Dual infrared band apparatus and method for thermally mapping a component in a high temperature combustion environment

Apparatus and method for thermally mapping a component in a high temperature environment. An optical probe (10) has a field of view (14) arranged to encompass a surface of a component (15) to be mapped. The probe (10) captures infrared (IR) emissions in the near or mid IR band. An optical fiber (16) has a field of view to encompass a spot location (18) on the surface of the component within the field of view (14) of the probe (12). The fiber (16) captures emissions in the long IR band. The emissions in the long IR band are indicative of an emittance value at the spot location. This information may be used to calibrate a radiance map of the component generated from the emissions in the near or mid IR band and thus map the absolute temperature of the component regardless of whether the component includes a TBC.

FIELD OF THE INVENTION

The present invention is generally related to infrared (IR) thermography, and, more particularly, to dual IR band apparatus and methodology for thermally mapping a component in a high temperature combustion environment, such as in a turbine engine.

BACKGROUND OF THE INVENTION

It is known to use various superalloy materials, such as cobalt or nickel-based superalloys, for making blades, vanes and other components for power generating turbine engines, propulsion equipment, etc. These turbine engines can operate at relatively high temperatures and are generally protected by a series of protective coatings. The coatings may comprise layers of metallic base coats, thermally grown oxide layers, as such layers grow in service-run components and a final ceramic thermal barrier coating (TBC). Long-term exposure of these ceramic coatings to the hostile, high temperature, abrasive environment in which such turbine engines typically operate can cause phase destabilization, sintering, microcracking, delamination and ultimately spallation within the coating layers, exposing the superalloy component and possibly resulting in rapid degradation or failure and potentially requiring costly and burdensome repairs.

U.S. Pat. No. 7,690,840 titled “Method And Apparatus For Measuring On-Line Failure Of Turbine Thermal Barrier Coatings” describes an IR imaging apparatus configured to non-destructively measure the radiance of a rotating turbine component (e.g., a blade) in a turbine engine in the context of monitoring the formation and progression of TBC defects, where images of relative high spatial resolution are needed but where accurate absolute temperature information may not be needed. The foregoing patent is commonly assigned to the assignee of the present invention and herein incorporated by reference in its entirety.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have recognized certain opportunities and certain challenges in connection with known infrared (IR) imaging apparatuses. For example, one known IR imaging apparatus is designed to operate in the near IR band of the IR spectrum. This IR band is suitable for measuring surface temperature of components comprising relatively high emittance values (such as metal blade components, etc.) but not the surface temperature of components having a ceramic thermal barrier coating (TBC), which comprises relatively low emittance values in the near or mid IR band. By way of comparison, the ceramic TBC comprises emittance values close to unity in the long IR band of the IR spectrum. Accordingly, detection of IR emissions in the long IR band can provide substantially more accurate temperature measurement in components involving TBCs. However, it has been challenging to find suitable optical materials for capturing emissions in the long IR band, (e.g., optical materials having appropriate transmissivity properties in the long IR band) and that can also operate in a hostile turbine engine environment with the same robustness as the near or mid IR materials do.

In view of their recognition, the present inventors propose an innovative dual (hybrid) IR band apparatus involving a non-imaging long wave IR optical fiber with a near or mid IR imaging device. This hybrid band design synergistically exploits the advantages associated with the relatively high spatial resolution and robustness of a near or mid IR imaging apparatus with the temperature accuracy of a long wave IR measurement, while skillfully avoiding the concomitant challenges discussed above. In one non-limiting application, the proposed apparatus is useful for mapping absolute temperature of a surface in a component comprising a TBC. That is, a TBC coated component.

In the following detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation.

Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent unless otherwise so described. Moreover, repeated usage of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising”, “including”, “having”, and the like, as used in the present application, are intended to be synonymous unless otherwise indicated.

FIG. 1is a schematic representation of an apparatus embodying aspects of the present invention. In one non-limiting application, the apparatus may be used for thermally mapping a component in a turbine engine100during operation of turbine engine100. In one non-limiting embodiment, the apparatus may include a viewing tube10mounted onto turbine engine100and positioned to extend between a radially outer casing wall102and in an inner casing wall104located radially inwardly from the outer casing wall104.

