A thermal analysis and test is performed to determine flux and temperature variability for Phase change thermal energy to investigation feasibility of use in a Stored Thermal Energy Cookstove (STEC). The phase change material (PCM) NaNO_3-KNO_3 Eutectic (52:48) Solar Salt is identified for energy storage in STEC due to a melting temperature of 222℃ which is deemed appropriate for use in cooking up to temperatures of 200℃ ±20 ℃. 1-D planar and cylindrical analytical multiphase solutions are correlated with a transient non-linear ANSYS Finite Element Model (FEM). 1-D idealized models of planar and cylindrical analytical multiphase solutions show the flux stability of cylindrical solidification is twice that of planar solidification. Flux drops a linear average of 0.5%/min in the last half hour of a one hour cooking session in cylindrical solidification vs 1%/min in planar solidification under a constant temperature (dirichlet) boundary condition of 42 ℃ below the melting point of the PCM. Solidification progresses more quickly in the planar case yielding a solid PCM thickness of 3.3 cm after one hour vs 2.4 cm in the cylindrical case. A test is performed on a simplified simple STEC apparatus to investigate cooling rates of the cooking surface while boiling water. 0.5L of water is brought to boil from room temperature with a linear average cooking surface flux of 21,000 W/m2 and a cooking surface cooling rate of 3.8 ℃/min. Results show increasing the thermal conductivity of the PCM and reducing the total thickness of the solidifying PCM layer before and after discharge will reduce cooling rates, improve stability of the flux delivery device, and increase feasibility of use. Pursuing lower flux cooking and non-cooking applications may increase likelihood of adoption by reducing thermal gradients during discharge. A proposal to explore further development of STEC to aid adoption is discussed.

This dissertation examines the use of electric fields as one mechanism for controlling combustion as flames are partially extinguished when impinging on nearby surfaces. Electrical aspects of flames, specifically, the production of chemi-ions in hydrocarbon flames and the use of convective flows driven by these ions, have been investigated in a wide range of applications in prior work but despite this fairly comprehensive effort to study electrical aspects of combustion, relatively little research has focused on electrical phenomena near flame extinguishment, nor for flames near impingement surfaces. Electrical impinging flames have complex properties under global influences of ion-driven winds and flow field disturbances from the impingement surface. Challenges of measurements when an electric field is applied in the system have limited an understanding of changes to the flame behavior and species concentrations caused by the field. This research initially characterizes the ability of high voltage power supplies to respond on sufficiently short time scales to permit real time electrical flame actuation. The study then characterizes the influence of an electric field on the impinging flame shape, ion current and flow field of the thermal plume associated with the flame. The more significant further examinations can be separated into two parts: 1) the potential for using electric fields to control the release of carbon monoxide (CO) from surface-impinging flames, and 2) an investigation of controlling electrically the heat transfer to a plate on which the flame impinges. Carbon monoxide (CO) results from the incomplete oxidation of hydrocarbon fuels and, while CO can be desirable in some syngas processes, it is usually a dangerous emission from forest fires, gas heaters, gas stoves, or furnaces where insufficient oxygen in the core reaction does not fully oxidize the fuel to carbon dioxide and water. Determining how carbon monoxide is released and how heat transfer from the flame to the plate can be controlled using the electric field are the two main goals of this research. Multiple diagnostic techniques are employed such as OH chemiluminescence to identify the reaction zone, OH PLIF to characterize the location of this radical species, CO released from the flame, IR imaging and OH PLIF thermometry to understand the surface and gas temperature distribution, respectively. The principal finding is that carbon monoxide release from an impinging diffusion flame results from the escape of carbon monoxide created on the fuel side of the flame along the boundary layer near the surface where it avoids oxidation by OH, which sits to the air side of the reaction sheet interface. In addition, the plate proximity to the flame has a stronger influence on the emission of toxic carbon monoxide than does the electric field strength. There is, however, a narrow region of burner to surface distance where the electric field is most effective. The results also show that heat transfer can be spatially concentrated effectively using an electric field driven ion wind, particularly at some burner to surface distances.

