US2989842A - Fuel pumping system for engines having afterburners - Google Patents

Description

June 27, 1961 c. F. WOOD ETAL 2,989,842

FUEL PUMPING SYSTEM FOR ENGINES HAVING AFTERBURNERS Filed April 14, 1960 as A I I. l rm i? 97 y mm CYRUS E W000 ROBERT A. NEAL 2,989,842 FUEL PUMPING SYSTEM FOR ENGINES HAVING AFTERBURNERS Cyrus F. Wood, Bryn Mawr, Pa., and Robert A. Neal,

Shawnee, Kans., assignors, by mesne assignments, to

the United States of America as represented by the Secretary of the Navy Filed Apr. 14, 1960, Ser. No. 22,376 7 Claims. (Cl. 60-356) The present invention relates to fuel pumping apparatus and more particularly to the provision of flow control means for the output of dual parallel-connected fuel pumps.

With the advent of aircraft power plants of the type having an extensive range of thrust output, such as a turbojet engine, it has become increasingly desirable to provide fuel control systems to render the power plant safely operable even in the event of failure of certain elements. This is especially true in the design of a fuel control system for a turbojet engine particularly in the case of an engine having an afterburner. Such an engine could norm-ally be expected to be equipped with a main fuel pump and an emergency pump therefor in case of failure, a fuel pump for the afterburner and possibly an emergency pump for the afterburner fuel pump as well. Such an arrangement involves a serious weight penalty.

It is therefore an object of the present invention to provide a fuel pump system having an output of wide variation employing two pumps exhibiting emergency control features heretofore available only with separate emergency pump apparatus, thereby resulting in substantial weight savings.

Another object of the invention is the provision of fuel supply apparatus having means of control providing for automatic pump selection in case of the failure of one pump.

Still another object of the invention is the provision of fuel supply apparatus having means for maintaining the flow of fuel to the main fuel system at the expense of flow to the afterburner fuel system in the event of failure of one pump.

A further object of the invention is the provision of fuel supply apparatus having means for preventing pump overspeed and consequent damage thereto.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein a preferred form of the present invention is clearly shown, the single figure being a diagrammatic elevational view of a conventional turbo-jet engine equipped with improved fuel pumping apparatus and controls therefor.

Referring to the drawing in detail, it may be pointed out that the details of the turbo-jet engine as such are immaterial to the invention and that the invention may be incorporated in turbojet engines of various configurations. The invention is directed to a fuel pumping system, and therefore the known type of turbo-jet engine that is shown will be described only briefly. The engine comprises an outer casing 19 Within which is an axial flow compressor 11 that is connected by a shaft 12 to an axial flow turbine 18. An inner casing 14 cooperates with the outer casing 10 to define an annular combination chamber or combustor that includes the perforated flame tubes 16. The outer casing 10 terminates in a jet propulsion nozzle 18 which may have its discharge area varied by the movable eyelids 19 that pivot at 21. A tailcone 22 supported by radial struts 23 and the afterburner fuel nozzles 24 that are fed from ring manifold 26, lie on the exhaust side of turbine 14 in the aft portion of casing 10. Main fuel nozzles 27 Unite States. Patent F that feed the flame tubes 16 are fed by ring manifold 28.

In operation, air is taken into casing 10 and compressed by compressor 11. The compressed air then flows into the combustion chamber flame tubes 16 where it is mixed with the fuel that is injected therein by nozzles 27 for combustion. Compressor 11 supplies a larger amount of air to the combustion chamber than is actually re quired for combustion in order to keep temperatures within the limitations imposed by the materials available for turbine construction. Thus, the gases that exhaust from the combustion chamber comprise a mixture of the actual products of combustion and a large percentage of unburned air that flows through nozzle ring 29 to impinge upon the blading of turbine 13 to supply the motive power therefor. Upon exhausting from turbine 13 the gases then discharge from nozzle 18 to furnish the propulsive power from the turbo-jet installation.

When it is desired to augment the velocity of the turbine exhaust gases to increase the jet propulsion effect of the engine the afterburner is employed. Afterburner operation includes opening eyelids 19 by any suitable mechanism so as to attain a maximum discharge area and the injection of fuel into the aft portion of casing 10 by afterburner fuel nozzles 24 for combustion with the unburned air in the turbine exhaust. Afterburners are generally operated only when an aircraft is traveling at very high speeds and altitudes or when maximum power output is desired since they are too ineificient for use during normal flight conditions.

Recently there has been considerable interest in the use of air-turbine driven fuel pumps for both the main combustor fuel and the afterburning fuel systems of turbojet engines. Such a successful fuel pumping system including the control devices therefor is shown diagrammatically in FIG. 1 in combination with the turbojet engine. Fuel enters the system through supply line 31 from the fuel tank 32 and passes through manual shut off valve 33 to primary pump 34 by way of inlet line 36 and also to secondary pump 37 by way of inlet line 38. In general pumps 34 and 37 will be of the same capacity and will be so designed that either one will be capable of supplying the fuel required by both the engine and afterburner for take-off operations. Both pumps, however, will have to operate in parallel to supply the full flow requirements of engine and afterburner at maximum flight speed. Primary pump 34 is driven by air-turbine 39 I through shaft 41 and secondary pump 37 is driven by air- 7 available to supply air to air-turbine 42 via line 52 and governor valve 46. Manual shut-off valve 53 controls the passage of air through branch 49 while the air in branch 51 is controlled by automatic shut-off valve 54.

