Abstract:
A method for reducing self-induced flame oscillations is provided. In a first fluid mass flow flowing through a jet nozzle from a fluid inlet opening to a fluid outlet opening, a second fluid mass flow is injected on an axial position of the jet nozzle positioned downstream from the fluid inlet opening. One fluid mass flow includes air, and the other fluid mass flow includes a fuel. A second method for reducing self-induced flame oscillations is also provided. In a first fluid mass flow flowing through a jet nozzle from a fluid inlet opening to a fluid outlet opening, a second fluid mass flow is injected on a radial position of the jet nozzle in relation to the circumference of the jet nozzle. One mass flow includes air and the other fluid mass flow includes a fuel. Burners which ensure the execution of the method are also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2008/054969, filed Apr. 24, 2008, and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 08000497.1 EP filed Jan. 11, 2008. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a method for reducing self-induced flame oscillations and to a burner with which this method can be carried out. 
       BACKGROUND OF INVENTION 
       [0003]    Self-induced flame oscillations frequently occur in combustion chambers and in this context are also known as combustion hum. Combustion chamber oscillations are caused by feedback between pressure changes in the combustion chamber and fluctuations in the mass flow of fuel and air. The combustion chamber oscillations constitute an undesirable side-effect of the combustion process, as they place increased mechanical and thermal stress on the burner components and the combustion chamber components. In addition, combustion hum produces increased levels of noise pollution in the vicinity of the combustion chamber in question. 
         [0004]    Reducing combustion hum, i.e. minimizing self-induced flame oscillations, has hitherto been achieved in some cases with the aid of Helmholtz resonators. Another possibility is to supply an increased amount of pilot gas to the burner used. Pilot gas, i.e. pilot fuel, is normally used to stabilize the flame. However, increasing the pilot gas supply results in higher NO X  emissions. 
       SUMMARY OF INVENTION 
       [0005]    The object of the present invention is therefore to provide an advantageous method for reducing self-induced flame oscillations. Another object of the present invention is to provide an advantageous burner. 
         [0006]    The first object is achieved by a method as claimed in the claims. The second object is achieved by a burner as claimed in the claims. The dependent claims contain further advantageous embodiments of the invention. 
         [0007]    In the method according to the invention for reducing self-induced flame oscillations, into a first mass flow of fluid flowing through a jet nozzle from a fluid inlet opening to a fluid outlet opening, there is injected a second mass flow of fluid at least one axial position on the jet nozzle downstream of the fluid inlet opening, one of the two mass flows of fluid being air. The other mass flow of fluid comprises a fuel. By injecting the fuel and/or air at a plurality of axial positions into a main mass flow of fluid flowing through the jet nozzle, the response e.g. of the mass flow of fuel can be smeared such that resonance can only occur for a small portion of the mass flow. Smearing of the delay between injection and combustion is achieved by the method according to the invention. The method according to the invention can be used in particular for operating a jet burner, while still retaining the positive characteristics of a jet burner. 
         [0008]    Alternatively or additionally, the second mass flow of fluid can be injected at at least one radial position on the jet nozzle with respect to the circumference of the jet nozzle. 
         [0009]    This likewise achieves the smearing of the delay time between injection and combustion as described above. 
         [0010]    Different radial fuel distributions are preferably implemented. Here it is advantageous e.g. during part-load operation to run the inner areas richer, i.e. the areas leading to the center of a housing, thereby enabling flame extinction and CO emissions to be prevented. 
         [0011]    The second mass flow of fluid can preferably be injected into the first mass flow of fluid at a plurality of positions around the circumference of the jet nozzle. In particular, the second mass flow of fluid can be injected into the first mass flow of fluid at a plurality of positions disposed mutually offset in the axial direction around the circumference of the jet nozzle. As a result, the flow in the jet nozzle is not always attenuated at the same circumferential position. 
         [0012]    The mass flow of fluid comprising a fuel can be, for example, an air/fuel mixture. The fuel used can, in particular, be gaseous fuel, such as natural gas or a synthesis gas. For natural gas, as the mass flows of fuel are much smaller than the air mass flows, there is unlikely to be a significant increase in pressure loss even in the case of injection perpendicular to the flow direction of the air. Moreover, the method can also be applied to liquid fuels. 
