Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/100472

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Open Access
Controlled testing of next generation leak detection and quantification solutions to evaluate performance and develop consensus assessment metrics
(Colorado State University. Libraries, 2025) Ilonze, Chiemezie Okechukwu, author; Windom, Bret C., advisor; Zimmerle, Daniel, advisor; Olsen, Daniel B., committee member; Levin, Ezra, committee member; Pierce, Jeffrey, committee member
Reducing methane emissions, a potent short-term climate forcer, is critical for mitigating global warming. The oil and gas (O&G) industry is a major source of anthropogenic methane emissions, and regulations in the U.S. and Canada mandate leak detection and repair (LDAR) programs to mitigate these emissions. Traditional LDAR methods, which includes manually surveying O&G assets with handheld optical gas imaging (OGI) cameras or portable organic vapor analyzers, can be costly and labor-intensive given the vast spatial extent of O&G facilities. However, emerging, next-generation leak detection and quantification (LDAQ) solutions promise a more cost-effective alternative but must demonstrate equal or superior emissions mitigation potential to gain regulatory approval. Standardized controlled testing is essential for verifying this equivalence, yet no widely accepted framework currently exists to achieve this goal. This study evaluates and improves the first known standardized controlled testing protocols designed to address this gap. Two test protocols were developed for the two broad categories of LDAQ solutions: continuous monitors, which operate autonomously over extended durations, and survey solutions, which function over shorter durations with human supervision. These protocols, developed through multi-stakeholder collaboration, were used to test 29 LDAQ solutions (some tested multiple times) at the Methane Emissions Technology Evaluation Center (METEC). METEC is an 8-acre outdoor controlled testing facility that simulates methane emissions from North American onshore O&G equipment. Each survey solution and continuous monitor was tested for a minimum of 3 days and 11 weeks, respectively. Tested controlled release rates were up to 7100 g CH4/h for continuous monitors and 2100 g CH4/h for survey solutions. Key performance metrics, including probability of detection (POD), localization accuracy and precision, quantification accuracy, and survey times, were assessed. Seven solutions were retested 3 to 13 months after their initial tests to examine performance changes over time. Results showed that no single LDAQ solution or solution category achieved optimal performance across all the metrics evaluated. For continuous monitors, only two solutions achieved 90% POD within the tested range, failed to detect ≤ 40% of the controlled releases, and had ≤ 40% of their reported detections classified as false alerts. Camera- and laser-based continuous monitors demonstrated the highest emissions source localization accuracy, with most of them attributing ≥49% of their detection reports to the correct emission source. Quantification uncertainty varied widely, with solutions underestimating and overestimating actual emission rates by factors up to 50 and 46, respectively. For survey solutions, handheld OGI cameras exhibited better accuracy and repeatability in detecting and localizing small fugitive emissions compared to mobile (automobile-/drone-based) survey solutions, although the latter completed emission surveys faster. Additionally, performance improvements were observed with repeated testing, emphasizing the likely importance of regular, independent, and comprehensive evaluations in advancing LDAQ solutions. Findings from these controlled tests, combined with stakeholders feedback and insights from parallel field testing, informed the revision of the protocols to better reflect the application of LDAQ solutions at real O&G facilities. Study findings demonstrates that integrating multiple solutions can complement the limitations of any individual or category of LDAQ solutions. Continuous monitors and automobile-/drone-based survey LDAQ solutions can rapidly detect and narrow-down sources of emissions, enabling targeted follow-up investigations with handheld LDAQ survey solutions. In general, this work contributes significantly to efforts aimed at accelerating regulatory approval and adoption of next-generation LDAQ solutions for methane emissions mitigation through transparent and rigorous controlled testing.
Open Access
Improvement of oxide ceramic materials via cation substitution for thermionic emission applications: connecting cation characteristics to changes in atomistic structure and properties
(Colorado State University. Libraries, 2025) Fisher, Liam Eugene, author; Ma, Kaka, advisor; Weinberger, Chris, committee member; Neilson, Jamie, committee member; Bandhauer, Todd, committee member
My research aimed to improve oxide ceramic materials for thermionic emission applications through strategic cation substitution, focusing on enhancing material properties like thermal stability and electrical conductivity. In thermionic emission applications, low work functions and high thermal resilience are essential material properties for efficient electron emission under high temperatures. Two oxide-based material systems, mayenite electride and strontium vanadate, were selected in the present work, because of their promising low work function, reasonable thermal stability, and economical costs of precursors. But both materials require improvements to realize or increase their applicability in thermionic emission technologies. Moreover, these two material systems possess distinguishing lattice structures from each other and utilize different mechanisms for low work function. Thus, in-parallel investigation into and comparison of the results from these two types of oxide ceramics provide fundamental insights into the interplay between the atomistic structure and cationic substitution. A critical objective of this research is to discover how various cation substitutions affect the lattice structure and how these structural changes subsequently modify key material properties for the thermionic emission application. Different cations were substituted at select sites in mayenite electride and strontium vanadate structures, individually and in dual combinations, to assess their effects on thermal stability and electrical conductivity. The hypothesis was that substituting smaller cations at particular atomic sites might increase thermal stability by altering the lattice parameters, bonding environment, and electron density. The study also investigated how dual substitutions might synergize beneficial effects from individual cations, with a focus on combinations that can potentially balance thermal stability and electrical conductivity. To characterize structural modifications, this research employs Rietveld refinement of X-ray diffraction data to conduct detailed analysis of lattice parameter adjustments and cation disorder, providing insight into the structural intricacies induced by specific substitutions. Additionally, thermogravimetric and electrical conductivity analyses reveal trends in the change of oxidation resistance and conductivity that align with anticipated impacts of certain cations. Results suggest that substituting smaller cations into mayenite lattice significantly increases oxidation onset temperature. In strontium vanadate, substitutions at the A- and B-sites have limits to stability as the material drifts further from the ideal tolerance factor of one, with critical implications for phase stability and oxidation behavior. The calcium substitute for strontium led to a vast improvement in both thermal stability (onset of rapid oxidation increased to a temperature > 1050°C) and electrical conductivity (σ > 3000S/cm). The key findings from this work demonstrate that tailored cation substitutions can substantially improve the key properties of oxide ceramics, offering pathways for material optimization for thermionic applications in harsh environments.
