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  • ItemOpen Access
    Computational modeling of the lower cervical spine: facet cartilage distribution and disc replacement
    (Colorado State University. Libraries, 2009) Womack, Wesley J., author; Puttlitz, Christian, advisor
    Anterior cervical fusion has been the standard treatment following anterior cervical discectomy and provides sufficient short-term symptomatic relief, but growing evidence suggests that fusion contributes to adjacent-segment degeneration. Motion-sparing disc replacement implants are believed to reduce adjacent-segment degeneration by preserving motion at the treated level. Such implants have been shown to maintain the mobility of the intact spine, but the effects on load transfer between the anterior and posterior elements remain poorly understood. In order to investigate the effects of disc replacement on load transfer in the lower cervical spine, a finite element model was generated using cadaver-based Computed Tomography (CT) imagery. The thickness distribution of the cartilage on the articular facets was measured experimentally, and material properties were taken from the literature. Mesh resolution was varied in order to establish model convergence, and cadaveric testing was undertaken to validate model predictions. The validated model was altered to include a disc replacement prosthesis at the C4/C5 level. The effect of disc-replacement on range of motion, antero-posterior load distribution, total contact forces in the facets, as well as the distribution of contact pressure on the facets were examined, and the effect of different facet cartilage thickness models on load sharing and contact pressure distribution predictions were examined. Model predictions indicate that the properly-sized implant retains the mobility, load sharing, and contact force magnitude and distribution of the intact case. Mobility, load sharing, nuclear pressures, and contact pressures at the adjacent motion segments were not strongly affected by the presence of the implant, indicating that disc replacement may not be a significant cause of post-operative adjacent-level degeneration. Variation in articular cartilage distribution did not substantially affect mobility, contact forces, or load sharing. However, mean and peak contact pressure, contact area, and center of pressure predictions were strongly affected by the cartilage distribution used in the model. These results indicate that oversimplification of the cartilage thickness distribution will negatively affect the ability of the model to predict facet contact pressures, and thus subsequent cartilage degeneration.
  • ItemOpen Access
    Development of a hyaluronan-polyethylene copolymer for use in articular cartilage repair
    (Colorado State University. Libraries, 2009) Oldinski, Rachael, author; James, Susan P., advisor
    Articular cartilage is the connective tissue which covers the ends of long bones, providing a lubricious, hydrodynamic surface for articulation and energy dissipation. Articular cartilage has a limited ability to repair itself; once the native tissue has become damaged, either from injury or disease (e.g., arthritis), it is irreversible and the tissue will degrade with time resulting in joint pain. The goal of this research was to develop a permanent (i.e., non biodegradable/bioerodible) bioactive material and assess its applicability for articular cartilage repair and/or replacement. Utilizing two constituents, polyethylene (the 'gold standard' bearing material for total joint replacements) and hyaluronan (HA, a native component of articular cartilage), a hyaluronan-polyethylene graft copolymer (HA-co-HDPE) was developed. The novel HA- co-HDPE material was successfully synthesized using an interfacial polymerization reaction in a non-aqueous environment. Although the material has limited melt-processability, it is more processable than HA and was successfully compression molded into samples for physical, mechanical and in vitro biological characterization (e.g., swell ratio, dynamic mechanical analysis). HA-co-HDPE exploits the strength, rigidity and melt-processability associated with HDPE, and achieves increased osteogenic potential by incorporating the highly hydrophilic biopolymer HA. In conclusion, the swelling, mechanical and degradation properties of the copolymer can be custom-optimized for biomedical applications by tailoring chemical or physical crosslinking strategies and varying the amount and molecular weights of HA and HDPE incorporated into the copolymer.
  • ItemOpen Access
    A biomechanical analysis of venous tissue in its normal, post-phlebitic, and genetically altered conditions
    (Colorado State University. Libraries, 2009) McGilvray, Kirk Cameron, author; Puttlitz, Christian M., advisor
    The incidence of vein disease is very high, affecting more than 2% of the hospitalized patients in the United States; a number that is expected to increase. Post phlebitic veins, the result of chronic deep vein thrombosis, is considered to be one of the most important venous disease pathologies. Unfortunately, little information is currently available on the biomechanical effects of thrombus resolution in the deep veins. The aim of this research was to characterize the biomechanical response of both healthy and diseased venous tissue using a murine model. It was hypothesized that biomechanical response parameters derived from healthy and diseased tissue would give insight into the resultant clinical complications observed in patients following thrombus resolution. Biomechanical analysis revealed that statistically significant deleterious changes in vein wall compliance were observed following thrombus resolution. Data also revealed that matrix metallopeptidase 9 expression has a statistically significant effect on the biomechanical response of the tissue. These results indicate that clinical complications following deep venous thrombosis manifest from significant decreases in the compliance of the vein wall. Finite element analyses were also performed. Biomechanical data served as input material parameters for modeling. Finite element modeling was used to evaluate the response of the inferior vena cava under physiologic loads. The results indicate that peak stresses are generated in the circumferential direction of loading during luminal pressurization. Decreased dilatation was observed following thrombus resolution. The data indicates that deep venous thrombosis lead to increased vein wall stress in correlation with decreased luminal distensability.
