Tunable Diode Laser Absorption Probe Techniques for Species Measurements in Combustion Gases PDF Download
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Author: Susan Marie Schoenung
Publisher:
ISBN:
Category : Carbon monoxide
Languages : en
Pages : 234
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Book Description
Author: Susan Marie Schoenung
Publisher:
ISBN:
Category : Carbon monoxide
Languages : en
Pages : 234
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Book Description
Author: Reynolds Reed Skaggs
Publisher:
ISBN:
Category :
Languages : en
Pages : 554
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Author: Julian Jon-Laurent Girard
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Spectroscopic measurement strategies enabled by in situ laser-based probes were implemented in low-pressure flames, shock tubes, and a hypersonic reflected shock tunnel. In particular, tunable diode laser absorption spectroscopy (TDLAS) was leveraged to accurately infer quantities of interest such as temperature, species concentration, and pressure. Targeted environments spanned both flowing and static samples, reacting and inert compositions, and varying degrees of thermal equilibrium. Two bodies of work falling under this general theme of research are presented. First, two applications of a single-ended optical probe that incorporates a mid-infrared (MIR) CO2 TDLAS diagnostic are summarized. The rovibrational CO2 diagnostic, with transitions centered near 4.2 um, was developed for sensitive two-line thermometry in combustion environments, optimal in the temperature range of 1200 -- 2100 K and the pressure range of 0 - 2 atm. The selected transitions correspond to the strong v3 asymmetric stretch mode of CO2, whose fundamental band boasts the strongest MIR lines among common combustion products (i.e. CO2, CO, H2O, OH, NO). In the first application of this diagnostic, an interband quantum cascade laser (ICL) was directed across a low-pressure burner-stabilized flame using a single-ended optical probe composed of two thin sapphire rod waveguides. Probe-based measurements of temperature and CO2 mole fraction were collected in flames of 25 torr and 60 torr total pressure, and at distances from the burner surface in the range of 3 - 23 mm. In another study, this CO2 diagnostic with a similar single-ended probe implementation was applied to shock tube experiments. The shock tube endcap probe developed enables measurements of relevant reflected-shock region (region 5) quantities (e.g. temperature and CO2) at variable distances from the shock tube endwall, and offers an alternative path length option to traditional sidewall optical portholes. TDLAS measurements of temperature and CO2 mole fraction made with the endwall probe were typically subject to uncertainties of 1% and 5%, respectively. The sensor performance was validated in inert shocked mixtures with 1 - 7% CO2 diluted in argon or nitrogen, and spanning the temperature range of 1200 - 2000 K and pressure range of 0.7 - 1.2 atm. Probe-based measurements were compared directly with traditional sidewall window measurements (i.e. full tube diameter path length) and empirically supported simulations. Finally, perturbation of region 5 conditions by the probe was assessed with a series of tests. The main body of work discussed in this thesis concerns a series of studies conducted at the T5 reflected shock tunnel located at the California Institute of Technology. The focus of these experiments was to conduct spectroscopic measurements of various species in hypersonic nonequilibrium air flows generated at the facility, in support of freestream and flow-model investigations. Freestream characterization of T5 was conducted through two iterative efforts, first involving quasi-quantitative path-averaged measurements of nitric oxide (NO) across the entire (nonuniform) test section. In a subsequent effort, a custom flow-cutting optical probe was used to measure absorbing rovibrational NO transitions in the (uniform) core flow of the freestream. Measured quantities included NO rotational and vibrational temperature, partial pressures of NO, CO, H2O, K, and flow velocity. During this set of experiments, the uniformity of the measured quantities across the core and beyond was assessed by repeating the experiment with distinct probe lengths (i.e. different optical path lengths). Finally, NO, CO and electronically excited oxygen absorption were measured at spatially-precise locations in the post-shock flow generated around a cylindrical model. The path-averaged measurements were processed to infer post-shock quantities of interest, using simple models of the pathwise condition distribution. Insights are drawn by comparing these preliminary measurements with existing 3D CFD simulations of the cylinder post-shock flowfield.