         [0013]    In addition to the second mass flow of fluid, a third mass flow of fluid can be injected into the first mass flow of fluid. For example, the second mass flow of fluid can comprise a fuel and the first mass flow of fluid can comprise air. The third mass flow of fluid can likewise comprise air, steam or another gas, e.g. an inert gas. The second and/or the third mass flow of fluid can be injected into the first mass flow of fluid at an angle of between 0° and 90°. For example, the second mass flow of fluid can be injected into the first mass flow of fluid at an angle of 90° and the third mass flow of fluid can be injected into the first mass flow of fluid at an angle of 45°. Said first and third mass flow of fluid can be, for example, a mass flow of air, and the second mass flow of fluid can be a mass flow of fuel. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the air/fuel mixture, while wall film formation is primarily a measure to counteract flashback. 
         [0014]    The burner according to the invention comprises at least one jet nozzle with a main fluid inlet opening and a fluid outlet opening, the main fluid inlet opening being connected to a fluid supply line. The burner according to the invention is characterized in that at least one secondary fluid inlet opening connected to a fluid supply line is disposed at least one axial position on the jet nozzle downstream of the main fluid inlet opening. 
         [0015]    The fluid supply line connected to the main fluid inlet opening can be implemented, for example, as a fuel supply line, as an air supply line or as a fuel/air mixture supply line. The main fluid inlet opening is preferably connected to an air supply line. Although the fluid supply line connected to at least one secondary fluid inlet opening can preferably be implemented as a fuel supply line, it can also be implemented as an air supply line, as a steam supply line, as a nitrogen supply line or as an air/fuel mixture supply line. 
         [0016]    It is basically advantageous if the secondary fluid inlet openings are disposed at a plurality of axial positions on the jet nozzle. The secondary fluid inlet openings, which can be disposed at different axial positions, can be, in particular, air inlet openings. In addition, secondary fluid inlet openings can be disposed at a plurality of positions along the circumference of the jet nozzle. In this case it is advantageous if secondary fluid inlet openings are disposed at a plurality of positions disposed mutually offset in the axial direction along the circumference of the jet nozzle. This means that the flow in the jet nozzle is not always attenuated at the same circumferential position. 
         [0017]    The main fluid inlet opening can preferably be connected to an air supply line and a portion of the secondary fluid inlet openings can be connected to a fuel supply line. In particular, a first portion of the secondary fluid inlet openings can be connected to a fuel supply line and a second portion of the secondary fluid inlet openings can be connected to an air supply line. 
         [0018]    In addition, the secondary fluid inlet openings and the main fluid inlet opening can have a central axis in each case. Said central axes of the secondary fluid inlet openings can be at an angle of between 0° and 90° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle. Advantageously, the central axes of a first portion of the secondary fluid inlet openings can be at 90° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle, and the central axes of a second portion of the secondary fluid inlet openings can be at 45° to the central axis of the main fluid inlet opening and/or to the central axis of the jet nozzle. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the air/fuel mixture, while wall film formation is primarily a measure to counteract flashback. 
         [0019]    The secondary fluid inlet openings and the main fluid inlet opening may have a central axis in each case and the central axes of the secondary fluid inlet openings can be at an angle of between 0° and 90° to a radial direction with respect to the central axis of the main fluid inlet opening. This enables injection to take place tangentially along the circumference of the jet nozzle, thereby producing a wall film on the inner surface of the jet nozzle. Injection along the circumference of the jet nozzle can also be used to produce swirl in the jet nozzle. 
         [0020]    A plurality of fluid supply lines connected to secondary fluid inlet openings can be interconnected via an annular distributor disposed along the circumference of the jet nozzle. 
         [0021]    In addition, a fuel nozzle can be disposed in the main fluid inlet opening or immediately preceding the main fluid inlet opening. The fuel nozzle can comprise a fuel distributor which is disposed in or immediately preceding the main fluid inlet opening. 
         [0022]    At least one secondary fluid inlet opening can be implemented as an annular gap running along the circumference of the jet nozzle. In this case the burner according to the invention can comprise a plurality of jet nozzles, the annular gaps of the different jet nozzles being disposed at different axial positions in each case. Varying the axial positions of the annular gaps provides an additional design parameter for counteracting thermoacoustic flame oscillations. 
         [0023]    The burner according to the invention can comprise a plurality of jet nozzles disposed e.g. annularly with respect to the central axis of the burner. It can also incorporate one or more pilot burners. 
         [0024]    The burner according to the invention is preferably used in a gas turbine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Further features, characteristics and advantages of the present invention will now be described in greater detail using exemplary embodiments and with reference to the accompanying drawings in which: 
           [0026]      FIG. 1  schematically illustrates a section through a jet burner at right angles to its longitudinal direction. 
