EP1512913A1 - Injection system for air and fuel with means to produce cold plasma - Google Patents

Abstract

The system has internal and external spins arranged in downstream of a fuel injector. Cold plasma generation units are arranged in the downstream of the internal and external spins to generate active species in the flow of an air/fuel mixture. The generation units pre-break the molecules of the mixture. Control systems (48) control the generation units according to the functioning speed of a turbo-machine. The cold plasma generation units are formed by two pairs of electrodes (42, 42) disposed on the circumference of the end of a venturi (26).

Description

The present invention relates to the general field of systems for injecting an air / fuel mixture into a chamber of turbomachine combustion. It aims more particularly at a system Injection equipped with a cold plasma generator capable of controlling the reactivity of the air / fuel mixture during injection into the chamber of combustion.

The traditional process of developing and optimizing a The main purpose of the combustion chamber of a turbomachine is to reconcile the implementation of the operational performance of the chamber (combustion efficiency, stability domain, domain ignition and re-ignition, lifetime of the combustion chamber, etc.) in according to the mission envisaged for the airplane on which the turbomachine while minimizing polluting emissions (nitrogen oxides, carbon monoxide, unburnt hydrocarbons, etc.). To do this, it is possible to play in particular on the nature and the performances of the injection system of the air / fuel mixture in the chamber of combustion, the distribution of dilution air in the chamber and the dynamic air / fuel mixture in the chamber.

The combustion chamber of a turbomachine is composed typically of several systems: a system for injecting a mixture air / fuel in a flame tube, a cooling system and a dilution system. The combustion is organized mainly within of a first part of the flame tube (primary zone) in which it is stabilized by means of recirculation zones of the mixture air / fuel induced by the flow of air from the injection system. In this primary zone of the mixing tube, different phenomena are implemented: injection and atomization into fines fuel droplets, evaporation of droplets, mixture of fuel vapors with air and chemical oxidation reactions of the fuel by the oxygen of the air. In the second part of the tube mixture (dilution zone), the chemical activity used is more low and the flow is diluted by means of dilution holes.

In order to reduce polluting emissions, in particular those nitrogen oxides (of the NOx type), it is known to seek to eliminate the areas of the flame tube where the temperature is above 1800 ° K about. To do this, it is necessary for the combustion flame to be in the presence of a rich or poor air / fuel mixture. For example, the depletion of the air / fuel mixture from the flame tube zone where the chemical reactions take place can be obtained by increasing the air flow rate assigned to combustion. In this case, we contribute to evaporate and mix more and more fuel with the air before supply the flame located in the combustion zone. The flame combustion therefore sees its wealth decrease.

However, increasing the airflow is not enough to completely remove areas of stoichiometric mixtures to inside the combustion chamber. Generally, the depletion of combustion leads to an increase in vulnerability of the firebox to extinction so that the phases engine slows can no longer be obtained.

To solve this problem, engine manufacturers have developed the concept called "staged combustion" which can be presented under two forms: double-headed combustion chambers and so-called "multipoint" injection systems.

Staged double-head combustion chambers are rooms whose fuel injectors are distributed over a so-called head "Pilot" and on a so-called "take-off" head. The pilot head works in permanence and thus prevents the combustion chamber from goes off, while the take-off head is designed to reduce NOx emissions. Although this solution appears satisfactory, a room with double stepped head remains difficult to fly and expensive given the doubling of the number of fuel injectors per compared to a conventional single head combustion chamber.

The injection systems of the air / fuel mixture "Multipoint" are systems in which the injection of air and fuel is carried by several independent ducts and is regulated in function of the operating speed of the turbomachine. Disadvantage The main feature of such multipoint injection systems lies in the complexity different fuel systems and the control system.

We also know the US Pat. No. 6,453,660 which proposes a multipoint injection system equipped with a hot plasma generator. In this document, it is planned to equip the end of the main injector of fuel from a hot plasma generator device. A discharge energy occurs in the fuel flow thereby allowing to ionize and partially dissociate the fuel molecules. However, such an injection system is not completely satisfactory. On the one hand, the multipoint architecture remains complex and difficult to control. On the other hand, the energy discharge only takes place in the flow main fuel which limits the efficiency of such an injection system against the risk of extinction of the combustion chamber.

