EP0965791B1 - Nozzle to inject fuel as a mist like spray for a fuel burner and burner comprising such a nozzle - Google Patents

Description

The invention relates to fuel injectors in the form of a mist (known in the art as spray name), for oil burners with a rod crossed by coaxial channels, one of which leads to a spray fluid and another a liquid fuel which are then transmitted to this injector. It relates to also burners fitted with such an injector.

We know a wide variety of devices spraying or spraying of liquid comprising coaxially a number of channels for bringing under pressure one or more spray liquids and one or more gases spray at a spray outlet.

Indeed, the means adapted to spray a liquid given under the best conditions do not give necessarily the best results for another liquid having different physical properties, and moreover the composition sought for the mist varies from application to another.

We know for example from US Patents 2,565 696, 3,035,775, 3,533,558, 3,662,960 and 3,805,869, devices intended respectively for spraying concrete, projection of the components of a polyurethane foam, spraying very viscous starch solutions, injection of liquid fuels for rocket engines, and spraying polyvinyl chloride solutions into dry atmosphere for processing into powder; these devices have very diverse structures so to create, in the channels, flows according to modes specific, for example helical in the case of the document US 3,533,559, with a view to optimally bringing together the various components immediately before or at the time of their device output.

However, spraying combustible liquids in the burners also poses specific problems such as avoiding flashbacks and coking of the output injector, which lead to the impossibility directly apply or simply adapt the devices other areas, and that we have always sought to be resolved by appropriate means.

Patent GB 209691 A describes a fuel injector comprising internally a channel through which a liquid fuel and a spraying fluid can be transmitted to the downstream part of the injector. The downstream part presents internally in the longitudinal alignment of the channel and in succession towards the free end, a chamber having a cross section greater than that of said channel, a neck extending the chamber having a cylindrical shape and a cross section smaller than that of said chamber, and a projection mouth open at the free end of the injector, having a cross section greater than that of said neck.

US Patent 792,265 shows a burner coaxially comprising a central channel traversed by a combustible liquid, and two annular canals traversed by a stream of pressurized steam, fed in their upstream region respectively by the liquid to be sprayed and by steam ; the free end (downstream) of the first partition annular, common to the central channel and to the annular channel immediately adjacent, is far upstream of the free end (downstream) of the second annular partition; in this way, a first external spraying of combustible liquid is performed during shearing from the outside, of the liquid jet, by the vapor arriving annularly around this jet, at the free end forming the nozzle of the first annular bulkhead; the second annular partition determines internally from this free end a new central channel through which the resulting current flows from the first spray; this current is subject to a second external spray at the free ends, lying in the same transverse plane, of the two partitions forming the nozzle of the second annular channel. With this structure, obtaining a fog of characteristics precise is very difficult.

US Patent 1,279,315 shows a structure burner neighbor, but in which the first annular channel is traversed by a current of air, while the second is traversed by a current of air or vapor, with the same disadvantages than those mentioned above.

It was considered that by bringing a liquid fluid to spray, annularly around a first gaseous fluid spraying, we could better control the process spray.

Thus, there are also known devices spraying of liquid coaxially comprising, inside to outside, a central channel crossed by a spray gas, an annular channel through which the liquid product to be sprayed and an annular channel also traversed by a spray gas, supplied in a first end region (upstream region) by spraying and spraying fluids, and comprising respective nozzles in the second region end (downstream region) in order to project the product initially in the liquid state, in the form of droplets in suspension in spraying fluids.

This is particularly the case for the objects of documents GB 672 441, EP 0 105 493 and EP 0 593 171, but there still the prior art is not entirely satisfactory for spraying a combustible liquid in the quarry of an oven.

Indeed, in these three documents, the ends respective downstream at least of the two annular channels terminate by a nozzle whose downstream end of the central channel, slightly recessed inside the intermediate annular canal, is nevertheless very close; it follows that although the liquid product to be sprayed is transmitted through the intermediate annular channel, spraying produced by the interior spray gas can be assimilated to external spraying (it results from shearing of the liquid jet through the angular end of the outer wall of the annular channel for the liquid); the spraying by external spraying gas is naturally also an external spray, and thus these devices can be considered to be at two external sprays. Consequently, mastery fine mist spray state (diameter medium of drops and fraction of small drops) is therefore very delicate.