Open Access
Autonomous robot control: integrated control strategies for a mobile robotic arm
(Colorado State University. Libraries, 2025) Weinmann, Katrina, author; Simske, Steve, advisor; Chen, Thomas, committee member; James, Susan, committee member; Zhao, Jianguo, committee member
Autonomous robots open up a wide range of potential applications for robotic systems beyond the controlled manufacturing environments where they were originally used. These applications can include agriculture, space exploration, search and rescue, fire-fighting, performing tasks in hazardous environments, personal care robots, and much more. Some of these applications have the potential to replace humans in dangerous environments or improve quality of life for elderly or disabled individuals, thus providing great positive societal impacts. However, the technologies needed for robots to operate safely and autonomously in unstructured environments, and especially when interacting with humans, are still being developed. Designing and controlling autonomous robotic systems is a very challenging problem, with some of the major objectives including efficient autonomous navigation in both known and unknown environments; real-time, dynamic obstacle avoidance; real-time and energy-efficient trajectory generation; and safe operation with and/or in close proximity to humans. While all of these topics have been researched in the field of robotics, existing solutions still have limitations which encourage further developments improving on existing autonomous robotic capabilities. Furthermore, each application and configuration of autonomous robotic systems has a unique set of requirements. In this dissertation, the platform of a mobile robotic arm was chosen for its wide range of potential applications achieved from the combined navigation and manipulation abilities of such a robot configuration. Within the scope of autonomous mobile robot arm control, the following topics were identified and chosen for research: (1) indoor target localization; (2) efficient navigation in partially known environments; (3) integrated control (i.e. coordinated base and arm motion) of a mobile robot arm, including both navigation and trajectory generation and tracking. For each topic, a novel or improved methodology was developed, all relevant to a wide range of autonomous robot deployments. The contributions of this dissertation are as follows: (1) Bluetooth-based homing controller for indoor target localization achieving a mean target localization accuracy of 0.12m or less with various levels of simulated sensor noise; (2) modified artificial potential field-based method for efficient navigation in a partially-known environment and for integrated control of a mobile robot arm improving autonomous navigation success rate and efficiency over existing APF-based methods in environments of varying levels of complexity; (3) real-time many objective optimization-based approach trajectory generation method for integrated motion of a mobile robot arm to reach a desired end-effector configuration, demonstrating a 100% success rate in achieving the desired configuration and reaching the configuration in under 30s in 77% of trials; (4) offline trajectory generation for mobile robot arm end-effector trajectory tracking using a sampling-based combinatorial optimization method to generate integrated motion trajectories (coordinated mobile base and robotic arm motion) achieving over 99% success rate in high accuracy (<5mm position tracking error and <0.1 radian orientation tracking error) end-effector trajectory tracking tested on 500 sample trajectories; and (5) integrated controller design for differential drive mobile robot arm trajectory tracking consisting of a fuzzy logic-based differential drive robot (DDR) controller reducing irregular trajectory tracking errors by 2.4X to 6.8X over existing DDR controller designs, and integrated robotic arm-facilitated DDR base tracking error compensation reducing mean maximum end-effector tracking errors by 18%.
Open Access
Viability and sustainability of desalinating produced water in the oil and gas industry
(Colorado State University. Libraries, 2025) Grauberger, Brandi M., author; Bandhauer, Todd M., advisor; Tong, Tiezheng, advisor; Sharvelle, Sybil, committee member; Quinn, Jason C., committee member
Unconventional oil and gas extraction consumes considerable amounts of water, with up to 11 million gallons of freshwater used for the fracturing of a single well. Millions of gallons can come back to the surface of a well as flowback and produced waters, which are collected and disposed of through deep well injection. Water reallocation and reduction of resource waste can be aided by treating produced water from these operations but is rarely practiced. In particular, treating produced water to zero-liquid-discharge allows for management of dry wastes and generates a clean water source as its only other product. Eliminating the disposal of brines from produced water management would eliminate the need for deep well injection, which has shown to be an unsustainable option for produced water management. A major barrier to produced water treatment is the cost and availability of energy for treatment. Other barriers arise from an incomplete understanding of the system. Specifically, environmental and social impacts of produced water treatment are not understood. For example, it is not known if the discharge of treated produced water will have a negative effect on drinking water supplies or flow of rivers and streams. Without solving these challenges, produced water will continue to be disposed into injection wells, wasting the potential to reduce freshwater consumption, and further threatening seismic stability and access to freshwater reserves in oil and gas producing regions. This work completes three major analyses to understand the potential of produced water desalination. First, the accessibility of waste heat from the oil and gas industry, which is limited due to spatial and temporal disparities in waste heat and produced water production, was quantified and compared to energy requirements for produced water treatment. The results show that there is potential for waste heat utilization by membrane distillation, a thermal-membrane desalination technology option, in the oil and gas industry for produced water desalination with appropriate waste heat storage system integrations. The next major evaluation is of the economic and environmental impacts for multiple zero liquid discharge desalination options. Economic results show that the existing technology of mechanical vapor compression is difficult to reliably challenge, in terms of cost. However, environmental emissions can be much improved when using waste heat as an energy source for desalination or when treating with electrodialytic crystallization. Finally, this work evaluates options for zero liquid discharge desalination in the oil and gas industry using a triple bottom line sustainability framework. This framework considers the economic, environmental, and social competitiveness of technologies in multiple stakeholder-preference scenarios, which weight the importance of the three categories in different ratios. Results show that the use of waste heat is paramount to the consideration of membrane distillation as a technology option in the oil and gas industry. Further results show that the comprehensive consideration of economic, environment, and social impacts provide context to overall fit of technology options in the oil and gas industry. More detail of each major objective of this work are shared in the following paragraphs. The use of waste heat has been proposed to reduce the energy footprint of membrane distillation for flowback and produced water treatment. However, its feasibility has not been fully understood for produced water treatment. Accordingly, the third chapter of this