Diode Laser Sensor for Gas Temperature and H2O Concentration in a Scramjet Combustor Using Wavelength Modulation Spectroscopy (Postprint). PDF Download
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Author:
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Languages : en
Pages : 13
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Book Description
A diode laser absorption sensor which probes three spectral features of water vapor in the near infrared region to infer gas temperature and water vapor concentration near the exit of a scramjet combustor is presented. Optical engineering is used to overcome beam steering and fiber mode noise sources. A method to make absolute measurements using wavelength modulation spectroscopy (WMS) with second harmonic detection (2f) is described, along with the advantages of the technique over direct absorption spectroscopy. Measurements using both techniques in the scramjet combustor are compared to show superior noise rejection and overall signal to noise ratios with WMS-2f. Results of temperature and water vapor partial pressure under various scramjet operating conditions show the utility of the sensor for scramjet engine design and optimization.
Author:
Publisher:
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Category :
Languages : en
Pages : 13
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Book Description
A diode laser absorption sensor which probes three spectral features of water vapor in the near infrared region to infer gas temperature and water vapor concentration near the exit of a scramjet combustor is presented. Optical engineering is used to overcome beam steering and fiber mode noise sources. A method to make absolute measurements using wavelength modulation spectroscopy (WMS) with second harmonic detection (2f) is described, along with the advantages of the technique over direct absorption spectroscopy. Measurements using both techniques in the scramjet combustor are compared to show superior noise rejection and overall signal to noise ratios with WMS-2f. Results of temperature and water vapor partial pressure under various scramjet operating conditions show the utility of the sensor for scramjet engine design and optimization.
Author:
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Category :
Languages : en
Pages : 13
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Book Description
Tunable diode laser absorption measurements of gas temperature and water concentration were made at the exit of a model scramjet combustor fueled on JP-7. Multiplexed, fiber-coupled, near-infrared distributed feedback lasers were used to probe three water vapor absorption features in the 1.34 to 1.47 mum spectral region (2v1 and v1 + v3 overtone bands). Ratio thermometry was performed using direct absorption wavelength scans of isolated features at a 4-kHz repetition rate, as well as 2f wavelength modulation scans at a 2-kHz scan rate. Large signal-to-noise ratios demonstrate the ability of the optimally engineered optical hardware to reject beam steering and vibration noise. Successful measurements were made at full combustion conditions for a variety of fuel/air equivalence ratios and at eight vertical positions in the duct to investigate spatial uniformity. The use of three water vapor absorption features allowed for preliminary estimates of temperature distributions along the line of sight. The improved signal quality afforded by 2f measurements, in the case of weak absorption, demonstrates the utility of a scanned wavelength modulation strategy.
Author: Marco E. Leon
Publisher:
ISBN:
Category :
Languages : en
Pages : 76
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Book Description
Tunable Diode Laser Absorption Spectroscopy (TDLAS) provides an accurate, fast, and non-intrusive solution for species and temperature measurement. The application of this technology to measure temperature, H2O, and CO2 content from an industrial gas turbine has been demonstrated by this research. The multi-gas sensor system, consisting of inexpensive commercially available tunable diode lasers used in the telecommunications industry, uses Wavelength Modulation Spectroscopy (WMS) to quantify path-averaged temperature and concentrations. H2O and CO2 spectroscopic information was first gathered in the laboratory and then the system was packaged for field use. The work culminated in an eight-day test in April 2006 where actual stationary gas turbine emissions data were captured. The results demonstrate the capability for measurement of temperature, H2O, and CO2 in an industrial environment using two tunable diode lasers.