           [0027]      FIG. 2  schematically illustrates a section through another jet burner at right angles to its longitudinal direction. 
           [0028]      FIG. 3  schematically illustrates a section through part of a jet burner in the longitudinal direction. 
           [0029]      FIG. 4  schematically illustrates a section through part of another jet burner in the longitudinal direction. 
           [0030]      FIG. 5  schematically illustrates a section through part of an alternative jet burner in the longitudinal direction. 
           [0031]      FIG. 6  schematically illustrates a section in the longitudinal direction through another jet burner. 
           [0032]      FIG. 7  schematically illustrates a section through part of a jet burner in the longitudinal direction. 
           [0033]      FIG. 8  schematically illustrates a jet burner having an annular gap, in the longitudinal direction, 
           [0034]      FIG. 9  schematically illustrates an alternative arrangement of the annular gap of the jet burner shown in  FIG. 8 . 
           [0035]      FIG. 10  shows a cross-section of a jet burner and of the annular distributor with a plurality of radial secondary fluid inlet openings. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0036]    A first exemplary embodiment of the invention will now be explained in greater detail with reference to  FIGS. 1 to 4 .  FIG. 1  schematically illustrates a section through a jet burner  1  perpendicular to a central axis  4  of the burner  1 . The burner  1  comprises a housing  6  having a circular cross-section. Inside the housing  6 , a particular number of jet nozzles  2  are disposed in an essentially annular manner. Each of said jet nozzles  2  has a circular cross-section. The burner  1  can also incorporate a pilot burner. 
         [0037]      FIG. 2  schematically illustrates a section through a jet burner  101 , said section running perpendicular to the central axis of the burner  101 . The burner  101  likewise has a housing  6  of circular cross-section in which are disposed a number of inner and outer jet nozzles  2 ,  3 . The jet nozzles  2 ,  3  each have a circular cross-section, said outer jet nozzles  2  having a cross-sectional area that is the same size as, or larger than, that of the inner jet nozzles  3 . The outer jet nozzles  2  are disposed in an essentially annular manner inside the housing  6  and form an outer ring. The inner jet nozzles  3  are likewise disposed in an essentially annular manner inside the housing  6 . The inner jet nozzles  3  fond an inner ring which is disposed concentrically to the outer jet nozzle ring. 
         [0038]      FIGS. 1 and 2  merely show examples of the arrangement of jet nozzles  2 ,  3  inside a jet burner  1 ,  101 . Alternative arrangements, as when using a different number of jet nozzles  2 ,  3 , are self-evidently possible. 
         [0039]      FIG. 3  schematically illustrates a section through part of a jet burner  1  according to the invention in the longitudinal direction, i.e. along the central axis  4  of the burner  1 . The burner  1  has at least one jet nozzle  2  disposed in a housing  6 . The central axis of the jet nozzle  2  is identified by the reference character  5 . The jet nozzle  2  comprises a main fluid inlet opening  8  and a fluid outlet opening  9 . The combustion chamber  18  is connected to the fluid outlet opening  9 . In addition, the jet nozzle  2  is disposed in the housing  6  such that the main fluid inlet opening  8  faces the back wall  24  of the burner  1 . The housing  6  also comprises an outer housing section  27  disposed radially with respect to the central axis  4  of the burner  1 . 
         [0040]    The jet nozzle  2  is fluidically connected to a compressor. The compressed air from the compressor is conveyed via an annular gap  22  to the main fluid inlet opening  8  and/or is conveyed radially with respect to the central axis  5  of the jet nozzle  2  via an air inlet opening  23  to the main fluid inlet opening  8 . In the event that the compressed air is supplied through the annular gap  22  of the jet nozzle  2 , said compressed air flows through the annular gap  22  in the direction of the arrow identified by the reference character  15 , i.e. parallel to the central axis  5  of the jet nozzle  2 . The air flowing in the direction of the arrow  15  is then deflected through 180° at the back wall  24  of the burner  1  and then flows through the main fluid inlet opening  8  into the jet nozzle  2 . The flow direction of the air inside the jet nozzle  2  is indicated by an arrow  10 . 
         [0041]    Additionally or alternatively to feeding the compressed air through the annular gap  22 , the compressed air from the compressor can also be supplied through an opening  23  disposed radially in the housing  6  of the burner  1  with respect to the central axis  5  of the jet nozzle  2 . The flow direction of the compressed air flowing through the opening  23  is indicated by an arrow  26 . In this case the compressed air is then deflected through 90° and then flows into the jet nozzle  2  through the main fluid inlet opening  8 . 
