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No description available.

The use of Silicon Carbide Field Effect Transistor (SiC-FET) sensors in cyclic operation is a proven way to quantify different gases. The standard workflow involves extracting shape-defining features such as averages and slopes of the sensor signal. This work’s main goal is to verify if frequency modulation can be used to simultaneously quantify Nitric Oxide (NO), Nitrogen Dioxide (NO2) and Ammonia (NH3). Linear models were chosen, namely: Ordinary Least Squares (OLS), Principal Components Regression (PCR), Partial Least Squares Regression (PLSR) and Ridge regression. Results indicate that these models fail to predict concentrations completely for every gas. Analysis indicates that the features are not linear in terms of concentrations. This work is concluded by recommending a few other alternatives before discarding frequency cycling completely: non-parametric models of regression and different frequency regime, namely the use of triangular waves in future experiments.

Energetic materials (i.e., explosives, propellants, and pyrotechnics) have been used for centuries in a wide variety of applications that include celebratory firework displays, the demolition of ‘immovable’ structures, mining resources from the earth’s crust, launching humans into outer space, and propelling munitions across the battlefield. Many different scientific and engineering domains have found unique value in their characteristic release of significant heat and pressure. While the rate at which energetic materials react is often dependent on the source of initiation, surrounding thermodynamic conditions, and formulation sensitivity, many applications aim for a controlled combustion process to produce large amounts of work output – solid and liquid rocket motors and gun-launched projectiles are a few key examples. Other energetic material systems are often inadvertently exposed to thermal insults, which can result in similar combustion behavior. To accurately model these systems, it is important to have a fundamental understanding of the chemical kinetics that control various aspects of the combustion process (e.g., changes in temperature (T), pressure (P), and species mole fractions (X)). Detailed chemical kinetic models are often used to understand and subsequently predict such behavior. Understanding the gas-phase reaction kinetics of energetic materials is essential when trying to predict critical performance parameters such as flame speeds, temperature and pressure profiles, and heat flux between material phases. These parameters can have significant impact on predictions of system-level performance (e.g., the specific impulse of solid rocket motors, propellant burn rates in projectile systems, and munition responses to thermal insult and extended temperature cycling). While the gas-phase reaction kinetics of energetic material combustion were heavily studied from the late 1970’s to the early 2000’s, research efforts beyond this time frame have primarily focused on condensed-phase chemistry as it is thought to be less understood. Over the past two decades, however, there have been significant advances in our understanding of small molecule reactions that have not yet been accounted for in many energetic material models. One such example are chemically termolecular reactions – a new class of phenomenological reactions that have not yet been considered for inclusion in any energetic material kinetic models. Recent studies have indicated that chemically termolecular reactions, mediated through ephemeral collision complexes, have significant impact on the global kinetics of certain combustion systems. This discovery has since prompted the question of which systems are significantly influenced by chemically termolecular reactions and should therefore account for their presence in gas-phase phenomenological models. Although a select number of systems have already been investigated, such as flame speed and ignition delay predictions in common hydrocarbon combustion scenarios, the influence of chemically termolecular reactions on the kinetics of energetic materials has not yet been explored. As an initial investigation into energetic materials, a case study for RDX was performed, for which abundant computational and experimental data are available. To aid in assessing the impact of chemically termolecular reactions, for which almost no data are available, this study leveraged an automated procedure to identify and estimate rate constants for potential chemically termolecular reactions based exclusively on data available for related reactions. Four detailed kinetics models for RDX were independently screened for potential chemically termolecular reactions. Model predictions including these chemically termolecular reactions revealed that they have significant potential impact on profiles of major species, radicals, and temperatures. T he analysis pinpointed ∼20-40 chemically termolecular reactions, out of the thousands of possibilities, estimated to have the largest impact. These reactions, including many mediated by ephemeral HNO** and NNH** complexes, are therefore worthwhile candidates for more accurate quantification via master equation calculations. More generally, just as the importance of including