Object and summary of the invention

The main object of the present invention is therefore to overcome such disadvantages by proposing a system for injecting a mixture air / fuel in a combustion chamber that can increase the resistance of the combustion chamber to extinction while maintaining a simple architecture and limiting polluting emissions.

For this purpose, there is provided a system for injecting a mixture air / fuel in a turbomachine combustion chamber, having a hollow tubular structure for the flow of the mixture air / fuel to the combustion chamber, means for injecting fuel disposed at an upstream end of the tubular structure hollow, and air injection means arranged downstream of the means fuel injection system, characterized in that it further comprises means for generating cold plasmas arranged downstream of the means injection of air to generate active species in the flow of air / fuel mixture and to pre-break the molecules of the air / fuel mixture, and means for controlling the means of generation of cold plasmas according to the operating regime of the turbomachine.

The cold plasma generator makes it possible to adapt the times characteristics of the chemical reactions according to the operation of the turbomachine. Time control characteristics of the chemical reactions is ensured by the production and the injection of active species (radical species and excited species) in the flow of the air / fuel mixture and by pre-breaking the molecules of air and fuel.

In this way, it is possible to increase the resistance of the combustion to extinction and thus to ensure combustion stability, particularly at low operating speeds of the turbomachine, while by allowing to limit pollutant emissions.

The means for generating cold plasmas can as well adapt to aeromechanical injection systems as aerodynamic type injection systems.

The means for generating cold plasmas may comprise at least one pair of electrodes connected to a current generator alternative which is controlled by the control means.

Alternatively, and according to their location, these means of generation of cold plasmas may include a winding solenoidal connected to an alternating current generator which is also driven by the control means.

Thus, the present invention makes it easy to adapt to known systems for injecting an air / fuel mixture without causing important transformations of these injection systems.

The means for generating cold plasmas can be associated with one or all injection systems of the same chamber of combustion, which improves the operation of the chambers existing combustion.

The injection system according to the present invention can also work for operating points of the turbomachine where the combustion is stabilized so that the output of combustion is increased for these points. For example, if we considers a re-ignition point at altitude in auto-rotation, the volume of the focus must be sufficient to ensure combustion efficiency allowing the turbomachine to accelerate. In these circumstances, this invention reduces the volume of combustion fires and therefore to reduce the mass of the turbomachine.

Moreover, by pushing the extinction limits of the combustion, it removes the fuel system from the head pilot for the rooms with double stepped head but also for chambers with multipoint injection systems.

Finally, the present invention makes it possible to simplify the systems ignition of the combustion chamber by integrating this function into injection system. The ignition is in fact carried out by the means of generation of cold plasmas powered with energy and frequency adapted. It is thus possible to delete conventional devices spark plugs and avoid the problems associated with them (cooling of the body and nose of the candle, disturbance of the fireplace cooling, spark plug life, etc.).

Brief description of the drawings

• la figure 1 est une vue en coupe longitudinale d'un système d'injection selon un mode de réalisation de l'invention ;
• les figures 2A et 2B illustrent deux variantes d'implantation des moyens de génération de plasmas froids du système d'injection selon l'invention ;
• la figure 3 est une vue en coupe longitudinale d'un système d'injection selon un autre mode de réalisation de l'invention ; et
• la figure 4 est une vue en coupe longitudinale d'un système d'injection selon encore un autre mode de réalisation de l'invention.

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures:

• Figure 1 is a longitudinal sectional view of an injection system according to one embodiment of the invention;
• FIGS. 2A and 2B illustrate two implantation variants of the cold plasma generation means of the injection system according to the invention;
• Figure 3 is a longitudinal sectional view of an injection system according to another embodiment of the invention; and
• Figure 4 is a longitudinal sectional view of an injection system according to yet another embodiment of the invention.

Detailed description of an embodiment

FIG. 1 represents, in longitudinal section, a system injection according to one embodiment of the invention. In this mode of realization, the injection system is of the aeromechanical type.

The X-X longitudinal axis injection system 10 consists of essentially a tubular structure for the flow of a mixture air / fuel to the firebox of a combustion chamber 12 of a turbine engine. This air / fuel mixture is intended to be burned in the combustion chamber 12.

