EP2482990B1 - Device and method for electrostatically spraying a liquid, fuel injector comprising said device, and uses of same - Google Patents

Description

The present invention relates to a device and a projection method, in particular in the form of a sheet of a liquid that can be electrically insulating at least by electrostatic forces, the device being designed to spray this liquid or to control oscillations by generating therein beats. The invention also relates to a fuel injector for a combustion chamber of a combustion engine incorporating this device, for both land and air or space vehicles, as well as other uses of this device, for example in the fields of pumps. electro-hydrodynamic for heat exchangers, cooling of embedded systems by spraying heat transfer liquids, spraying cutting oils or cleaning surfaces, without limitation.

Spraying a fuel is an essential step for all engines, as the pollution rate and efficiency of a combustion engine are closely related to the quality of the fuel spray. In aeronautical engines of the turbojet type, the spraying is obtained by disintegrating a sheet of fuel. To obtain this disintegration in a turbojet engine, a shear air jet blown at high speed (typically 200 m / s) is usually used in the combustion chamber which impacts the fuel ply and sprays it.

To improve this efficiency and reduce the pollution generated by these turbojets, it is therefore necessary to control the spraying, which is performed relatively satisfactorily under normal operating conditions since the spraying device is sized to function properly when the aircraft is in cruising speed.

However, this is not the case for the other regimes, particularly at low speeds, when for example the plane is on the runway. At this time, the air that enters the combustion chamber usually reaches a speed of about 30 m / s, insufficient to properly atomize the fuel which therefore burns poorly and generates both loss of power and pollution. The solution adopted by the aeronautical manufacturers then consists of having several injection systems in the same aircraft corresponding to the same operating speeds, which has the disadvantage of a complex, expensive, high-weight solution which also increases the risk of breakdowns. Other disadvantages of this multiplicity of injectors reside in the lack of flexibility of the device which does not make it possible to move continuously from one operating mode to another and in the insufficiency of the results obtained by the low-speed injectors (the speed air jet being too weak at low speed, the spray may be only partial).

To provide a solution to these pollution problems, new injectors have been developed, still on the same principle mentioned shearing air jets, to obtain fog with low fuel concentration. Although effective in terms of pollution, it happens nevertheless that the poverty of the mixture in fuel causes the extinction of the engine. Re-ignition of the engine is then difficult if it takes place at altitude (where the pressure is low and the air intake can for example be at -45 ° C).

Another recently explored route is to electrify the fuel prior to atomization in a jet engine by electrostatically injecting electric charges into a jet of fuel flowing at high speed. Article Priol L., Baudel P., Louste C., Romat H., "Laser granulometry measurements on electrified jets for different lengths of injector", Journal of electrostatics, Vol. 63, pp. 899-904, 2005 , teaches to use such an electrostatic spraying of a fuel flowing at an average speed of between 40 and 100 m / s by means of a symmetry-of-revolution nozzle incorporating an axial needle-shaped electrode connected to a source of high voltage and a substantially radial counter-electrode connected to the earth which is arranged downstream of the needle in the nozzle and which like the other electrode is intended to be in contact with the fuel. This counter electrode is provided upstream of a terminal axial pipe of this nozzle of length L and diameter D (with L / D ranging from 2 to 10) through which the electrified fuel flows before being sprayed out of the nozzle through the outlet of this pipe.

The document WO-A1-2008 / 052830 has a spray nozzle of an electrically conductive fuel incorporating a crown-shaped radial planar electrode which is housed between two electrically insulating radial layers and whose inner edge is pointed upstream of the nozzle of the fuel projection out of the nozzle . This conductive fuel is previously rotated upstream of this electrode and along an axis of rotation perpendicular thereto and then comes into contact with this pointed electrode edge before being projected out of the nozzle.

The document EP-B1-1 139 021 has a spray nozzle terminating in two axial metal electrodes which are intended to be in contact with the fuel and which alone define the edge of the fuel projection orifice out of the nozzle.

The document GB2096022 describes a device according to the preamble of the subject matter of claim 1.

A major disadvantage of this latter electrode sputtering device which are both non-electrically insulated is the relatively small value of the intensity of the electrostatic field generated by these electrodes, which affects the quality of the atomization obtained.

An object of the present invention is to provide a projection device in particular in the form of a sheet of a liquid that can be electrically insulating at least by electrostatic forces that overcomes all of the aforementioned drawbacks, this device being designed to spray this liquid or to control the oscillation beat and comprising a nozzle which forms a channel for supplying the liquid to at least one projection orifice of the latter out of the device and which incorporates in the vicinity of this orifice a first and a second electrode arranged to inject electric charges into the liquid.

For this purpose, a liquid projection device according to the invention is such that the edge of this orifice comprises, on one side of the channel, at least one projecting end of the first electrode which projects into this channel and which is intended to be in contact with the liquid and, on the other side of the channel, an electrically insulating nozzle body in which the second electrode is embedded adjacent the first electrode, so that the intensity of the electrostatic field in said or each projecting end is maximized.

It will first be noted that a device according to the invention thus defined not only optimally sprays in the form of a sheet a liquid which may initially be electrically unloaded, such as a diesel fuel (it being specified that by "electrically insulation "is meant for this liquid a resistivity equal to or greater than 10 ⁸ Qm), but also to control the variation of the oscillation amplitude of the projected web in the unsprayed state.