Author:
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Category :
Languages : en
Pages : 20
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Two laser-based measurement techniques are implemented in a direct-connect hydrocarbon-fueled scramjet combustor. Planar laser-induced fluorescence (PLIF) of the OH radical is used to examine the flame structure within the combustor. Tunable diode laser-based absorption spectroscopy (TDLAS) is used to measure water vapor concentration and static temperature near the combustor exit. Combined with conventional measurements and Reynolds-averaged CFD simulations, these optical diagnostic techniques significantly enhance the information that is obtained from the scramjet combustor. Wall pressure data show the combustor to be operating in dual-mode with two regions of elevated pressure corresponding to the primary and secondary flameholding zones. The OH radical is well-distributed across the combustor with high OH concentrations occurring along the body, side, and cowl walls. TDLAS measurements indicate non-uniform body-to-cowl profiles in both temperature and water concentration. Near-wall regions are found to be the hottest while the core region is cooler.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721575411
Category :
Languages : en
Pages : 34
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Research is reported on the development of sensors for gas turbine combustor applications that measure real-time gas temperature using near-infrared water vapor absorption and concentration in the combustor exhaust of trace quantities of pollutant NO and CO using mid-infrared absorption. Gas temperature is extracted from the relative absorption strength of two near-infrared transitions of water vapor. From a survey of the water vapor absorption spectrum, two overtone transitions near 1800 nm were selected that can be rapidly scanned in wavelength by injection current tuning a single DFB diode laser. From the ratio of the absorbances on these selected transitions, a path-integrated gas temperature can be extracted in near-real time. Demonstration measurements with this new temperature sensor showed that combustor instabilities could be identified in the power spectrum of the temperature versus time record. These results suggest that this strategy is extremely promising for gas turbine combustor control applications. Measurements of the concentration of NO and CO in the combustor exhaust are demonstrated with mid-infrared transitions using thermo-electrically cooled, quantum cascade lasers operating near 5.26 and 4.62 microns respectively. Measurements of NO are performed in an insulated exhaust duct of a C2H4-air flame at temperatures of approximately 600 K. CO measurements are performed above a rich H2-air flame seeded with CO2 and cooled with excess N2 to 1150 K. Using a balanced ratiometric detection technique a sensitivity of 0.36 ppm-m was achieved for NO and 0.21 ppm-m for CO. Comparisons between measured and predicted water-vapor and CO2 interference are discussed. The mid-infrared laser quantum cascade laser technology is in its infancy; however, these measurements demonstrate the potential for pollutant monitoring in exhaust gases with mid-IR laser absorption. Hanson, Ronald K. and Jeffries, Jay B. Ames Research Center
Author: Yufei Ma
Publisher: MDPI
ISBN: 3039283987
Category : Technology & Engineering
Languages : en
Pages : 278
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Book Description
Trace gas sensing technologies are widely used in many applications, such as environmental monitoring, life science, medical diagnostics, and planetary exploration. On the one hand, laser sources have developed greatly due to the rapid development of laser media and laser techniques in recent years. Some novel lasers such as solid-state, diode, and quantum cascade lasers have experienced significant progress. At present, laser wavelengths can cover the range from ultraviolet to terahertz, which could promote the development of laser gas sensing technologies significantly. On the other hand, some new gas sensing methods have appeared, such as photothermal spectroscopy and photoacoustic spectroscopy. Laser spectroscopy-based gas sensing techniques have the advantages of high sensitivity, non-invasiveness, and allowing in situ, real-time observation. Due to the rapid and recent developments in laser source as well as the great merits of laser spectroscopy-based gas sensing techniques, this book aims to provide an updated overview of the state-of-the-art laser gas sensing technologies.
Author: Alan Fried
Publisher: SPIE-International Society for Optical Engineering
ISBN:
Category : Science
Languages : en
Pages : 278
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Author: Thomas Benoy
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Tunable diode laser spectroscopy (TDLS) is a widely used technique for the measurement of gas species and offers in-situ operation, accuracy and faster response time compared to other optical and non-optical gas sensing techniques.The work in this thesis focusses on the measurement of CO2 in the harsh environment of a gas turbine engine (GTE). The work is part of a much larger initiative called Fibre Laser Imaging of gas Turbine Exhaust Species (FLITES) aimed at obtaining concentration distributions of gas species such as CO2 and NO, unburnt hydrocarbons, and soot in a gas turbine exhaust plume using optical tomography. In the FLITES system, a thulium doped fibre amplifier (TDFA) is used to boost the optical power output from a 2 mW, 1997 nm, multi-quantum well distributed feedback (DFB-MQW) laser to feed 126 measurement channels