In one non-limiting embodiment, an imaging optical probe12may be housed in viewing tube10. Optical probe12has a field of view14(FIG. 2) arranged to fully encompass a surface of a component15, e.g., a rotatable blade, to be thermally mapped in a high temperature combustion environment of turbine engine100. Optical probe12is effective to concurrently capture infrared (IR) emissions that fully encompass the surface of component15. The IR emissions comprising a first IR band in an IR spectrum. In one non-limiting embodiment, this first IR band may be a near IR wavelength band comprising a range from approximately 1 μm to approximately 2 μm. In another non-limiting embodiment, in lieu of the near IR wavelength band, one can use a mid IR band in a range from approximately 3 μm to approximately 5 μm.

As noted above, the IR emissions in the first IR band may be susceptible to emittance attenuation at the surface of the component in the combustion environment of the turbine engine. In one non-limiting embodiment, optical probe12may comprise at least one optical lens13(FIG. 3) having appropriate transmissivity properties in the near IR or the mid IR band. Non-limiting examples of optical materials that may be used for optical elements in optical probe12, such as lenses, mirrors, etc., may include fused silica (near IR), sapphire, alon optical ceramic, spinel optical ceramic (mid and near IR), ZnS, Ge, or gold coated mirrors, molybdenum mirrors, etc.

In one non-limiting embodiment, an optical fiber16may be housed in viewing tube10. A field of view of optical fiber16may be arranged to encompass a spot location18(FIG. 2) on the surface of component15disposed within the field of view14of optical probe10. Optical fiber16is effective to capture IR emissions comprising a second IR band in the IR spectrum. The IR emissions in the second IR band are indicative of an emittance value at the spot location18on the surface of the component, such as a TBC coated component. In one non-limiting embodiment, this second band in the IR spectrum may be a long IR wavelength in a range from approximately 8 μm to approximately 12 μm. This band may be specially tailored to reduce effects of hot gas absorption. For instance, a relatively narrow spectral band in a range from approximately 10 μm to approximately 10.3 μm has been shown to be outside any significant gas absorption. Non-limiting examples of optical fiber16may include hollow metal waveguides, such as may comprise silver dad layers, dielectrically coated photonic bandgap fibers, hollow sapphire fibers, polycrystalline AgCl, AgBr solid fibers, etc.

In one non-limiting embodiment, a thermal imager20including a near IR focal array22, such as a charged coupled device (CCD) array or digital IR camera, is coupled to sense the IR emissions captured by optical probe12. Thermal imager20may further include a photodetector24coupled to sense the IR emissions captured by optical fiber16.

In one non-limiting embodiment, a processor26is connected to thermal imager20to generate a radiance map of the component based on the IR emissions from optical probe12. Processor26includes a temperature calibration module28configured to calibrate the radiance map based on the value of the emittance at the spot location. A monitor30may be used to display a calibrated radiance map32effective to map the absolute temperature of the component.

In one non-limiting embodiment, a further optical fiber16′ (FIG. 3) may be optionally housed in viewing tube10to encompass a further spot location18′ (FIG. 2) at a different location on the surface of component15. The further spot location is disposed within the field of view14of optical probe12. Further optical fiber16′ is effective to capture further IR emissions in the second band of the IR spectrum. The further IR emissions are indicative of an emittance value at the further spot location18′ on the surface of the component.

In one non-limiting embodiment, such as where the component of the turbine engine comprises a TBC subject to emittance variation in the combustion environment of the turbine engine, temperature calibration module28may be configured to calibrate the radiance map based on the respective emittance values at the different spot locations18,18′ and thus reduce a temperature error effect due to the emittance variation of the TBC. For example, the emittance variation may take different values throughout the surface of the component depending on varying degrees of degradation of the TBC and/or depending on varying degrees of soot contamination throughout the surface of the component.

In another non-limiting embodiment, such as where the component of the turbine engine may comprise a thermally cooled component subject to thermal gradients, temperature calibration module28may be configured to calibrate the radiance map based on the respective emittance values at the different spot locations18,18′ and thus reduce a temperature error effect due to the thermal gradients.