         [0042]    The burner according to the invention  1  can basically also be implemented without the outer housing section  27 , i.e. without an external casing  27 . In this case the compressed air can flow directly into the “plenum”, i.e. the area between the back wall  24  and the main fluid inlet opening  8 . The burner according to the invention  1  can also be implemented even without the back wall  24 . 
         [0043]    The jet nozzle  2  is encircled radially by an annular distributor  7  which is supplied with fuel  12  via a fuel supply line  13 . The annular distributor  7  has a number of secondary fluid inlet openings  14  through which fuel can be injected into the mass flow of air flowing through the jet nozzle  2 . The secondary fluid inlet openings  14  can be implemented as a slit or an oval nozzle. This is particularly advantageous for synthesis gas injection, as it means that a smaller inflow surface is offered to the flow of air. This also results in a lesser tendency to recirculation downstream of fuel injection. The flow direction of the fuel  12  injected into the jet nozzle  2  through the secondary fluid inlet openings  14  is indicated by arrows  17 . Said flow direction  17  of the injected fuel  12  runs perpendicular to the central axis  5  of the jet nozzle  2  and therefore also perpendicular to the main flow direction  10  of the compressed air  11  flowing through the jet nozzle  2 . 
         [0044]    In  FIG. 3 , secondary fluid inlet openings  14  are disposed at three different axial positions, two secondary fluid inlet openings  14  being disposed opposite one another at each axial position. A number of secondary fluid inlet openings  14  are advantageously disposed along the circumference of the jet nozzle  2 . These can in particular also be disposed in an axially offset manner with respect to one another. Secondary fluid inlet openings  14  can basically be disposed at only one or at additional axial positions along the circumference of the jet nozzle  2 . 
         [0045]    Inside the jet nozzle  2 , the injection of fuel  12  into the compressed air  11  flowing through the jet nozzle  2  creates a fuel/air mixture which leaves the jet nozzle  2  through the fluid outlet opening  9  in the direction of the combustion chamber  18 . 
         [0046]      FIG. 4  schematically illustrates a section through a burner  201  which constitutes a development of the burner  1  shown in  FIG. 3 . The compressed air  11  from a compressor can again either be supplied to the jet nozzle  2  via an annular gap  22  or, as shown in  FIG. 3 , injected via an air inlet opening perpendicularly to the central axis  5  of the jet nozzle. In this variant, the compressed air  11  is preferably supplied to the jet nozzle  2  via an annular gap  22 . Injection perpendicular to the central axis  5  is therefore only denoted by a dashed arrow  26 . 
         [0047]    In addition to the features already described in connection with  FIG. 3 , the burner  201  shown in  FIG. 4  not only has the secondary fluid inlet openings  14  through which fuel is injected into the jet nozzle  2 , but also secondary fluid inlet openings  25  through which the additional compressed air is injected into the jet nozzle  2  in the flow direction indicated by the arrows  16 . Said additional secondary fluid inlet openings  25  are connected to the annular gap  22 . This means that a portion of the compressed air  11  coming from the compressor is conveyed through the annular gap  22  to the back wall  24  of the burner where it is deflected through 180° and is then fed through the main fluid inlet opening  8  into the jet nozzle  2 . This mass flow of air flows through the jet nozzle  2  in the direction indicated by the arrow  10 . Another portion of the compressed air from the compressor is injected from the annular gap  22  into the jet nozzle  2  through the secondary fluid inlet openings  25  in the flow direction indicated by the arrows  16 . Said secondary fluid inlet openings  25  can be disposed at different axial positions around the jet nozzle  2 . In  FIG. 4 , the secondary fluid inlet openings  25  through which compressed air is injected into the jet nozzle  2  are disposed such that a secondary fluid inlet opening  25  is disposed in each case in the flow direction  10  downstream of a secondary fluid inlet opening  14  through which fuel  12  is injected into the jet nozzle  2 . Any other arrangements are self-evidently also possible. However, it is advantageous if the secondary fluid inlet openings  25  are disposed in a radial offset manner along the circumference of the jet nozzle  2 . This means that the flow is not always attenuated at the same circumferential position. 
