US2703961A

US2703961A - Apparatus for limiting the fuel flow/air flow ratio in liquid fuel systems for continuous combustion turbine engines

Info

Publication number: US2703961A
Application number: US242938A
Authority: US
Inventors: John K Harding
Original assignee: Dowty Equipment Ltd
Current assignee: Dowty Equipment Ltd
Priority date: 1950-09-11
Filing date: 1951-08-21
Publication date: 1955-03-15
Anticipated expiration: 1972-03-15

Description

March 15, 1955 HARDlNG 2,703,961

APPARATUS FOR LIMITING THE FUEL FLOW/AIR FLOW RATIO IN LIQUID FUEL SYSTEMS FOR CONTINUOUS COMBUSTION TURBINE ENGINES Filed Aug. 21, 1951 Y Z/ 7 /7 /5 I f-- {Hr- I I I Z4\ I I I I I I l I 4 I 25-% 5i i I I /4 27 r I I E I 94 26 ;/z a7 2 i Z/-1 I V 57 I 3M 4 I l I f 1 V I l I I I I I I I I I I I INVENTOR. JOA/A/ ,6. A/AED/A/ United States Patent APPARATUS FOR LIlVIITIN G THE FUEL FLOW/ AIR FLOW RATIO IN LIQUID FUEL SYSTEMS FOR gt gv r muous COMBUSTION TURBINE EN- John K. Harding, Cheltenham, England, assignor to Dowty Equipment Limited, Cheltenham, England Application August 21, 1951, Serial No. 242,938

Claims priority, application Great Britain September 11, 1950 3 Claims. (Cl. 6039.78)

This invention relates to known systems for supplying liquid fuel to the burners of a continuous combustion turbine engine, in which the fuel is fed to the engine by an engine-driven pump which is either (I) of the fixed stroke type operating in conjunction with a variably restricted by-pass, or (II) of the variable-stroke type. In either such type fuel flow to the engine is controlled during normal running by the expedient of venting, through what is usually termed the all-speed governing vent, one side of a fiuid-pressure-balanced device; in type I (the fixed-stroke fuel pump with variably restricted by-pass) this venting is arranged to control, by unbalancing the pressure-balanced device, restriction of the by-pass passage of the fixed-stroke pump, whereas in type II (the variable-stroke fuel pump) the venting is arranged to control, again through the pressurebalanced device, movement of the stroke-regulating element of the fuel pump.

Such known systems include apparatus for automatically controlling a vent (not necessarily the all-speed governing vent mentioned above, which functions during normal running, but preferably a separate and distinct vent, termed hereinafter the acceleration vent) and operatively connected to the pressure-balanced device, whereby said latter device is capable of being unbalanced and so being moved automatically, and independently of the all-speed governing vent, in a manner to limit the fuel supply to the engine whenever a predetermined fuel fiow/ air flow ratio is approached, so as to prevent said ratio from being exceeded. By so doing the occurrence of an excessive fuel flow/air flow ratio is prevented, especially during accelerations, during which at certain engine speeds an excessive ratio would cause excessive engine temperatures, and possibly surging. The automatic acceleration vent of this invention and its controls constitute an improved form of such a control, and safeguard the engine, during acceleration, from excessive combustion temperatures and from the danger of surging.

The present invention provides improved means for controlling the acceleration vent and, according to this invention, the closure member of said vent is subjected to two opposed loading means of which one (the air flow loading) is responsive proportionally to pressure developed in the air compressor stage of the engine which pressure provides a measure of the amount of air being consumed by the engine, and the other (the fuel flow loading) is responsive proportionally to the rate of fuel flow to the engine, said opposed loadings being arranged to actuate the vent closure member so as to bring about a limitation of fuel flow to the engine whenever the fuel flow loading means overcomes the air flow loading means, the fuel flow loading means comprising spring means reacting upon the vent closure member and upon a movable throttle member in a fuel flow line, wherein the pressure difference across the throttle member is maintained constant by servo means which moves the throttle member against the spring means so that the latter applies a loading on the closure member which is directly proportional to the fuel flow past said throttle member.

The improved fuel/air ratio limiting apparatus according to the preferred embodiment of the invention will now be described with reference to the accompanying diagrammatic drawing, which is a diagram of the system incorporating the apparatus, the latter being shown in enlarged detail.

