US3882675A

US3882675A - Device for programming the afterburning-initiation phase in a turbojet engine

Info

Publication number: US3882675A
Application number: US333371A
Authority: US
Inventors: Pierre Michel Andre Galmiche; Henri Jacques Jourdier; Pierre Paul Louis Odeyer
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1972-02-18
Filing date: 1973-02-16
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13
Also published as: FR2172006B1; DE2307305A1; DE2307305C3; DE2307305B2; FR2172006A1; GB1411172A

Abstract

In and for a turbojet engine of the kind comprising a compressor, an afterburning duct, means for supplying the afterburning duct with fuel and means for metering the flow of fuel injected into the duct, the flow-metering means being sensitive to a parameter Beta P2, in which P2 is a characteristic working pressure of the compressor and Beta is a coefficient which is less than or equal to one, a programming device for the afterburning-initiation phase, which device comprises means for modifying the coefficient Beta to reduce temporarily the coefficient Beta during the afterburninginitiation phase, and means for automatically bringing the Beta -modifying means out of action after the moment at which the fuel has actually been ignited in the afterburning duct.

Description

States atent 1 Galmiche et a1.

DEVICE FOR PROGRAMMING THE AFTERBURNING-INITIATION PHASE IN A TURBOJET ENGINE Inventors: Pierre Michel Andre Galmiche, Le

Mee-sur-Seine; Henri Jacques Jourdier, Moissy-Cramayel; Pierre Paul Louis Odeyer, Paris, all of France Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France Filed: Feb. 16, 1973 Appl. No.: 333,371

Assignee:

Foreign Application Priority Data Feb. 18, 1972 France 72.05566 US. Cl 60/243; 60/241; 60/3928 R Int. Cl. F02k 3/10 Field of Search 60/241, 239, 261, 233,

References Cited UNITED STATES PATENTS 6/1965 Herbert 60/239 3,271,946 9/1966 Desmazes 3,298,180 l/1967 Trinkler 60/239 X 3,714,784 2/1973 Glaze 60/243 3,719,047 3/1973 Briotet 60/239 FOREIGN PATENTS OR APPLICATIONS 796,203 6/1958 United Kingdom 60/243 Primary Examiner-C1arence R. Gordon Attorney, Agent, or Firm-William .1. Daniel [57] ABSTRACT In and for a turbojet engine of the kind comprising a compressor, an afterburning duct, means for supplying the afterburning duct with fuel and means for metering the flow of fuel injected into the duct, the flowmetering means being sensitive to a parameter BP in which P is a characteristic working pressure of the compressor and B is a coefficient which is less than or equal to one, a programming device for the afterburning-initiation phase, which device comprises means for modifying the coefficient B to reduce temporarily the coefficient B during'the afterburning-initiation phase, and means for automatically bringing the B-modifying means out of action after the moment at which the fuel has actually been ignited in the afterburning duct.

16 Claims, 9 Drawing Figures PATENTED HAY I 31975 Angle of lever o( and 72-.- 720% Engagement of afterourn/ng (67) Afterburning feed de vice (78. 73

Afterburn/n igniting de vi c QQZS Ignition de iECtiO/I Flow of afterbur n/ng fuel.

thro tt/ed. do an after:

burning in operation out of operation 0 eration P t j in operation out of operation :out of operation lit extinguished extinguished I lit extinguished fu/ /oad after urn/ng zero /thrott/ed down afterburn/ng time (seconds) mmgn MAY] 3 m5 Angle of lever ix Afterpurning rese/ec; t/on device (7 0) X X ref.

Y: Yref.

Locking (102) Afterburning feed device (78- 79) ffi-modifierj Signal. lampe for after.

burn ing ignition de vlceKiS? Signal lamp for actual funct oning of aftcr purn/ng(52) Flow of af terburnin g fu e/ SHEET 7 0i 7 fu/L load afterburning DRY' locked out of ope ation in operation out of operation out of opera ion V 7 s in oat/0n out of act/on lit extinguished extinguished lit ext/ngui'shed fu// /oad restrained afterburn/ng flow zero time (seconds) DEVICE FOR PROGRAMMING THE AFTERBURNING-INITIATION PHASE IN A TURBOJET ENGINE This invention relates to a device for programming the afterburning-initiation phase in a turbojet engine which is intended to propel a flying vehicle such as an aircraft, the turbojet engine comprising, in particular, a compressor, an afterburning duct, a device for supplying the afterburning duct with fuel, and a device for metering the flow of fuel injected into the duct, the flow-metering device being sensitive to a parameter ,BP in which P is a characteristic working pressure of the compressor, and ,8 is a coefficient which is lower than, or at the most equal to, one.

As is already known, a turbojet engine having afterburning comprises the following elements, arranged one after the other in the direction in which the gas flow passes through; a compressor, a main combustion chamber, an expansion turbine, an afterburning duct, and a propulsion nozzle.

A supply device, which can be brought into, or out of, operation, makes it possible to direct a flow of afterburning fuel towards the afterburning duct when extra thrust is required. This flow is usually regulated with the aid of a regulator/metering device which is associated with an engine control lever operated by the pilot. An ignition device, which can be brought into, or out of, operation, is generally provided in order to facilitate the initiation of combustion of the fuel which discharges into the afterburning duct.

The initiation of afterburning is only allowed under certain circumstances which, in the case of aircraft equipped with turbojet engines having afterburning of the known type, represent many restraints or instructions for the pilot.

Thus, the pilot must see to it that, at the moment at which he tilts the engine-control lever to the AFTER- BURNlNG position, the speed of rotation of the compressor and the temperature of the gases are equal to their respective fullload values under dry operating conditions, that is to say without afterburning. The use of afterburning is, in fact, only necessary and advanta geous when the rest of the engine is already working at full load. In addition, correct regulation of afterburning presupposes that the abovementioned parameters are kept constant throughout the period for which afterburning is in operation.

In order to prevent any premature initiation of afterburning (that is to say, before the dry full load has really been reached), the pilot must therefore have kept the engine control lever in the FULL-LOAD DRY position for a sufficiently long time to enable the parameters to actually settle at their desired values. He therefore may not directly swing the control lever from the THROTTLED-DOWN DRY position into any position whatsoever in the AFTERBURNING sector, without having marked time for a period of stoppage at the FULL-LOAD DRY position, and having made sure that the conditions allowing the engagement of afterburning are really complied with.