         [0048]    In  FIG. 4 , the secondary fluid inlet openings  14  and  25  are disposed such that the fuel  12  is injected through the secondary fluid inlet openings  14  perpendicularly to the flow direction  10  of the compressed air  11  flowing through the main fluid inlet opening  8  into the jet nozzle  2 . Further compressed air is injected into the jet nozzle  2  through the secondary fluid inlet openings  25  at an angle of about 45° to the main flow direction  10 . Both the fuel  12  and the additional compressed air can be injected into the jet nozzle  2  at any other angle of between 0° and 90° to the main flow direction  10  at different axial positions. As e.g. for natural gas, the mass flows of fuel are much smaller than the mass flows of air, a significant increase in the pressure loss is unlikely to occur even in the case of perpendicular fuel injection. The fuel  12  can also be injected against the air flow direction  10 . 
         [0049]    The fuel can basically be supplied via one or more fuel supply lines  13  and transported to the individual jet nozzles  2  via an annular distributor  7 . If a plurality of fuel supply lines  13  are present, these can be advantageously disposed along the circumference of the burner. It is further advantageous if the injection of the fuel into the air jet is carried out at more than one axial position of the jet pipe  2 . In addition, to ensure better mixing, injection can take place at a plurality of circumferential positions on the jet pipe  2 . 
         [0050]    A second exemplary embodiment will now be described in greater detail with reference to  FIGS. 5 to 7 . Elements corresponding to elements already described in the first exemplary embodiment are provided with the same reference characters and will not be described again in detail. 
         [0051]      FIGS. 5 to 7  each show sections through part of a burner  301  along the central axis  4  of the burner  301 . The burner  301  has at least one, but advantageously a plurality of jet nozzles  2  disposed in an essentially annular manner about the central axis  4 . For possible arrangements of the jet nozzles  2 ,  3 , please refer to  FIGS. 1 and 2  and the statements made in that context. 
         [0052]    In  FIGS. 5 to 7 , a fuel nozzle  19  is disposed in the region of the main fluid inlet opening  8  of the jet nozzle  2 . Through said fuel nozzle  19 , fuel  12  is injected into the jet nozzle  2 . The fuel  12  is preferably injected at an angle of about 45° to the flow direction  10  of the compressed air  11  flowing into the jet nozzle through the main fluid inlet opening  8 . The flow direction of the fuel  12  injected through the fuel nozzle  19  is indicated by arrows  17 . The fuel  12  can also be injected into the jet nozzle  2  at an angle of between 0° and 90° with respect to the flow direction  10  of the compressed air  11 . 
         [0053]    Disposed at different axial positions on the jet nozzle  2  are further secondary fluid inlet openings  25  through which compressed air can be injected into the jet nozzle  2 . Said compressed air is fed to the secondary fluid inlet openings  25  via an annular gap  22 . In  FIGS. 5 and 6 , the compressed air is injected through the secondary fluid inlet openings  25  into the jet nozzle  2  perpendicularly to the central axis  5  of the jet nozzle. In  FIG. 5 , said compressed air from a compressor flows through the annular gap  22  in the direction of the arrow  15 . 
         [0054]    In  FIG. 6 , the compressed air coming from a compressor is injected into the burner  301  perpendicularly to the central axis  5  of the jet nozzle  2  through an air inlet opening  23 . The flow direction of the compressed air  11  passing through the opening  23  is indicated by an arrow  26 . The compressed air  11  now flows through the annular gap  22  to the secondary fluid inlet openings  25  and is fed via the latter into the jet nozzle  2 . However, the main portion of the compressed air  11  is introduced into the jet nozzle  2  though the main fluid inlet opening  8  in the flow direction  10 . 
         [0055]      FIG. 7  shows an alternative embodiment of the burner  301  shown in  FIG. 5 . Unlike in  FIG. 5 , in  FIG. 7  the secondary fluid inlet openings  25  are disposed such that the compressed air injected into the jet nozzle  2  through the secondary fluid inlet openings  25  is injected into said jet nozzle at an angle of approximately 45° to the central axis  5  of the jet pipe  2 . Another injection angle between 0° and 90° is basically possible and practical. 
         [0056]    The air used for the axially stepped air injection in this exemplary embodiment can either be extracted from the annular gap  22  or directly from a plenum surrounding the burner  301  and injected into the fuel/air mixture in the jet nozzle. Said air can be introduced as a jet into the crossflow or as a wall film. The advantage of jet-in-crossflow injection is that it helps to increase the mixing of the fuel/air mixture, while wall film formation is primarily a measure to counteract possible flashback. In addition, the air can be injected into the jet nozzle  2  tangentially to the circumference thereof. Said wall film can be produced over the entire inner surface of the jet nozzle  2 . Tangential injection can also be used to generate swirl in the jet nozzle  2 . 