In the system shown, a fuel pump 6 driven by the turbine engine 7 withdraws fuel from a fuel tank 8 and delivers it along a line 13a, 13b to the burners 9 of the engine. The fuel pump 6 is of the fixed stroke type and has an associated by-pass 11a controlled by a known servo-operated device in the form of a by-pass valve 11b. The by-pass valve 11b assumesa position in accordance with the rate of flow through a restricted communication between the pressure spaces 11d and 11s at opposite sides respectively of a piston portion 11 of the valve. The space He is connected by conduit 15a extending to the inlet or low pressure side of the fuel pump 6. In this conduit 15a there is provided one or more servo vent valves for controlling flow in known manner along the conduit and hence controlling the position of the by-pass valve 11b, which in turn controls the quantity of fuel that is permitted to return along the by-pass 11a, and the quantity that is allowed to reach the burners 9 by way of 13a, 13b. The apparatus of the present invention is supplemental to the known controls thus far described, being concerned with the control over the closure member of what may be termed an acceleration vent which latter is normally closed but which is opened when the rate of fuel flow to the burners 9 tends to exceed a safe amount. So long as the engine is receiving fuel at a rate below the maximum permitted rate, the acceleration vent will play no part in controlling the by-pass valve 11b, which latter will be controlled by another servo vent in the conduiting 15a, for example by a servo vent forming part of in (all-speed governor 15b of any known or convenient The portion of the conduit 15a between the pressure space He and the governor 15b has a branch line or vent pipe 11g which terminates in a vent 12 which is the acceleration vent as hereinbefore specified.

The acceleration vent 12 opens into a chamber 14 which is connected to drain or to low pressure by a pipe 15c which leads into the conduit 15a at the downstream side of the governor 15b. The vent 12 is controlled by a vent closure member such as the beam 16 mounted in the chamber 14 to rock about a fulcrum 17. The beam is subjected in a counterclockwise or ventclosing direction to the air flow loading, and in a clockwise or vent-opening direction to the fuel fiow loading, as hereinafter explained. When the fuel flow loading overcomes the air flow loading the beam rocks about its fulcrum 17 to open the acceleration vent 12 which, through vent pipe 11g, vents the pressure space He of the pressure-balanced by-pass valve 11b to low pressure through the pipe and the corresponding part of the conduit 15a, and so limits the amount of fuel delivered by the fuel supply pump 6 to the engine.

The beam 16 is engaged by a pin 18 on a diaphragm 19 which latter forms part of the boundary wall of a chamber 20 which is subjected to the output pressure of the air compressor stage 10 of the engine along a pipe 21. At the underside of the beam 16 directly opposite the pin 18 there is a capsule 23 of the same diameter as the diaphragm 19 and the resilience of which is balanced by the spring 24 above the diaphragm 19. Any variations in the low pressure in the chamber 14 act equally upon the diaphragm 19 and upon the capsule 23 so that the net effect of the capsule 23, spring 24, and air pressure in the chamber 20, is a true measure of the output pressure of the air compressor stage 10 of the engine, which is a measure of the amount of air being consumed by the engine. This loading as a whole (the air flow loading means) acts on the beam 16 to influence the beam in a counter-clockwise direction to try to maintain the vent 12 closed.

