Burner system, method for operating a burner system and method for manufacturing

Abstract

A burner system with a combustion chamber and a combustion chamber wall aligned along a longitudinal axis, and with a supply nozzle opening into the combustion chamber via an end wall for adding fresh gases into the combustion chamber. The system is designed such that, during operation, a large-scale recirculation zone of hot combustion products with a hot stagnation point flow comprising a stagnation point opposite the combustion chamber wall is formed within the combustion chamber. Advantageous cooling is provided by forming a cooling nozzle in the combustion chamber wall opposite the position of the recirculation zone, with a cooling medium opening arranged at its downstream end, by means of which cooling medium can be supplied to the combustion chamber for cooling the combustion chamber wall. The cooling nozzle is designed to generate a flow of cooling medium that is aligned coaxially with the hot stagnation point flow.

Description

BACKGROUND

[0001] The invention relates to a burner system, in particular for use in a gas turbine, with a combustion chamber aligned along a longitudinal axis and a combustion chamber wall comprising an end wall arranged on the inlet side of the combustion chamber, and with at least one supply nozzle opening into the combustion chamber via the end wall for adding fresh gases, fuel and / or oxidizer to the combustion chamber, wherein the burner system is designed such that, during operation, a recirculation zone of hot combustion products with a hot stagnation point flow, in particular a large-scale recirculation zone, forms within the combustion chamber to stabilize the combustion process, comprising a stagnation point opposite the combustion chamber wall, in particular the end wall. The invention further relates to a method for operating a burner system and a method for manufacturing it.

[0002] Such burner systems include, for example, jet-stabilized burner systems designed for high-speed combustion, especially without swirling. In this process, the combustion zone in the combustion chamber is stabilized during operation by a stationary, large-scale, combustion chamber-internal recirculation of exhaust gas, which is formed due to the introduction of oxidizer / fuel jets with a sufficiently high axial impulse into the combustion chamber. The recirculation brings the burned, hot exhaust gas back to the jet root near the supply nozzles and mixes it with the incoming fresh gases. In a known ring-shaped arrangement of the supply nozzles, the recirculation zone typically consists essentially toroidally and radially within the nozzle ring, with a backflow running along the central axis.

[0003] The recirculation zone creates a hot stagnation point flow of combustion products directed towards the end wall. In this way, the hot combustion products are convected to the end wall of the burner system, causing a high thermal load there.

[0004] A jet-stabilized burner system of the type mentioned above is known, for example, from EP 1 918 641 A2.

[0005] Other jet-stabilized burner systems are specified, for example, in DE 10 2015 205 069 A1, EP 35 34 070 A1, EP 33 01 371 A1 and EP 35 84 501 A1.

[0006] DE 692 05 855 T2 shows a combustion chamber and a mixer with a fuel nozzle arranged on the inlet side of the combustion chamber. Furthermore, the mixer has two vortex generators, with the fuel nozzle located in the middle of the vortex generator, centrally on a longitudinal axis. During operation, air flows through the two vortex generators and then into a mixing channel. Fuel is injected upstream of the combustion chamber through injection holes in the fuel nozzle. The fuel-air mixture burns in the combustion chamber.

[0007] DE 25 17 756 A1 shows a two-component burner swirl nozzle arranged via an opening on a front plate. The swirl nozzle has a nozzle mouthpiece for introducing liquid fuel into a combustion chamber. The nozzle mouthpiece comprises several spray channels that run inclined to the longitudinal axis of a nozzle body of the swirl nozzle.

[0008] U.S. Pat. No. 4,718,359 A shows a coal burner for the combustion of a solid material with a substantially ring-shaped inlet to a combustion chamber.

[0009] U.S. Pat. No. 4,845,940 A shows a burner with a first recess, within which a central nozzle is arranged for introducing a fuel mixture. The nozzle is surrounded by ring-shaped air channels.

[0010] US 2001 / 0 026 911 A1 shows a combustion chamber with a combustion space that has an anchor outlet located opposite a recirculation zone during operation. Through the anchor outlet, anchor fuel is directed radially outwards onto an anchor surface. The anchor fuel is fed into the combustion chamber parallel to a surface.

