Gas turbine engine control using acoustic pyrometry

A method and apparatus for operating a gas turbine engine including determining a temperature of a working gas at a predetermined axial location within the engine. Acoustic signals are transmitted from a plurality of acoustic transmitters and are received at a plurality of acoustic receivers. Each acoustic signal defines a distinct line-of-sound path from one of the acoustic transmitters to an acoustic receiver corresponding to the line-of-sound path. A time-of-flight is determined for each of the signals traveling along the line-of-sound paths, and the time-of-flight for each of the signals is processed to determine a temperature in a region of the predetermined axial location.

FIELD OF THE INVENTION

The present invention relates to temperature measurement in turbine engines and, more particularly, to determination of temperature using acoustic measurements to control a gas turbine engine.

BACKGROUND OF THE INVENTION

Combustion turbines, such as gas turbine engines, generally comprise a compressor section, a combustor section, a turbine section and an exhaust section. In operation, the compressor section can induct and compress ambient air. The combustor section generally may include a plurality of combustors for receiving the compressed air and mixing it with fuel to form a fuel/air mixture. The fuel/air mixture is combusted by each of the combustors to form a hot working gas that may be routed to the turbine section where it is expanded through alternating rows of stationary airfoils and rotating airfoils and used to generate power that can drive a rotor. The expanding gas exiting the turbine section can be exhausted from the engine via the exhaust section.

The fuel/air mixture at the individual combustors is controlled during operation of the engine to maintain one or more operating characteristics within a predetermined range, such as, for example, to maintain a desired efficiency and/or power output, control pollutant levels, prevent pressure oscillations and prevent flameouts. In a known type of control arrangement, a bulk turbine exhaust temperature may also be monitored as a parameter indicative of a condition in the combustor section. For example, a controller may monitor a measured turbine exhaust temperature relative to a reference temperature value, and a measured change in temperature may result in the controller changing the fuel/air ratio at the combustor section.

In a known temperature monitoring system for controlling combustion operations, temperature monitors, such as thermocouples, are located directly in the exhaust flow of the turbine. Such monitoring systems generally require locating thermocouples at different fixed axial locations along the exhaust flow, which may introduce uncertainties in relation to temperature calculations for controlling the engine as conditions affecting operation of the engine change, such as a varying load condition on the engine.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a method of operating a gas turbine engine may be provided including determining a temperature of a working gas passing through a flow path within the gas turbine engine. The method comprises transmitting acoustic signals from a plurality of acoustic transmitters located at a predetermined axial location adjacent to and downstream from a last stage of a turbine section of the gas turbine engine, and receiving the acoustic signals from the acoustic transmitters at a plurality of acoustic receivers located at the predetermined axial location. Each acoustic signal may comprise a distinct line-of-sound path from one of the acoustic transmitters to an acoustic receiver corresponding to the line-of-sound path. The method additionally includes determining a time-of-flight for the signals traveling along each of the line-of-sound paths, and processing the time-of-flight for the signals traveling along the line-of-sound paths to determine a temperature in a region of the predetermined axial location.

In accordance with another aspect of the invention, a gas turbine engine may be provided including an apparatus for controlling operation of the gas turbine engine. The apparatus for controlling the gas turbine engine may comprise a plurality of acoustic transmitters located circumferentially on a boundary structure defining a flow path for a working gas passing through the gas turbine engine. The plurality of acoustic transmitters may be located at a predetermined axial location adjacent to and downstream from a turbine section of the gas turbine engine. A plurality of acoustic receivers may be located circumferentially around the boundary structure defining the flow path at the predetermined axial location. A plurality of line-of-sound paths may be defined by acoustic signals, each acoustic signal being transmitted from an acoustic transmitter and received by an acoustic receiver for a respective line-of-sound path. A controller may be configured to determine a time-of-flight for the acoustic signals traveling along each of the line-of-sound paths, and the controller may be configured to process a measured time-of-flight for the signals traveling along the line-of-sound paths to determine a local temperature in each of a plurality of locations located circumferentially around the flow path at the predetermined axial location.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, embodiments of the invention are directed to an acoustic pyrometer system10that may be incorporated in a gas turbine engine12and to methods of using the acoustic pyrometer system10to determine temperatures at predetermined locations in the engine12and to control an operation of the engine12. Aspects of the invention will be explained in connection with various possible configurations, but the detailed description is intended only as exemplary.

