US2971336A - Fuel feed and power control system for gas turbine engines having means for avoidingcompressor stall - Google Patents

Description

3 Sheets-Sheet 1 C. MOCK FOR AVOIDING COMPRESSOR STALL FUEL FEED AND POWER CONTROL SYSTEM FOR GAS TURBINE ENGINES HAVING MEANS Feb. 14, 1961 Filed March 15, 1952 K Y MC 5 m M g WM 0 mg m w 5 c A. M M A A EMT i 6 0% Y E E B N L m [P I 57/6 4/ 6 \L Us F A A v/ 7 E/ 0 WW7 W m V WWM, 5 1. a 5 ii L F C 0 0 MC w w w c E WE W F 1. F M 2 T MW ML Aw Pp I. 0 W E 0 0 w m w m. m MH QMK Qmmk fisk Feb. 14, 1961 Filed March 15. 1952 F. C. MOCK FUEL FEED AND POWER CONTROL SYSTEM FOR GAS TURBINE ENGINES HAVING MEANS FOR AVOIDING COMPRESSOR STALL 5 Sheets-Sheet 2 UNA/[C750 7'0 /LOTCJ CO/VTEOL MEMBER 26 INVENTOR.

AT TOE/V5) Feb. 14, 1961 F. c. MOCK FUEL FEED AND POWER CONTROL SYSTEM FOR GAS TURBINE ENGINES HAVING MEANS FOR AVOIDING COMPRESSOR STALL 3 Sheets-Sheet 3 Filed March 15, 1952 Y m m E M M m E 0 h w W E Q K A, .Q m E :5 h w wmw l a 1 m F Q B FUEL FEED AND POWER CONTROL SYSTEM FOR GAS TURBINE ENGINES HAVING MEANS FOR AVOIDING COMPRESSOR STALL Frank C. Mock, South Bend, Ind., assignor to The Bendix Corporation, a corporation of Delaware Filed Mar. 15, 1952, Ser. No. 276,791

9 Claims. (Cl. 60-3938) This invention relates to a fuel feed and power controi system for gas turbine engines; more particularly for gas turbine engines adapted for the propulsion of aircraft, such as what are now commonly known as turbojet and turboprop engines.

It is, of course, highly desirable that a pilot or operator of a turbojet or turboprop engine be free to accelerate rapidly and smoothly at all altitudes without worrying about, or danger of, (a) exceeding the upper tempera ture limit for that particular engine, (b) causing flame blow out in the burner or burners, or (c) producing surge or compressor stall. There are presently known means of producing a metering device which will meet the above requirements for the full range of engine speed at one altitude and one temperature, but such devices grow quite complex and may not suffice for all operational altitudes and temperatures. An object of the instant invention, therefore, is to employ a certain parameter that is particularly suitable for the conversion of the engine requirements at one altitude and temperature to another altitude and temperature, and to utilize a relatively simple mechanical and hydraulic system to obtain these corresponding regulations.

First discussing the problem of compressor stall, with a dynamic air compressor running at a given speed and delivering through an orifice of fixed size, the air weight delivery tends to vary as the entering pressure and inversely as the entering temperature. If the air be raised in temperature after leaving the compressor but before reaching the discharge orifice, this will in general cause the weight delivery to decrease and the delivery pressure to rise, up to a point where the compressor stalls. If, however, the delivery conditions be such that the velocity of flow through the orifice approximates that of sound, as indicated or defined by the absolute temperature of the air approaching the orifice, this absolutely limits the weight flow through the orifice; the velocity varies with the square root of the absolute temperature, and the density inversely as the absolute temperature (and directly with the pressure), so that the net weight flow varies inversely with the square root of the absolute temperature at any given pressure.

This latter is generally the case with a gas turbine in the maximum power range. The velocity is sonic through the nozzles through which the gas enters the turbine blades; the weight flow varies with the square root of the gas temperature entering the turbine and directly with its pressure; and all this is only remotely connected with the temperature eptering the compressor.

