EP0428174B1 - Mixing device for oil burner with swirling flame generation - Google Patents

Abstract

A mixing device for oil burners with swirling flame generation with, arranged in a burner pipe (1) which narrows conically downstream, an atomising nozzle (7), with a baffle plate (12) which is assigned to the atomising nozzle and axially displaceable and which has a central opening (13), from which slots (14) extend essentially radially outwards, which are formed by wing-like sections bent off out of the plane of the baffle plate, and which is provided with a cylindrical limitation (16) in continuation of its external periphery, seen in the direction of flow, is intended to afford the flame increased swirling which favours ignition and practically harmful substance-free combustion of the fuel oil. To this end, the burner pipe (1) has, downstream of the constriction (3), a reduction of cross-section (6) and/or fins (4) having an angle of setting in relation to the longitudinal axis of the burner pipe and/or the atomising nozzle (7) projects with a nozzle mouth (17) into the plane of the baffle plate (12). <IMAGE>

Description

The invention relates to a swirl flame mixing device for oil burners according to the preamble of claim 1.

In the mixing device according to DE-PS 35 42 174, a smaller diameter guide tube is arranged in the burner tube, which is axially adjustable and receives a cup-shaped baffle plate. The baffle plate is used to hold the flame, ie it establishes a balance between the outflow speed of a fuel-air mixture and the re-ignition speed of the flame in the event of intended recirculation in the combustion chamber. The Baffle plate forms an adjustable annular gap with the burner tube, the baffle plate being flowed through by a primary air flow for substoichiometric pre-combustion and the annular gap by a secondary air flow for complete combustion of the heating oil. The heating oil passes from the atomizer nozzle into the combustion zone through a central opening in the downstream baffle plate, which forms a six-pointed passage. Slits in the baffle plate give the primary air passing through a swirl, which promotes a mixture of heating oil and air and gasification of the heating oil. A comparatively large slot width in the area of the central opening achieves a locally limited strong swirl effect, which favors the ignition after every control activation of the burner.

With this mixing device, however, it is disadvantageous that the swirl movement of the combustion gas mixture is converted relatively unhindered into an axial outflow movement, as a result of which the mixing of heating oil and air and gasification of the heating oil are impaired. This is further supported by the primary air flowing at a high speed of, for example, more than 10 meters per second through the central opening of the baffle plate in jet form, which has the desired swirl guidance in the center of the mixing and combustion zone hindered and reduced by their shock pulse the ignitability of the combustion gas mixture. Furthermore, the secondary air flowing primarily in the axial direction of the burner tube reduces the swirl of the combustion gas mixture.

DE-GM 77 24 029 discloses a similar mixing device in which the guide tube is provided with four fins evenly distributed around the circumference, which are formed by means of angle profile pieces and ensure that the guide tube is inserted exactly coaxially into the burner tube. However, this support of the guide tube and the baffle plate used is structurally relatively complex and does not change the swirl-reducing effect of the axially aligned secondary air flow.

DE-PS 24 61 078 already discloses a firing system with a burner which has an annular gap on the outside for the supply of secondary air which, before exiting into a combustion chamber, flows through openings in a plate to which vane-shaped baffles are assigned in order to deflect the air to the outside of the flame core so that an air jacket is formed with a helical flow direction. However, the perforated plate has high pressure losses and is generated as a result discontinuous transitions an incompletely formed swirl jacket flow, which does not yet have the desirable mixing and gasification effect. In addition, the additional swirl plate holding a central guide tube is relatively complex to manufacture.

From DE-U-86 04 089 a swirl flame mixing device for oil burners of the type mentioned at the outset is known, in which the burner tube has, in addition to the burner tube mouth, a plurality of rib-like projections which are arranged uniformly distributed around the longitudinal axis of the burner tube and are oriented towards the center of the burner tube and which define the cylindrical boundary of the baffle plate Guide sideways and have an angle of attack to the longitudinal axis of the burner tube. The projections are designed as flat centering webs and are obviously welded against the inner wall of the burner tube. The flat centering bars with their sharp inflow and outflow edges can adversely affect the flow and thus the flame formation in the flame space. In addition, the welded construction is disadvantageous in terms of production technology.