[0011] In previously common jet-stabilized burner systems, the thermal load on the burner face is reduced by cooling the outer wall of the combustion chamber, for example, by impact cooling or by structural cooling using cooling channels within the combustion chamber wall, e.g., the end wall. Furthermore, or alternatively, the thermal stress on the end wall is reduced, for example, by enlarging the combustion chamber through axial relocation of the end wall. This leads to a weakening of the stagnation point flow caused by the recirculation zone and consequently to a reduced thermal load on the end wall.

[0012] The resulting high temperature gradients in the combustion chamber wall reduce the lifespan of the material and thus of the burner system. Enlarging the combustion chamber by moving the end wall back reduces the compactness of burner systems, which is advantageous and / or necessary in many applications.

[0013] The problem of a thermally highly stressed end wall or combustion chamber wall also arises in other burner systems where two opposing or one (large-scale) toroidal recirculation zone(s) of hot combustion products are formed between spatially separated flames or in the inner region of a single, ring-shaped flame.

[0014] The invention is based on the objective of providing a burner system with advantageous cooling, as well as a method for operating and a method for manufacturing such a burner system.

[0015] The object is achieved for the burner system with the features of claim 1, for the method of operation with the features of claim 12, and for the method of manufacture with the features of claim 13.SUMMARY

[0016] The burner system is designed so that at least one cooling nozzle with a cooling medium opening arranged at its downstream end is formed in the combustion chamber wall, in particular the end wall, opposite (offset in one of the directional components, e.g., in the wall normal direction and / or axial direction, with respect to the other directional components, for example in the radial direction and in the direction of circulation, at the corresponding position) the position of the recirculation zone during operation, by means of which cooling medium can be supplied or is supplied to the combustion chamber for cooling the combustion chamber wall, in particular the end wall, during operation, wherein the cooling nozzle is designed to generate a flow of cooling medium aligned coaxially with the hot stagnation point flow.

[0017] The coaxially aligned flow forms in particular a cold stagnation point flow in the manner of a counter-current stagnation point flow to the hot stagnation point flow, wherein the hot and the cold stagnation point flows flow along the same axis, but in opposite directions. The axis is aligned in particular in the wall normal direction (orthogonal to the combustion chamber wall, especially the end wall), for example along a longitudinal axis of the combustion chamber or combustion space. For this purpose, in particular a downstream section of the cooling nozzle is aligned along the corresponding axis, for example orthogonally to the combustion chamber wall, especially the end wall.

[0018] At least one supply nozzle opens into the combustion chamber with a fresh gas outlet opening, which is arranged, for example, at the level of the end wall or axially downstream of it, recessed into the combustion chamber.

[0019] “Large-scale” means that the recirculation zone, i.e., the zone within which hot combustion products are deflected and flow back towards the end wall, extends in operation, for example, at least three diameters (or an equivalent dimension) of the fresh gas outlet openings in the axial direction.

[0020] In addition to the end wall, the combustion chamber wall can also include lateral combustion chamber walls extending in the axial direction of the combustion chamber to form a closed combustion chamber. The combustion chamber can also be designed to be open in such a way that lateral combustion chamber walls are, for example, only partially present and / or at a great distance from the flame, so that the flow field is essentially unaffected by the combustion chamber walls, at least in the immediate vicinity of the fresh gas outlet opening(s).

[0021] The hot stagnation point flow is formed from the hot combustion products (i.e., an exhaust gas flow).

[0022] At least one cooling nozzle is present, in addition to the supply nozzles, which serve to supply fresh gases for the combustion process. In particular, the flow from the cooling nozzle does not contribute to generating a combustion chamber flow that stabilizes the combustion process, especially not to generating the large-scale recirculation zone. In this case, at least one cooling nozzle, or a group of cooling nozzles, is surrounded by the combustion chamber wall, in particular by the end wall, for the purpose of cooling it. The cooling nozzle(s) are not directly surrounded (for example, only by an intermediate wall surrounding the supply nozzle) by one and / or the supply nozzle(s).

[0023] By supplying the cooling medium to the combustion chamber on the hot side of the combustion chamber wall, coaxial to the stagnation point flow, extremely efficient and material-friendly cooling of the burner wall, especially the otherwise thermally heavily loaded end wall, can be achieved with a compact design. Thus, by means of the design according to the invention, the burner system is provided with an effective, material-friendly cooling concept, which may also allow for a compact design of the burner system.

