A trapped vortex interstage combustion chamber with a pre-evaporation swirl oil supply device

Abstract

The present invention discloses a trapped vortex interstage combustion chamber with a pre-evaporation swirl oil supply device, comprising: an outer shell, a trapped vortex flame tube, an oil-gas swirler, an air pipe, an oil pipe, an oil-gas mixing pipe and an inner shell; the trapped vortex flame tube is arranged inside the outer shell; the middle portion of the trapped vortex flame tube protrudes outward, and a concave cavity is formed on the inner side of the middle portion of the trapped vortex flame tube, and a concave cavity inlet is arranged at the side wall of the concave cavity near the rear section of the trapped vortex flame tube; the oil-gas swirler comprises: swirl blades and an oil-gas pipe; the oil-gas pipe is located at the concave cavity inlet, the interior of the swirl blades is hollow, and an oil-gas outlet is opened on the surface; the air pipe is arranged outside the outer shell; the oil pipe is arranged outside the outer shell; the inlet end of the oil-gas mixing pipe is connected to the air pipe and the oil pipe respectively; the inner shell is arranged inside the trapped vortex flame tube. The trapped vortex interstage combustion chamber of the present invention can achieve rapid and uniform mixing of oil and gas in the concave cavity, and can achieve ignition and stable combustion within a lower limit of the oil-gas ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation engines, and more particularly to a trapped vortex interstage combustion chamber with a pre-evaporation swirl oil supply device. Background Art

[0002] The trapped vortex combustor (TVC) is a highly efficient combustor design that utilizes vortex flow to stabilize the flame and improve combustion efficiency. Since its introduction by the U.S. Air Force Research Laboratory and General Electric in the 1990s, the TVC has been extensively researched and applied in the aeroengine field. The TVC has evolved from its initial single-outer-cavity axisymmetric design to a single-tube axisymmetric design, and now to single- or dual-cavity annular structures. These structural changes aim to improve combustion efficiency, reduce emissions, and enhance combustion stability. Research has shown that compared to conventional vortex-stabilized combustors, the TVC achieves 50% improvements in start-up ignition, lean burnout, and high-altitude reignition performance, a 40% wider operating range, and combustion efficiency above 99%. Due to the outstanding performance of the TVC, researchers have proposed applying this technology to the inter-stage turbine burner (ITB) to increase overall cycle power and enhance engine performance.

[0003] To gain a deeper understanding of the flow characteristics and combustion performance of the trapped vortex interstage combustor, researchers have conducted extensive numerical simulations and experimental studies, including combustion characteristics such as the temperature field distribution within the combustor, the ignition-extinguishing boundary, flame morphology, combustion efficiency, and outlet temperature distribution. These studies have revealed that the uniformity of the mixing of the evaporated fuel with the secondary gas within the trapped vortex cavity significantly influences the combustion characteristics. Uneven oil and gas distribution directly leads to localized oil enrichment, concentrated high-temperature zones, and poor circumferential flame crossover, resulting in ignition difficulties, reduced combustion efficiency, and poor outlet temperature distribution.

[0004] Therefore, it is an urgent problem for technical personnel in this field to develop a trapped vortex interstage combustion chamber with a pre-evaporation swirl oil supply device that can achieve rapid mixing of oil and gas in the cavity and uniform distribution of oil and gas under the condition of extremely short airflow residence time. Summary of the Invention

[0005] In view of this, the present invention provides a trapped vortex interstage combustion chamber with a pre-evaporation swirl oil supply device, which can achieve rapid mixing of oil and gas in the cavity and uniform distribution of oil and gas under the condition of extremely short airflow residence time.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A trapped vortex interstage combustor with a pre-evaporation swirl oil supply device, comprising:

