Author: Eric L. Petersen
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Stanford University. Department of Aeronautics and Astronautics
Publisher:
ISBN:
Category : Gas lasers
Languages : en
Pages : 186

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Author: Batikan Koroglu
Publisher:
ISBN:
Category :
Languages : en
Pages : 120

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The dissertation discusses the details of the four following items: 1) design, assembly, and testing of a shock tube setup as well as a laser diagnostics apparatus for studying ignition characteristics of fuels and associated reaction rates, 2) measurements of methane and propanal infrared spectra at room and high temperatures using a Fourier Transformed Infrared Spectrometer (FTIR) and a shock tube , 3) measurements of ignition delay times and reaction rates during propanal thermal decomposition and ignition, and 4) investigation of ignition characteristics of methane during its combustion in carbon-dioxide diluted bath gas. The main benefit and application of this work is the experimental data which can be used in future studies to constrain reaction mechanism development.

Author: Erik Ninnemann
Publisher:
ISBN:
Category :
Languages : en
Pages : 104

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The United States government has set 2050 as the target for net-zero greenhouse gas emissions due to their increasing levels and the subsequent rise in global temperatures. To meet this target, there has been renewed interest in the combustion of high-energy biofuels that could combat these issues. Thus, the Department of Energy started the Co-Optimization of Fuels and Engines program to find bioderived blendstocks that can harmonize with current and future generation engines to increase power and efficiency, all while reducing overall emissions. As part of this program, it is crucial to understand the combustion of these fuels at the temperatures and pressures internal combustion engines operate at. Therefore, the oxidation and pyrolysis of several advanced biofuels--cyclopentanone, prenol, 1-pentene and trans-2 pentene, and methyl propyl ether--have been studied in a shock tube reactor to quantify some of their fundamental combustion properties. Measurements include ignition delay times and time-resolved species concentrations, including that of fuel decomposition and formation of intermediate species such as carbon monoxide and ethylene. These measurements are useful for validating and updating chemical kinetic mechanisms that provide the chemistry input into computational fluid dynamic codes. This study's measured data are compared to the predictions of the most recent literature chemical kinetic mechanisms for each fuel. When appropriate, sensitivity analyses were conducted to highlight reactions sensitive to the conducted measurements, and some reaction rate modifications were made.

Author: Yiming Ding
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Absorption spectroscopy is an important branch of spectroscopy that quantitatively measures the level of attenuation on electromagnetic radiation by a test sample. It offers the promise of in-situ, non-intrusive, fast, and sensitive diagnostics for application to transient harsh environments, such as exoplanets, flames, combustion systems, and hypersonic flows. In the endeavor to expand upon existing spectroscopic knowledge of infrared absorption and offer optical sensing solutions to the practical challenges in these complex environments, better experimental strategies of measurement and calibration for the associated high-temperature gas-phase atoms and molecules are warranted. This dissertation describes the development of two experimental approaches for the studies of potassium line shapes and broadband molecular absorption using state-of-the-art lasers at previously unexplored temperature conditions that are made possible by a shock tube. I first present a new approach to seed and produce alkali metal vapor in a shock tube and the resulting measurements of the high-temperature potassium vapor in a controlled laboratory environment. To overcome the experimental challenges associated with the extreme reactivity of potassium, the new method employs shock waves to break apart potassium chloride (KCl) salt precursors and produce atomic potassium in the shock-heated buffer gas. This potassium seeding approach was demonstrated to be effective between 1100 -- 1900 K and is readily deployable for other absorbing species of alkali metals. To overcome the hurdle of the relatively short test time of a shock tube, high-speed tunable diode laser absorption spectroscopy (TDLAS) was deployed. The lasers interrogated the potassium D1 and D2 transitions near 0.77 μm and yielded well-resolved absorption line shapes every 40 μs. The measured spectra were modeled as Voigt profiles. Line shape parameters are presented with temperature-dependent power-law relations for the potassium resonance doublets with argon, nitrogen, helium, and hydrogen as the collisional partners. Secondly, a novel methodology is presented of rapid-tuning broad-scan laser absorption spectroscopy that measures broadband mid-infrared absorption cross sections of gaseous molecules at elevated temperatures. The new method deploys rapid-tuning, broad-scan external-cavity quantum-cascade lasers (EC-QCLs) in a shock tube and can provide quantitative absorption information at a rate over 30,000 cm-1/s at spectral intervals between 0.35 -- 0.6 cm-1. Within the shock tube test time of a few milliseconds, the lasers can sweep across over 100 cm-1 to cover the entire branches, or even entire bands, of the absorption spectra for these species. In total, this method was used to measure the cross section profiles of ethylene, propene, 1-butene, i-butene, cis-2-butene, trans-2-butene, 1,3-butadiene, methanol, ethanol, formaldehyde, acetaldehyde, and acetone. The measurements focus on their strongest mid-infrared absorption bands between 5.4 -- 6.1 μm and 8.4 -- 11.7 μm for various temperatures and pressures up to 1600 K and 5 atm, respectively. The resulting spectra are distributed in a plain text format and archived as the Stanford ShockGas-IR database through a permanent URL https://purl.stanford.edu/cy149sv5686.

