Patent Application
20180100650
This application claims priority to German Patent Application 102016219424.0 filed Oct. 6, 2016, the entirety of which is incorporated by reference herein.
The present invention relates to a combustion chamber arrangement, in particular to an aircraft gas turbine, as well as to a gas turbine with a combustion chamber arrangement.
Gas turbines with combustion chambers are known from the state of the art in different designs. The combustion chamber may for example be embodied in an annular manner with an inner and an outer combustion chamber wall. At the combustion chamber head, fuel is supplied by means of a plurality of fuel nozzles. Admixed air holes, which supply admixed air to the combustion chamber for a complete combustion of the fuel, are provided in the combustion chamber walls. Further, cooling air openings are provided in the combustion chamber walls, wherein in double-walled combustion chamber walls so-called impingement cooling holes are provided in the outer wall, and effusion cooling holes are provided in the inner wall of the double-walled combustion chamber wall. These cooling holes form a cooling air film to protect the combustion chamber walls from the hot combustion gases. As is for example known from US 2011/0048024 A1, the admixing air holes are arranged in a row along the circumference of the combustion chamber walls. At that, admixing air holes with a larger and a smaller diameter are arranged in an alternating manner. Further, cooling air holes are arranged in a second row along the circumference at a very small distance to the admixing air holes in the circumferential direction, in a manner offset with respect to the admixing air holes. With such combustion chambers, NOx emissions represent a problem area.
It is the objective of the present invention to provide a combustion chamber arrangement as well as a gas turbine that facilitates an improved admixture of air to a combustion chamber so as to significantly reduce the generation of NOx.
This objective is achieved through a combustion chamber arrangement with the features of claim 1 as well as a gas turbine with the features of claim 14. The subclaims respectively show preferred exemplary embodiments of the invention.
The combustion chamber arrangement of a gas turbine according to the invention with the features of claim 1 comprises an annular combustion chamber with an inner ring wall and an outer ring wall. Arranged at one end of the combustion chamber is a combustion chamber head with a plurality of fuel nozzles that introduce fuel into the combustion chamber. Further, a first admixed air row and a second admixed air row are provided. The first admixed air row comprises a plurality of first admixing air holes that are embodied as passage holes, wherein the first admixing air holes are arranged in the inner ring wall and/or the outer ring wall. The second admixed air row comprises a plurality of second admixing air holes that are also embodied as passage holes, which are also arranged in the inner ring wall and/or the outer ring wall. Admixed air is introduced into the combustion chamber via the admixing air holes of the first and second admixed air row. In order to significantly reduce NOx emissions during operation, the first and second admixing air holes are arranged in such a manner that the equation L=D2/D1*(D2−D1)/C2 is fulfilled. The first admixing air holes have first inner and first outer center points, and the second admixing air holes have second inner and second outer center points. Here, the inner center points are respectively located at a side of the admixing air holes that is oriented towards the combustion chamber. The inner center points thus form the piercing points of the respective central axes of the admixing air holes to the combustion space. The outer center points are located at a side of the admixing air holes that is facing away from the combustion chamber.
In the equation, L is a distance between the first and second inner center points and/or the first and second outer center points of the first and second admixing air holes. D1 is a first flow diameter of the first admixing air holes at an entry side and/or an exit side to the combustion chamber, and D2 is a second flow diameter of the second admixing air holes at the entry side and/or exit side to the combustion chamber. Further, the second flow diameter D2 is larger than the first flow diameter D1. Further, C is an average flow rate coefficient of the first and second admixing air holes. The average flow rate coefficient C of an admixing air hole is a measure for the effective stream tube through the admixing air hole and thus describes what portion of a cross sectional area of the admixing air hole is passed on average by a flow from the inflow side to the outflow side. Through this arrangement of the exit flow cross sections of the admixing air holes into the combustion space as well as of the distance L of the admixed air into the axial direction of the combustion chamber, significant improvements in the NOx emissions can be achieved. By observing this arrangement requirement for the admixing air holes, efficient leaning of the fuel-air mixture in the combustion chamber can be achieved, so that no areas with fuel, which have a negative impact on NOx emissions, are present in the combustion chamber. Through the targeted arrangement of the admixing air holes according to the above-described equation, steady leaning can be achieved in the axial direction through the combustion chamber. In this manner, in particular NOx emissions can be optimally reduced, and a complete combustion of the supplied fuel can be achieved.
