Patent Publication Number: US-2020284432-A1

Title: Combustor for gas turbine engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-41205 filed Mar. 7, 2019 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a combustor for a gas turbine engine, comprising an outer wall part having formed therein an impingement cooling hole, an inner wall part having formed therein an effusion cooling hole, and a tubular dilution air introduction passage providing a connection between an outer opening formed in the outer wall part and an inner opening formed in the inner wall part, the dilution air introduction passage introducing dilution air into a combustion chamber. 
     Description of the Related Art 
     U.S. Pat. No. 8,161,752 B2 has made known an arrangement in which an insert 174 (dilution air introduction passage) that connects a low temperature wall 156 (outer wall part) and a high temperature wall 154 (inner wall part) of a combustor 100 of a gas turbine engine and introduces dilution air to a combustion chamber 116 includes a cylindrical part 220 and a conical part 222 opening in a funnel shape from the cylindrical part 220, the cylindrical part 220 extends through an opening of the high temperature wall 154 and extends to the interior of the combustion chamber 116, and the conical part 222 opposes an opening 170 of the low temperature wall 156 via a gap 284. 
     In the conventional arrangement, there is a possibility that, since the gap 284 is present between the open end of the conical part 222 of the insert 174 and the opening of the low temperature wall 156, cooling air flowing between the low temperature wall 156 and the high temperature wall 154 will leak to the interior of the insert 174, the amount of dilution air supplied to the combustion chamber 116 will become unstable, the flow rate of cooling air 216 passing through an effusion cooling hole 214 of the high temperature wall 154 will decrease, and the cooling effect of the high temperature wall 154 will be degraded. There is also a possibility that, since the cylindrical part 220 of the insert 174 protrudes into the combustion chamber 116, the extremity of the cylindrical part 220 will be thermally damaged. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in light of the above circumstances, and it is an object thereof to stabilize the amount of dilution air introduced into a combustion chamber via a dilution air introduction passage while ensuring the cooling performance and durability of a combustor. 
     In order to achieve the object, according to a first aspect of the present invention, there is provided a combustor for a gas turbine engine, comprising an outer wall part having formed therein an impingement cooling hole, an inner wall part having formed therein an effusion cooling hole, and a tubular dilution air introduction passage providing a connection between an outer opening formed in the outer wall part and an inner opening formed in the inner wall part, the dilution air introduction passage introducing dilution air into a combustion chamber, wherein a radially outer end part of the dilution air introduction passage is radially slidably fitted into an inner periphery of the outer opening, and a radially inner end part of the dilution air introduction passage axially slidably abuts against an open edge of the inner opening. 
     In accordance with the first aspect, dilution air is introduced into the combustion chamber via the tubular dilution air introduction passage, which provides a connection between the outer opening formed in the outer wall part and the inner opening formed in the inner wall part, thus enabling the temperature distribution of the combustion chamber outlet to be appropriately maintained. With regard to the inner wall part, which faces the combustion chamber and therefore easily attains a high temperature, the outer face of the inner wall part is cooled due to air passing through the impingement cooling hole provided in the outer wall part colliding therewith, the inner face of the inner wall part is cooled by an air film formed by the air passing through the effusion cooling hole provided in the inner wall part, and it is thus protected from high temperature combustion gas. 
     Since the radially outer end part of the dilution air introduction passage is radially slidably fitted into the inner periphery of the outer opening, and the radially inner end part of the dilution air introduction passage axially slidably abuts against the open edge of the inner opening, even if the outer wall part and the inner wall part undergo relative movement in the radial direction or in the axial direction due to a difference in the amount of thermal expansion, not only is it possible to prevent an excessive stress from being generated, but it is also possible to ensure airtightness for both the outer opening and the inner opening of the dilution air introduction passage, thereby stabilizing the amount of dilution air introduced into the combustion chamber via the dilution air introduction passage and appropriately maintaining the temperature distribution at the combustor outlet. Moreover, since air is prevented from leaking into a space between the outer wall part and the inner wall part from the radially outer end part of the dilution air introduction passage, air passing through the impingement cooling hole of the outer wall part collides with the inner wall part without decreasing the flow rate, thus enhancing the cooling effect of the inner wall part. 