The combustion chamber 12 is for example of the type annular. It is delimited by two annular walls (not shown in Figure 1) spaced radially from the axis of the turbomachine and connected upstream by a chamber bottom 14. The bottom of chamber 14 has a plurality of openings 16 regularly spaced circumferentially around the axis of the turbomachine. In each of these openings 16 is mounted an injection system 10 according to the invention. The gases resulting from the combustion of the air / fuel mixture flow downstream into the combustion chamber 12 to supply a high-pressure turbine (not shown) disposed at the outlet of the combustion chamber.

An annular deflector 18 is mounted in the opening 16 by through a sleeve 20. This deflector is mounted parallel to the chamber bottom 14 and plays a role of heat shield against the radiation from the combustion flame.

A bowl 22 is mounted inside the sleeve 20. This bowl 22 has a wall 22a flared downstream in the extension of a substantially cylindrical wall 22b arranged coaxially with the axis longitudinal X-X injection system 10. Through its angle opening, the bowl 22 distributes the air / fuel mixture in the primary zone of the combustion chamber. Moreover, the flared wall 22a of bowl has a plurality of holes 24 for introducing air into the hearth of combustion. These holes 24 make it possible to refocus the flow of the air / fuel mixture around the X-X longitudinal axis at the bowl outlet.

The bowl 22 has an annular flange 25 which extends parallel to the chamber bottom 14. As for the deflector 18, this flange 25 forms a heat shield between the radiation of the combustion flame and bowl 22. The collar is cooled by impact of air passing through holes 25a through the flared wall 22a of the bowl.

The cylindrical wall 22b of the bowl 22 surrounds a venturi 26 having an inner contour of convergent divergent form. The venturi 26 allows to delimit the air flows coming from an internal swirler 28 and of an external swirler 30. At its upstream end, the venturi 26 comprises a radial flange 26a separating the internal swirler 28 and the external swirler 30.

The internal swirler 28 is of radial type. She is willing to upstream of the venturi 26 and delivers an internal radial air flow inside the venturi. The external swirler 30 is also of the radial type. She is willing upstream of the cylindrical wall 22b of the bowl 22 and delivers a flow of air external radial between the venturi 26 and the cylindrical wall 22b of the bowl 22. The internal 28 and outer 30 tendrils rotate the flow of the air / fuel mixture and thus increase turbulence and shear to promote the atomization of the fuel and its mixing with the air.

Upstream, the internal swirler 28 is secured to a piece of retainer 32 having an annular groove 34 open on the axis side X-X longitudinal injection system. A support ring 36 is mounted in the annular groove 34. This support ring 36 allows the fixation of the downstream end of a fuel injector 38 centered on the longitudinal axis X-X injection system. The support ring 36 can move radially in the annular groove 34 to allow a catching up gambling that can cause the thermal stresses that are subjected the various elements of the injection system 10.

In its part in contact with the fuel injector 38, the support ring 36 is pierced with a plurality of orifices 40 regularly Circularly spaced around the X-X longitudinal axis of the system injection. These orifices 40 act as a purge by ventilating the jet of fuel 38 and avoiding the formation of coke at the downstream end of this one.

The support ring 36, the internal 28 and external 30 tendrils, the venturi 26 and the bowl 22 thus form the hollow tubular structure 41 of injection system 10 in which flows the air / fuel mixture.

The fuel injector 38 is secured upstream of an arm injector (not shown). After flowing in the arm injector, the fuel is sprayed by the injector 38 in the form of a fuel cone that comes in part to hit the venturi 26. Once sprayed, the fuel is mixed with the air from the internal tendrils 28 and external 30 and holes 24 of the bowl 22.

At the outlet of the bowl 22, the fuel is sprayed in the form of fine droplets under the effect of aerodynamic shear differences between the velocities of the liquid flow and of the gas flow. The air / fuel mixture thus formed is then introduced into the combustion chamber 12 to be burned.

According to the invention, the injection system 10 further comprises means for generating cold plasmas in order to generate species active in the flow of the air / fuel mixture and to achieve a pre-breaking molecules of the air / fuel mixture. Means of command are also provided in order to control these means of generation of cold plasmas according to the operating regime of the turbomachine.