work performed systematic assessments through thermodynamic modelling of waste heat capture, storage, and transportation for decentralized produced water treatment at well pads located in the Denver-Julesburg Basin. A wide range of sensible, phase-change, and thermo-chemical storage materials were assessed for their effectiveness at the utilization of waste heat from on-site hydraulic fracturing engines and natural gas compressor stations, in order to overcome the temporal or spatial mismatch between waste heat availability and produced water generation. Results show that the type of storage material being used can have a high impact on the efficiency of waste heat utilization and the treatment capacity of membrane distillation. Sensible storage materials only utilize sensible heat capacities, while phase-change materials have improved performance because they are able to additionally store latent heat. However, sensible and phase-change storage materials lose 11–83% of heat due to conversion inefficiencies caused by their changing temperatures. Thermo-chemical materials, on the other hand, have the highest potential for use because they collect and release heat at constant temperatures. Three thermo-chemical storage materials (magnesium sulfate, magnesium chloride, and calcium sulfate) were identified as those with the best efficiencies due to their elevated discharge temperatures which reduce the energy consumption of membrane distillation. In addition, these materials have high volumetric energy storage density, which enables capture and transportation of waste heat from remote locations such as natural gas compressor stations to the well sites, yielding up to 70% reduction in transportation costs relative to moving produced water to centralized treatment facilities at natural gas compressor stations. The third chapter of this work demonstrates the importance of selecting appropriate energy storage material for leveraging low-grade thermal energy such as waste heat to power membrane distillation for decentralized wastewater treatment. With more certainty given in the possibility and logistics of using waste heat for the membrane distillation system in the oil and gas industry, further analysis was needed to evaluate new technologies with existing brine desalination technologies in terms of replacement potential. Four technologies were considered: mechanical vapor compression with a crystallizer, electrodialytic crystallization, membrane distillation with a crystallizer using electrical heating, and membrane distillation with a crystallizer using waste heat. The fourth chapter of this work evaluates the economic and environmental competitiveness of said technologies. Zero liquid discharge desalination has garnered considerable attention for its potential to mitigate the impact of water scarcity while minimizing environmental consequences associated with ill-managed brine wastes. In the fourth chapter of this work, the economic and environmental competitiveness of an electrodialytic crystallization system designed in recent works was evaluated. It was found that when compared to existing zero liquid discharge technologies, electrodialytic crystallization could compete economically with the potential to reduce costs of zero liquid discharge by over 60% in optimal conditions. However, this high economic competitiveness is not consistent in more conservative operating scenarios. Furthermore, electrodialytic crystallization has 42% lower global warming potential than existing technologies. Scenario and sensitivity assessments completed in this chapter identify the operating parameters of electrodialytic crystallization that greatly affect economic and environmental impacts. Most notably, improvements to the cost and performance of ion exchange membranes will provide the highest benefit to electrodialytic crystallization competitiveness. With appropriate concentration of future research on these high-impact areas, the economic and environmental viability of electrodialytic crystallization should continue to increase in the coming years and electrodialytic crystallization will compete with existing zero liquid discharge technologies to provide a low-cost, efficient, and low-impact replacement to existing technologies. This chapter also shows the limited viability of membrane distillation with a crystallizer in replacing existing zero liquid discharge technologies due to high costs. In either case of electrical heating or waste heat use for membrane distillation, energy costs or infrastructure costs stemming from high energy intensity of membrane distillation result in costs far exceeding those of existing technologies. Through economic and environmental analysis expand the understanding of the potential for technologies to reach industrial application, further analysis can be leveraged to evaluate the fit of technologies into specific applications based on multiple stakeholder perspectives of the system needs. In the fifth chapter of this work, technology options were qualitatively evaluated under a stakeholder-informed triple bottom line sustainability perspective Chapter 5 of this work evaluates proposed technical solutions to produced water desalination and considers the additional economic, environmental, and social barriers that exist within the oil and gas industrial system. The consideration of these three impact areas (i.e., economic, environmental, and social) are defined as the triple bottom line considerations. The drivers, pressures, states, impacts and responses framework, first developed by the European Environmental Agency and later updated by the United States Environmental Protection Agency, was used to support the work of chapter 5 by organizing broad system considerations collected from stakeholder-generated literature into an orderly and approachable list of system indicators to evaluate technology compatibility within the applied system. System indicators are quantified, and overall system compatibility scores are calculated based on a variety of stakeholder preference scenarios. The results show that, given current models, emerging technologies have the potential to compete with existing zero liquid discharge technologies when applied to the oil and gas industry for produced water desalination under applications where stakeholders have low economic preference. Careful consideration of stakeholder preferences is necessary because technologies rank differently based on weightings of economic, environmental, and social impact importance. In summary, through thermodynamic and system modeling, techno-economic analysis, life cycle assessments, and triple bottom line sustainability considerations, four zero liquid discharge desalination technology options for the oil and gas industry (i.e., mechanical vapor compression with a crystallizer, electrodialytic crystallization, membrane distillation with a crystallizer using electrical heating, and membrane distillation with a crystallizer using waste heat) were evaluated for the Denver-Julesburg Basin in Northern Colorado. Overall, development of ion exchange membranes with improved performance for electrodialytic crystallization and developments in lowering membrane distillation energy intensity will determine the future economic competitiveness of electrodialytic crystallization and membrane distillation, respectively, as desalination technology options over mechanical vapor compression. However, when evaluating triple bottom line sustainability, results show potential for applications where there is lower preference to economic performance. In such applications, electrodialytic crystallization and membrane distillation with a crystallizer using waste heat consistently compete with mechanical vapor compression-based systems. Further understanding of the applied system needs and stakeholder preferences will determine overall applicability of technologies into the system.