         [0057]    It is also conceivable for jet-in-crossflow injection to be combined with wall film injection by disposing the nozzles in very close succession. Jet-in-crossflow injection ensures improved mixing, particularly also in the core region of the jet, and the film of the second nozzle strengthens the flow boundary layer, thereby preventing flashback. This design is particularly advantageous for central co-flow injection into the main fuel injection, e.g. for synthesis gas. If there is a high proportion of air in the axial stepping, it is possible to adjust the nozzle diameter of the jet nozzle such that the flow rate in the nozzle remains essentially the same. 
         [0058]    A third exemplary embodiment will now be explained in greater detail with reference to  FIGS. 8 and 9 . Elements corresponding to elements already described in the first exemplary embodiment are provided with the same reference characters and will not be described again in detail. 
         [0059]      FIGS. 8 and 9  schematically illustrate different variants of a burner  401  in the longitudinal direction along the central axis  4  of the burner  401 . The burner  401  has a number of jet nozzles  2  which are disposed in an essentially annular manner about the central axis  4  of the burner  401 . For possible arrangements of the jet nozzles  2 ,  3 , please refer to  FIGS. 1 and 2  and the statements made in that context. 
         [0060]    Each jet nozzle  2  comprises a main fluid inlet opening  8  and a fluid outlet opening  9 . The fluid outlet opening  9  leads into the combustion chamber  18 . A fuel nozzle  19  is disposed in the main fluid inlet opening  8 . The fuel nozzle  19  comprises a fuel distributor  20  which enables fuel  12  to be injected into the jet nozzle  2  at different radial positions and different circumferential positions of the main fluid inlet opening  8 . The flow direction of the injected fuel  12  is indicated by arrows  17 . 
         [0061]    An annular gap  21  is disposed at another axial position on the jet nozzle  2  downstream in respect of the flow directions  10  and  17 . Air is injected into the jet nozzle  2  through the annular gap  21 . The flow direction of the injected air is indicated by arrows  16 . Said air is injected into the jet nozzle  2  virtually parallel to the central axis  5  thereof. In contrast to the variant shown in  FIG. 8 , in  FIG. 9  the annular gap  21  is disposed at a position further downstream of the main fluid inlet opening  8 . In the two variants shown in  FIGS. 8 and 9 , the compressed air used from a compressor can be either passed through an annular gap  22  in the flow direction  15  to the main fluid inlet opening  8  of the jet nozzle  2  and/or injected perpendicularly to the central axis  5  in the flow direction  26 . 
         [0062]    The variants shown in  FIGS. 8 and 9  include the possibility of inserting into the burner  401 , from the back wall  24  of the burner, the nozzle section located downstream in terms of the flow direction  15  of the compressed air coming from the compressor and on which the fuel distribution also depends, and positioning it by means of the front combustion-chamber-side section, e.g. by means of spacers in the annular space. In the extreme case, the downstream nozzle section sits directly in the bottom of the fire tube. 
         [0063]      FIG. 10  shows a cross-section of a jet burner  1  and of the annular distributor  7  with a plurality of radial secondary fluid inlet openings  14 . Said annular distributor  7  comprises a complete annulus of jet nozzles  2 . Radiating from the annular distributor  7  are secondary fluid inlet openings  14  which meet the jet nozzles  2  at different circumferential positions. Long secondary fluid inlet openings  14  can be used. Secondary fluid inlet openings  14  can also be at an angle to the jet nozzle  2 . The jet nozzles  2  can be disposed in any manner. It is also conceivable merely for an annular distributor  7  with fuel to be present and the jet nozzles to be disposed in any manner within it (central jet burner  1 ). 
         [0064]    In all the exemplary embodiments and variants, the inventive burner  1 ,  101 ,  201 ,  301 ,  401  can also be implemented without the outer housing section  27  or rather without an outer casing  27 . In this case, the compressed air can flow directly into the “plenum”, i.e. the area between the back wall  24  and the main fluid inlet opening  8 . The inventive burner  1 ,  101 ,  201 ,  301 ,  401  can also be implemented without the back wall  24 . 
         [0065]    Varying the axial positions of the annular gaps  21  provides an additional design parameter to guard against thermoacoustic flame oscillations. It is also possible to provide different jet nozzles  2  of a burner  401  with annular gaps  21  at different axial positions.