A polymer electrolyte membrane (PEM) fuel cell is probably the most promising technology that will replace conventional internal combustion engines in the near future. As a primary power source for an automobile, the transient performance of a PEM fuel cell is of prime importance. In this thesis, a comprehensive, three-dimensional, two-phase, multi-species computational fuel cell dynamics model is developed in order to investigate the effect of flow-field design on the magnitude of current overshoot/undershoot and characteristics of current response when the cell is subjected to different voltage change patterns representing an automotive operation. The meshing strategy specific to PEM fuel cell modelling is studied in a systematic manner and employed in all analyses presented in this thesis. The predicted results compare very well with experimental data under both steady-state and transient operations. Two computational domains are used – the straight single-channel and practical-scale square cells with parallel, single-serpentine, and triple-serpentine flow-fields. The results from the straight single-channel cell suggest that the magnitude of current overshoot/undershoot increases with the voltage change rate. The behaviour of a current response curve is the result of complex interplay between water content at both sides of the membrane. It is also found that current overshoot/undershoot is amplified with the presence water flooding in the cell. The results from the square cell reveal that current overshoot/undershoot is caused by non-uniformity of local current density over the active area confirming the effect of flow-field geometry on transient response of the cell. By comparing the transient performance between the three flow-fields, a direct relationship between degree of water flooding in the cell and magnitude of current overshoot/undershoot has been found. A conclusion has been drawn which states that a cell with superior water removal ability will experience smaller current overshoot/undershoot.

The study presents a one-dimensional, transient and compressible flow models of a commercial Common Rail Injector (CRI) and a prototype of a single-fuel Hydraulically actuated Electrically controlled Unit Injector (HEUI) developed at the University of New South Wales (UNSW) in conjunction with local industry. The unique feature of the UNSW HEUI is the fact that it uses diesel fuel as the driver for pressure amplification within the unit injector. The work undertaken is part of a wider study aimed at optimization of the design of diesel injectors for dual-fuel systems to reduce green house gas emissions. The contribution of this thesis is the development of the model of the UNSW HEUI injector, which can be used to investigate possible modifications of the injector for its use in dual-fuel injection systems. The developed models include electrical, mechanical and hydraulic subsystems present in the injectors. They are based on Kirchhoff??s laws, on the mass and momentum conservation equations and on the equilibrium of forces. The models were implemented in MATLAB/SIMULINK graphical software environment, which provides a high degree of flexibility and allows simulation of both linear and nonlinear elements. The models were used to perform sensitivity analysis of both injectors. The sensitivity analysis has revealed that the temperature of the solenoid coil is one of the critical parameters affecting the timing and the quantity of the fuel injection of both injectors. Additional critical parameters were found to be the dimensions of the piston of the CRI, the stiffness of the needle spring of the HEUI and the dimensions of the intensifier of the HEUI. The models also revealed that in the case of pilot injections the speed of the solenoid is the major limiting factor of the performance. The developed models provide better understanding of the issues and limitations of the injectors. They give detailed insight into their working principles. The investigations of the models permit making quantitative analysis of the timing of the HEUI solenoid and to evaluate the proposed change of the direction of the pressure acting on the HEUI solenoid plunger.

Thesis (M.S.)--Oregon State University, 1981. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisor: Ardeshir Faghri, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 1976. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Effective combustion of waste fuels requires an understanding of the fuels characteristics. Gaseous and particulate emissions, ash residues and combustion properties are of interest to many; those that produce and sell heating units, utilities interested in using the fuels for power generation, regulatory agencies, municipalities needing to solve a disposal problem, and environmentally conscious people interested in maximum utilization of resources. A study was conducted at Oregon State University to test and evaluate the use of two types of waste: mixed waste paper (MWP) and refuse derived fuel (RDF). Wood biomass (ponderosa pine) was used as a benchmark and also cofired with MWP. Samples collected from the Pacific Northwest were tested for physical, chemical, combustion, and emission characteristics. Raw fuel samples were tested for moisture content and bulk density. The samples were then shredded and pelletized. Pelletized fuels were tested for ultimate and proximate analyses, ash fusion temperature, elemental ash analysis, higher heating value, moisture content, bulk density, and pellet durability. Using an existing biomass combustion facility, the samples were fired to determine the optimum thermodynamic conversion combustion condition for each fuel. Observations were made of physical problems associated with firing of the samples. Combustion products were continuously monitored for temperature and composition with a combustion analyzer. An EPA Method 5 sampling train was used to determine particulate, heavy metals, chloride, fluoride, and sulfate emissions. Leachate testing was performed on the bottom ash residue to determine heavy metal concentrations. Waste fuels provided a challenge for combustion study in a biomass combustion unit. Modifications were required to alleviate high ash content problems. Observations of corrosion and clinkers provided another comparison for fuel evaluation. Comparison of emissions resulting from different fuel types provided good practical information for industrial purposes. Observed trends indicated possible minimization of emissions corresponding to optimum thermodynamic conversion. Cofiring analysis revealed possible increases and decreases of heavy metal emissions for MWP and wood. / Graduation date: 1992

