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Thesis (Ph.D.). / Written for the Dept. of Mechanical Engineering. Title from title page of PDF (viewed 2009/06/11). Includes bibliographical references.

Thesis (M.Eng.). / Written for the Dept. of Mechanical Engineering. Title from title page of PDF (viewed 2009/06/17). Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on December 6, 2007) Vita. Includes bibliographical references.

<p>This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane (NM) in a shock tube. Reflected shock tube experiments on NM decomposition, using mixtures of 0.2 to 1.5 vol% NM in nitrogen or argon were performed over the temperature range 850-1550 K and pressure range 190-900 kPa, with 46 experiments diluted in nitrogen and 44 diluted in argon. By residual error analysis of the measured decomposition profiles it was found that NM decomposition (CH₃NO₂ + M -> CH₃ + NO₂ + M, where M = N₂ /Ar) corresponds well to a law of first order. Arrhenius expressions corresponding to NM diluted either in N₂ or in Ar were found as k_N2 = 1017.011×exp(-182.6 kJ/mole / R×T <cm³/mole×s> and k_Ar = 1017.574×exp(-207 kJ/mole / R×T )<cm3^/mole×s>, respectively. A new reaction mechanism was then proposed, based on new experimental data for NM decomposition both in Ar and N₂ and on three previously developed mechanisms. The new mechanism predicts well the decomposition of NM diluted in both N₂ and Ar within the pressure and temperature range covered by the experiments.</p><p>In parallel to, and following the decomposition experiments, oxidative experiments on the ignition delay times of NM/O₂/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous NM and oxygen diluted in argon, with pressures ranging between 44.3-600 kPa, and temperatures ranging between 842-1378 K.</p><p>The oxidation experiments were divided into different categories according to the type of decomposition signals achieved. For signals with and without emission, the apparent quasi-constant activation energy was found from the correlations, to be 64.574 kJ/mol and 113.544 kJ/mol, respectively. The correlations for the ignition delay for time signals with and without emission were deduced as τemission = 0.3669×10^-2×[NM]^-1.02[O₂]^-1.08×[Ar]^1.42×exp(7767/T) and τno emission = 0.3005×10^-2×[NM]^-0.28[O₂]^0.12×[Ar]^-0.59×exp(13657/T), respectively.</p><p>The second approach to molecular decomposition concerned the application of non-thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air. Experiments with a gliding arc discharge device were performed at the university of Orléans on the decomposition/reforming of low-to stoichiometric concentration air/CH₄ mixtures. The presented results show that complete reduction of methane could be obtained if the residence time in the reactor was sufficiently long. The products of the methane decomposition were mainly CO₂, CO and H₂O. The CH₄ conversion rate showed to increase with increasing residence time, temperature of the operating gas, and initial concentration of methane. To achieve complete decomposition of CH₄in 1 m³ of a 2 vol% mixture, the energy cost was about 1.5 kWh. However, the formation of both CO and NOx in the present gliding discharge system was found to be significant. The produced amount of both CO (0.4-1 vol%) and NO_x (2000-3500 ppm) were in such high quantities that they would constitute an important pollution threat if this process as of today was to be used in large scale CH₄ decomposition. Further experimental investigations were performed on self-built laboratory scale, single- and double dielectric-barrier discharge devices as a means of removing CH₄ and C₃H_{8 f}rom simulated reactive inlet mixtures. The different discharge reactors were all powered by an arrangement of commercially available Tesla coil units capable of high-voltage high-frequency output. The results from each of the different experiments are limited and sometimes only qualitative, but show a tendency that the both CH₄ and C₃H₈are reduced in a matter of a 3-6 min. retention time. The most plausible mechanism for explaining the current achievements is the decomposition by direct electron impact.</p>