The study of liquid jet breakup near the nozzle exit under the complex conditions, where the liquid/gas density ratio is relatively low, where rapid shearing and droplet formation is intense, and where the optical scattering obscures the condensed phase structure, has been an important sub-field of spray and spray combustion research for decades. With combustion chamber pressures on the rise, and engine performance improvement demands unrelenting (reduced emissions, fuel tolerance, increased power density, and efficiency), gaining diagnostic access to this critical jet breakup domain is more important than ever. This research project contributes to the understanding of the near nozzle region of realistic fuel sprays by developing and quantitatively demonstrating ultra-short pulse off-axis holography (USPODH) as a coherence filtering tool for 3D evaluation, obscuration avoidance, and transient imaging. USPODH is an interference-based single-shot technique that uses coherence filtering to allow single-shot imaging through media with optical density (OD) up to 12, conditions where other techniques resort to hardware time-gating solutions, multiple shot averaging or a synchrotron light source. The results show how USPODH can be successfully used in such environments. In particular, Monte Carlo photon transport simulations and experimental results show how coherence filtering can outperform picosecond time-gating for imaging in optically dense environments. Droplets as small as 25 µm, generated by a water spray hidden by a field of polydisperse droplets with OD up to 12 were successfully resolved. Performance in engine-relevant environments was demonstrated by imaging a USAF resolution chart at pressures up 20 bar and temperatures up to 450 K. The effects on pulse broadening and image quality from pressure and temperature gradients and the presence of thick fused quartz windows were quantified. A gas-liquid interface in the near-nozzle region of a single-orifice dodecane spray injected at 1550 bar was imaged in a vessel at pressures up to 20 bar. Surface perturbations and ligaments detaching from the spray liquid core were observed with an object-side resolution of approximately 14 µm at a working distance of 35cm, and off-line numerical focusing allowed to focus on features of interest in depth planes tens of centimeters apart from each other. USPODH reconstructions were also compared to lensed shadowgraph images and inline holograms reconstructions acquired in the same conditions, and the results show that USPODH is effectively rejecting the scattering light noise signature from the shroud of droplets surrounding the spray core in the nozzle proximity.

The understanding of thermal and chemical effects of water addition to the fuel side of a diffusion flame is relevant for improving the combustion of naturally wet fuels such as methane hydrates, emulsified fuels and wet biomass, as well as for cases where water is intentionally added to the fuel stream, as for example in steam-assisted flares for the reduction of emissions. In this work, the role of water is evaluated by adding high concentrations of water vapor to the fuel side of a steady non-premixed coflow flame. The steady nature of the flame allows temperature profiles, extinction limits, and OH relative concentrations to be measured at different conditions of inlet velocities, with increasing dilution levels. This work is unique in its attention to the very high dilution levels near extinction and in the detailed measurement campaign providing comprehensive information for laminar 2-D diffusion flames. Temperatures are measured with thin filament pyrometry (TFP). Results from Ar, N2 and CO2 diluted flames are also reported to compare the effects of water vapor with those of different diluents. Comparisons in terms of temperatures and extinction limits show close correspondence when adding equivalent levels of diluent thermal capacitance. OH concentrations are obtained through planar laser-induced fluorescence (PLIF) for water and carbon dioxide diluted flames. For a better understanding of the fluorescence signal, and of the radical pool in the combustion process, the experimental measurements are complemented with results from CFD simulations of the flame. Results confirm that both water and CO2 are not passive thermal diluents in flames but contribute to chemical pathway changes, particularly near extinction. The difference between these two diluents is evident in that water vapor diluted flames lift before extinguishing while CO2 diluted flames simply blow out. In addition to assessing the chemical versus thermal role of water dilution in non-premixed flames, this work provides a comprehensive data collection to validate numerical simulations, providing sufficient information to help to assess uncertainties in third body efficiencies of water and shifts in chemical paths when high concentrations of diluents are introduced in the combustion process.

