Combustion chamber and burner for suppressing combustion oscillations

Abstract

The present invention relates to the field of energy and power technology, and provides a combustion chamber for suppressing combustion oscillation and a burner including the combustion chamber; the combustion chamber includes: a pre-combustion stage, a main combustion stage, a combustion chamber body and an anti-vibration ring; the pre-combustion stage includes a center body and a pre-combustion stage swirler and an interstage section arranged on the periphery of the center body; the main combustion stage is arranged on the periphery of the pre-combustion stage, and the main combustion stage includes a main combustion stage swirler and a main combustion stage outer ring; the combustion chamber body includes an end wall and a side wall, and the end wall connects the main combustion stage outer ring and the side wall; the anti-vibration ring is fixed to the inner surface of the end wall and / or the outlet end of the main combustion stage outer ring, and the anti-vibration ring forms a flame channel that is gradually expanded in the direction away from the main combustion stage. During operation, the flame will flow as close to the flame channel as possible, thereby reducing the pulsation of the heat release rate and finally suppressing the combustion oscillation; compared with the combustion chamber of the prior art, the combustion chamber described in the present invention has the advantages of low modification cost and wide application range.

Description

Technical Field

[0001] The present invention relates to the field of energy and power technology, and in particular to a combustion chamber and a burner for suppressing combustion oscillation. Background Art

[0002] The main way for humans to obtain energy and power is still the combustion of fossil fuels. In the relevant application equipment in the field of energy and power, combustion oscillation is a common technical challenge in various burners, which is widely present in boilers, gas water heaters, gas turbines and other combustion devices. Especially under increasingly stringent emission requirements, in order to reduce the emission of pollutants mainly composed of nitrogen oxides (NOx), advanced combustion devices now often adopt lean premixed combustion mode. The combustion device often works in a state close to flameout, which is very sensitive to external disturbances and easily affected by external disturbances, resulting in heat release rate pulsation. When the heat release rate pulsation is coupled with the acoustics of the combustion system (which can be simply understood as satisfying the Rayleigh criterion), it is easy to cause large heat release rate pulsation and pressure pulsation, which may affect the stable operation of the combustion device at the least, or cause structural damage to the combustion device or other components at the worst, and seriously threaten the operation safety of the entire system. Therefore, combustion oscillation is something that modern advanced combustion devices must try their best to avoid.

[0003] In order to solve the problem of combustion oscillation, a variety of methods have been proposed for controlling combustion oscillation, which can be mainly divided into two categories: active control and passive control. Active control is to use special monitors and active actuators to actively apply appropriate external excitations (such as inlet air or fuel supply) according to the pressure pulsation and other signals monitored in the combustion system, so as to suppress or eliminate the coupling between heat release rate pulsation and pressure oscillation (sound waves). However, this type of method requires additional control systems and actuators, and has high requirements for control algorithms, which will increase additional costs and have limited applicable scenarios. Passive control refers to the addition of certain fixed devices to the combustion system to suppress or eliminate combustion oscillations. Common types of acoustic components, such as Helmholtz resonators, can suppress combustion oscillations of specific frequencies. The disadvantage is that it is large in size and is only effective for specific frequencies, requiring a lot of experiments and debugging in advance. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a combustion chamber for suppressing combustion oscillation, so as to suppress the occurrence of combustion oscillation.

[0005] The invention also provides a burner.

[0006] A combustion chamber for suppressing combustion oscillation according to an embodiment of a first aspect of the present invention comprises:

[0007] A pre-combustion stage, the pre-combustion stage comprising a center body and a pre-combustion stage swirler and an interstage section arranged on the periphery of the center body;

[0008] A main combustion stage, the main combustion stage is arranged at the periphery of the pre-combustion stage, and the main combustion stage includes a main combustion stage swirler and a main combustion stage outer ring;

[0009] A combustion chamber body, comprising an end wall and a side wall, wherein the end wall connects the main combustion stage outer ring and the side wall;

[0010] An anti-vibration ring is fixed to the inner surface of the end wall of the end wall and / or the outer ring outlet end surface of the outer ring of the main combustion stage, and the anti-vibration ring forms a flame channel that gradually expands along the direction away from the main combustion stage, the inlet end of the flame channel is connected to the outlet end of the main combustion stage, and the outlet end of the flame channel is connected to the inner cavity of the combustion chamber body.

