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Soot Formation in Non-premixed Laminar Flames at Subcritical and Supercritical PressuresJoo, Hyun Il 13 August 2010 (has links)
An experimental study was conducted using axisymmetric co-flow laminar diffusion flames of methane-air, methane-oxygen and ethylene-air to examine the effect of pressure on soot formation and the structure of the temperature field. A liquid fuel burner was designed and built to observe the sooting behavior of methanol-air and n-heptane-air laminar diffusion flames at elevated pressures up to 50 atm. A non-intrusive, line-of-sight spectral soot emission (SSE) diagnostic technique was used to determine the temperature and the soot volume fraction of methane-air flames up to 60 atm, methane-oxygen flames up to 90 atm and ethylene-air flames up to 35 atm. The physical flame structure of the methane-air and methane-oxygen diffusion flames were characterized over the pressure range of 10 to 100 atm and up to 35 atm for ethylene-air flames. The flame height, marked by the visible soot radiation emission, remained relatively constant for methane-air and ethylene-air flames over their respected pressure ranges, while the visible flame height for the methane-oxygen flames was reduced by over 50 % between 10 and 100 atm. During methane-air experiments, observations of anomalous occurrence of liquid material formation at 60 atm and above were recorded. The maximum conversion of the carbon in the fuel to soot exhibited a strong power-law dependence on pressure. At pressures 10 to 30 atm, the pressure exponent is approximately 0.73 for methane-air flames. At higher pressures, between 30 and 60 atm, the pressure exponent is approximately 0.33. The maximum fuel carbon conversion to soot is 12.6 % at 60 atm. For methane-oxygen flames, the pressure exponent is approximately 1.2 for pressures between 10 and 40 atm. At pressures between 50 and 70 atm, the pressure exponent is about -3.8 and approximately -12 for 70 to 90 atm. The maximum fuel carbon conversion to soot is 2 % at 40 atm. For ethylene-air flames, the pressure exponent is approximately 1.4 between 10 and 30 atm. The maximum carbon conversion to soot is approximately 6.5 % at 30 atm and remained constant at higher pressures.
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Soot Formation in Non-premixed Laminar Flames at Subcritical and Supercritical PressuresJoo, Hyun Il 13 August 2010 (has links)
An experimental study was conducted using axisymmetric co-flow laminar diffusion flames of methane-air, methane-oxygen and ethylene-air to examine the effect of pressure on soot formation and the structure of the temperature field. A liquid fuel burner was designed and built to observe the sooting behavior of methanol-air and n-heptane-air laminar diffusion flames at elevated pressures up to 50 atm. A non-intrusive, line-of-sight spectral soot emission (SSE) diagnostic technique was used to determine the temperature and the soot volume fraction of methane-air flames up to 60 atm, methane-oxygen flames up to 90 atm and ethylene-air flames up to 35 atm. The physical flame structure of the methane-air and methane-oxygen diffusion flames were characterized over the pressure range of 10 to 100 atm and up to 35 atm for ethylene-air flames. The flame height, marked by the visible soot radiation emission, remained relatively constant for methane-air and ethylene-air flames over their respected pressure ranges, while the visible flame height for the methane-oxygen flames was reduced by over 50 % between 10 and 100 atm. During methane-air experiments, observations of anomalous occurrence of liquid material formation at 60 atm and above were recorded. The maximum conversion of the carbon in the fuel to soot exhibited a strong power-law dependence on pressure. At pressures 10 to 30 atm, the pressure exponent is approximately 0.73 for methane-air flames. At higher pressures, between 30 and 60 atm, the pressure exponent is approximately 0.33. The maximum fuel carbon conversion to soot is 12.6 % at 60 atm. For methane-oxygen flames, the pressure exponent is approximately 1.2 for pressures between 10 and 40 atm. At pressures between 50 and 70 atm, the pressure exponent is about -3.8 and approximately -12 for 70 to 90 atm. The maximum fuel carbon conversion to soot is 2 % at 40 atm. For ethylene-air flames, the pressure exponent is approximately 1.4 between 10 and 30 atm. The maximum carbon conversion to soot is approximately 6.5 % at 30 atm and remained constant at higher pressures.