Liquid fuel injection in combustion systems involves multi-phase flows generated by fuel sprays. Studying the fluid mechanical phenomena integrated in these flows that influence the fuel’s combustion, such as liquid jet break up into droplets, can benefit from experimental approaches for imaging them. Such information can help with design choices to control stability and increase the efficiency of combustion systems. However, the high optical scattering from the cloud of small droplets obscures traditional imaging methods. In addition, conventional imaging does not provide depth information that is often critical in spray understanding. Digital holography (DH) is a well-established and powerful technique for high-resolution 3D imaging. Monochromatic laser beams and digital cameras are used in this technique to record digital holograms (diffracted object wave interfered with the non-diffracted reference wave) of the 3D objects. The object field is then numerically reconstructed using the digital hologram recorded on a CCD detector but it is not clear how the light scattered from small particles, as in the spray situation, will complicate the hologram analysis. Consequently, the current work examines the use of

ultra-short laser pulses for digital holography in multi-phase flows of combustion interest. A state-of-the-art Ti-Sapphire amplified laser system is used, with pulses as short as 100 fs and up to 1mj per pulse energy. Using this system creates the opportunity for coherence filtering and time-gating filtering, which can improve signal-to-noise ratio in highly scattering media like dense sprays. In this work, scattering media with optical conditions similar to the condition in combusting dense sprays is replicated with hydrosols. USAF resolution chart is used as test target to demonstrate quantitatively the imaging resolution and contrast of the system. The atomizing spray diagnostics literature study shows that optical Kerr effect (OKE) time-gating is the only promising technique that has been demonstrated to image the liquid structure inside the transient diesel sprays. Experimental results presented in this dissertation show high potential of ultra-short pulse DH for microscopic imaging though highly scattering media with competitive resolution and quality compared to OKE time-gating, and holography provides the additional feature of resolving the internal structure of dense sprays in 3D. The technique can potentially image an intact liquid core of diesel sprays, veiled behind the optically deep cloud of droplets, which has never been done before.

Solid fuel cookstoves have been used as primary energy sources for residential cooking and heating activities for ages, and the practice continues heavily, especially in developing countries. It has been estimated that domestic combustion of solid fuels (wood, animal dung, coal etc.) makes considerable contribution to global greenhouse gas (GHG) and aerosol emissions, degradation in local air quality, and deleterious

effects on resident’s health. Emissions from in situ solid fuel burning cookstoves have not been well characterized, and the majority of the data collected from simulated tests in laboratories do not reflect stove performance in actual use. This study characterized the in-field emissions of P M2.5, carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and total non-methane hydrocarbons (TNMHC) from residential cooking events with various fuel and stove types from field sites in the Himalaya

area, which includes Nepal, India, Tibet, and Yunnan province, China. Gravimetric filter and gas chromatography analysis were utilized, respectively, to measure PM2.5 and gas-phase pollutant concentrations from direct cookstoves emission and indoor microenvironments. Real-time monitoring of PM2.5, CO2, and CO concentration was conducted simultaneously. The corresponding emission factors were calculated based

on the field data using the carbon balance approach. The data set provides a unique resource for assessing the relationship between laboratory and in-use cookstove behavior. Detailed statistical analysis of the measurements confirmed the major factors responsible for emission variance among and between cookstoves. These factors in-

clude fuel type and cookstove type. A further analysis revealed that cookstove use dynamics (i.e., continuous use versus intermittent use) plays an important role in cookstove emission.