If the weight of air which can be passed by the turbine under the condition of maximum turbine gas temperature, which as above stated is practically independent of entering air temperature, is in excess of that quantity which the compressor could deliver at the same pressure (note that this last quantity does vary with entering air" temperature), the maximum turbine gas temperature dictates the maximum amount of fuel which can be fed,

But if raising the turbine gastemperature to the maximum ate-nt O 2,971,336. Patented Feb.. 1 4, 196 1 indicated by turbine endurance causes the compressor to stall, then lower combustion temperature, lower fuel flow, and lower'thrust must be tolerated. Obviously, the engine design must be such as to permit the engine to run at steady speed without compressor stall; hence the loss in performance imposed by compressor stall characteristics is usually confined to slower acceleration. in the mid-speed range. 1

In accordance with the present invention, maximum, fuel flow to the engine for any condition of operation is. based on the following: Weight of rue1=P,, ir ,,/P,, -K in which 1 is the total air pressure at the entrance to the compressor, P is the total pressure at the discharge end of the compressor, theta an expression of entering air tempera ture in terms of some standard temperature, and K a numerical constant. The actual value of the function f is multiplex. The expression P /P or pressure rise" ratio, is basically a function of engine speed squared,

and regulation according to it may be used to obtain an approximate equivalent of speed regulation. Similarly /P,, /P, is an indication of the volume of air flowingj .j Figure 1 through the compressor, as is well known, and when properly combined with the factor P times the square root of theta, it may be used to regulate fuel flow in proportion to mass air flow. Finally, it has been determined that the total expression above given,

is a parameter of the stall characteristic.

Basically, the system as devised for carrying out the above formula comprises a fuel supply conduit or flowpassage having a pair of metering orifices in series, one of said orifices having its area varied as a function of P g/P l, and the other orifice being subject to combined" manual and all-speed governor regulation; while the metering head across the two orifices is varied as (P xx/m so that the velocity of flow is proportional to a1X\/ 5 Such a system not only possesses the advantage of avoiding compressor surge but also reduces the tendency' towards blow-out, promotes improved all-speed governor operation at all altitudes, is adapted for both turbojet] and turboprop engines, compensates for variations in operating characteristics of individual compressors of' the? same design and for compressor bleed-off for accessory,

operation, and incorporates other features of advantage which will become apparent in view of the following description taken in conjunction with the drawings, wherein: Figure 1 is a sectional view of a turbojet engine' equipped with a fuel feed and power control system in. awordance with the invention;

Figure 2 is a schematic sectional view of the fueli feed and power control system used on the engine of Figure 3 is an enlarged view of the so-called stall. modulator section of Figure 2; f

Figures 4 and 5 aresections taken substantially on the lines 4-4 and 55, Figure 3; and

Figure 6 is a performance curve.

Referring to Figure 1, a gas turbine engine is generally indicated at 10; it includes a series of combustion chain bers 11, mounted in a casing having a header or air. intake section 12. A dynamic compressor is indicated; at 13; it is shown as of the axial flow type, driven bymeans of a turbine 14 through a shaft 15. Each of the combustion chambers is provided .with a burner nozzle 16, to which metered fuel is supplied under pres- 1 sure by way of a conduit 17, fuel manifold 18 and individual fuel lines 19, The conduit 17 receives metered p,

, section 22, and stall modulator section 23.

Fuel from a suitable source of supply such as a fuel tank, not shown, flows to chamber 24 of the regulator through inlet conduit 25, 25, having a suitable pres surizing device therein such as a pump 26. When the supply or P1 pressure in chamber 24 exceeds a predetermined value, excess fuel is returned to the low pressure side of the pump by way of port 27 and conduit 28. The port 27 is controlled by a by-pass valve 29, normally-urged to seated position by a spring 36), located ina chamber. 31, vented to metered fuel .(P4) pressure by way of damping restriction 32 and passage 33. A diaphragm 34 is connected to the stem of valve 29 and issubjected to the P1 minus P4 differential, so that the supply pressure will always be maintained at a given value above metered fuel or P4 pressure, as determined by'the force of spring 36}. Chamber 31 is vented to P'l or pump inlet pressure by way of a restriction 35, which is preferably smaller than restriction 32, to effect removal of any air or vapor bubbles that-may tend to form in the fuel in said chamber. A spring-pressed relief valve 36 is mounted in the larger by-pass valve 29; its purpose is to relieve excess pressure build-up should the valve 29 become. stuck, or the fueicut-oif valve 49 be closed.