[0008] outer shell,

[0009] A trapped vortex flame tube, wherein the trapped vortex flame tube is arranged inside the outer shell, and the end of the trapped vortex flame tube is connected to the outer shell; the middle portion of the trapped vortex flame tube protrudes outward, and a concave cavity is formed on the inner side of the middle portion of the trapped vortex flame tube, and a concave cavity inlet is provided at the side wall of the concave cavity near the rear section of the trapped vortex flame tube, and the concave cavity inlet is distributed in an annular manner along the side wall of the concave cavity;

[0010] An oil-gas cyclone, comprising: swirl blades and an oil-gas pipe; the oil-gas pipe is located at the inlet of the concave cavity and is distributed in an annular shape along the outer ring of the trapped vortex flame tube; the interior of the swirl blade is hollow, and an oil-gas outlet is opened on the surface; a plurality of swirl blades are evenly distributed along the inlet of the concave cavity, and the swirl blades are connected to the oil-gas pipe;

[0011] an air pipe, the air pipe being arranged outside the outer shell and distributed along the circumference of the outer shell;

[0012] an oil pipe, the oil pipe being arranged outside the outer shell and distributed along the circumference of the outer shell;

[0013] An oil-gas mixing pipe, the inlet end of which is connected to the air pipe and the oil pipe respectively, and the outlet end of which extends deep into the interior of the outer shell and is connected to the oil-gas pipe;

[0014] The inner shell is arranged inside the trapped vortex flame tube, and the outer shell, the trapped vortex flame tube and the inner shell are coaxially arranged; a secondary flow channel is formed between the trapped vortex flame tube and the outer shell, and a main flow channel is formed between the trapped vortex flame tube and the inner shell.

[0015] The beneficial effect of adopting the above technical solution is that, in the present invention, under the action of the swirl blades, the secondary flow gas will carry a tangential swirl when entering the concave cavity, forming a small-scale tangential vortex in the concave cavity, and at the same time forming a large vortex around the combustion chamber, further enhancing the stability of the flame in the concave cavity, and helping to widen the working range of the combustion chamber.

[0016] Preferably, the trapped vortex flame tube includes: a front cylinder and a rear cylinder; the end of the rear cylinder is connected to the outer shell; the rear end of the front cylinder protrudes outward, and the protruding portion and the front end of the rear cylinder form the concave cavity, and the concave cavity inlet for oil and gas to enter the concave cavity is left between the end of the front cylinder and the front end of the rear cylinder, and the swirl blade is placed in the concave cavity inlet and is connected to the front cylinder and the rear cylinder; the oil and gas enter the concave cavity from the concave cavity inlet after passing through the swirl blade.

[0017] Preferably, the swirl blades are distributed in an inclined shape and have an angle with the axis of the front cylinder, so that when the secondary flow gas enters the cavity, a large-scale vortex rotating along the axis of the combustion chamber is formed.

[0018] Preferably, the air pipe includes: an air intake pipe and an air distribution pipe; the air distribution pipe is arranged in a ring shape outside the outer shell and is connected to the oil-gas mixing pipe; a plurality of the air intake pipes are arranged along the air distribution pipe.

[0019] Preferably, the oil pipe includes an oil distribution pipe and an oil inlet pipe; the oil distribution pipe is annularly arranged outside the outer shell and communicates with the oil-gas mixing pipe; multiple oil inlet pipes are arranged along the oil distribution pipe. Both the gas pipe and the oil pipe are connected to the oil-gas mixing pipe to achieve uniform mixing of oil and gas.

[0020] Preferably, the oil distribution pipe is connected to a plurality of direct-injection nozzles; the oil inlet ends of the direct-injection nozzles are connected to the oil distribution pipe, and the oil outlet ends extend into the oil-gas mixing pipe. The direct-injection nozzles can spray liquid fuel to form a conical liquid film. Under the action of the high-temperature gas, the liquid fuel can be transformed into gaseous fuel in the oil-gas mixing pipe, thereby making the oil-gas mixture in the cavity more evenly mixed.

[0021] Preferably, the oil inlet pipe and the air inlet pipe are at the same circumferential position outside the outer shell; the oil-gas mixing pipe and the direct-injection nozzle are at the same circumferential position outside the outer shell.

