Data processing: measuring – calibrating – or testing – Measurement system – Temperature measuring system
Reexamination Certificate
1999-07-07
2002-05-21
Bui, Bryan (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Temperature measuring system
C702S130000, C702S134000, C374S121000, C374S133000, C374S134000, C250S339010, C250S339040
Reexamination Certificate
active
06393375
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combustion temperature sensor, and, more particularly, to a combustion temperature sensor that measures infrared energy emitted at several preselected wavelengths from a flame and/or a flame's hot gas at a turbine inlet location and applies the energy signals to a calculation model to yield temperature. Particular utility for the present invention is in the field of gas turbine engines; although other utilities are contemplated herein.
2. Description of Related Art
Combustion gas turbine designers and users can benefit from knowledge of flame temperature to determine, for example, NOx and CO emission concentrations, flame control, and flame-off conditions. Knowledge of these parameters can be used for increased turbine efficiency, and increased turbine blade life and reliability, as well as decreased pollution. While much effort has been devoted in the past to the problem of flame temperature determination, previously developed systems have been lacking in the ability to come up quickly and reliably with accurate and useful flame temperature measurements.
One example of such a temperature measurement system is shown in Cashdollar et al., U.S. Pat. No. 4,142,417. This patent discloses an IR measuring pyrometer used to calculate both particle and gas temperature from an explosion or fire. In this system three or four IR wavelength measurements (1.57, 2.30, 3.46, and 5.19 um) are obtained to compute temperature of the particles and gas. Significantly, these wavelengths are chosen to avoid discrete emission bands of gases in the hot flame, e.g., those emission bands which correspond to the quantized energies of the vibrational and rotational states of molecules. The wavelength measurements, as provided by Cashdollar et al., are restricted to dust cloud flames which are optically “thick” (i.e., gas cloud flame is optically opaque at the chosen wavelength), to eliminate the need to compensate for background radiation. Thus, this system would be incapable of operating in an optically thin environment, such a turbine, since background radiation from the wall on the other side of the flame would be detected and would destroy any measurement obtained.
In still other prior art examples, temperature measurement is determined by detecting UV radical (e.g., OH, CO, CH, CHO, C, etc.) emission bands in the combustion chamber. For example, German Laid Open Patent Application DE 4028922/A1 and published PCT Application WO 98/07013, each disclose methodologies for temperature determination in a combustion chamber using UV spectral emissions from a variety of gaseous radicals. Radicals, by their very nature, are short-lived as compared to molecular gas constituents, and thus, determination of temperature from molecular gas components is more stable. While UV-spectral combustion temperature determination may be adequate for some purposes, such a system cannot be used for temperature control at the turbine inlet location. In addition, UV combustion temperature determination cannot provide information that can be used to improve turbine blade life and stability.
It has been proposed (e.g., En Urga Paper 1997) to determine temperature by observing the entire IR spectrum and directly correlating certain radiation intensities of molecular CO
2
and H
2
O. However, the harsh operating environment inside the turbine prohibit such a direct measurement. In addition the cost of producing a fiber optic fiber that is capable of both transmitting the entire spectrum without degrading in the harsh operating environment is too prohibitive. Thus, engineering trade-offs must be reached between the ability to effectively observe and transmit optical energy signals within a turbine environment, and to obtain appropriate IR wavelength intensities for accurate temperature measurement.
The present invention solves the aforementioned shortcomings of the prior art by selecting an optical fiber and detector that can withstand the operating environment of a turbine and transmit certain, meaningful wavelengths of optical energy to determine temperature. More specifically, the present invention includes improvements in the relationship of the various elements of the optical system to each other and to the flame. A lens is positioned so that it collects infrared (IR) radiation from that portion of the flame nearest the inlet to the turbine section. The lens focuses the IR energy on one end of an optical fiber, with a mounting structure supporting one end of the optical fiber in fixed relation to the flame. Compressed air is supplied to the mounting structure to shield the lens from combustion gases in the flame. The other end of the fiber is positioned to direct a beam of IR energy onto a plurality of detectors positioned in a second mounting structure spaced from the turbine. A spectral separation mechanism is provided before the detectors to separate the incident IR radiation into a plurality of narrow-range IR frequencies. An optical chopping mechanism is provided for interrupting the IR beam (at a predetermined frequency) before the beam reaches the spectral separating mechanism. In this way, the detector receives a chopped, narrow-range IR signal. The signals are converted to appropriate electrical signals, processed to determine optical energy, and preferably compared to a predefined look-up table to determine a temperature value for a given set of detected optical energy signals.
It should be emphasized that the disclosure in this application includes “best mode” descriptions of preferred related technologies (e.g., temperature calculation via a look-up table) which are not part of the instant claimed invention. This disclosure is amplified for purposes of completeness.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a system and method for determining combustion temperature using infrared emissions. The present invention includes a sensor, a signal conditioning stage and a temperature determining stage to provide temperature measurement at a turbine inlet location.
In the present invention, an optical system is focused on the flame as the temperature to be measured. As mentioned above, it is desired to measure the flame temperature when the combustion process is essentially complete, i.e., the gaseous products of combustion contain stable compounds of H
2
O and CO
2
. For this purpose, the IR radiation for that portion of the flame closest to the turbine inlet is measured. The resultant optical signal is focused on one end of a fiber optic cable and the other end of the fiber optic cable emits light into an optical detection system. This optical detection system includes an optical chopper, after which the optically chopped signal impinges on a number of separate detectors which convert the optical signal into an electric current. Each of the optical sensors is preferably provided with a selective filter which passes only a very limited, discrete range (i.e., narrow band filter) of infrared wavelength. In the preferred embodiment, four wavelength filters are used: , three to pass wavelengths or radiation emitted by CO
2
and/or H
2
O and one to pass a background radiation wavelength that is free from gas band radiation. The resultant composite signal is then processed to obtain a stable optical energy signal at each of the selected wavelengths. Preferably, the signal processing includes programmable gain amplifiers and digital to analog circuits for preparation of the signals for computer calculations.
The IR signals must be fed to an optical detector which is subject to careful temperature control so that temperature effects of the detector can be eliminated in so far as is technically feasible. The optical chopper causes a zero optical signal to be available at a given chopping rate (such as 65 Hz) as well as the regular optical signal. Since only the difference between the two signals is used, any DC slow drift is eliminated. In this case, each channels' programmable gain amplifier is controlled
Bui Bryan
En'Urga Inc.
Hayes & Soloway PC
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