As illustrated inFIG. 1, the turbine engine12generally includes a compressor section14, a combustor section16, a turbine section18and an exhaust section20. The combustor section16may comprise a plurality of combustor baskets or combustors22and associated transition ducts24for conveying hot working gas to the turbine section18. The exhaust section20may be configured as a diffuser28, which can be a divergent duct formed between an outer shell30, defining an outer boundary, and a hub structure32, defining an inner boundary. The hot working gas is exhausted from the turbine section18through the exhaust section20, i.e., between the outer shell30and the hub structure32, to increase the pressure difference of the exhaust gas expanding across the last stage34of the turbine section16.

The acoustic pyrometer system10may be located in an area of the exhaust section20, adjacent to a rotating row of blades36of the last stage34of the turbine section18. Specifically, the acoustic pyrometer system10may be located in a measurement plane extending generally perpendicular to a longitudinal axis38of the engine12, i.e., perpendicular to a flow path39of the hot working gas, and positioned at a predetermined axial location defined by the line2-2inFIG. 1. In a preferred configuration, the acoustic pyrometer system10may be located relatively close to the last row of blades36, and may be located, for example, approximately 3 inches downstream from the last row of blades36. However, it should be understood that the particular axial location of the acoustic pyrometer system10may vary and may be selected depending on the particular design requirements of the engine12.

A diagrammatic view of the acoustic pyrometer system10is illustrated inFIG. 2, taken at a cross-section of the engine12along line2-2. The system10comprises a plurality of transmitters and receivers, illustrated herein as a plurality of transducers40(only one transducer40shown inFIG. 1), supported on the outer shell30. InFIG. 2, eight transducers are shown and are designated as transducers40A-H for the present description. However, it should be understood that, within the spirit and scope of the present invention, a greater number or fewer transducers40may be provided to perform a temperature sensing operation. For example, it may be desirable to provide a greater number of transducers to provide greater accuracy in mapping of temperatures within the flow path39, as is described in greater detail below. Each of the transducers40includes a portion that may extend through the outer shell30to emit acoustic signals and to receive acoustic signals. The transducers40are connected to a control unit or controller46including a data acquisition and processing unit48that is configured to control the transducers40to produce predetermined output signals and to receive time-of-flight signals corresponding to the output signals (seeFIG. 8). The data acquisition and processing unit48is further configured to store and process data corresponding to the received signals to calculate temperatures and to produce outputs in accordance with the calculated temperatures associated with the received signals. The controller46additionally comprises a combustion control unit50receiving signals from the data acquisition and processing unit48to output control signals for controlling operations affecting combustion, including signals to the individual combustors22, providing control of, for example, the fuel/air ratio at the combustors22.

During a data acquisition operation, at least one of the transducers40may comprise a transmitting transducer40producing a signal that traverses the hot gas flow path39in the plane of the system10, and at least one the transducers40may comprise a receiving transducer40, which may be a different transducer40or the same transducer40as the transmitting transducer40. The time-of-flight of a signal traveling between the transmitting and the receiving transducers40may be used to determine an average temperature of the gas through which the signal has traveled. Specifically, the present invention uses the principle that the speed of sound in a gas changes as a function of temperature. For a determined or known composition of the gas, it is possible to determine the temperature of the gas based on the measured time for an acoustic or sound signal to travel the distance between the transmitting and receiving transducers40, i.e., based on the speed of the sound signal traveling through the gas. The temperature, T (° C.), of the gas may be calculated using the equation:

Referring toFIG. 3, exemplary line-of-sound paths for the transducers40A-H will be described with reference to the transducers40A,40B and40H. When the transducer40A produces an acoustic signal, a plurality of line-of-sound paths42are defined within the flow path39defined between the outer shell30and the hub structure32. A first line-of-sound path42-1extends radially inwardly toward the hub structure32and reflects off the hub structure32perpendicular to a first reflection point44-1on the surface of the hub structure32. The first line-of-sound path42-1comprises a first path segment42-1aextending from the transducer40A to the reflection point44-1, and a second path segment42-1bextending from the reflection point44-1to the transducer40A. A second line-of-sound path42-2extends at an angle toward the hub structure32in the direction of the transducer40B, and reflects off the hub structure32at a second reflection point44-2in a direction toward the transducer40B. The second line-of-sound path42-2comprises a first path segment42-2aextending from the transducer40A to the reflection point44-2, and a second path segment42-2bextending from the reflection point44-2to the transducer40B. A third line-of-sound path42-3extends at an angle toward the hub structure32in the direction of the transducer40H, and reflects off the hub structure32at a third reflection point44-3in a direction toward the transducer40H. The third line-of-sound path42-3comprises a first path segment42-3aextending from the transducer40A to the reflection point44-3, and a second path segment42-3bextending from the reflection point44-3to the transducer40H. In addition, fourth and fifth line-of-sound paths42-4and42-5, respectively, extend from the transducer40A to the respective transducers40C and40G. The fourth and fifth line-of-sound paths42-4and42-5extend along a direct line-of-flight between the transducer40A and the transducers40C and40G.

It should be understood that a plurality of line-of-sound paths42similar to those described for the transducer40A may be associated with the other transducers40B-H in the acoustic pyrometer system10. Each of the plurality of line-of-sound paths42provides an average temperature measurement of the gas along the particular line-of-sound path42. Hence, a plurality of average temperature measurements may be provided traversing across the annular space forming the flow path39at the exit to the turbine section18.

Further, a plurality of intersections42Iof the line-of-sound paths are defined by intersections of the reflected line-of-sound paths42-1through42-3with the direct line-of-flight line-of-sound paths42-4and42-5, as well as intersections with the direct line-of-flight line-of-sound paths of adjacent transducers40, e.g., intersections of the line-of-sound paths42-1,42-2and42-3with a direct line-of-sound path42-6between transducers40B and40H. The data associated with each pair of intersecting line-of-sound paths42may be compared to each other to validate the temperature data corresponding to the pair of line-of-sound paths42. In particular, the average temperature of each intersecting pair of line-of-sound paths42should be substantially the same, i.e., have a substantially similar temperature at the intersection42I, and a substantial variation in temperature between an intersecting pair of line-of-sound paths42may provide an indication that the data provided by at least one of the pair of intersecting line-of-sound paths42may be invalid.

Time-of-flight data corresponding to each of the plurality of line-of-sound paths42may be transmitted to the data acquisition and processing unit48to map the temperatures in the measurement plane of the acoustic pyrometer system10, i.e., in the plane of line2-2inFIG. 1, wherein temperatures may be determined at a plurality of points within the radial and circumferential extent of the annular space at the exit of the turbine section18. For example, a plurality of isotherms for temperatures in the flow path39may be mapped, as is illustrated by two exemplary isotherms49A and49B superposed on an outline of the flow path39inFIG. 4.

The time-of-flight data may be acquired from the transducers40sequentially in time. That is, the transducers40may each be activated at a different time to produce an output acoustic signal in order to enable identification of the signal source, i.e., the transmitting transducer40, relative to the receiving transducers40that receive and provide time-of-flight data signals to the data acquisition and processing unit48. Alternatively, two or more output signals may be transmitted from two or more of the transducers40simultaneously, such that there is little or no time difference between measurements provided by the different output signals at a plurality of locations in the flow path39to provide simultaneous temperature data from a plurality of the transducers40. In particular, each of the transducers40may transmit an output signal at a different frequency than any other transducer40. Hence, the source of each transmitted signal may have a distinctive frequency that may be identified by the data acquisition and processing unit48when the signals are received at the receiving transducers40, such that each of the two or more output signals transmitted simultaneously may be uniquely identified by their frequency.

The acoustic pyrometer system10preferably may operate in a frequency range of from about 0.5 kHz to about 4 kHz. The energy of acoustic signals is generally greater at lower frequencies, enabling the signals to travel a longer distance. Hence, it may be desirable to provide output signals having a lower frequency. Further, in a configuration in which the transducers40produce output signals at different frequencies, it may be preferable that the variation between output signal frequencies be small in order that all of the output signals may have a similar energy, for example, by providing an output signal frequency for each of the signals near the lower end of the frequency range.