[0011] In the prior art, combustion oscillations are generally suppressed by processing the end wall or the side wall of the combustion chamber into a conical transition structure. The combustion chamber described in the present invention can achieve the same effect by installing the anti-vibration ring on the inner surface of the end wall and / or the outer ring outlet end face of the main combustion stage outer ring. Compared with the combustion chamber of the prior art, the combustion chamber described in the present invention has the advantages of low modification cost and a wide range of applications.

[0012] According to one embodiment of the present invention, the pre-combustion stage, the main combustion stage, the combustion chamber body and the anti-vibration ring are all coaxially arranged.

[0013] According to an embodiment of the present invention, a spoiler is formed on the inner wall of the anti-vibration ring.

[0014] According to one embodiment of the present invention, the spoiler comprises a plurality of steps distributed along the axis of the central body, or,

[0015] The spoiler comprises a plurality of annular spoiler grooves distributed along the axis of the central body, or,

[0016] The spoiler portion includes a longitudinal spoiler groove penetrating the inner wall along the axis direction of the central body, and the number of the longitudinal spoiler grooves is plural and distributed along the circumference of the inner wall.

[0017] According to an embodiment of the present invention, the cross section of the inlet end and the cross section of the outlet end are both circular, or the cross section of the inlet end and the cross section of the outlet end are both elliptical.

[0018] According to one embodiment of the present invention, the interstage section includes an interstage section outlet end face, the main combustion stage swirler includes a main combustion stage swirler outlet end face, and the interstage section outlet end face is staggered with the outer ring outlet end face.

[0019] According to one embodiment of the present invention, the outer ring outlet end surface and the end wall inner surface are coplanar.

[0020] According to one embodiment of the present invention, the spacing distance between the outlet end face of the main combustion stage swirler and the outlet end face of the interstage section along the axial direction of the center body is a first spacing; the spacing distance between the outlet end face of the main combustion stage swirler and the outlet end face of the outer ring along the axial direction of the center body is a second spacing, and the first spacing is greater than the second spacing.

[0021] According to one embodiment of the present invention, the spacing distance between the outlet end face of the main combustion stage swirler and the outlet end face of the interstage section along the axial direction of the center body is a first spacing; the spacing distance between the outlet end face of the main combustion stage swirler and the outlet end face of the outer ring along the axial direction of the center body is a second spacing, and the first spacing is smaller than the second spacing.

[0022] The burner according to the embodiment of the second aspect of the present invention comprises a combustion chamber for suppressing combustion oscillations as described in any of the above embodiments, and the burner is a swirl cup structure burner, a multi-swirl burner or a central staged burner.

[0023] The burner according to the embodiment of the present invention includes the above-mentioned combustion chamber and thus has all the technical effects of the above-mentioned combustion chamber, which will not be described in detail here.

[0024] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of a local structure of a combustion chamber for suppressing combustion oscillation provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of a partial structure of a spoiler provided by an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of a partial structure of another spoiler provided by an embodiment of the present invention;

[0029] Figure 4is a partial structural schematic diagram of another spoiler provided by an embodiment of the present invention;

[0030] Figure 5 is another schematic diagram of a local structure of a combustion chamber for suppressing combustion oscillations provided by an embodiment of the present invention;

[0031] Figure 6 It is a schematic diagram of a local structure of another combustion chamber for suppressing combustion oscillation provided by an embodiment of the present invention;

[0032] Reference numerals:

[0033] 1. Center body; 2. Pre-combustion stage swirler; 3. Interstage section; 4. Main combustion stage swirler; 5. Main combustion stage outer ring; 6. End wall; 7. Anti-vibration ring; 71. Flame channel; 711. Step; 712. Annular spoiler groove; 713. Longitudinal spoiler groove; 8. Side wall; 9. Main combustion stage flame; 10. Pre-combustion stage flame; 11. Outer ring outlet end face. DETAILED DESCRIPTION

[0034] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0035] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0036] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0037] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "above" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0039] An embodiment of the present invention provides a combustion chamber for suppressing combustion oscillations, such as Figure 1 As shown, the combustion chamber includes a pre-combustion stage, a main combustion stage, a combustion chamber body and an anti-vibration ring 7, the pre-combustion stage includes a center body 1 and a pre-combustion stage swirler 2 and an interstage section 3 arranged on the periphery of the center body 1; the main combustion stage is arranged on the periphery of the pre-combustion stage, and the main combustion stage includes a main combustion stage swirler 4 and a main combustion stage outer ring 5; the combustion chamber body includes an end wall 6 and a side wall 8, and the end wall 6 connects the main combustion stage outer ring 5 and the side wall 8; the anti-vibration ring 7 is fixed to the inner surface of the end wall 6 and / or the outlet end of the main combustion stage outer ring 5, and the anti-vibration ring 7 is formed with a flame channel 71 which is gradually expanded in the direction away from the main combustion stage, the inlet end of the flame channel 71 is connected to the outlet end of the main combustion stage, and the outlet end of the flame channel 71 is connected to the inner cavity of the combustion chamber body.

