Abstract
The invention refers to a method and a device for flame stabilization in a burner system of a stationary combustion engine, preferably a stationary gas turbine, in which a flow of an air/fuel mixture is produced and being swirled to form a vortex flow to which a swirl number is assignable before entering a combustion zone in which the vortex flow of the air/fuel mixture is ignited to form a flame within a reverse flow zone caused by vortex breakdown. The swirl number perturbation driven by thermoacoustic oscillation inside the burner system is controlled by affecting the vortex flow actively before entering the combustion zone on basis of changing a flame transfer function assigned to the burner system with the proviso of minimizing pulsation amplitudes of the flame transfer function.
Claims
1. A method for flame stabilization in a burner system of a stationary combustion engine, the method comprising: producing a flow of an air/fuel mixture; swirling the flow to form a vortex flow to which a swirl number is assignable before the vortex flow enters a combustion zone; igniting the vortex flow of the air/fuel mixture to form a flame within a reverse flow zone caused by vortex breakdown; and controlling a swirl number perturbation driven by thermoacoustic oscillation inside the burner system by affecting the vortex flow actively before the flow enters the combustion zone on basis of changing a flame transfer function assigned to the burner system with a proviso of reducing pulsation amplitudes of the flame transfer function, wherein the pulsation amplitudes are associated with a change in amplitude of flame oscillation, wherein actively affecting the vortex flow includes harmonically modulating a shape or position of a swirler by frictionless magnetic levitation using an electromagnetic field acting on the swirler.
2. The method according to claim 1, wherein swirling of the flow of air/fuel mixture takes place within the swirler having a swirler inlet and a swirler exit, and actively affecting the vortex flow is performed at the exit of the swirler by influencing flow dynamics of the vortex flow.
3. The method according to claim 1, wherein actively affecting the vortex flow is performed by embossing a velocity fluctuation characterized by phase and amplitude on said vortex flow such that the phase of the velocity fluctuation is altered to the phase of the flame transfer function at least at one frequency position on which an amplitude maximum of the flame transfer function occurs.
4. The method according to claim 2, wherein embossing a velocity fluctuation on said vortex flow is carried out by influencing amplitude and phase of a tangential velocity perturbation of the vortex flow at the swirler exit.
5. The method according to claim 1, wherein actively affecting the vortex flow is performed in an open-loop based on information determined during commissioning of the burner system.
6. The method according to claim 1, wherein actively affecting the vortex flow is performed in a closed-loop based on information measured sensorial based on pressure prevailing in the combustion zone.
7. The method according to claim 1, wherein a modulated injection of at least one separate fluid flow is realized by injecting at least one flow of air, flow of fuel and/or flow an air/fuel mixture into the vortex flow by a controllable fluidic device or rotating valve.
8. The method according to claim 1, wherein a modulated injection of at least one separate fluid flow is realized by injecting of a flow of combustions products into the vortex flow by harmonically ignition of an ignitable flow of reactants.
9. The method according to claim 1, wherein altering a flow velocity of the vortex flow in the vicinity of swirler contour surfaces is realized by inducing a fluid flow by dielectric barrier discharge at least in an area along the swirler contour surfaces.
10. The method according to claim 2, wherein actively affecting the vortex flow further includes controlling the vortex flow being released from the swirler by modulated injection of at least one separate fluid flow into the vortex flow.
11. The method according to claim 2, wherein actively affecting the vortex flow further includes controlling the vortex flow being released from the swirler by modulated altering of flow velocity of the vortex flow in the vicinity of swirler contour surfaces.