In the embodiment of the injection system illustrated by FIG. 1, these means for generating cold plasmas can be arranged around the downstream end of the venturi 26 (implantation A), either around the upstream end of the bowl 22 (implantation B), or around the downstream end of the venturi 26 and around the upstream end of the bowl 22 (implantation C).

FIG. 2A illustrates the implantation A of generation means of cold plasmas around the downstream end of the venturi 26. This figure schematically represents, in front view, the circular downstream end of the venturi.

In this configuration, the means for generating plasmas are made by at least one pair of electrodes 42 arranged on the circumference of the downstream end of the venturi 26. These electrodes 42 are connected by means of electrical wires 44 to a current generator 46. The generator is controlled by a control system steering 48 described later.

In FIG. 2A, the electrodes 42 are arranged on the same diameter of the venturi 26, ie they are aligned radially one with respect to the other. However, as illustrated in dashed lines by couple of electrodes 42 ', the latter can be radially offset relative to each other by being arranged on different radii of the venturi 26.

Depending on the nature and need of the application, the number of electrode pairs may be more important. These electrodes are then angularly distributed around the circumference of the venturi, for example uniform way. Moreover, in the case of several couples electrodes, these couples can be powered by the generator of alternating current 46 simultaneously or sequentially.

Alternatively, in the case of an implantation on the end downstream of the venturi, the means of generating cold plasmas can also be made in the form of a solenoidal winding connected to the AC generator. In this variant not illustrated, the outer surface of the venturi has a solenoidal winding.

The implantation of the means for generating cold plasmas around the upstream end of the bowl 22 (implantation B) corresponds to implementation A described above and will not be repeated.

FIG. 2B illustrates the implantation C of the generation means of cold plasmas around the downstream end of the venturi 26 and around the upstream end of the bowl 22. In this figure, the venturi 26 and the bowl 22 each have a substantially circular cross-section and are arranged concentrically with respect to each other.

In this configuration, the means for generating plasmas are made by at least one pair of electrodes 42, one of which electrodes is disposed on the circumference of the downstream end of the venturi 26 and the other electrode is disposed on the circumference of the end upstream of the bowl 22. These electrodes 42 are also connected by via electrical wires 44 to an alternating current generator 46 controlled by a steering system 48.

In FIG. 2B, the electrodes 42 are arranged on the same radius of the ring defined by the downstream end of the venturi 26 and the upstream end of the bowl 22, that is to say that they are aligned radially one with respect to the other. However, as illustrated in dashed lines by couple of electrodes 42 ', the latter can be radially offset relative to each other by being arranged on different radii of the crowned.

As for the previous configuration, the number of electrode pairs may be more important depending on the nature and the need of the application. In this case, the arrangement of these pairs of electrodes may vary on the circumference of the venturi and the bowl. Couples electrodes can also be powered simultaneously or sequentially.

In the two configurations described above with reference in FIGS. 2A and 2B, the pairs of electrodes (or the winding solenoid) allow to create, via the generator of alternating current 46 connected to the control system 48, a discharge in the air / fuel mixture flowing between the electrodes (or inside the solenoidal winding).

When the air / fuel mixture passes through this electric discharge, the air and fuel molecules become ionized and partially dissociated. The fuel molecules are partially dissociated into radical species of the type C _x H _y (C ₂ H ₂ , CH ₄ , etc.). In the same way, the oxygen of the air is dissociated and ionized (O ⁺ , etc.). This pre-breaking of the fuel and air molecules then makes it possible to facilitate the subsequent breaking of these molecules during combustion.

The parameters of the AC generator 46 (duration electrical impulses, voltage, repetition rate, etc.) are controlled by the pilotage system 48 in accordance with the operation of the turbomachine, compared to the active species (radical species, excited species) that one wishes to produce, by the desired degree of pre-breakage of the air molecules and fuel and in relation to the intended function (ignition, re-ignition altitude, extension of the stability domain, active control of the combustion, etc.).

However, the AC generator 46 presents the peculiarity to allow the generation of so-called "cold" plasmas. By compared to so-called "hot" plasmas, cold plasmas are characterized by an electric discharge of type "streamer", ie by a propagation of an ionization front. Cold plasmas are characterized also by a thermodynamic imbalance in which the temperature of the electrons emitted during the electric discharge is very high compared to the air / fuel mixture passing through the discharge electric. This feature has the main advantage of allowing the production of active radical species in the flow of the mixture air / fuel with less energy expenditure than with plasmas hot.