[0024] In a preferred embodiment, the cooling nozzle (or, in the case of several, a group of cooling nozzles) is positioned such that the cooling media opening (or, in the case of a group of cooling nozzles, at least one of the cooling media openings) is located opposite the stagnation point that develops during operation. “Opposite” means offset with respect to the flow axis of the hot stagnation point flow, for example, the wall normal direction to the end wall, and with respect to the other directional components, for example the radial and the circumferential directional component, at the position of the hot stagnation point. In the case of multiple stagnation points, several cooling nozzles or groups of cooling nozzles can be positioned according to the respective, allocated stagnation point.

[0025] In particular, it is preferably provided that the cooling nozzle is designed in such a way that during operation (at least in all essential, steady-state operating points) a cold stagnation point flow flowing in the direction of the stagnation point (especially in counterflow to the hot stagnation point flow) can be generated or is generated in such a way that, on the one hand, an outflow of the combustion products into and / or through the cooling nozzle is prevented and, on the other hand, the recirculation zone for stabilizing the combustion zone is maintained. The recirculation zone should remain largely unaffected by the generated flow of the cooling medium, wherein, for example, the cooling medium does not enter the combustion chamber as a jet beyond the stagnation point and dissolve the recirculation zone. In particular, the cooling medium opening is dimensioned and / or shaped accordingly, wherein a (suitable) mass flow of cooling medium achieving this effect flows through the cooling channel with the cooling medium opening. The cold stagnation point flow preferably shifts the stagnation point in the wall normal direction and / or axial direction, starting from the combustion chamber wall, in particular the end wall, further into the combustion chamber than in a design without a cooling nozzle. At the stagnation point or between the stagnation point and the combustion chamber wall, the cooling medium flows radially outwards along the combustion chamber wall (with respect to the stagnation point), forming a shielding, cooling fluid layer. In this way, counterflow wall cooling is provided, which achieves an effective cooling effect on the combustion chamber wall.

[0026] For effective cooling without dissolving the recirculation zone, the cooling nozzle can, for example, be designed such that the height (as the distance of the stagnation point in the direction of the axis of the stagnation point flow, in particular in the wall normal direction and / or axial direction) of the stagnation point from the cooling medium opening is at most half, preferably at most one third or one quarter of the axial distance (in particular in the same direction) of a vortex center of the recirculation zone from the combustion chamber wall, in particular the end wall.

[0027] In a suitable embodiment, the cooling nozzle can be in flow contact with a distributor side of the burner system for oxidizer (in particular an oxidizer plenum) arranged upstream of the combustion chamber, wherein in operation the cooling medium is formed by a portion of the oxidizer supplied to the combustion chamber from the distributor side. For example, the cooling nozzle is designed as, for example, a straight flow channel between an oxidizer plenum and the combustion chamber. The flow channel can, for example, be aligned at least partially orthogonally to the combustion chamber wall.

[0028] In a simple and robust design, the proportion of the oxidizer supplied as a cooling medium during operation to the oxidizer supplied via at least one supply nozzle (and / or from the distribution chamber) can be passively determined. “Passive” here means without active control elements, via fluid-mechanical design to obtain a suitable split (division) of the oxidizer starting from the distributor side. The fluid-mechanical design includes in particular the design of a corresponding ratio of the flow cross-sections of the cooling nozzle to the (total) flow cross-section of the at least one supply nozzle.

[0029] In this context in particular, it may be provided that the cooling nozzle is designed such that the proportion of the oxidizer supplied as a cooling medium during operation to the oxidizer supplied via the at least one supply nozzle is a maximum of 10%, preferably a maximum of 5% or 2%.

[0030] In a suitable embodiment, it can be provided that a group of cooling nozzles with their respective cooling media openings are arranged opposite the stagnation point, wherein in particular at least one, preferably a cooling media opening of a middle cooling nozzle, is arranged opposite the stagnation point. The cooling nozzles within the group are preferably arranged symmetrically to each other with respect to the stagnation point. The cooling nozzles can be identical or different, for example, and / or have a maximum distance (from edge to edge) of one flow diameter (or an equivalent dimension) between the cooling nozzles.

[0031] Advantageously, the end wall may be aligned orthogonally to the longitudinal axis and / or the at least one supply nozzle, preferably all present ones, and / or the at least one cooling nozzle, preferably all present ones, is / are aligned parallel to the longitudinal axis.

