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  • 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.
  • ItemOpen Access
    Reduction of methane emissions through in-cylinder methods on a lean-burn four-stroke natural gas engine
    (Colorado State University. Libraries, 2023) Bayer, Justin, author; Olsen, Daniel, advisor; Windom, Bret, committee member; Carlson, Kenneth, committee member
    The U.S. utilizes over 27 trillion cubic feet of natural gas per year for a wide range of uses, including heating and electricity production, according to the U.S. Energy Information Administration. Natural gas (NG) engines used to compress natural gas and generate electricity account for nearly one-quarter of the total methane emissions in the gathering and boosting sector. These methane emissions are referred to as fuel (methane) slip since they originate from the engine fuel supply and result from incomplete combustion. The primary mechanism leading to unburned methane is related to the engine crevice volume. The crevice volume is the region between the side of the piston and the cylinder wall. This region is particularly difficult for the flame to propagate into because the gap is generally smaller than the quench distance. This research evaluates multiple in-cylinder methods to attempt to reduce the methane slip. One of the mitigation strategies is hydrogen blending with the engine's natural gas fuel supply as a means of methane reduction. Converge Computational Fluid Dynamics (CFD) and a Caterpillar G3516J model are implemented to analyze the effects of hydrogen blending. The G3516J engine is a lean-burn engine commonly used for gas compression in the US NG pipeline system. Converge CFD is a solver that couples combustion chemistry and adaptive mesh refinement to model combustion accurately. Simulations of combustion with NG-hydrogen blended fuel are performed with constant fuel energy, achieved by adjusting boost pressure at a constant equivalence ratio. Combustion cycle simulations are performed at various hydrogen blending levels, and the methane emissions are evaluated at the end of the cycle and compared. In addition, the fuel mixtures' pressure is adjusted to reflect similar indicated power and a similar emission comparison is made. The second mitigation strategy that is explored is induced autoignition. This strategy involved advancing the engine's spark timing to hopefully increase the temperature and pressure in the cylinder to have the end-gas auto-ignite and thus burn more fuel that would otherwise become methane slip. This research also incorporates installing a G3516J engine at the Engines and Energies Conversion Laboratory. Advancing the spark timing in the simulations did not show signs of end gas auto-ignition. Although this is the case, the advanced spark timing showed a decrease in unburned methane compared to the baseline. The spark timing with the lowest unburned CH4 percentage decreases from 3.00% to 2.26% by advancing the spark timing by ten crank angle degrees. The hydrogen blending also showed lower unburned CH4 percentages compared to the baseline. After adjusting the simulations to match indicated power output, the lowest results decreased the unburned percentage from 3.00% to 1.20%. NOx emissions were increased by 129% compared to the baseline in the most extreme simulation case. Leaning the fuel mixture lowered the NOx emissions to within 6% of the baseline while still lowering the unburned percentage from 3.00% to 2.67%.