Embargo
Backyard to battlefield: multifunctional medical foam for enhanced wound management
(Colorado State University. Libraries, 2025) Stoner, Amelia, author; McGilvray, Kirk, advisor; Wong, Sing-Wan, committee member; Pezzanite, Lynn, committee member
Acute open wounds as a result of traumatic injuries are a prevalent issue for civilians and military personnel across the world. Unfortunately, advanced hospital care for these severe injuries is not always readily available, leaving the morbidity and mortality outcomes of people who suffer these injuries to rely on primary wound care, hopefully applied before it is too late. A complete understanding of traumatic injury's effect on the body remains elusive. However, known complications include hemorrhage and infection of wounds if not treated quickly and effectively. Many primary wound care products exist, but few can perform more than one function. For example, packing a wound with gauze can help stop bleeding, but will not do anything to combat infection. Thus, this work sought to generate a multifunctional therapeutic approach to primary wound care that includes bleeding (tranexamic acid) and infection (vancomycin) control agents delivered through a biopolymer carboxymethyl cellulose foam. This non-solidifying, volume-filling foam was hypothesized to improve the quality of care for those who sustain open wounds from traumatic injuries, especially those who are injured in rural or austere environments without immediate access to advanced care. This work is comprised of four aims that will contribute to the field of emergency wound care. The first aim included generating and characterizing the base foam responsible for delivering selected bleeding and infection control therapeutics topically to the wound. 200% tunability in temporal stability and volumetric expansion was demonstrated, indicating precise control over physical properties. The second aim was to evaluate the in vitro safety of the foam through monolayer live/dead staining of fibroblasts, one of the most prevalent cell types in skin. The foam and its constituents were found to be non-cytotoxic to both murine and human fibroblasts in vitro, indicating base-level safety of the material and potential for successful in vivo experimentation. The third aim focused on in vitro/ex vivo efficacy evaluation of antifibrinolytic and hemostatic properties of the foam on ovine blood with the chosen bleeding control therapeutic. Delivery with the foam demonstrated low clot lysis rates and mechanically robust blood clot rheology compared to other treatment formulations, indicating potential for successful in vivo experimentation in future work. The fourth and final aim evaluated the foam's in vitro/ex vivo antibiotic efficacy on methicillin-resistant Staphylococcus aureus with the selected infection control therapeutic. Delivery with the foam demonstrated 3-4 log bacterial killing of methicillin-resistant Staphylococcus aureus, indicating potential for successful in vivo experimentation in future work. Together, these aims provide novel preliminary data crucial to the product development process and in vivo implementation of the foam as a staple of primary wound care in acute open traumatic injuries.
Open Access
Development and characterization of a hidden anode-based plasma contactor
(Colorado State University. Libraries, 2025) Freestone, Tait H., author; Williams, John D., advisor; Yalin, Azer, committee member; Roberts, Jacob, committee member
The use of high-current, high-energy electron beams on spacecraft can result in excessive positive electrostatic charging beyond passive mitigation capabilities, potentially terminating beam emission. To counteract this, active charge mitigation via positive ion emission is necessary. This thesis evaluates the Hidden Anode Plasma Contactor (HAPC), developed for the University of Michigan's Beam-Spacecraft Plasma Interaction and Charging Experiment (BSPICE), designed specifically for rapid start, active charge mitigation of a sounding rocket mission. This study characterizes the plasma plume generated by the HAPC along with its operational characteristics, while also detailing the Krypton gas feed system and associated electronics. Ion current production required for the mission was verified through current density measurements and pulse bias testing. Measurements revealed a near-hemispherical plasma expansion, ion energy distributions resembling those of Hall thrusters, and predominant singly charged ions, though multiply charged ions were present. Langmuir probe analysis of the plasma plume downstream of the HAPC identified two distinct electron populations—thermal electrons and higher-energy primaries emitted directly from the cathode. Anode orifice erosion at high power and expellant utilization above 10% was observed, which would likely limit the lifetime of the HAPC to tens of minutes—times much greater than the 7-minute typical duration of a sounding rocket mission. The findings provide comprehensive insights into HAPC operation for BSPICE and highlight its applicability as an alternative plasma source where Hall thruster-like plume characteristics are desired.
Open Access
Experimental and numerical performance evaluation of a thermal oxidizer for industrial lean burn natural gas engines
(Colorado State University. Libraries, 2025) Huonder, Andrew Joseph, author; Olsen, Daniel, advisor; Windom, Bret, committee member; von Fischer, Joe, committee member
Methane slip in industrial lean burn natural gas engines is a significant source of greenhouse gas emissions. With growing regulations on the emissions of hydrocarbon pollutants, especially methane, new reduction technologies for these engines are needed. This research investigates the performance of a new type of thermal oxidizer, known as an Oxiperator, for reducing methane emissions from a lean burn natural gas engine. This study begins with baseline testing of a Cummins QSK19G engine to determine the optimal operating conditions for the Oxiperator. It was found that the most optimal operating condition for the Oxiperator is with a high air-to-fuel mixture. It was then followed by a performance evaluation of the Oxiperator to assess its ability to oxidize methane in the exhaust. The first key result from this performance evaluation is that the minimum concentration of total hydrocarbons required to maintain oxidation was found to be 4400 ppm. The second key result was that the lowest temperature that the Oxiperator can be where the oxidation reaction is still recoverable is 815 °C. The performance of the Oxiperator was also modeled using CONVERGE CFD. The simulation results were then compared to the actual test results. The CFD model shows that it could be an effective tool for predicting the performance of the Oxiperator, though there are many areas for improvement. This research contributes to the development of methane emissions control technologies for lean burn natural gas engines and identifies considerations for improvements on the future Oxiperator design.