[0032] The cooling concept according to the invention can be used particularly advantageously if the burner system is designed for operation based on a jet-stabilized combustion concept (in the manner of a recirculation-stabilized jet flame burner), wherein the fresh gases are introduced into the combustion chamber at least substantially without swirl and a combustion zone in the combustion chamber is stabilized by the stationary, large-scale, combustion chamber-internal recirculation zone of the hot combustion products, which forms in the combustion chamber due to the introduction of the fresh gases with a sufficiently high axial impulse, in particular by means of a supply velocity of the fresh gases of at least 60 m / s or at least 80 m / s, and for example up to a maximum of 220 m / s or more. “At least substantially without swirl” means that preferably no circumferential swirl is imposed on the fresh gas flow, or, despite a possible slight circumferential swirl, the stabilization of the combustion due to the axial impulse is achieved by means of the large-scale recirculation zone, not by means of local radial recirculation in the area of the nozzle cross-section.

[0033] Preferably, several supply nozzles are provided, wherein the supply nozzles are arranged on at least one, in particular circular, nozzle ring and / or (matrix-like) in a row arrangement with at least two (with respect to a center line), e.g., nozzle rows opposite each other on the end wall. In the opposing rows of nozzles, the nozzles are not offset from each other, but rather arranged opposite each other.

[0034] A continuously circulating supply nozzle may also be present if it creates a large-scale recirculation zone with a stagnation point flow and a stagnation point.

[0035] Other burner systems are also possible, including those with swirl stabilization, in which two opposing or one large-scale (toroidal) recirculation zone(s) of hot combustion products are formed between spatially separated flames or in the inner region of a single, ring-shaped flame, the stagnation point of which is not positioned opposite a fresh gas supply opening.

[0036] In the method for operating a burner system, in particular according to one of the preceding embodiments, the combustion process is stabilized by means of a, in particular large-scale, recirculation zone of hot combustion products with a hot stagnation point flow within a combustion chamber, wherein a cooling medium is added to the combustion chamber through a combustion chamber wall, in particular through an inlet-side end wall, by means of a cooling nozzle coaxial to the hot stagnation point flow, in particular in the wall normal direction, in particular in the wall normal direction and / or in particular parallel or coaxial to a longitudinal axis of the combustion chamber.

[0037] In the method for manufacturing a burner system, in particular according to one of the preceding embodiments, a cooling system for cooling at least a part of a combustion chamber wall, in particular an end wall, is implemented, wherein at least one cooling nozzle for adding a cooling medium to a combustion chamber is introduced coaxially to a hot stagnation point flow of a, in particular large-scale, recirculation zone of hot combustion products stabilizing the combustion process at a suitable position of a combustion chamber wall, in particular an end wall, wherein the cooling nozzle is designed for adding a suitable mass flow of cooling medium. The cooling with the cooling nozzle is designed accordingly. The burner system is manufactured according to design criteria determined in a design procedure.

[0038] In the design process, key aspects include the identification of a suitable position for the cooling nozzle and the estimation of the appropriate mass flow rate of cooling medium to be introduced. These are determined during the design of the burner system, e.g., taking into account the resulting flow conditions within the combustion chamber of the burner system in question without an existing cooling nozzle and / or without introduced cooling medium, e.g., experimentally and / or by means of numerical flow simulation (computer-aided).

[0039] First, the position of the hot stagnation point on the relevant burner system without a cooling nozzle is identified. The cooling nozzle is then placed at a location on the combustion chamber wall on the same axis as the stagnation point flow, in particular in the wall normal direction, e.g., the axial direction, opposite the stagnation point (i.e., offset in the wall normal direction and / or axial direction, preferably in the same position with respect to the other directional components) and is designed in particular with regard to the flow cross-section to maintain the appropriate mass flow rate during operation.

[0040] It has proven particularly advantageous to use potential theory in the design process to estimate the required mass flow rate of cooling medium.

[0041] The stagnation point flow directed towards the end wall, consisting of the hot combustion products, is exemplified as an axis-symmetric stagnation point flow with the velocity potentialΦstag=a2⁢(r2-2⁢z2)

[0042] and the cooling medium opening with the introduction of the cooling medium is approximated as a point source with theΦsource=-m4⁢π⁢1r2+z2

[0043] velocity potential. This is r the radial distance to the cooling medium opening, z is the distance to the end face in the wall normal direction, a is the strength of the axis-symmetric stagnation point flow with the unit s−1 and m is the volume flow emanating from the point source.

[0044] The superimposed velocity potential results inΦtotal=Φstag+Φsource=a2⁢(r2-2⁢z2)-m4⁢π⁢1r2+z2.

