In recent years a significant portion of proton exchange membrane fuel cell (PEMFC) work has been focused on understanding and optimizing the functions of the microporous layer (MPL). Researchers have found that including this layer, composed of carbon black and TeflonTM (PTFE), between the gas diffusion layer (GDL) and catalyst layer (CL) of PEMFCs improves performance. The major benefit of the MPL in conventional fuel cells is that it improves water management and reduces contact resistances between cell layers. Although the functions of the MPL in conventional PEMFCs are well understood, the essential functions and optimal formulation of the layer in planar PEMFCs which operate without stack compression, are for the most part unknown. This work determines the essential functions and optimal composition, loading and sintering pressure of the MPL in a planar fuel cell design called a Ribbon Fuel Cell. Adhesion as well as performance data were gathered to determine the essential functions and formulation of the MPL which leads to high performance and durability in Ribbon Fuel Cells. Statistical models were created based on performance data of cells constructed with various MPLs; and a MPL composed of 45 wt% PTFE, loaded at 3.5 mg/cm° and sintered between 20 and 40 psi was found to exhibit optimal performance and durability. The reason why such a high PTFE content yields optimal results is because it strengthens the MPL, allowing it to successfully join various cell layers together, a function that is essential in Ribbon Cells which operate without external stack compression. / Master of Science

Research and prototyping of a fuel cell stack system for micro aerial vehicles (MAVs) was conducted by Virginia Tech in collaboration with Luna Innovations, Inc, in an effort to replace the lithium battery technology currently powering these devices. Investigation of planar proton exchange membrane (PEM) and direct methanol (DM) fuel cells has shown that these sources of power are viable alternatives to batteries for electronics, computers, and automobiles. However, recent investigation about the use of microtubular fuel cells (MTFCs) suggests that, due to their geometry and active surface areas, they may be more effective as a power source where size is an issue. This research focuses on hydrogen MTFCs and how their size and construction within a stack affects the power output supplied to a MAV, a small unmanned aircraft used by the military for reconnaissance and other purposes. In order to conduct this research effectively, a prototype of a fuel cell stack was constructed given the best cell characteristics investigated, and the overall power generation system to be implemented within the MAV was modeled using a computer simulation program. The results from computer modeling indicate that the MTFC stack system and its balance of system components can eliminate the need for any batteries in the MAV while effectively supplying the power necessary for its operation. The results from the model indicate that a hydrogen storage tank, given that it uses sodium borohydride (NaBH4), can fit inside the fuselage volume of the baseline MAV considered. Results from the computer model also indicate that between 30 and 60 MTFCs are needed to power a MAV for a mission time of one hour to ninety minutes, depending on the operating conditions. In addition, the testing conducted on the MTFCs for the stack prototype has shown power densities of 1.0, an improvement of three orders of magnitude compared to the initial MTFCs fabricated for this project. Thanks to the results of MTFC testing paired with computer modeling and prototype fabrication, a MTFC stack system may be possible for implementation within an MAV in the foreseeable future. / Master of Science

Fuel-optimal rendezvous in orbit is examined using thrust-impulses and coasting arcs. Necessary conditions for the optimality of fuel-optimal rendezvous with and without radial constraints are derived. These conditions are then used to verify the optimality of trajectories obtained from a parameter-optimization technique. For rendezvous problems with radial constraint, locally optimal trajectories include constrained arcs or touch-point arcs. Numerical procedures to compute the costates and the jumps in the costates at the touch point and at the entry point to the constraint arc are provided. Locally optimal solutions for non-optimal trajectories with a minimum radius-constraint are obtained using criteria due to Lion and Handelsmann. Numerical solutions show that multiple-impulse trajectories almost always result in a lower cost function than the corresponding two impulse trajectories. It is also observed that trajectories comprised of only touch-point arcs can often be improved by using an additional impulse. / M. S.

Microbial fuel cells (MiFCs) have been suggested as a means to harness energy that is otherwise unutilized during the wastewater treatment process. MiFCs have the unique ability to treat influent waste streams while simultaneously generating power which can offset energy associated with the biological treatment of wastewater. During the oxidation of organic and inorganic wastes, microorganisms known as exoelectrogens have the ability to move electrons extracellularly. MiFCs generate electricity by facilitating the microbial transfer of these electrons from soluble electron donors in feedstocks to a solid-state anode. While MiFCs are a promising renewable energy technology, current systems suffer from low power densities which hinder their practical applicability. In this study, a novel anode design using flame-deposited carbon nanostructures (CNSs) on stainless steel mesh is developed to improve the electron transfer efficiency of electrons from microorganisms to the anode and thus the power densities achievable by MiFCs. These new anodes appear to allow for increased biomass accumulation on the anode and may aid in the direct transfer of electrons to the anode in mediatorless MiFC systems. Experiments were conducted using anaerobic biomass in single-chamber MiFCs with CNS-enhanced and untreated stainless steel anodes. Fuel cells utilizing CNS-enhanced anodes generated currents up to two orders of magnitude greater than cells with untreated metal anodes, with the highest power density achieved being 510 mW m-2. / Master of Science