[0040] The anti-vibration ring 7 is formed with a flame channel 71 which gradually expands along the direction away from the main combustion stage. During operation, based on the Coanda effect, the unburned mixture of air and fuel entering the flame channel 71 will flow along the flame channel 71, so that the flame front will flow as close to the inner wall of the flame channel 71 as possible, thereby reducing the pulsation of the heat release rate, decoupling it from the acoustic system of the combustion system, and ultimately suppressing combustion oscillations.

[0041] In the prior art, combustion oscillations are generally suppressed by processing the end wall 6 or side wall 8 of the combustion chamber into a conical transition structure, while the combustion chamber of the present invention can achieve the same effect by only installing an anti-vibration ring 7 on the outer ring outlet end face 11 and / or the inner surface of the end wall; compared with the combustion chamber of the prior art, the combustion chamber of the present invention has the advantages of low modification cost and a wide range of applications.

[0042] According to one embodiment of the present invention, the anti-vibration ring 7 is connected to the end wall 6 and / or the main combustion stage outer ring 5 by integral processing, welding or fastener connection. Of course, the connection method between the anti-vibration ring 7 and the end wall 6 and / or the main combustion stage outer ring 5 is not limited to the examples given here.

[0043] According to one embodiment of the present invention, the vibration-proof ring 7 is a hollow cylinder, a hollow truncated cone or a hollow cubic structure.

[0044] According to another embodiment of the present invention, Figure 1 As shown, the anti-vibration ring 7 is similar in shape to the flame channel 71. The anti-vibration ring 7 is a hollow truncated cone structure and extends in a gradually expanding shape in the direction away from the main combustion stage. The anti-vibration ring 7 designed in this way can reduce its thickness to the limit while ensuring the structural strength and heat load, thereby reducing the weight of the combustion chamber.

[0045] According to one embodiment of the present invention, Figure 1 As shown, the pre-combustion stage, the main combustion stage, the combustion chamber body and the anti-vibration ring 7 are all coaxially arranged.

[0046] According to one embodiment of the present invention, the vibration-proof ring 7 extends along the axial direction of the central body 1. It is worth noting that the vibration-proof ring 7 can also extend in other directions, as long as a flame channel 71 that gradually expands in the direction away from the main combustion stage is formed in the vibration-proof ring 7.

[0047] According to one embodiment of the present invention, a spoiler is formed in the flame channel 71 .

[0048] The spoiler can change the flow trajectory of the flame front in the flame channel 71, further improving the effect of the vibration-proof ring 7 in suppressing combustion oscillation.

[0049] The spoiler includes one or more of a step 711 , an annular spoiler groove 712 and a longitudinal spoiler groove 713 . Of course, the structure of the spoiler is not limited to the examples given here, as long as the flow trajectory of the flame front in the flame channel 71 can be changed.

[0050] According to one embodiment of the present invention, Figure 2As shown, the spoiler includes a plurality of steps 711 distributed along the axis of the central body 1. Based on the Coanda effect, the flame front approaches the steps 711, and the steps 711 interfere with the normal flow of the flame.

[0051] According to another embodiment of the present invention, the length L1 of the step 711 parallel to the axial direction of the center body 1 is L0 / n; the length L2 of the step 711 perpendicular to the axial direction of the center body 1 is L0 / n / tanɑ; wherein L0 is the channel length formed by the flame channel 71 along the axial direction of the center body 1, and n is the number of steps 711.

[0052] According to another embodiment of the present invention, Figure 3 As shown, the spoiler includes a plurality of annular spoiler grooves 712 distributed along the axial direction of the central body 1. Based on the Coanda effect, the flame flows in a circle around the annular spoiler grooves 712.

[0053] According to another embodiment of the present invention, the width f and the height e of the annular spoiler groove 712 are both in the range of 2-10 mm.