[0022] Preferably, the oil-gas mixing pipe is distributed in the middle position between two adjacent intake pipes on the gas distribution pipe.

[0023] Preferably, the direct injection nozzle is distributed in the middle position between two adjacent oil inlet pipes on the oil distribution pipe. The position arrangement of the oil inlet pipe, air intake pipe, oil-air mixing pipe and direct injection nozzle can ensure uniform distribution of bleed air and fuel.

[0024] Preferably, 6 to 12 oil-gas mixing pipes are evenly distributed in the circumferential direction of the air distribution pipe, which can ensure the uniform distribution of the fuel in the cavity while reducing the complexity of the air pipe and the oil pipe structure.

[0025] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a trapped vortex interstage combustor with a pre-evaporation swirl oil supply device, which has the following beneficial effects:

[0026] (1) Compared with conventional trapped vortex interstage combustors, the present invention forms a small-scale circumferential vortex with the centerline of the cavity as the axis in the cavity. At the same time, under the guidance of the swirl vanes at the cavity inlet, a large-scale vortex with the axis of the combustion chamber is formed, thereby enhancing the flame stability in the cavity and helping to widen the working range of the combustion chamber.

[0027] (2) Both the gas pipe and the oil pipe are arranged outside the outer shell, which avoids the problem of high-temperature coking and reduces the complexity of the oil supply pipeline inside the trapped vortex interstage combustion chamber;

[0028] (3) The use of swirl blades to supply the pre-evaporated gaseous fuel to the trapped vortex combustion zone can make the oil and gas distribution in the cavity more uniform, and can achieve ignition and stable combustion within a lower limit of the oil-gas ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0030] Figure 1 A schematic structural diagram of the trapped vortex interstage combustion chamber provided by the present invention;

[0031] Figure 2 A side view of the trapped vortex interstage combustion chamber provided by the present invention;

[0032] Figure 3 The present invention provides Figure 2 Cross-sectional view at AA in the middle;

[0033] Figure 4 A partial cross-sectional view of the trapped vortex interstage combustion chamber provided by the present invention;

[0034] Figure 5 The present invention provides Figure 4 Cross-sectional view at the middle BB;

[0035] Figure 6 A schematic diagram of the structure of the connection between the oil-gas cyclone and the oil-gas mixing pipe provided by the present invention;

[0036] Figure 7 A side view of the oil and gas cyclone provided by the present invention;

[0037] Figure 8 The present invention provides Figure 7 Cross-sectional view at CC;

[0038] Figure 9 A schematic diagram of the swirl flow in the concave cavity provided by the present invention;

[0039] Figure 10 This is a working schematic diagram of the trapped vortex interstage combustion chamber provided by the present invention.

[0040] Among them, in the figure,

[0041] 1- outer shell;

[0042] 2-trapped vortex flame tube;

[0043] 21-concave cavity; 22-concave cavity inlet; 23-front cylinder; 24-rear cylinder;

[0044] 3-Oil and gas cyclone;

[0045] 31-swirl blade; 32-oil and gas pipe; 33-oil and gas outlet;

[0046] 4-trachea;

[0047] 41-intake pipe; 42-air distribution pipe;

[0048] 5-Oil pipe;

[0049] 51- oil distribution pipe; 52- oil inlet pipe; 53- direct injection nozzle;

[0050] 6-oil-gas mixing pipe; 7-inner shell; 8-main flow channel; 9-secondary flow channel; 10-tangential vortex; 11-large vortex.