By "sheet" is meant in the present description a thin film whose thickness can typically vary from 200 microns to 500 microns and which defines a surface that can be plane or three-dimensional, being advantageously in the latter case with symmetry of revolution and delimiting an internal space, as opposed to a three-dimensional jet of liquid which by definition is full and therefore does not define an internal space.

Note that the device according to the invention, which can be based solely on the use of the Coulomb force, is able to inject electric charges into the fuel simultaneously with its projection out of the device to obtain a local electrostatic field. of extremely high intensity, thanks to the specific arrangement of the two electrodes, one of which forms the outlet end of the nozzle via its projecting end (ie pointed or sharp at a small radius of curvature) and the other of which is electrically insulated being immediately adjacent to this output end and, therefore, to the other protruding electrode. We then obtain locally a real forced injection of electrical charges into the fuel, and the Applicant has verified that the intense electrostatic effects thus obtained are of a nature to disrupt the fuel table or even to cause its explosion, with an optimization of the secondary spraying of the sheet and a homogeneity of the droplet mist obtained which is improved compared to the sprays obtained by the aforementioned known devices.

Recall that in a known manner by "primary oscillation" of a pulverized fuel ply, we mean longitudinal waves of small amplitude relative to the thickness of the ply and corresponding to an oscillation of the interface, and that downstream of this primary oscillation are formed ligaments in the direction of flow. These ligaments, which correspond to a so-called secondary oscillation, are regularly spaced in the transverse direction of the sheet and are separated by thin membranes which break rapidly under the effect of aerodynamic forces forming a mist of small drops. These ligaments in turn rupture to form a population of relatively large sized liquid clusters, the creation of these clusters corresponding to the end of the primary spraying phenomenon. As for secondary spraying, it corresponds to the disintegration of these unstable clusters into smaller droplets because of the kinetic pressure which opposes the surface tension forces.

According to another preferred feature of the invention, said channel is delimited by first and second electrically insulating nozzle bodies which are mounted facing each other and which respectively incorporate said first and second electrodes into profiled zones of these bodies leading to said projection orifice, the first electrode extending on a first inner wall to said channel defining the profiled zone of the first body and ending beyond this wall by said or each end projecting into the channel, and the second electrode being adjacent to a second outer wall of the channel defining the profiled zone of the second body.

Advantageously, said or each projecting end may have a main radius of curvature of between 5 μm and 15 μm and is preferably in the form of a point, said projection orifice having a smaller transverse dimension of between 100 μm and 500 μm. It will be noted that this small radius of curvature combined with the isolation of the second electrode makes it possible to obtain a very large local electrostatic field, with an intensity that may be greater than 1 MV / cm at the said or each projecting end when one applies an alternating voltage (of amplitude preferably equal to several kV and for example at least equal to ± 20 kV) between the first and second electrodes.

According to another characteristic of the invention, said first electrode may be generally rectilinear in longitudinal section, said second electrode may have a convex outer surface which is preferably elliptical or circular in longitudinal section, this convex or rounded shape making it possible to minimize the intensity of the electrostatic field at this surface.

Advantageously in the case of the preferential use of a fuel as a liquid, the device of the invention is such that said first nozzle body has a relative permittivity ε _r preferably less than or equal to 10 (even more preferential less than or equal to 5), and that said second nozzle body has a relative permittivity ε _r equal to or greater than 2 (preferably equal to or greater than 5) so as to further maximize the intensity of the electrostatic field in the vicinity of said first electrode. To avoid the breakdown of the device, this second electrode is thus placed inside an insulating material of high permittivity to transmit the electric field but especially of high dielectric strength to not slam (ceramics meet this double constraint and are therefore usable to form the second nozzle body). This second electrode is thus fully protected by this insulating material and is designed to never be in contact with the fuel or with the air. By way of examples of materials that can be used to constitute all or part of these two nozzle bodies, mention may be made in addition to ceramics of PVC and "Plexiglas", without limitation. As materials usable for constituting said first and second electrodes, all electrically conductive materials can be cited but also chemically neutral vis-à-vis the liquid to be sprayed.

To spray this fuel in the form of a sheet, this device according to the invention can furthermore be provided with means for bringing at least one gas stream, such as an air jet, downstream of said projection orifice so as to optimize further this spray.

According to a first embodiment of the invention, said channel has a substantially rectangular cross-section so as to project the liquid in the form of a plane sheet, said first electrode generally having a flat blade shape and said second electrode having a geometry in the form of a plane. bar, each electrode being independently continuous or discontinuous (for example in the manner of a comb) seen in cross section.

According to a second embodiment of the invention, said channel has a generally annular cross-section (eg elliptical or circular) so as to project the liquid in the form of a symmetrical sheet of revolution, said first electrode having a substantially conical shape diverging towards said or each protruding end and said second electrode having a substantially toroidal shape concentrically surrounding the first electrode, each electrode being independently continuous or discontinuous seen in cross section.

In a preferred embodiment according to this second embodiment of the invention, said first nozzle body is located radially inside said second nozzle body which concentrically surrounds it so that said first and second walls are respectively divergent and convergent in shape. direction of said channel, and said means for supplying gas streams are located radially inside said first body and radially outside said second body.

It will be noted that the device according to this second embodiment of the invention does not require modifying the geometry of the current injectors, the electrostatic action can be used alone or be superimposed on the usual mechanical action of the jet of air on the sheet to increase efficiency and safety. In fact, it suffices to provide said electrodes with this current injector with two concentric inner and outer nozzle bodies providing such radially inner and outer air flows and with respectively divergent and convergent end walls, the structure of these two nozzle that can be unchanged elsewhere.