chemically termolecular reactions in hydrocarbon combustion models is becoming recognized, the present results show compelling evidence for the need for their inclusion in energetic material models as well. The investigation into chemically termolecular reactions yielded a secondary conclusion based on the observed influence of the small molecule C/H/N/O chemistry on overall predictions of energetic material combustion – updating the small molecule chemistry in RDX models produced significant changes to predictions of major species and temperature, suggesting that the development of a comprehensive gas-phase energetic material combustion model would be of great value and have broad utility as a foundational model for a great variety of C/H/N/O energetic materials. To begin developing such a model, all small molecule chemistry in current kinetic models was reviewed with the intent of identifying a sub-model in need of revisions and subsequently addressing its uncertainties using targeted experiments to improve overall predictions. The ammonia sub-model was selected as it is both highly uncertain and highly influential in many energetic material models. Ammonia (NH₃) has garnered substantial attention in recent years due to its importance across many scientific domains – including its potential use as a carbon-free fuel and long-term energy storage option, its use in reducing combustion-generated nitrogen oxide emissions, its role as a decomposition fragment of many energetic materials, and its presence as an important impurity during biofuel and biomass combustion that can affect overall system kinetics, among others. Yet, it is generally recognized that there are still significant gaps in the present understanding of ammonia kinetics -– in both experimental data sets and sub-models within the overall ammonia kinetic mechanism. For example, most experimental studies of ammonia oxidation have used molecular oxygen as the primary or sole oxidizer. While large mole fractions of molecular oxygen are encountered in many combustion scenarios, there are select systems where ammonia is more likely to be oxidized via nitrogen-containing species (e.g. N₂O and NO₂) and, more generally, there are relatively untested reaction sets that would be accentuated in such conditions. To address these gaps in available experimental data needed for the validation of ammonia kinetics models, jet-stirred reactor experiments were performed for mixtures of NH₃/N₂O/N₂ over an intermediate temperature range (850-1180 K). In these experiments, the mole fractions of NH₃, N₂O, and NO were measured using a combination of gas chromatography, chemiluminescence, electrochemical detection, and infrared absorption – where agreement among the different diagnostics (within 3% for N₂O and 7% for NO) ensured high confidence in the experimental measurements. Comparison of the experimental results and model predictions suggested deficiencies in commonly used models for nitrogen kinetics. Various modeling analyses pointed to the central role of the N₂O + NH₂ = N₂H₂ + NO reaction, on which recent kinetic models all rely on the same rate constant estimate that appears to have not been tested in previous validation data sets for NH₃ kinetics. A second set of jet-stirred reactor experiments were performed for mixtures of NH₃/NO₂/O₂/N₂ over a slightly different temperature range (700–1100 K). Agreement among different diagnostics (≤7% for NO₂ and ≤4% for NH₃) and excellent experimental repeatability confirmed high confidence in all species measurements. Measured mole fractions were compared to predictions from five recently developed kinetic models using flux analysis and uncertainty-weighted kinetic sensitivity analysis, both of which pointed to the importance of reactions involving H₂NO that are both influential in this system and highly uncertain. The measurements from the jet-stirred reactor experiments presented here were combined with comprehensive sets of experimental data and high-level theoretical kinetics calculations using the MultiScale Informatics (MSI) approach to unravel the large uncertainties present in current NH3 oxidation kinetic sub-models. Emphasis was placed on NH₃ oxidation via nitrogen-containing species as this chemistry has been shown to accentuate influential reactions (e.g., the NO₂+NH₂ and NH₂+NO reactions) that are known to be important during the combustion of many energetic materials (e.g., AN, ADN, and AP). The resulting MSI model accurately predicted nearly all of the experimental and theoretical target data within estimated or reported uncertainties. Additional predictions of two NH₃/NO₂ validation data sets, which were not included in the MSI framework, demonstrated its ability to accurately extrapolate predictions to untested T/P/X conditions, indicating that the converged MSI model demonstrates truly predictive behavior. The MSI NH₃ oxidation model presented here should be considered for inclusion in many energetic material models as the NH₃/NOₓ kinetic system is known to be important to the combustion of various propellant and explosive formulations. This sub-model will help to form a foundational gas-phase kinetic model relevant to many different energetic materials, including those that contain inorganic additives for increased energy density and blast effects.