No / Traditionally materials with the fluorite and perovskite structures have dominated the research in the area of oxide ion/proton conducting solid electrolytes. In such cases, the key defects are oxide ion vacancies, and conduction proceeds via a simple vacancy hopping mechanism. In recent years, there has been growing interest in alternative structure types, many of which contain tetrahedral moieties. For these new systems, an understanding of the accommodation of defects and the nature of the conduction mechanism is important for the optimisation of their conductivities, as well as to help target related structures that may display high oxide ion/proton conduction. Computer modelling studies on a range of systems containing tetrahedral moieties are presented, including apatite-type La9.33+xGe6O26+3x/2, cuspidine-type La4Ga2-xTixO9+x/2 and La1-xBa1+xGaO4-x/2. The type of anion defect (vacancy or interstitial), their location and the factors affecting their incorporation are discussed. In addition, modelling data to help to understand their conduction mechanisms are presented, showing novel aspects including the important role of the tetrahedral moieties in the conduction processes.

No / Traditionally materials with the fluorite and perovskite structures have dominated the research in the area of oxide ion/proton conducting solid electrolytes. In such cases, the key defects are oxide ion vacancies, and conduction proceeds via a simple vacancy hopping mechanism. In recent years, there has been growing interest in alternative structure types, many of which contain tetrahedral moieties. For these new systems, an understanding of the accommodation of defects and the nature of the conduction mechanism is important for the optimisation of their conductivities, as well as to help target related structures that may display high oxide ion/proton conduction. Computer modelling studies on a range of systems containing tetrahedral moieties are presented, including apatite-type La9.33+xGe6O26+3x/2, cuspidine-type La4Ga2¿xTixO9+x/2 and La1¿xBa1+xGaO4¿x/2. The type of anion defect (vacancy or interstitial), their location and the factors affecting their incorporation are discussed. In addition, modelling data to help to understand their conduction mechanisms are presented, showing novel aspects including the important role of the tetrahedral moieties in the conduction processes

EPA testing methods for calculation of fuel economy label ratings, which were revised beginning in 2008, use equations that weight the contributions of fuel consumption results from multiple dynamometer tests to synthesize city and highway estimates that reflect average U.S. driving patterns. The equations incorporate effects with varying weightings into the final fuel consumption, which are explained in this thesis paper, including illustrations from testing. Some of the test results used in the computation come from individual phases within the certification driving cycles. This methodology causes additional complexities for hybrid electric vehicles, because although they are required to have charge-balanced batteries over the course of a full drive cycle, they may have net charge or discharge within the individual phases. The fundamentals of studying battery charge-balance are discussed in this paper, followed by a detailed investigation of the implications of per-phase charge correction that was undertaken through testing of a 2010 Toyota Prius at Argonne National Laboratory's vehicle dynamometer test facility. Using the charge-correction curves obtained through testing shows that phase fuel economy can be significantly skewed by natural charge imbalance, although the end effect on the fuel economy label is not as large. Finally, the characteristics of the current 5-cycle fuel economy testing method are compared to previous methods through a vehicle simulation study which shows that the magnitude of impact from mass and aerodynamic parameters vary between labeling methods and vehicle types. / Master of Science