As discussed above, each line-of-sound path, comprises a known distance between transmitting and receiving transducers40. Hence, for a given data collection event comprising the collection of data from the receiving transducers40at a predetermined time, or within a predetermined time frame for sequential data produced by sequential output signals from the transducers40, a plurality of temperature measurements may be provided traversing across different sections of the measurement plane. The data acquisition and processing unit48may process the plurality of temperature measurements by a cross-correlation technique to determine the temperature of the gas flow at different locations radially and circumferentially across the measurement plane.

In accordance with an aspect of the invention, the temperatures determined at the measurement plane of the acoustic pyrometer system10may be used to determine both a bulk exhaust temperature and to determine individual operating temperatures for each of the combustors22(FIG. 8). With regard to the bulk temperature measurement, the acoustic pyrometer system10determines average temperatures across multiple paths42that may be used to provide a true bulk average temperature at the measurement plane defined by the acoustic pyrometer system10. In particular, the data acquisition and processing unit48may determine a bulk or global exhaust temperature across the flow path39that may be used by the controller46to control overall combustion operations, such as controlling a firing temperature in the combustion section16.

The data acquisition and processing unit48may also determine temperatures at each of the combustors22to ensure proper operation of the individual combustors22. For example, referring toFIG. 5, outer and inner temperature regions52,54, specifically identified as outer regions52A-L and inner regions54A-L, may be defined for use in identifying the temperature at circumferential and radial locations of regions in the measurement plane defined by the acoustic pyrometer system10. The temperature for each region of the outer region52A-L and inner region54A-L may be an average temperature for the area covered by the particular region. The number of regions for each of the outer and inner regions52A-L,54A-L may correspond to the number of combustors22, i.e., corresponding to twelve combustors22in the exemplary embodiment. Although the measurement plane of the acoustic pyrometer system10is displaced axially downstream of the individual combustors22and the turbine section18, it is possible to infer the temperature at each individual combustor22based on the measurements at the measurement plane. That is, the temperature at each of the regions52A-L and/or54A-L may be used to determine the temperature at a combustor22wherein the regions52A-L and/or54A-L corresponding to a combustor22will typically be displaced circumferentially relative to the associated combustor22due to the rotational flow of the exhaust gases through the turbine section18. The temperature of the combustors22, as determined by the data acquisition and processing unit48, may be used to determine an output of the combustion control unit50to control the fuel and/or air flow to each of the respective combustors22to avoid flame-out of individual combustors22, as well as to provide combustor-to-combustor flame temperature variation information for feed back control for optimized, energy-efficient combustion. Hence, the temperature measurements provided by the transducers40may provide both a global temperature measurement and individual temperature measurements of the combustors22at a common axial location defined by the plane of the acoustic pyrometer system10.

As noted above, the particular location of the measurement plane may be selected based on the particular configuration and operation of the engine, and is preferably adjacent a last stage34of the turbine section18. In particular, the location of the measurement plane is preferably at an axial location in the exhaust section20where the working gas exiting the turbine section18has not substantially mixed within the exhaust section20. For example, the measurement plane may preferably be located at an upstream region of the exhaust section20prior to substantial expansion of the gases through the diffuser28of the exhaust section20, such that individual temperature measurements corresponding to the individual combustors22may be obtained. It may also be noted that obtaining the average temperature measurements corresponding to different portions of the flow path39traversed by the line-of-sound paths42further permits the location of the measurement plane to be used for determining a bulk temperature of the working gas as it exits the turbine section18and passes through the exhaust section20.