According to EP-A1-0 030 217, the outer edge of a conical baffle plate has three punched-out tabs which form centering heads for the plate in the burner tube. However, flow guidance is not effected.

DE-A1-35 19 509 discloses a baffle plate holder with baffle plate for oil or gas burners, in which the baffle plate is guided on beads of the burner tube. However, the projections only serve to guide the baffle plate and should not influence the flow. They are aligned with the burner tube axis and have an elongated cross-sectional shape.

Proceeding from this, the object of the invention is to create an improved mixing device of the type mentioned at the outset, which can be manufactured more easily with sufficient accuracy and which results in more favorable flow guidance.

This object is achieved by a mixing device according to claim 1. Advantageous embodiments of the mixing device are specified in the subclaims.

In the device according to the invention it is provided that in addition to the burner tube mouth, the burner tube has a plurality of rib-like projections which are arranged around the longitudinal axis of the burner tube and are preferably distributed uniformly and are oriented towards the center of the burner tube, that the projections laterally guide the cylindrical boundary of the baffle plate, and that the projections to the longitudinal axis of the burner tube have an angle of attack to have. The angle of attack can be 0 °, but is preferably significantly larger.

The projections are beads formed in the burner tube and, on the one hand, form a guide which is favorable in terms of production technology and form a lateral holder for the baffle plate. On the other hand, they give the secondary air flow a swirl due to its angle of attack above 0 ° to the longitudinal axis of the burner tube, which stabilizes the enclosed flame and can support the swirl of the primary air flow. The swirl of the secondary air thus also hinders a conversion of the rotary movement of the primary air into a longitudinal movement.

The beads are drop-shaped in a section parallel to the longitudinal axis of the burner tube. The correspondingly known wing profiles in the cross-section of teardrop-shaped beads ensure a well-formed swirl flow of the secondary air and uniform and controlled flow conditions in the mixing and combustion zone.

Four to six beads are preferably arranged distributed around the longitudinal axis of the burner tube, which form the swirl flow well and at the same time negligibly reduce the flow cross section in the annular gap.

The beads preferably have an angle of attack of 15 to 45 ° to the longitudinal axis of the burner tube, as a result of which the desired short flame can be achieved with a sufficient flame escape speed.

According to another embodiment, the beads give a secondary air flow passing between the burner tube and the cylindrical boundary of the dust disk the same sense of rotation as the baffle plate of a primary air flow flowing through the slots, so that the swirl effect of the two partial air flows support one another.

Preferably, the burner tube has a constriction protruding radially from the conical constriction.

The constriction reduces the flame escape speed in the axial direction of the burner tube and thus supports the baffle plate already provided as the flame holding device. As a result, the swirl of the primary air of the flame is retained to a greater extent, so that an intensive mixing of the heating oil with the air and its greater gasification takes place in a mixing zone before the constriction. The result is an intensely mixed combustion gas, which burns out quickly with a shorter flame with the characteristic of a so-called "Blue flame" promotes, whereby less solid carbon, but more carbon monoxide is processed. Advantageously, there is practically no soot in the exhaust gas, smaller amounts of carbon monoxide are contained in the exhaust gas and a reduction in nitrogen oxide formation can also be found.

In a preferred embodiment of the invention, the ratio of the smallest constriction diameter to the smallest diameter of the adjacent conical constriction is approximately 0.85 to 0.8, a practically satisfactory reduction in the flame escape speed being achieved while increasing the flame swirl.

In a practical development, the constriction is formed by an annular body held in the burner tube, preferably by crimping a burner tube mouth. Different applications can be easily taken into account by using different ring bodies.

In an alternative embodiment, the constriction is formed by a shape, in particular crimping, of the burner tube opening of the burner tube, which saves an additional component.

According to one embodiment, the constriction forms a conical nozzle with a cone angle of 90 ° to 180 °, the cone tip of which lies in front of or in the plane of the burner tube opening. The nozzle is e.g. formed by an annular body held in the burner tube or a shape of the burner tube and in particular causes a low-loss and uniform outflow behavior of the combustion products.

