A BURNER WITH FUEL AND AIR SUPPLY INCORPORATED IN A WALL OF THE BURNER

Abstract

A burner of a turbomachine has an upstream burner section providing a first fuel and an oxygen containing fluid to an upstream end of a burner interior, a downstream burner section for providing a second fuel to a downstream end of the burner interior, and an intermediate burner section between the two sections. The intermediate burner section has an annular wall surrounding a mid-section of the burner interior. The annular wall has an annular cooling fluid passage, for guiding the oxygen containing fluid, and an annular fuel passage for guiding the second fuel to the downstream burner section, the annular fuel passage being more distant to the burner interior than the annular cooling fluid passage. Two annular slots are incorporated into the annular wall. The upstream burner section has at least one integrated fuel tube through a body of the upstream burner section, configured to feed the annular fuel passage.

Claims

1.-14. (canceled)

15. A burner of a turbomachine or a gas turbine engine, comprising: an upstream burner section for providing a first fuel and an oxygen containing fluid to an upstream end of a burner interior, wherein the burner interior is substantially a hollow space in which a mixing of fuel and the oxygen containing fluid can take place; a downstream burner section for providing a second fuel to a downstream end of the burner interior or to a combustion chamber; and an intermediate burner section between the upstream burner section and the downstream burner section; wherein the intermediate burner section comprises an annular wall surrounding a mid section of the burner interior, the annular wall comprising: an annular cooling fluid passage; and an annular fuel passage for guiding the second fuel to the downstream burner section, the annular fuel passage being more distant to the burner interior than the annular cooling fluid passage, wherein the upstream burner section comprises at least one integrated fuel tube through a body of the upstream burner section, that is configured to feed the annular fuel passage.

16. The burner according to claim 15, wherein the annular wall further comprises a plurality of film cooling holes that pierce the annular wall from an exterior of the burner to the mid section of the burner interior, the film cooling holes piercing the annular cooling fluid passage and piercing the annular fuel passage but being fluidically separate from the annular cooling fluid passage and from the annular fuel passage.

17. The burner according to claim 15, wherein the annular wall further comprises at least one cooling fluid inlet hole providing the annular cooling fluid passage with cooling fluid from an exterior of the burner, the cooling fluid inlet hole piercing the annular fuel passage but being fluidically separate from the annular fuel passage.

18. The burner according to claim 15, wherein the annular wall further comprises a plurality of effusion holes for ejecting cooling fluid from the annular cooling fluid passage to the mid section of the burner interior.

19. The burner according to claim 15, wherein the annular wall further comprises spacer elements within the annular cooling fluid passage and/or the annular fuel passage, wherein the spacer elements are physically connected to one surface and only in loose contact with an opposite surface of the respective annular passage.

20. The burner according to claim 15, wherein the annular wall is an integrally formed component, joined with the upstream burner section and the downstream burner section, or wherein the upstream burner section, the intermediate burner section and the downstream burner section are an integrally formed component.

21. The burner according to claim 15, wherein the annular cooling fluid passage and the annular fuel passage each are defined as a slot with an expansion along a complete axial length of the intermediate burner section.

22. The burner according to claim 15, wherein the upstream burner section comprises a plurality of swirler vanes, each of the swirler vanes providing an integrated fuel tube, that is configured to feed the annular fuel passage.

23. The burner according to claim 22, wherein the plurality of swirler vanes each comprise an integrated further fuel supply line, wherein the integrated further fuel supply line is configured for feeding first fuel nozzles to eject the first fuel into the upstream end of the burner interior.

24. The burner according to claim 15, wherein the upstream burner section provides a swirler and first fuel nozzles for swirling air and injecting the first fuel into the swirled air, wherein the intermediate burner section provides a pre-mixing zone for mixing the air and the injected first fuel, and wherein the downstream burner section provides a burner tip and second fuel nozzles for ejecting the second fuel.

25. A combustor, comprising: a plurality of burners, at least one burner arranged according to claim 15; and at least one combustion chamber arranged downstream of the burner.

26. The combustor according to claim 25, wherein a burner shaft is attached to the upstream burner section and comprises at least one supply channel for providing the first fuel and/or the second fuel to the at least one burner.

27. The burner according to claim 15, wherein the intermediate burner section comprises a cylindrical wall surrounding the mid section of the burner interior.

