26 under the control of a valve 55 which is actuated by a diaphragm 52 subject to the pressures before and after the metering orifice. A spring 54 loading the diaphragm 52 is adjustable to provide compensation for ambient pressure by a servomotor 66 controlled by a bellows-actuated valve 64. A device 75, e.g. as described in Specification 832,195, applies to a diaphragm 79 a pressure difference that is proportional to speed, and the diaphragm actuates a bleed valve 74 controlling escape of metered fuel. To alter the datum of the speed-responsive device a servomotor 85 controlled by a valve 84 actuated by the lever 70 acts to control the compression of a spring 81 opposing the diaphragm 79. The speed of operation of the servomotor 85 in both directions is controlled by restrictions to limit the rate of acceleration and deceleration of the turbine. It is stated that the fuel supply may also be controlled to limit the maximum turbine inlet temperature, and to limit the rate of increase of fuel flow in the event of the control lever being advanced rapidly to increase the turbine speed. The system may also include manual and/or automatic safety devices for shutting off and dumping fuel, and speedresponsive means for setting the compressor inlet guide vanes during starting and acceleration. Provision may also be made for introducing coolant into the compressor intake during emergency operation beyond the normal power range.