As will be realised, this constitutes a particularly dis advantageous operating restriction since it complicates the task of the pilot without, however, ruling out all risk of incorrect operation. It is, moreover, the basic cause of a loss of time during the acceleration process of an aircarft (for example on take-off or when climbing) which is propelled by a turbojet engine of this kind. Nevertheless, it has hitherto seemed difficult, or even impossible, to escape this problem.

Another constraint concerns the starting-up of combustion in the afterburning duct. The ignition device used for this purpose is often constituted by means which make it possible to inject into the main combustion chamber, for a certain period, an additional quantity of fuel, via an ignition injector the opening of which is located, for example, slightly upstream of the turbine. The flame which results from this passes through the turbine and thus makes it possible to obtain ignition of the fuel in the afterburning duct. This device, which has the advantage of being simple, nevertheless possesses the drawback that it causes, when brought into operation, an additional rise in the temperature of the turbine blades, which temperature, under dry operating conditions (that is to say under normal operating conditions, without afterburning), is already very high in modern jet propulsion engines.

In order to reduce this additional temperature rise to a minimum, it is therefore expedient to limit, to the greatest possible extent, the period for which fuel is injected through the ignition injector. Consequently, this injection must not start too early (that is to say before the conditions permitting the engagement of afterburning have been fulfilled), or be extended too late (that is to say after ignition of the fuel has actually been achieved in the afterburning duct) or for too long a time (in the event of unsuccessful igniting). The taking into acount of these restraints therefore adds still further to the complexity of the pilots task.

The primary object of the present invention is to free the pilot from all the instructions and restraints mentioned above, and to enable him to initiate afterburning without any special precaution having to be observed.

A further object of the invention is to provide better protection for the turbine, by the automatic monitoring of the start and finish of injection of the igniting fuel.

For this purpose, the invention provides a device for programming the afterburning-initiation phase, which comprises means for modifying the coefficient B, which are designed to temporarily reduce the coefficient B during the afterburning-initiation phase, and means for automatically bringing the ,8-modifying means out of action after the moment at which ignition of the fuel has actually been obtained in the afterburning duct.

These means for modifying the coefficient B thus constitute a device for temporarily restraining the flow of afterburning fuel.

The action of this flow restraining device is such that, for the entire duration of the afterburning-initiation phase, the flow of fuel actually injected into the afterburning duct remains very small (for example, equal to, or lower than, the flow corresponding to Throttleddown Afterburning), and this remains true whatever the position displayed by the engine control lever.

Starting, for example, from the THROTTLED- DOWN DRY position, the pilot can therefore move the engine control lever in one go direct to any position in the AFTERBURNING sector including the FULL- LOAD AFTERBURNING position in such a way as to preselect any load or rate of afterburning whatsoever, without having to worry about marking time for a period of stoppage at the FULL-LOAD DRY or THROTTLED-DOWN AFTERBURNING position. In actual fact, everything takes place during the period in which the fi-modifying means is in action, as if the control lever were being held artificially in the ENGAGE MENT AFTERBURNING or THROTTLED-DOWN -AFTERBURNING position. An awkward restraint and an idle period are thus eliminated.

According to one arrangement of the invention which is applicable to a turbojet engine equipped with an ignition-detecting device (for example an ionization probe) which emits a signal at the moment at which ignition of the fuel has actually been obtained in the afterburning duct, the means for disabling the B-modifying means are controlled by the ignition signal. A timing device may also be provided in order to introduce a predetermined delay into the bringing out of action of the B-modifying means, after the moment at which the ignition signal has been emitted. It is thus. possible to prolong the action of the B-modifying means slightly beyond the moment at which combustion has actually been initiated in the after-burning duct, so as to enable such combustion to become stable.

According to one arrangement of the invention, the B-modifying means comprise a pressure-modifying reducer which is supplied with fluid at a pressure of 3P The means for disabling the B-modifying means then comprise means for rendering the pressure-modifying reducer inoperative.

According to an arrangement of the invention which can be applied to a turbojet engine of the kind in which the pressure parameter [3P is generated, starting from the pressure P in a pressure-reducing device comprising at least one main reducer, the pressure-modifying reducer is constituted by an auxiliary reducer which is fed by the main reducer.

The pressure-modifying reducer may advantageously comprise a capacity or space which is fed, through a constricted orifice, with fluid at a pressure of 6P and communicates with a low-pressure space through another constricted orifice forming a leakage outlet through which, under operating conditions, the fluid escapes from the capacity at a sonic speed. The means for disabling the pressure-modifying reducer may, in that case, comprise means for stopping the escape of the fluid through the leakage outlet, for example, by cutting off communication between the capacity and the leakage outlet.

Another arrangement of the invention, which can be applied to a turbojet engine comprising, in addition, means (such as a valve) for bringing into, or out of, operation the supply device for the afterburning fuel, comprises an afterburning-preselection device, which may occupy either a dry operating position or an afterburning operation position, and also means (comprising, for example, a locking device) which are sensitive to at least one working parameter of the DRY turbojet engine, such means being designed to automatically activate the supply device when,'with the preselection a single lever which is capable of successively covering a DRY sector andan AFTERBURNING sector), the aforesaid preselection device. may advantageously be coupled to the control lever.

The pilotis thus freed from the duty of insuring that the speed of rotation and the temperature of the gases have reached the threshold permitting engagementof afterburning, and he can now, without taking any precautions, swing the engine control lever from any position whatsoever in the DRY sector into the AFTER- BURNING sector. By doing this, he is, in fact, exerting a double effect; on the one hand, he is calling upon the engine to function (if it was not doing so already) at full-load DRY, and, on the other hand, he is preselecting the functioning under afterburning conditions. But I this preselection does not, in turn, give rise to actual operation of the device for supplying the .afterburnin g fuel, until the above-mentioned parameter or parameters have reached values which show that full-load DRY has actually been obtained. 7 I

According to a further arrangement of the invention, which is applicable to a turbojet engine equipped with a device for igniting the fuel which discharges into the V afterburning duct, which igniting device can be brought into, or out of, operation, the means which are sensitive to the above-mentioned parameter(s) are also adapted to automatically bring such igniting device into opera-f tion when, with the preselection device in an afterburning operation position, the selected parameter or parameters have reached the threshold indicated previously.