28. The burner according to claim 15, wherein the annular cooling fluid passage guides the oxygen containing fluid.

29. The burner according to claim 18, wherein the effusion holes are distributed around a circumference and along an axial length of the intermediate burner section.

30. The burner according to claim 23, wherein the first fuel nozzles are distributed on a surface of the swirler vane.

31. The combustor according to claim 25, wherein the at least one combustion chamber comprises an annular or a can-annular combustion chamber arranged downstream of the burner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0040] FIG. 1 schematically illustrates a cross-sectional view of an exemplary embodiment of an inventive burner;

[0041] FIG. 2 illustrates a cross section of an intermediate burner section along II-II of FIG. 1;

[0042] FIG. 3 shows a section of an intermediate burner section, showing an embedded film cooling hole;

[0043] FIG. 4 schematically illustrates an alternative a intermediate burner section with incorporated spacer elements;

[0044] FIG. 5 illustrates a cross section of an intermediate burner section along V-V of FIG. 4;

[0045] FIG. 6 shows a cross sectional view of a swirler vane showing fuel supply lines in its vanes;

[0046] FIG. 7 schematically illustrates a cross-sectional view of a further exemplary embodiment of an inventive burner, which corresponds to FIGS. 4 and 5;

[0047] FIG. 8 shows a magnified cross-sectional view of FIG. 7, focusing on supply and ejection of cooling air to/from an annular cooling fluid passage of the burner;

[0048] FIG. 9 shows a cross sectional view of an alternative burner illustrating an annular wall with incorporated annular slots.

[0049] The illustration in the drawing is schematic. It is noted that for similar or identical elements in different figures, the same reference signs will be used.

[0050] Some of the features and especially the advantages will be explained for an assembled and operating gas turbine, but obviously the features can be applied also to the single components of the gas turbine but may show the advantages only once assembled and during operation. But when explained by means of a gas turbine during operation none of the details should be limited to a gas turbine while in operation.

[0051] In the following the problems and the proposed solution will mainly be explained for an annular combustor, but the principles may also apply to different types of combustors, like a can-annular combustor.

DETAILED DESCRIPTION OF THE INVENTION

[0052] FIG. 1 represents one exemplary burner 1 showing the inventive concept. The burner 1 is shown in a cross-sectional view and the consecutive figures may show detailed views or alternative implementation of that burner 1. This burner 1 may be part of a gas turbine engine and may be used for an annular combustor. The burner 1 may comprise an upstream burner section 2, intermediate burner section 3 and a downstream burner section 4. Upstream of the upstream burner section 2 a burner shaft 5 may be present to provide fuel to the burner 1. The upstream burner section 2 may particularly be a swirler 40 to mix fuel with air and may comprise also a transition piece that connects the swirler 40 with the intermediate burner section 3. Following in axial direction of the burner 1, the intermediate burner section 3 follows the upstream burner section 2 and provides a premixing zone 41 to further mix the previously provided air and fuel. Further downstream, the downstream burner section 4 is present and specifically provides also a burner tip 42. The upstream burner section 2, the intermediate burner section 3 and the downstream burner section 4 altogether enclose a bunter interior 6. At several locations of the burner 1 the burner interior 6 will be fluidically connected to an exterior 7 of the burner 1 via passages for passing air or cooling fluid.

[0053] As previously said, in the upstream burner section 2 the swirler 40 is present. The swirler 40 is comprised of a plurality of swirler vane 9. Each swirler vane 9 then merge in axial direction to walls of the intermediate section 3. The swirler vanes 9 and the consecutive transition section both can be defined as a body 8 of the upstream burner section 2. Incorporated in this body 8, a fuel passage for pilot fuel is included. This fuel passageidentified as fuel tube 30will provide pilot fuel to the further downstream intermediate burner section 3.

[0054] In the example, the intermediate burner section 3 substantially is configured as a cylindrical annular wall 10. Nevertheless the annular wall 10 may also be shaped differently, as long as being annular around a space. The annular wall 10 defines along its axial length a three wall cylindrical configuration in which an annular cooling fluid passage 11 and an annular fuel passage 12 is embodied. The annular fuel passage 12 defines an annular passage for the pilot fuel provided from the upstream burner section 2. Within the intermediate burner section 3 the annular fuel passage 12 guides the pilot fuel to the downstream section 4.