It will also be noted that the device of the second mode according to the invention makes it possible to considerably simplify the current injection systems on the aircraft by eliminating injectors dedicated to low operating speeds, since this device of the invention is able to ensure this spraying. at low speed by the electrostatic force according to the invention supplemented by air inlets due to a shearing wind for example at 30 m / s. This device of the invention is thus of simple structure (only two electrodes are to be expected), inexpensive (conventional manufacturing techniques with air jets being usable), is able to operate at all regimes including ground, consumes a very low electric power (a few watts only) and is extremely robust and therefore little wear due to the fact that it is devoid of any moving parts unlike some known devices implementing a rotation of the fuel.

In addition, this device according to the second embodiment of the invention can help reignite the engine by spraying the large amount of fuel required.

An injector according to the invention, for example an electrically insulating fuel for a combustion chamber of a land, air or space vehicle thermal engine, in particular for an airplane turbojet, comprises a device capable of spraying this fuel in the form of web as defined above and, preferably, according to this second preferred embodiment of the invention with said gaseous flows which are located radially inside said first body and radially outside said second body.

As indicated above, it should be noted that this injector is characterized in particular by the position of the two electrodes which are located as close as possible to the outlet of the injector (ie from the injection lip of the nozzle), it being specified that preferably this injector lip is constituted in part by the first electrode injecting the charges into the fuel reaching it, with the creation of the aforementioned intense electrostatic forces which destabilize the fuel film to spray it in the form of a web.

It will also be noted that the electrostatic spraying means included in an injector according to the invention can be used alone for spraying the fuel, ie without mechanical blowing means, but that the combination of these two means makes it possible to increase the performance and the reliability. of the aircraft especially in case of failure of one of these two electrostatic and mechanical means, the other taking over.

Note further that an injector according to the invention has a small footprint, because the space required for the installation of these electrostatic means (ie essentially the two electrodes, the high voltage source and an electronic control device ) is reduced, and represents an ecological gain since the optimization of the spraying is accompanied by a better combustion, thus a lower consumption and consequently a decrease in the pollution generated.

Other uses according to the invention of a device as defined above may consist, without limitation, in spraying a liquid selected from the group consisting of heat transfer liquids, cutting oils for machine tools and cleaning fluids for soiled surfaces, or for producing an electro-hydrodynamic pump for a heat exchanger without a rotating part, for example intended to equip an aerial or space vehicle with a heat engine.

A method according to the invention for projecting at least electrostatic forces and in particular in the form of a sheet electrically insulating liquid, such as a fuel, by spraying or controlling the beat oscillations, is to use a device as defined above by applying between said first and second electrodes an alternating voltage signal whose amplitude is preferably several kV and is for example at least equal to ± 20 kV, for obtaining a field local electrostatic at said or each projecting end in contact with the liquid of intensity greater than 1 MV / cm and up to 10 MV / cm, electric charges being thus directly injected into the liquid leaving the device at this end.

Note that the use of an alternating signal is essential for the proper functioning of the device according to the invention, to prevent the accumulation of electrical charges on the surface of the solid dielectric separating the first and second electrodes.

According to another characteristic of the invention, the Applicant has discovered that a use of particular electrical signals allows a fine and fast modulation of the electrical action according to the needs of the fuel injector and according to whether one is looking for a spray fuel or control of the fuel when it is not sprayed.

In addition, the modulation of the electrical signal makes it possible to obtain an immediate or progressive variation in the behavior of the injector by these electrostatic means, this modulation making it possible to continuously adapt the operation of the injector during the changes of regime, thanks to to an electronic control device used in connection with the injector.

To spray this liquid, it is advantageous to use a frequency of this signal at least equal to 1 kHz, this signal being preferably square with, for example, a frequency equal to or greater than 2 kHz and a rise time of about 400 V / microseconds. It should be noted, however, that all other existing forms of alternative signals are usable for obtain this spray, such as sinusoidal, triangular or even pulses.

To control the oscillation beat of this liquid without spraying it, it is advantageous to use a frequency of this signal between 5 Hz and 100 Hz, this signal preferably being of the sinusoidal or triangular type and of frequency substantially equal to 50 Hz. note that this beat control is particularly useful in case of association of one or more air jets in addition to these electrostatic means.

According to another preferred feature of the invention, the liquid is moved in said channel with a speed of between 0.5 m / s and 2 m / s, and a substantially flat or symmetric layer is obtained. of revolution for the projected liquid having a thickness of between 200 μm and 500 μm, preferably by additionally bringing at least one gaseous flow, such as an air jet, downstream of said projection orifice and at a speed for example between 30 m / s and 200 m / s, to optimize the spraying of fuel projected by the device.