  • ItemOpen Access
    Development and optimization of a stove-powered thermoelectric generator
    (Colorado State University. Libraries, 2008) Mastbergen, Dan, author; Willson, Bryan, advisor
    Almost a third of the world's population still lacks access to electricity. Most of these people use biomass stoves for cooking which produce significant amounts of wasted thermal energy, but no electricity. Less than 1% of this energy in the form of electricity would be adequate for basic tasks such as lighting and communications. However, an affordable and reliable means of accomplishing this is currently nonexistent. The goal of this work is to develop a thermoelectric generator to convert a small amount of wasted heat into electricity. Although this concept has been around for decades, previous attempts have failed due to insufficient analysis of the system as a whole, leading to ineffective and costly designs. In this work, a complete design process is undertaken including concept generation, prototype testing, field testing, and redesign/optimization. Detailed component models are constructed and integrated to create a full system model. The model encompasses the stove operation, thermoelectric module, heat sinks, charging system and battery. A 3000 cycle endurance test was also conducted to evaluate the effects of operating temperature, module quality, and thermal interface quality on the generator's reliability, lifetime and cost effectiveness. The results from this testing are integrated into the system model to determine the lowest system cost in $/Watt over a five year period. Through this work the concept of a stove-based thermoelectric generator is shown to be technologically and economically feasible. In addition, a methodology is developed for optimizing the system for specific regional stove usage habits.
  • ItemOpen Access
    Interaction space abstractions: design methodologies and tools for autonomous robot design and modeling
    (Colorado State University. Libraries, 2009) Kaiser, Carl L., author; Troxell, Wade O., advisor
    Current abstractions, design methodologies, and design tools are useful but inadequate for modern mobile robot design. By viewing robotics systems as an interactive and reactive agent and environment combination, and focusing on the interactions between the two, particularly those interactions that result in task accomplishment, one arrives at the interaction space abstraction. The role of abstractions, formalisms and models are discussed, with emphasis on several specific abstractions used for robotics as well as the strengths and shortcomings of each. The role of design methodologies is also discussed, again with emphasis on several currently used in robotics. Finally, design tools and the use thereof are briefly discussed. The concept of interaction spaces as an abstraction and a formalism is developed specifically for use in robot design. Types of elements within this formalism are developed, defined, and described. A formal nomenclature is introduced for these elements based on Simulink blocks. This nomenclature is used for descriptive models and the Simulink blocks are used for predictive models. The interaction space abstraction is combined with the concept of exploration-based design to create a design methodology specifically adapted for use in descriptive modeling of autonomous robots. This process is initially developed around a simple wall-following robot, then is expanded around a multi-agent foraging system and an urban search and rescue robot model, each of which demonstrates different aspects and capabilities of interaction space modeling as a design methodology. A design tool based on iterative simulation is developed. The three specific examples above are used to perform quantitative simulation and the results are discussed with emphasis on determination and quantification of factors necessary for task accomplishment. These simulations are used to illustrate how to explore the design space and evaluate trade offs between design parameters in a system.
  • ItemOpen Access
    Fiber delivery and diagnostics of laser spark ignition for natural gas engines
    (Colorado State University. Libraries, 2008) Joshi, Sachin, author; Yalin, Azer, advisor; Willson, Bryan, advisor
    Laser ignition via fiber optic delivery is challenging because of the need to deliver pulsed laser beam with relatively high energy and sufficient beam quality to refocus the light to the intensity required for creating spark. This dissertation presents work undertaken towards the development of a multiplexed fiber delivered laser ignition system for advanced lean-burn natural gas engines. It also describes the use of laser ignition system to perform in-cylinder optical diagnostics in gas engines. Key elements of the dissertation includes: (i) time resolved emission spectroscopy (TRES) of laser sparks in air to investigate the dependence of spark temperatures and electron number densities on ambient gas pressures, (ii) optical characterization of hollow core fibers, step-index silica fibers, photonic crystal fibers (PCFs) and fiber lasers, (iii) development and on-engine demonstration of a multiplexer to deliver the laser beam from a single laser source to two engine cylinders via optical fibers, and (iv) demonstration of simultaneous use of laser sparks for ignition and Laser Induced Breakdown Spectroscopy (LIBS) to measure in-cylinder equivalence ratios in a Cooperative Fuel Research (CFR) engine. For TRES of laser sparks, the ambient gas pressure is varied from 0.85 bar to 48.3 bar (high pressures to simulate elevated motored in-cylinder pressures at time of ignition in advanced gas engines). At later stages (~1μs) of spark evolution, spark temperatures become comparable at all pressures. Electron number densities increase initially with increasing ambient gas pressure but become comparable at pressures greater than ~20 bar. The effects of launch conditions and bending for 2-m long hollow core fibers are studied and an optimum launch f/# of ~55 is shown to form spark in atmospheric pressure air. Spark formation using the output of a pulsed fiber laser is shown and delivery of 0.55 mJ nanosecond pulses through PCFs is achieved. Successful multiplexed laser ignition of a CAT G3516C gas engine via hollow core fibers is shown. LIBS analysis conducted at equivalence ratios from 0.6 to 0.95 in the CFR engine show a linear variation and linear correlation (R2 > 0.99) of line intensity ratio (Hα/O777 and Hα/Ntot) with equivalence ratio.
