US2757511A - System for regulating the supply of liquid fuel to a gas turbine - Google Patents

Description

J. SYSTEM FOR REGULATING THE SUPPLY Aug 7, 1956 H. JAGGER 0F LIQUID FUEL TO A GAS TURBINE 2 Sheets-Sheet 1 Filed Jan. '7, 1952 CONNECTED TO COMP/P515501? OUTLET 10 4:2

INVENTOR HY :TA 66 E R B), Why/.4, 2 mwlh'fl Aug. V, 1956 .1. H. JAGGER 2,757,511

SYSTEM FOR REGULATING THE SUPPLY OF LIQUID FUEL. TO A GAS TURBINE Filed Jan. '7, 1952 2 Sheets-Sheet 2 C'fi/V/VECTED T0 COMPRESSOR OUTLET com/5c TED T0 comp/95550;? lNTA/(E IN E NTo R I HUI/#6651? States Patent SYSTEM FOR REGULA'HNG THE SUPPLY OF LIQUID FUEL TO A GAS TURBINE James H. Jagger, Coventry, England, assiguor to Armstrong Sitideley Motors Limited, Coventry, England Application January '7, 1952, Serial No. 265,330

Claims priority, application Great Britain lanuary 26, 1951 1 Claim. (Cl. 6il--39.28)

This invention relates to a system, for regulating the supply of liquid fuel to a gas turbine engine, of the kind including a constant-delivery, engine-driven pumping unit the effective delivery or which is controlled by a pressure-responsive control plunger, without any spring control, which serves as a spill valve and which has the effective delivery pressure applied to one face, whilst the opposite end of the chamber in which the control plunger works is connected to the end at which the eliective delivery pressure is supplied through a restrictor orifice, and it also communicates with a passage (hereinafter referred to as the control passage) the pressure in which can be regulated dependently upon operating conditions. To increase the etlective delivery the pressure in the control passage must be increased.

Such a pumping unit is provided with means to control the fuel flow at a predetermined maximum engine speed in order to prevent overspceding of the engine, the means acting upon the pressure in the control passage, or in another control passage provided in parallel therewith.

The main object of the invention is to prevent the engine from stalling, due to overfuelling, when the throttle control is rapidly opened.

The invention comprises the combination with a regulating system of the kind specified in the first paragraph of this specification, of an air/fuel ratio device through which the effective delivery of the pumping unit is passed, the device having a variable choke adapted to set up a pressure dilierence between the inlet and outlet sides of the choke without the choke being affected by the said pressure difference, and the pressure difference is applied for actuating a valve for the control passage, or for another control passage in parallel therewith, the choke being actuated responsively to a function of the output pressure of the compressor of the engine,

In the drawings:

Figure l shows, diagrammatically, one form of apparatus for carrying the invention into practice;

Figure 2 is a graph illustrating the corresponding operating conditions;

Figure 3 shows, diagrammatically, a modified apparatus;

Figure 4 is a graph illustrating the operating conditions of the apparatus in Figure 3; and

Figure 5 is a section on the line 5-5 of Figure 1.

in Figure l is shown a constant delivery, enginedriven pumping unit, indicated generally at A, and an air/fuel ratio device at The pump has a rotor ll. which is concentrically fast with a driven shaft 112, the two being formed separately but having a toothed engagement at 13 to lock them together. The bore of the rotor, also concentric with the shaft, is journalled on a core M.- which is fast at one end with the pump body lit. The rotor has radial bores M in which work pistons if? having, at their heads, slippers 18 which are journalled on transverse pins 19 of the pistons and make frictional contact with a bore 20 of the pump body, this bore being eccentric with respect 'ice to the shaft. Thus, as the shaft 12 is rotated, the slippers, in riding round the bore 2d, cause the pistons 17 to be reciprocated in the radial bores 16 of the rotor.

Fuel is fed from a line 21 to a duct 22 in the core, from which duct it is delivered through ports 23 to the radial bores 16 when the pistons are at their radially outmost position, and rotation of the rotor causes the fuel in the bore 16, on the return stroke of the pistons, to be delivered, through other ports 24a to a duct 24 in the core, to a pressure line 25.