Open Access
Characterization of femtosecond filaments in air
(Colorado State University. Libraries, 2025) Wilson, Seth William, author; Dumitrache, Ciprian, advisor; Yalin, Azer, advisor; Van Orden, Alan, committee member
Laser-induced plasmas (LIPs) offer a promising alternative to conventional ignition methods in high-performance engines, addressing inherent limitations of traditional approaches. Firstly, LIPs can be precisely located within the combustion chamber, enabling ignition in regions with a homogeneously mixed air-fuel ratio. Secondly, LIPs eliminate the need for solid electrodes that act as heat sinks and suffer from erosion in high-pressure environments. Finally, LIPs can achieve combustion with mixtures of lower air-fuel ratios than what is possible via conventional ignition, leading to an increase in fuel efficiency. Consequently, laser-based ignition systems are well-suited for engines with pressures and environments beyond the operating range of conventional spark plugs. In a nominal nanosecond laser ignition method, a high-power laser is focused down to a point until it reaches an intensity level high enough to begin to breakdown the gas molecules in which it is being focused. Whilst the study of nanosecond laser-induced plasma has been investigated thoroughly, this work aims to provide justification for the use of femtosecond lasers as a "foundational" pulse to prepare the combustion area through pre-ionization. Using femtosecond (fs) lasers for ignition purposes is supported by the large body of research which has investigated the formation of plasma filaments through the self-focusing effect that occurs when a laser exceeds a critical power. The length of these filaments has been shown to be on the order of meters under certain conditions and provide exciting promise in the fields of remote sensing, weather control, and waveguides. This work obtains information about the filament through the use of optical emission spectroscopy and finds that the lifetime of femtosecond filaments are on the order of nanoseconds whist studied nanosecond plasmas last in excess of tens of microseconds. The spectral emission from the filament is dominated by the N2(C-B) and N2+(B-X). These transitions are observed in nanosecond plasmas, but only at times of greater than 1 μs after the pulse. Femtosecond filaments produce these species almost immediately and their lifetimes are only a few nanoseconds. Using a radiative emission and absorption code, we were able to determine the gas temperatures of the filament to be 500±100 K. A zero-dimensional plasma kinetics model was developed to simulate experimental conditions derived from optical emission spectroscopy. It was found that N2(C) formation comes initially from direct electron excitation up from the ground state of N2(X) then from the dissociation of N4+. N2(C) is destroyed by quenching via O2 primarily, N2 secondarily, and deexcited down to N2(B) ternately. This work answers two questions. First, how is the plasma generated by a femtosecond laser different from that of a nanosecond laser? Second, what chemical reactions occur in a femtosecond plasma. Experimental testing found physical and thermochemical differences in the femtosecond plasma versus the extensively studied nanosecond plasma, namely the shape, lifetime, emissive properties, and temperature. Theoretical modeling unveiled the reaction pathways responsible for the dominant emissive species found spectrally. Concurrency was found between experimental and theoretical results for the reaction pathway of the dominant emissive species in femtosecond plasmas. This concurrence provides confidence to the reaction pathways presented and opens the door to further research using the knowledge of those reaction pathways to increase the viability of femtosecond laser filaments in combustion applications.
Embargo
Autonomous low-cost network of ozone sensors: to study the spatial distribution and exposure in underserved agricultural communities in central California
(Colorado State University. Libraries, 2025) Gunniah Vijayakumar, Akshay Kumar, author; Jathar, Shantanu, advisor; L'Orange, Christian, committee member; Magzamen, Sheryl, committee member; Quinn, Casey, committee member; Carter, Ellison, committee member
Ozone (O3), a criteria air pollutant, is often overlooked in rural and remote regions, leaving the spatial distribution and exposure levels poorly understood, particularly in underserved communities. In this study, we developed and deployed a network of 12 autonomous, low-cost, and solar-powered air quality monitoring units (VOZboxes) in California's San Joaquin Valley (SJV). Co-located with a reference monitor in Fresno, CA, the VOZboxes underwent calibration before and after field deployment in June and November 2023, respectively, to measure O3 concentrations over a dynamic range of 20 to 100 ppbv with an RMSE < 5 ppbv. Deployed across 11 unique locations in SJV from July to November 2023 at varying periods, the VOZboxes revealed modest spatial variability in O3 mixing ratios, with elevated concentrations recorded in bigger cities and smaller eastern townships, while lower concentrations were found in smaller western regions. By leveraging multivariate regression models for data calibration, the VOZboxes effectively assessed compliance with the national ambient air quality standard (NAAQS) for O3 (maximum daily 8-hour average of 70 ppbv) across locations. This study underscores the potential of low-cost environmental sensors for characterizing air quality and O3 exposure in rural and remote environments. Additionally, it emphasizes their utility as tools for addressing the monitoring needs of underserved communities and acts as a tool for environmental justice.
Open Access
Shape-morphing robotic fish
(Colorado State University. Libraries, 2025) Middlemist, Clint, author; Zhao, Jianguo, advisor; Yourdkhani, Mostafa, committee member; Bradley, Thomas, committee member
Robotic fish have gained attention for their potential applications in underwater exploration, environmental monitoring, and bio-inspired robotics research. These systems aim to replicate the efficient propulsion and maneuverability observed in biological fish. However, current robotic fish designs are limited by their fixed stiffness and inability to dynamically adapt to varying environmental conditions. Traditional solutions for modulating stiffness or morphology often rely on bulky hardware or complex external systems, limiting scalability and versatility. This thesis addresses these limitations through the development of an embedded morphing scheme that integrates actuation, sensing, and shape-locking mechanisms directly into the robot's structure. Utilizing Shape Morphing Modules (SMMs) composed of Shape Memory Polymers (SMPs) and Twisted and Coiled Actuators (TCAs), this scheme enables compact and efficient systems capable of real-time stiffness and shape modulation. Beyond robotic fish, this scheme demonstrates versatility in applications such as adaptive grippers, reconfigurable surfaces, and robotic manipulators requiring dynamic morphing. We first implemented the embedded morphing scheme in a robotic fish with a variable-stiffness tail. The tail's stiffness was adjusted by controlling the curvature of thin plates via TCAs, with the shape locked by SMP ribs. Experimental results revealed improved adaptability for both speed and maneuverability under different conditions, though excessive stiffness caused buckling under high forces, indicating a trade-off between stiffness and structural limits. The embedded morphing scheme was extended to a robotic fish with a morphing body to explore the relationship between body shape and swimming performance. Modified SMMs allowed for dynamic changes in body depth and width. The fish was controlled using a Central Pattern Generator (CPG) model, which enabled precise tuning of swimming parameters such as frequency, amplitude, and phase offset. Testing showed that body shape significantly influenced swimming performance, with a flat-flat configuration yielding higher speeds compared to a medium-large configuration due to reduced drag.