• la figure 1 est une vue schématique partielle et en section axiale d'un dispositif de projection d'une nappe selon l'invention à symétrie de révolution pour injecteur de carburant,
• la figure 2 est une vue schématique partielle et en section longitudinale suivant le plan II-II de la figure 9, d'un dispositif de projection selon l'invention d'une nappe plane de carburant correspondant à une variante simplifiée de la figure 1,
• la figure 3 est une vue schématique en agrandissement de l'extrémité de projection du dispositif de la figure 2 montrant notamment un exemple de forme et d'agencement des deux électrodes équipant ce dispositif,
• la figure 4 est une vue de dessous du premier corps de buse du dispositif de projection de la figure 2 (sans la première électrode à extrémité saillante prolongeant ce premier corps),
• la figure 5 est une vue latérale de ce premier corps de buse de la figure 2 montré dépourvu de sa première électrode,
• la figure 6 est une vue frontale de ce premier corps de buse de la figure 2 montré dépourvu de sa première électrode,
• la figure 7 est une vue de dessous du second corps de buse du dispositif de projection de la figure 2, montrant le logement pratiqué dans ce corps de buse pour y recevoir la seconde électrode électriquement isolée,
• la figure 8 est une vue latérale de ce second corps de buse de la figure 2,
• la figure 9 est une vue frontale de ce second corps de buse de la figure 2,
• la figure 10 est une juxtaposition de deux photographies montrant en vues de face deux nappes obtenues par le dispositif de la figure 2, la photographie de gauche montrant la nappe non pulvérisée obtenue sans les moyens électrostatiques de l'invention, et celle de droite la nappe pulvérisée selon l'invention qui est obtenue par ces moyens,
• la figure 11 est une juxtaposition de deux autres photographies montrant en vue de profil deux nappes obtenues par le dispositif de la figure 2, la photographie de gauche montrant la nappe non pulvérisée et sans battement obtenue sans les moyens électrostatiques de l'invention, et celle de droite la nappe non pulvérisée mais soumise au battement qui est obtenue par ces moyens,
• la figure 12 est une juxtaposition de deux rangées de quatre photographies chacune montrant en vue de face, pour quatre vitesses différentes de nappes, ces dernières à l'état non pulvérisé à la rangée du haut (i.e. sans les moyens électrostatiques) et à l'état pulvérisé à la rangée du bas (i.e. avec ces moyens, via un signal électrique carré de fréquence 2kHz et ± 30 kV d'amplitude),
• la figure 13 est une juxtaposition de deux rangées de quatre photographies chacune montrant les nappes de la figure 12 en vue de profil, (i.e. pour les mêmes vitesses de nappes, à l'état non pulvérisé à la rangée du haut et à l'état pulvérisé à la rangée du bas via ce même signal électrique),
• la figure 14 est une juxtaposition de six rangées de deux photographies chacune montrant en vue de face (pour les photographies de gauche) et en vue de profil (pour celles de droite) l'influence, sur la pulvérisation de la nappe, de la fréquence du signal électrique carré d'amplitude ± 30 kV utilisé en relation avec ces moyens, la vitesse de la nappe étant de 1 m/s,
• la figure 15 est une juxtaposition de quatre rangées de deux photographies chacune (à l'exception de la seconde rangée) montrant en vue de face (pour les photographies de gauche) et en vue de profil (pour celles de droite) l'influence, sur la pulvérisation de la nappe, de l'amplitude du signal électrique carré de fréquence 1 kHz utilisé en relation avec ces moyens,
• la figure 16 est une juxtaposition de quatre rangées de deux photographies chacune (à l'exception de la première rangée) montrant l'influence, sur le battement de la nappe, de la forme du signal (sinusoïdale pour les photographies de gauche et triangulaire pour celles de droite) et de la fréquence de ce signal d'amplitude ± 30 kV utilisé en relation avec ces moyens, la vitesse de la nappe étant de 1 m/s, et
• la figure 17 est une juxtaposition de deux rangées de trois photographies chacune montrant l'influence, sur le battement de la nappe, de la forme du signal (sinusoïdale pour la rangée supérieure et triangulaire pour la rangée inférieure) et de la fréquence de ce signal (avec trois fréquences pour chaque rangée) d'amplitude ± 30 kV utilisé en relation avec ces moyens, la vitesse de la nappe étant de 1 m/s.

The aforementioned characteristics of the present invention, as well as others, will be better understood on reading the following description of several exemplary embodiments of the invention, given by way of illustration and not limitation, said description being made in relation to the accompanying drawings, among which:

