Patent GB-760806-A (GB)
Title: Improvements in or relating to gas-turbine engines
Inventor: DAVIES DAVID OMRI
IPC: F02K1/16
Filed: 1953-07-16
Abstract: 760,806. Gas turbine jet propulsion engines. ROLLS-ROYCE, Ltd. June 29, 1954 [July 16, 1953], No. 19812/53. Class 110 (3). [Also in Group XXIX] In a gas turbine jet propulsion engine consisting of a low-pressure compressor delivering air to a high-pressure compressor, the compressors being driven by low and high-pressure turbines respectively, and reheat combustion equipment arranged downstream of the lowpressure turbine, means are provided to control the speed of the low-pressure rotor which means comprises means to vary the fuel supply to the reheat combustion equipment. The compound gas turbine jet-propulsion engine, Fig. 1, comprises a low-pressure compressor 10 which discharges to a high-pressure compressor 11 feeding the main combustion equipment 12. The combustion products from the equipment 12 drive a high-pressure turbine 13 connected to the high pressure compressor 11 by a hollow shaft 14 and a low-pressure turbine 15 connected to the low pressure compressor 10 by a shaft 16. The gases from the low-pressure turbine 15 pass through a jet pipe 17 to a variable area propulsion nozzle 18. Fuel supplied through injectors 19 is used to reheat the low-pressure turbine exhaust. Under normal conditions, fuel is supplied to the main combustion equipment 12 only and is controlled by a lever 26 and a temperature-responsive control 22. The variable area nozzle 18 is then in its minimum area position. When fuel is supplied to the fuel injectors 19 the variable area nozzle 18 is opened up, and the high-pressure rotor assembly 11a, 13a is controlled by varying the supply of fuel to the main combustion equipment 12 to maintain a selected temperature at the exhaust of the high pressure turbine 13. The speed of the lowpressure rotor assembly 10a, 15a is controlled by variation of the quantity of fuel delivered to the injectors 19. In the arrangement shown the pilot selects a degree of reheat and at the.same time the variable area nozzle is adjusted to have a corresponding area. The nozzle segments 18a are operated by a ram 28, Figs. 1 and 2, having a piston 29 the position of which is determined by a bleed valve 37. The bleed valve 37 is connected to a flexible diaphragm 38 which is loaded in the opening direction of the bleed valve 37 by a fluid-pressure depending on the selected degree of reheat and in the closing direction by a spring 39 arranged between the ram piston 29 and the diaphragm 38. The fluid pressure depending on the degree of reheat is provided by a source of high-pressure air or fuel which is passed into a conduit 42 containing fixed area restrictors 43, 44, 45. The downstream end 42a of the conduit 42 is connected to a low pressure point indicated by conduit 47. An independent compressor 46 may be provided to form the source or the air may be taken from the high-pressure compressor discharge and returned to low-pressure compressor discharge. A branch conduit 48 leading from the conduit 42 to the low-pressure end thereof 42a has a relief valve 49 the loading of which may be varied by the pilot to select the degree of reheat. Another branch conduit 53 from the conduit 42 between the restrictors 44, 45 leads to end 42a through a variable orifice 54, the effective area of which is adjusted by a valve member 55 controlled by a capsule 56 responsive to the temperature (T 1 ) at the intake of the compressor. The valve 55 is so shaped that as the temperature T 1  increases up to a first selected value, the effective area of the orifice remains unchanged, as the tempera. ture increases from the first to a second selected value the effective area is gradually decreased and that with an increase of temperature above the second selected value, the effective area again remains constant. A tapping conduit 59 is taken from the conduit 42 and led to a chamber 60 on one side of the diaphragm 38 and a second tapping conduit 61 is taken from the end 42a of the conduit 42 to the chamber 62 on the opposite side of the diaphragm. This control arrangement causes the effective area of the variable area propelling nozzle 18 to depend upon the selected degree of reheat and upon the temperature at the inlet of the compressor. This control is also used to determine a basic