[0054] According to another embodiment of the present invention, Figure 4 As shown, the spoiler includes a plurality of longitudinal spoiler grooves 713 penetrating the flame channel 71 along the axial direction of the central body 1, and the longitudinal spoiler grooves 713 are distributed along the circumference of the flame channel 71. Based on the Coanda effect, the flame is diverted by each longitudinal spoiler groove 713 at the inlet end of the flame channel 71.

[0055] According to another embodiment of the present invention, the depth of the longitudinal spoiler grooves 713 ranges from 2 to 10 mm, and the width of the longitudinal spoiler grooves 713 is S=2π / 2m, where m is the number of the longitudinal spoiler grooves 713 .

[0056] According to one embodiment of the present invention, the cross section of the inlet end of the flame channel 71 and the cross section of the outlet end of the flame channel 71 are both circular, or the cross section of the inlet end of the flame channel 71 and the cross section of the outlet end of the flame channel 71 are both elliptical. The cross section is circular or elliptical to satisfy the Coanda effect. Of course, the present invention is not limited to the above examples, for example, the shape of the flame channel 71 can also be: the cross section of the inlet end is circular, and the shape of the cross section of the outlet end is elliptical.

[0057] According to another embodiment of the present invention, when the cross section of the inlet end of the flame channel 71 is circular, the diameter of the cross section of the inlet end is 1-3 times the diameter D of the main combustion stage outlet end, and the angle α between the plane where the channel side wall of the flame channel 71 is located and the plane where the outer ring outlet end face 51 is located is in the range of 0-90°. The maximum channel length of the flame channel 71 is 3 times the diameter D of the main combustion stage outlet end.

[0058] When the cross section of the inlet end of the flame channel 71 is elliptical, the major axis dimension of the cross section of the inlet end is 1-3 times the diameter D of the main combustion stage outlet end, and the minor axis dimension of the cross section of the inlet end is 1-3 times the diameter D of the main combustion stage outlet end.

[0059] According to one embodiment of the present invention, Figure 5 As shown, when the vibration-proof ring 7 is fixed to the outlet end of the main combustion stage outer ring 5 and the inner surface of the end wall 6, the main changes are the angle α and the channel length L0. Different channel lengths L0 provide different attachment areas for the flame, thereby changing the flame morphology and suppressing the oscillation of the combustion chamber; at the same time, the change of the angle α, due to the Coanda effect, will cause the fluid to flow along the channel wall of the flame channel 71, thereby changing the physical expansion angle of the flow, and then changing the opening angle of the flame and the relative position of the main combustion stage flame 9, thereby achieving the ability to change the flame morphology and combustion chamber oscillation.

[0060] According to one embodiment of the present invention, Figure 6 As shown, the vibration-proof ring 7 is fixed to the inner surface of the end wall 6. The main variable is the difference L between the side wall at the inlet of the flame channel 71 and the inner side wall of the outer ring outlet end face 11. Different differences will lead to changes in the flame shape, such as Figure 6 As shown, when the difference L reaches a certain state, the main combustion stage flame 9 will have a double root state, which can play a beneficial role in the stability of the flame, thereby achieving the effect of suppressing oscillation. The pre-combustion stage flame 10 will generally be stabilized at two edge points of the interstage section 3 at the same time, and play a role in providing a high-temperature recirculation zone to keep the entire flame burning.

[0061] According to one embodiment of the present invention, the interstage section 3 includes an interstage section outlet end face, the main combustion stage swirler 4 includes a main combustion stage swirler outlet end face, the main combustion stage outer ring 5 includes an outer ring outlet end face 11, and the combustion chamber end wall 6 includes an end wall inner surface; the interstage section outlet end face and the outer ring outlet end face 11 are staggered.

[0062] The interstage outlet end face and the outer ring outlet end face 11 are staggered, which can change the starting position of the inner and outer shear layers of the swirl flow, thereby affecting the flame position in the inner cavity of the combustion chamber body and realizing the regulation of combustion oscillation.

[0063] According to one embodiment of the present invention, the outer ring outlet end surface 11 and the inner surface of the end wall are coplanar, so as to facilitate the installation of other equipment such as the vibration-proof ring 7 in the combustion chamber.

[0064] According to one embodiment of the present invention, the distance between the outlet end face of the main combustion stage swirler and the outlet end face of the interstage section along the axis of the center body 1 is the first distance; the distance between the outlet end face of the main combustion stage swirler and the outlet end face 11 of the outer ring along the axis of the center body 1 is the second distance, the first distance is greater than the second distance, the value of the first distance is S, and the distance between the outlet end face of the interstage section and the outlet end face 11 of the outer ring along the axis of the center body 1 is H, wherein S and H are both set values, and both can be taken in the corresponding interval, H / S≤1. Compared with the prior art, the length of the main combustion stage outer ring 5 designed in this way is shorter, so that the combustion chamber has a lighter weight while suppressing combustion oscillation.