Within the pump body there is a duct 26 which communicates with the delivery duct 24 and contains a pistontype valve 27 which is biassed against the delivery pressure by a spring 28. When the pump delivery reaches a predetermined pressure, the valve 27' opens to deliver fuel, through a lateral port, to react on an axial end wall 29 of a peripheral groove in the movable member 30 of a spill or by-pass valve. The delivery duct 24 also communicates, through a duct 3i having a constriction 32, with a duct 33 leading to an opposite end face 34 of the spill valve member 30, whereby, when the pressure in the delivery duct 24 exceeds a predeterm ned value, the pressure drop across the constriction causes the spill valve member 36 to control the opening of the lateral port communicating with the inlet duct 22. Thus the member Iii) can have a hollow end with V-shaped castellations 35 the spaces between which, when the member 39 is appropriately moved, establish the communication between the ducts 24 and 22.

The pump delivers through the line 25 to a chamber lid of the air/fuel ratio device it. This chamber communicates with a line 37, from which the combustion chamber burners of the engine are supplied, through a constriction 38 which is normally open but only to an extent controlled by a valve member 39 which is movable responsively to a function of the pressure of the compressor output. The valve member 39 is generally cylindrical, being a sliding fit in the constriction 38, and it is slotted on opposite sides to form curved portions 390, the axial position of which in the constriction controls the effective area of the passage through the latter, the constriction I-lS and member 39 thus constituting a variable choice.

The slotting of the valve member 39 bifurcates it at the top, Where a pin ill, which unites the arms formed by the bifurcation, serves as an anchorage for one end of a spring 41 of which the other end is fast with a lever 52 presently to be described. The valve member 39 is fast with a piston 43 working in a cylinder 44 formed in the body of the air/fuel ratio device, and the piston has a small leak path indicated at 46. Movement of the piston 43 causes the valve member 39 to move in the constriction 38 and thus varies the effective area of the constriction and, therefore, the pressure drop from the chamber as to the line 37 (although this pressure drop is subsequently restored as hereinafter described). The fuel which passes through the leak path as fills the cylinder M, and the latter has outlet path 4'7 which communicates, through a controlled valve orifice 48 (presently to be described) with the line 37.

The pressure drop across the constriction 3?. is apilied by ducts 4 ,9, Ell to opposite sides of a piston 51 working in a ring-like cylinder 52. The piston 53 is fast with a resilient diaphragm 53, which is trapped between the adjacent. end of the cylinder 52 and an interrupted peripheral flange 5d of a cup-like member 555 fast with the body 45, and the piston 51 is loaded by a spring 56 to balance the pressure difference when the latter is of a predetermined value.

it the engine throttle (not shown) be opened suddenly for accelerating the engine, there is a danger that the engine will be overfuelled and stall. To prevent this,

it is arranged for the fuel supply to the engine, consequent on a sudden opening of the throttle, to be under the control of a function of the compressor output pressure.

This is done, as shown diagrammatically in Figure l, by communicating the compressor output pressure through a duct 57 into a chamber 58 in which there is a pressurescnsitive capsule 59. Thus, when the compressor output commences to increase consequent on the throttle opening movement, the capsule is compressed, causing the lever 42 to move about its pivot 60 in the body 45 to increase the clearance between a half-ball-valve member 61 and the valve orifice 48. This relieves the pressure in the chamber 44 and enables the piston 43 to be depressed, responsively to the pressure in the chamber 36, against the effort of the spring 41. This depression of the piston 43 moves the valve member 39 to increase the effective area of the constriction 38 in step with the increasing compressor output pressure.

The depression of the piston 43 increases the tension in the spring 41 and thus applies a force to the lever 42 to restore the previous clearance between the halfballvalve member 61 and the orifice 48, but with the valve member 39 in a new position in which the effective area of the constriction 38 is increased.

At the same time, this further opening of the constriction reduces the pressure drop across it, and the new pressure drop is applied through the ducts 49 and 50 to cause the piston 51 to move, through a push rod 62,

an arm 63, pivoted at 64 to the cup-like member 55, moving a half-ball-valve member 65 towards the closed position.

The arm 63 is also acted upon by a spring 66 which, through a screw means 67, enables the effort of the spring 56 to be adjusted.

When the arm moves the half-ball-valve 65 towards the closed position it constricts a valve orifice 68 partially to cut off a leak path, through a control passage 100, from beneath the movable member 30 of the spill valve to pump supply line 21. This causes the pressure beneath the spill valve member 30 to increase, thus moving it in the direction to reduce the leak path from the duct 26 to the pump intake. In this way a greater proportion of the pump delivery is supplied through the line 25 to the fuel burners and restores the predetermined pressure difference across the constriction 38, permitting the piston 51 to recover and the half-ball-valve 65 to assume a position, relative to the orifice 68, for maintaining the fuel flow from the pump which rc-established the pressure difference across the constriction 38.