Description
BRIEF DESCRIPTION OF THE FIGURES
(1) The invention shall subsequently be explained in more detail based on exemplary embodiments in conjunction with the drawings. In the drawings
(2) FIG. 1a schematic burner system for operating a stationary gas turbine which comprise a premix burner with a actively controlled means for affecting the vortex flow perturbation
(3) FIG. 1b diagram illustrating the effect on FTF amplitude of altering the phase of swirl number perturbation at swirler exit,
(4) FIG. 2 cross sectional view through a swirler vane providing flow openings at the pressure side and suction side for harmonic modulation of flow between pressure and suction side,
(5) FIG. 3a, b embodiments for modulation of active control flow rate between pressure and suction sides of a swirler vane,
(6) FIG. 4 rotating valve for modulation of active control flow rate between pressure and suction side of a swirler vane,
(7) FIG. 5a,b,c schematic cross section of means for flow separation for redirection of main flow via trailing edge jets,
(8) FIG. 6a, b illustration of an active control of flow separation via dielectric barrier discharge,
(9) FIG. 7a, b, c illustration of piezoelectric and hot plasma generators arranged in the region of the trailing edge of a swirler vane,
(10) FIG. 8 schematic cross sectional view through a conical shapes premix burner providing means for dynamically modulating flow passage area and
(11) FIG. 9a, b schematic view of sections of flow bodies of a radial swirler providing dynamically modulated flow passage area.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
(12) FIG. 1a shows a schematic burner system preferably for operating a stationary gas turbine which comprise a premix burner 4 into which an air flow 5 and a fuel flow 6 is directed in which both flows are mixed for providing a homogenous air-fuel mixture. Said flow of air/fuel mixture will be swirled in case of a conically shaped premix burner by the premix burner 4 itself and/or by an additional swirler 7 providing a swirler inlet 7.1 and swirler outlet 7.2. Typically downstream the swirler 7 a mixing tube 8 is arranged along which the vortex flow 9 establishes before the vortex flow breaks 9 down by entering the combustor 10 forming a central revers flow zone CRZ in which the flame will occur. FTF which was already discussed in combination with FIG. 1b depends on the distance L between the swirler 7 and CRZ as well on the bulk velocity U of the vortex flow 9 along the mixing tube 8.
(13) For affecting the vortex flow 9 actively before entering the combustor 10 the swirler provides means, preferably at the swirler exit 7.2, in which said means change the FTF assigned to the burner system with a proviso of minimizing pulsation amplitudes of the flame transfer function. Hereto a control unit C controls the means 11 actively either on basis of stored information and/or on basis of currently measured operation values of the burner system, preferably on basis of sensor signals of a pressure sensor S inside the combustor 10.
(14) In FIG. 2 one embodiment of the means for affecting the vortex flow actively is illustrated. In case of FIG. 2 the swirler 7 is an axial swirler providing swirler vanes 12 being arranged circumferentially around an axis of rotation R. Said arrangement of swirler vanes 12 are positioned contactless within an electromagnetic arrangement 13 providing electromagnetic poles 14 which are activated such that the electromagnetic field between the electromagnetic poles 14 interacts with the arrangement of swirler vanes 12 such that the swirler vanes 12 may swing periodically clockwise and counter clockwise within an angle range given by +−Θ.sub.max. The amount of the angle range and the frequency of the rotatory back and force motion is tuned such to reach a significant reduction of the amplitude of the FTF.
(15) FIG. 3 shows a cross sectional view of a swirler vane 12 providing a trailing edge 15. Inside the swirler vane 12 in the region of the trailing edge 15 two separate chambers 16.1 and 16.2 are provided. Chamber 16.1 provides at least one flow opening 16.11 directed to the suction side of the swirl vane 12 and chamber 16.2 provides at least one flow opening 16.22 at the pressure side of the swirler vane. Preferably both chambers provide a multitude of openings being distributed at least in portions along the axial extension of the swirler vane 12.
(16) Both chambers 16.1 and 16.2 are pressurized with a fluid, for example air, fuel or an air-fuel mixture which can be emitted through the chamber openings 16.11, 16.22 under control. Both flow directions are directed more or less perpendicularly to the main vortex flow 9 which passes through the swirler 7. The impact of the additional fluid flow emitted through the chamber openings 16.11, 16.22 onto the vortex flow 9 affects the tangential velocity perturbation significantly. In a preferred way the fluid flows which are emitted through the chamber openings 16.11, 16.22 are tuned to each other such that the sum total of the fluid flow emitted through all chamber openings is constant. The fluid flow towards the pressure side and also towards the suction side of the swirler vane 12 is harmonically modulated under the proviso that the impact onto the vortex flow 9 associated herewith leads to a velocity fluctuation of the vortex flow 9 so that the phase of the velocity fluctuation of the vortex flow 9 is inverted to the phase of the FTF at least at one phase position on which an amplitude maximum of the FTF occurs.