  • ItemOpen Access
    Optimizing energy conversion efficiency of a proton exchange membrane green hydrogen generation system while incorporating balance of plant modeling
    (Colorado State University. Libraries, 2023) Landin, Nikolas, author; Windom, Bret, advisor; Bradley, Thomas, committee member; Montgomery, David, committee member
    Hydrogen has the potential to decarbonize several difficult to decarbonize sectors of the U.S. energy economy such as medium- and heavy-duty transportation, energy storage, and industrial processes such as steel making. Currently most of the hydrogen produced globally is produced with steam methane reforming and has a carbon intensity associated with partially burning natural gas. An alternative way of producing hydrogen is using electrolysis and renewable energy to split water into hydrogen and oxygen. Hydrogen produced in this way is called "green" hydrogen. The devices that are used to produce green hydrogen are electrolyzers and the most prominent type of electrolyzer today is the proton exchange membrane (PEM) electrolyzer. Most PEM systems are designed for continuous operation with a constant input of electricity. When PEM electrolyzers are coupled with renewable energy such as wind turbines and solar photovoltaics, the input electricity to the electrolyzer may follow the same variable and intermittent profile as renewable energy generation. System modeling while including balance of plant components can be used to optimize the green hydrogen generation system for the highest energy conversion efficiency across the range of possible operating conditions with renewable energy input. This work is focused on creating a system model of a PEM green hydrogen generation system including the balance of plant components such as power electronics, electrolyzer stack, hydrogen purification, hydrogen compression/storage, and system cooling. Literature primarily focuses on modeling the electrolyzer stack and ignores the balance of plant components. Some recent publications create system models with the balance of plant included but are unnecessarily complex. The model created in this work includes the balance of plant and reduces the complexity of recently published balance of plant models while maintaining the model's functionality in system optimization studies. Limited experimental data available in literature is used to verify and validate the model. The model is scaled to represent a utility scale system which would include multiple electrolyzer stacks and power electronics. A case study of wind and solar generation in Texas is used to demonstrate the model's capability in optimization studies. The model results show the effects of varying operating conditions such as electrolyzer cathode pressure and electrolyzer current density on the overall system efficiency for a single 120-kW electrolyzer green hydrogen generation system. At low electrolyzer power, the system energy conversion efficiency drops off significantly which is mainly driven by the increase in specific hydrogen loss in the balance of plant. Increasing the electrolyzer cathode pressure decreases the system efficiency and operating range but may provide benefit by allowing the hydrogen compressor to be removed from the system. Two different electrolyzer "loading" strategies were imposed on the multi-electrolyzer stack model with the Texas case study and show that there is a slight benefit in efficiency if the strategy maximizes the electrolyzer power and minimizes the amount of electricity that is wasted within the system. Other tradeoffs such as average electrolyzer power and the number of electrolyzer shutdowns are evaluated between the two loading strategies. If a minimum electrolyzer power is selected at 50% of the rated power, the parallel loading scheme produces 9,000 kg more hydrogen than the series loading scheme with the same input power profile. The model developed in this work is a valuable tool to optimize the production of green hydrogen by identifying and optimizing the interactions of different components within the system to maximize the energy conversion efficiency. Optimizing the green hydrogen generation system will improve the economic feasibility and accelerate the adoption of green hydrogen at a large scale.
  • ItemEmbargo
    Using prototypical sites to model methane emissions in Colorado’s Denver-Julesburg basin using mechanistic emissions estimation tool
    (Colorado State University. Libraries, 2023) Mollel, Winrose A., author; Olsen, Daniel B., advisor; Zimmerle, Dan, advisor; Baker, Dan, committee member; Quinn, Jason, committee member
    The BU methods estimate emissions by considering activity factors and emission factors averages for an extended period for a large area. Some TD methods use the ethane-methane ratio to attribute methane emissions from oil and gas facilities. The bottom-up (BU) inventory estimates are often used to drive the attribution of emissions indicated by TD data to different emission source categories. Despite widespread use, recent studies indicate that traditional bottom-up (BU) inventory methods do not adequately capture how variations in throughput and failure conditions impact gas composition and rate of emissions. Traditional BU methods typically do not model gas composition, although it differs among different facility configurations and impacts emissions from different equipment within one facility. Since most BU inventories utilize fixed emissions factors, emissions also do not scale due to throughput, which is particularly important for large emitters associated with failure conditions. Mechanistic emissions modeling can be used to address these shortcomings and make BU modeling more effective. This study illustrates how mechanistic modeling highlight changes in emissions due to variable throughput and equipment pressures and temperatures for the same production routed through the same or different production facility designs. The study uses the same mechanistic models to illustrate how the frequency of failure modes impacts both gas composition and total emissions. Results indicate mechanistic modeling could explain observed gas composition shifts in emitted emissions from production and midstream facilities over time, a key modeling input to improve voluntary and regulatory methane mitigation efforts.
