Combustion chamber, gas turbine engine, combustion organization method

Abstract

The application provides a combustion chamber, a gas turbine engine and a combustion organization method. The combustion chamber comprises a staged fuel nozzle and a main vortex finder which is arranged radially coaxially with the staged fuel nozzle; the staged fuel nozzle comprises a center nozzle, a pre-combustion stage swirler and an oil collecting ring; the main vortex finder comprises a U-shaped guide vane, a main combustion stage swirler and a main vortex finder outer ring; the U-shaped guide vane, the main combustion stage swirler, the main vortex finder outer ring and the oil collecting ring provide a main combustion stage passage; after the airflow is deflected by the U-shaped guide vane, an aerodynamic trapped vortex area is formed outside the main combustion stage passage and an acceleration area is formed inside the main combustion stage passage.

Description

Technical Field

[0001] This invention relates to the field of combustion chambers, and more particularly to combustion chambers, gas turbine engines, and combustion organization methods. Background Technology

[0002] The International Civil Aviation Organization's (ICAO) Committee on Aviation Environmental Protection (CAEP) has been setting increasingly stringent emission requirements. Based on the long-term (20-year) targets set at the 7th CAEP meeting in 2007, NOx emission targets are set at 60% lower than those required by the CAEP / 6 standard. The possibility of CAEP issuing even higher emission standards in the future cannot be ruled out. Other emissions, such as carbon monoxide (CO) and unburned hydrocarbons (UHC), are also required to maintain a certain margin compared to the ICAO emission targets.

[0003] Studies have shown that controlling the maximum combustion gas temperature and the uniformity of combustion zone temperature within the combustion chamber are key to controlling NOx emissions. One of the main technical approaches to controlling combustion zone temperature is to employ a lean premixed combustion mode. However, under operating conditions such as idle speed and start-up ignition, a near-chemically appropriate diffusion combustion fuel-air matching mode is required in the combustion zone to ensure combustion performance while also reducing CO and UHC emissions at low power levels. To resolve the contradiction between NOx emissions at high power levels and CO and UHC emissions at low power levels, domestic and international aero-engine development units typically employ zoned or staged combustion modes to ensure that local areas of the combustion chamber operate with optimal fuel-air matching at different engine power levels. For example, GE's dual-annular combustion chamber developed in its high-efficiency fuel-saving engine program uses a radial zoned combustion mode; Alstom's sequential combustion chamber developed for the GT36 gas turbine uses an axial zoned combustion mode; and GE's LEAP_X and GEnx engines use a TAPS combustion chamber, which employs a staged combustion mode.

[0004] Due to its compact structure and effective NOx control through staged lean combustion, central staged combustion technology has become a trend in the development of low-emission combustion chambers. However, existing staged combustion technologies often suffer from backfire within the main combustion stage passage when the premixed fuel-air mixture is easily disturbed by airflow pressure, leading to erosion of the main combustion stage passage's inner wall under high engine operating conditions.

[0005] This application proposes a combustion chamber using a counter-flow main swirl converter, which effectively avoids backfire and erosion problems in the main combustion stage premixing channel while ensuring low pollution emission levels in the combustion chamber, and can also improve the life of the fuel injector-level main swirl converter. Summary of the Invention

[0006] One object of the present invention is to provide a combustion chamber.

[0007] One object of the present invention is to provide a gas turbine engine.

[0008] One object of the present invention is to provide a combustion organization method.

[0009] According to one aspect of the present invention, a combustion chamber includes a staged fuel nozzle and a main vortex generator, wherein the main vortex generator is arranged radially coaxially with the staged fuel nozzle; the staged fuel nozzle includes a central nozzle, a pre-combustion stage vortex generator, and a fuel collecting ring; the main vortex generator includes a U-shaped guide vane, a main combustion stage vortex generator, and a main vortex generator outer ring; wherein the U-shaped guide vane, the main combustion stage vortex generator, the main vortex generator outer ring, and the fuel collecting ring provide a main combustion stage passage; wherein, after the airflow is deflected by the U-shaped guide vane, an aerodynamic vortex region is formed outside the main combustion stage passage, and an acceleration zone is formed inside the main combustion stage passage.

