Diode Laser Absorption Diagnostics for Measurements in Practical Combustion Flow Fields PDF Download

Author: J. T. C. Liu
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: M. P. Arroyo
Publisher:
ISBN:
Category :
Languages : en
Pages : 6

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A tunable diode laser diagnostic based spectrally resolved laser absorption has been developed to detect water vapor. The system uses a distributed feedback InGaAsP diode laser, emitting around 1.385 micrometer. The diode laser is tuned in wavelength by modulating its driving current at frequencies up to 5 KHz Temperatures, concentrations and pressures are inferred from the directly measured absorption spectra. Velocity is derived from the Doppler shift of these absorption spectra. The technique has been demonstrated for multiple-parameter measurements of the water vapor present in laboratory room air, in the postflame gases above a methane-air flat fame burner and in the high speed unidimensional transient flows generated in a shock tube. The results agree well with the calculated valves and independent measurements. (Author).

Author: Alan C. Eckbreth
Publisher: CRC Press
ISBN: 9782884492256
Category : Technology & Engineering
Languages : en
Pages : 632

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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: Yoshihiro Deguchi
Publisher: Taylor & Francis
ISBN: 1439853398
Category : Science
Languages : en
Pages : 301

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Tighter regulations of harmful substances such as NOx, CO, heavy metals, particles, emissions from commercial plants and automobiles reflect a growing demand for lowering the anthropogenic burdens on the environment. It is equally important to monitor controlling factors to improve the operation of industrial machinery and plants. Among the many me

Author: Quang-Viet Nguyen
Publisher:
ISBN:
Category : Lasers
Languages : en
Pages : 330

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Author: D. S. Baer
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Cameron Tropea
Publisher: Springer Science & Business Media
ISBN: 3540251413
Category : Science
Languages : en
Pages : 1570

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Accompanying DVD-ROM contains ... "all chapters of the Springer Handbook."--Page 3 of cover.

Author:
Publisher:
ISBN:
Category : Airplanes
Languages : en
Pages : 504

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Author: Christopher Lyle Strand
Publisher:
ISBN:
Category :
Languages : en
Pages :

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The work presented herein describes several advances in the evolution of combustion diagnostics based upon the technique of tunable diode laser absorption spectroscopy (TDLAS). The primary focus of this work was to provide the theoretical and practical means to perform in-situ TDLAS measurements within the harsh flow environments of hypersonic impulse ground-test facilities. In addition to this primary focus, the development and application of this work led to a comprehensive analytical framework for wavelength-modulation spectroscopy and enhanced the understanding of the complex flow environments within hypersonic flow facilities and hypersonic combustion experiments. Hypersonics is the field of aeronautics concerned with flight speeds that are highly supersonic, typically on the order of Mach 5 and above. Presently, it is the domain of spacecraft during re-entry and a select cadre of rocket-powered and air-breathing test vehicles (e.g., North American X-15, NASA X-43, Boeing X-51, HyShot I-IV, HiFiRE 0-3, etc.). It is also a regime of grand aspirations, including routine inexpensive space access, rapid intercontinental transport, atmospheric entry on other planets, and numerous strategic military applications. The development of hypersonic technology is confounded by the immensity of the problem, especially the complexity of interacting physical phenomena and the shortcomings in the fundamental understanding thereof. Understanding of this complex regime and the development of technologies to utilize this regime for flight require a comprehensive scientific and engineering approach including fundamental theory, computations, ground-testing, and flight testing. Due to the capacity of ground-test facilities to formulate tractable hypersonic experiments and, within those experiments, the capability of specialized diagnostics to extract critical information, ground-testing is the primary approach to cracking the multi-physics puzzle of hypersonic flight. Shock-tube-derived impulse flow facilities are a specific form of hypersonic ground-test facility and fill a critical niche within the field. These facilities are characterized by extremely short test times, often less than a few milliseconds, but excel at producing high-enthalpy flows with realistic flow chemistry. This capability is particularly valuable for the investigation of chemically reacting flows within air-breathing hypersonic vehicles such as the scramjet. Effective use of the short-duration test time is progressively being unlocked by the development of modern high-bandwidth instrumentation. Tunable diode laser absorption spectroscopy (TDLAS) offers the potential to provide quantitative measurement of numerous critical flow parameters within these facilities, including temperature, velocity, and species partial pressure. The violent flow environment of a flow model in an impulse ground-test facility creates a formidable challenge for the implementation of a TDLAS diagnostic. Impulse flow test times on the order of 1 ms necessitate exceptionally high measurement bandwidths to capture relevant transient phenomena. Harsh flow conditions introduce substantial measurement noise through mechanically- and density-gradient-induced beam-steering. Short optical paths within the model limit the magnitude of the optical absorption signal and the confined environment limits the resources available for required optical hardware. Further challenges are introduced through the requirements of generating an academically valuable dataset. Multiple simultaneous quantitative measurement parameters at numerous locations within the flow-field are often desirable in both reacting and non-reacting flows. To address the challenges of TDLAS sensing in impulse flow facilities, the efforts of this work include advances in both diagnostic methodology and optical hardware design. A new analytical framework has been developed for the technique of scanned-wavelength-modulation spectroscopy (scanned-WMS) to reject noise and achieve high-sensitivity while permitting the simultaneous measurement of temperature, partial pressure, and velocity. This new framework has enabled accurate measurements at unprecedented bandwidths in harsh flow environments. Integration of TDLAS optical components into flow models has led to novel approaches for harsh-environment optical alignment hardware, combining precision and sufficient robustness to survive repeated firings of an impulse facility. Furthermore, the intense beam-steering induced by facility vibrations and turbulent density gradients have motivated a comprehensive redesign of conventional beam collection approaches. TDLAS diagnostics leveraging these advances have been implemented in both the Stanford Expansion Tube Flow Facility for the purpose of facility characterization and in the HyShot II scramjet experiment at the High Enthalpy Shock Tunnel in Göttingen, Germany to investigate reacting and non-reacting scramjet flows. Results from each of these campaigns are presented as an illustration of the diagnostic capabilities developed in this work.