  • ItemOpen Access
    Plasma flow field measurements downstream of a hollow cathode
    (Colorado State University. Libraries, 2007) Farnell, Casey Coffman, author; Williams, John D., advisor; Wilbur, Paul J., advisor
    The focus of the research described herein is to investigate and characterize the plasma produced downstream of a hollow cathode with the goal of identifying groups of ions and possible mechanisms of their formation within a plasma discharge that might cause erosion, especially with respect to the hollow cathode assembly. In space applications, hollow cathodes are used in electrostatic propulsion devices, especially in ion thrusters and Hall thrusters, to provide electrons to sustain the plasma discharge and neutralize the ion beam. This research is considered important based upon previous thruster life tests that have found erosion occurring on hollow cathode, keeper, and ion optics surfaces exposed to the discharge plasma. This erosion has the potential to limit the life of the thruster, especially during ambitious missions that require ultra long periods of thruster operation. Results are presented from two discharge chamber configurations that produced very different plasma environments. Four types of diagnostics are described that were used to probe the plasma including an emissive probe, a triple Langmuir probe, a remotely located electrostatic analyzer (ESA), and an ExB probe attached to the ESA. In addition, a simulation model was created that correlates the measurements from the direct and remotely located probes.
  • ItemOpen Access
    Performance and lifetime simulation of ion thruster optics
    (Colorado State University. Libraries, 2007) Farnell, Cody Coffman, author; Williams, John D., advisor; Wilbur, Paul J., advisor
    A simulation code, ffx, was developed to study various aspects of ion thruster optics. Information concerning sheaths, impingement limits, perveance, electric potential, charge exchange, and sputtering is covered. Electron backstreaming and pit and groove wear are discussed in detail as two grid failure mechanisms. The code was used to study the effects of several parameters on grid performance and lifetime, including grid spacing, aperture diameter, and grid thickness. An evolutionary algorithm was used with the ffx code to design grid sets, utilizing net accelerating voltage and current density as primary input parameters. Validation of the ffx code was accomplished through comparison to other ion optics codes and to experimental data obtained from both gridlet and full thruster testing. Gridlet test comparisons included simulations of finite aperture grid sets. The NSTAR thruster was studied in detail with regard to lifetime. The methods used for accurate and efficient optics simulation are discussed, including the multigrid method for solving for electric potential.
  • ItemOpen Access
    Laser ignition for internal combustion engines via fiber optic delivery
    (Colorado State University. Libraries, 2009) DeFoort, Morgan, author; Yalin, Azer, advisor; Willson, Bryan, advisor
    In the effort to reduce emissions and improve the efficiency of Otto cycle engines, the ignition system is often a limiting factor. Many "high energy" ignition systems have been developed, but almost all of these are based on traditional electric arc spark plugs. Laser ignition represents a fundamentally different approach to igniting gas mixtures and opens the door to improvements in fuel-lean engine operation and high-pressure combustion environments. Yet the promise of laser ignition remains unexploited, as practical systems have not been developed. In this contribution, we work towards the goal of developing a practical laser ignition system for stationary natural gas engines. Specifically, we focus on fiber optic delivery of the laser beam to the engine, thereby making a significant advance relative to past open-air (free-space) configurations. A combination of modeling and experimentation has been used to develop the needed fiber optic delivery systems, culminating in the first demonstration of fiber-optically delivered laser ignition on an engine.
  • ItemOpen Access
    Extending the performance of net shape molded fiber reinforced polymer composite valves for use in internal combustion engines
    (Colorado State University. Libraries, 2007) Buckley, Richard Theodore, author; Stanglmaier, Rudolf, advisor; Radford, Donald, advisor
    Fiber Reinforced Composite (FRC) materials offer the possibility of reduced mass and increased structural performance over conventional metals. When used in reciprocating components of internal combustion engines, this may enable increased power and mechanical efficiency. Previously published work on FRC engine valves has both shown structural and thermal limitations.
  • ItemOpen Access
    Expanding the knock/emissions limits for the realization of ultra-low emissions, high-efficiency heavy-duty natural gas engines
    (Colorado State University. Libraries, 2023) Rodriguez Rueda, Juan Felipe, author; Olsen, Daniel B., advisor; Windom, Bret, committee member; Baker, Daniel, committee member; Quinn, Jason, committee member
    Heavy-duty on-highway natural gas (NG) engines are a promising alternative to diesel engines to reduce greenhouse gas and harmful pollutant emissions if the limitations (knock and misfire) for achieving diesel-like efficiencies are addressed. This study shows innovative technologies for developing high-efficiency stoichiometric, spark-ignited (SI) natural gas engines. To develop the base knowledge required to reach the desired efficiency, a Single Cylinder Engine (SCE) is the most effective platform for acquiring reliable and repeatable data. An SCE test cell was developed using a Cummins 15-liter six-cylinder heavy-duty engine block modified to fire one cylinder (2.5-liter displacement). A Woodward Large Engine Control Module (LECM) is integrated to permit real-time advanced combustion control implementation. Fixed location of 50% burn and Controlled End Gas Auto-Ignition (C-EGAI) were used to define the ignition timing. C-EGAI allows operation with an optimized fraction of end gas auto-ignition combustion. Intake and exhaust characteristics, fuel composition, and exhaust gas recirculated substitution rate (EGR) are fully adjustable. A high-speed data acquisition system acquires in-cylinder, intake, and exhaust pressure for combustion analysis. Further development includes advanced control methodologies to maintain stable operation and higher dilution tolerance. Controlled end-gas autoignition (C-EGAI) is used as a combustion control strategy to improve efficiency. A Combustion Intensity Metric (CIM) is used for ignition control while operating the engine under C-EGAI. During the baseline testing of the developed SCE test cell, effective control of intake manifold pressure, exhaust manifold pressure, engine equivalence ratio, speed, torque, jacket water temperature, and oil temperature was demonstrated. The baseline testing shows reliable and consistent results for engine thermal efficiency, indicated mean effective pressure (IMEP), and coefficient of variance of the IMEP over a wide range of operating conditions. High Brake Thermal Efficiency (BTE) was achieved using improved hardware and a high EGR rate. Due to the correlation of CIM to the fraction of EGAI (f-EGAI), CIM was used as the reference variable to implement C-EGAI. Achieving conditions of C-EGAI allowed for the utilization of high EGR at high IMEP without inducing knock. The operation of the engine under these conditions showed peak brake thermal efficiency above 46% using an EGR ratio of 30% The work described proves the concept of using new and innovative control algorithms and CFD-optimized combustion chamber designs, allowing ultra-high efficiency and low emissions for NG ICE's heavy-duty on-road applications.