Author: Susan M. Schoenung
Publisher:
ISBN:
Category : Absorption spectra
Languages : en
Pages : 21
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The initial work in a program at Stanford to develop laser-based combustion diagnostics has focused on tunable laser absorption spectroscopy using an infrared diode laser. An important aspect of this program is the validation of the laser technique under controlled conditions and by comparison with established probe-based methods. This paper reports preliminary results from such experiments, which consisted of CO concentration measurements in a flat premixed flame using a tunable diode laser, and both CO and CO2 measurements in a similar flame using an uncooled, aerodynamically quenched quartz sampling probe. CO was chosen for this study for several reasons: it is an important flame species whose concentration can be predicted under equilibrium conditions which prevail in the post-flame region of fuel-rich flames; its concentration in combustion products can be easily varied from 10 ppm to greater than 10%, a range which is compatible with commercial NDIR instruments; and it has a well-understood infrared absorption spectrum which simplifies analysis of the absorption measurements.
Author: Gordon S. Humphries
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In-situ optical techniques offer one of the most attractive options for measuring species concentration and spatial distribution profiles in reacting environments, such as flames. The generally non-intrusive nature and spatial resolution of these techniques are now preferred over on extractive sampling, followed by analysis using techniques such as gas chromatography. In this thesis two laser absorption measurement techniques are applied to measure the soot distribution, and acetylene concentration profiles in a flat-flame burner. The in-situ measurement of the distribution of particulate matter in flames is a key step in understanding the mechanism of its formation. Most in-situ measurement systems for this purpose are based on laser induced incandescence where particles are heated using high power laser sources and the increased incandescence emission of the soot particles is detected. However as the soot cools by heat transfer to the surrounding gas, following laser heating, the pressure of the gas is increased creating an acoustic effect. Photoacoustic detection has been applied to quantify low concentrations of particulate matter in ambient air but there have been few applications of photoacoustic detection to the in-situ measurement of particulate matter formation in combustion processes. A novel simple approach using a modulated continuous wave diode laser is presented in this thesis. The measurements taken using this new technique are compared to measurements of the visible emission from the flame, and previous soot distribution measurements using laser induced incandescence. Absorption spectroscopy using near-infrared tunable diode lasers has been applied to measure species in several harsh environments such as aero-engine exhaust plumes, flames, and other industrial processes. Simple single pass absorption techniques are not always suitable for this purpose due to the low absorption of the target species, either due to low concentration or weak absorption line-strength at high temperatures. One method to increase the sensitivity of such techniques is by using cavity enhanced methods which increase the effective path length of the laser through the absorbing medium. One such cavity enhanced method is Cavity Ring-Down Spectroscopy (CRDS). CRDS uses a cavity constructed of highly reflecting mirrors, laser light is then coupled into this cavity and absorption measurements can be evaluated from the decay rate of light from the cavity. The design and, novel application of continuous wave CRDS to measure the concentration profile of acetylene in the flat-flame burner is presented. Difficulties in deriving an absolute acetylene concentration from the measured ringdown times were encountered due to the large number of interfering features. Serveral fitting and extraction techniques are applied and compared to attempt to overcome these difficulties.
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: Aamir Farooq
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The development of diagnostics based on laser-absorption spectroscopy for combustion applications has been an important and active field of research over the past two decades due to the advantages of this non-intrusive optical sensing technique compared to traditional sampling-based sensing methods. Tunable diode laser (TDL) sensors, in particular, have shown the ability to provide in situ, time-resolved, line-of-sight measurements of temperature, gas species concentration, velocity, density, mass flux, and pressure in a variety of combustion environments. This thesis explores three new areas of TDL research: (a) extended near-infrared (NIR) diagnostics, (b) sensing under high-pressures, and (c) applications to chemical kinetics. Water vapor (H2O) and carbon dioxide (CO2) are attractive sensing targets for hydrocarbon-fueled systems as they are primary combustion products and their concentrations can be interpretrated to indicate combustion progress and efficiency. Both these gases have absorption spectra in the infrared (IR) region. Most previous TDL absorption sensors were designed to exploit robust telecommunications diode lasers and optical fiber technology in the 1.3-1.6 [mu]m (NIR) wavelength region. Recent developments in semiconductor diode-laser technology have extended the range of continuous wave (CW) room-temperature single-mode diode lasers to 2.9 [mu]m, allowing access to stronger vibrational bands of H2O and CO2 in the extended-NIR region. The first combustion diagnostics in the extended-NIR wavelength were demonstrated as part of this thesis work. The sensors were designed by selecting optimal transitions and then measuring the pertinent spectroscopic parameters in controlled laboratory environements. These sensors were then tested in the combustion environments of a flat flame and shock tube to validate their performance. These new sensors provide enhanced sensitivity and improved accuracy compared to previous TDL diagnostics. As part of this work, a novel diagnostic based on wavelength modulation spectroscopy (WMS) of CO2 was developed to make precise measurements of temperature behind reflected shock waves. This temperature diagnostic achieved an unprecedented uncertainty of
Author: Alan C. Eckbreth
Publisher: CRC Press
ISBN: 1000124622
Category : Technology & Engineering
Languages : en
Pages : 630
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Book Description
This book examines the variety of potential laser diagnostic techniques and presents a considerable theoretical foundation elucidating physics relevant to the laser diagnostics. It explains the Raman-based approaches for major species and temperature measurements.