• the figure 1 is a partial diagrammatic view in axial section of a device for projecting a lap according to the invention with symmetry of revolution for a fuel injector,
• the figure 2 is a partial diagrammatic view in longitudinal section along plane II-II of the figure 9 , a projection device according to the invention of a flat fuel ply corresponding to a simplified variant of the figure 1 ,
• the figure 3 is a schematic enlarged view of the projection end of the device of the figure 2 showing in particular a example of shape and arrangement of the two electrodes equipping this device,
• the figure 4 is a bottom view of the first nozzle body of the projection device of the figure 2 (without the first electrode with protruding end prolonging this first body),
• the figure 5 is a side view of this first nozzle body of the figure 2 shown devoid of its first electrode,
• the figure 6 is a front view of this first nozzle body of the figure 2 shown devoid of its first electrode,
• the figure 7 is a bottom view of the second nozzle body of the projection device of the figure 2 showing the housing in this nozzle body for receiving the second electrically insulated electrode,
• the figure 8 is a side view of this second nozzle body of the figure 2 ,
• the figure 9 is a front view of this second nozzle body of the figure 2 ,
• the figure 10 is a juxtaposition of two photographs showing in front views two sheets obtained by the device of the figure 2 the photograph on the left showing the unpowdered web obtained without the electrostatic means of the invention, and on the right the pulverized web of the invention obtained by these means,
• the figure 11 is a juxtaposition of two other photographs showing in profile two sheets obtained by the device of the figure 2 , the photograph on the left showing the non-atomized and non-beat web obtained without the electrostatic means of the invention, and on the right the unpowdered web but subjected to the beat obtained by these means,
• the figure 12 is a juxtaposition of two rows of four photographs each showing in front view, for four different speeds of webs, the latter in the unsprayed state at the top row (ie without the electrostatic means) and in the pulverized state. the bottom row (ie with these means, via a square electric signal of frequency 2kHz and ± 30 kV amplitude),
• the figure 13 is a juxtaposition of two rows of four photographs each showing the tablecloths of the figure 12 in profile view, (ie for the same web speeds, in the unsprayed state at the top row and in the pulverized state at the bottom row via this same electrical signal),
• the figure 14 is a juxtaposition of six rows of two photographs each showing in front view (for the photographs on the left) and in profile view (for those on the right) the influence, on the spraying of the sheet, of the frequency of the electrical signal square of amplitude ± 30 kV used in relation to these means, the speed of the sheet being 1 m / s,
• the figure 15 is a juxtaposition of four rows of two photographs each (except for the second row) showing in front view (for the photographs on the left) and in profile view (for those on the right) the influence, on the spray of the layer, the amplitude of the square 1 kHz frequency electric signal used in connection with these means,
• the figure 16 is a juxtaposition of four rows of two photographs each (except for the first row) showing the influence, on the beat of the sheet, of the shape of the signal (sinusoidal for left and triangular photographs for right) ) and the frequency of this amplitude signal ± 30 kV used in connection with these means, the speed of the web being 1 m / s, and
• the figure 17 is a juxtaposition of two rows of three photographs each showing the influence, on the beat of the web, of the signal shape (sinusoidal for the upper and triangular row for the lower row) and the frequency of this signal (with three frequencies for each row) of amplitude ± 30 kV used in relation to these means, the speed of the sheet being 1 m / s.

• un premier corps de buse 3 radialement interne, électriquement isolant et en forme de tube creux à surface externe 4 cylindrique dont l'espace interne est avantageusement conçu pour acheminer un jet d'air central 5 radialement à l'intérieur de la nappe de carburant 2 projetée par la buse 1 (cylindrique dans le schéma de la figure 1, étant entendu que cette nappe pourrait être conique) de sorte à en améliorer la pulvérisation par exemple, ce premier corps 3 se terminant par une surface interne conique 6 qui diverge radialement vers l'extérieur et qui est recouverte d'une première électrode 7 (par exemple métallique) épousant cette surface 6 et de section axiale rectiligne se terminant par une pointe en saillie 7a radialement à l'extérieur de la surface externe 4 de sorte à être au contact du carburant 2 projeté,
• un second corps de buse 8 radialement externe, électriquement isolant et en forme de tube creux à surface interne 9 cylindrique dont l'espace externe est avantageusement conçu pour acheminer un autre jet d'air périphérique 10 radialement à l'extérieur de la nappe projetée de carburant 2, ce second corps 8 se terminant par une surface externe conique 11 qui converge radialement vers l'intérieur pour se terminer sensiblement en regard de la pointe 7a de la première électrode 7, et qui renferme dans sa masse une seconde électrode 12 (par exemple métallique) à proximité immédiate de l'extrémité aval de ce second corps 8 et donc de la première électrode 7, et
• des moyens 13 de génération et de contrôle d'un signal électrique alternatif appliqué entre les électrodes 7 et 12 (de forme, d'amplitude et de fréquence réglables, comme expliqué ci-dessous), lesquelles sont reliées à une source de haute tension HT incluse dans ces moyens 13.

The device 1 for liquid projection 2 illustrated in FIG. figure 1 represents a preferred embodiment of a fuel injector nozzle according to the invention. As will be explained hereinafter, the nozzle 1 may be used optionally to spray the fuel 2 or to control the beat of its oscillation, and it essentially comprises:

• a first radially inner, electrically insulating and hollow tube-like body 3 having a cylindrical outer surface 4, the internal space of which is advantageously designed to convey a central air jet 5 radially inside the fuel ply 2 projected by the nozzle 1 (cylindrical in the diagram of the figure 1 , it being understood that this sheet could be conical) so as to improve the spraying for example, this first body 3 ending in a conical inner surface 6 which diverges radially outwards and which is covered with a first electrode 7 ( for example metallic) marrying this surface 6 and of straight axial section ending in a protruding tip 7a radially outside the outer surface 4 so as to be in contact with the projected fuel 2,
• a second radially external, electrically insulating and hollow-tube-shaped nozzle body 9 having a cylindrical inner surface, the outer space of which is advantageously designed to convey another peripheral air jet radially out of the projected layer of fuel 2, this second body 8 ending in a conical outer surface 11 which converges radially inwards and terminates substantially opposite the tip 7a of the first electrode 7, and which encloses in its mass a second electrode 12 (by metal example) in the immediate vicinity of the downstream end of this second body 8 and therefore of the first electrode 7, and
• means 13 for generating and controlling an alternating electrical signal applied between the electrodes 7 and 12 (of adjustable shape, amplitude and frequency, as explained below), which are connected to a high voltage source HT included in these means 13.

The relative positioning of the two nozzle bodies 3 and 8 defines a narrow channel 14 for supplying the fuel 2 to be sprayed with an annular section, with a spacing E between these two bodies 3 and 8, for example between 100 μm and 500 μm, determining and the thickness of the fuel ply 2 projected (with an output speed for example of the order of 1 m / s).