From chamber Z4-fue1 flows by-way of orifices 3'7 and multiple ports 38 across regulator valve as to chamberAtl. Here as well as in passage 41 the fuel is at P2 pressure. Between passage 41 and continuation passage 42 is an offset provided with an, orifice 43, the area of which is controlledor regulated by a modulator valve 44 in a manner and for a purpose to be described. After taking the drop, across valve 44, the fuel is at P2 pressure; it flows to governor chamber 45, thence through metering restrictions. 46, 46 into annular chamber 47 at P4 pressure, from which it flows across shut-off valve 49 and passage 48 to conduit 17, the latter, as heretofore noted, leading to the fuel manifold 18.

The pressure differential (P2P4) across themo'dulator orifice 43 and metering orifice or orifices 46 in series is determined by the action of the, regulator valve 3 9, which is urged toward open position by a substantially constant rate, spring 50 and toward closed position bythe fuel differential pressure across diaphragm 51, the latter constituting a movable or flexible wall between chambers 40 and 52. In chamber 52, the fuel is atvcompensating or P3 pressure, and While the pressure difference P2 minus P3 is substantially constant at all times as determined by spring 55 the ratio of the differential P2 minus P3 to the total meteringdifferential P2 minus P4 is modified as'a function of the pressure and temperature of the air flowing to thevengine, to thereby reposition the regulator valve in relation to changes in these respective parameters and correspondingly modify the fuel metering head across orifices 43 and 46. This is accomplished by a temperature needle 53 and a pressure needle 54, the former controlling an orifice 55 and the latter an orifice 56, arranged in series in a passage talcing fuel from P2 chamber 40 at 57 and continuing on across needle 53 through chamber 52, passage 58, across needle 54, thence by way of chamber 59, and passage 60, to metered fuel chamber 47. Temperature needle 53 is carried by the, movable end of a bellows 61, which together withcapillary tube 62 and bulb 63 are loaded with asuitable temperature-sensitive fluid, said bulb be ing exposed to the air entering the compressor 13. The pressure needle is connected to the movable end of arievacuated bellows by means, of'stem'65, arm- 66,3

shaft- 67' and arm 68. Bellows 64 is located sothat-it will be exposed to ram or compressor inlet pressure, Such pressure may be communicated to the bellows 64 by impact tube 64.

A brief description of the operation of the regulator and coasting pressure and temperature compensating cir-' cuit follows:

Starting with chamber 40, there is in effect a pair of flow passages in parallel leading therefrom and terminating in the P4 or metered fuel chamber 47. One of these, the main flow circuit, comprises passage 41, orifice 43, passage 42, governor chamber 45 and metering orifice or orifices 46; the other, the compensating circuit, comprisespassage 57, temperature orifice 535, P3 chamber 52, passage 58, pressure orifice 56, chamber 5% and passage 60. Since the respective pressure at the beginning and termination of these circuits, viz. P2 and P4, are common to both, at given areas of the orifices in series .therein, the total drop from the chamber 4% to chamber 47 will be the same for both. The spring 50, representing a substantially constant force, tends to maintain the pressure difference between P2 chamber 46 and P3 chamber 52, or P2 minus P3, constant, and if there isa variation in either of these pressures, the regulator valve 39 will open or close to a position such as will reestablish the differential. Thus, should there be an increase in entering air temperature, needle 53 will move in a diretcion to decrease the area of. temperature ori fiice 55, and assuming a given area of the orifices 56, 43' and 46, there will be a momentary increase in the P2 minus P3 differential over and above that set by spring es, and regulator valve 39 will move toward closed position to re-establish the differential, thereby auto matically reducing the metering head across orifices 46. Should there be a decrease in entering air pressure as by an increase in altitude, pressure needle dd will move in a direction to increase the area of orifice 56 and there will be a decrease in the drop across said orifice and a momentary decrease in pressure in chamber 52, where'-- upon regulator valve 39 will move toward closed posi-- tion to re-establish the differential across the diaphragm 51 as determined by spring 50 and there will be a cor responding decrease in the metering head (assuming a given area of orifices 55, 4 3 and 46). The profile of needle 54 is preferably such as to vary the metering head as the engine or compressor air intake pressure squared, and that of needle 53 such 'as Will cause the metering head to vary directly as the quantity theta (6). As is well known, there is a definite relationship between the rate of fuel supply and the r.p.m. of a gas turbine engine or turbine-compressor combination for a given entering air density, or pressure and temperature. Thus as altitude increases, for example, the speed will increase at constant fuel flow, and hence fuel. flow must be reduced to maintain the speedconstant. The pressure and temperature control circuit above described will automatically adjust the metering head in a manner such that dangerously'high burner'temperatures are avoided when accelerating at altitude; and this is accomplished Without restricting the area of the metering orifices and at a given position of the governor elements and valve which control said latter orifices for a given power or throttle setting. Also, the tendency toward flame-out or blow-out, which increases with altitude, may be great- .iy reduced by correspondingly reducing the fuel feed rate at low values of entering air density.