fuel supply to the fuel injectors 19. Fuel is supplied to the injectors 19 by a pump 63 driven by an air turbine 64 supplied with air from the outlet of the high-pressure compressor and controlled by a throttle valve 65. The throttle valve 65 is actuated by a ram 66 similar to the ram 28. The fluid load on the diaphragm 69 of the ram 66 is obtained from the conduit 42 through the branch 72 which is connected to the end 42a of the conduit 42 by a conduit 72a. The branch 72 contains a fixed orifice 73 and a variable area orifice 74 the area of which is controlled by a needle valve element 75 adjusted in accordance with the mass flow through the engine. The valve element 75 may be connected to an evacuated capsule 76 responsive to delivery pressure of the high or low pressure compressors at a given rotational speed or a diaphragm responsive to the pressure difference between the pressure at the delivery of the high-pressure compressor and the pressure in the jet pipe 17 or the pressure drop across either the highpressure turbine 13 or low-pressure turbine 15. The area of the orifice 74 is decreased with increase of mass flow. A branch conduit 77 taken from the conduit 72 between the fixed and variable orifices 73, 74 contains a fixed orifice 78 and a bleed valve 79. A tapping 80 is taken from the conduit 77 between the orifice 78 and bleed valve 79 and led to one side of the diaphragm 69 and a second tapping 81 leads from the conduit 72a to the other side of the diaphragm. The ram 66 is therefore adjusted, ignoring the effect of the bleed valve 79, in accordance with the engine air mass flow and the selected degree of reheat. The bleed valve 79 is controlled in accordance with the pressure ratio across either of the turbines 13, 15 or both or in accordance with the corrected rotational speed of the low-pressure compressor 10. If the corrected rotational speed rises the bleed valve 79 closes and causes an increase of the pressure drop across the diaphragm 69 causing the bleed valve 70 to open and so allow the ram 66 to increase the amount of fuel delivered to the injectors 19. The bleed valve 79 is connected to a diaphragm 82 which is loaded in one direction by a governor 83 driven by the low-pressure rotor and in the opposite direction by a spring 85 and a fluid-pressure. This fluid pressure is obtained from a high-pressure source such as a pump 87 which discharges into a conduit 86 containing two fixed area restrictors 88, 89 and a variable area restrictor 90. A relief valve 91 maintains the pressure between the restrictors 88, 89 constant. A variable load relief valve 93 is placed in a by-pass round the variable area restrictor 90, the effective area of which is controlled by a needle valve 97 controlled in accordance with the temperature at the inlet of the low-pressure compressor in a similar manner to the valve 55. The pressure drop across the restrictor 90 is applied to the diaphragm 82 so that the diaphragm is subjected to a load which varies with the inlet temperature to the low-pressure compressor. The variable load relief valve 93 acts as a safety device and sets a maximum value on the low-pressure rotor rotational speed. The loading of the relief valve is varied by the pilot's lever 101 which may be coupled with the lever 52. In a modification, the fuel supply to the reheat combustion chamber is divided, part flows to pilot injectors and part to main injectors. The part flowing to the pilot injectors passes through a linear flow valve, the pressure drop across which is balanced against the pressure at the discharge of the highpressure compressor 11 to control a servomotor controlling the air turbine throttle valve 65 so that the fuel supply to the pilot injectors is in a desired ratio to the compressor delivery pressure. The part flowing to the main injectors passes through two conduits arranged in parallel. One conduit is controlled by a pilot's lever which also controls the setting of the nozzle segments 18a. The other conduit is controlled by a valve connected to a governor driven by the lowpressure rotor. The loading of the governor spring is adjustable. Instead of the highpressure compressor delivery pressure, the pilot fuel supply may be controlled by any pressure or difference in pressures of the engine working fluid which is approximately or exactly proportional to the engine mass flow.