arranged in dodecagon geometry for optical tomography. Hence, agile TDLS techniques need to be developed which can be scaled up to the multi-channel measurement system.Attributed by the interference from noise in the measurement environment of a GTE, phase sensitive detection using a lock-in amplifier (LIA) has to be employed where an additional current modulation is applied to the DFB laser, creating an instantaneous intensity modulated output and a delayed wavelength modulation (WM) output. This technique falls under a metrology branch known as wavelength modulation spectroscopy (WMS).The unknown measurement conditions expected in a GTE engine necessitates the use of calibration-free WMS techniques for the simultaneous measurement of gas concentration and temperature. Calibration-free techniques in WMS have been developed at the Centre for Microsystems and Photonics (CMP) of Strathclyde University. These are known as the phasor decomposition method (PDM) and the residual amplitude modulation (RAM) technique. They employ the signals obtained using the first harmonic demodulation of the WMS signals, followed by post processing to recover the gas absorption line shape. It was known in the CMP group that the accuracy of these techniques was limited by the variation in the laser modulation parameters such as the phase of the wavelength modulation relative to the intensity modulation (WM-IM phase lag) and the wavelength modulation amplitude across the laser current scan.The solutions to two problems are addressed in this thesis, viz. the implementation of correction procedures to account for the variation in the laser modulation parameters across the current scan and the need for a calibration-free technique for the measurement of CO2 in a GTE exhaust plume scalable to a multi-channel measurement system.Accurate measurements of the wavelength modulation parameters were made across the current scan and correction algorithms were implemented to compensate for its effects on the recovered gas absorption line shape.The gas spectral parameters were measured in the lab for the R48 absorption line of CO2 near 1997.2 nm at the higher temperatures (up to 500°C) expected in a GTE exhaust plume, using a heated gas cell. A Fourier expansion model was developed for the WMS signals which employ the measured laser modulation and gas spectral parameters. 1f normalised 2f WMS technique was chosen as the calibration-free measurement approach due to the advantages of cancellation of the transmission fluctuations as well as signal normalisation. The 2f/1f measurement technique was validated in the lab at higher temperatures for the simultaneous recovery of the CO2 concentration and temperature with an accuracy of 3.39 % and 3.72 %, respectively. Subsequently, field campaigns were conducted at the Rolls-Royce test facility at East Kilbride, yielding concentration and temperature values having good correlation to the engine operating conditions such as the throttle and core temperature.Multi-channel tomographic measurements were conducted on the test phantoms at INTA, Madrid, using TFLAS-WMS (tunable fibre laser absorption spectroscopy). Accurate concentration images could be recovered using tomographic reconstruction algorithms.
Author: Kai Sun
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
To meet more rigorous criteria for environmental-unfriendly emissions and to increase energy efficiency, in-situ real-time sensors are needed to optimize the performance of next-generation energy systems. The emergence of high-quality (narrow linewidth, fast tuning capability) tunable diode lasers (TDLs) has enabled the use of wavelength modulation spectroscopy (WMS) for harsh industrial applications. Compared to conventional direct absorption measurements, WMS has the advantage of 10-100 times better detection sensitivity, avoids the need to obtain a zero-absorption baseline, and provides much better isolation from the beam steering, non-absorption transmission loss (e.g., light scattering) or mechanical vibrations. Many models have been developed to interpret the measured WMS signal into absolute absorption. However, most of these models are limited to specific applications by a wide variety of assumptions and approximation most of which deal with the simultaneous intensity and wavelength modulation of injection-current-modulated diode lasers. In this dissertation, two generalized approaches to analyze the WMS absorption signal were developed that account for non-ideal simultaneous intensity modulation of laser output when injection current variation is used for wavelength modulation. The first approach is ideal for wavelength-fixed WMS (the laser mean wavelength is fixed) analysis and the second approach is ideal for wavelength-scanned (the laser mean wavelength is scanned) WMS analysis, and both of them can be used for arbitrary modulation depth, or laser architectures even when severe non-linear intensity modulation occurs simultaneously with wavelength modulation. These new interpretations of WMS absorption signals provide the potential for extended and improved use of WMS for practical gas sensing in a much wider array of applications. The first approach built on earlier work in our laboratory. The analysis of calibration-free, 1f-normalized, WMS-2f absorption signals was extended to higher harmonics (for example 3f, 4f ...) using traditional Fourier analysis. The new approach and procedure developed also accounts for non-ideal wavelength-tuning of the injection-current tuned laser as well as etalon interference from the optical components in the laser line-of-sight (LOS). This approach was validated using measurements of the CO