In a further embodiment it is provided that the atomizer nozzle projects with a nozzle orifice into the central opening of the baffle plate and is arranged in the plane of the baffle plate.

The arrangement of the nozzle mouth in the opening and plane of the baffle plate reduces the relatively large cross section of the opening. This ensures that a twisted air supply is also established in the center, ie that the jet passing through the opening is damped and rotated at least on the outer circumference by the swirl of the primary air from the adjacent slots. This also favors a better mixing of the heating oil into the combustion air and a stronger gasification of the heating oil and improves the ignitability of the combustion gas mixture in front of the atomizer nozzle.

In a preferred embodiment, the atomizer nozzle carries a pair of ignition electrodes, each of which is bent approximately S-shaped downstream in the longitudinal direction of the burner tube to the longitudinal axis of the burner tube, each ignition electrode on the electrode base and electrode tip being aligned approximately parallel to the longitudinal axis of the burner tube, and are the ignition electrodes through the central opening of the baffle plate passed through and protrude with the electrode tips downstream over the level of the baffle plate. The electrode tips arranged in this way lie in a region of the combustion gas mixture which is favorable for the ignition. The ignition electrodes with the electrode tips preferably protrude about 3 mm above the level of the baffle plate.

To generate a strong spark, the ignition electrodes are bent towards one another, starting from the electrode base, and are aligned approximately parallel to one another next to the electrode tip. For this purpose, the electrode tips are preferably at a distance of about 3 mm from one another.

In the case of baffle plates, there is a risk that the flame which has not yet burned out will come into contact with relatively cold metal and the oil particles there will form coke deposits due to cracking processes. This danger also exists with the above described mixing devices according to the invention, especially since this generally strives to reduce the flame escape rate. In addition, in spite of the arrangement of the nozzle mouth according to the invention, ignition inconsistencies can arise with increased air back pressure. From DE-PS 35 42 174 advantageous measures are known which counteract the effects described above. These are advantageously also provided in a mixing device according to the invention.

According to one embodiment, it is therefore provided that the width of the slots following the central opening is greater than in the central area and that the width of the slots in the central area is dimensioned such that air film formation is still achieved. As a result, not only is a swirl effect favoring the ignition of the burner achieved near the central opening, but swirl formation is avoided in the central slot area, with sufficient air film formation on the subsequent surface area preventing coking thereof. By contrast, the oil particles flowing through the surface area are sufficiently burned.

According to one embodiment, the width of the slots in the radially outer end region is larger than in the central region.

In the outer slot area, a strong air flow impinges more or less directly on the cylindrical boundary, in order then to be diverted to the tear-off edge while rotating in the cup. This is advantageous for keeping the outer slot areas free from coke deposits. The course of the radially outer end regions of the slots is preferably such that the air flow passing through them meets the boundary at an angle of approximately 45 °. As a result, a relatively strong air flow is deflected through the cylindrical boundary and given a corresponding rotation. For this purpose, the radially outer end region of the slots can be curved in an arc. The slots are preferably curved in an arc shape overall, for example with a single radius. The arcuate course of the slots has the further advantage that the air flow passing through the slots is fanned out and the assigned surface area of the baffle plate is fully acted upon.

The ratio of the radius of the boundary to the radius of the slots is preferably approximately 1.82. An advantageous width of the slots in the radially inner and / or outer area can be approximately 2 mm. As already mentioned, the width of the slots in the middle area must be dimensioned such that an air film is still formed. This is at a width of about 0.7 mm.

It is further provided according to an embodiment of the invention that the central opening is six-pointed, the slots starting from the tips. This improves the manufacturing and flow conditions in particular.