Since activation of the igniting device and of the 'de-. 1 I

vice for supplying the afterburning fuel are controlled by the same signal, it will therefore be seen that the ig nition process proper cannot begin before the device for supplying afterburning fuel is actually. functioning. i

ming the afterburning-initiation phase, in accordance with the invention, possesses the three-fold advantage that it considerably simplifies the task of the pilot, provides better protection of the turbine, and leads to a major saving in the time required to establish after? burning.

The invention will now be further described, by way of example, with reference to the accompanying draw-- ings, in which:

FIG. 1 is a diagrammatic view of a turbojet engine with afterburning, which may be equipped with a programming device according tothe invention;

FIG. 2 is a diagrammatic. view of part of a regulator/metering device, fitted to the turbojet engine illustrated in FIG. 1, for the flow of afterburning fuel;

FIG. 3 is a chart illustrating the functioning of the regulator/metering device shown in FIG. 2; A

FIG. 4 is a simplified functional diagram illustrating a known afterburning-initiation sequence in a turbojet engine of the kind illustrated in FIG. I; FIG. 5 is a diagrammatic view of a pressure-reducing device of known type, which works in conjunction with the regulator/metering device shown in FIG. 2;

FIG. 6 is a diagrammatic view of a pressure-reducing device which is similar to that shown in FIG. 5 but is modified in order to form part of a device for programming the afterburning-initiation phase, according to the invention;

FIG. 7 is a simplified functional diagram showing an afterburning-initiation sequence which is obtained by using a programming device according to the invention;

FIG. 8 is a combination of charts showing the development, as a function of time, of various parameters or of the position of various members, in the course of the known initiation sequence shown in FIG. 4; and

FIG. 9 is a combination of charts which is similar to that shown in FIG. 8 but relates to the case of an afterburning-initiation sequence which is obtained by using a programming device according to the invention.

In FIG. 1 there is illustrated a turbojet engine which is intended for the high-speed propulsion of a vehicle, such as an aircraft. This turbojet engine comprises, after an air-intake (not shown), a compressor 1, a main combustion chamber 2, an expansion turbine 3, an afterburning or re-heating duct 4, and a propulsion nozzle 5 the cross-sectional area of which can be regulated by means of flaps 6. The arrows F symbolizes the flow of hot gases escaping from the turbine.

Main injectors 7 open into the main combustion chamber 2. A pump 8, which is supplied, via induction piping 9, with fuel originating from a source which is not shown, impels the fuel towards the injectors 7 through

delivery pipes

10, 11 between which there is interposed a flow regulator/metering device 12 of conventional type.

Mounted in the afterburning duct 4 are manifolds R R R;,, which are intended to permit the injection, into the flow F of hot gases, of a flow C of afterburning fuel which is impelled by a pump 13 through pipes l4, 15, a purger/distributor 16 and pipes CR CR CR the flow being metered with the aid of an afterburning regulator/metering device 17. The pump 13 is supplied with fuel from a source, which is not illustrated, via a supply device comprising an induction pipe 18 which can be blocked by means of an inlet valve 19. The supply device 18/19 is in, or out of, operation according to whether the inlet valve 19 is open or closed.

The rotational speed (if necessary corrected to take account of the flight altitude) of the compressor 1, and a characteristic working pressure, for example the delivery pressure of the compressor, have been designated by the reference symbols N and P respectively.

The pressure P which is taken off at a suitable point on the compressor 1, is transmitted, via a pipe 20, to a pressure-reducing device R which generates, from the pressure, a reduced-pressure parameter ,BP in which ,8 is a coefficient which is at most equal to one. The reduced-pressure parameter BP is transmitted, via a pipe 22, to the regulator/metering device for the flow of afterburning fuel.

The reference numeral 23 designates a control box which is connected, by

functional connections

24, 25, to the two regulator/metering devices 12 and 17 respectively, and from which there passes out an engine controllever M which is at the disposal of the pilot of the aircraft. This lever angularly covers a graduated sector, its position on the sector being defined by an angle a which is measured from a suitable starting point. Corresponding to each angle a of the lever, there is a given load which is set by the pilot. Five typical lever angles which correspond to the following situations: THROTTLED-DOWN DRY (that is to say without afterburning), FULL-LOAD DRY, ENGAGE- MENT AFTERBURNING, THROTTLED-DOWN AFTERBURNING and FULL-LOAD AFTERBURN- ING, have been designated by 01,, a a a and a, respectively. That portion of the sector which is covered between zero and a constitutes the dry sector, whereas that portion of the sector which is covered beyond 01 constitutes the afterburning sector. The engagement of afterburning is effected automatically when the lever M passes to the position defined by the angle a The turbojet is also equipped with a device for igniting the fuel which discharges into the afterburning duct. This device essentially comprises an auxiliary, or igniting, injector 26 which opens into the main combustion chamber 2 of the jet engine and makes it possible, when afterburning is being initiated, to deliver an extra quantity of fuel, upstream of the turbine 3, for a certain space of time. This fuel ignites because of the high temperature prevailing in the chamber 2 and thus produces a tongue of flame which passes through the bladings of the turbine 3 to ignite the afterburning fuel discharging, in particular, from the upstream injection distributor R1.

The igniting injector 26 is supplied, via a pipe 27 fitted with a one-way valve 28, with fuel which has been taken off at the outlet of the pump 13. An obturator 29, functioning on the all-or-nothing principle, makes it possible to bring the igniting device comprising the auxiliary injector 26 into, or out of, operation.

The afterburning duct is fitted with an ignitiondetecting device 30, which is adapted to emit a signal at the moment at which ignition of the fuel has actually been obtained in the afterburning duct. This signal, suitably amplified in an amplifying device 31, intervenes in the afterburning-initiation sequence, as will be explained later on. The ignition-detecting device may be of any known type, such as an ionization probe, fibre-optics detector, pressure-variation detector, etc..

The temperatures of the gaseous flow which prevail immediately upstream of the turbine 3, immediately downstream of the turbine, and in the nozzle 5, have been designated by T T and T respectively.

FIG. 2 shows, in greater detail, the regulator/metering device 17 for the flow of afterburning fuel.

This regulator/metering device is sensitive, on the one hand, to the above-mentioned reduced-pressure parameter BP and, on the other hand, to the lever angle a in the AFTERBURNING sector. It comprises, in particular, a rocking lever 40 which is articulated about a pin 41 and has two lever arms, the ratio between which is designated by a/b. One of the ends 40a of the rocking lever controls, via a servo-jack 42, the displacement of a metering piston device 43 which works in conjunction with a metering slit 44. A regulating valve (not illustrated) makes it possible, in known manner, to regulate the drop in pressure which takes place through the metering slit 44. For a given drop in pressure, therefore, the flow C of afterburning fuel is solely a function of the exposed cross-sectional area of the metering slit, that is to say, of the position of the metering piston device 43.