This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane (NM) in a shock tube. Reflected shock tube experiments on NM decomposition, using mixtures of 0.2 to 1.5 vol% NM in nitrogen or argon were performed over the temperature range 850-1550 K and pressure range 190-900 kPa, with 46 experiments diluted in nitrogen and 44 diluted in argon. By residual error analysis of the measured decomposition profiles it was found that NM decomposition (CH3NO2 + M -&gt; CH3 + NO2 + M, where M = N2 /Ar) corresponds well to a law of first order. Arrhenius expressions corresponding to NM diluted either in N2 or in Ar were found as kN2 = 1017.011×exp(-182.6 kJ/mole / R×T &lt;cm3/mole×s&gt; and kAr = 1017.574×exp(-207 kJ/mole / R×T )&lt;cm3/mole×s&gt;, respectively. A new reaction mechanism was then proposed, based on new experimental data for NM decomposition both in Ar and N2 and on three previously developed mechanisms. The new mechanism predicts well the decomposition of NM diluted in both N2 and Ar within the pressure and temperature range covered by the experiments. In parallel to, and following the decomposition experiments, oxidative experiments on the ignition delay times of NM/O2/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous NM and oxygen diluted in argon, with pressures ranging between 44.3-600 kPa, and temperatures ranging between 842-1378 K. The oxidation experiments were divided into different categories according to the type of decomposition signals achieved. For signals with and without emission, the apparent quasi-constant activation energy was found from the correlations, to be 64.574 kJ/mol and 113.544 kJ/mol, respectively. The correlations for the ignition delay for time signals with and without emission were deduced as τemission = 0.3669×10-2×[NM]-1.02[O2]-1.08×[Ar]1.42×exp(7767/T) and τno emission = 0.3005×10-2×[NM]-0.28[O2]0.12×[Ar]-0.59×exp(13657/T), respectively. The second approach to molecular decomposition concerned the application of non-thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air. Experiments with a gliding arc discharge device were performed at the university of Orléans on the decomposition/reforming of low-to stoichiometric concentration air/CH4 mixtures. The presented results show that complete reduction of methane could be obtained if the residence time in the reactor was sufficiently long. The products of the methane decomposition were mainly CO2, CO and H2O. The CH4 conversion rate showed to increase with increasing residence time, temperature of the operating gas, and initial concentration of methane. To achieve complete decomposition of CH4 in 1 m3 of a 2 vol% mixture, the energy cost was about 1.5 kWh. However, the formation of both CO and NOx in the present gliding discharge system was found to be significant. The produced amount of both CO (0.4-1 vol%) and NOx (2000-3500 ppm) were in such high quantities that they would constitute an important pollution threat if this process as of today was to be used in large scale CH4 decomposition. Further experimental investigations were performed on self-built laboratory scale, single- and double dielectric-barrier discharge devices as a means of removing CH4 and C3H8 from simulated reactive inlet mixtures. The different discharge reactors were all powered by an arrangement of commercially available Tesla coil units capable of high-voltage high-frequency output. The results from each of the different experiments are limited and sometimes only qualitative, but show a tendency that the both CH4 and C3H8 are reduced in a matter of a 3-6 min. retention time. The most plausible mechanism for explaining the current achievements is the decomposition by direct electron impact.

Propellants based on hydroxylammonium nitrate (HAN) have shown promise as a hydrazine replacement because of their comparably low toxicity, low vapor pressure, high specific impulse and high density. Herein, the recent history of advanced monopropellant research is explored, and new experimental techniques are presented to investigate the combustion behavior of a potential hydrazine replacement propellant. Nitromethane, a widely available monopropellant with a recent resurgence in research, is utilized in the current study as a proof of concept for the newly designed equipment and as a step towards investigating more-advanced, HAN-based monopropellants. A strand bomb facility capable of supporting testing at up to 340 atm was employed, and experiments were performed between 28 atm and 130 atm. Burning rate data for nitromethane are calculated from experiments and a power correlation is established as r(mm/s) = 0.33[P(MPa)]^1.02. A comparison with available literature reveals this correlation to be very much in agreement to other studies of nitromethane. Other physical characteristics of nitromethane combustion are presented. Updates to the facility and new methods to examine the combustion of liquid propellant are described in detail. Special focus is given to procedures and safety information.