It may be desirable to provide a minimum flow bleed 69 across the diaphragm 51.

Should the area of the metering orifices 46 be increased or decreased, there will be a momentary decrease or increase in the differential across the diaphragm 51, and

1 the regulator valve 39 will correspondingly open or close,

as the case may be, to restorethe difierential to the value determined by springfitl and thus meet. the demandsgof the control. Metering area is controlled or regulated by a throttle or governor valve 70, which is shown in the form of a cylindrical sleeve secured on a rod 71, said sleeve being slidably mounted in a cylindrical support 72, and provided with the metering orifices 46 heretofore noted. The rod 71 is provided at its right-hand end with a member 73 having a bearing sruface which is engaged by the shoes 74 of centrifugal governor weights 74, the latter being pivotally supported by the head or bracket portion 75 of a governor shaft 76, provided at its outer end with a drive spline 77, having a driving connection with the engine through shaft 77', note Figure 1. At its left-hand end, the rod 71 terminates in a flared head 78, which constitutes an abutment and spring socket for the one end of a governor spring 79, the opposite end of said spring engaging a member 80, slidably mounted on a rod 81, which in addition to supporting the governor spring assembly, also provides an exteriorly adjustable minimum closure stop for the governor valve 70. The governor, or more specifically the governor spring, may be selectively reset by the pilot through internal arm 82, which is secured on a shaft 83, projecting externally of the fuel control housing and having secured on its outer end an arm 84, note Figure l, to which is connected 8. link 85, extending back to the pilots control member or quadrant not shown.

The fuel shut-off valve indicated at 49 is used to completely blockfiow of fuel to the engine when the latter is shut down and may be operatively connected to the throttle control linkage for convenience of the pilot.

At this point, a brief reference to Figure 6 may be opportune. The curve a in this figure represents the fuel required to run at steady speeds as selected by the pilot when he resets the all-speed governor. At any point along this line the governor is in equilibrium, viz. the centrifugal weights 74 balance the opposing force of the governor spring.

Curve b-c-d-e represents the maximum rate of fuel feed that can be tolerated:

(1) Without danger of overheating during acceleration particularly in the low speed end of the range;

(2) Without danger of compressor stall; and

(3) Without blow-out in the upper speed range.

The acceleration range from b to 0 represents an appreciable number of seconds and it is quite important that the maximum turbine gas temperature be regulated within safe limits in this range. Therefore, the fuel feed here is calibrated to approximate a constant turbine gas temperature or a constant temperature rise of combustion. The stall range region, c to d, represents a dip in maximum operating temperature and as nearly as is known can only be determined empirically for each design of engine. In the range from d to e, acceleration occupies only a very few seconds and quite high turbine gas temperatures could be employed without harm to the engine; but, it is found that the fuel feed equivalent to such high temperatures frequently tends to cause blow-out. So again the range from d to e must be determined empirically. Further, as is well known, the tendency towards blow-out increases at high altitudes, and since the idling speed must be increased at high altitude to a value higher than that represented by the point d, one of the advantages of the present formula is that the factor P may be arbitrarily decreased at high altitude to reduce the fuel feed and danger of blow-out.

As the control of the instant invention operates, the rate of fuel feed is defined by curve b-c-d-e, following resetting of the governor by the pilot when he desires to accelerate from a given speed or setting on curve a to a higher speed or setting on the latter curve. Curve b-c-d-e, obtains its general slope characteristics from the action of the modulator valve 44, a description of which follows, while its vertical values are modified by the pressure and temperature compensation on the metering head in the manner heretofore described.