In a further embodiment it is provided that the burner tube carries a coaxial tube sleeve which is in the direction of flow protrudes beyond the conical constriction, has a radially projecting constriction at the front and has injection openings opening into a gap between it and the burner tube. The tube sleeve causes a tertiary gas flow through the injection openings in the area of the burner tube mouth due to the negative pressure prevailing there. On the one hand, the tertiary flow results in a reduction in the pollutant content of the combustion gases. On the other hand, the radially inward-directed tertiary flow reduces the flame escape speed in the axial direction, which is accompanied by the advantages already mentioned for constricting the burner tube. The mixing device can have a constriction only on the tube sleeve, but can also be provided with a constriction on the tube sleeve and burner tube.

In the latter case, it is particularly favorable with regard to the flow losses if, according to a further development, the internal dimensions of the constriction of the tube sleeve correspond to those of the constriction of the burner tube.

For a concentrated introduction of the tertiary flow into the mouth area, the constrictions of the tube sleeve and the burner tube are preferably at an axial distance of about 5 mm from one another.

According to a further development, the injection openings are arranged on the tube sleeve in the flow direction in front of the burner tube mouth, as a result of which the suction is promoted through the injection openings and a blow-out of the primary and secondary air flow through the injection openings is counteracted.

Basically, a single injection port is sufficient, e.g. in the form of an elongated hole. For a uniform flow distribution within the gap between the tubular sleeve and the burner tube, the injection openings are preferably (elongated) holes distributed over the circumference of the tubular sleeve.

Fig. 1

eine Mischvorrichtung mit einem Ringkörper als Einschnürung, einem Brennerrohr mit Sicken und in der Ebene einer Stauscheibe angeordneter Düsenmündung in einem Längs schnitt (mit winkligem Schnittverlauf);

Fig. 2

Zerstäuberdüse mit Zündelektroden derselben Vorrichtung in der Vorderansicht;

Fig. 3

Düsenbuchse mit Stauscheibe und Zentrumsscheibe derselben Vorrichtung im Längsschnitt;

Fig. 4

einen Schnitt entlang der Linie IV-IV der Fig. 3;

Fig. 5

einen Schnitt entlang der Linie V-V der Fig. 3;

Fig. 6

Brennerrohr derselben Vorrichtung im Längsschnitt;

Fig. 7

ein anderes Brennerrohr mit von einer Ausformung gebildeter Einschnürung in einem Teilschnitt neben der Brennerrohrmündung;

Fig. 8

ein anderes Brennerrohr mit von einer anders abgewinkelten Ausformung gebildeten Einschnürung in einem Teilschnitt nahe der Brennerrohrmündung;

Fig. 9

ein anderes Brennerrohr mit einer vorgesetzten Rohrhülse.

Further details and advantages of the subject matter of the invention result from the following description of the associated drawings, which show preferred embodiments of a device according to the invention. The drawings show:

Fig. 1

a mixing device with a ring body as a constriction, a burner tube with beads and in the plane of a baffle plate arranged nozzle mouth in a longitudinal section (with angled section);

Fig. 2

Atomizer nozzle with ignition electrodes of the same device in front view;

Fig. 3

Nozzle bush with baffle plate and center plate of the same device in longitudinal section;

Fig. 4

a section along the line IV-IV of Fig. 3;

Fig. 5

a section along the line VV of Fig. 3;

Fig. 6

Burner tube of the same device in longitudinal section;

Fig. 7

another burner tube with a constriction formed by a formation in a partial section next to the burner tube mouth;

Fig. 8

another burner tube with constriction formed by a differently angled shape in a partial section near the burner tube mouth;

Fig. 9

another burner tube with a tube sleeve.

Fig. 1 shows a device with a burner tube 1, which has a somewhat tapered, but cylindrical central portion 2 and adjoining it has a conical narrowing 3 which is formed along a mixing space of length A. In the area of the constriction 3, six beads 4 are formed in the burner tube, which delimit a partial cylinder jacket surface on the inside. In addition to a burner tube mouth 5, an annular body 6 is flanged into the burner tube 1, which limits the mixing space downstream in relation to a flow direction arrow ST.

In the burner tube 1, an atomizing nozzle 7 is held in a longitudinally displaceable manner. The atomizer nozzle 7 carries on the outside a nozzle bushing 8 which is fixed with a locking screw 9.