  • ItemOpen Access
    Modeling deformation twinning in BCC transition metals
    (Colorado State University. Libraries, 2023) Faisal, Anik H. M., author; Weinberger, Christopher, advisor; Radford, Donald, committee member; Ma, Kaka, committee member; Heyliger, Paul, committee member
    Deformation twinning is one of the important deformation mechanisms in body centered cubic (BCC) transition metals, especially under low temperature and high strain rate conditions. Plastic deformation via deformation twinning has been studied for decades both experimentally and computationally however, atomic level insights such as critical nuclei size, their local atomic structures and energetics which are important parameters in modeling twin nucleation has been lacking. In this work, deformation twins in BCC transition metals and their atomic level structures and energetics have been rigorously studied to reveal the full atomic level details of twin nucleation and propagation. As such, critical thickness of deformation twins in BCC transition metals have been a topic of debate with many computational and experimental studies accepting a three-layer twin thickness based on nucleation from a screw dislocation without proof whereas recent in-situ experiments suggest six-layer thick twin nuclei observed via High resolution transmission electron microscopy (HRTEM). In this study, we have determined the critical twin nuclei thickness in these metals using atomistic simulations to examine atomic structure and energetics of deformation twins under both zero and nonzero finite pure shear stresses. Our study reveals that twins in group VB BCC transition metals nucleate as two-layer thick nuclei under stress as opposed to the three-layer thick twin nuclei under zero stress. For group VIB BCC transition metals, for both zero and nonzero stresses, the critical twin nuclei thickness is two layer near reflection. As the twins grow and stress is relieved, twins under finite stresses adopt configurations that are much closer to the zero stress stability predictions. In addition to nucleation, growth of mechanisms of twins are explored and computational insights into the growth of twins in Tungsten bicrystals explaining multi-layer growth as opposed to layer-by-layer growth associated with small barriers. Free-end string simulations were used to investigate energy barrier associated with homogeneous twin nucleation using embedded atom method (EAM) potentials. Since homogeneous twin nucleation occurs near the ideal strengths of the material described by the potentials, energy barrier calculations were not possible for all BCC transition metals as some available potentials break down under large stresses. Moreover, density functional theory (DFT) simulations are known to be more accurate in describing atomic bonding but direct nucleation simulations in bulk crystals is prohibitively expensive. Hence, existing dislocation nucleation models are thoroughly analyzed to examine the behavior of these models near ideal strength of the material because spontaneous nucleation of dislocations occurs at high stresses. From there, a robust homogeneous twin nucleation model that includes elastic interaction among the twinning dislocation loops is developed which is able to replicate energy barrier data from free-end string simulations for multiple interatomic potentials. This model takes atomistic simulation inputs such as the concurrent twinning generalized stacking fault (GSF) energy curves and corresponding burgers vector of the twinning dislocations to compute the energy barriers as a function of applied stress. This model can be useful in modeling homogeneous twin nucleation all BCC transition metals and has the potential advantage of using DFT simulation inputs for accurate description of atomic bonding within the twin nuclei. Finally, nucleation stresses for twinning in bulk crystals have been studied to investigate whether the formation of twinning in experimental studies were initiated by homogeneous nucleation. Upper and lower bounds of stress values required for homogeneous twin nucleation has been computed and a semi-empirical model has been developed to predict homogeneous twin nucleation stresses as a function of temperature and strain rate. This analysis shows that reported critical resolved shear stress (CRSS) values in experimental studies are not associated with homogeneous twin nucleation despite some modeling studies claiming otherwise.
  • ItemOpen Access
    Diagnostics and characterization of direct injection of liquified petroleum gas for development of spray models at engine-like conditions
    (Colorado State University. Libraries, 2023) Sharma, Manav, author; Windom, Bret, advisor; Yalin, Azer, committee member; Yost, Dylan, committee member
    Research within the realm of internal combustion (IC) engines is concentrated on enhancing fuel efficiency and curbing tailpipe emissions, particularly CO2 and regulated pollutants. Promising solutions encompass the utilization of direct injection (DI) and alternative fuels, with liquefied petroleum gas (LPG) standing out as a notable candidate. LPG presents a pragmatic and economical option for fueling the heavy-duty transportation sector in the United States. However, widespread adoption hinges on achieving energy conversion efficiencies in LPG engines comparable to those in diesel engine platforms. The overarching goal of this research is to address fundamental limitations to achieving or surpassing near-diesel efficiencies in heavy-duty on-road liquefied petroleum gas engines. Owing to substantial differences in physical properties compared to traditional fuels, an enhanced understanding and modeling of LPG sprays become imperative. This work conducts an experimental and numerical analysis of direct-injected propane and iso-octane, serving as surrogates for LPG and gasoline, respectively, under diverse engine-like conditions. The overall objective is to establish a baseline for the fuel delivery system required in future high-efficiency DI-LPG heavy-duty engines. Propane, emulating LPG, undergoes injection across various engine-like conditions, encompassing early and late injections, as well as boosted engines, using a range of direct injectors available in both research and commercial domains. Optical diagnostics, including high-speed schlieren and planar Mie scattering imaging, were performed to study the spray penetration, liquid and vapor phase regions, and mixing of propane and to characterize bulk and the plume-specific spray behavior of propane. The study also investigates the influence of injector geometry on spray performance. Iso-octane was used as a surrogate for gasoline, and propane was used to compare LPG's behavior with more conventional DI fuel. The experimental results and high-fidelity internal nozzle-flow simulations were then used to define best practices in computational fluid dynamics (CFD) Lagrangian spray models. Optical imaging revealed that, unlike iso-octane, propane's spray propagation was fed by its flash boiling, spray collapse, and a high degree of vaporization, resulting in a direct proportionality of propane's penetration length to temperature. These unique attributes categorize propane as an unconventional spray, necessitating corrections to injection and breakup models to replicate under-expanded jet dynamics and emulate flash boiling-driven spray development across various research and commercial injectors.
