Sequential combustor arrangement with a mixer

1. A sequential combustor arrangement comprising:

a first burner, a first combustion chamber, a mixer for admixing a dilution gas to hotter gases leaving the first combustion chamber during operation, a second burner, and a second combustion chamber arranged sequentially in a fluid flow connection,

wherein the mixer is configured to guide combustion gases in a hot gas flow path extending between the first combustion chamber and the second burner,

wherein the mixer includes at least one injection opening for admixing the dilution gas to cool hot flue gases leaving the first combustion chamber, and

a damper for damping pressure pulsations inside the mixer having a damper wall which encloses a damper volume and a neck connecting the damper volume to the mixer;

an opening of the neck that opens to the hot gas flow path being spaced apart from the at least one injection opening such that a flow rate of the dilution gas passable into the mixer via the at least one injection opening is constant over time so that hot gas of the hot gas flow path is cooled to a predetermined temperature profile; and

a dilution gas feed connected to the at least one injection opening, wherein a ratio of a pressure loss coefficient of the dilution gas feed to a pressure loss coefficient of the at least one injection opening is smaller than a ratio of a pressure loss coefficient of a purge gas feed that is fed to the damper volume to a pressure loss coefficient of the neck.

2. The sequential combustion arrangement according to claim 1 , wherein one of:

a distance in flow direction of the hot gas along the hot gas flow path between the at least one injection opening and the opening of the neck to the hot gas flow path in a mixer wall of the mixer is less than three times a hydraulic diameter of the mixer at the opening of the neck; and

a distance between the at least one injection opening and the opening of the neck to the hot gas flow path in the mixer wall is less than the hydraulic diameter of the mixer at the opening of the neck.

3. The sequential combustion arrangement according to claim 2 , wherein the mixer wall of the mixer is enclosed by the damper wall forming a cooling duct for cooling the inlet section of the mixer between the upstream end of the mixer and a first injection opening of the at least one injection opening for admixing the dilution gas.

4. The sequential combustion arrangement of claim 2 , wherein the distance between the at least one injection opening and the opening of the neck to the hot gas flow path in the mixer wall is less than the hydraulic diameter of the mixer at the opening of the neck.

5. The sequential combustion arrangement according to claim 3 , wherein the neck extends from the damper wall through the cooling duct to the mixer wall.

6. The sequential combustion arrangement according to claim 5 , wherein a duct wall at least partly encloses the mixer wall delimiting a connecting duct for feeding dilution gas to the at least one injection opening.

7. The sequential combustion arrangement according to claim 5 , wherein the at least one injection opening comprises a plurality of injection openings and wherein the neck opens to the hot gas flow path between the injection openings or upstream of the injection openings in a hot gas flow direction.

8. The sequential combustion arrangement according to claim 1 , wherein the purge gas feed is positioned to supply the purge gas feed as cooling air to the damper volume.

9. The sequential combustion arrangement according to claim 1 , wherein the neck has a neck wall defining a neck volume inside the neck wall, wherein the neck is associated with the damper volume for fluid communication between the damper volume and the hot gas flow path in the mixer, and wherein the damper includes a gap between the neck wall and the damper wall.

10. The sequential combustion arrangement according to claim 1 , wherein the neck has a neck wall defining a neck volume inside the neck wall, wherein the neck is associated with the damper volume for fluid communication between the damper volume and the hot gas flow path in the mixer, and wherein the combustor arrangement includes a gap between the neck wall and the damper wall to avoid stresses at an interface between a wall of the mixer and the neck wall.

11. The sequential combustion arrangement according to claim 1 , wherein a flow capacity of a dilution gas flow path from a compressor plenum to the hot gas flow path in the mixer is at least two times larger than a flow capacity of a purge air flow path from the compressor plenum to the hot gas flow path in the mixer.

12. A gas turbine engine with at least one compressor, a combustor, and at least one turbine, wherein the gas turbine engine comprises: a sequential combustor arrangement according to claim 1 .

13. A method of operation of a gas turbine comprising the sequential combustor arrangement of claim 1 , the method comprising:

operating the mixer for admixing the dilution gas to hot gases leaving the first combustion chamber during operation, wherein the opening of the neck to the hot gas flow path is spaced apart from the at least one injection opening such that a distance in flow direction of the hot gas flow path between the at least one injection opening and the opening of the neck is one of: (i) less than three times a hydraulic diameter of the hot gas flow path at the opening of the neck, and (ii) is less than a hydraulic diameter of the mixer at the opening of the neck;

feeding the dilution gas into the mixer via the at least one injection opening such that a flow rate of the dilution gas passed into the mixer via the at least one injection opening is constant over time so that hot gas of the hot gas flow path is cooled to a predetermined temperature profile; and

affecting pulsation in the mixer via the damper such that a node of a pulsation wave of the pulsation is positioned adjacent the at least one injection opening by the opening of the neck of the damper, the pulsation in the mixer occurring during operation of the sequential combustor arrangement.

14. The method of operation of a gas turbine according to claim 13 , wherein an average velocity of the dilution gas in the at least one injection opening is at least twice as high as a time averaged flow velocity in the neck.

15. The method of operation of a gas turbine according to claim 13 , comprising:

feeding a purge gas of the purge gas feed to the damper, wherein a pressure drop over the purge gas feed connected to the neck is at least twice as large as a pressure drop over the neck.

16. A method of operation of a gas turbine comprising the sequential combustor arrangement of claim 1 , the method comprising:

operating the mixer for admixing the dilution gas to hot gases leaving the first combustion chamber;

using the damper for damping pressure pulsations inside the mixer during the operating of the mixer, such that a distance in flow direction of the hot gas flow path between the at least one injection opening and the opening of the neck facilitates formation of a node of a pulsation wave of a pulsation generated in the mixer during the operating of the mixer; and

feeding the dilution gas into the mixer via the at least one injection opening and performing the using of the damper so that the node of the pulsation wave is shifted toward the at least one injection opening and also has a reduced amplitude.

17. The method of claim 16 , wherein the distance that spaces apart the opening of the neck from the at least one injection opening of the mixer is one of: (i) less than three times a hydraulic diameter of the hot gas flow path at the opening of the neck, (ii) is less than a hydraulic diameter of the mixer at the opening of the neck, and (iii) is less than one sixth a wave length of the pulsation wave in the mixer.

18. The method of claim 16 , wherein there is a gap defined between a wall of the mixer and a wall of the neck to avoid stresses at an interface between the wall of the mixer and the neck.