Atmospheric emission of sulfuric acid (H2SO4) and its precursors, sulfate oxides SO2 and SO3, are generated by burning fuels such as coal, oil, and gas for energy production or in the metallurgical industry. While sulfuric acid is important in many industrial applications, in the atmosphere it is one of the culprits for acid rain formation. Steps have been taken to reduce the sulfur content of fuels (for example, the migration to low sulfur fuel in the marine industry), but sulfur emissions are still a significant problem, especially for coal-fired power-plants. In the atmosphere, sulfate constitutes a large fraction of particulate matter air pollutants with aerodynamic diameter <2.5 microns (PM 2.5), which has been found responsible for adverse health effects. Although the use of coal is sharply declining in theUnited States, it is still on the rise in China and in Southeast Asia. In coal-fired power-plants, most of the fuel sulfur content is oxidized to sulfur dioxide, while a small percentage can be further oxidized to sulfur trioxide (SO3) in the boiler and across the NOx reduction catalyst. In the presence of water, sulfur trioxide reacts at low temperatures to form sulfuric acid. The SO3/H2SO4 emissions can be reduced by injecting neutralizing sorbents, entailing an additional operating cost. With continuous monitoring, a closed-loop control for sorbent injection could be developed, reducing sulfate emissions, and improving the operational performance of power plants. Therefore, the continuous monitoring of SO3, H2SO4, and SO2 is a primary need for the coal industry. The goal of this dissertation is to evaluate the feasibility of continuous measurements in flue gas conditions using optical absorption methods, including providing a high temperature spectral database of SO2, SO3, and H2SO4. A further goal is the experimental investigation of the relationship between SO3 and H2SO4, often assumed to be at chemical equilibrium. The equilibrium has been hypothesized and relied on in many measurement techniques, however a direct experimental verification has not been accomplished. Specifically, this work examines the performance of Differential Optical Absorption Spectroscopy (DOAS) and External Cavity Quantum Cascade Laser (EC-QCL) as potential methods for continuous measurement. The results are validated using the Environmental Protection Agency (EPA) Method 8A, the current industry standard for the measurement of sulfur species. The experimental setup includes a unique high-temperature multi-pass optical cell and a flow system able to replicate appropriate levels of flue gas species. The gas temperature and spatial distribution of sulfur species in the measurement cell was also investigated using numerical simulations. The DOAS technique performed well for SO2 measurements in the UV, while SO3 and H2SO4 could not be evaluated with accuracy. The DOAS technique was found unsuitable for continuous sulfur species monitoring in flue gas conditions. The mid-IR ECQCL technique could successfully detect SO2 in flue gas conditions, in the spectral ranges near both 7um and 8um, and for the first time, high-temperature mid-IR spectral libraries for SO3 and H2SO4 were recorded. The equilibrium between SO3 and H2SO4 was verified through direct optical measurements at 3% water vapor concentration within +-12% uncertainty. At 7um, while SO3 measurements are successful, the strong absorbance of SO2 limits measurements only to low-sulfur coals (with SO2 concentrations <500ppm) in the current multi-pass configuration. Sulfuric acid does not absorb at 7um. At 8um, SO2 is a weak absorber, hence high-sulfur coal emission monitoring is feasible. Sulfuric acid is a strong absorber and can be measured even at low levels, while SO3 does not absorb at 8um and needs to be calculated from equilibrium. Unfortunately, however, sulfuric acid reacts with the windows material (BaF2) to form a layer of BaSO4, and at this wavelength, the layer formation causes a significant performance degradation, as BaSO4 absorbs strongly. As the BaSO4 layer thickens, it prevents the laser light from reaching the detector, and this poses a significant engineering challenge and limits the measurement to short time frames (10 to 30 minutes).

Urban air mobility as a fast transportation solution has captured the attention of private companies and government aviation departments in the 21st century. The new designs of aerial vehicles are coming one after another but often neglecting the aerodynamic characteristics and the effect of interacting rotors. The Multirotor Test Bed (MTB) project was initiated at NASA Ames Research center to support the NASA Revolutionary Vertical Lift Technology (RVLT) Project to study rotorcraft performance specifically for multirotor aircraft. The MTB is a modular multirotor that can make testing feasible for up to six rotors at different angles and rotor arrangements, including tall and short configurations at different horizontal and vertical distances. The MTB is assembled and tested in the U.S Army’s 7- by 10-Foot Wind Tunnel. This work focuses on the importance of aerodynamic interaction between MTB rotors using the Comprehensive Hierarchical Aeromechanics Rotorcraft Model (CHARM) software, developed commercially by Continuum Dynamics, Inc. The CHARM software is capable of modeling Vertical Take Off and Landing (VTOL) aircraft aerodynamics in maneuvering and steady flight conditions. CHARM allows the user to define flow and body characteristics, including the rotor geometry, aerodynamic condition, wind tunnel speed, and airfoil tables as inputs. This report first examines CHARM’s capability by comparing its predictions to the UH-60A Black Hawk rotor and SUI Endurance rotor experimental test results in hover and forward flight conditions. These comparisons can help to validate CHARM results, provide a better understanding of simulated flight characteristics, and demonstrate its predictive capability. With these validations as the foundation, this work then simulates one MTB rotor in hover, and further compares with wind tunnel test data as the confirmation of the CHARM parameters. Once accurate performance is verified, the MTB rotor is simulated in forward flight both in the wind tunnel and in a free field environment. The simulation variables include one, two, four, and six rotors at the short and tall configurations, and with shaft angles of 0, -5, and -10 degrees. These results can demonstrate the rotor wake interaction and its impact on rotor performance. This information can also help determine which configurations should be explored for the future wind tunnel tests. This study can be used as guidance for using CHARM to predict rotor behavior and understanding the importance of the rotor wake interaction for future air mobility designs.