Open Access
Operational conditions for an internal combustion engine in a SOFC-ICE hybrid power generation system
(Colorado State University. Libraries, 2025) Reyes-Flores, Victor A., author; Bandhauer, Todd, advisor; Olsen, Daniel B., committee member; Daily, Jeremy, committee member
Hybrid power generation systems utilizing pressurized solid oxide fuel cells (SOFC) have gained considerable attention recently as an effective solution to the increasing demand for cleaner electricity sources. Among the various hybridization options, gas turbines (GT) and internal combustion engines (ICE) running on off SOFC tail gas have been prominent. Although spark ignition (SI) tail gas engines have received less focus, they show significant potential for stationary power generation, particularly due to their ability to control combustion. This research experimentally characterized an SI engine fueled by simulated SOFC anode gas across a range of variations with fuel cell loads. The study aimed to optimize the engine operating conditions for each fuel blend and establish operational conditions that would sustain maximum performance. The results showed efficiencies as high as 31.4% at 1600 rpm, with a 17:1 compression ratio, equivalence ratio (φ) = 0.75, and a boost pressure of 165 kPa with low NOx emissions. The study also emphasizes the benefits of optimizing boost supply to minimize parasitic loads and improve brake thermal efficiency (BTE). Additionally, installing a catalytic oxidizer would enable the system to comply with new engine emission regulations. A proposed control scheme for automation includes regulating engine power by controlling the boost of the supercharger at a fixed throttle position.
Open Access
Development of advanced combustion strategies for heavy duty LPG engines to achieve near-diesel efficiency
(Colorado State University. Libraries, 2024) Fosudo, Toluwalase Jude, author; Olsen, Daniel B., advisor; Windom, Bret, committee member; Wise, Dan, committee member; Grigg, Neil, committee member
As the transportation sector evolves in response to increasingly stringent emissions regulations and economic realities in the wake of the decarbonization drive, several no/low carbon fuel options have emerged as viable options for internal combustion engines. Among these fuels, Liquefied Petroleum Gas (LPG) is uniquely positioned for spark ignited engine operation due to its favorable physical and chemical properties. Currently, much of its use as an engine fuel is limited to light-duty applications, dual fuel applications, or retrofitted gasoline engines, with a lesser degree of penetration into the heavy-duty sector where diesel fuel still dominates. A key reason for this is the deficit in performance and efficiency between diesel and other low carbon fuels, including LPG, necessitating the need for targeted research aimed at bridging this gap, and positioning LPG as a fuel of choice in the heavy-duty sector. Two prominent drawbacks responsible for this gap between diesel and LPG engine performance are the dearth of specialized fuel injection hardware and tailored injection strategies, and knock, which limits the performance of spark ignited engines. This work seeks to address these and other limitations and achieve near diesel efficiency on a heavy-duty engine platform. Two engine platforms were employed in this study. A cooperative fuel research (CFR) spark-ignited engine was used to study the knock dynamics and the performance, combustion, and emissions behavior of the LPG fuel in relation to key engine parameters, the LPG fuel composition, and other low carbon fuel options. Compression ratio, engine load, exhaust gas recirculation percents, and a novel combustion control tool, the combustion intensity metric (CIM), were all varied on the CFR engine and a computational fluid dynamics (CFD) model calibrated and validated. Key findings were then transferred to a heavy-duty engine platform, the Cummins ISX15L single cylinder engine. The engine is a converted 6-cylinder diesel engine with diesel brake thermal efficiency (BTE) of 44%. A baseline evaluation was conducted with liquid LPG port-injected at 16bar and 9.3:1 compression ratio. Then the engine was switched to direct injection (DI) configuration with a fuel delivery system capable of delivering liquid LPG at pressures up to 200bar. Three principal configurations were developed for operation of the heavy-duty engine employing a gasoline direct injector (GDI) with nozzle patterns adapted for optimal distribution of the LPG fuel in the combustion chamber, a GDI modified for higher LPG flow and a double-injector port-fuel injection (PFI) system optimized for injection location, and charge cooling and distribution. The experiments and modeling contained in this study demonstrate the impact of LPG composition on engine performance, the mitigating effect of EGR on knock and NOx emissions, the potential for a better controlled combustion using the CIM tool and the advantages in terms of knock, performance, and emissions of designing an injection strategy tailored to the LPG fuel. The results show that the heavy-duty engine operated on LPG achieved the target efficiency of 44% BTE at high EGR, high compression ratio, and high load conditions for both DI and PFI configurations. The outcomes of this study advance the literature on knock, end-gas autoignition, emissions, and EGR related to LPG and its use as a choice fuel for heavy-duty applications and advances the development of specialized fuel delivery hardware and injection strategies for the LPG fuel.
Embargo
Role of right ventricular anisotropic viscoelasticity in pathophysiology of RV failure
(Colorado State University. Libraries, 2024) LeBar, Kristen, author; James, Susan, advisor; Wang, Zhijie, advisor; McGilvray, Kirk, committee member; Chicco, Adam J., committee member; Popat, Ketul, committee member
Right ventricular (RV) failure is a key contributor to the mortality and morbidity of multiple cardiovascular diseases, such as congenital heart disease, heart failure with preserved ejection fraction, and pulmonary hypertension (PH). There has still, though, been a lack of treatment for such patients, due largely to a lack of understanding of the pathology and physiology of RV failure. Right ventricular passive stiffness is significantly increased in disease progression, and this change in mechanical behavior have been shown to markedly contribute to RV diastolic and systolic function. However, the myocardium is viscoelastic, and there is both energy storage (elasticity) and dissipation (viscosity) involved in the dynamic deformation within each cardiac cycle. Therefore, the long-ignored viscous component and its impact on organ performance must be investigated. Understanding of the impact of RV viscoelasticity in RV performance will fill a key knowledge gap in RV pathophysiology. Furthermore, the microtubule (MT), a cytoskeletal component of the cardiomyocyte (CM), is known to significantly contribute to the pathophysiology of multiple cardiovascular diseases. In the pressure-overloaded RV, MT density increases, leading to a stiffening of the CM and thus potentially the entire ventricular wall. Moreover, recent cell studies have shown that the pharmaceutical removal of the MT network reduces CM viscoelasticity and increases the extent of shortening, indicating a key role of the MT network myocardial viscoelasticity and contractile function. These findings suggest a regulation of myocardial viscoelasticity and organ contractility via the MT network. Therefore, the overall goal of my study is to determine the contribution of right ventricular anisotropic viscoelasticity to organ function during PH progression. The three specific aims of my dissertation research are: determine the alterations of RV anisotropic viscoelasticity in PH; delineate the contribution of the microtubules network to RV anisotropic viscoelasticity; explore the impact of the RV viscoelasticity on organ function using experimental and computational approaches.