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Laser-induced Incandescence of Soot at High PressuresGhasemi, Sanaz 20 November 2012 (has links)
Measurements of soot emission properties are of interest in both fundamental research and combustion-based industries. Laser-induced incandescence of soot particles is a novel technique that allows unobtrusive measurements of both soot volume fraction and particulate size with significant advantages. An apparatus utilizing this technique has been customized and used to provide measurements of soot concentration and particle sizing of a laminar, diffusion methane/air flame at pressures of 10, 20 and 40 atm at 6~mm above the burner. Soot volume fraction measurements correlate well with literature findings at all pressures. Despite similar trends, particle size values are found to be consistently larger than values reported in literature. Discussion on the errors of laser-induced incandescence as well as recommendations for improving the apparatus and results are herein.
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Laser-induced Incandescence of Soot at High PressuresGhasemi, Sanaz 20 November 2012 (has links)
Measurements of soot emission properties are of interest in both fundamental research and combustion-based industries. Laser-induced incandescence of soot particles is a novel technique that allows unobtrusive measurements of both soot volume fraction and particulate size with significant advantages. An apparatus utilizing this technique has been customized and used to provide measurements of soot concentration and particle sizing of a laminar, diffusion methane/air flame at pressures of 10, 20 and 40 atm at 6~mm above the burner. Soot volume fraction measurements correlate well with literature findings at all pressures. Despite similar trends, particle size values are found to be consistently larger than values reported in literature. Discussion on the errors of laser-induced incandescence as well as recommendations for improving the apparatus and results are herein.
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Investigation of High Pressure Combustion and Emissions Characteristics of a Lean Direct Injection Combustor ConceptAhmed, Abdelallah 11 October 2016 (has links)
No description available.
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Analysis Techniques for Characterizing High Power Turbulent Swirl FlamesRobert Z Zhang (6717671) 16 August 2019 (has links)
<div>High speed laser diagnostics are performed in two vastly differing swirl combustors at conditions relevant for industrial gas turbines. This high quality data can not only be used to elucidate key features of the flow field but also for validation of computational models simulating turbulence, chemistry, and their interactions. The first combustor is a piloted lean premixed prevaporized arrangement common in aviation applications. Fueling parameters are varied and sensitivity towards the pilot flame is observed. Conditioning to the stagnation line demonstrates increased fluctuations of shear and rotation in the inner shear layer when the pilot fueling is reduced.</div><div><br></div><div>The second flame has a simpler configuration with a single swirler and combusting natural gas. Thermoacoustic instability coupled to a helical precessing vortex core is found at certain conditions. Sparse Dynamic Mode Decomposition and phase averaging is applied to the velocity fields to create a three dimensional reconstruction of the helical vortex core in a non-precessing reference frame. Heat release is found to be correlated to the interaction strength of the central recirculation bubble and the helical vortex core. </div><div><br></div><div> </div><div>Finally, intermittent phenomena within a thermoacoustic instability are examined. The most prominent deviation is that the flame is observed to randomly lift and reattach. In addition, a convolutional neural network is employed to extract the morphology from otherwise qualitative OH species imaging. The average characteristics of the lifted and attached flame are compared and dramatic differences are found. All of the flow structures have been altered such as the precessing vortex core being greatly intensified during flame lift-off. Evaluating the average events before flame lift-off revealed the importance of conditions at the combustor inlet. However, evidence for a future reattachment event was only found with a less spatially confined perspective. In addition, transition to lift-off was very sudden while reattachment was far slower.</div>
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Ultrafast laser-absorption spectroscopy in the mid-infrared for spatiotemporally resolved measurements of gas propertiesRyan J Tancin (10711722) 27 April 2021 (has links)
<div>Laser-absorption spectroscopy (LAS) is widely used for providing non-intrusive and quantitative measurements of gas properties (such as temperature and absorbing species mole fraction) in combustion environments. However, challenges may arise from the line-of-sight nature of LAS diagnostics, which can limit their spatial resolution. Further, time-resolution of such techniques as scanned direct-absorption or wavelength-modulation spectroscopy is limited by the scanning speed of the laser and the optical bandwidth is often limited by a combination of a laser's intrinsic tunability and its scanning speed. The work presented in this dissertation investigated how recent advancements in mid-IR camera technology and lasers can be leveraged to expand the spatial, temporal, and spectral measurement capabilities of LAS diagnostics. Novel laser-absorption imaging and ultrafast laser-absorption spectroscopy diagnostics are presented in this dissertation. In addition, the high-pressure combustion chamber (HPCC) and high-pressure shock tube (HPST) were designed and built to enable the study of, among others, energetic material combustion, spectroscopy, non-equilibrium and chemistry using optical diagnostics.<br></div><div><br></div>
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Experiments with a High Pressure Well Stirred ReactorGross, Justin Tyler January 2014 (has links)
No description available.