During acceleration of the engine, the increasing compressor output tends to operate the valve 48, 61 in the opening direction, whereby to allow the piston 43 to move for opening more widely the constriction 38. The resultant temporary drop in the pressure difference across the constriction 38, however, is applied by the piston 51 for decreasing the passage of the fuel through the orifice 68 back to the line 21 from the line 100 whereby the pump is caused to deliver a greater proportion of its output to the line 25 to restore the pressure drop across the constriction 38. In these conditions the supply of fuel to the line 37 is increased to maintain an air/fuel ratio which is at all times below the stalling characteristic of the engine.

The lever 42 besides being biassed downwardly by the spring 41 is also biassed upwardly by a spring '70 with van adjustable anchorage 71, whereby the effort of the spring 41 can be adjusted.

These conditions of operation are illustrated by Figure 2 in which fuel supply in gallons per hour is plotted I against the compressor output pressure which, of course,

at any given altitude is related to the engine speed. The

.curves C and D represent, respectively, the engine running and stall lines at sea level, and it will be seen that,

,with the engine running smoothly in the lower speed w 4 range, a sudden opening of the throttle could result in a sufficient supply of fuel to stall the engine before the latter could accelerate sufficiently for adequately increasing the compressor output for burning the extra fuel. The control exerted by the invention is represented by curve B from which it will be seen that the increased supply of fuel, consequent on a sudden opening of the fuel valve, is restricted to a value beneath that at which there is a danger of stalling the engine.

From medium engine speeds upwards, the stall curve rises steeply and, so that high accelerations from such speeds can be obtained, it is arranged that the valve member 39 shall, in that speed range, be in a position in which the constriction 38 offers a minimum of resistance to the fuel flow to the line 37, and this is represented by the steeper portion of the curve E.

To prevent more fuel being supplied to the burners than the engine needs at a predetermined maximum speed, there is a disc 72 which is made rotatively fast with the pump shaft 12, by angularly-spaced balls 73 engaging longitudinal grooves of the shaft and of the disc. The space between the balls 73 communicates, through a duct 74, with the supply line 21 to the pump, the communication being through a diaphragm chamber 75, a clearance space 76, a chamber 77 and a duct 78. The disc 72 has radial bores 79 in which a centrifugal pressure is developed and transmitted, through an annular gallery 80 in the body 15, and a duct 81 to an opposed diaphragm chamber 82.

The diaphragm 83 separating the chambers 77 and 82 is biassed by a tension spring 84, having an adjustable anchorage 85. A compression spring 86 biasses a lever 87 about its pivot 88 to close a valve 89 in a duct 90 leading from the duct 31 with the constriction 32. When there is any tendency to over-speed and the pressure difierence in the chambers '77 and 82 exceeds a predetermined figure, as controlled by the spring 84, a stem 91 contacting the diaphragm 83 rocks the lever 87 to unseat the valve 89, allowing some of the fluid in line 33 to return to the intake line through the chamber 77 and duct 78. This reduces the pressure under the spill valve 30, enabling it to by-pass a greater proportion of the pump output to the intake line. In these circumstances, therefore, the fuel flow is controlled by the pump speed only, overriding the air/ fuel ratio control.

The previously described acceleration control, operating with the compressor output pressure only, does not operate satisfactorily at high altitudes owing to the air/fuel ratio control limiting the maximum speed of the engine. This is illustrated by Figure 4 in which the curves D1, Cl are the ones which correspond with curves D and C at a particular high altitude. It will be seen that the curve C1 is intercepted by the curve E so that the engine speed cannot rise above the value corresponding with the point of interception. With increasing altitude, therefore, it is necessary to modify the curve B by bringing its steeply rising portion nearer the origin so as to lie between the curves D1 and C1 as shown. This can be done by the pressure sensitive arrangement shown in Figure 3, which enables the air/fuel ratio control to act responsively to the compression ratio of the compressor.

The pressure sensitive arrangement of Figure 3 includes a pressure sensitive capsule 128 which has a common wall 121 with a second, and smaller capsule 122 which is evacuated. The wall 121 carries a movable valve member 123 which, at a predetermined compression ratio closes the outlet of a venturi passage 124 which otherwise establishes a communication between the interior of the capsule and the compressor outlet through a duct 125. The throat of the venturi passage communicates with an annulus 126 which, in turn, communicates through a duct 128 with the chamber 58. Thus when the valve member 123 is in open position the .static pressure in the venturi throat is transmitted to the chamber 58, and when the valve 123 is in closed position the compressor output pressure is transmitted to the said chamber 58.