It follows that despite the existence of the devices of these three documents, it remained to create a device causing internal spraying on the one hand and on the other hand an external spraying of the liquid to be sprayed.

To this end, in a known type of oil burner comprising a spraying device according to the document FR 2 737 138, there is provided a rod comprising an input part comprising coaxially from a channel central for an "internal" spray fluid fuel oil, an annular channel for fuel oil, and an annular channel for an "external" spray fluid; enter here outer wall of the cane, and the burner bulkhead, is determined an additional annular channel bringing a gas oxidizer. In the exit part of the rod but clearly upstream of its outlet end, the central channel for the internal spray fluid ends with a "internal" injector opening into the channel for fuel oil thus forming, downstream of the internal injector, a central channel containment constituting a pre-spray space for internal spraying fluid and fuel oil, surrounded by the annular channel for the spray fluid external, while the channel for the oxidant gas remains between the outer wall of the cane and the burner bulkhead.

All or part of the pre-spray space can be made in a room in the form of an injector "Mixing" by which is injected into the quill of the burner, fuel oil sprayed with spray fluid internal, and around which the spraying fluid is injected external.

The invention relates more precisely to such an injector of combustible mixture traversed by a fluid internal spraying and the fuel itself (liquid), and therefore aims to create a mist injector fuel allowing an improvement in the quality of spraying, on the one hand avoiding the presence of "Flakes" within the flame produced by the burner, the term “flakes” designating fuel drops big enough to stay individually very clearly visible when they burn within the flame, and on the other hand by increasing the stability of the flame, the attachment of the flame to the burner nose being made almost systematic.

We can expect to achieve this goal by reducing the average time required for the population to evaporate drops, increasing the mass fraction of small drops (diameter smaller than 20 µm) within the fog and decreasing the average diameter of the whole drops (at spray fluid and liquid flow rates constant fuel).

Indeed, in the mixing injector of the device known from document FR 2 737 I38, which can be arranged as shown in figure 1, the longitudinal central channel containment constituting the pre-spray space has two regions 11, 12 of different diameters truncated in a zone 13, region 11 of largest diameter constituting the entry region of the injector and the region 12 of smaller diameter its region Release.

Generally the ratio of the length of the region 12 at its diameter is of the order of 8 to 12, and typically equal to approximately 9.

In this fuel mixture injector under the in the form of a mist, we observe the formation of a film 21 liquid fuel of approximately constant thickness all along region 11 of large diameter of the canal central, connected to a film 22 extending along the region of small diameter by a frustoconical zone 23; however, the internally frustoconical shape of the film extends beyond the frustoconical connection of the two cylindrical regions of the canal, which leads to the formation of an additional thickness film in the small diameter region, the thickness of the film 22 of this region then decreasing to the free end of the injector.

It appears that under these conditions, the spraying liquid fuel results from tearing off the film lining the wall of the injector channel, which on the one hand, produces relatively large drops, and on the other hand quickly pulls small droplets into the stream spray fluid (e.g. air), flowing at high speed, which limits the amount of fuel evaporated locally and does not allow good combustion of the heavy fuel oil.

The invention therefore aims to remedy these drawbacks by increasing the mass fraction of small drops, and by decreasing the average diameter of the drops and the speed of small drops, and also improve the flame stability inside and outside of the burner outlet thanks to the adoption of an appropriate geometry for the injector, or at least for the downstream part of it which ends with its free end.