[0055] The annular cooling fluid passage 11 is supplied by cooling fluid, particularly air, from the exterior 7 of the burner 1 and guides this cooling fluid along the length of the intermediate burner section 3. The annular cooling fluid passage 11 is located radially inwards within the annular wall 10, compared to the annular fuel passage 12. That means that the annular cooling fluid passage 11 acts as a temperature shield so that the heat will not affect the annular fuel passage 12 as drastically.

[0056] Further cooling features may be present, particularly in the intermediate burner section 3. For example film cooling holes 13 may be located at different positions along the intermediate burner section 3. The film cooling holes 13 will merely pierce the annular wall 10 without merging into the annular fuel passage 12 and/or the annular cooling fluid passage 11.

[0057] Within the burner shaft 5 a first supply channel 35 for the main fuel is incorporated. Furthermore, the burner shaft 5 is configured to guide the pilot fuel via a second supply channel 35. The pilot fuel is guided from the second supply channel 34 via the fuel tube 30, which is incorporated within the swirler vanes 9, to the annular fuel passage 12 of the intermediate burner section 3. The main fuel provided from the first supply channel 35 is provided to the swirler vanes 9 for being injected into the interior 6 of the burner via fuel nozzles incorporated in the swirler vane 9.

[0058] It has to be noted though, that burners with a different geometry may inject main fuel at different spots and not only via surfaces of swirler vanes.

[0059] The burner 1 shown in FIG. 1 is substantially symmetric around an axis which is indicated by the letter A. Furthermore a radial direction is indicated in the figure by the letter R.

[0060] This burner 1 may be used in an annular combustion chamber or a can-annular combustion chamber. The combustion chamber, which is downstream of the burner 1, is highlighted in the figure in an abstract way as combustion chamber 50.

[0061] Starting from this configuration of FIG. 1 in the following figures several details of this configuration will be explained.

[0062] FIG. 2 is a cross-sectional view along a line II-II which is indicated in FIG. 1. As it can be seen in FIG. 2 the annular fuel passage 12 and the annular cooling passage 11 are merely narrow slots in the annular wall 10. The annular wall 10 defines a three wall circular structure in which two slots are incorporated, the annular fuel passage 12 and the annular cooling passage 11. In one specific embodiment, in the cross-sectional view of FIG. 2, the slots are circular. In an alternative these slots may also be oval in cross sectional view.

[0063] FIG. 3 shows a modification of FIG. 2and only a section of the annular wall 10 of FIG. 2in which a film cooling hole 13 is present. Even so the film cooling hole 13 may be angled, FIG. 2 is simplified and is showing the cooling hole 13 to connect the exterior of the wall 10 with the radial inwards burner interior 6 and piercing the overall annular wall 10. The film cooling hole 13 is completely surrounded by the material of the annular wall 10 so that the film cooling hole 13 is a passage through the annular wall 10. In that region of the film cooling hole 13, the annular fuel passage 12 and the annular cooling fluid passage 11 are interrupted locally, as a boundary wall surrounds and encompasses the film cooling hole 13.

[0064] FIG. 4 and FIG. 5 show spacer elements 20 located within the annular fuel passage 12 and/or the annular cooling fluid passage 11 in cross sectional views of the annular wall 10. The spacer elements 20 may be present for stability reasons and to keep the incorporated passages 11, 12 open. For example, as shown in FIG. 5 for the annular fuel passage 12, two spacer elements 20 may be aligned to another and will face another. Alternatively, also shown in FIG. 5 for the annular cooling fluid passage 11, a single spacer element may be present at the annular wall 10 and particularly one of the surfaces of the passages 11, 12. The spacer elements 20 may be hemispheres or semi-cylindrical components. The semi-cylindrical configuration is indicated in FIG. 4 in which the spacer elements 20 show an elongation along an axial direction.

[0065] FIG. 5 represents the same configuration as FIG. 4 and is a cross-sectional view along the line V-V of FIG. 4. What becomes clear from FIGS. 4 and 5, the spacer elements 20 are only connected to one of the surfaces of the respective passages 11, 12. Particularly the spacer elements 20 are not continued ribs or struts for joining two walls. This may be important as a heat transfer should be reduced or may become impossible via the single-sided spacer elements 20. As an example of a spacer element 20 for the annular cooling fluid passage 11 a single spacer element 20 is provided on a radial inward facing surface 21 of the annular cooling fluid passage 11. On the opposite surface, a radial outward facing surface 22 of that passage 11, no additional spacer element 20 is present.