The reduced pressure 3P which prevails in, or is taken off from, a capacity 45, controls the movements of the other end 40b of the rocking lever 40 via aneroid capsules 46 and a hydraulic amplifier 47. For a given drop in pressure through the metering slit 44, therefore, the regulator/metering device 17 makes it possible to keep the ratio C/BP constant and equal to the ratio a/b of the lever arms of the rocking lever 40.

This ratio can be changed by varying, with the aid of the regulating lever M, the position of the articulation pin 41 in a slide 400 carried by the rocking lever.

FIG. 3 is a chart which shows the functioning of the regulator/metering device 17 in the C, [3P plane, for each lever angle a, and in particular a a (THROT- TLED'DOWN AFTERBURNING) and a a (FULL- LOAD AFTERBURNING).

The principle of this afterburning regulation is known per se. Because the use of afterburning is only necessary when the dry engine is already working at full load, the main regulator/metering device 12 keeps the rotational speed N of the compressor and the temperature T upstream of the turbine (and therefore also the temperature T downstream of the turbine) constant throughout the period for which afterburning is in operation.

The afterburning load may be characterised by the increase in temperature T -T,. Now, this increase in temperature is proportional to the ratio C/D, in which C is the flow of afterburning fuel, and D the flow of air passing through the afterburning duct. This flow of air is itself proportional to a characteristic working pressure (for example the outlet pressure) P of the compressor, in view of the fact that the speed of rotation N and the temperatures T and T are kept constant by the main regulation. It will be deduced from this that the afterburning load is really represented by the ratio C/P In actual fact, the parameter P is often corrected by a coefficientfl lower than one (for example, of the order of 0.87), which makes it possible to adjust, on the bench, the maximum thrust of the turbojet engine under afterburning conditions, but which normally plays no part in the principle on which afterburning regulation functions. The flow Cof afterburning fuel is therefore supplied by the expression C BP f(a).

From his control lever M, the pilot can thus select an afterburning load by regulating the ratio C/BP while the main regulation system continues to keep the parameters N, T and T constant, and the disturbances brought about by the functioning of afterburning downstream of the turbine are compensated for by a more open position of the propulsion nozzle 5.

FIG. 5 shows, by way of an example, a pressurereducing device of known type (see, for example, French Pat. No. 1,376,588) which makes it possible to produce, from the pressure P the reduced-pressure parameter 3P This device R comprises a main pressure-reducer 21 which is made up, in particular, of a reduced-pressure capacity or space 50 of which the capacity 45 constitutes an extensionvia the pipe 22. The capacity 50 opens on to a space which is under low pressure (for example the atmosphere or, possibly, a space which is under subatmospheric pressure) through a constricted diaphragm 51 which is advantageously adjustable, and this capacity is connected, via a constricted orifice 52, with the pipe for taking-off the pressure P A blocking device, such as a valve 80 which is controlled from the regulating lever M via a functional connection 81, makes it possible to feed the pressurereducer 21 only when the lever M is in the afterburning sector (a 2 a Under these circumstances, an escape of air occurs through the constricted orifice Slat sonic speed and there is set up, in the capacity 50 (and consequently in the capacity 45), a reduced pressure (3P in which B is a constant coefficient of reduction which depends only upon the respective characteristics of the constricted

orifices

51 and 52. y

In order to permit an increase in richness in the afterburning duct under high-altitude conditions, an additional overload circuit may also be provided. This cir cuit comprises, in particular, a pipe 53 which is tappedi off from the pipe 20 and opens into the capacity 45 through a constricted orifice 54. An electrically controlled valve 55 makes it possible to shut off or open the pipe 53 according to whether the altitude at which the aircraft is flying is lower or higher than a certain ceiling (for example, 30,000 feet). The valve 55 is controlled by a contactor 56actuated by an altitudedetector 57. The coefficient ,8 thus passes from'a normal low-altitude value (for example ,8 0.87) to a normal high-altitude value (for example ,8 0.93).

It will be noted that, at rest, when the pressurereducer 21 is not being fed (that is to say, when the control lever M is in the dry sector), the coefficient B supplied .by the pressure-reducing device R. may be re-.

garded as being equal to one, because the capacity 50 is then at ambient pressure and there is no leakage through the constricted orifice 51. I

With reference to FIG. 4, there will now be described i The obturator 29 for controlling the igniting device 26 is'an electrically controlled valve which when at a rest, is in the blocking position. It will also be noted that the inlet valve 19 is of the hydraulic-control type and that it opens under the effect of a pressurised control fluid (such as pressurised fuel taken off from the main fuel circuit, between the pump 8 and the regulator/metering device 12) which is carried in a pipe 67 in which there is interposed the electrically controlled valve 65 which, in the rest condition, is also in the blocking posi 1 tion.

The contactor 61 is a contactor for engaging afterburning. It is controlled, via a functional connection 60, by means of the control lever M in such a way as to bring about engagement of afterburningas soon as the said lever has entered the AFTERBURNING sector The change over switch 66 can occupy one or other of two positions. In its firstposition, which is shown in FIG. 4 and is its normal rest position, it switches on the electrically controlled valve 29. In its second position, it switches on the lamp 62. This switch is driven to wards its second position by a relay 68 which is energized as soon as the ignition-detector 30 emitsa signal I indicating that ignition of the fuel has actually been obtained in the afterburning duct.

When the contactor 61 is engaged, the electrically operated valve 65 is immediately energized in the; opening direction in such a way as to cause, in turn,

opening of the inlet valve 19. From this moment on, therefore, the device for supplying afterburning fuel is in operation. In addition, and as long as no ignition signal is emitted by the detector 30, the electrically operated valve 29 is energized in the opening direction, so that the device 26 for igniting afterburning is in operation. On the other hand, as soon as the ignition signal is emitted, the switch 66 is driven towards its second position. The electrically operated valve 29 then resumes its rest position, that is to say its blocking posi tion, so that the device 26 for igniting afterburning is brought out of operation.

The lamp 62 (amber lamp) constitutes a lamp for signalling the actual functioning of afterburning. To this end, it is connected in such a way as to light up as soon as the afore-said signal is emitted. It therefore indicates, as soon as it is lit, that the igniting of afterburning has been successful.