Author: Christoph Dyroff
Publisher:
ISBN: 9783866443280
Category : Technology (General)
Languages : en
Pages : 0
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Book Description
This book discusses the mechanical and opto-electronic design of laser spectrometers for measuring two very important atmospheric gases, namely water vapor and its isotopic ratios, and formaldehyde. For measuring water vapor, shot-noise limited sensitivity has been achieved by a careful choice of system components and data processing. For measuring formaldehyde, a selective sample modulation exploiting the Stark effect has been used to greatly improve the sensitivity.
Author: James R. P. Bain
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Tunable diode laser spectroscopy is a widely used technique for recovering quantitative gas information in a range of industrial applications. Established methods often use readily available, robust and low cost optoelectronic hardware in the near-infrared, with output wavelengths that coincide with the absorption spectra of several important gas species of interest, providing a versatile platform for gas analysis instrumentation. In this work the challenges associated with the recovery of gas information from harsh detection environments, particularly for aero engine diagnostics, are considered. For stand-alone instrumentation, calibration-free direct absorption measurements are highly advantageous yet calibrated techniques employing wavelength modulation spectroscopy are often favoured due to their significantly higher sensitivities. Recent developments have enabled calibration-free line shape recovery using lock-in amplifier detection of the residual amplitude modulation in wavelength modulated signals. These techniques have significant potential in harsh environments, but the overall sensitivity is limited by distortions to the recovered line shapes at high modulation amplitudes and by large background signals that saturate the detection electronics. In this thesis, solutions to these two problems are proposed, investigated and validated. A correction function is derived that is able to account for line shape distortions at arbitrarily high modulation indices. Application of the function depends upon knowledge of the experimental modulation index and two methods for extracting this information directly from the experimental signals are described. The full correction procedure has been experimentally validated. An investigation was made into the use of autobalanced photoreceivers, typically used for common mode noise cancellation, for direct absorption measurements and in a different configuration for nulling of the residual amplitude modulation (RAM) in wavelength modulation spectroscopy. Initial measurements suggest that removal of the background RAM can increase the lock-in detection sensitivity by over an order of magnitude. In addition an external amplitude modulator has been iv shown to be an effective method for producing sensitive absorption signals that are free of distortions, recoverable at frequencies that are outside the bandwidth of most environmental noise sources. A temperature sensor based on ratio thermometry of ambient water vapour absorption was designed and evaluated. The sensor is intended to provide accurate intake gas temperature information during aero engine ground testing when misting conditions prevent standard thermocouples from providing reliable data. Direct detection and second harmonic wavelength modulation spectroscopy experiments were undertaken in an environmental chamber, over the range 273-313K, to test the potential accuracy of the proposed system. Using a second harmonic peak height method, temperature information based on a calibration was able to recover temperature measurements with precision of ±0.4K however the overall accuracy suffered from a problematic calibration drift. Three engine test campaigns are described in which a range of recovery methods and potential optical system layouts are evaluated for the purposes of intake and exhaust mounted test bed sensor systems. The effects of extreme noise conditions were observed on a variety of measurements and favourable detection and modulation options were identified for the purpose of planning proposed future engine tests. Exhaust plume measurements of high temperature water vapour on the Rolls-Royce Environmentally Friendly Engine demonstrator established the viability of temperature and concentration measurements up to 850K.