The enormous energy reserve of methane gas stored in gas hydrate structures is substantially more than all known fossil fuel reserves around the world. Efficient extraction of methane from the hydrate cavity structures is still a technological challenge but the use of CO2 injection and substitution is a potentially viable approach. Gas hydrates in sediments are in a state of stationary balance with their surroundings. They are not in thermodynamic equilibrium and competing phase transitions of hydrate dissociation and hydrate reformation determines the stationary situation. The specific objective of this research is to dictate the phase transition conditions that enhance the growth rate of CO2 hydrate and increase the dissociation rate of methane hydrate in porous media by understanding the behavior of surfactants in promoting the growth rate of CO2 hydrate experimentally. In addition, the investigation explores the addition of a small amount of nitrogen gas to increase permeability following dissociation of CH4 hydrate. The CO2-CH4 gas exchange concept is theoretically more efficient than any other methods for extracting methane from gas hydrate reservoirs but the theory has not previously been demonstrated experimentally. Furthermore, due to increased concerns regarding carbon dioxide emissions as a driver of global warming, CO2 hydrate formation may be a promising form of CO2 storage as well as an efficient strategy for CH4 recovery. New CO2 hydrate forms from injected CO2 and free liquid water in the porous media. When the CO2 hydrate forms, the released heat from this formation is directed through the water phase and causes CH4 hydrate to dissociate. The experimental results illustrate that 20 moles% N2 and 1 mole% NFM (N-formylmorpholine) with CO2 liquid injection is the most effective of the conditions tested for conversion between CO2/CH4 hydrates. Maximum conversion in this study was 88 moles% of CO2, and 2 moles% N2 taking the place of methane hydrate in large and small cavities. This research work also uses theoretical modeling to evaluate efficient production schemes in order to develop a feasible method for future practical implementation. It is known that a critical element in the dynamics of hydrate phase transitions is the mass transport, as the hydrate forms across a thin interface layer between liquid water and the interacting gas phase. An efficient production scheme needs to be able to break the water hydrogen bonds in this interface. On the other hand, the kinetic rate of hydrate growth also depends strongly on hydrate formation at the interface. This study shows how the balance of film barrier and hydrate growth at the interface can be affected by a judicious selection of surfactants.

Combustion is expected to remain one of the main sources of power in the world. Therefore, the understanding of the underlying physical and chemical processes needs to continue improving, to increase efficiency and to reduce emissions of combustion systems. In order to study the steady-state characteristics of complex flame configurations, laminar surrogate models can aid significantly in the description of more complicated systems. One valuable class of surrogate configurations is the nonpremixed laminar flame, in which fuel and oxidizer are initially separated. In nonpremixed flames the mixing process is a necessary part of the flow to be investigated and the chemical process can be represented by a global reaction mechanism. Such simplification allows the conservation equations to be treated with analytical or semi-analytical methods, while still capturing the critical physical characteristics of the system. The dissertation describes and analyzes three laminar nonpremixed stagnation flow models based on canonical flame configurations: a coflow impinging flame, a water-laden counterflow flame, and a tubular counterflow burning condensed fuels. The performance of the theoretical models is validated with experimental data available in the literature. In addition, the nonpremixed swirl-type tubular flame configuration is presented for the case of a liquid fueled porous wall fed system. The experimental system and the mathematical model that describes theoretically the configuration are evaluated. To this end, a novel analytical solution based on asymptotic methods is presented.