(17) The harmonically modulation of the fluid flows from each chamber 16.1, 16.2 through the chamber openings into the vortex flow can be realized by a rotating valve 17 which is illustrated in FIG. 4 providing a pressurized flow chamber 17.1, in which a hole aperture 17.2 is arranged rotatable for opening one of two outlet ports 17.3, 17.4 alternately.
(18) FIG. 3b shows a schematic cross section of a swirler vane 12 which encloses a fluid chamber 12.1 which opens along a slit 18 at the trailing edge 15. Through the slit 18 pressurized fluid emerges in form of a main flow 19 which is not deviated normally. At the trailing edge 15 two opposite actuators 20.1 and 20.2 are arranged which have influence on the dynamics of the main flow 19 when being activated by the control unit. The actuators 20.1 and 20.2 being activated harmonically such that the main flow 19 will deviate towards the suction side or towards the pressure side of the swirler vane 12. The amount and the dynamics of the harmonically modulation of the main flow 19 leads to an impact onto the vortex flow 9 in a way described before with the proviso of minimizing pulsation amplitudes of the flame transfer function.
(19) FIG. 5a shows one example for affecting the flow rate of a main stream 19 emitting straight of the trailing edge of a swirler vane 12. Starting from a pressurized fluid chamber 21 providing one outlet port 22 which divides into two separate flow channels 23.1, 23.2, the amount of fluid flow through each of the flow channels 23.1 and 23.2 can be controlled by a little control flow 24 which enters the outlet port 22 perpendicularly to the flow direction either from above or below or both. In case of a control flow from the upper side, the main stream 19 will follow the below outlet port 23.2, as shown in FIG. 5a. This mechanism is also known as Coanda effect. On basis of the Coanda effect fluidic devices 20.1, 20.2 shown in FIG. 3b can be realized.
(20) An alternative fluidic device for modulation of active control of flow rate is illustrated in FIG. 5b. Here a cross sectional view of a swirler vane 12 is shown. Within the swirler vane 12 a pressurized fluid chamber 21 is provided having an outlet port 22 which divides into three different flow channels 23.1, 23.2 and 23.3. Further a control flow device 24 is arranged in the region of the outlet port 22. In case of an inactivated control flow device 24 the main flow will leave via flow channel 23.3 which opens at the trailing edge 15 of the swirler vane 12. Depending on activation of the control flow device 24 the flow shares which flow through the individual flow channels 23.1, 23.2, 23.3 can be set individually. The control flow device 24 can be realized by a pressure device or by a plasma or piezoelectric device which generates a pulsed jet as will be described in more detail below.
(21) FIG. 5c shows an embodiment of flow affection onto a primary flow 19 emerging out of an outlet opening 16.11 or 16.22 like in case of embodiment shown in FIG. 3a. An actuator 20.1/20.2 generates a synthetic jet which influences the propagation performance of the main flow 19. In case of jet generation the flow resistance in the region of the jet rises due to local turbulences so that the main stream 19 is deflected in direction of the jet, see FIG. 5c.
(22) FIG. 6a shows a dielectric barrier discharge device DBD which can be positioned onto the swirler vane 12 in the region of the trailing edge 15 to influence the vortex flow 9 which passes over each swirler vane 12, see FIG. 6b. The DBD provides a first electrode e1 placed onto the surface of the swirler vane 12 being in contact with the main flow 9. A second electrode e2 is buried into the vane 12 and being separated from the first electrode e1 by a dielectric material d. In case of activating the DBD high voltage HV is applied between both electrodes e1, e2 so that plasma is generated which induces via a drag effect an additional velocity into the main flow main 9. In case of activation of the DBD the main flow 9 separates from the surface of the swirler vane 12 near the trailing edge 15 due to formation of an additional swirl effect s. Depending on the activation of the DBD the main flow 9 can be modulated harmonically between separation of the main flow 9 from the vane's surface and re-attachment to it.
(23) FIG. 7a, b, c illustrates a further alternative of a flow device acting onto the vortex flow directly or acting as a flow separator onto a main flow 19 as it is illustrated for example in FIG. 3a.