Open Access
Design and flow characterization of an indraft supersonic wind tunnel for scramjet testing
(Colorado State University. Libraries, 2024) Teeter, Spencer J., author; Dumitrache, Ciprian, advisor; Windom, Bret, committee member; Bradley, Thomas, committee member
This thesis describes the Colorado State University supersonic wind tunnel design, manufacture, assembly, and validation. The overarching goal of this research is to develop a ground testing platform for studying airbreathing hypersonic propulsion systems. Problems of interest include design of isolators, fuel injection systems, ignition and flame stabilization, shock-boundary layer interaction, and aero-thermo-elastic interactions in scramjet vehicles. An indraft-type tunnel was chosen for its simplicity, low capital investment, and low power requirement. Its main features are large windows for advanced optical flow diagnostics, modular experimental mounting system, cycle time under 15 minutes, and adjustable size up to 5.25" x 5.25" x 25". The bulk of this thesis research focuses on flow characterization using a Mach 2.5 nozzle and a test section of 5.25" x 1.57". To this effect, we determined the Mach number using shockwave schlieren and stagnation pressure measurements over longitudinal and transverse scans in the tunnel test section. Experiments show that steady-state flow consistently develops in 0.5 seconds at a uniform Mach 2.4 at the entrance of the test section decreasing to 1.5 at the exit. Nozzle outflow and shot-to-shot Mach number variation was low, while measurement deviation increased near the test section walls and exit due to boundary layer growth. By studying phenomena such as fuel mixing, ignition, and flame stability at high Mach numbers inside of a supersonic wind tunnel, research at the CSU's Aerospace Propulsion and Diagnostics Laboratory seeks to overcome the limitations of current scramjet technologies.
Embargo
Effects of nanostructured polymeric surfaces on bacterial adhesion and erythrocyte (RBCs) integrity
(Colorado State University. Libraries, 2024) Sathyanarayanan, Vignesh, author; Popat, Ketul C., advisor; Ghosh, Soham, committee member; Li, Yan Vivian, committee member
Blood-contacting devices, such as stents, artificial heart valves, vascular grafts and catheters, placed within a host body, are subjected to complications such as thrombosis, restenosis, hemolysis etc. These complications result in the frequent need for revision surgeries or long-term drug therapies post implantations. Natural and synthetic biocompatible polymers are used as potential solutions for these issues due to their superior characteristic of biodegradability. Recent advancements in nanoscale fabrication and modification of these surfaces has shown improved results with platelets, leukocytes and other whole blood components. However, disruptions in erythrocyte's cell structure, caused by the foreign body materials, can compromise their oxygen-carrying capacity. This can further affect the overall tissue oxygenation and potentially lead to myocardial ischemic conditions. Therefore, it is also vital to understand the effect of bio-implant surfaces on erythrocyte integrity and viability, to enhance their biocompatibility. In this study, PCL nanostructured surfaces, nanofibers and nanowires, were fabricated and modified with organic compounds, Tanfloc and CMKC, to investigate their antibacterial properties and their effect on erythrocyte's cell integrity. Results indicate that the modified PCL nanostructured surfaces exhibit enhanced antibacterial properties and retain erythrocyte integrity.
Open Access
Computational modeling of plasma-assisted shock wave control using the Cartesian cut cell method
(Colorado State University. Libraries, 2024) House, Elijah D., author; Dumitrache, Ciprian, advisor; Windom, Bret, committee member; Bangerth, Wolfgang, committee member
To control shock waves using plasma discharges, we have developed a numerical model focusing on improving the accuracy and efficiency of simulating supersonic channel flow. Shock waves are essential in high-speed air-breathing propulsion devices such as ramjets and scramjets. The lack of turbomachinery means that shock waves compress air prior to combustion. The shocks decelerate the high-speed flow, increasing static temperature and pressure, which is necessary for efficient combustion. However, the advantage of simplicity (no moving parts) to achieve compression is counteracted by increased wave drag, total pressure losses, and flow separation inside the engine. In this context, the generation of shock wave trains (a sequence of reflected oblique and normal shocks propagating through the engine) must be appropriately managed and optimized to reduce drag and enhance thrust. To tackle these challenges, we use the APDL-CFD code to model a Ma=2.5 supersonic flow over a 10-degree triangular wedge inside a straight channel. The wedge generates a shock wave train that is typically encountered inside the isolator of a scramjet engine. These conditions are indicative of conditions that are currently being tested in supersonic wind tunnels. The code solves the compressible Navier-Stokes equations, incorporating advective and diffusive fluxes. The advective fluxes account for mass, momentum, and energy transport, while the diffusive fluxes capture viscous stresses and thermal conduction. This formulation includes viscous dissipation and heat diffusion, ensuring accurate modeling of compressible flow behavior. Furthermore, we enhance the APDL-CFD code with the Cartesian cut cell method, which allows the representation of complex geometries on a Cartesian mesh. This research represents geometries found in wind tunnel models and internal vehicle designs. Using the cut cell method, the model can capture flow caused by geometries that do not conform to a Cartesian mesh, like the wedge that generates the oblique shock waves. This improves accuracy and significantly reduces computational costs, allowing for lower grid resolutions on a Cartesian mesh. The cut cell method is implemented to research the use of plasma actuators as an active control mechanism. The model investigates how varying key parameters, such as the location and temperature of the plasma, affect shock wave dynamics and the associated separation bubbles. Results show that the plasma kernel alters the flow and provides an effective way to shift the position and reduce the intensity of the shock waves inside the channel. The numerical simulations aim to optimize this control, showing that shocks can be dynamically managed with the proper plasma parameters to enhance flow stability and performance. The results demonstrate significant improvements in controlling shock waves and flow separation when plasma actuators are employed, showing potential for their use in high-speed propulsion systems such as scramjets. Moreover, incorporating the cut cell method has optimized the APDL-CFD code, making it more efficient and better suited for running rapid test simulations. The results can inform future experiments, such as those planned for the Colorado State University (CSU) wind tunnel. Overall, the research offers valuable insights into active flow control in supersonic and hypersonic vehicles for improving vehicle performance, efficiency, and reliability.