[0045] The components of the velocity field in cylindrical coordinates are thus given byur=∂Φtotal∂r=ar+m4⁢π⁢r(r2+z2)3 / 2′uθ=∂Φtotal∂r=0uz⁢∂Φtotal∂r=-2⁢az+m4⁢π⁢z(r2+z2)3 / 2.

[0046] At the stagnation point in the embodiment shown in FIG. 2,uz(r=0,z=h)=0=-2⁢ah+m4⁢π⁢h2′⁢ applies,

[0047] which results in a distance between the stagnation point and the end wallh=(m8⁢π⁢a)1 / 3

[0048] h. Furthermore, the volume flow exiting the cooling nozzle {dot over (V)}. e.g., as half of the volume flow originating from the point source approximated byV.=m2=π⁢rjet2⁢Ujet,

[0049] where rjet denotes the radius of the cooling nozzle and Ujet denotes the exit velocity of the cooling medium from the cooling nozzle. The reason for considering half the volume flow rate of the point source is that only a portion, for example half, of the volume flow rate flows into the combustion chamber. At the stagnation point itself, there is an equilibrium of dynamic pressureρstag⁢Ustag 2=ρjet⁢Ujet2,

[0050] wherein ρjet and ρstag describe the densities of the cooling medium and the hot combustion products in the hot stagnation point flow in the recirculation zone as well as Ustag represents a virtual release velocity of the hot stagnation point flow caused by the recirculation zone. ItUstag=Ujet⁢ρjetρstag

[0051] follows that, given a density difference between the hot combustion products and the cooling medium, the height h remains unchanged if the density ratio is taken into account when considering the exit velocity of the cooling medium. The result ish=(ρjetρstag⁢rjet2⁢Ujet4⁢a)1 / 3.

[0052] In the above exemplary derivation, a single central cooling nozzle was assumed, through which the mass flow of cooling medium flows from the imagined point source into the combustion chamber.

[0053] For example, in the group of n Identical cooling nozzles with, for example, the same effective flow cross-section result in the height h toh=(ρjetρstag⁢nrjet2⁢Ujet4⁢a)1 / 3.

[0054] Starting from the initial estimate using potential theory, a further iteration of the geometry, e.g., of the cooling nozzle, can be carried out experimentally and / or in a numerical flow simulation to obtain the final design of the burner system.

[0055] Advantageous design variants of the method for operating and / or the method for manufacturing the burner system are also specified in connection with the burner system.

Claims

1. A burner system (1), in particular for use in a gas turbine, with a combustion chamber (3) aligned along a longitudinal axis (L) and a combustion chamber wall (4) comprising an end wall (6) arranged on the inlet side of the combustion chamber (3), and with at least one supply nozzle (10) opening into the combustion chamber (3) via the end wall (6) for adding fresh gases (8), fuel and / or oxidizer to the combustion chamber (3), wherein the burner system (1) is designed such that, during operation, a recirculation zone (5) of hot combustion products (20) with a hot stagnation point flow (26), in particular a large-scale recirculation zone (5), forms within the combustion chamber (3) to stabilize the combustion process, comprising a stagnation point (28) opposite the combustion chamber wall (4), in particular the end wall (6),characterized in thatthat in the combustion chamber wall (4), in particular the end wall (6), opposite the position of the recirculation zone (5) during operation, at least one cooling nozzle (14) with a cooling medium opening (16) arranged at its downstream end is formed, by means of which cooling medium (18) can be supplied or supplied to the combustion chamber (3) during operation for cooling the combustion chamber wall (4), in particular the end wall (6), wherein the cooling nozzle (14) is designed to generate a flow of cooling medium (18) that is aligned coaxially with the hot stagnation point flow (26).

2. The burner system (1) according to claim 1,characterized in thatthat the cooling nozzle (14) is positioned such that the cooling medium opening (16) is located opposite the stagnation point (28) that forms during operation.

3. The burner system (1) according to claim 1,characterized in thatthat the cooling nozzle (14) is designed in such a way that, during operation, a cold stagnation point flow (30) flowing in the direction of the stagnation point (28) can be generated or is generated in such a way that, on the one hand, an outflow of the combustion products (20) into and / or through the cooling nozzle (14) is prevented and, on the other hand, the recirculation zone (5) is maintained for stabilization.