Air quality management strategies in the US are developed largely from estimates of emissions, some highly uncertain, rather than actual measurements. Improved knowledge based on measurements of real-world emissions is needed to increase the effectiveness of these strategies. Consequently, the objectives of this research were to (1) quantify relationships among urban emissions sources, land use, and demographics, (2) determine the spatial and temporal variability of emissions, and (3) evaluate the accuracy of official emissions estimates. These objectives guided three field campaigns that employed a unique mobile laboratory equipped to measure pollutant fluxes by eddy covariance. The first campaign, conducted in Norfolk, Virginia, represented the first time fluxes of nitrogen oxides (NO_x) were measured by eddy covariance in an urban environment. Fluxes agreed to within 10% of estimates in the National Emissions Inventory (NEI), but were three times higher than those of an inventory used for air quality modeling and planning. Additionally, measured fluxes were correlated with road density and increased development. The second campaign took place in the Tijuana-San Diego border region. Distinct spatial differences in fluxes of carbon dioxide (CO₂), NO_x, and particles were revealed across four sampling locations with the lowest fluxes occurring in a residential neighborhood and the highest ones at a port of entry characterized by heavy motor vehicle traffic. Additionally, observed emissions of NO_x and carbon monoxide were significantly higher than those in emissions inventories, suggesting the need for further refinement of the inventories. The third campaign focused on emissions at a regional airport in Roanoke, Virginia. NOx and particle number emissions indices (EIs) were calculated for aircraft, in terms of grams of pollutant emitted per kilogram of fuel burned. Observed NO_x EIs were ~20% lower than those in an international databank. NO_x EIs from takeoffs were significantly higher than those from taxiing, but relative differences for particle EIs were mixed. Observed NO_x fluxes at the airport agreed to within 25% of estimates derived from the NEI. The results of this research will provide greater knowledge of urban impacts to air quality and will improve associated management strategies through increased accuracy of official emissions estimates. / Ph. D.

Master of Science

A "leveling off" trend in NOx emissions with high amounts of steam addition has been observed in industrial gas turbine diffusion flame combustors. Experiments were performed to try to reproduce this trend in a laminar, opposed flow diffusion flame burner. Experiments were performed with Cli4, C2H4, CO, COIH2 (1:1), and COIH2 (1:2) as fuels. Both hydrocarbon fuels and non-hydrocarbon fuels were tested to study the contribution of the Fenimore mechanism to the "leveling off" trend. Probe sampling with chemiluminescent analysis was used to fmd NOx concentrations; Pt/PtRh thermocouples corrected for radiation losses were used to measure flame temperatures. The experiments reproduced the "leveling off" of NOx emissions, but a "leveling off" of temperatures also occurred. There were no significant differences in the results from the hydrocarbon and non-hydrocarbon fuels. The "leveling off" of NOx emissions is attributed to the "leveling off" of temperatures in the burner. It is not necessary to invoke the Fenimore mechanism to explain this trend. At least 55% of the NOx was eliminated from the flames using steam injection, which implies that at least 55% of the NOx was formed by the Zeldovich mechanism Evidence of Fenimore NO was provided by the fact that the existence of hydrocarbon coking on the fuel nozzle encouraged NOx production in all flames. / Master of Science

The effect of temporal variations in equivalence ratio on the NO_x emissions of a premixed methane-air flame was measured in a burner. The NO_x emissions are compared among steady flames with spatially uniform equivalence ratio distributions, steady flames with spatially nonuniform equivalence ratio distributions, and unsteady flames with temporal equivalence ratio fluctuations. Time-varying equivalence ratio was measured optically, time-varying temperatures were measured with thermocouples, and mean NO_x emissions were measured by probe sampling and a chemiluminescent analyzer. These measurements quantify the effect of temporal unsteadiness and spatial nonuniformity of equivalence ratio on NO_x emissions. For lean flames, both spatial nonuniformities and temporal fluctuations in equivalence ratio contribute to an increase in NO_x emissions with respect to steady uniform flames at the same mean flame temperatures. For lean flames, higher amplitude temperature fluctuations result in larger increases in NO_x with respect to steady flames. The dissertation also describes the optical technique for nonintrusive temporal measurements of equivalence ratio fluctuations and techniques for thermocouple compensation at frequencies up to 10 Hz. / Ph. D.