     According to a second aspect of the present invention, in addition to the first aspect, the inner opening protrudes from the inner wall part radially outward in a tubular shape. 
     In accordance with the second aspect, since the inner opening protrudes from the inner wall part radially outward in a tubular shape, the inner opening does not protrude into the combustion chamber from the inner wall part, thus preventing the inner opening from protruding into the combustion chamber and being thermally damaged. 
     According to a third aspect of the present invention, in addition to the second aspect, the radially inner end part of the dilution air introduction passage includes an annular flange portion, the annular flange portion axially slidably abutting against the open edge of the inner opening. 
     In accordance with the third aspect, since the radially inner end part of the dilution air introduction passage includes the annular flange portion, which axially slidably abuts against the open edge of the inner opening, even if the dilution air introduction passage, which moves in the axial direction integrally with the outer wall part, undergoes relative movement in the axial direction with respect to the inner wall part, airtightness can be ensured in a range in which the open edge of the inner opening does not become detached from the annular flange portion, and it is possible to reliably ensure airtightness for the radially inner end part of the dilution air introduction passage. 
     The above and other objects, characteristics and advantages of the present invention will be clear from detailed descriptions of the preferred embodiments which will be provided below while referring to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the overall structure of a gas turbine engine. (first embodiment) 
         FIG. 2  is an enlarged view of part  2  in  FIG. 1 . (first embodiment) 
         FIG. 3  is an enlarged view of part  2  in  FIG. 1 . (second embodiment) 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention is explained below by reference to  FIG. 1  and  FIG. 2 . In the present specification, the axial direction is defined as a direction in which a low pressure system shaft  15  and a high pressure system shaft  16  of a gas turbine engine extend, and the radial direction is defined as a direction orthogonal to the axial direction. 
     As shown in  FIG. 1 , a gas turbine engine for an airplane to which the present invention is applied includes an outer casing  11  and an inner casing  12 , a front part and a rear part of a low pressure system shaft  15  being rotatably supported in the interior of the inner casing  12  via a front first bearing  13  and a rear first bearing  14  respectively. A tubular high pressure system shaft  16  is relatively rotatably fitted around the outer periphery of an axially intermediate part of the low pressure system shaft  15 , a front part of the high pressure system shaft  16  is rotatably supported on the inner casing  12  via a front second bearing  17 , and a rear part of the high pressure system shaft  16  is relatively rotatably supported on the low pressure system shaft  15  via a rear second bearing  18 . 
     A front fan  19  having a blade tip facing an inner face of the outer casing  11  is fixed to the front end of the low pressure system shaft  15 ; part of the air sucked in by the front fan  19  passes through stator vanes  20  disposed between the outer casing  11  and the inner casing  12 , part thereof then passes through an annular bypass duct  21  formed between the outer casing  11  and the inner casing  12  and is made to issue rearward, and the rest of the air is supplied to an axial low pressure compressor  22  and a centrifugal high pressure compressor  23  disposed in the interior of the inner casing  12 . 
     The low pressure compressor  22  includes stator vanes  24  that are fixed in the interior of the inner casing  12  and a low pressure compressor wheel  25  that includes compressor blades on the outer periphery and is fixed to the low pressure system shaft  15 . The high pressure compressor  23  includes stator vanes  26  that are fixed in the interior of the inner casing  12  and a high pressure compressor wheel  27  that includes compressor blades on the outer periphery and is fixed to the high pressure system shaft  16 . 
     A reverse flow combustor  29  is disposed to the rear of a diffuser  28  that is connected to the outer periphery of the high pressure compressor wheel  27 , and fuel is injected into the interior of the reverse flow combustor  29  from a fuel injection nozzle  30 . The fuel and air are mixed in the interior of the reverse flow combustor  29  and undergo combustion, and the combustion gas thus generated is supplied to a high pressure turbine  31  and a low pressure turbine  32 . 