The flow rate coefficient of an admixing hole represents a measure for the effective stream tube through the admixing hole, and thus describes which portion of the admixing hole cross-sectional surface is passed on average by the flow from the annulus to the flame tube. The mass flow (impulse flow) that is put through such an admixing hole depends on the applied driving pressure gradient across the admixing hole, on the form and shape of the admixing hole, and on the Reynolds and Mach number. What is understood here by the form and shape of an admixing hole is the average cross-sectional shape (e.g. circle, ellipse), the inlet geometry at the upstream end of the admixing hole (e.g. rounded inlet or stepped inlet), the orientation of the hole relative to the flow (relevant with non-circular cross-sectional shapes and with circular cross-sectional shapes that have a central angulation relative to the surface (outer channel structure (annulus)/combustion chamber (flame tube)), which is not perpendicular to the surface), as well as the effective guide length of the admixing holes. What is understood by an effective guide length here is a length which leads to an improved guiding of the flow inside the admixing hole. This can be obtained by lengthening the hole in such a way that the admixing hole (not necessarily identically across the circumference) projects into the flame tube; but an elongation of the effective flow control can also be obtained already through a cooling arrangement based on the structural design, a liner shingle arrangement. The flow rate coefficient is a variable that can differ for every admixing hole, since the dependence on the flow state has an influence upstream and downstream of the admixing hole in addition to the already mentioned influence quantities. For example, in a rich-lean combustion chamber arrangement, the inflow state to the admixing hole is influenced by components such as the injector, the injector arm, mechanical components that depend on the cooling pattern, such as for example screws in the case of a liner shingle cooling, where applicable by structurally relevant structural components such as fastening pins and ignition devices. Likewise, design deviations and cooling differences, such as they for example occur in a shingled combustion chamber between the shingles, are decisive for the homogeneity of the incident flow. In addition, the flow is influenced by uncontrollable leakage flows which occur due to the assembly and manufacture that is subject to tolerances. Since the rich-lean combustion chamber mostly has a flow control in the form of an inlet hood about the injector and towards the annuli, the geometrical variations of such an inlet hood and the acceleration conditions around such a hood are also decisive for the formation of a flow profile inside the annulus. What is common to all mentioned influencing factors is that the inflow state is neither homogenous in the radial nor in the circumferential direction, which influences the flow rate coefficient of an admixing hole. [These considerations are not limited to the conditions upstream of the admixing hole, since an admixing hole can lie on all sides, that is, for example also downstream of the inlet.] With respect to the flow rate coefficient, it also has to be differentiated whether what is present is an individual admixing hole or multiple admixing holes. The latter case is the case which is relevant for the present invention. In the case of multiple admixing holes, the flow rate coefficient depends on how the admixing holes are oriented and arranged relative to each other, as every admixing hole itself influences the flow inside the annulus and inside the flame tube. In the flame tube, it is in particular decisive whether the jets of neighboring admixing holes interact. Here, the jets of different admixing holes can for example combine to form a common jet, the jet trajectory can differ from the nominal course because of the pressure field that is formed with the jet, and not least it has to be differentiated whether jets of the facing annuli interact with each other. The present invention takes into account admixing arrangements of facing annuli that lead to configurations according to which jets are substantially guided past each other, but also configurations according to which jets are arranged so as to be arranged facing each other. The flow inside the flame tube of a rich-lean combustion chamber is twisted, highly turbulent, and has local differences in temperature and thus also differences in density due to the locally varying thermal release. The turbulence influences the viscous behavior of the flow, and the differences in density lead to an inhomogeneous impulse distribution. These properties are decisive for the pressure field in the flame tube, and thus for the driving pressure gradient of the flow through the admixing hole, i.e. for the flow rate coefficient of an admixing hole.
It is to be understood that, according to the invention, the term flow diameter is not limited to the circle diameter, but rather a flow diameter according to the invention can be understood to be a circle diameter as well as an ellipse diameter. At that, the ellipse diameter is calculated according to the equation D1=4*a1*b1/(a1+b1), wherein a1 and b1 are the semi-axes of an ellipse.
Preferably, the first flow diameter is a first circle diameter of the first admixing air holes. Alternatively, the first flow diameter is a first ellipse diameter of the first admixing air holes.
The second flow diameter D2 can also be a second circle diameter of the admixing air holes or a second ellipse diameter of the second admixing air holes.
The average flow rate coefficient C is a measure for the average effective through-flow of all admixing air holes, and preferably lies in a range of 0.60 to 0.75, and in an especially preferred case is 0.69.