[0010] In one or more embodiments of the combustion chamber, the main combustion stage swirler includes a bladed swirler with 20 to 60 blades and a blade installation angle between 20° and 60°.

[0011] In one or more embodiments of the combustion chamber, the main combustion stage swirler includes a multi-oblique-hole swirler with 10 to 30 holes and an inclination angle between 20° and 60°.

[0012] In one or more embodiments of the combustion chamber, the pre-combustion stage swirler includes a first-stage pre-combustion stage swirler and a second-stage pre-combustion stage swirler, wherein both the first-stage and second-stage pre-combustion stage swirlers are axial or radial swirlers.

[0013] In one or more embodiments of the combustion chamber, the main combustion stage swirler is an axial swirler.

[0014] In one or more embodiments of the combustion chamber, the staged fuel nozzle is manufactured by welding and / or integral casting and / or 3D printing.

[0015] In one or more embodiments of the combustion chamber, the main swirl generator is integrally formed by welding and / or integral casting and / or 3D printing, and the staged fuel nozzle and the main swirl generator are radially floating fit.

[0016] In one or more embodiments of the combustion chamber, the airflow path through the main combustion stage passage includes: after passing through the main combustion stage vortex, the airflow is guided by the first part of the U-shaped guide plate and the outer wall of the outer ring of the main vortex to flow in a first direction; then the airflow is guided by the second part of the U-shaped guide plate to flow in a second direction, the second direction being perpendicular to the first direction; then the airflow is guided by the second airflow passage defined by the inner wall of the outer ring of the main vortex and the outer wall of the oil collecting ring to flow in a third direction, the third direction being opposite to the first direction, forming an aerodynamic vortex region on the outside of the second airflow passage and an acceleration zone on the inside of the main combustion stage passage.

[0017] According to another aspect of the present invention, a gas turbine engine includes a combustion chamber as described above.

[0018] According to another aspect of the combustion organization method of the present invention, in the main combustion stage, the main combustion stage channel is configured as a U-shaped channel aerodynamic vortex structure, and the airflow after passing through the U-shaped channel forms an aerodynamic vortex region on the outside of the main combustion stage channel and an acceleration zone on the inside of the main combustion stage channel.

[0019] In one or more embodiments of the combustion organization method, a U-shaped guide vane, a main combustion stage swirler, a main vortex outer ring, and an oil collecting ring provide a main combustion stage passage. After the airflow passes through the main combustion stage swirler, the airflow is guided by a first airflow passage defined by the first part of the U-shaped guide vane and the outer wall of the main vortex outer ring to flow in a first direction. Then, the airflow is guided by a second part of the U-shaped guide vane to flow in a second direction, which is perpendicular to the first direction. Then, the airflow is guided by a second airflow passage defined by the inner wall of the main vortex outer ring and the outer wall of the oil collecting ring to flow in a third direction, which is opposite to the first direction. An aerodynamic vortex region is formed on the outside of the second airflow passage, and an acceleration zone is formed on the inside of the main combustion stage passage. Fuel is injected from the nozzles on the outer wall of the oil collecting ring into the second airflow passage and mixes with the airflow in the second airflow passage.

[0020] The beneficial effects of adopting the above embodiments include, but are not limited to: by adopting a U-shaped channel aerodynamic vortex design in the main combustion stage channel, the airflow after passing through the U-shaped channel deflection forms an aerodynamic vortex region on the outside of the main combustion stage channel with a lower flow velocity, and forms an acceleration zone on the inside of the main combustion stage channel with a higher flow velocity. While ensuring the low pollution emission level of the combustion chamber, it effectively avoids backfire and ablation problems in the main combustion stage premixing channel, and can also improve the life of the fuel nozzle-level main vortex generator. Attached Figure Description

[0021] The above and other features, properties, and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, in which the same reference numerals always denote the same features. It should be noted that these drawings are merely illustrative and are not drawn to scale, and should not be construed as limiting the scope of protection actually claimed by the present invention, wherein:

[0022] Figure 1 This is a schematic diagram of a gas turbine engine according to an embodiment.

[0023] Figure 2 This is a schematic diagram of the combustion chamber according to one embodiment.