  • ItemEmbargo
    Informing methane emissions inventories using facility aerial measurements at midstream natural gas facilities
    (Colorado State University. Libraries, 2023) Brown, Jenna A., author; Windom, Bret, advisor; Zimmerle, Daniel, advisor; Blanchard, Nathaniel, committee member
    Increased interest in greenhouse gas (GHG) emissions, including recent legislative action and voluntary programs, has increased attention on quantifying, and ultimately reducing, methane emissions from the natural gas supply chain. While inventories used for public or corporate GHG policies have traditionally utilized bottom-up (BU) methods to estimate emissions, the validity of such inventories has been questioned. To align with climate initiatives, multiple reporting programs are transitioning away from BU methods to utilizing full-facility measurements using airborne, satellite or drone (top-down (TD)) techniques to inform, improve, or validate inventories. This study utilized full-facility estimates from two independent TD methods at 15 midstream natural gas facilities in the U.S.A., and were compared with a contemporaneous daily inventory assembled by the facility operator, employing comprehensive inventory methods. Methods produced multiple full-facility methane estimates at each facility, resulting in 801 individual paired estimates (same facility, same day), and robust mean estimates for each facility. Mean estimates for each facility, aggregated across all facilities, differed by 28% [10% to 43%] for the first deployment and nearly 2:1 (49% [32% to 68%]) the second deployment. Estimates from the two TD methods statistically agreed in 12% (97 of 801) of the paired measurements. These data suggest that one or both methods did not produce accurate facility-level estimates, at a majority of facilities and in aggregate across all facilities. Operator inventories, which included extensions to capture sources beyond regular inventory requirements and to integrate local measurements, estimated significantly lower emissions than the TD estimates for 96% (1535 of 1589) of the paired comparisons. Significant disagreement is observed at most facilities, both between the two TD methods and between the TD estimates and operator inventory. Overall results were coupled with two case studies where TD estimates at two pre-selected facilities were coupled with comprehensive onsite measurements to understand factors driving the divergence between TD and BU inventory emissions estimates. In 3 of 4 paired comparisons between the intensive onsite estimates and one of the TD methods, the intensive on-site work did not conclusively diagnose the difference in estimates. In these cases, the preponderance of evidence suggests that the TD methods mis-estimate emissions an unknown fraction of the time, for unknown reasons. The results presented here have two implications. Firstly, these findings have important implications for the construction of voluntary and regulatory reporting programs that rely on emission estimates for reporting, fees or penalties, or for studies using full-facility estimates to aggregate TD emissions to basin or regional estimates. Secondly, the TD full-facility measurement methods need to undergo further testing, characterization, and potential improvement specifically tailored for complex midstream facilities.
  • ItemOpen Access
    Advanced photovoltaic module architecture for high value recycling and lower cost
    (Colorado State University. Libraries, 2023) Ruhle, Ryan J. E., author; Sampath, Walajabad, advisor; Sites, James, committee member; Weinberger, Crhis, committee member
    As climate concerns continue to bolster solar energy production, the need to consider how solar panels are treated at end of life as well as the cost of solar panel production is becoming a more significant issue. Traditionally, Crystalline Silicon (c-Si) solar panels are made by laminating solar cells with glass under high heat and high mechanical pressure. The most common material used for this lamination between the glass and the c-Si solar cell is Ethylene Vinyl Acetate (EVA), a copolymer of ethylene and vinyl acetate. The first and primary issue is that it requires high temperature and a significant amount of pressure to be adhered to both the glass and the c-Si cell. Another related issue is that the c-Si cell and EVA encapsulant do not have the same thermal expansion coefficients. This leads to stresses which can cause the formation and growth of microcracks which can hinder performance and reliability of the effected solar cells. End-of-life recycling is also significantly hampered by cross-linking of EVA. The Materials Engineering Laboratory (MEL) has long worked on vacuum lamination free module architectures, though this has been primarily for use for Cadmium Telluride (CdTe) solar panels. These CdTe panels have passed IEC 61215 tests and have been applied in the field. These Edge-sealed photovoltaics modules based on Insulating Glass (IG) industry technology have many advantages including lower cost, improved manufacturability, increased durability, and enable high-value recycling with the potential for material reuse. The edge-sealed modules eliminate EVA (Ethylene Vinyl Acetate) lamination, but a gap filled with air or inert gas between the glass and solar cell increases optical reflection losses. The use of edge sealed modules for c-Si was explored in this study. A prototype manufacturing system (2 ft X 4 ft substrates) has been developed at MEL and was used in this study. Many c-Si modules were fabricated with edge sealing and were studied at the National Renewable Energy Laboratory (NREL) in various tests including accelerated tests. These studies have shown that optical reflection losses can be reduced by using nanostructures made from acrylic polymers. The nanostructures are produced by hot embossing which is intrinsically a low-cost process. The edge sealed structure has demonstrated extreme robustness to moisture ingress (5000 hrs. vs 1000 hrs. in damp heat), improved mechanical robustness, significant reduction in Potential Induced Degradation (PID), survive thermal cycling and small manufacturing footprint (80% less) while improving module reliability. The edge sealed modules have demonstrated high value recycling of the components and have the potential to make recycling of c-Si PV modules economical.