A center disk 10 is attached to the nozzle bushing 8 upstream, which serves air distribution purposes. A holder 11 for a baffle plate 12 is fixed downstream on an end face of the nozzle bushing 8.

The baffle plate 12 has a central opening 13 and, starting therefrom, slots 14 which extend essentially radially outward. The baffle plate 12 is connected on the outside via a peripheral edge bead 15 to a cylindrical boundary 16 which is guided on the inner surfaces of the beads 4 of the burner tube 1 . Upstream is the Mixing space of length A limited by the baffle plate 12. Details of the nozzle bushing and the parts attached to it will be discussed below.

The combustion air flowing in the direction of flow ST is partially deflected radially outward from the center disk 10, so that a secondary air flow S flows through the channels between the burner tube 1, beads 4 and the cylindrical boundary 16 and reaches the mixing chamber of length A from the outside. Another portion of the combustion air passes as primary air flow P through the slots 14 and the opening 13 of the baffle plate 12 into the mixing chamber. Due to the orientation of the beads 4 and the slots 14, which will be explained further below, secondary and primary air flows each enter the mixing chamber with a rectified swirl, the conversion of which into an axial movement is impeded by the annular body 6.

In addition to the combustion air, heating oil is also added to the mixing chamber of length A, for which purpose the atomizing nozzle 7 projects with a nozzle mouth 17 into the central opening of the baffle plate 12 and is arranged exactly in the plane of the baffle plate. Due to the swirl of the combustion air, the heating oil emitted by the atomizing nozzle 7 is mixed finely in the mixing room and gasified at the same time.

As can be seen from FIGS. 1 and 2, an insulating carrier 18, which has a pair of ignition electrodes 19 downstream, is screwed to the nozzle bushing 8 for igniting the combustion gas mixture generated in the mixing space of length A. The ignition electrodes 19 are bent approximately S-shaped in the longitudinal direction of the burner tube downstream of the longitudinal axis of the burner tube, wherein they are held in the carrier 18 with an electrode foot 20 oriented approximately parallel to the longitudinal axis of the burner tube. With an electrode tip 21 they reach through the opening 13 of the baffle plate 12, with an ignition distance Z of approximately 3 mm from the plane of the baffle plate 12, an electrode distance E of approximately 3 mm and an orifice distance M from the center of the nozzle mouth for optimum ignition 17 of about 6 mm.

To regulate the ratio of secondary and primary air flow and the length A of the mixing chamber, the atomizing nozzle 7 together with the nozzle bushing 8 and the baffle plate 12 attached to it and the ignition electrodes 19 can be moved axially. If the baffle plate 12 is displaced further downstream, the free cross section for the secondary air flow S is reduced due to the conical narrowing 3, so that this decreases at the expense of the primary air flow P.

As shown in FIG. 3 in relation to FIG. 1, the nozzle bushing 8 has a receptacle 22 on the inside corresponding to the outer contour of the atomizing nozzle 7 with threaded bores for the locking screw 9 and for the fastening screw of the carrier 18. The center disk 10 and the holder 11 are each held on the face of the nozzle bushing 8 by crimping. 3 to 5 show, the holder 11 has a central retaining ring 22 for this purpose, from which three holding arms 23 extend and are guided to fastening tabs 24 for the baffle plate 12. In addition, support arms 25 for the carrier 18 of the ignition electrodes are integrally formed on the retaining ring 22.

4 that the central opening 13 of the baffle plate 12 has the shape of a six-pointed passage, the clear width of which is more than 15 mm. The slots 14 extend from the tips of the opening 13 and are formed by means of wings 26 which are bent outwards from the plane of the baffle plate 12 (cf. FIG. 3). The slots are curved in a circular arc, with variable slot widths in the radial direction. This and the arc shape of the slots causes a strong vortex formation near the opening 13 and a fanning out of the air flow over the entire surface area between the slots, so that a good ignitability is achieved and coking on the surface area is avoided.

