The present disclosure relates generally to liners used in gas turbine engines, and more specifically to ceramic matrix composite (CMC) combustor liners.
Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft.
Combustors and turbines made of metal alloys requiring significant cooling to be maintained at or below their maximum use temperatures. The operational efficiencies of gas turbine engines are increased with the use of ceramic matrix composite (CMC) materials that require less cooling and having operating temperatures which exceed the maximum use temperatures of metal alloys. The reduced cooling required by CMC combustor liners when compared to metal alloys permits combustor profiles to be flattened and thereby leads to reduced NOx emmisions.
CMC combustor liners sometimes utilize a single wall design in which a single wall having an inner liner wall and an outer liner wall is formed using a pair of hoops. Accomplishing a transition between the CMC liner material and a metal shell surrounding the liner material is a significant concern. The selection of means for attaching the liners used in CMC tiled liners to the surrounding metal shell also poses significant challenges.
The present application discloses one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter.
According to one aspect of the present disclosure, a combustor for use in a gas turbine engine may include an annular metallic shell and an annular liner. The annular metallic shell may form an annular cavity. The annular liner may be arranged in the annular cavity of the annular metallic shell and may define an annular combustion chamber. The annular liner may include a first ceramic tile coupled to the metallic shell by a first fastener extending through the first ceramic tile and a second ceramic tile coupled to the metallic shell by a second fastener extending through the second ceramic tile. An overlapped portion of the first ceramic tile may be arranged to extend between the second fastener and the annular combustion chamber to shield the second fastener from the annular combustion chamber.
In some embodiments, the combustor may include a heat shield. The heat shield may be arranged to extend between the first fastener that extends through the first ceramic tile to shield the first fastener from the annular combustion chamber.
In some embodiments, the annular metallic shell may include an annular outer shell member and an annular inner shell member concentrically nested inside the annular outer shell member. The annular inner shell member may be formed to include joggles (or steps) extending inwardly (or outwardly) in the radial direction.
In some embodiments, the annular inner shell member may be formed to include dimples extending outward in the in the radial direction. The annular outer shell member may be formed to include dimples extending inward in the radial direction.
In some embodiments, the first ceramic tile may be formed to include a radially-inwardly opening hollow sized and arranged to receive at least a portion of one of the dimples included in the annular inner shell member. The second ceramic tile may be formed to include a radially-inwardly opening hollow sized and arranged to receive at least a portion of another one of the dimples included in the annular inner shell member.
In some embodiments, the first fastener and the second fastener may be formed to include passages configured to receive active cooling air. The combustor may also include at least one fuel nozzle arranged to inject fuel into the annular combustion chamber.
In some embodiments, the second ceramic tile may include a body and at least one tab extending from the body. The second fastener may extend through one of the tabs included in the second ceramic tile.
According to another aspect of the present disclosure, a method for assembling a liner for a combustor of a gas turbine engine comprises positioning a first end of a first tile included in the liner against a first joggled portion of a shell included in the liner, positioning a second tile included in the liner against a second joggled portion of the shell so that a second end of the first tile engages the second tile and the first tile overlaps the second tile, fastening the first tile to the shell using a first fastener, and fastening the second tile to the shell using a second fastener so that the second fastener is sheltered from heat generated by the combustor by the first tile.
These and other features of the present disclosure will become more apparent from the following description of the illustrative embodiments.
For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments illustrated in the drawings and specific language will be used to describe the same.
CMC combustor liners offer many advantages to engine performance. CMC combustor liners require less cooling than metal alloys typically used combustors and turbines, and the reduction in liner cooling permits a flattening of the combustor profile to be achieved. Higher turbine inlet temperatures and flatter combustor profiles lead to reduced NOx emissions. In addition, reduced liner cooling allows a greater fraction of airflow in the gas turbine engine to be dedicated to the combustion process. As a result, in a “lean” burn application, greater airflow for combustion provides a reduction in emissions and/or provides a greater temperature increase for a given emissions level. In a “rich” burn application, greater airflow for combustion allows more air used to be used for quenching and provides reduced NOx emissions.
The principal advantage to any CMC combustor liner is cost. The driving cost of the CMC combustor liner fabrication process is furnace time, which is approximately three weeks. Given the high temperatures that must be maintained to properly cure the CMC combustor liner, the cost of the CMC combustor liner fabrication process is high. The single wall CMC combustor liner design allows for one combustor to be cured at a time in the furnace. However, the CMC tiled liner design allows tiles for several combustors to be cured at the same time which provides for dramatic cost savings. For example, the overall cost of the fabrication process for the CMC tiled liner design may be one half of the cost of the single wall CMC liner design for a wall liner of the same size.