  • ItemOpen Access
    Hydrogen-natural gas fuel blending and advanced air fuel ratio control strategies in a "rich burn" engine with 3-way catalyst
    (Colorado State University. Libraries, 2023) Katsampes, Nicholas, author; Olsen, Daniel B., advisor; Thorsett-Hill, Karen, committee member; Sharvelle, Sybil, committee member
    Interest in hydrogen (H2) fuels is growing, with industry planning to produce it with stranded or excess energy from renewable sources in the future. Natural gas (NG) utility companies are now taking action to blend H2 into their preexisting pipelines to reduce greenhouse gas (GHG) emissions from burning NG. "Rich burn" (stoichiometric) engines with 3-way catalysts are not typically used with H2-NG blending; however, many of these engines operate on pipeline NG and will receive blended fuel as more gas utilities expand H2 production. These engines are typically chosen for their low emissions owing to the 3-way catalyst control, so the focus of this paper is on the change in emissions like carbon monoxide (CO) and nitrogen oxides (NOx) as the fuel is blended with up to 30% H2 by volume. The Caterpillar CG137-8 natural gas engine used for testing was originally designed for industrial gas compression applications and is a good representative for most "rich burn" engines used across industry for applications such as power generation and water pumping. Results indicate a significant reduction in greenhouse gas (GHG) emissions as more H2 is added to the fuel. Increasing H2 in the fuel changes combustion behavior in the cylinder, resulting in faster ignition and higher cylinder pressures, which increase engine-out NOx emissions. Pre-catalyst emissions behave as expected; CO decreases and NOx increases. Unexpectedly, post-catalyst CO and NOx both decrease slightly with increasing H2 while operating at the optimal "air-fuel" equivalence ratio (λ or "lambda"). This testing shows that a "rich burn" engine with 3-way catalyst can tolerate up to 30% H2 (by vol.) while still meeting NOx and CO emissions limits. However, this research found that at elevated levels of H2, increased engine-out NOx emissions narrow the λ range of operation. As H2 is added to NG pipelines, some "rich burn" engine systems may require larger catalysts or more precise λ control to tolerate the increased NOx production associated with a H2-NG blend. This paper includes additional investigation into transitioning H2 concentrations. Sudden step-increases in H2 cause dramatic changes in λ, resulting in large emissions of post-catalyst NOx during the transition. Comparable changes in H2 at elevated concentrations cause larger spikes in NOx than at lower concentrations. The amount of post-catalyst NOx produced during a step-transition is influenced by the engine controller and how quickly it adapts to the change in λ. Better tuned engine controllers respond more quickly and produce less NOx during H2 step-transitions. This research shows that some engines can violate NOx emissions limits with as little as a 5% increase in H2 due to slow engine controller response.
  • ItemEmbargo
    Development of an artificial temporomandibular joint disc replacement
    (Colorado State University. Libraries, 2023) Kuiper, Jason Paul, author; Puttlitz, Christian M., advisor; Prawel, David, committee member; McGilvray, Kirk, committee member; Henry, Charles, committee member
    The temporomandibular joint (TMJ) is a complex bilateral ginglymoarthroidal joint containing a fibrocartilaginous disc and is essential for chewing, speaking, and swallowing. Due to the high loading frequency, small imbalances in joint homeostasis can overcome the natural capacity for adaptation and lead to a cascade of degenerative changes. For progressive TMJ disorders, resection of the TMJ disc is the leading treatment, but disc resection inherently increases stress and friction on the articular cartilage surfaces, leading to a progression to total joint replacement in 11.7% of patients. The current methods of treatment for disorders of the TMJ musculoskeletal complex are predominantly palliative and do not reliably address disorders of arthrogenous origin. Unfortunately, no synthetic TMJ disc replacements currently exist due to profound implant failures in earlier attempts. Introduction of a robust artificial TMJ disc replacement after resection will prevent further joint degradation and improve patient outcomes. Rigorous preclinical evaluation of artificial TMJ disc replacement strategies must be conducted to support future translation to humans. Therefore, the following aims are proposed: (1) Characterize the biomechanical behavior of the ovine temporomandibular joint soft tissues, (2) identify and evaluate a material candidate for a temporomandibular joint disc replacement, (3) develop in silico and in vitro methods for evaluating design candidates for artificial TMJ disc replacement, and (4) implement a temporomandibular joint disc replacement strategy in an ovine model.