[0024] Figure 3 This is a schematic diagram of the head of a combustion chamber according to one embodiment.

[0025] Figure 4 This is a schematic diagram of the main vortex generator of a combustion chamber according to one embodiment. Detailed Implementation

[0026] Reference will now be made in detail to various embodiments of the invention, examples of which are shown in the accompanying drawings and described below. Although the invention will be described in conjunction with exemplary embodiments, it should be understood that this specification is not intended to limit the invention to those exemplary embodiments. Rather, the invention is intended to cover not only these exemplary embodiments, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the invention as defined by the appended claims.

[0027] In the following description, the orientation or positional relationship indicated by terms such as "axial," "radial," "circumferential," "upstream," "downstream," "inner," "outer," or other directional terms is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing the invention and simplifying the description, and is not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In addition, "upstream" and "downstream" are based on the direction of airflow, for example, air flows from "upstream" to "downstream."

[0028] Furthermore, this application uses specific terms to describe its embodiments. For example, "an embodiment" and / or "one embodiment" refers to a particular feature, structure, or characteristic associated with at least one embodiment of this application. Therefore, it should be emphasized and noted that "an embodiment" or "one embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of this application can be appropriately combined.

[0029] The combustion chambers described below are applicable to gas turbine engines, taking aero engines as an example, but this is not a limitation. For example, they can also be applied to marine gas turbines, ground gas turbines, and other scenarios.

[0030] like Figure 1 As shown, a gas turbine engine, taking an aero engine as an example, includes a low-pressure compressor 1, a high-pressure compressor 2, an annular combustion chamber 3, a high-pressure turbine 4, and a low-pressure turbine 5. Air is compressed by the low-pressure compressor 1 and then enters the high-pressure compressor 2. The high-pressure air then enters the annular combustion chamber 3 to burn with fuel. The resulting high-temperature, high-pressure gas enters the high-pressure turbine 4 and the low-pressure turbine 5, driving the high-pressure compressor 2 and the low-pressure compressor 1 respectively through the turbine's work.

[0031] like Figure 2 As shown, in some embodiments, the combustion chamber may be an annular combustion chamber. Figure 2 An enlarged view of the annular combustion chamber 3 is shown. The annular combustion chamber 3 may include a diffuser 300, an outer combustion chamber casing 302, an inner combustion chamber casing 304, an outer ring of the flame tube 306, an inner ring of the flame tube 308, a staged fuel nozzle 310, a main swirl diffuser 320, a splash guard 330, and a head transition section 340.

[0032] Multiple staged fuel nozzles 310 and main swirl generators 320 are uniformly arranged along the circumferential direction of the single-annular cavity structure of the annular combustion chamber 3. For example, the number of staged fuel nozzles 310 and main swirl generators 320 is 10 to 30, which are circumferentially distributed in the single-annular cavity. After passing through the diffuser 300, the incoming air enters the flame tube through the staged fuel nozzles 310 and main swirl generators 320 for combustion. The remaining air is cooled by the outer ring 306, the inner ring 308, and the splash plate 330 of the flame tube. A portion of the remaining air flows into the high-pressure turbine 4 through the inner and outer annular cavity channels of the combustion chamber to cool the high-pressure turbine blades.

[0033] Figure 3 The diagram shows a central staged nozzle assembly for a combustion chamber, comprising a staged fuel nozzle 310 and a main swirl generator 320. The staged fuel nozzle 310 and the main swirl generator 320 are arranged coaxially, with the staged fuel nozzle 310 at the center and the main swirl generator 320 surrounding it. The staged fuel nozzle 310 and the main swirl generator 320 together constitute the pre-combustion stage 31 and the main combustion stage 32 of the central staged nozzle assembly in an annular combustion chamber.

