Patent Application
20120164589
The present application relates generally to an optical combustor probe system and more particularly relates to an optical combustor probe system with a number of fiber optic probes positioned about a combustion chamber to detect flame holding and other types of combustion events.
Certain types of known gas turbine combustors use lean premixed combustion to reduce emissions of gases such as NOx (nitrogen oxides) and the like. Such combustors generally have a number of burners attached to a single combustion chamber. During operation, fuel is injected through a number of fuel injectors and mixes with a swirling airflow to produce a combustion flame. Because of the lean stoichiometry, lean premixed combustion may achieve lower flame temperatures and thus may produce lower emissions of NO gases and the like.
One facet of lean combustion environments is that the flame speed may increase with an increase in fuel concentration. Overall combustion zone aerodynamics thus may be designed to accommodate the lean flame speed. The fuel-air mixture approaching the combustion zone, however, may not always be homogenous. As a result of local variations in the fuel air mixture, the local flame speed may exceed combustion zone design limits. If conditions that support the elevated lean flame speed persist, the flame may encroach upon upstream structures and cause damage due to increased heat loads or otherwise.
There is thus a desire for improved combustor monitoring systems and methods such as optical combustor probe systems that may detect flame holding events and precursors thereof such that remedial action may be taken before damage occurs. Further, such an improved reaction time also may provide the ability to reduce operating margins to permit even leaner operations and, hence, lower emissions of NO gases and the like.
The present application thus provides an optical probe system for use with a combustion flame in a combustion chamber. The optical probe system may include a number of optical probes fixedly attached about the combustion chamber and positioned such that the optical probes collect light generated by the combustion flame in a field of view of each of the optical probes. One or more components external to the combustion chamber may produce and analyze signals indicative of the light generated by the combustion flame in the field of view of each of the optical probes.
The present application further provides a method of monitoring a combustion flame in a combustion chamber. The method may include the steps of positioning a number of optical probes about the combustion chamber, generating a number of signals indicative of the combustion flame in a field of view of each of the optical probes, and analyzing the signals to determine a location of the combustion flame within the combustion chamber.
The present application further provides a combustor with a combustion flame therein. The combustor may include a combustion chamber and a number of optical probes fixedly attached about the combustion chamber. The optical probes may be positioned such that the optical probes collect light generated by the combustion flame in a field of view of each of the optical probes. A number of components external to the combustion chamber may produce and analyze signals indicative of the light generated by the combustion flame in the field of view of each of the optical probes.
These and other features and advantages of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
Each optical combustor probe 110 may include a bundle of optical fibers 120. The optical fibers 120 may be quartz fibers and the like. Other types of optical fibers 120 may be used herein. The optical fibers 120 preferably are relatively small diameter quartz fibers so as to enable a tighter bend radius as compared to a single large diameter fiber. Moreover, the small diameter quartz fibers may possess a similar light collection power. Any suitable optical fiber material may be used herein. A bundle 125 of the optical fibers 120 may be used.
The optical fibers 120 may have a coating 30 thereon. The coating 30 may be a gold coating or another type of precious metal. Similar coatings may be used herein so as to provide thermal protection. Other types of coatings resistant to high temperature also may be used herein. The optical fibers 120 may be positioned within a guide tube 140. The guide tube 140 may be made out of stainless steel or other types of temperature resistant materials. The optical combustor probes 110 with the optical fibers 120, the coatings 130, and the guide tube 140 thus may withstand the high operating temperatures and pressures within the combustion chamber 40 or otherwise. For example, the temperature and pressure within the combustion chamber 40 may exceed about 1400° Fahrenheit (about 760° Celsius) and about 750 pounds per square inch (gauge) (about 5200 kilopascals) or more.
The optical combustor probe system 100 further may includes a number of external components 150 positioned outside of the combustion chamber 40. The external components 150 may include a photo-detector module 160. The photo-detector module 160 contains optical components to separate spectrally the incoming collected light from the optical combustor probes 110. The photo-detector module 160 produces signals proportional to the intensity of the tight. The photo-detector module 160 generates output signals based upon the data received from the optical combustor probes 110 to a signal processing module 170. The signal processing module 170 analyzes the signals from the photo-detector module 160 to provide combustion information. Specifically, the signal processing module 170 may include a number of metal-can photomultiplier tubes 180 and the like. Because the photomultiplier tubes 180 have a fast response time, the photomultiplier tubes 180 may be used to monitor temporal variations within the combustion chamber 40. The signal processing module 170 also may include a spectrometer 190 and the like so as to capture the optical emission spectrum. The signal processor 170 thus processes both temporal frequency based upon the photomultiplier tubes 180 and the light frequency domains via the spectrometer 190. Interference filters also may be used herein. Other configurations and other types of components may be used herein.
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In use, the optical combustor probes 110 of the optical combustor system 100 may be used to determine a combustion event by observing the “chemiluminescence” of the combustion flame 90 in a localized region of interest. Generally described, chemiluminescence is the optical radiation produced by combustion reactions. The combustion reactions produce molecules with high energy states. The excited molecules may transfer to lower energy states in part by emitting a light. The intensity of the emission may be proportional in part to the chemical production rate in a specific reaction. Chemiluminescense thus may measure reaction rates and heat release rates for information on the present strength of the combustion process in a specific region of view.
Specifically, signals indicative of the combustion flame 90 in the field of view 210 of each optical combustor probe 110 may be collected by the optical fibers 190 and guided to the photo-detector module 160. The photo-detector module 160 produces signals in proportional to the intensity of the light. The signals then may be analyzed in the signal processor 170 both temporally and based upon wavelength. The spectrometer 190 of the signal processor 170 may be configured to detect spectral radiation indicative of chemical emission effecting combustion stability. Further, spectral radiation indicative of fuel contaminants or impurities also may be detected. The photomultiplier tubes 180 of the signal processor 170 may measure temporal fluctuations. Other types of signal processing may be used herein. The signals provided by the photo-detector module 160 may be filtered to account for reflective background emissions cause by combustor geometry. By discriminating the signal levels from the background signals, combustion events in the regions of interest may be more accurately determined.
The optical combustor probe system 100 thus may be able to detect combustion events such a flame encroachment, flame holding, and the like with time constants of less than about 500 microseconds. Such a rapid response time generally permits an operator or a control system to take remedial action. Active feedback control thus may be provided herein. A feedback control system 220 may be in communication with the external components 150 and the control components of the compressor 25 and/or the gas turbine engine 10 in general.
In addition to the rapid response time, the use of the optical combustor probe system 100 actively prevents undesirable combustion events such that overall operating margins may be reduced Reducing overall operating margins may permit a leaner operation and hence greater operating efficiency with fewer emissions. Reducing operating margins also may lead to more compact geometries that may be lighter in overall weight. Moreover, undesirable combustion events now may be recorded and logged so as to provide improved prediction capability on product life and maintenance requirements.
It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