The modulator valve 44 operates to varythe areaof the orifice 43 as a function of at! al or compressor pressure ratio. Its primary operating components comprise two evacuated bellows or sylphons and 91, the former bellows 90 being located in a chamber 92, to which compressor intake pressure is communicated by conduit 93, and the latter bellows 91 being located in a chamber 94, to which compressor outlet pressure is communicated by conduit 95. The modulator valve 44 is normally urged toward open position by a spring 96. A stem or rod 97 is pivotally connected at one end, as at 98, to the valve 44 and at its opposite end carries a center roller 99 and a pair of side rollers 100 and 100', compare Figures 3,4 and 5, all three rollers being mounted on a common axis or journal pin 101, These rollers constitute a traveling pivot or fulcrum point for varying the advantage of a suspended horizontal lever or bar 102, which is in effect a lower or bottom track for said rollers 100 and 101). The ,bar 107. is pivotally suspended at its opposite ends from the movable end of bellows 9G by rod 103 and side links 104, 104' (see Fig ure 4) and from the movable end of bellows 91 by rod N5 and side links 106, 106 (see Figure 5). An upper fixed track is indicated at 107; it is secured to the adjacent frame structure by a bolting-on bracket 108. At its left-hand end the rocking bar or lever 102 is provided with a guide pin or rod 109, and at its right-hand end it is adapted to engage a follower roller 110, mounted on a journal pin 111, which also connects the lower ends of links 104, 194, note Figure 4. A contact member in the form of a rod 112 extends downwardly from links 104, 104, and at its lower end engages an adjustable abutment screw 113, carried by theadjacent end of an arm 114, fulcrumed at 115, the opposite end of arni 114 carrying a ball valve 116, which controls a pressureescape orifice 117 at the terminus of a passage 118, com pare Figures 2 and 3, by means of which fuel under pressure may flow from a servo bellows 119, the latter receiving its operating pressure by way of a passage 120, leading from the passage 42 and provided with a cali brated restriction 121. The movable end of bellows 119 has connected thereto a lever 122, pivoted at 123, and at its free end provided with a fork or yoke 124, engaging" the adjacent bearing surface of a collar on the outer end of modulator valve 44. A follower spring 126 norrn-ally urges the outer end of valve arm 11.4 upwardly and hence tends to close ball valve 116. i

The pressure ratio control just described operates as follows: 1

When the engine is at rest, the pressures in chambers 92 and 94 are equal. (it could be atmospheric) and the pull or upward forces exerted by the evacuated bellows 9t) and 91 on opposite ends of the rocking bar 102 are equal. The pressure in servo bellows 119 being at this time relatively low, spring 96 forces modulator valve 44 open and moves rollers 99, 100, 100 to their extreme left-hand position. Note dotted position in Figures 2 and 3. Since the upward forces at opposite ends of rocking bar 1112 are equal and the said rollers are consider .ably off-center, valve arm 114 is urged clockwise and ball valve 116 closes escape orifice 117. As soon as the engine starts, fuel pressure builds up in bellows 119, turning lever 122 counter clockwise and forcing rollers 99, 1%, 109' to the right; also there is a build-upof'compressor outlet pressure in bellows chamber 94. Since the upward forces exerted by the bellows 90 and 91 are proportional to compressor inlet and outlet pressures, respectively, the quotient or geometrical ratio of these forces is proportional to compressor ratio, Rollers 99, 100, 100' continue to the right until the differential of the pressures in chambers 92 and 94, actingthrough bellows 9t) and 91, rocking bar 102 and rod 112, ettectg unseat'ing of ball v'alve1l6 to a pointwhere the servo bellows 119 is unable to further compress spring 96. This positions modulator valve 44 at a point of equibrium for the then existing compressor pressure ratio.

General description of operation In the respectivepositions of the various parts as shown in'Figures 2 and 3; assume that the engine is operating at steady speed 'at a pointin the low speed range, say at point x'on curve a in Figure 6; because of the low speed the value of F /P is low and the modulator valve is well closed.