More specifically, the first electrode 7 is designed to directly inject electric charges into the fuel 2 in which its tip 7a is immersed in operation, serving as an injector lip to the nozzle 1 because this electrode 7 is partially the edge 15 of the nozzle projection orifice 1. This direct injection at the tip 7a is achieved through an electrostatic field of very high intensity (several MV / cm up to 10 MV / cm) that the 7a is generated by the high voltage HT applied between the two electrodes 7 and 12, thanks to the sufficiently small radius of curvature of this tip 7a which is for example about 10 microns. As for the material of the first body 3 constituting the insulating support of this first electrode 7, it is chosen to permittivity ε _r low to maximize the intensity of the electrostatic field in the vicinity of the tip 7a, this permittivity preferably being lower than that of the liquid 2 to project is less than 2.2 for a diesel fuel type "GASOIL", for example.

The second electrode 12 is entirely embedded in the second nozzle body 8 which electrically isolates it to prevent arcing between the two electrodes 7 and 12. The electrode 12 has a geometry devoid of angles or edges (advantageously convex or rounded, being generally torus-shaped in the example of the figure 1 ) which limits the electric field to its surface as well as the stresses on the insulating material which is in contact with this electrode 12. This insulating material has a dielectric rigidity chosen as high as possible, and a permittivity also high (ε _r > 5 of preferably) to maximize the intensity of the electrostatic field in the vicinity of the first electrode 7.

As for the two air jets 5 and 10 above which are designed to blow on the inner and outer faces respectively of the sheet 2 emitted, their speed can vary from 30 m / s to 200 m / s by way of example.

It will be noted that the electrostatic injector 1 according to the invention of the figure 1 is distinguished only from an injector of the prior art by the addition and the specific arrangement of the two electrodes 7 and 12 in connection with the means 13 for generating and controlling the alternating electrical signal between these electrodes 7 and 12. In other words, the general architecture of such a known injector has not been modified, the electrostatic effect being advantageously superimposed or not on the aeromechanical effect, which makes it possible to have a mechanical action only electrostatic action alone or both of these actions simultaneously for spraying the fuel 2.

As explained above, it should be noted that the fuel ply 2 thus charged undergoes the action of the electrostatic forces which generate either its spray or its controlled oscillation, according to the electrical signal applied between the electrodes 7 and 12, and that this sputtering or the control of this oscillation are optimized by the respective geometries of these electrodes 7 and 12 which are designed to maximize the electrostatic field on the first electrode 7 and thus the direct injection of the electric charges into the fuel 2.

We have tested, with reference to Figures 2 to 9 (dimensions expressed in mm), a jet projection nozzle 101 with a plane projection channel 114, this geometry having been retained for the sake of simplicity and because it is representative of the results obtained with a device with symmetry of revolution ( ie axisymmetric of the type of that of the figure 1 ) with projection channel 14 of annular section. Two flat prototypes of the same structure but made with different electrically insulating materials were used for these tests, the first having its two nozzle bodies 103 and 108 made of PVC and the second one in "plexiglass" (with a permittivity ε _r of 4, 5, a resistivity of 10 ¹⁵ Ω.m and a dielectric strength> 40 kV / mm in alternating current). As for the fuel used, it is "GASOIL" with a density equal to 860 kg / m ³ , relative permittivity ε _r = 2.2, resistivity ranging between 10 ⁹ and 10 ¹⁰ Ω.m and viscosity kinematic equal to 4.3 10 ^-6 m ² / s.

The projection nozzle 101 visible to these Figures 2 to 9 comprises two first and second nozzle bodies 103 and 108 which are respectively provided with the first and second electrodes 107 and 112 and which are essentially different from those of the figure 1 in that these bodies 103 and 108 each have the same geometry of rectangular cross section, instead of the annular cross section of those of the figure 1 (This rectangular shape is visible Figures 4 and 6 for the first body 103 and to Figures 7 and 9 for the second 108).

The upstream end of these two bodies 103 and 108 is in the example of the figure 2 surmounted by a cap 116 closing a plenum 117 of fuel which has a rectangular longitudinal section and which is delimited by the respective inner faces of the two bodies 103 and 108, symmetrical to each other with respect to the central channel 114 of fuel projection. More specifically, the chamber 117 and this channel 114 are centered on the longitudinal axis of symmetry X of the nozzle 101, and a central orifice 116a formed in the cap 116 allows the arrival of the fuel in the chamber 117, which narrows to right angle near the downstream end of the nozzle 101 by two shoulders 103a and 108a that have the internal faces of the bodies 103 and 108. This channel 114 forms a terminal section of small width l (1 mm, see figure 3 ) which communicates upstream with the chamber 117 and leads to the profiled downstream end of the nozzle 101 formed by the respective oblique outer surfaces 103b and 108b of the two bodies 103 and 108.

The first electrode 107 (made of chromed steel) is in the form of a flat blade which extends over most of the oblique outer surface 103b of the first body 103 and which ends with a pointed end 107a projecting obliquely into the channel 114 , so that this protruding end 107a partially defines the edge 115 of the downstream orifice of projection of the nozzle 101 (see figure 3 ) in conjunction with the acute terminal edge of the second body 108, the width e between this projecting end 107a and this facing edge being in this example of 300 microns.