     The high pressure turbine  31  includes nozzle guide vanes  33  fixed in the interior of the inner casing  12  and a high pressure turbine wheel  34  that includes turbine blades on the outer periphery and is fixed to the high pressure system shaft  16 . The low pressure turbine  32  includes nozzle guide vanes  35  fixed in the interior of the inner casing  12  and a low pressure turbine wheel  36  that includes turbine blades on the outer periphery and is fixed to the low pressure system shaft  15 . 
     Therefore, when the high pressure system shaft  16  is driven by means of a starter motor, which is not illustrated, air sucked in by the high pressure compressor wheel  27  is supplied to the reverse flow combustor  29 , is mixed with fuel, and undergoes combustion, and the combustion gas thus generated drives the high pressure turbine wheel  34  and the low pressure turbine wheel  36 . As a result, the low pressure system shaft  15  and the high pressure system shaft  16  rotate and the front fan  19 , the low pressure compressor wheel  25 , and the high pressure compressor wheel  27  compress air and supply it to the reverse flow combustor  29 , and the gas turbine engine thus continues to run even when the starter motor is stopped. 
     While the gas turbine engine is running, part of the air sucked in by the front fan  19  passes through the bypass duct  21 , is made to issue rearward, and generates the main thrust, particularly at a time of low speed flying. The rest of the air sucked in by the front fan  19  is supplied to the reverse flow combustor  29 , is mixed with fuel, undergoes combustion, drives the low pressure system shaft  15  and the high pressure system shaft  16 , is then made to issue rearward, and generates a thrust. 
     The reverse flow combustor  29  is formed from an outside liner portion  29   a  extending forward from a position at which the fuel injection nozzle  30  is provided, and an outside turn duct portion  29   b  that extends rearward while bending through  1800  from the front end of the outside liner portion  29   a  and is connected to the nozzle guide vanes  33 . As is shown in  FIG. 2  in an enlarged state, the outer shell of the reverse flow combustor  29  has a double layer structure formed from an inner wall part  42  facing a combustion chamber  41  and an outer wall part  43  covering the outer side of the inner wall part  42 , the inner wall part  42  having a large number of effusion cooling holes  42   a  formed therein and the outer wall part  43  having a large number of impingement cooling holes  43   a  formed therein. The effusion cooling holes  42   a  of the inner wall part  42  are inclined together in the same direction so as to extend obliquely through the inner wall part  42 , and the impingement cooling holes  43   a  extend through the outer wall part  43  so as to be orthogonal to the inner wall part  42  in their vicinity. 
     A plurality of dilution air introduction passages  44  are provided in the outside liner portion  29   a  of the reverse flow combustor  29 , the dilution air introduction passage  44  extending through the inner wall part  42  and the outer wall part  43 . The dilution air introduction passage  44  includes a cylindrical passage portion  44   a  and an annular flange portion  44   b  formed by bending a radially inner end of the passage portion  44   a  outward through right angles. A short cylindrical outer opening  43   b  bending inward in the radial direction is formed in the outer wall part  43 , and the cylindrical passage portion  44   a  of the dilution air introduction passage  44  is radially slidably fitted into the outer opening  43   b . A short cylindrical inner opening  42   b  bending outward in the radial direction is formed in the inner wall part  42 , and the annular flange portion  44   b  of the dilution air introduction passage  44  abuts against the open edge of the inner opening  42   b  from the radially outer side. 
     While the gas turbine engine is running, the annular flange portion  44   b  of the dilution air introduction passage  44  abuts against the inner opening  42   b  of the inner wall part  42  due to a difference in air pressure, but in order to reliably make the annular flange portion  44   b  abut against the inner opening  42   b  when starting the gas turbine engine, it is possible to urge the dilution air introduction passage  44  toward the inner wall part  42  by means of a conical spring  45 . 
     The operation of the embodiment of the present invention having the above arrangement is now explained. 
     High pressure air that has been compressed by the low pressure compressor  22  and the high pressure compressor  23  and supplied from the diffuser  28  to a space encircling the reverse flow combustor  29  is supplied from an outer peripheral part of the fuel injection nozzle  30  to the combustion chamber  41  of the reverse flow combustor  29 , mixed with fuel injected from the fuel injection nozzle  30 , and subjected to combustion. At the same time as this, high temperature combustion gas is diluted with air that has been introduced into the combustion chamber  41  through the plurality of dilution air introduction passages  44 , thus appropriately maintaining the temperature distribution of combustion gas discharging from the reverse flow combustor  29 . 