Such an alternating current generator 46 making it possible to generate cold plasmas is reflected in particular by a duration electrical pulses between 2 and 50 nanoseconds, and preferably between 2 and 30 nanoseconds. By comparison, a generator of electric current for the production of hot plasmas delivers electrical pulses typically having a duration of the order of the hundred microsecond.

In addition, where an active control function of the combustion focus is required, the 48 steering system can use information captured in real time within the home of combustion.

For example, it may be planned to connect to the control system 48 an instability detector placed in the combustion chamber. Such instability detector measures the pressure (or any other parameter) at inside the combustion chamber and transmits it in real time to the steering system. In another example, it is also possible to connect to the control system an optical detector of the flame of combustion. Such an optical detector thus makes it possible to inform in time real the driving system in case of extinction of the flame of combustion.

We will now describe an injection system according to another embodiment of the invention with reference to FIG. embodiment, the injection system is also of type aeromechanical so that only the differences with the injection system illustrated in Figure 1. In particular, compared with injection system of Figure 1, this injection system is of the type LLP (for "Lean Premixed Prevaporized").

As for the embodiment described above, the Injection system 50 of longitudinal axis Y-Y is essentially composed of a hollow tubular structure 51 for the flow of a mixture air / fuel to the firebox hearth 12 of a turbine engine.

An annular baffle 52 is mounted in the opening 16 practiced in the chamber bottom 14 via a sleeve 54. A bowl 56 forming a vaporization and premix tube is mounted inside the sleeve 54. This bowl 56 has a downstream wall 56a divergent which is formed in the extension of an intermediate wall 56b convergent, itself formed in the extension of a wall substantially cylindrical upstream 56c arranged coaxially with the axis longitudinal Y-Y injection system.

In addition to the functions described in the embodiment previous, this bowl 56 can feed the combustion chamber by a homogeneous air / fuel mixture poor to avoid settlement in the focus of generating stoichiometric combustion conditions NOx emissions.

The bowl 56 surrounds a first venturi 58. This first venturi 58 has the function of guiding air through holes 60 formed in through the cylindrical wall 56c of the bowl 56, at its end upstream. This air is intended to cool the bowl 56 while circulating along the internal face of it.

The first venturi 58 surrounds a second venturi 62 having a internal contour of convergent divergent form. The second venturi 62 delimits the air flows coming from a radial internal swirler 64 and a radial external swirler 66. The internal swirler 64 delivers a radial air flow to the inside of the second venturi 62 and the external swirler 66 delivers a flow of air radial between the first venturi 58 and the second venturi 62.

A fuel injector 68 centered on the Y-Y longitudinal axis of the injection system is arranged upstream of the internal swirler 64. fuel injector is attached to the injection system via a support ring 70.

The support ring 70, the internal 64 and external 66 tendrils, the Venturis 58, 62 and bowl 56 thus form the hollow tubular structure 51 of the injection system 50 in which flows the air / fuel mixture.

In this embodiment, the generation means of cold plasmas to generate active species in the flow of the air / fuel mixture and to pre-break the air / fuel mixture molecules are arranged around the end downstream of the bowl 56 (implantation D in FIG. 3).

The implantation D of cold plasma generation means around the downstream end of the bowl 56 corresponds to the illustrated implantation in Figure 2A. As described above, the generation means cold plasmas can thus be realized in the form of at least one pair of electrodes disposed on the circumference of the downstream end of the bowl or in the form of a solenoidal winding.

Of course, the configuration variants described in reference to Figure 2A are also applicable to this mode of realization and the electrodes (or the solenoidal winding) are connected to the AC generator controlled by the control system.

In this embodiment, the implantation D of the means of generation of cold plasmas allows, on the one hand to increase the area of stability of the combustion chamber by pushing the extinction limits a poor mixture of air / fuel and, on the other hand, to control the in order to reduce its vulnerability to instabilities of combustion.

In this case of controlling the combustion chamber, it is appropriate, as mentioned before, to set up a detector of instability or an optical detector of the combustion flame connected to the active control system of the AC generator.