As FIG. 6 shows in more detail, the burner tube 1 has a cone angle α of approximately 12 ° in the area of the constriction 3. The beads 4 have a teardrop-shaped profile parallel to the longitudinal axis of the burner tube and are inclined at an angle of attack β of approximately 15 ° to the longitudinal axis of the burner tube. The angle of attack β is a maximum of approximately 45 °,

Instead of the additional ring body 6, the burner tube mouth 5 - as shown in FIGS. 7 and 8 - may also have a flange 27 or 28 adjacent to the conical constriction 3. The flange 27, which is oriented perpendicular to the longitudinal axis of the burner tube, better retains the flame in the mixing chamber, but causes greater flow losses. The crimp 27 is equivalent to a nozzle with a cone angle of 180 °. In contrast, the crimp 28 is inclined by approximately 45 ° to the longitudinal axis of the burner tube, which is equivalent to a nozzle angle γ of 90 °. This keeps the swirl in the flame when the flow losses are not too high.

To the extent that the burner tube according to FIG. 9 corresponds to that from FIGS. 1 and 6, identical reference numerals have been used and reference is made to the above explanations.

In addition, the burner tube 1 has an essentially cylindrical tube sleeve 29 which is pushed onto the cylindrical central section 2 and welded there, which projects somewhat beyond the burner tube mouth 5 in the direction of flow ST and has a radially projecting constriction 30 at the front. The distance between the constrictions 6 and 30 is approximately 5 mm.

In the area of the conical narrowing 3 of the burner tube 1, an annular gap 31 diverging towards the front is formed between the burner tube and the tubular sleeve 29. Elongated holes 32, which are arranged in the flow direction in front of the burner tube mouth 5 on an annular circumferential line of the tubular sleeve 29, are evenly distributed.

As a result of the negative pressure prevailing in the area of the burner tube mouth 5, a tertiary gas flow is drawn in through the elongated holes 32 and introduced radially into the combustion mixture. This further promotes the mixing of the combustion gases, especially since the tertiary gas flow can also have a swirl due to the flow guidance through the outer surface of the beads 4.

The tubular sleeve 29 can also be fastened in the region of the conical narrowing 3 of the burner tube.

The burner tube 1 or the tube sleeve 29 is preferably made of steel with the material number 1.4878.

Claims (28)