As for the second electrode 112 (also made of chromed steel), it is embedded in this embodiment in an epoxy-type insulating resin 112a which fills a cavity opening on the oblique outer surface 108b of the second body 108 in the profiled zone of the latter and in the immediate vicinity of said ridge. We see Figures 2 and 3 that this insulating resin 112a thus forms a portion of the oblique surface 108b and is in contact with the insulating material (eg PVC or "plexiglas") of the second body 108. This second electrode 112 has in this example an oblong and rounded longitudinal section which is substantially elliptical.

It will be noted that the connection of the electrodes 107 and 112 has not been represented on these Figures 2 to 9 for the sake of clarity.

Thus, substantially flat projected plies were obtained with web speeds of between 0.5 m / s and 2 m / s, each ply having a rectangular section of length approximately equal to 8 cm (in the transverse direction of Figures 6 and 9 ) and of width approximately equal to 4 cm (in the longitudinal direction of these figures), with a thickness of sheet of about 300 microns (corresponding to the aforementioned width e of the projection orifice).

The Figures 11 to 17 present the plies obtained during tests carried out in the absence of air flow (ie only by the electrostatic means comprising these electrodes 107 and 112), by means of the projection device 101 according to these Figures 2 to 9 whose nozzle bodies 103 and 108 are made of "plexiglass" (with the exception of the aforementioned epoxy resin 112a).

On the left image of the figure 10 it can be seen that the projected non-atomized fuel layer (due to the absence of an electrical signal generated between the electrodes) is perfectly stable in front view, whereas the right image of this figure 10 illustrates the effective spray obtained by the only forced injection of electric charges according to the invention (via an alternating electric signal), the electrostatic means being thus alone capable of spraying the sheet.

On the left image of the figure 11 it can be seen that the projected slick of unsprayed fuel (due to the absence of an electrical signal) is perfectly linear (ie without beat) seen in profile, while the right-hand image of this figure 11 shows that the generation of a suitable alternating signal between the electrodes (see below) makes it possible to constrain the fuel layer with a given beating of oscillations.

On the top row of pictures of the figure 12 , are shown in front view four non-spraying projected sheets (due to the absence of an electrical signal) at speeds of 0.6 m / s, 1 m / s, 1.5 m / s and 2 m / s, respectively. s, while the lower row of images from this figure 12 shows the spray obtained according to the invention at these four sheet speeds via a square electrical signal of 2 kHz and amplitude ± 30 kV.

On the top row of pictures of the figure 13 , are shown in profile view four non-spraying projected plies (due to the absence of electrical signal) at these same four speeds, whereas the lower row of images of this figure 13 shows the spray obtained according to the invention at these web speeds via the same square electrical signal of 2 kHz and amplitude ± 30 kV. It is seen in this lower row that the large drops (from 1 mm to 3 mm in diameter) which come for most of the edges of the sheet are visible in the center, and a multitude of small drops of very small diameter (less than 100 μm) are also visible on both sides of the central jet.

The figure 14 shows the influence on the quality of the obtained sputtering (with a sheet speed of 1 m / s) of the frequency of a square electrical signal of amplitude ± 30 kV, this frequency varying from 0 Hz to the top row (ie in the absence of signal) at the maximum frequency of 2 kHz at the bottom row. It can be seen that the use of high frequencies (ie of at least 500 Hz) and preferably of between 1 and 2 kHz provides a satisfactory spraying of the sheet.

The figure 15 shows the influence on the quality of the obtained sputtering of the amplitude of the square 1 kHz electrical signal. We see that this amplitude must be in this example greater than ± 20 kV to obtain a finely pulverized sheet.

The two columns of images of the figure 16 (front views) show the influence on the resulting web beat of the shape and frequency of the AC signal, for the same signal amplitude equal to ± 30 kV and for a fuel speed of 1 m / s. In the left column are illustrated the plies obtained for a sinusoidal signal and the right one for a triangular signal, in both cases for frequencies ranging from 5 Hz to 100 Hz.

The two rows of images of the figure 17 (profile views) complement these views of the figure 16 for three of these frequencies (5 Hz, 10 Hz and 50 Hz) and allow to visualize the beat obtained for the sinusoidal signals (upper row) and triangular (lower row).

It emerges from these Figures 10 to 17 that the projection devices according to the invention operate satisfactorily with all types of conventional alternating signals (ie of the square, sinusoidal, triangular and even pulse type). More specifically, the specific use of a low frequency (greater than 50 Hz) associated with a "soft" signal of sinusoidal or triangular type makes it possible to obtain a beat of the sheet without spraying, while the use of high frequencies (up to 2 kHz) allows a fine spraying of the water table (excellent quality sprays have been obtained with a 2 kHz square wave). Nevertheless, it is possible to envisage spraying the layers satisfactorily (ie with optimized secondary spraying) with a device according to the invention at alternating signal frequencies greater than 2 kHz.