The lamp 63 (red lamp) constitutes a lamp for signalling the functioning of the device for igniting afterburning, and indicates, while it is lit, that the device is in operation. For this purpose, it is associated with the pressure-operated switch 64 which is itself controlled by the afterburning-fuel pressure prevailing downstream of the valve 29. While the latter is open, the pressureoperated switch 64 closes the circuit of the lamp 63, which therefore remains lit. On the other hand, the lamp 63 goes out as soon as the valve 29 is closed.

The known, afterburning-initiation sequence of a turbojet engine thus equipped, will now be described.

It will be assumed that, at the moment when the pilot finds it necessary to have maximum thrust, under afterburning conditions, at his disposal as quickly as possible, the control lever M for the turbojet engine is in the THROTTLED-DOWN DRY position (a 04 As has been explained above, the pilot cannot abruptly swing this control lever into the FULL-LOAD AFTERBURNING position (a a His first duty is to shift it to the FULL-LOAD DRY position (a a and to wait there until full-load dry has actually been established and stabilized. For this purpose, he must keep under observation certain parameters, such as N and T and it is only when each of these parameters has reached a predetermined threshold (for example, N

8,100 rpm and T 720C), that he is allowed to engage afterburning (a a and push the lever into the THROTTLED-DOWN AFTERBURNING position (04 01 This move brings into operation the device for generating the parameter ,8P (by opening the valve 80), and closes the contactor 61, the effect of which is to energize the electrically operated

valves

65 and 29. The device 18/19 for supplying afterburning fuel is thus brought into action. The pump 13 is then supplied with fuel, which pressurizes the entire afterburning-fuel circuit14 17 -15 16 R R R and also the ignitingfuel circuit 27 29 28 26 (since the electrically operated valve 29 is energized towards its open position). In parallel with all this, the amplifier 31 associated with the ignition-detector is fed.

The injection of fuel into the combustion chamber 2 by means of the igniting injector 26 gives rise to a tongue of flame which passes through the turbine 3 and causes ignition of the fuel escaping from the manifolds R R R in the afterburning duct 4. As long as the valve 29 is open, the signal-lamp 63 (red lamp) remains lit under the effect of the pressure-operated switch 64.

When ignition has actually been obtained in the afterburning duct, the ignition-detector 30 emits a signal which, after being amplified in the amplifier 31, simultaneously gives rise to the closure of the electrically operated valve 29, (and therefore to the bringing of the igniting device 26 out of operation), extinction of the signal-lamp 63, and lighting-up of the signal-lamp 62 (amber lamp).

At this moment, but only at this moment, is the pilot allowed to push the control lever further into the AF- TERBURNING sector, as far as the FULL-LOAD AF- TERBURNING position (a (1 In the event of unsuccessful igniting (for example if the signal-lamp 63 still remains lit after 10 seconds), the pilot is obliged to bring the control lever M back into the DRY sector in order to avoid any thermal over loading of the turbine.

The course of this known sequence is diagrammatically shown in FIG. 8 in the form of a combination of charts.

It will be seen that this sequence is long and requires the observance of special precautions on the part of the pilot, but does not thereby exclude all risk of incorrect operation or thermal overloading of the turbine.

A device for programming the afterburning-initiation phase according to the invention will now be described with reference to FIGS. 6 and 7.

A first improvement relates to the utilization, under conditions which will be described later on, of a device for temporarily restraining the flow of afterburning fuel.

As will be seen, the temporary restraining of the flow of fuel is achieved by modifying the coefficient B with the aid of a pressure-modifying reducer such as the one shown in FIG. 6. This pressure-modifying reducer is supplied with fluid, for example air, at a pressure of 3P and essentially comprises a capacity 145 (which may, if necessary, be identical to the capacity 45 described in connection with FIG. 5) working in conjunction with two constricted

orifices

70, 71. Through the orifice 71, the capacity 145 opens on to a space which is under low pressure (for example the atmosphere or a space which is under subatmospheric pressure). Through the orifice 70, this capacity is supplied with fluid at the pressure ,BP In the example illustrated, the modifying pressure-reducer /145/71 is fed by the main pressure-reducer 21 and thus constitutes, in the pressure-reducing device R, an auxiliary pressurereducer. The constricted orifice 71 forms a leakage path through which, during operation, the fluid escapes from the capacity at a sonic speed.

Means, such as an electrically operated valve ADF, make it possible to establish or cut off communication between the capacity or space 145 and the leakage path 71 so as to permit, or block, the passage of the fluid through the leakage path.

When the valve ADF is closed, the pressures prevailing in the two

capacities

50 and 145 are equal, because there is no flow through the constricted orifice 70. Under these circumstances, there is set up, in the capacity 145, a pressure 8?; which is equal to that prevailing in the capacity 45 of the pressure-reducing device illustrated in FIG. 5. In other words, when the valve ADF is closed, the pressure-reducing device improved in accordance with the invention functions exactly like the known device shown in FIG. 5.

If, on the other hand,the valve ADF is open, the fluid having a pressure of P which arrives by way of the pipe 20 undergoes two successive pressure-reducing opera tions, the first in the main pressure-reducer 21 (52/50/51) and the second in the auxiliary pressurereducer 70/145/71. Under these circumstances, there is set up, in the capacity 145, a reduced pressure B'P in which B is a coefficient of reduction which is very much lower than B. The auxiliary pressure-reducer 70/145/71 thus constitutes asimple contrivance for modifying the coefficient B, with the aid of which the flow of afterburning fuel metered by the regulator/metering device 17 can be modified so as to change from its normal value C= BP fla) to a greatly reduced value C BP f (a).

With reference to FIG. 7, a description will now be given of a simplified functional diagram of an installation equipped with a programming device permitting the initiation of afterburning in accordance with a sequence which is in conformity with the invention.

In this Figure, there will again be found a number of elements which have already been described in connection with FIG. 4, in particular the electrically operated valve 65 for controlling the supply device 18/19 for afterburning fuel, the electrically operated valve 29 for controlling the igniting device 26, the signal-lamp 62 for indicating the actual functioning of afterburning (amber lamp), the signal-lamp 63 for indicating that the igniting device is functioning (red lamp), the pressure-operated switch 64, the ignition-detector 30, and the amplifier 31. The auxiliary pressure reducer 70/145/71, which has already been described in connection with FIG. 6 and which can be brought into, or out of, action with the aid of the electrically operated valve ADF, will also be recognised.