[0034] The staged fuel nozzle 310 may include a center nozzle 311, a first-stage pre-combustion stage swirler 312, a second-stage pre-combustion stage swirler 313, a venturi tube sandwiched between swirlers 312 and 313, a peripheral sleeve 315 for swirler 313, an interstage section 316, and a collecting ring 317. It is understood that the structure of the pre-combustion stage swirler is not limited to the two-stage swirler structure described above. Fuel from the main fuel line is divided into two stages: the first stage supplies fuel to the center nozzle 311, which is ejected from the centrifugal fuel injection orifice 318 at the end of the center nozzle 311, supplying the pre-combustion stage 31; the second stage supplies fuel to the collecting ring 317, which is ejected from the circumferentially evenly arranged direct injection orifices 324 on the collecting ring 317, supplying the main combustion stage 32. The fuel ejected from the centrifugal fuel injection orifice 318 forms a cone-shaped spray that hits the wall of the venturi tube 314 and mixes with the air from the first-stage cyclone separator 312 and the second-stage cyclone separator 313 of the pre-combustion stage to form a pre-combustion stage flame downstream. The sleeve 315 is connected to the interstage section 316 and is connected to the inner wall surface 319 of the oil collecting ring 317 to form a cavity. The end 328 of the sleeve 315 is provided with at least one row of cooling holes along the circumference of the center line of the staged fuel nozzle 310. Air from upstream enters the cavity and passes through the cooling holes to impact and cool the interstage section 316. The cooled air enters the main combustion stage passage 325 along the inner wall of the interstage section 316.

[0035] refer to Figure 3 As shown, the main vortex generator 320 may include a U-shaped guide plate 321, a main combustion stage swirler 322, a main vortex generator outer ring 323, and a mounting base 327. The internal channel of the main vortex generator is U-shaped. The airflow from the diffuser 3 is deflected by the main vortex generator and enters the main combustion stage channel 325 formed by the main vortex generator outer ring 323 and the outer wall 326 of the oil collecting ring 317. It mixes with fuel 38 ejected from the circumferentially evenly arranged direct-injection nozzles 324 on the oil collecting ring 317, forming a main combustion stage flame downstream of the main combustion stage channel 325. The U-shaped guide plate 321 here refers to the ability to form a U-shaped channel, and does not mean that the guide plate itself is U-shaped. Figure 3 , Figure 4 As shown, the U-shaped deflector itself is closer in shape to an L-shaped structure.

[0036] refer to Figure 4 The enlarged view of the main vortex generator 320 shown illustrates the beneficial effects of its structure. The airflow, after being deflected by the U-shaped channel, forms an aerodynamic vortex region 36 near the outer ring 323 of the main vortex generator within the main combustion stage passage 325, where the flow velocity is low. Conversely, an acceleration zone with a higher flow velocity is formed near the outer wall 326 of the oil collecting ring within the main combustion stage passage 325. This effectively prevents backfire and erosion of the outer wall 326 of the oil collecting ring within the main combustion stage passage 325 due to excessively low flow velocity under high engine operating conditions. Furthermore, as... Figure 4As shown, the main combustion stage fuel 38 is mainly concentrated on the side of the main combustion stage passage 325 near the outer wall 326 of the oil collecting ring. Under the action of swirling shear, it is atomized, evaporated, and mixed. The main vortex generator, with the aforementioned design features, has a high flow velocity and strong swirling shear on this side, which is beneficial for the atomization, evaporation, and mixing of the main combustion stage fuel 38, thereby helping to reduce NOx, CO, and other pollutant emissions from the combustion chamber. Specifically, the airflow path through the main combustion stage passage 325 is as follows: Figure 3 The path shown by the dashed line, combined with... Figure 4 As shown, the airflow path can include: after passing through the main combustion stage vortex 322, the airflow is guided by the first airflow channel 3251 defined by the first part 3211 of the U-shaped guide plate 321 and the outer wall of the main vortex outer ring 323 to flow in a first direction. Then, the airflow is guided by the second part 3212 of the U-shaped guide plate 321 to flow in a second direction, which is perpendicular to the first direction (it should be understood that this perpendicularity is approximately perpendicular, not strictly 90°, and has some error). The second part 3212 can be perpendicular to the first part 3211, as described above, forming an L-shaped structure. Afterward, the airflow is guided by the second airflow channel 3252 defined by the inner wall of the main vortex outer ring 323 and the outer wall 326 of the oil collecting ring to flow in a third direction, which is opposite to the first direction, for example... Figure 3 , Figure 4 As shown, the first direction is the flow direction from right to left, while the third direction is the flow direction from left to right. An aerodynamic vortex region 36 is formed on the radial outer side of the second airflow channel 2352, and an acceleration zone is formed on the radial inner side of the second airflow channel 2352, that is, on the side close to the outer wall 326 of the oil collecting ring.