To this end, the invention relates to a fuel injector, in particular for oil burner, internally comprising a duct through which a fuel in the li ^q fluid at least partially in the form of a film lining the internal wall of the channel and a spraying fluid are transmitted to the downstream part of the injector ending in the free end of the latter through which the fuel is projected out of the injector, forming a mist with the stream of spraying fluid, characterized in that this downstream part has internally in the longitudinal alignment of the channel and in succession towards the free end, a film destabilization chamber having a cross section greater than that of the channel, a film tearing neck extending the chamber destabilization and having a cylindrical shape and a cross section smaller than that of this chamber, and a projection mouth open to the ex free end of the injector, into which the tearing neck opens, and having a cross section greater than that of the neck, and in that the projection mouth is a cylinder, and its length is at most equal to the diameter of the neck .

Thanks to this configuration, the fuel film liquid is more easily detached from the wall of the canal than in the fuel mixture injectors according to the prior art, when it has entered the bottleneck intended for this purpose, and this results in the formation of droplets thinner in greater quantity.

• le goulet d'arrachage présente une section transversale inférieure à celle du canal ;
• la chambre de déstabilisation présente une section circulaire dont le diamètre est supérieur environ de moitié au diamètre du canal, de section également circulaire ;
• la chambre de déstabilisation présente une section circulaire, et sa longueur est approximativement triple de son diamètre ;
• le goulet d'arrachage présente une longueur qui est plus faible que son diamètre ;
• le goulet d'arrachage présente une longueur qui est supérieure au quart de son diamètre ;
• la bouche de projection présente une longueur qui est au moins égale à la moitié du diamètre du goulet ;
• la bouche de projection présente un diamètre qui est supérieur environ de moitié au diamètre du goulet d'arrachage, de section également circulaire ;
• la bouche de projection est entourée par une cloison annulaire dont le diamètre extérieur est supérieur d'environ 1 mm au diamètre intérieur ;
• ladite partie aval est métallique ;
• il est entièrement métallique.

The injector according to the invention can also have one or more of the following characteristics:

• the tearing neck has a cross section smaller than that of the channel;
• the destabilization chamber has a circular section, the diameter of which is approximately half the diameter of the channel, also of circular section;
• the destabilization chamber has a circular section, and its length is approximately three times its diameter;
• the tearing neck has a length which is smaller than its diameter;
• the tearing neck has a length which is greater than a quarter of its diameter;
• the projection mouth has a length which is at least equal to half the diameter of the neck;
• the projection mouth has a diameter which is approximately half the diameter of the tearing neck, also of circular section;
• the projection mouth is surrounded by an annular partition whose outside diameter is approximately 1 mm greater than the inside diameter;
• said downstream part is metallic;
• it is entirely metallic.

The invention also relates to a burner of the type comprising a rod with a downstream end carries a mixture injector as mentioned above and an external injector, characterized in that the rod has internally a thread in which is screwed the mixture injector and externally a thread around which the external injector is screwed, and has a annular canal extending by a determined space between the external injector and the mixture injector.

Thanks to this structure, the adaptation of the injector according to the invention on a burner, whether in "Original equipment" or to replace a previous injector is simple and fast.

• les extrémités libres des deux injecteurs débouchent dans le même plan ;
• il comporte un corps portant extérieurement une bride de fixation à un bloc ouvreau, et une bride d'assemblage à une bride de la canne ;
• il comporte un corps portant extérieurement des chapes comportant chacune un pivot autour duquel est articulée une tige filetée adaptée pour se loger dans des encoches correspondantes en regard dans la région périphérique de deux brides portées respectivement par le corps du brûleur et par la canne, qu'elle traverse de part en part et qui est bloquée par un écrou.

The burner according to the invention can also have one or more of the following characteristics:

• the free ends of the two injectors open in the same plane;
• it comprises a body externally carrying a flange for fixing to an opening block, and an assembly flange to a flange of the rod;
• it comprises a body externally carrying yokes each comprising a pivot around which is articulated a threaded rod adapted to be housed in corresponding notches opposite in the peripheral region of two flanges carried respectively by the body of the burner and by the rod, which it crosses right through and is blocked by a nut.