  • ItemOpen Access
    Synthesis, properties, and suitability of various oxymethylene ethers for compression ignition fuels
    (Colorado State University. Libraries, 2023) Lucas, Stephen P., author; Windom, Bret, advisor; Foust, Thomas, committee member; Reardon, Kenneth, committee member; Marchese, Anthony J., committee member
    Compression ignition (CI) engines are currently the most common prime mover for medium and heavy duty vehicles; these engines contribute roughly a quarter of US greenhouse gas emissions from transportation, and even higher percentages of particulate and nitrogen oxide emissions. As a result, there have been significant efforts made to reduce these emissions, particularly through selection of low-emissions alternative fuels. Oxymethylene ethers (OMEs) are a class of molecule, typically structured R-O-(CH2O)n-R', which have been considered as a possible blendstock in CI fuels for the goal of soot reduction. Generally, past work has focused on methyl-terminated OMEs, CH3-O-(CH2O)n-CH3, which by virtue of containing no C--C bonds, produce negligible soot. These molecules show significant reductions in soot emission from engines when blended in moderate to high ratios with traditional diesels, however, they have been shown to have inferior physical properties and poor compatibility with some legacy systems. Recent theoretical work has shown that OMEs with non-methyl alkyl groups may have superior performance, albeit at the cost of increased soot formation. In this work, a variety of OMEs with terminating alkyl groups from methyl to butyl are considered for their suitability as CI fuels. The synthesis of these extended OMEs is studied, including formation of n=1 OMEs from common chemical sources, and extension of the chain length to heavier molecules, via reactions over acidic ion exchange resins. Following the synthesis, the properties of these OMEs are studied with respect to their engine applicability. It is found that heavier (propyl- and butyl-terminated) OMEs have superior properties for diesel compatibility, particularly in reactivity, volatility, and water solubility. Extended-alkyl OMEs are found to have higher soot production than methyl-terminated OMEs, but remain superior to diesel soot production on a per-unit-energy basis. A sample of a butyl-terminated OME mixture, n=2-4, is selected as the ideal OME blend for close compatibility with legacy diesel systems. This mixture is blended with certified diesel and tested for ASTM D975 compatibility, passing all required tests but lubricity; decreased heat of combustion is observed but not governed by the diesel standard. Fundamental combustion tests of various mid-weight OMEs are performed in a rapid compression machine, where it is shown that low-temperature chemistry causes a region of decreased dependence of ignition delay on temperature, consistent with methyl-terminated OME behavior. An isopropyl-terminated OME is observed to have low reactivity compared to other OMEs; this fuel is investigated via further rapid compression machine testing and CFR engine testing. It is found that this OME has strong negative-temperature-coefficient ignition behavior - a first for OMEs - and has reactivity lower than other OMEs, but insufficient for direct spark ignition engine testing.
  • ItemOpen Access
    Environmental and economic evaluation of algal-based biofuels through geographically resolved process and sustainability modeling
    (Colorado State University. Libraries, 2023) Quiroz, David, author; Quinn, Jason C., advisor; Windom, Bret, committee member; Willson, Bryan, committee member; Reardon, Kenneth, committee member
    Advanced algal renewable fuels have been the subject of extensive research during the last decades. Their advantages over conventional biofuel feedstocks position algal biomass as a promising feedstock for the development of a sustainable and circular bioeconomy. Despite recent technological improvements, techno-economic analyses (TEAs) show that algae-derived fuels fail to be cost-competitive with petroleum fuels. Moreover, results from life-cycle assessments (LCAs) indicate declining greenhouse gas emissions when compared to petroleum fuels, but their water, health and air pollution impacts are still uncertain. This is explained by the fact that most published TEAs and LCAs of algal systems are not supported by high-resolution models and can only provide average sustainability metrics based on results from restricted data sources. These assessments often lack the resolution to correctly analyze the temporal and regional variations of biomass yields which have a direct impact on TEA and LCA metrics. Based on the current state of the field, there is a critical need to develop dynamic models that can inform sustainability assessments and consequently assist decision-making and technology development. This first part of this research work focuses on establishing the foundations for spatially explicit and temporally resolved LCA and TEA by developing and validating models that capture the thermal and biological dynamics of open algal cultivation systems. The modeling work is heavily focused on providing accurate predictions of evaporation losses in open algae raceway ponds and investigating the effects of evaporation rates on pond temperatures and growth rates. To date, this is the first modeling effort focused on predicting the evaporation losses of open algal ponds at the commercial scale. The outputs from the thermal model are then used to inform a biological algae growth model that is validated with experimental data representing the current biomass productivity potential. When integrated with hourly historical weather data, the modeling tools provide spatiotemporal mass and energy balances of the algal cultivation, dewatering, and conversion to fuel processes. These results are then leveraged with sustainability tools such as LCA and TEA to provide sustainability metrics at a high temporal and spatial scale. After developing a robust modeling framework, the modeling tool is leveraged with two distinct water LCA methods to provide a comprehensive assessment of the water impacts of algae-derived renewable diesel production across the United States. First, a water footprint analysis is conducted to understand the direct freshwater and rainwater consumption of algal cultivation and provide a framework for comparison to traditional biofuel feedstocks. The second method provides a county-level water scarcity footprint by analyzing the impact of algal systems on local water demand and availability. This assessment allows for the proper identification of potential algal sites for algal cultivation and locations where the deployment of algal systems will exacerbate local water stress. Ultimately, this research chapter provides the first holistic investigation of the water consumption and environmental water impacts of algal systems across the U.S. and establishes benchmarks for comparison to other fuels. Finally, the work comprising the third research chapter includes a novel global sustainability assessment that integrates the developed process modeling framework with regional-specific TEA and LCA. The spatially explicit TEA considers regional labor costs, construction factors, and tax rates to assess the economic viability of algal biofuels across 6,685 global locations. Similarly, a well-to-wheels LCA was performed by accounting for the regional life cycle impacts associated with electricity generation, hydrogen, and nutrient production across ten different environmental categories including health, air pollution, and climate impacts. This framework enables the identification of algal sites with optimal productivity potential, environmental impacts, and economic viability. Discussion focuses on the challenges and opportunities to reduce costs and environmental impacts of algal biofuels in various global regions.