This installation is supplemented as will be explained below.

The reference numeral 100 has been used to designate an afterburning-preselection device which can occupy either a position involving DRY functioning or a position involving functioning under AFTERBURN- ING conditions. This preselection device is constituted by an electrical contactor which is controlled, via a functional connection 101, by meansof the engine control lever M in such a way that passage from the DRY position to the AFTERBURNING position occurs when this lever enters the AFTERBURNING sector (a The contactor 100 preselects the feeding of an electrical circuit comprising, in particular, an electronic switch 102, such as a transistor, and a change-over electrical switch 110.

The transistor 102is biased on its base by a signal which is emitted by a threshold-type comparator 103 and amplified in an amplifier 104. The comparator 103 receives one or a number of signals, such as X and Y, which are emitted by one or a number of suitable pickups (not illustrated) and are compared with one or a number of reference signals X Y The signals X, y are constituted by at least one signal which is representative of a working parameter of the DRY turbojet engine, such as the rotational speed N of the compressor, or the gas temperatures, T or T at the entrance to, or exit from, the turbine. The reference signals are advantageously constituted by signals which are representative of a predetermined threshold (preferably the full-load DRY value) of the abovementioned parameters, for example N 8,100 r.p.m. and T 720C. So

long as the parameter or parameters X, Y have not reached the above-mentioned threshold, the signal emitted by the comparator 103 has the effect of keeping the transistor 102 in the blocked non-conductive I 7 state. On the other hand, as soon as this threshold "is reached, the comparator 103 emits a signal for the pur-.

pose of unblocking the transistor. The automatic maintenance of the transistor 102 in the conductive state'is then effected with the aid of a return loop 105 comprising, in particular, a diode 106. As will berealised, the purpose of this automatic maintenance is to eliminate all risk of premature stoppage of afterburning in the v I event of a momentary variation in one of the abovementioned parameters, in particular the speed ofrotation N.

The transistor 102 thus constitutes the equivalent of a locking device which prohibits the actual functioning; of afterburning until full-load DRY hasbeen reached.

The change'over switch may occupy one or other of two positions. In its first position, which is illustrated in .FIG. 7 and is its normal rest position, it switches on, via a time switch120, the electrically opelectrically operated valve 29 is then energized in vthe direction of opening, sothat the ignitingdevice 26 is brought intooperation- In its second position, the change-over switch 110 switches on, on the one hand, the signal-lamp 62 indicating the actual functioning of afterburning (amber lamp) and, on the other hand, the electricallyoperated valve ADF, through a timing device 130. Assuming that the preselection device 100 and the electronic switch 7 V 102 are closed, the lamp 62 then lights up. Concurrently, the electrically operated valve ADF is energized through the timing device 130, but only after a prede; termined delay, for example of the order of 1.5 sec-' onds, in such a way as to bring the auxiliary pressure reducer 70/145/71 out of action.

The change-over switch 110 is driven towards its second position by a relay 111 which is energized as soon as the ignition-detector 30 emits a signal indicating that 1 ignition of the fuel has actually been obtained in the afterburning duct.

In the absence of any signal emanating from the ignition-detector 30, that is to say,.in the event of unsuccessful igniting, the time switch makes it possible to interrupt the energization of the operated valve v29,

so as to bring the igniting device 26 out ofoperation.

The time switch 120 may be designed to open automatically at the end of a predetermined period of time (for example eight seconds), counting from the start of the injection of igniting fuel (that is to say, from the mo-;

ment at which the transistor 102 has been unblocked).

A two-position change-over switch has been designated by the reference numeral .140. In its first position which is its normal position,.as illustrated in FIG. "I,

and which alone will be considered below the switch enables the electrically operated valve ADF to control, under the circumstances which will be considered below, the bringing of the auxiliary pressure reducing device 70/145/71 into, or out of, action. In' its I second position which, in principle, is only an emergency position it connects the valve ADF with a source of electrical power 150, so that the valve ADF is permanently energized towards its blocking position. Everything then takes place as if the auxiliary pressure reducing device 70/145/71 were eliminated. This arrangement may be useful, particularly in the event of a breakdown in the normal regulation of afterburning, and may facilitate the implementation of simplified, emergency regulation.

A description will now be given of the afterburninginitiation sequence which can be accomplished with the aid of the programming device according to the invention, which has just been described.

It will be assumed, as in the case of FIG. 4, that at the moment at which the pilot finds that he needs to have the maximum afterburning thrust at his disposal as quickly as possible, the engine control lever M is in the Tl-lROTTLED-DOWN DRY position (a 01,).

At this moment, the preselection device 100 is still in its DRY operating position, the transistor 102 is blocked, the change-over switch 110 is in its first position (illustrated in FIG. 7), the electrically operated

valves

65 and 29 are in the blocking position, the electrically operated valve ADF is in the opening position (the auxiliary pressure reducing device 70/145/71 is therefore ready to operate) and the

lamps

62 and 63 are extinguished.

Without waiting, the pilot then swings his control lever directly into the AFTERBURNING sector, as far as the FULL-LOAD AFTERBURNING position. At the moment at which this lever enters the AFTER- BURNING sector (a 01 the contactor 100, which constitutes the afterburning-preselection device, takes up its position for functioning under afterburning conditions. From this moment on, functioning under afterburning conditions is preselected and the sequence continues in an automatic manner.

Because the control lever M has reached and passed the FULL-LOAD DRY position (a the turbojet engine is, to start with, called upon to working at fullload dry. The functioning parameter or parameters, X, Y, of the DRY engine (in particular, the rotational speed N of the compressor, and the temperatures, T;, or T of the gases at the turbine) progressively reach the threshold X Y indicating that the DRY full load has actually been obtained. At this moment, the threshold-type comparator 103 emits a signal which un- 2 blocks the transistor 102.

The electrically operated valve 65 is then energized towards its opening position, so that the inlet valve 19 opens and brings into operation the supply device 18/19 for afterburning fuel. The pump 13 is thus supplied with fuel, which pressurizes the entire afterburning-fuel circuit l4/l7/l5/l6/R /R /R and gives rise to the injection of fuel into the afterburning duct 4 through the manifolds R R R In parallel with this, the electrically operated valve 29 is energized towards its opening position, so that the igniting fuel circuit 27/29/28/26 is pressurized. The igniting device comprising the igniting injector 26 is therefore brought into operation, and the signal-lamp 63 (red lamp) lights up.