• la figure 1 est une section longitudinale schématique d'un injecteur selon la technique antérieure,
• la figure 2 est une section longitudinale schématique de la partie aval d'un injecteur selon l'invention,
• la figure 3 est une section longitudinale schématique montrant la partie aval d'une canne de pulvérisation munie d'un injecteur selon l'invention ; et
• la figure 4 montre schématiquement le montage d'un brûleur comportant une telle canne, selon l'invention, sur un bloc ouvreau d'un four par exemple de fusion de verre.

Other characteristics and advantages of the invention will emerge from the description which follows of an embodiment of the invention given by way of nonlimiting example, and illustrated by the accompanying drawings in which:

• FIG. 1 is a schematic longitudinal section of an injector according to the prior art,
• FIG. 2 is a schematic longitudinal section of the downstream part of an injector according to the invention,
• Figure 3 is a schematic longitudinal section showing the downstream part of a spray cane provided with an injector according to the invention; and
• FIG. 4 schematically shows the mounting of a burner comprising such a rod, according to the invention, on an opening block of a furnace, for example of glass melting.

The fuel mixture injector 3, in particular for oil burner, the downstream part of which is shown in FIG. 2, can be made in one piece, or still be made up of several separate pieces including one consists, for example, mainly of the part downstream of this figure.

This injector internally comprises a cylindrical channel 31 by which a fuel in the liquid state and a spray fluid is transmitted to its end free downstream so that the fuel is projected in forming a mist with the spray fluid stream.

In its downstream part, the injector has internally, in the longitudinal alignment of channel 31 and in succession towards the free end of this part, a room 32 of destabilization of the film having a section transverse greater than that of the canal, a neck 33 tear film extending the destabilization chamber and having a cylindrical shape and a cross section less than that of this room and that of the canal, and a mouth of projection 34 open at the free end of the injector, into which the tearing opening opens, and having a cross section greater than that of the neck.

The projection mouth 34 is a cylinder, and its length is at most equal to the diameter of the neck 33.

Chamber 32 connects to channel 31 and the neck 33 by shoulders defining perpendicular surfaces at the direction of flow indicated by an arrow in the figures; on the other hand, the neck 33 and the mouth 34 connect frusto-conically, the trunk of cone of connection with a very obtuse angle at the top.

The thickness of the partition surrounding the mouth of projection 34 is weak, as we will see below, to avoid the risks of coking at the end of the injector.

Thus, as in the known injectors, the fuel in the liquid state traverses the channel 31 at least partially in the form of a film lining the inner wall of the canal.

However, it is through the room 32 that the channel 31 is connected to the region of tearing off the film constituted by the bottleneck 33 raising an obstacle to the flow and thus favoring the bursting of the film of liquid fuel through the gaseous spray fluid stream.

Thanks to chamber 32, the hanging of the film on the inner wall of the injector is destabilized, the abrupt section variations which result in the presence of shoulders whose surface extends perpendicular to the direction of flow facilitating lifting and spraying then made at the neck 33. Also, the chamber 32 of larger diameter than the channel 31 decreases the speed of small drops transported by atomizing air whose inertial effect is negligible due to their low mass.

To avoid any coalescence of the drops formed, the length of the bottleneck is relatively short compared to its diameter.

The mist resulting from the spray is then guided into the projection mouth 34, which must not not be too long also to avoid coalescence drops, but should be enough to allow the return to an established flow of fog.

As we have seen, the small thickness of the partition surrounding the projection mouth 34 makes it possible to prevent risks of coking at the end of the injector, reducing the surface exposed to radiation from the oven.

However, for reasons of mechanical strength, the thickness in the other regions is greater, and this downstream part externally has a general shape cylindrical connecting frustoconically to the region surrounding the mouth 34.

In the example shown in Figure 2, the channel 31, the destabilization chamber 32, the neck 33 and the projection mouth 34 has a circular straight cross section.

• D1 est le diamètre du canal 31,
• D2 et L1 sont respectivement le diamètre et la longueur de la chambre 32 de déstabilisation du film,
• D3 et L2 sont respectivement le diamètre et la longueur du goulet 33 d'arrachage du film,
• D4 et L3 sont respectivement le diamètre et la longueur de la bouche de projection 34,
• D5 est le diamètre extérieur de la cloison entourant la bouche de projection 34 : D2/D1 ≈ 1,5 et L1 ≈ 3D2 ; 0,25 < L2/D3 < 1 1 < D3/L3 < 2 et D4/D3 ≈ 1,5.