Open Access
Development, testing, and validation of a heat transfer model for bi-propellant liquid rocket engines
(Colorado State University. Libraries, 2024) Roberts, Jadon A., author; Windom, Bret, advisor; Wise, Dan, committee member; Adams, Jim, committee member
Accurately modeling the heat transfer characteristics in a bi-propellant liquid rocket engine is a time and resource intensive process. The highly unpredictable and turbulent nature of the combustion requires complex modeling to predict the temperatures and fluid properties. These properties are required to evaluate material requirements and thermal performance. The primary objective of this project was to determine the effectiveness of an adaptable analytical heat transfer model implemented in MATLAB. The analytical model was pursued for the dramatic speed increase over numerical techniques such as computational fluid dynamics (CFD). The effectiveness of the model is determined by comparing results to CFD simulations as well as data obtained from testing. Strong correlations can be drawn with variations a low at 1\% between the CFD and analytical models. Three separate engines were analyzed to gauge the effectiveness of the analytical model across various engine and cooling configurations. A 10 N, 250 N and 2.9 kN thrust engines were developed. Extensive analysis was done on all engines using both the analytical model and CFD. These engines were designed with a wide range of cooling methods including radiative, ablative and regenerative cooling. A test stand previously only capable of testing hybrid rocket engines, was modified to allow for the testing of liquid bi-propellant rocket engines. The needed modifications included the addition of a fuel tank with mass measurement, venting and control valves, and fuel line sensing equipment. Upgrades were completed on the data acquisition system to incorporate additional sensors and controls. Further work was done to improve the safety of the test stand through redundancy and automation. These modifications culminated in two successful static fires of the 2.9 kN engine. The predicted temperatures of the 2.9 kN engine were compared to the test results from the static fires.
Open Access
High efficiency air delivery system for solid oxide fuel cell power generation
(Colorado State University. Libraries, 2024) Mitchel, Lars Jared-Brian, author; Bandhauer, Todd M., advisor; Windom, Bret C., committee member; Cale, James, committee member
Distributed power generation systems can be used in the electric grid to reduce peak loads, raise power quality, and reduce/eliminate transmission losses. One distributed energy system with distinct advantages is a Solid Oxide Fuel Cell (SOFC) integrated with an Internal Combustion Engine (ICE) which has the capability to operate at electric efficiencies as high as 70%. This research aimed to produce and test a high efficiency air delivery system that supports the SOFC-ICE to generate power on the scale of 80 kW. The air balance of plant (BOP) system utilized low speed scroll-type rotating compressors and brazed plate and frame heat exchangers for efficient preheating. The scroll compressors were modeled in GT-Suite and the remaining air BOP system was modeled with thermodynamic and heat transfer equations. Then testing was done on the compressors and heat exchangers to validate the model so that the air BOP system performance could be accurately predicted within a range of conditions. Both compressors were run from a range of 20 g/s to 60 g/s with the heat through the system being swept from 100°C to 600°C which yielded compressor efficiencies over 60% and heat exchanger effectiveness over 0.90. The validated model was then used to make predictions about system performance at on and off-design conditions.
Open Access
Experimental evaluation of a standalone hollow cathode apparatus with a magnetic field
(Colorado State University. Libraries, 2024) Ku, Emily X., author; Williams, John, advisor; Dumitrache, Ciprian, committee member; Thornton, Christopher, committee member
Testing hollow cathode assemblies independently from their use in Hall or gridded ion thrusters offers advantages such as reduced test facility size, lower power requirements, and improved diagnostic access. Standalone tests can reveal important cathode characteristics like ignition time, keeper ignition voltage, tip temperature, and current capability. Replicating the plasma phenomena that occur when a cathode operates within a thruster is challenging but essential, as these phenomena can generate energetic ions that erode cathode and keeper surfaces, limiting thruster lifespan. The primary challenge is to accurately emulate thruster conditions in standalone tests and verify this emulation through comparison with cathode-thruster operations. This thesis presents data on a standalone hollow cathode operated with magnetic fields that emulate those in electric propulsion devices, testing it both without an applied magnetic field and with permanent and solenoidal magnetic fields. Measurements of keeper, anode, and cathode-to-ground voltages were conducted over a range of anode currents and flow rates. At certain conditions, the plasma discharge transitioned to a less stable mode known as plume mode, with higher flow rates shifting this transition to higher anode currents. Introducing a magnetic field decreased the anode current at which this voltage shift occurred. Important findings in this work include: (1) Repeat tests with no magnetic field show that the transition behavior was different from one test to another, indicating that transition behavior may be affected by minute changes in cathode apparatus, or there are significant uncertainties associated with the transition and (2) Significant hysteresis in plume mode transition was observed when increasing and then decreasing anode current. These two findings along with the deleterious effects of the magnetic field have important implications on cathodes operating with Hall thrusters, which often exhibit large, rapid oscillations in discharge current.
Open Access
Single power supply operation of a Hall thruster
(Colorado State University. Libraries, 2024) Robertson, Zachary K., author; Williams, John, advisor; Fankell, Doug, committee member; Roberts, Jacob, committee member
Interest in operating Hall thrusters with a single power supply, facilitated by heaterless hollow cathodes, has motivated this research. Initial investigations into the Safran PPS 1350 confirmed the potential for this configuration. Building on these findings, modifications were made to a laboratory Hall thruster to enable operation with a single power supply and changes were made to the electrical configuration to promote smooth cathode ignition and decrease the influence of the inductance in the magnetic coils. In addition to operating with a laboratory power supply, CisLunar Industries supplied a prototype anode supply that demonstrated capability of running the laboratory Hall thruster under these conditions without efficiency losses, as verified by thrust stand data. A phenomenological efficiency analysis was performed using a Faraday probe and a retarding potential analyzer which supported these results, while also providing pertinent sub-efficiencies. The study concludes that a single power supply configuration is a viable approach to starting and operating a Hall thruster equipped with a heaterless hollow cathode.