1. A mixing device for oil burners with swirling flame generation which comprises an atomizing nozzle (7) arranged within a burner pipe (1) tapered downstream, an axially displaceable breaker plate (12) associated to said atomizing nozzle, which breaker plate includes a central opening (13) wherefrom substantially radial grooves (14) are led outwardly which are defined by wing-type portions (26) deflecting from the surface plane of said breaker plate (12) and which are provided with a cylindrical boundary in continuation of their outer surface - seen in the direction of flow - said burner pipe (1) adjacent to the outlet (5) of the latter including a plurality of rib-type projections (4) distributed - preferably uniformly - about the longitudinal axis of said burner pipe and aligned to the center of the latter, which projections are guiding said cylindrical boundary (16) of said breaker plate (12) at the side and are at a setting angle (β) with the longitudinal axis of said burner pipe, characterized in that said projections are beads (4) formed in said burner pipe (1), and that said beads are drop-shaped in longitudinal section.
2. The device according to claim 1, characterized in that four to six beads (4) are distributed about the longitudinal axis of said burner pipe.
3. The device according to claim 1 or 2, characterized in that said beads (4) are at a setting angle (β) of 15° to 45° with the longitudinal axis of said burner pipe.
4. The device according to any of the claims 1 to 3, characterized in that said beads (4) impart to a secondary current of air (S) flowing between said burner pipe (1) and said cylindrical boundary (16) of said breaker plate (12) the same sense of rotation as said breaker plate (12) does to a primary current of air (P) flowing through said grooves (14).
5. The device according to any of the claims 1 to 4, characterized in that in downstream direction of said tapering (3) said burner pipe (1) comprises a constriction (6, 27, 28) radially projecting from said tapering.
6. The device according to claim 5, characterized in that the ratio between a smallest constriction diameter and a smallest diameter of said adjoining tapering (3) is about 0.85 to 0.8.
7. The device according to any of the claims 5 and 6, characterized in that said constriction is defined by an annular body (6) preferably held within said burner pipe (1) by crimping an outlet (5) of said burner pipe.
8. The device according to any of the claims 5 and 6, characterized in that said constriction is defined by a shaping (27, 28) of said burner pipe (1).
9. The device according to any of the claims 5 to 8, characterized in that said constriction (6, 27, 28) defines a conical nozzle at a cone angle ( ) of 90° to 180°, the conical tip end of which is provided in front of or in the plane of said outlet (5) of said burner pipe.
10. The device according to any of the claims 1 to 9, characterized in that said atomizing nozzle (7) with a nozzle end (17) projects into said central opening (13) of said breaker plate (12) and is arranged in the plane of said breaker plate.
11. The device according to claim 10, characterized in that said atomizing nozzle (7) comprises one pair of initiating electrodes (19), each of which being bent approximately S-shaped downstream in longitudinal direction towards said longitudinal axis of said burner pipe, each initiating electrode (19) at the electrode base (20) and electrode tip end (21) being aligned to said longitudinal axis of said burner pipe approximately parallel, and that said initiating electrodes (19) are led through said central opening (13) of said breaker plate (12) and with said electrode tip ends (21) project from the surface plane of said breaker plate downstream.
12. The device according to claim 11, characterized in that said initiating electrodes (19) with said electrode tip ends (21) project from the surface plane of said breaker plate (12) by about 3 mm.
13. The device according to any of the claims 11 and 12, characterized in that, starting from said electrode base (20), said initiating electrodes (19) are bent towards each other and are approximately parallel aligned to each other near said electrode tip end (21).
14. The device according to any of the claims 11 to 13, characterized in that said electrode tip ends (21) are spaced from each other by a spacing of about 3 mm.
15. The device according to any of the claims 1 to 14, characterized in that adjacent to said central opening (13) the width of said grooves (14) is larger than in the central area thereof, and that the width of said grooves (14) in the central area is rated so that an air film can still be formed.
16. The device according to claim 15, characterized in that the width of said grooves (14) in the radially outward end portion is larger than in the central area.
17. The device according to claim 16, characterized in that the run of the radially outward end portions of said grooves (14) is such that the flow of air passing through them strikes against said boundary (16) at an angle of about 45°.
18. The device according to claim 17, characterized in that the radially outward end portion of said grooves (14) is curved.
19. The device according to claim 18, characterized in that all of said grooves (14) are curved, preferably with one radius only.
20. The device according to claim 18 or 19, characterized in that the ratio between the radius of said boundary (16) and the radius of said grooves (14) is about 1.82.
21. The device according to any of the claims 15 to 20, characterized in that the width of said grooves (14) radially inward and/or radially outward is about 2 mm.
22. The device according to any of the claims 15 to 21, characterized in that the width of said grooves (14) in the central area is about 0.7 mm.
23. The device according to any of the claims 15 to 22, characterized by a central opening (13) formed in a way known per se so as to include six peaks where said grooves (14) are starting from.
24. The device according to any of the claims 1 to 23, characterized in that said burner pipe (1) comprises a coaxial tube jointing sleeve (29) which projects from said tapering (3) in the direction of flow (ST) , comprises a radially protruding constriction (30) at the front and includes injection holes (32) opening into a recess (31) provided between said constriction and said burner pipe (1).
25. The device according to claim 24, characterized in that the inside dimensions of said constriction (30) of said tube jointing sleeve are the same as those of said constriction (6) of said burner pipe (1).
26. The device according to claim 24 or 25, characterized in that said constrictions (30, 6) of said tube jointing sleeve (29) and said burner pipe (1) are spaced from each other by an axial spacing of about 5 mm.
27. The device according to any of the claims 24 to 26, characterized in that said injection holes (32) are arranged on said tube jointing sleeve (29) in the direction of flow (ST) in front of said burner pipe outlet (5).
28. The device according to any of the claims 24 to 27, characterized in that said injection holes are (elongated) holes (32) distributed over the circumference of said tube jointing sleeve (29).

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