     Furthermore, the inner wall part  42  of the reverse flow combustor  29  facing the combustion chamber  41  attains a high temperature, but due to air passing through the impingement cooling hole  43   a  formed in the outer wall part  43  colliding with the inner wall part  42  at right angles the high temperature inner wall part  42  is thus cooled. Air that has passed through the impingement cooling hole  43   a  further passes through the effusion cooling hole  42   a  of the inner wall part  42  and forms an air film along an inner face of the inner wall part  42 . The high temperature inner wall part  42  is cooled by the air film preventing combustion gas of the combustion chamber  41  from making direct contact with the inner face of the inner wall part  42 . 
     While the gas turbine engine is running, since each member undergoes relative movement in the axial direction and the radial direction of the gas turbine engine due to a difference in the amount of thermal expansion, it is necessary to absorb the relative movement, thus preventing excessive stress from being generated in each member. 
     In particular, since a large difference in temperature is caused between the low temperature outer wall part  43  and the high temperature inner wall part  42  of the reverse flow combustor  29 , the amount of relative movement in the axial direction and the radial direction between the inner wall part  42  and the outer wall part  43  becomes large in a section of the dilution air introduction passage  44 , and there is a possibility that excessive stress will be generated and the amount of dilution air will become unstable. 
     However, in accordance with the present embodiment, even if the inner wall part  42  and the outer wall part  43  undergo relative movement in the radial direction, due to the cylindrical passage portion  44   a  of the dilution air introduction passage  44  sliding radially with respect to the outer opening  43   b  of the outer wall part  43 , it is possible to absorb the relative movement in the radial direction between the inner wall part  42  and the outer wall part  43  while preventing air from leaking via the outer opening  43   b.    
     Moreover, even if the inner wall part  42  and the outer wall part  43  undergo relative movement in the axial direction, due to the annular flange portion  44   b  of the dilution air introduction passage  44  sliding in the axial direction with respect to the inner opening  42   b  of the inner wall part  42 , it is possible to absorb the relative movement in the axial direction between the inner wall part  42  and the outer wall part  43  while preventing air from flowing into the dilution air introduction passage  44 . 
     In this way, since the air in the space sandwiched between the outer wall part  43  and the inner wall part  42  does not flow into the dilution air introduction passage  44 , it becomes possible to stabilize the amount of dilution air that passes through the dilution air introduction passage  44  and is supplied to the combustion chamber  41 , thus enabling the temperature distribution of combustion gas at the outlet of the reverse flow combustor  29  to be appropriately maintained. Moreover, since the air in the space sandwiched between the outer wall part  43  and the inner wall part  42  does not flow into the dilution air passage  44 , the flow rate of air passing through the effusion cooling hole  42   a  of the inner wall part  42  will not decrease, thus enhancing the cooling effect of the inner wall part  42 . 
     Furthermore, since the inner opening  42   b  of the inner wall part  42  does not protrude into the combustion chamber  41  but does protrude into the space sandwiched between the outer wall part  43  and the inner wall part  42 , it is possible to prevent the inner opening  42   b  of the inner wall part  42  from being directly exposed to high temperature combustion gas flowing through the interior of the combustion chamber  41  and being thermally damaged. 
     Second Embodiment 
     A second embodiment of the present invention is now explained by reference to  FIG. 3 . 
     In the first embodiment the outer opening  43   b  of the outer wall part  43  protrudes radially inward toward the inner wall part  42 , but in the second embodiment the outer opening  43   b  of the outer wall part  43  protrudes radially outward so as to be away from the inner wall part  42 . 
     In accordance with the second embodiment, the same effects as those of the first embodiment can also be achieved. 
     Embodiments of the present invention are explained above, but the present invention may be modified in a variety of ways as long as the modifications do not depart from the gist of the present invention. 
     For example, a combustor to which the present invention is applied is not necessarily a reverse flow type.