4. The burner system (1) according to claim 3,characterized in thatthat the cooling nozzle (14) is designed such that the height (h) of the stagnation point (28) from the cooling media opening (16) is at most half, preferably at most one third or one quarter of the axial distance of a vortex center (35) of the recirculation zone (5) from the combustion chamber wall (4), in particular the end wall (6).

5. The burner system (1) according to claim 1,characterized in thatthat the cooling nozzle (14) is in flow contact with a distributor side (2) of the burner system (1) arranged upstream of the combustion chamber (3), wherein in operation the cooling medium (18) is formed by a portion of the oxidizer supplied to the combustion chamber (3) from the distributor side (2).

6. The burner system (1) according to claim 5,characterized in thatthat the proportion of the oxidizer supplied as cooling medium (18) during operation to the oxidizer supplied via the at least one supply nozzle (10) is passively determined.

7. The burner system (1) according to claim 5,characterized in thatthat the cooling nozzle (14) is designed such that the proportion of the oxidizer supplied as cooling medium (18) during operation to the oxidizer supplied via the at least one supply nozzle (10) is a maximum of 10%, preferably a maximum of 5% or 2%.

8. The burner system (1) according to claim 2,characterized in thatthat a group of cooling nozzles (14, 14.1, 14.2) with their respective cooling medium openings (16, 16.1, 16.2) is arranged opposite the stagnation point (28), wherein the cooling nozzles (14, 14.1, 14.2) are, e.g., identically designed and / or have a maximum distance of one flow diameter of the cooling nozzles (14, 14.1, 14.2) from each other.

9. The burner system (1) according to claim 1,characterized in thatthat the end wall (6) is aligned orthogonally to the longitudinal axis (L) and / or that the at least one supply nozzle (10) and / or the at least one cooling nozzle (14) is / are aligned parallel to the longitudinal axis (L).

10. The burner system (1) according to claim 1,characterized in thatthat the burner system (1) is designed for operation based on a jet-stabilized combustion concept, wherein the fresh gases (8) are introduced into the combustion chamber (3) at least substantially without swirl and a combustion zone (24) in the combustion chamber (3) is stabilized by the stationary, large-scale, combustion chamber-internal recirculation zone (5) of the hot combustion products (20), which is formed in the combustion chamber (3) due to the introduction of the fresh gases (8) with a sufficiently high axial impulse, in particular by means of a supply velocity of the fresh gases (8) of at least 60 m / s.

11. The burner system (1) according to claim 1,characterized in thatthat several supply nozzles (10) are present, wherein the supply nozzles (10) are arranged on at least one, in particular circular, nozzle ring (42) and / or in a row arrangement with at least two opposing nozzle rows (44.1, 44.2) on the end wall (6).

12. A method for operating a burner system (10), in particular according to claim 1, in which the combustion process is stabilized by means of a, in particular large-scale, recirculation zone (5) of hot combustion products (20) with a hot stagnation point flow (26) within a combustion chamber (3), wherein a cooling medium (18) is added to the combustion chamber (3) coaxially to the hot stagnation point flow (26), in particular in the wall normal direction, by means of a cooling nozzle (14) through a combustion chamber wall (3), in particular through an inlet-side end wall (6).

13. A method for manufacturing a burner system (1), in particular according to claim 1, in which a cooling system for cooling at least a part of a combustion chamber wall (3), in particular an end wall (6), is implemented, wherein at least one cooling nozzle (14) for adding cooling medium (18) into a combustion chamber (3) is introduced coaxially to a hot stagnation point flow (26) of a, in particular large-scale, recirculation zone (5) stabilizing the combustion process from hot combustion products (20) at a suitable position of a combustion chamber wall (4), in particular at an end wall (6), wherein the cooling nozzle (14) is designed for adding a suitable mass flow of cooling medium (18).

14. The method according to claim 13,characterized in thatthat the cooling system with the at least one cooling nozzle (14) and the mass flow of the cooling medium (18) is such that it is matched to a hot stagnation point flow (26) of a recirculation zone (5) formed in the combustion chamber (3) in such a way that, during operation, a cold stagnation point flow (30) flowing in the direction of the stagnation point (28) of the hot stagnation point flow (26) is generated in such a way that, on the one hand, an outflow of combustion products (20) into and / or through the cooling nozzle (14) is prevented and, on the other hand, the recirculation zone (5) is maintained in a stabilizing manner.

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