[0051] Figure 10 The meanings of the arrows are shown in the following table:

[0052] DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0054] The embodiment of the present invention discloses a trapped vortex interstage combustor with a pre-evaporation swirl oil supply device, comprising:

[0055] Outer shell 1,

[0056] The trapped vortex flame tube 2 is arranged inside the outer shell 1, and the end of the trapped vortex flame tube 2 is connected to the outer shell 1; the middle portion of the trapped vortex flame tube 2 protrudes outward, and a concave cavity 21 is formed on the inner side of the middle portion of the trapped vortex flame tube 2. A concave cavity inlet 22 is provided on the side wall of the concave cavity 21 near the rear section of the trapped vortex flame tube 2, and the concave cavity inlet 22 is distributed in an annular manner along the side wall of the concave cavity 21;

[0057] The oil and gas cyclone 3 includes: swirl blades 31 and an oil and gas pipe 32; the oil and gas pipe 32 is located at the cavity inlet 22 and is distributed in an annular shape along the outer ring of the trapped vortex flame tube 2; the interior of the swirl blades 31 is hollow, and an oil and gas outlet 33 is opened on the surface; multiple swirl blades 31 are evenly distributed along the cavity inlet 22, and the swirl blades 31 are connected to the oil and gas pipe 32;

[0058] The trachea 4 is arranged outside the outer shell 1 and distributed along the circumference of the outer shell 1;

[0059] The oil pipe 5 is arranged outside the outer shell 1 and distributed along the circumference of the outer shell 1;

[0060] The oil-gas mixing pipe 6 has an inlet end connected to the air pipe 4 and the oil pipe 5 respectively, and an outlet end extending into the interior of the outer shell 1 and connected to the oil-gas pipe 32;

[0061] Inner casing 7 is positioned within trapped vortex flame tube 2, with outer casing 1, trapped vortex flame tube 2, and inner casing 7 coaxially arranged. A secondary flow channel 9 is formed between trapped vortex flame tube 2 and outer casing 1, while a primary flow channel 8 is formed between trapped vortex flame tube 2 and inner casing 7. The air pipe 4, oil pipe 5, and oil-air mixing pipe 6 comprise the fuel supply device. The distribution of these three pipes reduces the structural complexity of the fuel supply device while ensuring uniform distribution of fuel within cavity 21.

[0062] In order to further optimize the above technical solution, the trapped vortex flame tube 2 includes: a front cylinder 23 and a rear cylinder 24; the end of the rear cylinder 24 is connected to the outer shell 1; the rear end of the front cylinder 23 protrudes outward, and the protruding portion and the front end of the rear cylinder 24 form a concave cavity 21, and a concave cavity inlet 22 for oil and gas to enter the concave cavity 21 is left between the end of the front cylinder 23 and the front end of the rear cylinder 24. The swirl blade 31 is placed in the concave cavity inlet 22 and is connected to the front cylinder 23 and the rear cylinder 24; the oil and gas enter the concave cavity 21 from the concave cavity inlet 22 after passing through the swirl blade 31. Figure 1 As shown, the cross section of the front cylinder 23 along the axial direction is Z-shaped, and the cross section of the rear cylinder along the axial direction is L-shaped.

[0063] In order to further optimize the above technical solution, the swirl blades 31 are distributed in an inclined shape and have an angle with the axis of the front cylinder 23. Figure 8 The angle α shown indicates the angle between the swirl blade 31 and the axis of the front barrel 23. The interior of the swirl blade 31 is connected to the interior of the oil and gas pipe 32. The oil and gas mixture in the oil and gas pipe 32 enters the swirl blade 31 and exits from the oil and gas outlet 33. Driven by the secondary flow, it enters the concave cavity 21.

[0064] In order to further optimize the above technical solution, the air pipe 4 includes: an air intake pipe 41 and an air distribution pipe 42; the air distribution pipe 42 is arranged in a ring shape outside the outer shell 1 and is connected to the oil-gas mixing pipe 6; there are multiple air intake pipes 41 along the air distribution pipe 42.

[0065] In order to further optimize the above technical solution, the oil pipe 5 includes: an oil distribution pipe 51 and an oil inlet pipe 52; the oil distribution pipe 51 is arranged in a ring shape outside the outer shell 1 and is connected to the oil-gas mixing pipe 6; multiple oil inlet pipes 52 are arranged along the oil distribution pipe 51.