The means by which the beam 16 is loaded by the fuel flow loading will now be explained. The beam 16 is influenced in a clockwise direction by a spring 25 reacting between the beam and an adjustable abutment in the chamber 14a. As the extent of rocking movement of the beam 16 is extremely small, the spring 25 exerts a substantially constant downward force on the corresponding end of the beam 16. This susbtantially constant force is resisted to variable extents by the compression in a spring 22 reacting between the underside of the beam opposite the spring 25 and the upper end 26 of a movable throttle member 27. The throttle member 27 extends through a partition 28 and forms with the partition a variable orifice 29. The fuel delivery line 13a, 1311 extends from the fuel supply pump to the engine burners, and it will be seen that fuel flowing along this line 13a, 13b has to pass through the variable orifice 29. Below the partition 28 the throttle member 27 terminates in a piston 30. The space above the piston 30 communicates with the space below it by way of a pipe 31 including a filter 310, a chamber 37, and a pipe 32 from the chamber 37. The inlet end of the pipe 32 forms a throttle piston vent 33 which is regulated by a diaphragm 34, while the other end of the pipe 32 has a branch 35 which leads through a fixed restriction 35a into the low pressure chamber 14. The diaphragm 34 at all times controls a restricted flow of fuel from the space above the piston 30 to the low pressure chamber 14 whence it flows into the pipe 150, and the pressures established across the vent 33 by the said flow act differentially on the piston 30 to control its reaction against the spring 22. The diaphragm 34 is thus influenced to move away from the throttle piston vent 33 by the fuel pressure at the downstream side of the variable orifice 29. It is also urged in the same direction by an adjustable tension spring 36. The diaphragm 34 is influenced to move towards the throttle piston vent 33 by being exposed at its outer side to the fuel pressure at the upstream side of the variable orifice 29 by way of passage 38 which communicates freely with the fuel delivery line 13a. When the pressure drop across the variable orifice 29 is at the predetermined value governed by the setting of the spring 25, the throttle member 27 will be in a state of equilibrium and the position of the throttle member 27 will correspond to the rate of fuel flow along the pipe line 13a, 13b. Any change in the rate of fuel flow along the pipe 13a, 13b will tend to change the pressure drop across the variable orifice 29, and this tendency, as hereinafter explained, will react through the diaphragm 34 and throttle piston vent 33 to cause the throttle member 27 to take up a new position of equilibrium at which the pressure drop across the orifice 29 remains at the predetermined constant value.

Assuming the engine to be operating under steady conditions under the control of the vent of the all-speed governor b, during which the fuel/air ratio is below the value permitted by the acceleration vent 12, the throttle member 27 will be in a state of equilibrium with the pressure drop across the variable orifice 29 at the predetermined constant value. The position of the throttle member 27 will correspond to the amount of fuel flowing through the orifice 29, and the spring 22 will be compressed correspondingly and the spring 25 will have a corresponding effect upon the beam 16. In this condition the acceleration vent 12 is closed by the beam 16, and the throttle piston vent 33 is opened sufficiently that the pressure in the

lines

32 and 35 between the vent 33 and the fixed restriction 35a, and hence in the space below the piston 30, will be at such a value below the pressure downstream of the orifice 29 as, on account of the differential piston area, to exert an upward thrust on the throttle member 27 to give the spring 22 the requisite compression in accordance with the rate of fuel flow. Assuming now that the rate of fuel flow is arbitrarily increased, the immediate effect will be the tendency for the pressure drop across the orifice 29 to rise. The pressure acting upon the diaphragm 34 will thus tend to reduce the size of the throttle piston vent 33 and this will result in an increased pressure drop as between the upstream and downstream sides of said vent 33 which will reduce the pressure acting beneath the throttle member 27 which latter will move down to enlarge the orifice 29 until a state of equilibrium is restored at which the pressure drop across the orifice 29 will be maintained at the predeter mined constant value. The compression in the spring 22 will be correspondingly relieved so that the effect of the spring 25 is correspondingly increased. Conversely, if the rate of fuel flow be arbitrarily reduced, the pressures acting on the diaphragm 34 will move the diaphragm to enlarge the size of the throttle piston vent 33 so that there will be a lower pressure difference across said vent 33, and the throttle member 27 will move up until a state of equilibrium is restored for the new rate of fuel flow at which the pressure drop across the orifice 29 is again maintained at the predetermined constant value.

The position of the throttle member 27 in relation to its housing, and hence the size of the variable orifice 29, is thus dependent on two pressures of which one is the pressure at the downstream side of the orifice 29 and the other is a pressure less than that at the said downstream side of the orifice 29, said latter pressure operating over a greater area of the throttle member 27 than the former pressure and both pressures acting to maintain the pressure drop across the orifice 29 at the constant value.