[0065] According to another embodiment of the present invention, the first spacing is greater than the second spacing, and the value of the second spacing is S, H / S≤1.

[0066] According to another embodiment of the present invention, the first spacing is smaller than the second spacing, and a value of the first spacing is S, where H / S≤1.

[0067] According to another embodiment of the present invention, the first spacing is smaller than the second spacing, and the value of the second spacing is S, where H / S≤1.

[0068] Another embodiment of the present invention provides a burner, comprising a combustion chamber provided by any technical solution of the present invention.

[0069] According to one embodiment of the present invention, the burner includes but is not limited to a conventional swirl cup structure burner, a multi-swirl burner and a center-staged burner.

[0070] The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and should be covered within the scope of the claims of the present invention.

Claims

1. A combustion chamber for suppressing combustion oscillations, characterized in that: include: A pre-combustion stage, the pre-combustion stage comprising a center body (1) and a pre-combustion stage swirler (2) and an inter-stage section (3) arranged on the periphery of the center body (1); A main combustion stage, the main combustion stage being arranged at the periphery of the pre-combustion stage, the main combustion stage comprising a main combustion stage swirler (4) and a main combustion stage outer ring (5); A combustion chamber body, comprising an end wall (6) and a side wall (8), wherein the end wall (6) connects the main combustion stage outer ring (5) and the side wall (8); an anti-vibration ring (7), the anti-vibration ring (7) being fixed to the inner surface of the end wall of the end wall (6) and / or the outer ring outlet end surface (11) of the main combustion stage outer ring (5), and the anti-vibration ring (7) being formed with a flame channel (71) which is gradually expanded in a direction away from the main combustion stage, the inlet end of the flame channel (71) being butted against the outlet end of the main combustion stage, and the outlet end of the flame channel (71) being connected to the inner cavity of the combustion chamber body; The pre-combustion stage, the main combustion stage, the combustion chamber body and the anti-vibration ring (7) are all coaxially arranged; The inner wall of the anti-vibration ring (7) is formed with a spoiler; The spoiler comprises a plurality of steps (711) distributed along the axis direction of the central body (1), or, The spoiler portion comprises a plurality of annular spoiler grooves (712) distributed along the axis direction of the central body (1), or, The spoiler portion comprises a longitudinal spoiler groove (713) penetrating the inner wall along the axial direction of the central body (1); the longitudinal spoiler grooves (713) are multiple in number and distributed along the circumference of the inner wall.

2. The combustion chamber for suppressing combustion oscillation according to claim 1, characterized in that: The cross section of the inlet end and the cross section of the outlet end are both circular, or the cross section of the inlet end and the cross section of the outlet end are both elliptical.

3. The combustion chamber for suppressing combustion oscillation according to claim 2, characterized in that: The interstage section (3) comprises an interstage section outlet end face, the main combustion stage swirler (4) comprises a main combustion stage swirler outlet end face, and the interstage section outlet end face and the outer ring outlet end face (11) are arranged in a staggered manner.

4. The combustion chamber for suppressing combustion oscillation according to claim 3, characterized in that: The outer ring outlet end surface and the end wall inner surface are coplanar.

5. The combustion chamber for suppressing combustion oscillation according to claim 4, characterized in that: The distance between the outlet end face of the main combustion stage swirler and the outlet end face of the interstage section along the axial direction of the center body (1) is a first distance; the distance between the outlet end face of the main combustion stage swirler and the outlet end face of the outer ring (11) along the axial direction of the center body (1) is a second distance, and the first distance is greater than the second distance.

6. The combustion chamber for suppressing combustion oscillation according to claim 4, characterized in that: The distance between the outlet end face of the main combustion stage swirler and the outlet end face of the interstage section along the axial direction of the center body (1) is a first distance; the distance between the outlet end face of the main combustion stage swirler and the outlet end face of the outer ring (11) along the axial direction of the center body (1) is a second distance, and the first distance is smaller than the second distance.

7. A burner, characterized in that: The burner comprises a combustion chamber for suppressing combustion oscillations as described in any one of claims 1 to 6, and the burner is a swirl cup structure burner, a multi-swirl burner or a center-staged burner.

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