Further, the first flow diameter and/or the second flow diameter are preferably different within the respective admixed air rows, wherein in that case the first flow diameter or the second flow diameter is determined as the mean value of the differently sized first and second flow diameters for each admixed air row.
An especially good inflow of the admixed air through the first and second admixing air holes is obtained if the flow diameters of the first and second admixing air holes are constant in the through-flow direction through the admixing air holes.
Further, it is preferred that the number of first and second admixing air holes is equal at the outer ring wall and/or at the inner ring wall.
According to an especially preferred embodiment of the present invention, a number of the first admixing air holes is equal to twice the number of fuel nozzles.
An especially good NOx reduction is obtained if the second admixing air holes at the outer ring wall and/or at the inner ring wall are arranged so as to be offset in the circumferential direction with respect to the first admixing air holes. At that, the second admixing air holes are especially preferably offset with respect to the first admixing air holes in such a manner that the second admixing air holes are positioned centrally between the first admixing air holes in the circumferential direction with the axial distance L.
Preferably, the first admixing air holes in the outer ring wall are arranged in the through-flow direction of the combustion chamber respectively on a central axis of a fuel nozzle, and the first admixing air holes in the inner ring wall are offset in the circumferential direction by an angle α=360°/(2*N1), wherein N1 is the number of the admixing air holes of the first admixed air row. Alternatively, the first admixing air holes in the inner ring wall are arranged in the through-flow direction of the combustion chamber respectively on a central axis of a fuel nozzle, and the first admixing air holes in the outer ring wall are offset in the circumferential direction by an angle α=360°/(2*N1), wherein N1 is the number of the admixing air holes of the first admixed air row. Through this arrangement requirement, it is ensured that the admixed air of the first admixed air row as far as possible comes into contact directly with the fuel that is discharged from the fuel nozzle, and that a very good mixing is realized.
A further reduction in NOx emissions can be achieved if the first admixing air holes have first central axes that lie in a first plane, and the second admixing air holes have second central axes that lie in a second plane. At that, the first and second plane are preferably arranged in parallel to each other. Especially preferably, the first and second central axes of the first and second admixing air holes are perpendicular to a middle cone of a conical combustion chamber.
Preferably, the first and/or second central axes are perpendicular to a tangent at the inner ring wall and/or perpendicular to a tangent at the outer ring wall of the combustion chamber.
Alternatively, the combustion chamber has a barrel-like ring shape with a barrel-like middle shell surface, and the first and second central axes of the first and second admixing air holes are arranged perpendicular to the barrel-like middle shell surface.
Preferably, the combustion chamber has a barrel-like shape, and/or the first and/or second admixing air holes have a central axis that is arranged at an angle not equal to 90° with respect to a tangent at the outer ring wall of the combustion chamber.
Further, the NOx emissions can be additionally reduced if a first admixing air hole is assigned to each fuel nozzle of the combustion chamber in the axial direction. If at that the number of first admixing air holes is preferably twice the size of the number of fuel nozzles, respectively a further first admixing hole is arranged in the circumferential direction, in the circumferential direction between the first admixing air holes that are respectively assigned to a fuel nozzle.
It is further preferred if the first and/or second admixing holes in the outer ring wall are respectively coaxial to the first and/or second admixing air holes in the inner ring wall. As a result, respectively one admixing air hole in the first admixed air row of the inner ring wall is assigned to each admixing air hole in the first admixed air row of the outer ring wall. The same preferably applies to the second admixed air rows of the second admixing air holes. Thus, a design of the admixing air holes can be realized in such a manner that the admixing air holes are for example designed in the outer ring wall of the annular combustion chamber according to the equation L, and a transition of the axial positions for the admixing air holes is realized in the inner ring wall. Thus, the distance L at the inner ring wall is the same as at the outer ring wall. Alternatively, the design of the admixing air holes can also be realized in such a manner that the admixing air holes in the inner ring wall of the annular combustion chamber can be designed according to the equation L, and a transition of the axial positions to the admixing air holes of the outer ring wall is realized. Also in this way, the distance L at the inner ring wall between the admixing air holes is the same as on the outer ring wall. Further, alternatively it is of course also possible that a design of the admixing air holes at the outer ring wall of the annular combustion chamber is realized separately from a design of the admixing air holes at the inner ring wall, but respectively according to the equation L=D2/D1*(D2−D1)/C2.