  • ItemOpen Access
    Characterization of plasma conductivity by laser Thomson scattering in a high-voltage laser-triggered switch
    (Colorado State University. Libraries, 2023) Gottfried, Jacob A., author; Yalin, Azer P., advisor; Dumitrache, Ciprian, committee member; Rocca, Jorge, committee member
    High-voltage laser-triggered switches (HV-LTSs) are used in pulsed-power applications where low jitter and high current are required. The switches allow operation in the mega-ampere, megavolt regime while maintaining low insertion losses. Low inductance HV-LTS designs have shown discrepancies between modeled and experimental behavior, reinvigorating interest in the physics of HV-LTS operation. Detailed spatially- and temporally- resolved measurements of plasma properties within the switches could contribute to validating and advancing numeric models of these systems by checking the assumptions used in their derivation. To date, there is minimal experimental data detailing the evolution of plasma properties during switch operation. This work investigates HV-LTS plasma channel conductivity (the assumption within current models drawing the most critique) during the rising edge of the current pulse through both derivative (V-Dot) electrical probes and electron temperature measurements via laser Thomson scattering. A HV-LTS testbed utilizing an aqueous (variable impedance) resistive load was designed to produce experimental conditions found in larger pulsed power applications. This work describes the design of the load and experimental results under a variety of load conditions and operating voltages of 5 - 6 kV. The results indicate the electron temperature increases during the rising edge of the current pulse, suggesting that the plasma conductivity is temporally evolving. Further, electrical measurements show an increase in plasma conductivity during the rising edge of the current pulse. Evidence from both optical and electrical measurements calls into question the assumption of a temporally constant plasma conductivity as both the optical and electrical diagnostics show a temporally increasing plasma conductivity during the rising edge of the current pulse.
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    Hydrothermal surface modifications on titanium for biomedical applications
    (Colorado State University. Libraries, 2023) Manivasagam, Vignesh K., author; Popat, Ketul C., advisor; Cox-York, Kimberly, committee member; Walajabad, Sampath, committee member; Wang, Zhijie, committee member
    Titanium and its alloys are widely used in different biomaterial applications due to their remarkable mechanical properties and bio-inertness. However, titanium-based materials still face some challenges, with an emphasis on hemocompatibility. Blood-contacting devices such as stents, heart valves, and circulatory devices are prone to thrombus formation, restenosis, and inflammation due to inappropriate blood–implant surface interactions. After implantation, when blood encounters these implant surfaces, a series of reactions takes place, such as protein adsorption, platelet adhesion and activation, and white blood cell complex formation as a defense mechanism. Currently, patients are prescribed anticoagulant drugs to prevent blood clotting, but these drugs can weaken their immune system and cause profound bleeding during injury. Extensive research has been done to modify the surface properties of titanium to enhance its hemocompatibility. Results have shown that the modification of surface morphology, roughness, and chemistry has been effective in reducing thrombus formation. A simple hydrothermal treatments with different acidic/basic medium were investigated in this dissertation. The first treatment with sodium hydroxide and the second treatment with sulfuric acid. Hemocompatability, cytocompatibility and antibacterial properties of these surfaces were investigated. The results indicated that sodium hydroxide surface is suitable for orthopedic application and sulfuric acid surface with silane coating is highly suitable for blood contacting implant surface.
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    Advanced manufacturing of thermoset polymers and composites
    (Colorado State University. Libraries, 2023) Ziaee, Morteza, author; Yourdkhani, Mostafa, advisor; Radford, Donald W., committee member; James, Susan, committee member; Bailey, Travis, committee member
    Thermoset polymers and composites are lightweight materials extensively used in many industries from aerospace to automotive to prosthetics due to their excellent specific mechanical properties and high chemical resistance. However, these products are conventionally manufactured by labor-intensive processes using subtractive manufactured tooling or molds followed by thermal curing inside an oven or autoclave at elevated temperatures for several hours. Hence, conventional manufacturing approaches are energy- and time-consuming and require expensive equipment. Moreover, lack of design flexibility and poor repeatability are additional challenges, which limit the structural and functional capabilities of such products. In this dissertation, I present a novel approach to address the existing limitations in manufacturing thermosets and their composites by developing rapid curing resin systems and integrating them in additive manufacturing (AM) processes. In the first chapter, state-of-the-art manufacturing methods are reviewed and frontal polymerization (FP) as a promising curing strategy for rapid and energy-efficient manufacturing of thermosets and composites is introduced. In the second chapter, the effect of ambient conditioning and resin chemistry on thermal frontal polymerization of a high-performance resin system is explored. In the third chapter, FP is used to demonstrate, for the first time, simultaneous printing and curing of short carbon fiber-reinforced composites for high performance applications. In the following chapter, AM of a soft and stretchable elastomer with tunable thermomechanical properties manufactured via FP is discussed. In the fifth chapter, the printing process is further improved using an external localized heat source, instead of relying on the exothermic heat of polymerization of the resin, to accelerate the curing rate and make the printing process more robust and applicable to the manufacture of large-scale components. Finally in the last chapter, bubble-free frontal polymerization of polyacrylates is introduced for the developed 3D printing process.