Thus, fuel leaves pump 34 via line 56 passing through check valve 57 into line 58. When pump 37 is in operation fuel leaves therefrom via line 59 through check valve 61 and also passes into line 58. Line 58 then carries the fuel to by-pass valve assembly 62 and then to flow divider valve 63. By-pass valve 62 serves to establish control and govern the pressure in line 58 by varying the location of piston 64 under the influence of the force of spring 66 and the pressure in chamber 67. Thus piston 64 may be made to cooperate with abutment 68 so as to seal off return line 69 or may be moved varying distances from abutment 68 thereby uncovering part or all of return line 69 allowing varying amounts of excess fuel to escape and return via line 69 to the inlet lines 36 and 38 leading to pumps 34 and 37.

Therefore, that fuel not by-passed from line 58 via return line 69 is carried on by line 58 into flow divider valve 63 where the flow is divided or apportioned between the main combustor and the afterburner. Flow divider valve 63 contains a spool 72 having lands 73, 74, 76 which divide the valve cavity into chambers 77, 78, 79, 81. Chambers 79 and 81 are connected by main combustor feed line 82 to main combustor throttle valve 83 and by pressure indicator line 84 via check valve 86 and line 87 to chamber 67 of by-pass valve 62. Chamber 77 is connected via line 88 to the downstream (low pressure) side of main combustor throttle valve 83. In normal operation spool 72 is located approximately in the position as shown in FIG. 1 wherein land 76 cooperates with abutment 89 impeding the flow of fuel from line 58 to main combustor fuel line 82 sufficiently to cause a pressure reduction from line 58 to line 82 and to also maintain a constant pressure drop across main combustor throttle valve 83. This normal operating position of spool 72 is established by a balancing of the force of spring 91 versus the pressure difference between chambers 77 and 81.

When spool 72 is in this normal operating position fuel is passed without restriction through the valve formed by land 73 cooperating with abutment 92 from line 58 via line 93 to the regulating valve 94. Regulating valve 94 consists of spool 96, chambers 97, 98 and 99 and biasing spring 101. This valve acts in a manner similar to the normal operation of flow divider valve 63 to regulate the pressure drop across the afterburner fuel throttle valve 102 in afterburner feed line 103 via line 105. Further, the pressure in chamber 99 is communicated through line 104, check valve 106 and line 87 to chamber 67 of by-pass valve 62. Thus, in effect regulating valve 94 determines the extent of flow allowed to reach the afterburner in response to varying operating conditions.

Fuel in afterburner feed line 103 passes from afterburner fuel throttle valve 102 through shut-off valve 107, which valve is mechanically linked to manual shut-off valve 53. Thus, valves 107 and 53 are arranged to be open for afterburner operation, only. Fuel leaving main combustor throttle valve 83 passes through manual shutoff valve 108 to the main engine combustion chamber 16. Valves 33 and 108 are mechanically linked and close when the engine is shut down.

In order to ascertain a pressure in line 58 sufficient to supply the fiow of fuel required either by the main engine combustor or by the afterburner, the pressures in chambers 81 and 99 are applied to chamber 67. In connection therewith check valves 86 and 106 act in cooperation with orifice 109 to block out the lower of the two pressures. Thus, should the pressure required in chamber 81 be higher than that in chamber 99 fuel from chamber 81 will flow through line 84, check valve 86, line 87, chamber 67, orifice 109 and line 69 back to the inlet of the pumps. Because of this flow, line 87 is essentially at the same pressure as chamber 81 and is thus at a pressure higher than in chamber 99. Check valve 106, therefore, closes preventing the flow of fuel from line 87 into chamber 99. The reverse situation would be true if chamber 99 were at a pressure higher than chamber 81. The pressure in line 58 is maintained higher than the pressure in chamber 67 by an amount determined by the force of spring 66.

To illustrate the operation of the control system in emergency conditions it will be assumed that either pump 34 or pump 37 has failed while the engine is in afterburner operation. If under these conditions, the fuel flow required is greater than can be supplied by the single operating pump, the pressure in line 58 will drop causing the spools 72 and 96 of valves 63 and 94 respectively, to move upward. Valve 62, of course, will close off preventing the by-passing of fuel back to the pump inlets. If the pressure in line 56 is insuflicient to maintain the desired pressure drop across main combustor throttle valve 83, spool 72 of valve 63 will continue its upward movement causing a restriction of the flow from line 58 to line 93 and thus to valve 94 by closing off the area between land 73 and abutment 92. In this manner flow divider valve 63 insures that the flow to the main engine combustor will be maintained at the expense of the afterburner fuel flow.