It should be understood that the spacial resolution of the temperature map provided by the transducers40may be increased by increasing the number of the transducers40around the circumference of the outer shell30at the measurement plane of the acoustic pyrometer system10. Further, it should be understood that although particular outer and inner regions52,54are described for designating temperatures within the measurement plane of the acoustic pyrometer system10, a different number of regions may selected for identifying temperatures in both the radial and circumferential directions. Also, it should be understood that the regions, as used by the data acquisition and processing unit48for determining combustor temperatures, may comprise temperatures at point locations within the measurement plane, such as may be determined from the temperature map, as generally depicted by the isotherm map ofFIG. 4. The locations of the temperature regions52,54or point locations may each correspond to a “hot spot” in the exhaust flow corresponding to the outlet temperature of exhaust from a predetermined one of the combustors22.

During operation of the engine12, the load on the engine12may change, such as in changing from a base load operation, i.e., a design operating point, of the engine12to a partial load operation of the engine12. As a result of a change in load on the engine12, the condition of the gas flow may vary, and the locations of the hot spots corresponding to each of the combustors22may change radially and/or circumferentially. In the past, temperature sensors, such as thermocouples have been mounted at fixed locations on thermocouple rakes in the exhaust section20of the turbine engine12, wherein the locations of the thermocouples were optimized for steady state base load operation of the engine. In accordance with an aspect of the present invention, the temperature measurement locations, i.e., the regions52and54, designated for providing temperatures corresponding to each of the combustors22, may be changed in real time to provide an optimum temperature measurement location for each load condition of the engine12, or for varying load conditions of the engine12. For example, as the load on the turbine engine12changes from a base load to a partial load condition, the temperature monitoring locations may be adjusted or changed in the radial and/or circumferential directions within the annulus between the outer shell30and the hub structure32in the plane of the acoustic pyrometer system10. That is, a first set of temperature monitoring locations may be selected, corresponding to each of the combustors22, for a base load operation of the engine12, and a second, different set of temperature monitoring locations may be selected, corresponding to each of the combustors22, for a partial load operation of the engine12. Hence, the acoustic pyrometer system10may provide an increased accuracy of the temperature measurements used for controlling operation of the engine12throughout a range of varying operating conditions.

It should be noted that the distance along the line-of-sound paths42may vary slightly due thermal expansion and/or distortion of the outer shell30. In accordance with an aspect of the invention, a non-intrusive distance measuring device may be included in the acoustic pyrometer system10to provide distance-of-flight measurements (FIG. 8). For example, a laser triangulation, time-of-flight measurement may be provided by laser emitting devices and detectors built into the transducers40, as is depicted diagrammatically by an exemplary laser emitter53and receiver55inFIG. 2, and providing a measurement between each pair of transmitting and receiving transducers40. That is, a plurality of laser emitter and receivers, similar to the illustrated laser emitter53and receiver55, may be provided associated with a plurality of transducers40. The measurements from the distance measuring devices may be used to determine the thermal expansion and/or distortion of the outer shell30, and may be used by the data acquisition and processing unit48to correct for variations in distance of the line-of-sound paths42.

In accordance with a further aspect of the invention, one or more temperature sensors may be provided on the outer shell30, such as is illustrated by a thermocouple56associated with the transducer40A (FIG. 2). For example thermocouples56may be provided as part of or associated with each of the transducers40to provide a temperature measurement at the inner surface of the outer shell30at or adjacent to the measurement plane. The temperature measurement at the outer shell30may be provided to the controller46to adjust or correct the temperature measurements provided by the transducers40for a boundary layer temperature gradient at the wall of the outer shell30(FIG. 8).

In accordance with a further aspect of the invention, background noise at the measurement plane of the acoustic pyrometer system10may be detected by the transducers40. The background noise received by the transducers40may be input to the controller46(FIG. 8) and provided to the data acquisition and processing unit48and processed as a background noise level used to adjust a noise level attenuation for signals received by the transducers40. In particular, the noise level within the engine12will change, depending on the load condition of the engine12. The data acquisition unit48may monitor the noise level and adjust an attenuation threshold to filter the output signals from the transceivers40for the noise level, such as by increasing the threshold for attenuation as the noise level increases. Hence, the present acoustic pyrometer system10may provide an adjustable acoustic measurement that varies the sensing sensitivity with varying noise, so that the detection of the signals may be optimized to the extent possible with respect to the ambient sound, i.e., noise, in the combustion system.