The optimization of the operation of this downstream part is linked to a certain geometry and more particularly to the existence of the following dimensional relationships, in which

• D1 is the diameter of channel 31,
• D2 and L1 are respectively the diameter and the length of the film destabilization chamber 32,
• D3 and L2 are respectively the diameter and the length of the film tearing neck 33,
• D4 and L3 are respectively the diameter and the length of the projection mouth 34,
• D5 is the outside diameter of the partition surrounding the projection mouth 34: D2 / D1 ≈ 1.5 and L1 ≈ 3D2; 0.25 <L2 / D3 <1 1 <D3 / L3 <2 and D4 / D3 ≈ 1.5.

Finally, D5 - D4, as we have seen, must be weak, but for reasons of mechanical resistance, we adopt D5 - D4 ≈ 1 mm.

Preferably, at least this downstream part of the injector is metallic, for reasons of resistance mechanical and temperature resistance.

The injector which has just been described is intended for equip a burner comprising a cane 4 whose end downstream carrying the injector and opening into the opening block of an oven is shown diagrammatically in FIG. 3, mounting the burner according to the invention with respect to the block workman being himself represented schematically in the figure 4.

The downstream end of the rod 4 has externally a thread around which an external injector is screwed 5, and internally a thread into which is screwed the mixture injector 3 which has just been described; space annular 51 determined between the external injector and the mixing injector, in the extension of an annular channel 41 of the cane for the external spraying fluid, follows the contour of the mixture injector up to respective free ends of the two injectors 3, 5 which lead into the same plane; however, the internal injector by which the internal spraying fluid is introduced in the fuel stream is receding in the rod 4, upstream of the mixture injector.

The opening block 6 into which the rod 4 passing from upstream to downstream of the burner body 7, internally has two regions respectively upstream 61 and downstream 62 opening respectively to the outside and to the interior of the oven, generally cylindrical, connected by a frustoconical intermediate region 63. More precisely, the downstream cylindrical region 62, of larger diameter, opens into the oven, opening out slightly, and the upstream region 61 has a shoulder for positioning in abutment the outer wall of the burner body 7.

Rod 4 is positioned in the opening block of so that is defined between its outer wall and the inner wall of the block, an annular channel for the oxidizer, and that the free end of the external injector 5 is around the downstream end of the upstream region 61 se connecting to the frustoconical region 63. The centering of the rod in the upstream region 61 is produced by means of a ring 42 fixed around the cane, presenting naturally passages extending from upstream to downstream, for the oxidant. The oxidizer is brought into the body of the burner 7 by a lateral pipe 71 opening into the upstream region thereof.

Externally and upstream side, the opening block presents a burner attachment region in the form of a projection with walls opposite shoulders 64, 65 whose upper shoulder 65 is connected to the body of the block workman by a bleeding 66; the burner body has an outer flange 72, and the removable fixing of the burner to the workman is carried out by means of a device 8 comprising hooking elements 81 made of folded sheet metal fitting approximately the shape of the shoulders; these elements hooking have an end flange 82 inserted in the groove 66, and are provided with threaded members 83 adapted to be housed in notches 73 extending in the region device of the flange 72 which they pass right through part and locked by nuts 84.

The burner body 7 and the rod 4 are fixed to each other at flanges 74, 43 respective welded around them, by means of a removable fixing device comprising screeds 75 carried by the peripheral wall of the burner body each comprising a pivot 76 around from which is articulated a threaded rod 77 adapted for be housed in corresponding notches opposite in the peripheral region of the two flanges 74, 43 which it crosses right through and which is blocked by a nut 78.