Pump overspeed is prevented in two ways. When the pumps (or one pump) are delivering more fuel than is required by the engine, the excess fuel is returned by return line 69 to inlet lines 36 and 38. In this manner, the pumps (or one pump) are at all times run at the minimum speed necessary to deliver the required pressure to line 58. Governor valves 44 and 46 have the primary purpose of limiting pump speed in the case of a fuel interruption. Check valves 57 and 61 prevent the recirculation of fuel through an inoperative pump.

Automatic pump selection is provided by automatic shut-off valve 54. During normal, non-afterburning op eration of the engine, valve 53 will be closed manually and valve 54 will be closed by the fuel pressure in line 55 leading from line 56 and acting on bellows 111. If, for any reason, pump 34 fails, the pressure in line 56 will drop allowing valve 54 to open. Air pressure will then be admitted to turbine 42 to bring pump 37 into operation to supply fuel flow to the engine.

Gbviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected to deliver fuel to a common point in said fuel system, a fuel line receiving said fuel, means for governing the pressure in said fuel line, said pressure-governing means being located in said fuel line, and means having one input and a plurality of outputs and a single actuator for controlling flow through the plurality of outputs for dividing the fuel flow from said pressure-governing means whereby the fuel demand of the main combustor is satisfied and substantially the remainder of said fuel flow from said pressure-governing means is directed to the afterburner, said dividing means being in series with said pressure-governing means in said fuel line.

2. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected in parallel, a fuel line receiving said fuel, first valve means for governing the pressure in said fuel line, said first valve means being located in said fuel line, by-pass means to return excess fuel from said first valve means to the inlets of said pumps, second valve means having one input and a plurality of outputs and a single actuator for controlling flow through the plurality of outputs in series with said first valve means in said fuel line for dividing the fuel flow from said first valve means whereby said second valve means promotes fuel flow through a first feed line to the main combustor to meet the fuel demand thereof and directs fuel in excess of said fuel demand through a second feed line to the afterburner.

3. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected in parallel, a fuel line receiving said fuel, first valve means for governing the pressure in said fuel line, said first valve means being located in said fuel line, by-pass means to return excess fuel from said first valve means to the inlets of said pumps, second valve means having one input and a plurality of outputs and a single actuator for controlling flow through the plurality of outputs in series with said first valve means in said fuel line for dividing the fuel flow from said first valve means whereby said second valve means promotes fuel flow through a first feed line to the main combustor to meet the fuel demand thereof and directs fuel in excess of said fuel demand through a second feed line, third valve means to limit fuel flow to the afterburner, said third valve means being connected in said second feed line.

4. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected to deliver fuel to a common point in said fuel system, a fuel line receiving said fuel, an air-turbine drive for each of said pumps, means for controlling the pressure of said fuel in said fuel line, by-pass means to return excess fuel from said pressure-controlling means to the inlets to said pumps, means for dividing the fuel flow from said pressure-controlling means to apportion said fuel flow between the main combustor and the afterburner, said flow dividing means being connected in said fuel line in series with said pressurecontrolling means, means for automatically impressing upon said flow dividing means changes in the fuel fiow to said main combustor whereby said flow dividing means responds by reapportioning the flow of fuel leaving said flow dividing means to meet the fuel requirements of said main combustor and simultaneously adjusting the flow of fuel available for delivery to said afterburner.

5. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected in parallel, a fuel line connected to said pumps, means for controlling the pressure of the fuel in said fuel line, means for apportioning the fuel output from said pressure-controlling means between the main combustor and the afterburner, said pressure-controlling means and said apportioning means being connected in series in said fuel line, a first feed line connecting said apportioning means with said main combustor, a second feed line connecting said apportioning means with said afterburner and means connected between said first feed line and said apportioning means to 6 automatically adjust said apportioning means to reapportion the flow of fuel passing therethrough to said first feed line to meet the fuel requirements of said main combustor and simultaneously adjusting the flow of fuel available for delivery to said afterburner.

6. A fuel system for an aircraft power plant having a main combustor and an afterburner, said fuel system comprising two pumps connected in parallel, a fuel line connected to said pumps, means for controlling the pressure of the fuel in said fuel line, means for apportioning the fuel output from said pressure-controlling means between the main combustor and the afterburner, said pressure-controlling means and said apportioning means being connected in series in said fuel line, a first feed line conmeeting said apportioning means with said main combustor, a second feed line connecting said apportioning means with said afterburner, means to limit the flow of fuel through said second feed line to said afterburner, said flow-limiting means being connected in said second fuel line, first automatic means connected between said first feed line and said apportioning means to adjust said apportioning means to reapportion the fiow of fuel passing therethrough to said first feed line to meet the fuel requirements of said main combustor and simultaneously adjusting the flow of fuel available for delivery to said flow-limiting means and second automatic means connected between said second feed line and said flow-limiting means to vary said flow-limiting means to determine the allowable fuel flow to pass therethrough to said afterburner under varying operating conditions.

7. The fuel system recited in claim 6 wherein the pres sure-controlling means is responsive to the higher of the pressures in said apportioning means and said flow-limiting means.

References Cited in the file of this patent UNITED STATES PATENTS

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