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Waste plastic disposal and excessive use of fossil fuels have caused environment concerns in the world. Both plastics and petroleum derived fuels are hydrocarbons that contain the elements of carbon and hydrogen. The difference between them is that plastic molecules have longer carbon chains than those in LPG, petrol, and diesel fuels. Therefore, it is possible to convert waste plastic into fuels. The main objectives of this study were to understand and optimize the processes of plastic pyrolysis for maximizing the diesel range products, and to design a continuous pyrolysis apparatus as a semi-scale commercial plant. Pyrolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) has been investigated both theoretically and experimentally in a lab-scale pyrolysis reactor. The key factors have been investigated and identified. The cracking temperature for PE and PP in the pyrolysis is at 450 ºC, but that of PS is lower, at 320 ºC. High reaction temperature and heating rate can significantly promote the production of light hydrocarbons. Long residence time also favours the yield of the light hydrocarbon products. The effects of other factors like type of reactor, catalyst, pressure and reflux rate have also been investigated in the literature review. From the literature review, the pyrolysis reaction consists of three progressive steps: initiation, propagation, and termination. Initiation reaction cracks the large polymer molecules into free radicals. The free radicals and the molecular species can be further cracked into smaller radicals and molecules during the propagation reactions. β-scission is the dominant reaction in the PE propagation reactions. At last, the radicals will combine together into stable molecules, which are termination reactions. There are three types of cracking of the polymers: random cracking, chain strip cracking, and end chain cracking. The major cracking on the polymer molecular backbone is random cracking. Some cracking occurs at the ends of the molecules or the free radicals, which is end chain cracking. Some polymers have reactive functional side group on their molecular backbones. The functional groups will break off the backbone, which is chain strip cracking. Chain strip cracking is the dominant cracking reaction during polystyrene pyrolysis. The reaction kinetics was investigated in this study. The activation energy and the energy requirement for the pyrolysis are dependent on the reaction process and the distribution of the final products. Following the equations from other literatures, the theoretical energy requirement for pyrolyze 1kg PE is 1.047 MJ. The estimated calorific value of the products is about 43.3 MJ/kg. Therefore, the energy profit is very high for this process. The PE pyrolysis products are mainly 1-alkenes, n-alkanes, and α, ω-dialkenes ranging from C1 to C45+. The 1-alkenes and the n-alkanes were identified with a special method developed in this research. It was found that secondary cracking process has a significant influence on the distribution of the product. This process converts heavy hydrocarbons into gas or light liquid product and significantly reduces 1-alkenes and α, ω-dialkenes. This secondary process can be controlled by adjusting the reflux rate of the primary product. The product of PE pyrolysis with maximized diesel range output consist of 18.3% non-condensable gases, 81.7% w/w liquid product, and less than 1% pure carbon under high reflux rate process. Some zeolite catalysts were tested to reduce the heavy molecular weight wax. It was found that NKC-5 (ZSM-5) was the most effective catalyst among zeolites tested. The proportion of the non-condensable gases was promoted from 17% w/w to 58% w/w by adding 10% w/w NKC-5 into the PE feedstock. The products of PP pyrolysis are mainly methyl- oligomers. The reflux effect on the product from pyrolysis of PP is not as great as that on PE. The PP pyrolysis product with high reflux rate consists of 15.7% non-condensable gases, 84.2% condensed liquid product, and less than 0.25% char. Cyclohexane is the dominant component, 21%w/w in the liquid product. 44%v/v of the non-condensable gases is propene. In the pyrolysis product of PS, there are 4% non-condensable gases, 93% liquid, and 3% char. Styrene accounts for 68.59%w/w in the PS liquid pyrolysis products due to the chain strip reactions. There was 19% v/v hydrogen in the gas product, which did not exist in the PE pyrolysis gas product. The composition of the char is almost pure carbon, which is similar to that from PE pyrolysis. The mixture of virgin and post-consumer PE, PP and PS have also been investigated to identify the feedstock interaction and the effect of the contamination on the product. The interaction promotes the production of non-condensable gases. However, the effect of the interaction on the distribution of total product is not significant. Contamination of paper labels on the post-consumer plastics may result in higher solid residue in the product but no significant effect on the product was found in this study. Based on the achievements, a continuous semi-scale reactor has been designed and constructed at maximum capacity of 27.11kg/hr in this research. From the experiments of pyrolysis of both virgin PE and post-consumer PE on this semi-scale pyrolysis reactor, it was found that the major components are 1-alkenes, n-alkanes, and α, ω- dialkenes. The distribution of the condensed products of PE pyrolysis from the semiscale reactor is the same as that of the products from low reflux rate process with the lab-scale reactor. However, the proportion of non-condensable gases is much higher than that from pyrolysis in the lab-scale tests with low reflux rate because the semiscale plant has higher reaction temperature and heating rate. Lower proportion of unsaturated hydrocarbons was found in the condensed product from the post-consumer PE pyrolysis than in the virgin PE product because of the contamination on the postconsumer PE. The actual energy consumption for cracking and vaporizing PE into fuels is 1.328 MJ/kg which is less than 3% of the calorific value of the pyrolysis products. Therefore, the pyrolysis technology has very high energy profit, 42.3 MJ/kg PE, and is environmental-friendly. The oil produced has very high quality and close to the commercial petroleum derived liquid fuels. The experience of design and operation of the semi-scale plant will be helpful for building a commercial scale plant in the future.

4 pp. / discontinued 3/4/11 / Carbohydrate is the main fuel for the body's muscles and brain. Adequate carbohydrate intake is important for supplying fuel in an athlete's diet.