The injection of fuel into the combustion chamber 2 by means of the igniting injector 26 produces a tongue of flame which passes through the turbine 3 and gives rise, after a certain period of time, to igniting of the fuel discharging from the manifolds R R R in the afterburning duct 4.

When ignition has actually been obtained in the afterburning duct, the ignition-detector 30 emits a signal which, after being amplified in the amplifier 31, causes the change-over switch 110 to swing towards its second position. At this moment, the electrically operated switch 29 ceases to be energized and returns to the blocking position, which gives rise to the bringing out of operation of the igniting device 26, and to extinction of the signal-lamp 63. At the same time, the signal lamp 62 (amber lamp) lights up, indicating that igniting has been successful and that afterburning is beginning to function in an effective manner.

In the event of unsuccessful igniting, the time switch 120 automatically effects the return of the electrically operated switch 29 to its blocking position after a predetermined period of time (for example eight seconds), in order to bring the igniting device 26 out of operation. The pilot then returns the control lever M to the DRY sector, and attempts to effect igniting again.

Consideration will now be given to the behaviour of the regulator/metering device 17 associated with the auxiliary pressure reducing device /145/71, throughout the period of after burning-initiation.

Until the pilot has preselected functioning under afterburning conditions with the aid of the control lever M, the pressure-reducing device R intended to produce the reduced-pressure parameter ,BP is at rest, that is to say, is not supplied with air at a pressure of P The coefficient B is then equal to one, as has been seen.

As soon as the pilot has preselected functioning under afterburning conditions with the aid of the lever M, the pressure-reducing device R begins to function. Now, as has been seen, the electrically operated valve ADF is in the opening position at this moment, so that the auxiliary pressure-reducer 70/145/71, is in operation. The pressure-reducer R then produces a reduced pressure B'P which is very much lower than the reduced pressure 8P required for normal metering of the flow of afterburning fuel, since B is a coefficient of reduction which is very much lower than the coefficient B. It is thus reduced pressure BP which, according to one of the essential aspects of the invention, makes it possible to temporarily restrain the flow of afterburning fuel when afterburning is being initiated.

The auxiliary pressure reducing device 70/145/71 may be contrived in such a way, by suitable dimensioning of the constricted

orifices

70 and 71, that the restrained flow of afterburning fuel is very low, for example equal to or lower than the flow of fuel normally corresponding to Throttled-down Afterburning and this in spite of the fact that the engine lever M is already occupying the FULL-LOAD AFTERBURING (a a position at this moment. Everything therefore takes place during the period of intervention of the auxiliary pressure reducing device, as if the lever M were being kept in the ENGAGEMENT AFTERBURNING (a 0: or THROTTLED-DOWN AFTERBURNING (a a,,) position. An idle period in the operation of establishing afterburning, and an awkward restraint for the pilot are thus eliminated.

The auxiliary pressure reducing device 70/145/71 remains in action until the moment when ignition of the fuel has actually been obtained in the afterburning duct. At this moment, as has been seen, the changeover switch swings towards its second position, in

whichit switches on not only the signal-lamp 62 but also the electrically operated valve ADF. The latter is then energized towards its closing position, so that the auxiliary pressure reducing device 70/145/71 is brought out of action. The reduced-pressure parameter then resumes its normal value [3P and the regulation of afterburning can then proceed under the usual conditions,

The timing device 130 makes it possible to introduce a predetermined delay (for example of the order of 1.5 seconds) in the command for bringing the auxiliary pressure reducing device 70/145/71 out of action, after the moment at which the ignition signal has been emitted. It is thus possible to prolong the intervention of the auxiliary pressure reducing device slightly beyond the moment at which afterburning has actually been started in the afterburning duct, so as to enable the afterburning to become stable.

The development of the initiation sequence according to the invention is shown in FIG. 9 in the form of a combination of charts.

A comparative examination of the charts illustrated in FIGS. 8 and 9 clearly shows the characteristic advantage obtained by the invention.

There will more particularly be noticed the difference which exists between lever-control at one go (direct movement from 11 to a according to the invention, and lever control, by successive stages (01,, d a which has hitherto seemed obligatory when initiating afterburning. Being freed from conventional duties, the pilot can in fact, by virtue of to the invention, directly preselect FULL-LOAD AFTERBURN ING, the production of which only becomes effective after an automatic sequence comprising the unlocking of the transistor 102 and the closure of the electrically operated valve ADF.

This automatic sequence which simplifies the task of the pilot and reduces the risk of incorrect operations leads to a major saving in time. It is because of this, for example, that the maximum thrust under afterburning conditions can be obtained, thanks to the use of the programming device according to the invention, at the end of 8 to 10 seconds, whereas the waiting time, in the case of a turbojet engine having conventional control, could be as much as to seconds.

Another major advantage lies in the limitation of the period of functioning of the igniting injector 26, particularly in the event of unsuccessful ignition, by means of the time switch 120 which in any case limits the period,

for which igniting fuel is injected to, for example, eight seconds. On the other hand, in the case of a turbojet engine having conventional control, the pilot was himself obliged to keep this injection period under observation and bring the control lever M back into the DRY sector, for example after ten seconds. If this requirement were overlooked, therefore, there was a serious danger of thermal overloading of the turbine, a risk which is particularly eliminated, owing to the invention.

The programming device according to the invention may, if necessary, be simplified as regards the control of the locking transistor 102. In fact, the reaching of its reference threshold by only one of the above mentioned parameters X, Y may be sufficient for it to be assumed, under certain circumstances, that the turbojet engine has virtually attained full-load DRY conditions. Thus, for example, it was ascertained by experi- 116 ment that, in the case of certain turbojets engines, the rotational speed N and the temperature T were reaching their full-load DRY values in a substantially concomitant manner, with, for example, a delay of the] order of three seconds between the moment at which the rotational speed N settled at its full-load DRY.

value, and that at which the temperature T, in turn reached its full-load DRY threshold, It is then possible,

in this event, to rely solely upon the speed signal N. for

the purpose of controlling the unlocking of the transistor 102.

It has been assumed up to now that the igniting de-.

vice was being supplied with igniting fuel emanating from the afterburning-fuel circuit. But it is clear that the igniting fuel might also be taken off from the main fuel circuit 8/9/l0. The igniting device might, moreover, comprise means other than a fuel injector, such as, for example, an electric ignition of the spark, or incandescent filament types. As regards the means, which were described in detail in the form of an inlet valve 19, for bringing into,,or out a of, operation the device for supplying afterburning fuel,

thismeans might comprise, either additionally or as a I variant form, means which make it possible to bring the pump 13, or a member driving the pump, into, or out of, operation.