(24) Concerning FIG. 7a it is assumed that directly below a surface of a swirler vane 12 at least one closed chamber 24 is provided having an outlet opening 25 at the surface of the swirler vane 12 near the trailing edge. A metal disc 26 is attached opposite to the outlet opening 25 as a part of the chamber wall. The metal disc 26 is driven by a piezoelectric driver (not shown) so that the metal disc 26 can be deflected in direction towards the outlet opening 25 and in opposite direction. By actuating the piezoelectric driver jet pulses 28 emits through the outlet opening 25 having an impact of the vortex flow.
(25) FIG. 7b shows an alternative device which also provides a closed chamber 24 beneath the surface of a swirler vane 12 in which a plasma generation device 29 is arranged. In case of activating the plasma generator, see stage 1, jet pulses 28 emits through the outlet opening 25 into the area of the vortex flow, see stage 2. Due to pressure equalization a revers flow takes place after the discharge step shown in stage 3. The devices shown in FIGS. 7a and b can be arranged along the trailing edge 15 of the swirler vane 12 distributed axially along the trailing edge 15 as shown in FIG. 7c.
(26) FIG. 8 discloses a part view of a radial swirler in which two flow bodies 30 are shown bordering a flow channel 31 in between. The swirler effect onto the main stream 19 which flows between two neighbouring flow bodies 30 depends on the width w the length l and the orientation of the body flanks relative to the main flow direction. For affecting purposes onto the flow performance of the vortex flow which exits the radial swirler means 32 for affecting the vortex flow 19 are arranged at least at one of the flow bodies 30 along the flow channel 31. The means 32 of affecting the vortex flow influences the flow dynamics of the flow through each flow channel 31. For example by providing a synthetic jet generator, such as a piezoelectric driver unit as explained in FIG. 7a or a plasma generator as explained in FIG. 7b a dynamical impact can be performed onto the main flow 19 passing through the flow channel 31. In fact by activating such means 32 of affecting the vortex flow dynamically modulating the flow passage area between the two neighbouring flow bodies 30 along the flow channel 31 can be realized.
(27) Alternative or in combination with the synthetic jet generators in form of a piezoelectric driver or hot gas plasma generator a dielectric barrier discharge unit as described in FIG. 6 can be applied onto the surface of the swirler body of a radial swirler unit shown in FIG. 8. Also it is possible to provide outlet openings through which a fluid flow can be injected into the flow channel 31 as described in combination with the embodiment shown in FIG. 3a.
(28) FIG. 9a shows a cross section through a cone shaped premix burner providing four cone shaped shells 33 enclosing in pairs so called inlet slots 34 through which air and/or fuel and/or air/fuel mixture is injected into the conical burner space 35 in which a vortex flow establishes. FIG. 9b shows a detailed section of two neighbouring burner shells 33 bordering one inlet slot 34. One of the two burner shells 33 provides at its surface a means 32 for affecting the vortex flow. The means 32 influences the flow performance within the flow passage area along the inlet slots 34. Like described before the means 32 can be realized by synthetic jet generators or outlet opening for injecting a fluid flow into the inlet slots.
LIST OF REFERENCE NUMEROUS
(29) 1 flame transfer function FTF 2 modified flame transfer function 3 modified flame transfer function 4 premix burner 5 air flow 6 fuel flow 7 swirler 7.1 swirler entrance 7.2 swirler exit 8 mixing tube 9 vortex flow 10 flame, CRZ 11 means for affecting the vortex flow actively 12 swirler vane 13 electromagnetic arrangement 14 electromagnetic pulse 15 trailing edge 16.1, 16.2 Chamber 16.11, 16.22 opening 17 rating valve 17.1 flow chamber 17.2 outlet port 17.3 outlet port 18 slit 19 main flow 20.1, 20.2 actuators 21 pressurized fluid chamber 22 outlet port 23.1, 23.2, 23.3 flow channel 24 control flow device 25 outlet opening 26 metal disc 27 piezoelectric driver 28 jet pulses 29 plasma generator 30 flow body 31 flow channel 32 means for affecting the vortex flow 33 burner shell 34 inlet slot 35 conical burner space DBD Dielectric barriers discharge e1, e2 First and second electrode S Additional swirl D Dielectric material HV High voltage