[0066] In order to further optimize the above technical solution, the oil distribution pipe 51 is connected to a plurality of direct-injection nozzles 53 ; the oil inlet end of the direct-injection nozzle 53 is connected to the oil distribution pipe 51 , and the oil outlet end extends into the oil-gas mixing pipe 6 .

[0067] To further optimize the above technical solution, the oil inlet pipe 52 and the air inlet pipe 41 are positioned at the same circumferential position outside the outer shell 1; the oil-air mixing pipe 6 and the direct-injection nozzle 53 are positioned at the same circumferential position outside the outer shell 1. The oil inlet pipes 52 and the air inlet pipe 41 are the same in number and positioned in a corresponding manner, and the oil-air mixing pipes 6 and the direct-injection nozzle 53 are the same in number and positioned in a corresponding manner.

[0068] In order to further optimize the above technical solution, the oil-gas mixing pipe 6 is distributed in the middle position between two adjacent air inlet pipes 41 on the air distribution pipe 42 .

[0069] In order to further optimize the above technical solution, the direct injection nozzle 53 is distributed in the middle position between two adjacent oil inlet pipes 52 on the oil distribution pipe 51.

[0070] In order to further optimize the above technical solution, 6-12 oil-gas mixing tubes 6 are evenly distributed in the circumferential direction of the gas distribution tube 42. The angle between adjacent oil-gas mixing tubes 6 is between 30° and 60°.

[0071] Working principle:

[0072] Under the action of the front cylinder 23, the airflow is divided into a mainstream and a secondary flow. The secondary flow enters the secondary flow channel 9 between the outer shell 1 and the front cylinder 23, and the mainstream enters the mainstream channel 8 between the inner shell 7 and the front cylinder 23. Since the concave cavity inlet 22 between the front cylinder 23 and the rear cylinder 24 is equipped with a swirl blade 31, the secondary flow will carry a tangential swirl when entering the concave cavity 21, forming not only a small-scale tangential vortex 10 in the concave cavity 21, but also a large vortex 11 surrounding the combustion chamber. In addition, the air inlet pipe 41 of the fuel supply device introduces high-temperature and high-pressure gas from the front end of the engine, and distributes the gas to the oil-gas mixing pipe 6 installed at an equal angle to the annular combustion chamber through the gas distribution pipe 42. At the same time, the oil inlet pipe 52 of the fuel supply device is connected to the engine oil circuit, and distributes the fuel to the direct-injection nozzle 53 installed at an equal angle to the annular combustion chamber through the oil distribution pipe 51. Liquid fuel is ejected from the nozzle of the direct-injection nozzle 53 to form a conical liquid film. Under the action of the introduced high-temperature gas, the liquid fuel forms gaseous fuel in the oil-gas mixing pipe 6 and is transported to the oil-gas pipe 32. Finally, the gaseous fuel flows out from the oil-gas outlets 33 on both sides of the swirl blade 31. Under the action of the strong swirl, a uniform oil-gas mixture can be formed in the concave cavity 21, which is beneficial to the trapped vortex interstage combustion chamber to achieve reliable ignition and stable combustion at a low oil-gas ratio, and broadens the stable working range of the trapped vortex interstage combustion chamber.