This investigation examines the effects of load, speed, exhaust gas recirculation (EGR) level and hydrogen addition level on the exhaust gas emissions, particulate matter size distribution and chemical composition. The experiments were performed on a 2.0 litre, 4 cylinder, direct injection engine. EGR levels were then varied from 0% to 40%. Hydrogen induction was varied between 0 and 10% vol. of the inlet charge. In the case of using hydrogen and EGR, the hydrogen replaced air. The load was varied from 0 to 5.4 bar BMEP at two engine speeds, 1500 rpm and 2500 rpm. For this investigation the carbon monoxide (CO), total unburnt hydrocarbons (THC), nitrogen oxides (NOX) and the filter smoke number (FSN) were all measured. The in-cylinder pressure was also captured to allow the heat release rate to be calculated and, therefore, the combustion to be analysed. A gravimetric analysis of the particulate matter size distribution was conducted using a nano-MOUDI. Finally, a GC-MS was used to determine the chemical composition of the THC emissions. The experimental data showed that although CO, FSN and THC increase with EGR, NOX emissions decrease. Inversely, CO, FSN and THC emissions decrease with hydrogen, but NOX increases. When hydrogen was introduced the peak cylinder pressure was increased, as was the maximum rate of in-cylinder pressure rise. The position of the peak cylinder pressure was delayed as hydrogen addition increased. This together with the obtained heat release patterns shows an increase in ignition delay, and a higher proportion of premixed combustion. The experimental work showed that the particulate matter size distribution was not dramatically altered by the addition of EGR, but the main peak was slightly shifted towards the nucleation mode with the addition of hydrogen. Hydrogen addition does not appear to have a large effect on the chemical composition of the THC, but does dramatically decrease the emissions.

Os ânions inorgânicos nitrato (NO3-) e nitrito (NO2-) por muito tempo foram considerados produtos finais inertes do metabolismo do óxido nítrico (NO) e constituintes indesejáveis da dieta. Entretanto, é crescente o interesse das potenciais reações que podem se processar em meio fisiológico e, que envolvem especialmente o íon nitrito mediadas por complexos de metais de transição. Ferro-heme presente em proteínas como a mioglobina podem formar complexos porfirínicos com NO, gerando espécies que podem atuar principalmente como catalisadores em diversas vias biológicos importantes. Complexos com NOx coordenado a ferro-heme estão envolvidos tanto no processo da cura da carne (pigmentação da carne), como em processos redox, nos quais são capazes de oxidar substratos indiretamente pela produção de espécies reativas ou diretamente por reações de transferência de átomo de oxigênio (TAO). Os lipídeos, constituintes celulares fundamentais na composição de membranas e lipoproteínas, podem servir como substratos para essas reações e, sua oxidação pode ocasionar danos ao organismo. Tióis, importantes antioxidantes e constituintes de proteínas, também podem participar desse tipo de reações e, conseqüentemente gerar danos ao organismo. Considerando que o mecanismo e os parâmetros cinéticos e termodinâmicos destas reações ainda não foram completamente estabelecidos para explicar a vasta funcionalidade destes complexos, o presente projeto de pesquisa visa proporcionar um melhor conhecimento das reações redox envolvendo NOx e mediadas por porfirinas de ferro em alimentos e sistemas biológicos. / For long time, the anions nitrate (NO3-) and nitrite (NO2-) were considered inert end products of nitric oxide (NO) metabolism and undesirable constituents of the diet. Currently, there is an increasing interest for potential reactions which may occur in physiological conditions involving specially the nitrite ion and mediated by transition metal complexes. Heme NOx iron complexes are involved in meat curing process (meat pigmentation) and are able to oxidize substrates indirectly generating reactive species or directly by oxygen atom transfer reactions (OAT). Lipids, fundamental cellular constituents of membranes and lipoproteins, and thiols, important antioxidants and protein constituents, may serve as substrates to OAT and their oxidation may promote damage to the organism Considering that the mechanism and kinetic and thermodinamic parameters of these reaction have not yet been fully elucidated to explain the varied functionality of these complexes, the present research project aim to bring a better understanding of redox reactions involving NOx mediated by iron porphyrins in foods and biological systems. Thiols, important antioxidants and protein constituents, may serve as substrates to OAT and their oxidation may promote damage to the organism. The present work aims to bring a better understanding of the mechanism, kinetic and thermodynamic parameters of the reaction involving nitrite mediated by iron-porphyrins in food and biological systems.