Nitromethane is the simplest organic-nitro compound as well as the archetype of an important class of high explosive. Homogeneous nitromethane reactions have been the subject of extensive studies. Particularly the unimolecular isomerization of nitromethane to methyl nitrite is proven to be competitive with simple C-N bond (bond energy 60 kcal/mol) rupture. The activation energy for the rearrangement was measured to be 55.5 kcal/mol and methyl nitrite has a very weak CH3O-NO bond energy 42 kcal/mol lower than that for homolysis. The thermal chemistry of nitromethane on Cu(111) was studied by a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) techniques. TPD spectra show that the desorption features include the physisorbed multilayer and monolayer of CH3NO2 at 150 and 190 K, respectively. The major decomposition pathway is via cleavage of O-N bond to yield a major product NO, which is characterized by m/z 30(NO+). A possible contribution from isomerization of nitromethane to methyl nitrite (CH3NO2 CH3ONO) on the surface cannot be ruled out at 278 K. In addition to isomerization, the dehydrogenation products CO and CO2 are also unveiled as part of the desorption features at 314 and 455 K, respectively. We can further prove the reactivity of nitromethane on Cu(111) at 367 K by using the deuterated form of nitromethane which reveals the corresponding desorption TPR/D signals of D2, D2O and CD4. However, we find that nitromethane also reacts by dissociating the C-H bond and the O-N bond, however, leaving the C-N bond intact. Along this reaction channel, HCN desorbs as a product above 360 K, as evidenced by a broad desorption feature of m/z 27. Dimerization of CN to C2N2 occurs at 815 K. The RAIR spectroscopy demonstrates that nitromethane is indeed adsorbed on Cu(111) at 100 K. The formation of methoxy and formyl are supported by the observation of desorption of NO at 278 K with the characteristic NO stretching mode found at 1535 cm-1. Moreover, we assign side-bonded CN and aminomethylene (HC-NH2) present on Cu(111). After the surface is annealed to 330 K, a signature band at 2173 cm-1 is assigned to terminal-bounded CN stretching mode. This band eventually fades out above 900 K consistent with the evolution of cyanogen at 815 K.

Nébulex est un appareil permettant de solubiliser les vapeurs d’analytes présents dans l’atmosphère via la formation d’un spray. L’objet de ce travail est de développer un nouveau système de détection in-situ par électrochimie pour le nitrométhane, un constituant de compositions explosives artisanales. Les paramètres ont d’abord été optimisés pour évaluer la limite de détection qui peut être atteinte avec un système simple et robuste. Le mécanisme de réaction a été revisité dans nos conditions spécifiques et comparé à celui décrit dans la littérature. Ensuite, différentes voies de fonctionnalisation d’électrodes ont été explorées afin d’améliorer la répétabilité de la mesure et la sensibilité au nitrométhane. Enfin, le système de détection a été miniaturisé et intégré au prototype Nébulex. Des essais de détection de vapeurs ont pu être menés, conduisant à un temps de détection de l’ordre de la minute pour des teneurs en nitrométhane de quelques ppmv. / Nebulex is a device allowing the solubilization of atmospheric analyte vapors via a spray formation. The aim of this work is to develop a new in-situ electrochemical detection system for the nitromethane, a constituent of home-made explosives. The parameters were first optimized to determine the limit of detection which can be reached with a simple and robust system. The reaction mechanism was revisited in our specific conditions and compared to the one described in the literature. Next, several functionalization ways were explored to enhance the measurement stability and the sensitivity for nitromethane. Finally, the detection system was miniaturized and integrated to the Nebulex prototype. Vapor detection experiments were performed, leading to detection time in the range of a minute for few ppmv of nitromethane content.

<pre>The plethora of potential homemade explosive (HME) formulations combined with the fact they often exhibit large critical diameters make them expensive to characterize with traditional large-scale tests. A relatively new method for small-scale characterization was investigated using non-ideal explosive charges consisting of ammonium nitrate (AN) and various fuels. This optical characterization technique utilizes the rate of reaction wave velocity decay in the failing detonations of sub-critical diameter charges as a metric for the shock sensitivity of an explosive. The conditions for detonation initiation and failure have long been used to investigate shock sensitivity (critical diameter, gap tests, run-to-detonation experiments); however, the failure regime still remains largely unexplored. The utility of this small-scale characterization technique lies in its ability to determine the relative shock sensitivity of explosive with minimal material and tests while simultaneously providing transient velocity data for potential use in modeling efforts. In this work, high speed imaging was used and analyzed to determine rates of reaction wave velocity decay in the AN-fuel samples. Among the fuels tested with AN were diesel (ANFO), nitromethane (ANNM), and aluminum (ANAl). It was found that nitromethane was the most effective at sensitizing the AN of the systems considered. In both ANNM and ANAl, maximum shock sensitivity occurred at fuel percentages below stoichiometric mixtures. This was speculated to be due to the competing effects of stoichiometry and hot spot criticality. Sensitivity results were compared to run-to-failure distances and published critical diameter trends and showed good agreement. </pre>