One advantage of the disclosed CMC tiled liner design is how to attach the tiles to the surrounding metal shell. Metal fasteners lose their strength and even melt at CMC combustor liner operating temperatures. CMC fasteners are not as strong as a metal fastener of equivalent size by almost an order of magnitude, and CMC fasteners do not permit the tile to be snugly fastened to the shell in the same way that screw threads do. Since the operating temperature of the metal fastener is so much lower than the operating temperature of the CMC combustor liner, cooling the metal fastener to preserve its strength would in most cases undo the desired high temperature capability of the CMC combustor liner.
Referring now to
Referring now to
The forward-most tile 112 and the fastener 118 are sheltered from heat generated by the combustor by a heat shield 122 that overhangs the tile 112 as shown in
As shown in
Referring again to
Referring now to
As shown in
Similar to the first embodiment 10 and unlike the second embodiment 110, no joggles are formed in the shell 216 of the third embodiment 210. For the purposes of the present disclosure, the arrangement shown in
The tiles 212, 214 may be dished shaped as shown in
The principal embodiments of the CMC combustor liner are shown in
Referring now to
As indicated above with respect to the first embodiment, fasteners used to secure the tiles to the shell require active cooling during use. The dimples 317 formed in the shell 316 reduce the distance between the shell 316 and the tiles to enhance heat transfer on the back of the tiles and thereby improve cooling. The dimples 317, as discussed below, may increase convective heat transfer between the shell 316 and the tiles and enhance impingement cooling thereby.
Thermal gradients, such as the thermal gradient regions 20, 120, associated with the CMC combustor liner are managed using well known heat transfer conduction and convection technologies. For example, impingement cooling involves using one or more streams of a fluid (i.e. one or more streams of air produced using “jets”) to impinge on a surface and thereby increase the convective heat transfer coefficient to effect increased cooling. Impingement cooling may be used to manage the thermal gradient regions 20, 120. The dimples 317 of the shell 316 may increase convective heat transfer between the shell 316 and the tiles so that impingement cooling is enhanced. In another example, effusion cooling involves passing coolant through arrays of closely spaced holes formed in a surface to effect increased cooling of the surface. Effusion cooling may also be used to manage the thermal gradient regions 20, 120.
Referring now to
CMC material starts off as overlapping leaves of woven fiber. Forming the CMC material in three dimensions complicates the process of making the tiles (i.e. any of the tiles of the first-third embodiments) and also complicates the process for making the dimpled shell 316. The forming of the dimpled shell 316 may require both a stamping and a rolling process, and the rolling process may require special tooling in order to preserve the stamped dimpled shape while making the overall shape cylindrical. Therefore, it is desirable for the sake of manufacturing simplicity to define an essentially “two dimensional” tile arrangement. For the purpose of the present disclosure, the phrase “two dimensional” means that the tiles can be formed without cutting or joining the fibers of the CMC material.
Referring to
The tiles 412 interface with one another as shown in
The positioning of each interlocking tab 413 beneath the neighboring tile 412 provides sufficient stiffness so that the tiles 412 are prevented from vibrating excessively while the CMC combustor liner is being used. However, the use of the “shipped lapped” joint 421 as described above results in an uneven heat load applied to the interlocking tabs 413 positioned beneath the tiles 412 and the portions of the tiles 412 positioned above the interlocking tabs 413.
Referring now to
For the purpose of the present disclosure, the interlocking tabs 413 discussed with respect to
Referring now to
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The “overlapped” tiles 612 do not expose any of the fasteners to the hot gasses of the combustor. The tiles 612 are “ship-lapped” circumferentially as described above to discourage leaks. The tiles 612, with the exception of the forward-most tile 612, may be circumferentially segmented into tabs to relieve any circumferential growth issues. However, one drawback to the “overlapping” arrangement is that the outermost portion of each overlapped tile 612 is spaced apart from the shell 616, so much so that impingement heat transfer may not be adequate. It is estimated that the “overlapped” arrangement has approximately 67% of the cooling effectiveness of a similar impingement effusion liner relative to a simple effusion liner. Typically, impingement effusion liners tend to provide approximately a 30% improvement relative to simple effusion liners. It is estimated therefore that the “overlapped” arrangement provides approximately a 20% improvement to simple effusion liners.
While the disclosure has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.
This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 61/798,253, filed Mar. 15, 2013, which is incorporated herein by this reference.
Number | Date | Country | |
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61798253 | Mar 2013 | US |