It will also be noted that certain, at least, of the electrical or electronic components of the various detection or control circuits might be replaced by fluidic components.

We claim:

1. In and for a turbojet engine comprising a compressor, an afterburning duct, means for supplying said afterburning duct with fuel, and means for metering the flow of fuel injected into said duct, said flow-metering means being sensitive to a parameter ,BP in which P5 is a characteristic working pressure of said compressor,

and B is a coefficient which is lower than, or at most equal to one, in combination, a device for programming the afterburning-initiation phase comprising, means for modifying said coefficient B to temporarily reduce said coefficient ,8 during the afterburninginitiation phase, and means for automatically disabling said B-modifying means after the moment at which ignition of the fuel has actually been obtained in the aftion-detecting device which emits a signal at the moment at which ignition of the fuel has actually been .obtained in the afterburning duct, in which saidmeans for disabling said ,B-modifying means are controlled by said ignition signal. 4. Aprogramming device according to claim 3 in which a timing device is provided which is designed in such a way as to introduce a predetermineddelay into the disabling of said fl-modifying means, after the moment at which said ignition signal has been emitted.

5. A programming device according to claim I in which said ,B-modifying means comprise a pressure modifying reducer which is supplied with fluid at a pressure of 3P and said means for disabling the B-modifying means comprise means for disabling said pressure-modifying reducer.

6. A programming device according to claim 5 for application to a turbojet engine of the type in which the pressure parameter ,BP is generated from the pressure P in a pressurereducing device comprising at least one main pressure-reducer, in which said pressuremodifying reducer comprises an auxiliary pressurereducer which is fed by said main pressure-reducer.

7. A programming device according to claim 5 in which said pressure-modifying reducer comprises a Ca pacity which is fed through a constricted orifice with fluid at a pressure of 8P and communicates with a low pressure space through another constricted orifice forming a leakage path through which, under operating conditions, the fluid escapes from said capacity at sonic speed, and said means for disabling said pressuremodifying reducer comprise means for stopping the escape of the fluid through said leakage path.

8. A programming device according to claim 7 in which said means for disabling the pressure-modifying reducer comprise means for cutting off the communication between said capacity and said leakage path.

9. A programming device according to claim 1 and comprising, in addition, means for activating or deactivating said device for supplying afterburning fuel; an afterburning-preselection device, which may occupy either a DRY functioning position or else a position for functioning under afterburning conditions; and means sensitive to at least one working parameter of the DRy turbojet engine; said means being designed to automatically activate said supplying device when, with said preselection device in the position for functioning under afterburning conditions, such parameter reaches a predetermined threshold.

10. A programming device according to claim 9 for application to a turbojet engine equipped with a device for igniting the fuel discharging into the afterburning duct, which igniting device can be activated or deactivated; in which said means sensitive to such functioning parameter of the turbojet are also adapted to automatically activate said igniting device when, with said preselection device in the position for functioning under afterburning conditions, such parameter reaches said threshold.

11. A programming device according to claim 10, and comprising, in addition, timing means designed to automatically deactivate said igniting device after a predetermined period of time, starting from the moment at which said igniting device has been activated.

12. A programming device according to claim 10 for application to a turbojet engine equipped with an ignition-detecting device which emits a signal at the moment at which ignition of the fuel has actually been obtained in the afterburning duct, in which means are provided which are controlled by said ignition signal and are designed to automatically deactivate said igniting device.

13. A programming device according to claim 9 in which said means sensitive to such working parameter of the DRY turbojet engine comprise a locking device which is kept in the locked position until such parameter reaches said threshold.

14. A programming device according to claim 9 in which such working parameter comprises the rotational speed of the compressor of the turbojet engine.

15. A programming device according to claim 9 in which such working parameter comprises the temperature prevailing immediately downstream of the expansion turbine.

16. A programming device according to claim 9 for application to a turbojet engine equipped with a lever for controlling the afterburning load, in which said afterburning-preselection device is coupled to said control lever.

Claims

1. In and for a turbojet engine comprising a compressor, an afterburning duct, means for supplying said afterburning duct with fuel, and means for metering the flow of fuel injected into said duct, said flow-metering means being sensitive to a parameter Beta P2, in which P2 is a characteristic working pressure of said compressor, and Beta is a coefficient which is lower than, or at most equal to one, in combination, a device for programming the afterburning-initiation phase comprising, means for modifying said coefficient Beta to temporarily reduce said coefficient Beta during the afterburning-initiation phase, and means for automatically disabling said Beta -modifying means after the moment at which ignition of the fuel has actually been obtained in the afterburning duct.

2. A programming device according to claim 1 for application to a turbojet engine equipped with a lever for controlling the afterburning load, in which said Beta -modifying means are designed to reduce the flow of afterburning fuel to a value which is close to the Throttled-down afterburning flow, whatever the position of said control lever.

3. A programming device according to claim 1 for application to a turbojet engine equipped with an ignition-detecting device which emits a signal at the moment at which ignition of the fuel has actually been obtained in the afterburning duct, in which said means for disabling said Beta -modifying means are controlled by said ignition signal.

4. A programming device according to claim 3 in which a timing device is provided which is designed in such a way as to introduce a predetermined delay into the disabling of said Beta -modifying means, after the moment at which said ignition signal has been emitted.

5. A programming device according to claim 1 in which said Beta -modifying means comprise a pressure-modifying reducer which is supplied with fluid at a pressure of Beta P2, and said means for disabling the Beta -modifying means comprise means for disabling said pressure-modifying reducer.

6. A programming device according to claim 5 for application to a turbojet engine of the type in which the pressure parameter Beta P2 is generated from the pressure P2 in a pressure-reducing device comprising at least one main pressure-reducer, in which said pressure-modifying reducer comprises an auxiliary pressure-reducer which is fed by said main pressure-reducer.

7. A programming device according to claim 5 in which said pressure-modifying reducer comprises a capacity which is fed through a constricted orifice with fluid at a pressure of Beta P2, and communicates with a low pressure space through another constricted orifice forming a leakage path through which, under operating conditions, the fluid escapes from said capacity at sonic speed, and said means for disabling said pressure-modifying reducer comprise means for stopping the escape of the fluid through said leakage path.