The microbial fuel cell (MFC) is an innovative renewable energy technology that also serves to treat wastewater through the bacteria-driven oxidation of organic substrates. The liquid anolyte contains the organic substrate to be oxidized, while the catholyte contains the substance to be reduced. In a dual-chamber MFC, the catholyte typically contains dissolved oxygen or another easily reducible compound (e.g., ferricyanide) in an aqueous solution, while in a single-chamber MFC, gaseous airborne oxygen reacts directly at the cathode. A single-chamber air-cathode microbial fuel cell was operated using an acetate substrate and a 0.2 mg/cm2 platinum catalyst cathode in the initial stages of the project. The platinum catalyst was airbrushed onto a carbon paper cathode and hot-pressed onto a Nafion 117 membrane. After the platinum runs were completed, the MFC was disassembled, cleaned and reassembled with a new non-precious nitrogen-doped carbon composite catalyst replacing the platinum. Two MFCs were operated at different loading levels (1.0 mg/cm2 and 2.0 mg/cm2) of the new catalyst. The cell was configured to operate in a fed-batch and upflow modes. Preliminary experiments were conducted using two non-precious catalysts synthesized with different nitrogen precursors, polyaniline and ethylenediamine (EDA). These experiments showed the ethylenediamine-based-catalyst exhibited higher catalytic activity for oxygen reduction (ORR) with a half-wave potential of 0.57 V versus 0.43 V for the polyaniline catalyst. These values were lower than the expected half-wave potential of 0.65 – 0.70 V. Consequently, the catalyst based on EDA was used in all subsequent experiments. SEM images revealed that this catalyst has a fluffy, bulbous, highly porous structure, while EDAX and XRD both detected the presence of residual iron and cobalt from the preparation procedure. Nitrogen (3.57 wt %) and oxygen (4.87 wt %) were also detected from the EDAX analysis. Operation with a hydraulic residence time (HRT) of 24 hours and feed COD concentration of 6.44 g COD/L-day was found to produce the highest power density of 141.7 ± 2.4 mW/m2 from the experiments conducted on the platinum catalyst. A subsequent run at a 12 hour HRT and 3.22 g COD/L-day feed produced only 104.4 ± 5.2 mW/m2. When the cell operation was reverted to the original high HRT and high feed COD concentration, the original current was not recovered and in fact remained virtually unchanged from the level attained at the lower HRT and COD feed level (105.7 ± 2.7 mW/m2). It was suspected that the decreased acetate concentration in the second phase, and the biomass accumulation in the replicate third phase were the cause of the decreased currents. Overall, the COD removal in each phase was high, between 87 – 95% although only a maximum of 4.24% was due to electricity generation. A significant portion of the COD removal during operation at high HRT and feed concentration was due to methane generation (30-50%), while the effect of oxygen leakage from the cathode into the anode compartment was estimated to account for a flux of up to 3.08 g COD/L-day, leading to significant biomass accumulation within the cell. Upon replacement of the platinum catalyst with the non-precious catalyst at the cathode, the current and power densities generated in the 1.0 mg/cm2 and 2.0 mg/cm2 cells rose by 50.5% and 205%, respectively, to 213.2 ± 13.9 mW/m2 and 431.8 ± 23.6 mW/m2. Importantly, the current generated in these cells was found to be exactly proportional to the catalyst loading level. The COD removal in these runs amounted to 79.6% and 92.2% of acetate, comparable to that achieved with the platinum catalyst. The coulombic efficiency increased as a result of the improved current densities to 6.71% and 12.18%, respectively. The improved performance with the non-precious catalyst demonstrates that it is a potentially attractive replacement for the conventional platinum as the catalyst for energy production. The proportionality between the generated current density and the catalyst loading also suggests that operation at higher catalyst loading levels will lead to further improvement in performance.