We will now describe an injection system according to another another embodiment of the invention with reference to FIG. this embodiment, the injection system is of the aerodynamic type.

As for the previous embodiments, the system injection device 72 with a longitudinal axis Z-Z essentially consists of a hollow tubular structure 73 for the flow of a mixture air / fuel to the firebox hearth 12 of a turbine engine.

A deflector 74 is mounted in the opening 16 made in the chamber bottom 14 via a sleeve 76. A bowl 78 is mounted inside the sleeve 76. This bowl has a divergent wall downstream.

At its upstream end, the bowl 78 is extended by a ring retaining ring 80 which surrounds and maintains an injector fuel 82 centered on the Z-Z longitudinal axis of the injection system.

The fuel injector 82 has a first part tubular 84 disposed coaxially with the longitudinal axis Z-Z of the system 72. This first tubular portion 84 defines a first axial internal volume 86 which opens at its downstream end for mixing air / fuel.

The outer surface of the first tubular portion 84 and the inner surface of the annular retaining ring 80 define between they have a first annular passage 88. Air supply orifices 89 practiced through the retaining ring 80 open to the outside of the injector 82 and open into this first annular passage 88. These orifices 89 make it possible to inject air at the downstream end of the first tubular portion 84 in a substantially axial direction.

The inner surface of the first tubular portion 84 of the nozzle of fuel 82 surrounds a second tubular portion 90 which is also arranged coaxially with the longitudinal axis Z-Z of the system injection. The first tubular portion 84 and the second tubular portion 90 define between them a second annular passage 92. This second tubular part 90 further defines a second axial internal volume 94 which opens in the axial internal volume 86 of the first tubular portion 84.

The fuel injector 82 also has a plurality air supply channels 96 opening out of the injector and opening into the second axial internal volume 94, at one end upstream of the second tubular portion 90. These air supply channels 96 thus making it possible to inject air at an upstream end of the second tubular portion 90 in a substantially axial direction.

At its upstream end, the fuel injector 82 comprises at minus a fuel input 98 in the form of a cylindrical recess. This cylindrical recess is fed with fuel by an injector arm (not shown).

Fuel supply channels 100 open in this cylindrical recess 98 and open into the second annular passage 92. These fuel supply channels therefore make it possible to inject fuel fuel between the first tubular portion 84 and the second portion tubular 90.

The fuel injector 82, the retaining ring 80 and the bowl 78 thus form the hollow tubular structure 73 of the injection system 72.

In this injection system, the injected fuel is atomized by the shear effect of the air. Indeed, a film of fuel is formed at the second annular passage 92. At the exit of the second tubular part 90, this film of fuel is subjected to the action of the air coming from air supply channels 96 before being subjected, at the exit of the first tubular portion 84, to the action of the air from the first passage ring 88.

In this embodiment, the generation means of Cold plasmas can be implanted in three different zones: around the downstream end of the second tubular portion 90 (implantation E), around the downstream end of the first tubular portion 84 (implantation F) or around the downstream end of the annular retaining ring 80 and around the downstream end of the first tubular portion 84 (implantation G).

Implantation E around the downstream end of the second part tubular 90 and implantation F around the downstream end of the first tubular portion 84 both correspond to the implantation illustrated by Figure 2A and will not be detailed. In both cases, the means for generating cold plasmas can be made under the at least one pair of electrodes or in the form of a solenoidal winding.

The implantation G around the downstream end of the ring annular holding 80 and around the downstream end of the first tubular portion 84 corresponds to the implantation illustrated in FIG. 2B and so will not be detailed either. In this case, the means of generation of cold plasmas can be realized in the form of at less a pair of electrodes.

Of course, the different variants described with reference FIGS. 2A and 2B also apply to implantations E, F and G of this embodiment and the electrodes (or the solenoidal winding) are connected to the AC generator controlled by the system piloting.