If now the pilot desires to accelerate to the point z, which may represent the maximum speed setting, he would advance his'throttle. lever to stiffen the governor spring, and the throttle valve would go Wide open, or move to the right against its full open stop. This would result in a sharp increase in the rate of fuel fiow up to the point x, on curve b-c, as determinedby the then existing area of the modulator valve orifice; (also the increased fuel delivery will probably raise the compressor pressure ratio somewhat to give a sli htly greater modulator valve opening than existed under operation at point x). Since the value at x is in excess of that required to run at steady speed, the engine accelerates, thefpressure ratio increases,- and the modulator valve opening similarlyincreases to give the fuel curve bca'e, with the metering area of the modulator valve controlled as a function of Fag/P l, and the meteringheadas a function of P i -As the engine-speed-and compressor pressure ratio approach thespeed of governor cut-off at point z, the governor weights fly outand close the governor valve slightly,".to determine the final steady speed point z.

An important advantage should be noted at this point, namely, that since the head across the governor or throttle valve varies with entering air pressure and temperature, the governor elements including the governor spring 79 and weights 74 will assume about the same relative positions for a given speed at all altitudes.

Since the acceleration fuel flow is largely dictated by pressure ratio, the herein disclosed method of metering tends to compensate for variation in design of individual compressors, or for changes in characteristics due to service deterioration. Further, compensation is in the right direction when part of the compressor air is taken off at diiferent stages to operate accessories, auxiliaries or for other purposes. 'Another advantage is that the bellows and half-ball type of servo system involves no pistons or other moving parts having close tolerances which are easily incapacitated by dirt and other foreign matter in the fuel.

:For'turboprop controls there is a power range in which engine speed is controlled by the propeller governor. In this range a 'pilot should be able to select or regulate fuel flow independently of engine speed. To obtain such regulation with the system of the instant invention, the lever indicated at 127, Figures 2 and 3, is provided, said lever being secured on a shaft 127', which projects exteriorly of the control housing and has on its outer end an arm '128, which is connected to the throttle or allspeed governor control linkage in a manner such that in the power range above noted, the governor reset lever 82 of Figure 2 is in its maximum speed position, or at least in a position such that the governor valve metering orifice 46 does not change with changes in engine speed, although successive positions of the pilots control member will produce different settings of lever 127 and modulator valve 44. By this means, when operating in the above noted'power range, governor valve metering area and modulator valve area are controllable independently of engine 'spe'edgwhile" the metering .head will be automatically'compensated for-changes in pressure. and temperature-of the air flowing" tothe engine. Then for a (iii given setting of the pilots control member, fuel feed'will be proportional to the power required to turn the propeller' at a given speed and at a given propeller blade pitch, while the metering'head will follow (P X- 0)? or it will beautomatically compensated forchanges in entering air pressure and temperature. 1

Although'only one physical embodiment of the invention has been schematically illustrated and described, such disclosure obviously constitutes a teaching-Which will enable those skilled in the artto practice the invention and to make the required changes in form and relative arrangement of parts-to adapt the improved control to engines having difierent characteristics.

I claim:

1. In a system for controlling the rate of fuel feed 'to a gasturbine engine having a compressor, means for metering fuel to the engine at a rate proportionalto P: al

including a first element responsive to changes in compressor inlet pressure, a second element responsive. to changes in compressor discharge pressure and means operably connecting said first and second elements with said device, where P represents. the air pressure entering the compressor, P the air pressureleaving the compressor and theta the temperature of the air entering the compressor in terms or some standard temperature.

2. In a system for controlling the rate of fuel feed to a gas turbine engine having a compressor, a fuel metering orifice, a valve for controlling said orifice, means for regulating the metering-head across said orifice, means for automatically obtainng the ratio between compressor inlet and compressor discharge pressurcs, rneans for regulating one of said fuel flO controlling means by said ratio obtaining means, and means for regulating the othe'r of said fuel flow controlling means as a function ofthe pressure and temperature of the air entering the compressor.

3. in system for controlling the ratevof fuel feed to a gas turbine engine having a compressor, 'a fuel metering orifice, a valve for controlling said orifice, means for automatically obtaining the ratio between compressor inlet and compressor discharge pressures, means for regulating said valve by said ratio obtaining means, and means ior automatically regulating the fuel metering head across said orifice as a function of the pressure and temperature of. the flowing to the compressor.