[0073] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0074] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A trapped vortex interstage combustor with a pre-evaporation swirl oil supply device, characterized in that: include: Outer shell (1), A trapped vortex flame tube (2), wherein the trapped vortex flame tube (2) is arranged inside the outer shell (1), and the end of the trapped vortex flame tube (2) is connected to the outer shell (1); the middle portion of the trapped vortex flame tube (2) protrudes outward, and a concave cavity (21) is formed on the inner side of the middle portion of the trapped vortex flame tube (2), and a concave cavity inlet (22) is provided at the side wall of the concave cavity (21) near the rear section of the trapped vortex flame tube (2), and the concave cavity inlet (22) is arranged along the concave cavity (21). ) sidewalls are distributed in an annular manner; the trapped vortex flame tube (2) comprises: a front cylinder (23) and a rear cylinder (24); the end of the rear cylinder (24) is connected to the outer shell (1); the rear end of the front cylinder (23) protrudes outward, and the protruding portion and the front end of the rear cylinder (24) form the concave cavity (21); the concave cavity inlet (22) for supplying oil and gas into the concave cavity (21) is left between the end of the front cylinder (23) and the front end of the rear cylinder (24); An oil and gas cyclone (3), the oil and gas cyclone (3) comprising: a swirl blade (31) and an oil and gas pipe (32); the oil and gas pipe (32) is located at the concave cavity inlet (22) and is distributed in a ring shape along the outer ring of the trapped vortex flame tube (2); the interior of the swirl blade (31) is hollow, and an oil and gas outlet (33) is opened on the surface; a plurality of the swirl blades (31) are evenly distributed along the concave cavity inlet (22), and the swirl blades (31) are connected to the oil and gas pipe (32); the swirl blades (31) are placed in the concave cavity inlet (22) and are connected to the front cylinder (23) and the rear cylinder (24); the oil and gas enter the concave cavity (21) from the concave cavity inlet (22) after passing through the swirl blades (31); the swirl blades (31) are distributed in an inclined shape and have an angle with the axis of the front cylinder (23); an air pipe (4), the air pipe (4) being arranged outside the outer shell (1) and distributed along the circumferential direction of the outer shell (1); An oil pipe (5), the oil pipe (5) being arranged outside the outer shell (1) and distributed along the circumferential direction of the outer shell (1); An oil-gas mixing pipe (6), wherein the inlet end of the oil-gas mixing pipe (6) is respectively connected to the air pipe (4) and the oil pipe (5), and the outlet end extends into the interior of the outer shell (1) and is connected to the oil-gas pipe (32); An inner casing (7), wherein the inner casing (7) is arranged inside the trapped vortex flame tube (2), and the outer casing (1), the trapped vortex flame tube (2), and the inner casing (7) are coaxially arranged; a secondary flow channel (9) is formed between the trapped vortex flame tube (2) and the outer casing (1), and a primary flow channel (8) is formed between the trapped vortex flame tube (2) and the inner casing (7).

2. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 1, characterized in that: The air pipe (4) comprises an air intake pipe (41) and an air distribution pipe (42); the air distribution pipe (42) is arranged in an annular shape outside the outer shell (1) and is connected to the oil-gas mixing pipe (6); a plurality of the air intake pipes (41) are arranged along the air distribution pipe (42).

3. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 2, characterized in that: The oil pipe (5) comprises: an oil distribution pipe (51) and an oil inlet pipe (52); the oil distribution pipe (51) is arranged in an annular shape outside the outer shell (1) and is connected to the oil-gas mixing pipe (6); a plurality of oil inlet pipes (52) are arranged along the oil distribution pipe (51).

4. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 3, characterized in that: The oil distribution pipe (51) is connected to a plurality of direct-injection nozzles (53); the oil inlet ends of the direct-injection nozzles (53) are connected to the oil distribution pipe (51), and the oil outlet ends extend into the oil-gas mixing pipe (6).

5. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 4, characterized in that: The oil inlet pipe (52) and the air inlet pipe (41) are located at the same circumferential position outside the outer shell (1); the oil-air mixing pipe (6) and the direct injection nozzle (53) are located at the same circumferential position outside the outer shell (1).

6. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 2, characterized in that: The oil-gas mixing pipe (6) is distributed in the middle position of two adjacent intake pipes (41) on the gas distribution pipe (42).

7. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 4, characterized in that: The direct-injection nozzle (53) is distributed in the middle position of two adjacent oil inlet pipes (52) on the oil distribution pipe (51).

8. The trapped vortex interstage combustor with a pre-evaporation swirl oil supply device according to claim 6, characterized in that: 6-12 oil-gas mixing tubes (6) are evenly distributed in the circumferential direction of the gas distribution tube (42).

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