Referring toFIG. 6, an alternative embodiment of the acoustic pyrometer system10is illustrated and identified as acoustic pyrometer system110. Elements of the acoustic pyrometer system110corresponding to the acoustic pyrometer system10are identified with the same reference numeral increased by 100.

The acoustic pyrometer system110may be provided at the same location within the exhaust section20of a turbine engine12as is described for the acoustic pyrometer system10above. The acoustic pyrometer system110includes a plurality of transmitters and receivers, illustrated herein as a plurality of acoustic or sound emitting transmitters162, identified as transmitters162A-H, located on the outer shell130, and a plurality of receiving microphones164, identified as microphones164A-P, located on the hub structure132. It should be understood that the locations of the transmitters162and microphones164may be reversed, or transceivers may be provided in place of the transmitters162and microphones164.

The transmitters162and microphones164are connected to a control unit or controller146including a data acquisition and processing unit148that is configured to control the transmitters162to produce predetermined output signals and to receive time-of-flight signals from the microphones164corresponding to the output signals. The data acquisition and processing unit148further stores and processes data corresponding to the received signals to produce outputs in accordance with calculated temperatures associated with the received signals. The controller146additionally comprises a combustion control unit150receiving signals from the data acquisition and processing unit148to output control signals for controlling operations affecting combustion in a manner similar to that described above for the data acquisition and processing system10

Referring toFIG. 7, exemplary line-of-sound paths for the output signals provided by the transmitter162A will be described. When the transmitter162A produces an acoustic signal, a plurality of line-of-sound paths142are defined within a flow path139defined between the outer shell130and the hub structure132. A first line-of-sound path142-1extends radially inwardly toward the microphone164A. A second line-of-sound path142-2extends radially inwardly toward the microphone164B. A third line-of-sound path142-3extends radially inwardly toward the microphone164C. A fourth line-of-sound path142-4extends radially inwardly toward the microphone164P. A fifth line-of-sound path142-5extends radially inwardly toward the microphone164N.

It should be understood that a plurality of line-of-sound paths142similar to those described for the transmitter162A may be associated with the other transmitters162B-P. Further, the line-of-sound paths142of each transmitter162intersect line-of-sound paths142of the adjacent transmitters162, such that verification of the data associated with pairs of intersecting line-of-sound paths142may be performed, as described above for the acoustic pyrometer system10. The microphones164receiving acoustic signals from the transmitters162provide output signals to the data acquisition and processing unit148which determines time-of-flight data for each line-of-sound path142, to provide an average temperature measurement of the gas along each line-of-sound path142. Hence, the time-of-flight data of the transmitters162and microphones164may be used to determine a temperature map of the plane defined by the acoustic pyrometer system110to control operation of the turbine engine in a manner similar to that described for the acoustic pyrometer system10. The plural direct line-of-sound paths140provided by the acoustic pyrometer system110may provide a reduction in an uncertainty of the data provided to the data acquisition and processing unit148in that the acoustic signals providing the data of the system110do not reflect off structure within the exhaust section20. That is, the acoustic pyrometer system110may provide additional accuracy to the data by providing shorter path lengths with each line-of-sound path142providing a direct line-of-flight between the signal transmitter162and microphone (receiver)164.

The acoustic pyrometer system10,110of the present invention provides a combined temperature measurement function that permits elimination of a sensor location typically provided for sensing an exhaust temperature in a turbine engine. In particular, the present invention provides temperature measurements comprising individual combustor temperature measurements and a bulk or global exhaust temperature measurement in a common measurement plane downstream from the turbine section18. The present system may be used to replace existing exhaust temperature measurement systems, such as both blade path thermocouple rakes at the exit to the turbine section and bulk exhaust temperature thermocouple rakes located downstream in the exhaust section that may be provided in a typical turbine exhaust temperature sensing system.

Further, the acoustic pyrometer system10,110provides a configuration in which the temperature measurement elements, e.g., the transceivers40or the transmitters162and receivers164, are located out the path39,139of the hot gas flow. In addition, mounting of the transceivers40or transmitters162to the outer shell32,132may permit replacement of these components without stopping operation of the turbine engine12, reducing inefficiencies associated with maintenance of the temperature sensor system for the engine12.