It has further been stated that a positive effect on NOx emissions can be further improved if the first and/or second admixing air holes preferably partially project into the combustion space. The admixing air holes thus have a circumferential flange that projects into the combustion space, so that the discharge of the admixed air from the first and/or second admixing air holes is realized with some distance from the inner combustion chamber wall of the combustion chamber. Further, the height of the flange preferably varies in the circumferential direction of the flange.
Further, the present invention relates to a gas turbine, in particular an aircraft gas turbine, with a combustion chamber arrangement according to the present invention.
Subsequently, preferred exemplary embodiments of the invention are described in detail by referring to the accompanying drawing. At that, the same or functionally identical parts are respectively identified by the same reference signs. In the drawing:
Subsequently, a gas turbine engine 100 and a combustion chamber arrangement 1 according to a first exemplary embodiment of the invention are described in detail by referring to
The gas turbine engine 100 according to
The gas turbine engine 100 has, arranged in succession in the flow direction A, an air inlet 110, a fan 12 rotating inside a housing, a medium-pressure compressor 13, a high-pressure compressor 14, an annular combustion chamber 15, a high-pressure turbine 16, a medium-pressure turbine 17 and a low-pressure turbine 18 as well as an exhaust nozzle 19, which are all arranged about a central engine axis X-X.
The medium-pressure compressor 13 and the high-pressure compressor 14 respectively comprise multiple stages, of which each has an arrangement of fixedly arranged stationary guide vanes 20 that are generally referred to as stator vanes and project radially inward from the core engine shroud 21 through the compressors 13, 14 into a ring-shaped flow channel. Further, the compressors have an arrangement of compressor rotor blades 22 that project radially outward from a rotatable drum or disc 26, and are coupled to hubs 27 of the high-pressure turbine 16 or the medium-pressure turbine 17.
The three turbine sections of the high-pressure turbine 16, of the medium-pressure turbine 17 and the low-pressure turbine 18 have similar stages, comprising an arrangement of stationary guide vanes 23 that project radially inward from the housing 21 into an annular flow channel through the three turbine sections, and a subsequent arrangement of turbine blades/vanes 24 projecting outwards from the rotatable hub 27. During operation, the compressor drum or compressor disc 26 and the blades 22 arranged thereon as well as the turbine rotor hub 27 and the turbine rotor blades/vanes 24 arranged thereon rotate around the engine axis X-X.
The annular combustion chamber 15 comprises an inner ring wall 7 and an outer ring wall 8. The inner ring wall 7 is embodied with two walls and comprises an inner shingle support 71 and an inner combustion chamber shingle 72. The outer ring wall 8 is also designed with two walls and comprises an outer shingle support 81 and an outer combustion chamber shingle 82. It is to be understood that alternatively the inner ring wall and the outer ring wall can also be embodied with a single wall.
Further, a heat plate 4 and a heat shield 5 for thermal protection of the combustion chamber head 3 are also arranged at the combustion chamber head 3.
As can be seen in
Further, the reference sign 80 identifies a combustion chamber suspension, and the reference sign 90 identifies a combustion chamber flange.
The combustion chamber arrangement 1 further comprises a first admixed air row Z1 with a plurality of first admixing air holes 10 that are embodied as passage holes. Further, the combustion chamber arrangement comprises a second admixed air row Z2 with a plurality of second admixing air holes 11 that are embodied as passage holes. The first and second admixing air holes are respectively arranged in the inner ring wall 7 and the outer ring wall 8.
Each of the first admixing air holes 10 has a first inner center point 10a, and each of the second admixing air holes 11 has a second inner center point 11a. As can be seen in
Here, the first and second inner central points 10a, 11a are respectively located at a side of the admixing air holes 10, 11 that are oriented towards the combustion chamber 15. The first and second admixing air holes in the combustion chamber walls are now arranged in such a manner that the following equation is fulfilled:
L=D2/D1*(D2−D1)/C2,
wherein L is a distance between the first and second inner center points 10a, 11a of the first and second admixing air holes 10, 11 in the axial direction of the combustion chamber 15, wherein D1 is a first flow diameter of the first admixing air holes 10 at the exit side to the combustion chamber 15, and D2 is a second flow diameter of the second admixing air holes 11 at the exit side to the combustion chamber 15. Further, C is an average flow rate coefficient of the first and second admixing holes.
Here, the flow diameter D1 and D2 of the first exemplary embodiment is chosen in such a manner that the flow diameter D1 of the first admixing air holes 10 and the second admixing air holes 11 is circular. Thus, the flow diameter is embodied as a circle diameter.