4. in a system for controlling the rate or" fuel feed to a gas turbineengine having a compressor, a fuel metering orifice, a valve for controlling said orifice, a pair of pres sure sensitive devices, one responsive to compressor in take pressure and the other responsive to compressor out let pressure, means for obtaining the ratio of said pressures, means connecting said ratio obtaining means to said valve for regulating the latter, and means responsive to changes in the pressure and temperature of the air entering the compressor for regulating the fuel metering modulator valvecontrolling the other of said orifices,

means for automatically obtaining the ratio between com- 6. In a system for controlling the rate offuel feed to a gas turbine engine having a-coinpressor, a fuel conduit for supplying fuel to the engine, a pair of. fuel metering orifices in series in said conduit, an adjustable all-speed governor and associated valve for controlling one of said orifices, a modulator valve for controlling the other of said orifices, means responsive to the ratio between compressor inlet and compressor discharge pressures for controlling said modulator valve, a regulator valve for controlling the fuel metering head across said modulator and all-speed governor valves, and means responsive to changes in pressure and temperature of the air entering the compressor for modifying the action of said regulator valve.

7. In a system for controlling the rate of fuel feed to a gas turbine engine having a compressor, a fuel conduit for supplying fuel to the engine, a pair of fuel metering orifices in series in said conduit, an adjustable all-speed governor and associated valve for regulating flow across one of said orifices, a modulator valve for regulating flow across the other of said orifices, a power servo for actuating said modulator valve, means responsive to the ratio between compressor inlet and compressor discharge pressures for controlling said servo, a regulator valve for controlling the fuel metering head across said modulator and all-speed governor valves, and means responsive to changes in pressure and temperature of the air entering the compressor for modifying the action of said regulating valve.

8. In a system for controlling the rate of fuel feed to a gas turbine engine having a burner and a compressor for supplying air under pressure to said burner, a fuel conduit for supplying fuel under pressure to the burner, a pair of fuel metering orifices in series in said conduit, an adjustable all-speed governor and associated valve for controlling the other of said orifices, a device for adjusting said modulator valve, means responsive to changes in the ratio between compressor inlet and compressor discharge total pressures for controlling said device, means responsive to changes in'pressure and temperature of the air flowing to the engine for controlling the fuel metering head across said modulator and all-speed governor valves, 21 pilots control member for resetting said all-speed governor to select an operating speed for the engine, and an alternate control device for said modulator valve adapted for connection to said pilots control member whereby during a certain range of engine operation governor valve orifice area and modulator valve orifice are controllable independently of engine speed with automatic compensation for changes in entering air pressure and temperature.

9. In a system for controlling the rate of fuel feed to a gas turbine engine having a compressor, a fuel metering orifice, valve means for controlling said orifice, means for automatically measuring a predetermined function of the ratio of pressures across the compressor and operatively connected to said valve means for controlling same in such a manner that the flow of fuel through said orifice varies as a predetermined function of said ratio, and means for regulating the fuel metering head across said orifice as a function of P V5, where P represents the air pressure entering the compressor, and theta the temperature of the air entering the compressor in terms of some standard temperature.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,842 McFarland Mar. 10, 1936 2,256,121 McCarty Sept. 16, 1941 2,385,366 Lysholm Sept. 25, 1945 2,400,048 Jones May 7, 1946 2,422,808 Stokes June 24, 1947 2,447,263 Mock Aug. 17, 1948 2,531,780 Mock Nov. 28, 1950 2,581,275 Mock Jan. 1, 1952 2,581,276 Mock Ian. 1, 1952 2,598,681 Garbarini et a1 June 3, 1952 2,599,288 Schaefer June 3, 1952 2,643,513 Lee June 30, 1953 2,643,514 Jubb June 30, 1953 2,657,530 Lee Nov. 3, 1953 2,857,739 Wright Oct. 28, 1958 FOREIGN PATENTS 934,814 France Ian. 19 1948 941,556 France July 19, 1948 429,682 Great Britain June 4, 1935 569,196 Great Britain Mar. 24, 1944 575,008 Great Britain Jan. 30, 1946 595,357 Great Britain Dec. 3, 194-7

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