[0066] FIG. 6 now shows a segment of a sectional view of the upstream burner section 2. The section is a cut through one of the swirler vanes 9. The swirler vanes 9 and a consecutive transition section are also indicated as body 8. Through the swirler vane 9 and the body 8 a fuel tube 30 is incorporated, which guides the pilot fuel to the further downstream components of the burner 1. Besides, a further fuel supply line 31 for a main fuel is also shown in this cross-sectional view. This further fuel supply line is also incorporated within the swirler vane 9. Main fuel nozzles 32 as first fuel nozzles are present on a surface of the swirler vane 9. Particularly a plurality of main fuel nozzles 32 are present. This allows to inject main fuel into passing-by air as oxygen containing fluid, which is guided between two adjacent swirler vanes 9 for further mixing and guiding into the burner interior 6.

[0067] FIG. 7 now shows a further variant of the previously introduced burner 1 as introduced in FIG. 1. Again, an upstream burner section 2, an intermediate burner section 3, and a downstream burner section 4 is shown. The upstream burner section 2 again comprises a swirler 40. Also main fuel nozzles 32 are again indicated on a surface of the swirler vane 9. As before, an annular fuel passage 12 is present in the annular wall 10 of the intermediate burner section 3. As before and in accordance with the invention, the annular cooling fluid passage 11 is present radially inwards compared to the annular fuel passage 12 in respect of a burner axis.

[0068] First a specific focus is taken on the burner interior 6 in the region of the intermediate burner section 3. This area is also called the premixing zone 41. Again, film cooling holes 13 are present in the intermediate burner section 3. To provide air into the annular cooling fluid passage 11, cooling fluid inlet holes 14 are present in the annular wall 10. Only two of these cooling fluid inlet holes 14 are shown in FIG. 7 but a plurality of these cooling fluid inlet holes may be present around a circumference of the annular wall 10. The cooling fluid inlet holes 14 are fluidically connected to the annular cooling fluid passage 11. Furthermore, the cooling fluid inlet holes 14 pierces the annular wall 10 such that there is no fluidic connection to the annular fuel passage 12.

[0069] It has to noted that FIG. 7 focuses on the cooling air inlet to the annular cooling fluid passage 11 and does not show features for evacuating again this cooling fluid passage 11. This may be shown in FIG. 8 instead.

[0070] FIG. 8 also shows specifically a transition from the annular fuel passage 12 to an outlet 44 on the burner tip 42. In one embodiment, not shown in FIG. 8, the annular fuel passage 12 directly merges into pilot fuel nozzle(s), which may be an annular outlet or a plurality of holes arranged on the face of the burner tip 42. Thus, in this configuration, the pilot fuel nozzles 33 are located on the face of the burner tip 42. In this configuration pure fuel is exhausted, particularly diffused, into the combustion chamber.

[0071] In a different configuration, as shown in FIG. 8, the annular fuel passage 12 allows exhaustion of pilot fuel via pilot fuel nozzles 33 into a local pre-mixing zone 43, in which pilot fuel is mixed, particularly with air, before the mixture is finally exhausted via the outlet 44 into the combustion chamber.

[0072] The air for the local pre-mixing zone 43 may be a fraction of air branched off from the annular cooling fluid passage 11 (not shown) or may be provided from separate air supply passages (not shown) leading into the local pre-mixing zone 43. The configuration with additional air for local pre-mixing can be called pilot fuel with assist air.

[0073] The pilot fluid nozzles 33 may also called second fuel nozzles in this document, as the pilot fuel may also be called second fuel.

[0074] What can be seen in FIGS. 7 and 8, the pilot fuel is guided through a wall structure along the axial length of the burner 1. Particularly the pilot fuel is guided within swirler vanes 9, the annular wall 10 of the intermediate burner section 3 and within a wall of the downstream burner section 4 which ends in a tip region 42 of the burner 1 for ejection of the pilot fuel into the combustion chamber.

[0075] FIG. 8 also shows this pilot fuel passage system with focus on the annular wall 10 and the downstream burner section 4. Additionally, a main focus of FIG. 8 is the ejection of air from the annular cooling fluid passage 11. Air provided via the cooling fluid inlet hole 14 is distributed in the annular cooling fluid passage 11 and may be exhausted via numerous effusion holes 15. The effusion holes may provide effusion cooling of the interior of the annular wall 10. For this, the effusion holes 15 may be distributed along an axial length of the annular wall 10. Furthermore the effusion holes 15 may also be distributed around a circumference of the annular wall 10. Therefore an expanded surface region can be provided with effusion cooling in the region of the intermediate burner section 3.