Claims (16)

Injection system (10; 50; 72) of an air / fuel mixture in a turbomachine combustion chamber (12), comprising: a hollow tubular structure (41, 51, 73) for the flow of the air / fuel mixture to the combustion chamber (12); fuel injection means (38; 68; 100) disposed at an upstream end of the hollow tubular structure; and air injection means (28, 30; 64, 66; 89, 96) disposed downstream of the fuel injection means (38; 68; 100); characterized in that it further comprises: cold plasma generation means (42, 42 ') disposed downstream of the air injection means (28, 30; 64, 66; 89, 96) for generating active species in the flow of the air mixture fuel and to pre-break the molecules of the air / fuel mixture; and control means (48) for said cold plasma generating means (42, 42 ') as a function of the operating speed of the turbomachine. System (10) according to claim 1, characterized in that it comprises a fuel injector (38) disposed at an upstream end of the hollow tubular structure (41) and for injecting fuel into the hollow tubular structure (41). ) in a substantially axial direction, an internal air swirler (28) disposed downstream of the fuel injector (38) and for injecting air into said hollow tubular structure (41) in a substantially radial direction an external air swirler (30) disposed downstream of the internal air swirler (28) and for injecting air into said hollow tubular structure (41) in a substantially radial direction, a venturi (26); ) interposed between the internal (28) and outer (30) air vortices, and a bowl (22) disposed downstream of the external air vortex (30). System (10) according to claim 2, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around a downstream end of the venturi (26). System (10) according to claim 2, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around an upstream end of the bowl (22). System (10) according to claim 2, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around a downstream end of the venturi (26) and around an upstream end of the bowl (22). ). System (50) according to claim 1, characterized in that it comprises a fuel injector (68) disposed at an upstream end of the hollow tubular structure (51) and for injecting fuel into the hollow tubular structure (51). ) in a substantially axial direction, an internal air swirler (64) disposed downstream of the fuel injector (68) and for injecting air into said hollow tubular structure (51) in a substantially radial direction , an external air swirler (66) disposed downstream of the internal air swirler (64) and for injecting air into said hollow tubular structure (51) in a substantially radial direction, a first venturi ( 58) interposed between the inner (64) and outer (66) air frills, a second venturi (62) disposed downstream of the outer air swirler (66), and a premix bowl (56) disposed downstream of the second venturi (62). System (50) according to claim 6, characterized in that said cold plasma generating means (42, 42 ') is arranged around a downstream end of the premix bowl (56). System (72) according to claim 1, characterized in that it comprises: a fuel injector (82) having a first tubular portion (84) surrounding a second tubular portion (90) to define an annular passage (92) between said first (84) and second (90) tubular portions; an annular retaining ring (80) surrounding said first tubular portion (84) of the fuel injector (82) so as to define an annular passage (88) between said annular retaining ring (80) and said fuel injector ( 82); a bowl (78) disposed in the downstream extension of said annular retaining ring (80); air supply ports (89) opening into the annular passage (88) between said holding ring (80) and said fuel injector (82) and for injecting air downstream of said first tubular portion (84) of the fuel injector (82); air supply ducts (96) opening at an upstream end of said second tubular portion (90) of the fuel injector (82); and fuel supply channels (100) opening into the annular passage (92) between said first (84) and second (90) tubular portions and for injecting fuel between said first (84) and second (90) parts tubular. System (72) according to claim 8, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around a downstream end of said second tubular portion (90) of the fuel injector (82). ). System (72) according to claim 8, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around a downstream end of said first tubular portion (84) of the fuel injector (82). ). System (72) according to claim 8, characterized in that said means for generating cold plasmas (42, 42 ') are arranged around a downstream end of said first tubular portion (84) of the fuel injector (82). ) and around a downstream end of the annular retaining ring (80). System (10; 50; 72) according to any one of claims 1 to 11, characterized in that said means for generating cold plasmas comprise at least one pair of electrodes (42, 42 ') connected to a current generator alternative (46). System (10; 50; 72) according to claim 12, characterized in that the electrodes (42,42 ') of said pair of electrodes are aligned radially with respect to one another. System (10; 50; 72) according to claim 12, characterized in that the electrodes (42,42 ') of said pair of electrodes are radially offset relative to one another. System (10; 50; 72) according to any one of claims 3, 4, 7, 9 and 10, characterized in that said means for generating cold plasmas comprise a solenoidal winding connected to an alternating current generator (46) . System (10; 50; 72) according to any one of Claims 12 to 15, characterized in that the said alternating current generator (6) delivers electrical pulses with a duration of between 2 and 50 nanoseconds.

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