FIG. 4is a flow chart of a method embodying aspects of the present invention. In one non-limiting embodiment, subsequent to start step48, step50allows capturing in a field of view14(FIG. 2) of an optical probe (e.g., optical probe12(FIG. 1)) infrared (IR) emissions from a surface of a component to be thermally mapped in a high temperature combustion environment of a turbine engine. The IR emissions comprise a first IR band, such as a near or mid IR wavelength band, in an IR spectrum. Step52allows arranging in an optical fiber (e.g., optical fiber16(FIG. 1) a field of view to encompass a spot location18(FIG. 2) on the surface of the component. The spot location is disposed within the field of view of the optical probe. Step54allows capturing in the field of view of the optical fiber, IR emissions comprising a second IR band, such as a long IR wavelength band. The IR emissions in the second IR band of the IR spectrum may be indicative of an emittance value at the spot location on the surface of the component.

In one non-limiting embodiment one may optionally proceed as follows: step56allows capturing further IR emissions in the long IR wavelength band of the IR spectrum. The further IR emissions may be indicative of an emittance value at a different spot location18′ (FIG. 2), such as on the surface of a TBC coated component. Step58allows determining the surface temperature of the TBC coated component at the various spot locations, as may be measured with one or more long IR detectors (e.g., photodetector24(FIG. 1)). These temperature measurements may be used to calculate a near or mid IR emittance of the TBC coated component.

Step60allows generating a radiance map of the component based on the IR emissions in the near or mid IR band from the optical probe. Prior to end step64, step62allows calibrating the radiance map based on the respective emittance values at the different spot locations18,18′. In one non-limiting embodiment, such as where the component of the turbine engine comprises a TBC subject to emittance variation in the combustion environment of the turbine engine, this may allow to reduce a temperature error effect due to the emittance variation of the TBC. In another non-limiting embodiment, such as where the component of the turbine engine may comprise a thermally cooled component subject to thermal gradients, this may allow to reduce a temperature error effect due to the thermal gradients.

In yet another aspect of the present invention, step70allows calibrating a spot position error that may develop in connection with the spot location detected by the long IR optical fiber. For example, spot location18(FIG. 2) may be the location intended during the design of the apparatus, but not necessarily the actual spot location realized subsequent to installation of the apparatus onto the turbine. For example, as would be appreciated by those skilled in the art, in a real world application, due to manufacturing and/or installation alignment tolerances present in connection with the elements housed in the viewing tube, let us presume a certain spot position error is introduced.

In one non-limiting embodiment, the calibrating of the spot position error may be performed as follows: step72allows transmitting an IR laser beam by way of the optical fiber. This laser beam impinges on the surface of the component on a laser-radiated location expected to correspond with spot location18. However, because of the introduced spot position error, let us presume the laser beam actually impinges at spot location19(FIG. 3, represented by a dashed circle). In this case, step74allows capturing with the optical probe, IR emissions comprising a response to the impinging laser beam, and this response may be processed to indicate the spot position error in connection with the spot location.

In one non-limiting embodiment, it is contemplated that an apparatus embodying aspects of the present invention may be implemented without a need of active cooling for the portion of the apparatus (e.g., the portion of the viewing tube) within the pressurized environment of the turbine engine, such as spaces encased by outer casing wall102and/or inner casing wall104. This may be feasible in long term applications, where calibration of the near or mid IR emittance values need not be performed for every measurement. It will be appreciated that depending on the needs of a given application, active cooling may be used to cool the long IR optical fiber during the relatively short period of time that may be needed to acquire the emittance value at a given spot location. This aspect is conducive to a more practical apparatus with increased operational versatility, such as may be effective for deployment at remote power plant sites.

In operation, the proposed combination of near or mid IR imaging with a long wave IR non-imaging optical fiber measurement without limitation provides at least the following example advantages: high spatial imaging resolution, accurate absolute temperature measurement on both metal and TBC components, and robust apparatus for reliable online monitoring of components in a high temperature combustion environment of a turbine engine.

While various embodiments of the present invention have been shown and described herein, it will be apparent that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.