[0076] All these embodiments show several advantages which now will be summarized in the following. The burner 1 shows a simplified geometry which is possible to be manufactured by additive manufacturing technology, for example selective laser melting or selective laser sintering. By this, fuel and air passages can be incorporated into a load carrying structure of the burner. Pilot fuel feeding can then be incorporated inside the swirler and the mixing tube instead of having a separate pilot supply line at the exterior of the burner. In consequence the air flow of air in the surrounding of the burner will not be disturbed anymore by an exterior fuel pipe. So the air will be undisturbed and a better well-defined airflow into the burner is achieved. The integrated pilot fuel passagethe annular fuel passage 12is easy to adjust in size, if needed, to accommodate a specific fuel specification. Besides, the annular wall configuration by having an annular fuel passage 12 allows a more even distribution of pilot fuel around the circumference at the burner tip 42. Furthermore, this new design allows reducing the number of components that otherwise would be needed for assembly of the burner and by that also the number of welding steps and manufacturing operations are decreased.

[0077] The integrated annular cooling fluid passage 11 acts as a thermal shield for heat affecting otherwise the annular fuel passage 12. Therefore it counteracts coking in case of liquid fuel.

[0078] The integrated pilot fuel feeding via the annular fuel passage 12 and the corresponding components enables possibilities for fuel flexibility, for example high to low calorific fuels.

[0079] The even flow of the pilot fuel injection will eventually also improve emissions, as the conditions for combustion are also improved by the integrated pilot fuel within the annular wall 10. Besides, the improved distribution at the burner tip 42 also results in a better condition for combustion and allows possibilities for improved emissions.

[0080] If film cooling holes 13 or spacer elements 20 are present within the annular wall 10 these additionally can act as turbulators for the annular fuel passage 12 which in consequence helps to even out the pilot fuel flow within the annular fuel passage 12.

[0081] The spacer elements 20 can be considered as distance bumps to secure a minimum slot height and to even provide varying slot heights within the annular fuel passage 12 or the annular cooling fluid passage 11.

[0082] Due to the improved cooling functionality due to the effusion holes 15, this configuration reduces the likelihood of coking and reduces also the risk of flame back within the intermediate burner section 3. A protection of the fuel pipe, the annular fuel passage 12, is obtained by the most inner concentric cylinder, separated via the annular cooling fluid passage 11. The most inner concentric cylinder may be equipped the effusion holes in a pattern distributed around the surface which eventually will prevent coking of the mixing wall at liquid fuel operation and also act as protection for overheating of the fuel feeding structure.

[0083] The invention provides heat load protection at flame back of the fuel feeding structure by the inner cylinder and the cooperating air slot of the annular cooling fluid passage 11. The protection can be enhanced by the effusion holes in the inner cylinder wall. Coking is prevented also by the effusion hole distribution in the inner cylinder wall. Further advantages may become apparent dependent on the geometry of the burner 1.