  • ItemOpen Access
    Simulating cut to length forest treatment effects on fire behavior over steep slopes
    (Colorado State University. Libraries, 2023) Pittman, Kyle Tait, author; Jathar, Shantanu, advisor; Hoffman, Chad, advisor; Linn, Rod, committee member; Windom, Bret, committee member; Wei, Yu, committee member
    The increase of wildfire size and behavior in many western U.S. forests is due to increased fuel loads resulting from the past century's fire suppression, logging, and grazing policies of the 20th century, along with compounding climactic changes including increased drought and temperatures. Fuel hazard treatments are the key land management tool used to reduce fire intensity and severity however these treatments are often not possible on steep terrain of over 30% slope. Cable tethered cut to length machinery opens new avenues for managers to treat forests in steep slopes, but there is limited data on how effective the treatments will be. I conducted a numerical experiment using the wildfire model, FIRETEC, coupled with the atmospheric dynamics model, HIGRAD, to understand the complex interactions of wind, topography, and fire behaviors of two cut to length forest treatments on slopes of up to 60%. Results show that treatments can effectively reduce some fire behaviors such as heat release and canopy consumption when compared to untreated forests on slopes. However, increased sub canopy wind penetration along the slopes following treatments results in marginal fire severity reduction regarding biomass consumption and variable results on rates of spread. The results of these numerical experiments indicate that CTL treatment can effectively reduce some fire behavior and severity, however the effects were marginal and additional research is needed to better understand treatment's effects.
  • ItemOpen Access
    Secondary organic aerosol formation from volatile chemical product emissions: parameters and contributions to anthropogenic aerosol
    (Colorado State University. Libraries, 2023) Sasidharan, Sreejith, author; Jathar, Shantanu, advisor; Volckens, John, committee member; Pierce, Jeffrey, committee member
    Volatile chemical products (VCP) are an increasingly important source of hydrocarbon and oxygenated volatile organic compound (OVOC) emissions to the atmosphere, and these emissions are likely to play an important role as anthropogenic precursors for secondary organic aerosol (SOA). While the SOA from VCP hydrocarbons is often accounted for in ambient air quality models, the formation, evolution, and properties of SOA from VCP OVOCs remains uncertain. We use environmental chamber data and a kinetic model to develop SOA parameters for ten OVOCs representing glycols, glycol ethers, esters, oxygenated aromatics, and amines. Model simulations suggest that the SOA mass yields for these OVOCs are on the same magnitude as widely studied SOA precursors (e.g., long-chain alkanes, monoterpenes, and single-ring aromatics) and these yields exhibit a linear correlation with the difference between the carbon and oxygen numbers of the precursor. When combined with emissions inventories for two megacities in the United States (US) and a US-wide inventory, we find that VCPs form 0.8-2.5× as much SOA, by mass, as mobile sources. Hydrocarbons (terpenes, branched and cyclic alkanes) and OVOCs (terpenoids, glycols, glycol ethers) make up 60-75% and 25-40% of the SOA arising from VCP use, respectively. This work contributes to the growing body of knowledge focused on studying VCP VOC contributions to urban air pollution.