[0037] In some embodiments, the main combustion stage cyclone 322 is a bladed cyclone with 20 to 60 blades and a blade installation angle between 20° and 60°.

[0038] In some embodiments, the main combustion stage cyclone separator 322 is a multi-slant-hole cyclone separator with 10 to 30 holes and the inclination angle of the holes is between 20° and 60°.

[0039] In some embodiments, the first-stage cyclone separator and the second-stage cyclone separator of the pre-combustion stage are axial or cyclone separators, and the cyclone separator of the main combustion stage is an axial cyclone separator.

[0040] In some embodiments, the staged fuel nozzle 310 is designed to be integrally formed by welding and / or integral casting and / or 3D printing, and the main swirl generator 320 is also designed to be integrally formed by welding and / or integral casting and / or 3D printing. The staged fuel nozzle 310 and the main swirl generator 320 are radially floatingly fitted, with the mating surface located between the lower end face of the guide plate 321 and the outer ring surface 326 of the oil collecting ring 317. During assembly, the main swirl generator 320 is first connected to the splash plate 330 and the head adapter section 340 via the mounting base 327. Then, the staged fuel nozzle 310 is inserted into the combustion chamber through the outer casing 302 and mates with the main swirl generator 320. The staged fuel nozzle 310 is then fixed to the outer casing with bolts.

[0041] Based on the above description of the annular combustion chamber staged fuel nozzle 310 and the main swirl generator 320, it can be understood that an annular combustion chamber 3, which adopts the aforementioned annular combustion chamber staged fuel nozzle 310 and main swirl generator 320, can achieve the effects of reducing pollution emissions and avoiding backfire and erosion in the main combustion stage passage under any engine operating conditions. At the same time, the design scheme of the aforementioned annular combustion chamber staged fuel nozzle 310 and main swirl generator 320 has a simple structure and is easy to manufacture.

[0042] As described above, this application also provides a combustion organization method, including: in the main combustion stage, the main combustion stage channel is configured as a U-shaped channel aerodynamic vortex structure, the airflow after passing through the U-shaped channel forms an aerodynamic vortex region on the outside of the main combustion stage channel, and an acceleration zone is formed on the inside of the main combustion stage channel.

[0043] Preferably, in some embodiments, the specific steps for the airflow after passing through the U-shaped channel to form an aerodynamic vortex region outside the main combustion stage channel and an acceleration zone inside the main combustion stage channel can be as follows: the U-shaped guide plate, the main combustion stage vortex generator, the outer ring of the main vortex generator, and the oil collecting ring provide the main combustion stage channel; after the airflow passes through the main combustion stage vortex generator, the airflow is guided by the first part of the U-shaped guide plate and the outer wall of the outer ring of the main vortex generator to flow in a first direction, and then the airflow is guided by the second part of the U-shaped guide plate to flow in a second direction, the second direction being perpendicular to the first direction; then the airflow is guided by the second airflow channel defined by the inner wall of the outer ring of the main vortex generator and the outer wall of the oil collecting ring to flow in a third direction, the third direction being opposite to the first direction, forming an aerodynamic vortex region outside the second airflow channel and an acceleration zone inside the main combustion stage channel; fuel is ejected from the nozzle of the outer wall of the oil collecting ring into the second airflow channel and mixes with the airflow in the second airflow channel.

[0044] In summary, the beneficial effects of the combustion chamber, gas turbine engine, and combustion organization methods described above include, but are not limited to, the use of a U-shaped channel aerodynamic vortex design in the main combustion stage channel. After the airflow is deflected by the U-shaped channel, an aerodynamic vortex region with a lower flow velocity is formed on the outside of the main combustion stage channel, while an acceleration zone with a higher flow velocity is formed on the inside of the main combustion stage channel. This effectively avoids backfire and ablation problems in the main combustion stage premixing channel while ensuring low pollution emission levels in the combustion chamber, and can also improve the lifespan of the fuel nozzle-level main vortex generator.