Thanks to this arrangement, the mounting of the body of the burner on the quarry block by means of the fixing device 8 is fast since it suffices to set up the hooking elements 81 on the shoulder projection 64, 65 and attaching the flange 72 thereto by means of the nuts 84; then the mounting of the rod 4 in the burner body is carried out easily by putting its flange 43 opposite the flange 74 of the burner body and tightening the nuts 78 around the rods threaded 77 after these have been flipped into the notches of the two flanges.

The burner being mounted under these conditions, of a most of the mist from the injector is made up finer droplets than by injectors of the prior art, and also trained unless high speed, which promotes the combustion of fuel oils heavy, and on the other hand the flame is more stable in the workman region.

Claims (16)

1. Fuel injector, especially for an oil burner, internally comprising a duct (31) through which a fuel in the liquid state at least partially in the form of a film lining the internal wall of the duct and an atomizing fluid are transmitted to the downstream part of the injector which terminates at the free end thereof through which the fuel is sprayed from the injector forming a mist with the stream of atomizing fluid, characterized in that this downstream part has internally, in longitudinal alignment with the duct (31), and in succession towards the free end, a chamber (32) for destabilizing the film which has a cross section that is larger than that of the duct, a throat (33) for detaching the film extending the destabilization chamber and having a cylindrical shape and a cross section that is smaller than that of this chamber, and a spray orifice (34) which is open at the free end of the injector, into which the detachment throat opens, and which has a cross section that is larger than that of the throat, and in that the spray orifice (34) is a cylinder and its length (L3) is at most equal to the diameter (D3) of the throat (33).
2. Fuel injector according to Claim 1, characterized in that the detachment throat (33) has a cross section that is smaller than that of the duct (31).
3. Fuel injector according to Claim 1, characterized in that the destabilization chamber (32) has a circular cross section, the diameter (D2) of which is greater approximately by half than the diameter (D1) of the duct (31), which is also of circular cross section.
4. Fuel injector according to Claim 1, characterized in that the destabilization chamber (32) has a circular cross section, and its length (L1) is approximately three times its diameter (D2).
5. Fuel injector according to Claim 1, characterized in that the detachment throat (33) has a circular cross section, and its length (L2) is smaller than its diameter (D3).
6. Fuel injector according to Claim 1, characterized in that the detachment throat (33) has a circular cross section, and its length (L2) is greater than one quarter of its diameter (D3).
7. Fuel injector according to Claim 1, characterized in that the spray orifice (34) has a circular cross section, and its length (L3) is at least equal to half the diameter (D3) of the throat (33).
8. Fuel injector according to Claim 1, characterized in that the spray orifice (34) has a circular cross section, and its diameter (D4) is greater approximately by half than the diameter (D3) of the detachment throat (33), which is also of circular cross section.
9. Fuel injector according to Claim 1, characterized in that the spray orifice (34) is surrounded by an annular partition, the outside diameter (D5) of which is approximately 1 mm greater than the inside diameter (D4).
10. Fuel injector according to Claim 1, characterized in that the said downstream part is made of metal.
11. Fuel injector according to Claim 1, characterized in that it is entirely made of metal.
12. Burner of the type comprising a tube (4), a downstream end of which bears a mixture injector (3) according to any one of the preceding claims and an external injector (5), characterized in that the tube internally has a screwthread into which the mixture injector (3) is screwed and externally has a screwthread around which the external injector (5) is screwed and comprises an annular duct (41) extended by a space (51) determined between the external injector and the mixture injector.
13. Burner according to Claim 12, characterized in that the free ends of the two injectors (3, 5) open into the same plane.
14. Burner according to Claim 12, characterized in that it comprises a body which externally has a flange (72) for fixing it to a charging unit, and a flange (74) for connection to a flange (43) of the tube (4).
15. Burner according to Claim 12, characterized in that it comprises a body which externally has clevis blocks (75) each comprising a pivot (76) about which is articulated a threaded shank (77) designed to be housed in corresponding facing cut-outs in the peripheral region of two flanges (74, 43) borne respectively by the body of the burner and by the tube right through which it passes, and which is locked by a nut (78).
16. Use of the injector according to one of Claims 1 to 11 in an oil burner.

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