The microbial fuel cell (MFC) is an innovative renewable energy technology that also serves to treat wastewater through the bacteria-driven oxidation of organic substrates. The liquid anolyte contains the organic substrate to be oxidized, while the catholyte contains the substance to be reduced. In a dual-chamber MFC, the catholyte typically contains dissolved oxygen or another easily reducible compound (e.g., ferricyanide) in an aqueous solution, while in a single-chamber MFC, gaseous airborne oxygen reacts directly at the cathode. A single-chamber air-cathode microbial fuel cell was operated using an acetate substrate and a 0.2 mg/cm2 platinum catalyst cathode in the initial stages of the project. The platinum catalyst was airbrushed onto a carbon paper cathode and hot-pressed onto a Nafion 117 membrane. After the platinum runs were completed, the MFC was disassembled, cleaned and reassembled with a new non-precious nitrogen-doped carbon composite catalyst replacing the platinum. Two MFCs were operated at different loading levels (1.0 mg/cm2 and 2.0 mg/cm2) of the new catalyst. The cell was configured to operate in a fed-batch and upflow modes. Preliminary experiments were conducted using two non-precious catalysts synthesized with different nitrogen precursors, polyaniline and ethylenediamine (EDA). These experiments showed the ethylenediamine-based-catalyst exhibited higher catalytic activity for oxygen reduction (ORR) with a half-wave potential of 0.57 V versus 0.43 V for the polyaniline catalyst. These values were lower than the expected half-wave potential of 0.65 – 0.70 V. Consequently, the catalyst based on EDA was used in all subsequent experiments. SEM images revealed that this catalyst has a fluffy, bulbous, highly porous structure, while EDAX and XRD both detected the presence of residual iron and cobalt from the preparation procedure. Nitrogen (3.57 wt %) and oxygen (4.87 wt %) were also detected from the EDAX analysis. Operation with a hydraulic residence time (HRT) of 24 hours and feed COD concentration of 6.44 g COD/L-day was found to produce the highest power density of 141.7 ± 2.4 mW/m2 from the experiments conducted on the platinum catalyst. A subsequent run at a 12 hour HRT and 3.22 g COD/L-day feed produced only 104.4 ± 5.2 mW/m2. When the cell operation was reverted to the original high HRT and high feed COD concentration, the original current was not recovered and in fact remained virtually unchanged from the level attained at the lower HRT and COD feed level (105.7 ± 2.7 mW/m2). It was suspected that the decreased acetate concentration in the second phase, and the biomass accumulation in the replicate third phase were the cause of the decreased currents. Overall, the COD removal in each phase was high, between 87 – 95% although only a maximum of 4.24% was due to electricity generation. A significant portion of the COD removal during operation at high HRT and feed concentration was due to methane generation (30-50%), while the effect of oxygen leakage from the cathode into the anode compartment was estimated to account for a flux of up to 3.08 g COD/L-day, leading to significant biomass accumulation within the cell. Upon replacement of the platinum catalyst with the non-precious catalyst at the cathode, the current and power densities generated in the 1.0 mg/cm2 and 2.0 mg/cm2 cells rose by 50.5% and 205%, respectively, to 213.2 ± 13.9 mW/m2 and 431.8 ± 23.6 mW/m2. Importantly, the current generated in these cells was found to be exactly proportional to the catalyst loading level. The COD removal in these runs amounted to 79.6% and 92.2% of acetate, comparable to that achieved with the platinum catalyst. The coulombic efficiency increased as a result of the improved current densities to 6.71% and 12.18%, respectively. The improved performance with the non-precious catalyst demonstrates that it is a potentially attractive replacement for the conventional platinum as the catalyst for energy production. The proportionality between the generated current density and the catalyst loading also suggests that operation at higher catalyst loading levels will lead to further improvement in performance.

No description available.

Bipolar plates used in a PEM fuel cell must have high electric conductivity, good mechanical and chemical stability, low gas permeability, and low cost. For portable applications, lightweight and low volume should also be considered. Our laboratory has developed a new heterogeneous composite bipolar plate. Which has many advantages, such as low contact resistance, good chemical stability, low cost, lightweight and high performance. Since automation is the key to low cost, this research is to develop the automatic fabrication process of the new plate. The process involves mainly the making of carbon fiber bunches by sticking the central portion of the carbon fiber together with glue but leaving both ends free. Secondly, use injection molding to form the plastic main body with all the carbon fiber bunches. In order to shorten the developing time, we divide the process into four parts: (1) the unfolding of carbon fiber (2) the automation of gluing (3) harden and cutting to sizes (4) Injection molding of bipolar plates. This thesis has completed the study of the first three parts of the manufacturing processes. We have compared the contact resistances between our product and the previously handmade ones and found that the results are satisfactory.