transition of R (11) in the 1st overtone band near 2.3æm in a laboratory cell at room temperature for a range of CO mole fractions (0.21-2.8%) and pressures (5-20atm). For high-pressure gas sensing, wavelength modulation spectroscopy with higher-order harmonic detection (WMS-nf, n> 2) was found to have less influence from the WMS background signals when the selected modulation depth was near the optimal modulation depth for the WMS-2f signal. This WMS approach was then used for measurements in a pilot-scale entrained-flow coal gasifier at the University of Utah. Even though the particulate scattering reduced the laser transmission as much as 99.997%, and pressure broadening at the 18atm (~250psig) operating pressure blended the absorption transitions, successful in-situ rapid-time-resolved 1f-normalized WMS-2f absorption measurements for gas temperature and H2O mole fraction were made. Based on lessons learned during the gasifier measurements at Utah and a desire to eventually develop real-time sensors for long-term monitoring, a second approach for WMS analysis was developed that differs from previous WMS analysis strategies in two significant ways: (1) the measured laser intensity without absorption is used to simulate the transmitted laser intensity with absorption and (2) digital lock-in and low-pass filter software is used to expand both simulated and measured transmitted laser intensities into harmonics of the modulation frequency, WMS-nf (n=1,2,3 ...), avoiding the need for an analytic model of intensity modulation or Fourier expansion of the simulated WMS harmonics. The new method was demonstrated and validated with WMS of H2O dilute in air (1atm, 296K, near 1392nm). WMS-nf harmonics for n=1 to 6 are extracted and the simulations and measurements are found in good agreement for the entire WMS lineshape. This new analysis scheme was applied to monitor the synthesis gas output from an engineering-scale transport reactor coal gasifier at the National Carbon Capture Center. There the pressures ranged up to 15 atm (~220psig) and temperatures up to 650K. Continuous monitoring of moisture level in the gasifier output with 2s time resolution was performed by the TDL sensor for more than 500 hours, including the periods of burner ignition, combustion heating with a propane flame, coal combustion, coal gasification, and reactor shut-down via coal-feed termination. In addition, a novel and rapid approach to determine the collisional linewidth via the WMS signals at different harmonics at the modulation frequency is presented. The peak values of the WMS-nf absorption spectrum near the transition line center are used to infer the absorption lineshape, which is exploited here to extract collision-broadening halfwidth from the ratio of WMS-4f/WMS-2f (or other even harmonics) signals when the mean laser wavelength is tuned to line center. Measurement of the absorption linewidth enables quantitative WMS measurements without the need for a collision-broadening database. Alternatively, when collision-broadened spectral data are available, a WMS-based pressure sensor can be realized, and a demonstration using the 4fpeak/2fpeak ratio gives less than 0.7% difference for the pressure for cell measurements from 100 torr to 753 torr. These new WMS analysis schemes have been validated in near commercial environments and illustrate the potential of their use to develop practical TDL sensors for a wide variety of industrial applications.
Author: William VonDrasek
Publisher:
ISBN:
Category :
Languages : en
Pages : 128
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This work represents the collaborative effort between American Air Liquide and Physical Sciences, Inc. for developing a sensor based on near-IR tunable diode lasers (TDL). The multi-species capability of the sensor for simultaneous monitoring of CO, O2, and H2O concentration as well as gas temperature is ideal for in-situ monitoring on industrial furnaces. The chemical species targeted are fundamental for controlling the combustion space for improved energy efficiency, reduced pollutants, and improved product quality, when coupling the measurement to a combustion control system. Several add-on modules developed provide flexibility in the system configuration for handling different process monitoring applications. For example, the on-Demand Power Control system for the 1.5?m laser is used for high particle density exhaust streams where laser transmission is problematic. For long-distance signal collection a fiber optic communication system is used to reduce noise pick-up. Finally, hardened modules to withstand high ambient temperatures, immune to EMF interference, protection from flying debris, and interfaced with pathlength control laser beam shielding probes were developed specifically for EAF process monitoring. Demonstration of these different system configurations was conducted on Charter Steel's reheat furnace, Imco Recycling, Inc. (now Aleris International, Inc.) aluminum reverberatory furnace, and Gerdau Ameristeel's EAF. Measurements on the reheat furnace demonstrated zone monitoring with the measurement performed close to the steel billet. Results from the aluminum furnace showed the benefit of measuring in-situ near the bath. In this case, low-level furnace optimization was performed and demonstrated 5% fuel savings. Monitoring tests on the EAF off-gas demonstrated the level of industrialization of the sensor to survive the harsh EAF environment. Long-term testing on the EAF has been on-going for over 6 months with essentially zero maintenance. Validation of the TDL measurement on the EAF was confirmed by comparison with extractive sampling CO measurements.