Claims (15)

1. A device for spraying (1,101), in particular in the form of a sheet, a liquid (2) that can be electrically insulating at least through electrostatic forces, the device being designed to atomize this liquid or to control the beat of the oscillations thereof, this device comprising a nozzle which forms a channel for feeding (14,114) the liquid to at least one orifice for spraying (15,115) said liquid out of the device and which incorporates, in proximity to this orifice, a first electrode and a second electrode (7,107 and 12,112) configured to inject electric charges into the liquid, characterized in that the edge of this orifice comprises, on one side of the channel, at least one protruding end (7a,107a) of the first electrode which protrudes into this channel and which is configured to be in contact with the liquid and, on another side of the channel, an electrically insulating nozzle body (8,108) in which the second electrode (12,112) is embedded adjacent to the first electrode, so that the intensity of the electrostatic field at said or each protruding end is maximized.
2. The device (1,101) according to claim 1, wherein said channel (14,114) is delimited by a first and a second electrically insulating nozzle bodies (3,103 and 8,108) which are mounted facing one another and which respectively incorporate said first and second electrodes (7,107 and 12,112) in profiled regions of these bodies ending at said spraying orifice (5,115), the first electrode extending on a first wall (6, 103b) inside said channel defining the profiled region of the first body and ending beyond this wall by said or each end protruding(7a,107) into the channel, and the second electrode being adjacent to a second wall (11,108b) outside the channel defining the profiled region of the second body.
3. The device (1,101) according to claim 1 or 2, wherein said or each protruding end (7a,107) has a main radius of curvature of between 5 µm and 15 µm and is preferably pointed, said spraying orifice (15,115) having a smaller transversal dimension of between 100 µm and 500 µm.
4. The device (1,101) according to any of preceding claims, wherein said first electrode (7,107) is overall rectilinear in longitudinal section, said second electrode (12,112) having a convex outer surface which is preferably elliptical or circular in longitudinal section so as to minimize the intensity of the electrostatic field at this surface.
5. The device (1,101) according to claim 2 and any of claims 3 and 4, this device being suitable for spraying a fuel as liquid (2), wherein said first nozzle body (3,103) has a relative permittivity ε_r less than or equal to 10, and in that said second nozzle body (8,108) has a relative permittivity ε_r equal to or greater than 2, so as to further maximize the intensity of the electrostatic field in the vicinity of said first electrode (7,107), and preferably wherein said device is capable of generating said local electrostatic field with an intensity greater than 1 MV/cm at said or each protruding end (7a,107a) when an alternating voltage is applied between said first and second electrodes (7,107 and 12,112).
6. The device (1) according to any of preceding claims, this device being suitable for atomizing a fuel as liquid (2) in the form of a sheet, wherein it also comprises means for feeding at least one gaseous flow (5,10), such as a jet of air, downstream of said spraying orifice (15) so as to optimize the atomization of the fuel sprayed by the device.
7. The device (101) according to any of preceding claims, wherein said channel (114) has a substantially rectangular transversal section so as to spray the liquid in the form of a flat sheet, said first electrode (107) having overall the form of a flat plate and said second (112) electrode having a bar-shaped geometry, each electrode being independently continuous or discontinuous seen in transversal section.
8. The device (1) according to any of claims 1 to 6, wherein said channel (14) has an overall annular transversal section so as to spray the liquid (2) in the form of a sheet with symmetry of revolution, said first electrode (7) having a substantially divergent tapered form toward said or each protruding end (7a) and said second electrode (12) having a substantially toroidal form concentrically surrounding the first electrode, each electrode being independently continuous or discontinuous seen in transversal section.
9. The device (1) according to any of claims 2, 6 and 8, wherein said first nozzle body (3) is situated radially inside said second nozzle body (8) which surrounds it concentrically so that said first and second walls (6 and 11) are respectively divergent and convergent toward said channel (14), and in that said means for feeding the gaseous flows (5,10) are located radially inside this first body and radially outside this second body.
10. The device according to any of preceding claims, wherein it forms an electro-hydrodynamic pump for a heat exchanger with no rotating parts, for example intended to equip an air or space vehicle with heat engine.
11. An injector of a fuel (2) that can be electrically insulating for a combustion chamber of a heat engine of a land, airborne or space vehicle, in particular for an airplane jet engine, wherein it comprises a device suitable for atomizing this fuel in the form of a sheet according to any of claims 1 to 9 and, preferably according claim 9.
12. The use of a device according to any of claims 1 to 9 for atomizing a liquid chosen from the group consisting of heat-transfer liquids, cutting oils for machine tools and liquids for cleaning soiled surfaces.
13. A method for spraying, at least by electrostatic forces and in particular in sheet form, a liquid (2) that can be electrically insulating, such as a fuel, by atomizing it or by controlling the beat of the oscillations thereof, wherein it consists in using a device according to any of claims 1 to 10 by applying, between said first and second electrodes (7,107 and 12,112), an alternating voltage signal, the amplitude of which is preferably several kV, to obtain a local electrostatic field at said or each protruding end (7a,107a) with an intensity greater than 1 MV/cm, electrical charges thus being directly injected into the liquid leaving the device at this end.
14. The method according to claim 13, wherein, to atomize this liquid, a frequency of this signal at least equal to 1 kHz is used, this signal preferably being square and preferably having a frequency equal to or greater than 2 kHz, or wherein to control the beat of the oscillations of this liquid without atomizing it, a frequency of this signal of between 5 Hz and 100 Hz is used, this signal preferably being of sinusoidal or triangular type and with a frequency substantially equal to 50 Hz.
15. The method according to claim 13, wherein, liquid (2) is set in motion in said channel (4,14) with a speed of between 0.5 m/s and 2 m/s, and in that a sheet that is substantially flat or with symmetry of revolution for the sprayed liquid with a thickness of between 200 µm and 500 µm is obtained, preferably by also feeding at least one gaseous flow (5,10), such as a jet of air, downstream of said spraying orifice (15) and at a speed for example of between 30 m/s and 200 m/s, to optimize the atomization of the fuel sprayed by the device (1,101).

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