Author: Clayton Reed Mulvihill
Publisher:
ISBN:
Category :
Languages : en
Pages :

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H2O time-histories were studied within the H2/O2 system using a tunable diode laser system and a pressure-driven shock tube. Stoichiometric H2/O2 mixtures were prepared in high amounts of argon dilution. The mixtures were heated using a shock tube with a driver length of 3.04 m, a driven length of 6.78 m, and an inner diameter of 16.2 cm. A tunable diode laser (TDL) was used to measure H2O concentration near the endwall region of the shock tube after the passage of the reflected shock wave, 1.6 cm from the endwall. Both the incident and transmitted beam intensities were measured using IR photodetectors. The laser was tuned to access the H2O transition at 7204 cm−1. Experiments in the H2/O2 system were performed from 1100 to 1500 K and at an average pressure of 2.8 atm. The experimental results were compared with a mechanism from Hong et al. (2011). Preliminary results show good agreement in ignition delay time between experiment and model. A computer routine was created to modify the absorption coefficient as a function of temperature to account for the temperature variation during the experiment due to the chemical reaction. After rescaling, the corrected H2O profiles showed excellent agreement with the chemical kinetics model. Topics related to mechanism validation, the potential effects of impurities, and measurement accuracy are also addressed in the thesis. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155232

Author: Julian Jon-Laurent Girard
Publisher:
ISBN:
Category :
Languages : en
Pages :

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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:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 702

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Author: Christopher Andrew Almodovar
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Motivated by thermometry in high-enthalpy air, advancements towards the measurement and modeling of high-pressure laser absorption spectroscopy (LAS) of nitric oxide (NO) are presented. The primary application of this thermometer is to characterize the stagnation conditions (T = 1000--2500 K and P = 10--130 atm) in a clean-air hypersonic wind tunnel facility. By characterizing the thermodynamic conditions upstream of the expansion nozzle, the flow conditions of the expanding air can be determined via enthalpy matching. At high temperatures, the Zeldovich mechanism describes increasing NO formation in air with increasing temperature, making NO an attractive species for LAS-based temperature measurements in air. Two optical transitions in the R-branch of the fundamental rovibrational band of NO are selected and their fundamental spectroscopic parameters are characterized at high temperatures. The temperature sensor design is demonstrated in reflected shock wave experiments in a large diameter shock tube at pressures up to 5 atm. Although the target application's operating pressure range is well outside the demonstration range, the fundamental concept of two-wavelength absorption is still valid. However, at high pressures, the selected optical transitions begin to blend with their neighboring transitions. Thus, accurate knowledge of the high-temperature and high-pressure absorption at the selected wavelengths requires knowledge of the spectroscopic parameters defining the neighboring transitions. To measure the spectroscopic parameters of the many neighboring transitions, a high-pressure, high-temperature (HPHT) optical cell (up to 800 K and over 30 atm) is designed and demonstrated for mid-infrared spectroscopy with usable transmission up to approximately 8 microns. With a functional HPHT optical cell, a detailed, temperature-dependent study (up to 800 K) of the optical transitions in the NO R-branch near 5.3 microns is performed. To extend the study to temperatures relevant for the target sensing application, shock tube measurements from 1000 to 2500 K supplement the detailed study. Finally, the spectrum is studied at high pressures. Static cell measurements reveal deviations from the classical line shape models used accurately at low pressures. The deviations are attributed to collisional line mixing that emerges when the line widths of the optical transitions are of similar or greater magnitude than the separation of optical transitions. A temperature-dependent line mixing model is built using statistically-based energy gap fitting laws and the full relaxation matrix expression. A comparison with measured data reveals good agreement in the regions where inter-branch coupling can be neglected. In the end, a thorough treatment of the NO spectrum has provided a temperature- and pressure-dependent model that can be used to predict the absorption spectra of NO in the R-branch of the fundamental rovibrational band.

Author: Ronald K. Hanson
Publisher: Springer
ISBN: 3319232525
Category : Technology & Engineering
Languages : en
Pages : 290

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This text provides an introduction to the science that governs the interaction of light and matter (in the gas phase). It provides readers with the basic knowledge to exploit the light-matter interaction to develop quantitative tools for gas analysis (i.e. optical diagnostics) and understand and interpret the results of spectroscopic measurements. The authors pair the basics of gas‐phase spectroscopy with coverage of key optical diagnostic techniques utilized by practicing engineers and scientists to measure fundamental flow‐field properties. The text is organized to cover three sub‐topics of gas‐phase spectroscopy: (1) spectral line positions, (2) spectral line strengths, and (3) spectral lineshapes by way of absorption, emission, and scattering interactions. The latter part of the book describes optical measurement techniques and equipment. Key subspecialties include laser induced fluorescence, tunable laser absorption spectroscopy, and wavelength modulation spectroscopy. It is ideal for students and practitioners across a range of applied sciences including mechanical, aerospace, chemical, and materials engineering.