When for a given air mass flow the rate of fuel flow is increased to such an extent that the fuel/air ratio has reached the maximum critical value, the position of the throttle member 27 will have relieved the compression in the spring 22 sufliciently to permit the spring 25 to overcome the loading on the beam 16 by the air flow loading acting on the beam, and the beam 16 will rock in a clockwise direction to open the acceleration vent 12. This will relieve one side of the pressure-balanced device 11b associated with the fuel pump 6 to prevent the rate of fuel flow to the engine from being increased beyond this value. It will be appreciated that any variation in the rate of air flow to the engine will vary the air flow loading on the beam 16 which has to be overcome by the

spring loading

25, 22 before the apparatus can operate to limit the fuel flow to the engine.

The beam is thus governed in relation to the acceleration vent 12 in accordance with changes in air mass flow and with changes in fuel mass flow, and the vent 12 will accordingly control the pressure-balanced device of the fuel pump to automatically prevent the fuel/ air ratio from rising above a predetermined value at any speed of operation of the engine.

Although in the example illustrated the movement of the pressure-balanced device 1112 is utilized to vary the restriction of a by-pass passage across a fuel pump of the fixed stroke type, such movement of the pressure-balanced device could alternatively be employed to vary the stroke of a fuel pump of the variable stroke type, in known manner.

I claim:

1. Means for automatically controlling the supply of liquid fuel from an engine-driven variable-delivery pump to a gas turbine engine essentially incorporating an engine-driven blower for supplying the air required for combustion of the fuel, and wherein the delivery of said pump is regulated by altering the balance of pressures acting upon a pressure-balanced device, comprising the combination of: a fuel supply line through which fuel flows from the pump to the engine; liquid fuel controlling means comprising an acceleration vent for connection to such pressure-balanced device and a closure member movable with respect to said acceleration vent to open or to close the same, and consequently to alter or to maintain, respectively, the balance of pressures effective upon such pressure-balanced device; a first, air flow, loading means operatively connected to said closure member and arranged to close said vent, said first loading means including a fluid-pressure-responsive element and a conduit leading thereto and adapted for connection to the output from the engines blower whereby the force of said element varies in accordance with the airflow through the engine; a second, fuel-flow, loading means operatively connected to said closure member and arranged to open said vent; said second loading means including an orifice disposed in said fuel supply line and a throttle member guided for throttling movement with respect to said orifice, and including additionally spring means disposed to react upon the closure member and upon the throttle member to provide a resilient connection between said two members, and a piston fixed for movement with said throttle member and operative through the latter and the spring means to exert a controlling influence on said closure member; servo-valve means including a valve, a spring-loaded pressure-responsive member operatively connected to said valve, and a pair of fluid passageways connecting opposite sides of said pressure-responsive member respectively with opposite sides of said orifice, to subject the pressure-responsive member to changes in the pressure difference across said orifice; and a source of pressure fluid arranged for control by said servo-valve means and operatively connected to said piston to actuate the latter,

and thereby said throttle member, whereby the throttle member is movable automatically to maintain constant the pressure difference across the orifice despite variation in the rate of fuel flow therethrough, and whereby the throttle member can apply through said spring means a vent-opening force on said closure member which varies in accordance with the fuel flow to the engine.

2. Automatic control means as and for the purpose set forth in claim 1, including means to adjust the spring load upon the servo-valves pressure-responsive member, whereby to vary the pressure difference across the orifice.

3. Automatic control means as and for the purpose set forth in claim 1, wherein the source of pressure fluid which is operatively connected to actuate the piston includes a duct communicating past said servo-valve valve with the pressure effective upon one side of the pressureresponsive member, and extending thence to a region of low pressure, a fixed restriction in said duct, and a connection from said duct, intermediate said valve and said restriction, to one face of said piston; and said piston being exposed at its opposite face to the fuel flowing in the fuel supply line, and the piston being of different areas at its two faces, to efiect its movement in opposite senses in accordance with differences in the pressures acting upon its opposite faces as influenced by change in fuel flow to the engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,415,326 Wright Feb. 4, 1947 2,422,808 Stokes June 24, 1947 2,450,535 Watson et al. Oct. 5, 1948 2,503,048 Ifield Apr. 4, 1950 2,519,624 Ballantyne et a1 Aug. 22, 1950 2,537,681 Lawrence Jan. 9, 1951 FOREIGN PATENTS 429,682 Great Britain June 4, 1935 580,149 Great Britain Aug. 8, 1946