  • ItemOpen Access
    Economic and environmental evaluation of emerging electric vehicle technologies
    (Colorado State University. Libraries, 2023) Horesh, Noah, author; Quinn, Jason, advisor; Bradley, Thomas, committee member; Jathar, Shantanu, committee member; Willson, Bryan, committee member
    As the transportation sector seeks to reduce costs and greenhouse gas (GHG) emissions, electric vehicles (EVs) have emerged as a promising solution. The continuous growth of the EV market necessitates the development of technologies that facilitate an economically comparable transition away from internal combustion engine vehicles (ICEVs). Moreover, it is essential to incorporate sustainability considerations across the entire value chain of EVs to ensure a sustainable future. The sustainability of EVs extends beyond their usage and includes factors such as battery production, charging infrastructure, and end-of-life management. Techno-economic analysis (TEA) and life cycle assessment (LCA) are key methodologies used to evaluate the economic and environmental components of sustainability, respectively. This dissertation work uses technological performance modeling combined with TEA and LCA methods to identify optimal deployment strategies for EV technologies. A major challenge with the electrification of transportation is the end of life of battery systems. A TEA is utilized to assess the economic viability of a novel Heterogeneous Unifying Battery (HUB) reconditioning system, which improves the performance of retired EV batteries before their 2nd life integration into grid energy storage systems (ESS). The modeling work incorporates the costs involved in the reconditioning process to determine the resale price of the batteries. Furthermore, the economic analysis is expanded to evaluate the use of HUB reconditioned batteries in a grid ESS, comparing it with an ESS assembled with new Lithium-ion (Li-ion) batteries. The minimum required revenue from each ESS is determined and compared with the estimated revenue of various grid applications to assess the market size. The findings reveal that the economical market capacity of these applications can fully meet the current supply of 2nd life EV batteries from early adopters in the United States (U.S.). However, as EV adoption expands beyond early adopters, the ESS market capacity may become saturated with the increased availability of 2nd life batteries. Despite the growing interest in EVs, their widespread adoption has been hindered, in part, by the lack of access to nearby charging infrastructure. This issue is particularly prevalent in Multi-Unit Dwellings (MUDs) where the installation of chargers can be unaffordable or unattainable for residents. To address this, TEA methodology is used to evaluate the levelized cost of charging (LCOC) for Battery Electric Vehicles (BEVs) at MUD charging hubs, aiming to identify economically viable charger deployment pathways. Specifically, multiple combinations of plug-in charger types and hub ownership models are investigated. Furthermore, the total cost of ownership (TCO) is assessed, encompassing vehicle depreciation, maintenance and repair, insurance, license and registration, and LCOC. The study also conducts a cradle to grave (C2G) LCA comparing an average passenger BEV and a gasoline conventional vehicle (CV) using geographical and temporal resolution for BEV charging. The TCO is coupled with the C2G GHG emissions to calculate the cost of GHG emissions reduction. The analysis demonstrates that MUD BEVs can reduce both costs and GHG emissions without subsidies, resulting in negative costs of GHG emissions reduction for most scenarios. However, charging at MUDs is shown to be more expensive compared to single-family homes, potentially leading to financial inequities. Additional research is required to assess the advantages of public charging systems and commercial EVs. While home charging is typically the primary option for EVs, public charging infrastructure is necessary for long-distance travel and urgent charging. This is especially important for commercial vehicles, which rely on public charging to support their operational requirements. Various charging systems have been proposed, including Direct Current Fast Charging (DCFC), Battery Swapping (BSS), and Dynamic Wireless Power Transfer (DWPT). This work includes a comparison of the TCO and global warming potential (GWP) of EVs of various sizes, specifically examining the charging systems utilized to determine precise location-specific sustainability outcomes. Nationwide infrastructure deployment simulations are conducted based on the forecasted geospatial and temporal demand for EV charging from 2031 to 2050. The TEA and LCA incorporate local fuel prices, electricity prices, electricity mixes, and traffic volumes. To account for the adaptability of variables that highly influence TCO and GWP, optimistic, baseline, and conservative scenarios are modeled for EV adoption, electricity mixes, capital costs, electricity prices, and fuel prices. The change to TCO by switching from ICEVs to EVs is shown to vary across scenarios, vehicle categories, and locations, with local parameters dramatically impacting results. Further, the EV GWP depends on local electricity mixes and infrastructure utilizations. This research highlights the dynamic nature of EV benefits and the potential for optimal outcomes through the deployment of multiple charging technologies. In conclusion, this research underscores the significance of strategically deploying EV charging infrastructure and utilizing retired EV batteries for grid energy storage. Instead of posing a challenge at end of life, these batteries are shown to be a solution for grid energy storage. The study also highlights the economic advantages of different charging infrastructure types for EVs and their role in driving EV adoption, resulting in potential GHG emissions reductions and consumer savings. Ultimately, widespread EV adoption and decarbonization of electrical grids are pivotal in achieving climate goals.