[0045] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A combustion chamber, characterized by, The combustion chamber comprises a staged fuel nozzle and a main swirler arranged radially coaxially with the staged fuel nozzle. The staged fuel nozzle comprises a center nozzle, a pre-combustion stage swirler, and an oil collecting ring. The main swirler comprises a U-shaped guide vane, a main combustion stage swirler, a main swirler outer ring, and a mounting seat. The U-shaped guide vane, the main combustion stage swirler, the main swirler outer ring, and the oil collecting ring provide a main combustion stage passage. The internal passage of the main swirler is in a U shape. After the air flow is deflected by the main swirler, the air flow enters the main combustion stage passage formed by the outer wall of the main swirler outer ring and the oil collecting ring, mixes with the fuel sprayed from the straight jet nozzles arranged uniformly in the circumferential direction on the oil collecting ring, and forms a main combustion stage flame downstream of the main combustion stage passage.

2. The combustion chamber of claim 1, wherein The main combustion stage swirler comprises a vane swirler, the number of vanes is 20-60, and the vane installation angle is between 20° and 60°.

3. The combustion chamber of claim 1, wherein The main combustion stage swirler comprises a multi-inclined-hole swirler, the number of holes is 10-30, and the inclination angle of the holes is between 20° and 60°.

4. The combustion chamber of claim 1 wherein, The pre-combustion stage swirler comprises a pre-combustion stage primary swirler and a pre-combustion stage secondary swirler, wherein the pre-combustion stage primary swirler and the pre-combustion stage secondary swirler are both axial or radial swirler.

5. The combustion chamber of claim 1 wherein, The main combustion stage swirler is an axial swirler.

6. The combustion chamber of claim 1 wherein, The staged fuel nozzle is manufactured by welding and / or integral casting and / or 3D printing.

7. The combustion chamber of claim 1 wherein, The main swirler is formed as a whole by welding and / or integral casting and / or 3D printing, and the staged fuel nozzle and the main swirler are radially floatingly matched.

8. The combustion chamber of claim 1 wherein, The air flow path through the main combustion stage passage comprises: after the air flow passes through the main combustion stage swirler, the air flow is guided to flow in a first direction by a first air flow passage defined by a first part of the U-shaped guide vane and an outer wall of the main swirler outer ring, then the air flow is guided to flow in a second direction by a second part of the U-shaped guide vane, the second direction is perpendicular to the first direction, then the air flow is guided to flow in a third direction by a second air flow passage defined by an inner wall of the main swirler outer ring and an outer wall of the oil collecting ring, the third direction is opposite to the first direction, an aerodynamic trapped vortex area is formed outside the second air flow passage, and an acceleration zone is formed inside the main combustion stage passage.

9. A gas turbine engine characterized by, The combustion chamber comprises the combustion chamber according to any one of claims 1-8.

10. A method of burning tissue, characterized by, The combustion chamber comprises the combustion chamber according to claim 1. In the main combustion stage, the main combustion stage passage is arranged as a U-shaped passage aerodynamic trapped vortex structure, and the air flow deflected by the U-shaped passage forms an aerodynamic trapped vortex area outside the main combustion stage passage and an acceleration zone inside the main combustion stage passage. The U-shaped guide plate, the main combustion stage swirler, the main vortex outer ring, and the oil collecting ring provide a main combustion stage passage. After the air flow passes through the main combustion stage swirler, the air flow is guided to flow in a first direction by a first air flow passage defined by a first part of the U-shaped guide plate and an outer wall of the main vortex outer ring, and then the air flow is guided to flow in a second direction by a second part of the U-shaped guide plate, the second direction being perpendicular to the first direction, and then the air flow is guided to flow in a third direction by a second air flow passage defined by an inner wall of the main vortex outer ring and an outer wall of the oil collecting ring, the third direction being opposite to the first direction, an aerodynamic trapped vortex area being formed outside the second air flow passage and an acceleration area being formed inside the main combustion stage passage; fuel is injected from injection holes in the outer wall of the oil collecting ring to the second air flow passage and mixed with the air flow in the second air flow passage.

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