[0084] According to FIGS. 1 to 8 an exemplary burner for an annular combustor was discussed. That exemplary burner was configured as the following, which was previously possibly not defined in full detail: The burner includes a burner head, a burner interior, a swirler, and a premixing section. The burner head includes a burner head end. The swirler is arranged in series between the burner head and the premixing section. The burner 1 has a main axis. The burner head, the swirler and the premixing section are arranged along the main axis. The swirler according to the figures is an elongated three-dimensional body. The swirler is open at both ends and has a side wall enclosing a volume or limiting a volume within the side wall and the open ends. Similarly, the premixing section is an elongated three-dimensional body. The premixing section is open at both ends and has a side wall enclosing a volume or limiting a volume within the side wall and the open ends. The volume enclosed by swirler and the volume enclosed by the premixing section together form a volume referred to as the burner interior. As shown in FIG. 1, the swirler may be conically designed for example having a conical frustum shape. The conical frustum shape of the swirler has a top side and a bottom side. A cross-sectional area of the bottom side is greater than a cross-sectional area of the top side, or in other words, a cross-section of the conical frustum increases from the top side towards the bottom side along the main axis. The top side is connected to the burner head end of the burner head and the bottom side is connected to the pre-mixing section. The swirler includes an inlet section. The inlet section is fluidly connected to the compressor (not shown) of the turbomachine (not shown). The inlet section receives compressed air from the compressor and introduces the compressed air into the burner interior, more precisely into the upstream side of the burner interior. Similarly, the inlet section is fluidly connected to a fuel supply (not shown) of the turbomachine. The inlet section receives main gas fuel from the fuel supply and introduces the main gas fuel into the burner interior, more precisely into the upstream side of the burner interior. The inlet section of the swirler includes at least one air inlet and at least one main fuel gas inlet. The compressed air is introduced into the burner interior via the air inlet and the main gas fuel is introduced into the burner interior via the main fuel gas inlet. The air inlet may be tangentially arranged along the swirler with respect to the main axis. Similarly, the main fuel gas inlet may be tangentially arranged along the swirler with respect to the main axis. For example, when the swirler is conical frustum shaped, the air inlet and/or the main fuel gas inlet may be formed as longitudinally extending slots through a body wall (now shown) of the conical frustum. In an exemplary embodiment of the burner, the inlet section includes a plurality of the air inlets and a plurality of the main fuel gas inlets arranged around the swirler in a distributed way such that when the main gas fuel and the compressed air enter the burner interior though the air inlets and the main fuel gas inlets, a swirl is generated in the compressed air and the main gas fuel.

[0085] The basic technique in such dual fuel combustor is to premix the main fuel with air from a compressor of the turbomachine before igniting the combustion mixture, i.e. mixture of the air from the compressor and the main fuel, in the combustion chamber. Usually the air from the compressor is mixed with the main gaseous fuel, either inside the swirler or just before introduction into the swirler, and then swirled by the swirler to create a swirling flow of the air and the main gaseous fuel. This swirling flow of the pressurized air from the compressor and the main gaseous fuel then enters from the swirler into the premixing section. At the premixing section the pressurized air from the compressor and the main gaseous fuel are allowed to mix well before exiting into the combustion chamber or the combustion space where the combustion mixture undergoes combustion.

[0086] In dual fuel combustors, the main fuelliquid or gaseous fuelis discharged by a nozzle positioned at the burner head or at the swirler vanes. The main fuel after exiting the nozzle, advantageously in atomized form if liquid fuel is used, enters the swirler and then continues into the premixing section and finally into the combustion chamber where the main fuel participates in the combustion reaction.

[0087] Just to briefly explain that the invention can also be used in different burner design, in FIG. 9 an alternative burner design is shown. Same reference numerals are used if similar components are to be identified than before.

[0088] According to FIG. 9 a combustor is shown, in which a burner 1 is shown, connected to a combustion chamber 50. An upstream burner section 2 comprises burner head 60, a radial swirler 40 comprising a plurality of swirler vanes 9, followed by an intermediate burner section 3. Downstream, the intermediate burner section 3 is connected to the combustion chamber 50 via a downstream burner section 4.

[0089] The intermediate burner section 3 comprises an annular wall 10, which encompasses an annular cooling fluid passage 11 and an annular fuel passage 12. Inlet and outlet to the annular cooling fluid passage 11 is not shown. A fuel inlet 61 to feed the annular fuel passage 12 is given as an example through the burner head 60 and piercing the solid portion of the swirler vanes 9, so that the fuel inlet 61 can be connected to the annular fuel passage 12. At a downstream end of the annular fuel passage 12, the pilot fuel is ejected into the combustion chamber 50, as indicated by arrow 62.

[0090] The radial swirler 40 is present to guide air, indicated by arrow 63, to swirl the air and to guide it to the burner interior 6. Typically at the swirler vanes 9, it will also be mixed with main fuel (not indicated in the figure).

[0091] In consequence, the annular wall 10 shown in FIG. 9 can also be provided with the inventive three cylindrical wall structure, with embedded slots for pilot fuel and air.

[0092] This was one example for an alternative burner design. Other burner designs, can also be equipped with the inventive features.

[0093] While the present technique has been described in detail with reference to certain embodiments, it should be appreciated that the present technique is not limited to those precise embodiments. Rather, in view of the present disclosure which describes exemplary modes for practicing the invention, many modifications and variations would present themselves, to those skilled in the art without departing from the scope and spirit of this invention. The scope of the invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.