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MICROWAVE SCATTERING FOR DIAGNOSTICS OF LASER-INDUCED PLASMAS AND DENSITIES OF SPECIES IN COMBUSTION MIXTURESAnimesh Sharma (8911772) 16 June 2020 (has links)
<p>Laser-induced plasmas since their discovery in the
1960’s have found numerous applications in laboratories and industries. Their
uses range from soft ionization source in mass spectroscopy, development of
compact particle accelerator, and X-ray and deep UV radiation sources to
diagnostic techniques such as laser-induced breakdown spectroscopy and laser
electronic excitation tagging. In addition, the laser-induced plasma is important
for studying of various nonlinear effects at beam propagation, such as laser
pulse filamentation.</p>
<p>This
work deals with two challenging aspects associated with laser-induced plasmas.
First is the study of Multi-Photon Ionization (MPI) as
a fundamental first step in high-energy laser-matter interaction critical for
understanding of the mechanism of plasma formation. The
second is application of laser induced plasma for diagnostics of combustion
systems.</p>
<p>Numerous attempts to determine the basic
physical constants of MPI process in direct experiments, namely photoionization
rates and cross-sections of the MPI, were made; however, no reliable data was
available until now, and the spread in the literature values often reached 2–3
orders of magnitude. This work presents the use of microwave scattering in
quasi-Rayleigh regime off the electrons in the laser-induced plasma as method
to measure the total number of electrons created due to the photoionization
process and subsequently determine the cross-sections and rates of MPI.
Experiments were done in air,<i> O<sub>2</sub>, Xe, Ar,
N<sub>2</sub>, Kr</i>, and <i>CO</i> at room temperature and atmospheric pressure and femtosecond-laser pulse at 800 nm wavelength was utilized. Rayleigh microwave scattering (RMS) technique was used to
obtain temporally resolved measurements of the electron numbers created by
the laser. Numbers of electrons in the range 3 × 10<sup>8</sup>–3 × 10<sup>12</sup> were
produced by the laser pulse energies 100–700 <i>μ</i>J and corresponding
electron number densities down to about 10<sup>14</sup> cm<sup>-3</sup> in the
center of laser-induced spark were observed. After the laser pulse, plasma
decayed on the time scale from 1 to 40 ns depending on the gas type and
governed by two competing processes, namely, the creation of new electrons from
ionization of the metastable atoms and loss of the electrons due to
dissociative recombination and attachment to oxygen. </p>
<p>Diagnostics
of combustion at high pressures are challenging due to increased collisional
quenching and associated loss of acquired signal. In this work, resonance
enhanced multiphoton photon ionization (REMPI) in conjunction with measurement
of generated electrons by RMS technique were used to develop diagnostics method
for measuring concentration of a component in gaseous mixture at elected
pressure. Specifically, the REMPI-RMS diagnostics was developed and tested in
the measurements of number density of carbon monoxide (<i>CO</i>) in mixtures with nitrogen (<i>N<sub>2</sub></i>) at pressures up to 5 bars. Number
of REMPI-induced
electrons scaled linearly with <i>CO</i> number density up to about 5×10<sup>18</sup>
cm<sup>-3</sup> independently of buffer gas pressure up to
5 bar, and this linear scaling region can be
readily used for diagnostics purposes. Higher <i>CO</i> number densities were associated laser beam energy loss while travelling
through the gaseous mixture. Four (4) energy level model of <i>CO</i> molecule was developed and direct measurements
of the laser pulse energy absorbed in the two-photon process during the passage
through the <i>CO</i>/<i>N<sub>2</sub></i> mixture were conducted in order to analyze the
observed trends of number of REMPI-generated electrons with <i>CO</i> number density and laser energy.</p>
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