At that, a first diameter D1 is smaller than the second diameter D2.
In circumferential direction, the admixing air holes 10 of the first admixed air row Z1 are arranged at the same distance, and have a distance U from the first inner center points 10a that are respectively adjacent to one another (cf.
Further, the first admixing air holes 10 are arranged in such a manner that a first admixing air hole 10 is always arranged in alignment with the through-flow direction A of the combustion chamber on the central axis 60 of each fuel nozzle 6 (cf.
Here, the average flow rate coefficient C of the first and second admixing holes lies in a range of 0.60 to 0.75, and especially preferably is 0.69. The flow rate coefficient C is approximately the same in each of the admixing air holes 10, 11, so that the flow rate coefficient C can always be preferably chosen to be 0.69, also taking into consideration tolerance bands.
It is to be understood that the flow diameter D1, D2 does not necessarily have to be a circle diameter, but can for example be an ellipse diameter.
In the first exemplary embodiment, the first and second admixing air holes 10, 11 are cylindrical (cf.
The number of the first admixing holes 10 equals the number of the second admixing holes 11. The second admixing holes 11 of the second admixing row Z2 are arranged so as to be respectively centrally offset in the circumferential direction with respect to the admixing air holes 10 of the first admixed air row Z1, which is schematically shown in
B=N*(0.25*π*D12+0.25*π*D22).
For the design, either the distance L between the two admixed air rows and the surface B with the number of holes N of an admixed air row, e.g. N1 of the first admixed air row, or the surface B and the number of holes N and one of the diameters D1, D2 of the first and second admixing air holes or the ratio of the diameter of the first and second admixing air holes with respect to each other can be indicated.
For example, the surface B, the number N of the admixing air holes of the first (N1) or second (N2) admixed air row, which in this exemplary embodiment is identical in both admixed air rows, and the ratio D2/D1 are specified:
Total area B: 12.000 mm2
Number N of the admixing holes of the first or second admixed air row: 48
D2/D1=1.3.
Since the flow rate coefficient is known as 0.69, what results for the first diameter D1 is a value of 10.9 mm, what results for the second diameter D2 is a value of 14.1 mm, and what results for the length L is a value of 8.74 mm.
Thus, it can be ensured according to the invention that a sufficient amount of admixed air can be introduced into the combustion chamber 15, so that the generation of undesired NOx emissions can be significantly reduced. Through the even distribution of the first and second admixing air holes 10, 11 along the circumference, it can thus be avoided that any areas rich in combustion fuel and areas of high combustion temperatures remain in the combustion chamber 15. The advantageous arrangement of the admixing air holes thus makes it possible to achieve a uniform leaning in the combustion chamber 15.
As can be seen in
Thus, according to the invention, a connection between the flow diameters D1, D2 of the first and second admixing air holes 10, 11 and the distance L is established in the through-flow direction A of the combustion chamber 15 in order to achieve an optimization of the reduction of NOx emissions.
D1=4*a1*b1/(a1+b1),
wherein a1 and b1 are the semi-axes of the ellipse of the first admixing holes 10.
The second flow diameter D2 is calculated as follows:
D2=4*a2*b2/(a2+b2),
wherein a2 and b2 are the semi-axes of the ellipse of the second admixing air holes 11.
As in the first exemplary embodiment, in the fourth exemplary embodiment the second admixing air holes 11 of the second admixed air row Z2 are centrally offset in the circumferential direction with respect to the admixing air holes 10 of the first admixed air row Z1. Again, the inner first and second center points 10a and 11a lie in a first plane E1 or a second plane E2. At that, each second first admixing hole 10 of the first admixing hole row Z1 is again positioned so as to be aligned with the central axis 60 of the fuel nozzles 6. Thus, exactly one first admixing air hole 10 is assigned to each fuel nozzle 6 in the axial direction.
It is stated with regard to all escribed exemplary embodiments that any desired combination between circle diameters and ellipse diameters are also possible. Also, the longer semi-axis of the ellipse can be arranged perpendicular to the through-flow direction A. Alternatively, circle diameters and ellipse diameters can be arranged in an alternating manner in at least one admixed air row, or admixing air holes are embodied so as to alternatingly have circle diameters and ellipse diameters, which can also be offset in the circumferential direction, in both admixed air rows Z1, Z2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 219 424.0 | Oct 2016 | DE | national |