  • ItemOpen Access
    Multi-day evolution of organic aerosol mass and composition from biomass burning emissions
    (Colorado State University. Libraries, 2023) Dearden, Abraham C., author; Jathar, Shantanu, advisor; Bond, Tami, committee member; Pierce, Jeffrey, committee member
    Biomass burning is an important source of primary and secondary organic aerosol (POA, SOA, and together, OA) to the atmosphere. The photochemical evolution of biomass burning OA, especially over long photochemical ages, is highly complex and there are large uncertainties in how this evolution is represented in models. Recently, we performed photooxidation experiments on biomass burning emissions using a small environmental chamber (~150 L) to study the OA evolution over multiple equivalent days of photochemical aging. In this work, we use a kinetic, process-level model (SOM-TOMAS; Statistical Oxidation Model-TwO Moment Aerosol Sectional) to simulate the photochemical evolution of OA in 18 chamber experiments performed on emissions from 10 different fuels. A base version of the model was able to simulate the time-dependent evolution of the OA mass concentration and its oxygen-to-carbon ratio (O:C) at short photochemical ages (0.5 to 1 equivalent days) but substantially underestimated the enhancement in both metrics at longer photochemical ages (>1 equivalent day). The OA after several days of equivalent photochemical aging was dominated by SOA (58%, on average) with the remainder being POA (42%, on average). Semi-volatile organic compounds, oxygenated aromatics, and heterocyclics accounted for the majority (86%, on average) of the SOA formed. Experimental artifacts (i.e., particle and vapor wall losses) were found to be much more important in influencing the OA evolution than other processes (i.e., dilution, heterogeneous chemistry, and oligomerization reactions). Adjustments to the kinetic model seemed to improve model performance only marginally indicating that the model was missing precursors, chemical pathways, or both, especially to explain the observed enhancement in OA mass and O:C over longer photochemical ages. While far from ideal, this work contributes to a process-level understanding of biomass burning OA that is relevant for its evolution at regional and global scales.
  • ItemOpen Access
    Autoigntion and flame speed of premixed liquefied petroleum gas in a rapid compression machine: experimental results and reduced chemical kinetic mechanism
    (Colorado State University. Libraries, 2023) Slunecka, Colin, author; Olsen, Daniel, advisor; Marchese, Anthony, advisor; Windom, Bret, committee member; von Fischer, Joe, committee member
    Liquefied petroleum gas (LPG) has many properties that make it an attractive alternative fuel such as lower cost than conventional fuels and an established distribution infrastructure. The development of high efficiency, spark ignited LPG engines is currently limited by engine knock and misfire. The knock and misfire limits are further complicated by the wide range of chemical reactivity in LPG, particularly in international markets. In this study, a rapid compression machine (RCM) was used to characterize the effects of variation in LPG fuel reactivity, equivalence ratio, and exhaust gas recirculation (EGR) on the autoignition and flame speeds of LPG/oxidizer/inert/EGR blends. Experiments were conducted with 100% propane and blends of propane with propene, ethane, isobutane, or n-butane. EGR was simulated with mixtures of Ar, CO2, CO, and NO at substitution percentages from 0 to 30 mass percent. Equivalence ratio was varied from 0.75 to 1.5. Ignition delay period under homogeneous autoignition conditions was measured at compressed pressures and temperatures of 23 to 25 bar and 701 to 921 K, respectively. Laminar flame speeds and apparent heat release rates (AHRR) at 24 bar with mixture temperatures of 700 K or 867 K were obtained by firing a laser ignition system into the reaction chamber shortly after compression and analyzing the propagating flame with high speed schlieren imaging. Zero-dimensional simulations of published autoignition experiments were performed using Chemkin-Pro with several detailed chemical kinetic mechanisms to determine their suitability at predicting ignition delay periods. Multiple reduced chemical kinetic mechanisms were created from the NUIGMech1.1 mechanism to determine the optimal balance between accuracy and computational efficiency for future three-dimensional, time-dependent spark-ignited engine simulations. The chosen reduction, ALPINE 153, was used to model ignition delay periods and flame speeds measured in the RCM during this study.