Pressure from the duct 125 is also delivered, through an adjustable needle valve 127, to the exteriors of the capsules 120 and 122, the pressure in the chamber around the capsules acting on the capsule assembly in the direction for closing the valve member 123. The air which has passed the needle valve 127 also passes into the interior of the capsule 120 through a restrictor orifice 129, the interior of the said capsule 120 communicating, through a duct 130, with the compressor intake.

During a rapid acceleration of the engine the pressure ratio of the compressor increases with speed, and while the valve 123 is in open position a lower pressure than the compressor output pressure is transmitted to the chamber 58 from the throat of the venturi 124. This lower pressure is arranged to produce a fuel flow to the engine at all times below the stall line of the engine. At the same time, a reduced value of the compressor output pressure is also acting on the exterior of the capsule assembly 120, 122 and at a value of the compressor pressure ratio at which a sudden increase in fuel flow will not produce stall conditions, this pressure closes the valve 123. As the valve 123 closes, the pressure in the chamber 58 rises to the actual value of the compressor outlet pressure since the air flow through the venturi ceases, giving a larger opening of the constriction 38 and hence a suddenly increased fuel flow to the engine.

Since the valve 123 is closed responsively to the compressor pressure ratio, which in turn is related to the speed of the engine, the relationship of the sudden increase in fuel flow to the engine stall line at any altitude will not vary.

For matching the air/fuel ratio device to any particular engine, the needle valve 127 can be adjusted in order to secure that the valve 123 will close at an appropriate pressure ratio of the compressor.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

A regulating system, for the supply of liquid fuel to a gas turbine engine including an air compressor and a burner for the fuel, comprising the combination of a constant-delivery pumping unit, to be driven from the engine, and an air/ fuel ratio device for regulating the fuel supply dependently on the air available at the compressor outlet at both steady and fluctuating speeds, said unit including a delivery passage and a spill passage, a pressureresponsive control plunger for controlling said spill passage and thus the elfective delivery through said delivery passage, a communication from said delivery passage to one face of said plunger, a communication, containing a restrictor orifice, from said delivery passage to an opposite face of said plunger, a valve in said air/fuel ratio device, a control passage communicating between said opposite face of said plunger and said valve of said air/fuel ratio device, a variable choke in said device, said choke in the path of a communication between said delivery passage and said burner, said choke adapted to set up a pressure difference between its inlet and outlet sides without said choke being affected by said pressure difference, means responsive to such pressure difference for actuating said valve of said device, a piston fast with a movable member of said choke, said piston having a leak path in parallel with said choke, a movable valve member controlling said leak path, a pressure sensitive device, said sensitive device being a pneumatic capsule which is biassed to an extended position, said capsule being in a chamber to which is led through a change-over device a pressure which is a function of the compressor output pressure, said change-over device including a pair of aligned, opposed pneumatic capsules of different sizes, a common wall at the adjacent ends of said pair of capsules, a coaxial duct in the larger capsule of said pair, a valve member fast with said common wall and coacting with the adjacent end of said duct, the remote end of said capsule to receive air at the compressor output pressure, said duct of venturi formation and having a lateral communication with said chamber, an envelope containing said pair of capsules, a restrictor through which the compressor output air passes with pressure reduction to be applied to the exterior of said pair of capsules, and a restrictor through which air from said envelope passes with further pressure reduction to the interior of the larger of said pair of capsules, the interior of the larger of said pair of capsules communicating with the compressor intake, whereby, above a predetermined pressure ratio of said compressor, the valve member fast with said common Wall closes said adjacent end of said duct to cause the compressor output pressure to be applied to said chamber, and below said predetermined pressure ratio said valve member fast with said common wall opens said adjacent end of said duct to cause a lower pressure than that of said compressor output to be applied to said chamber, and a lever interconnecting said pressure sensitive device and said movable member whereby to vary the effective size of said leak path for enabling said movable member to adjust itself for maintaining constant the pressure difference between the inlet and. outlet sides of said choke.

References Cited in the file of this patent UNITED STATES PATENTS 2,429,005 Watson et al Oct. 14, 1947 2,450,535 Watson et al. Oct. 5, 1948 2,503,048 Ifield Apr. 4, 1950 2,604,756 Greenland July 29, 1952

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