In this study, we capture the moderating effect of aggressive driving behavior while assessing the influence of a comprehensive set of variables on injury severity. In doing so, we are able to account for the indirect effects of variables on injury severity through their influence on aggressive driving behavior, as well as the direct effect of variables on injury severity. The methodology used in this study to accommodate the moderating effect of aggressive driving behavior takes the form of two models – one for aggressive driving and another for injury severity. These are appropriately linked to obtain the indirect and direct effects of variables. The data for estimation is obtained from the National Motor Vehicle Crash Causation Study (NMVCCS). From an empirical standpoint, we consider a fine age categorization until 20 years of age when examining age effects on aggressive driving behavior and injury severity. There are several important results from the empirical analysis. Young drivers (especially novice drivers between 16-17 years of age), drivers who are not wearing seat belt, under the influence of alcohol, not having a valid license, and driving a pickup are found to be most likely to behave aggressively. Situational, vehicle, and roadway factors such as young drivers traveling with young passengers, young drivers driving an SUV or a pick-up truck, driving during the morning rush hour, and driving on roads with high speed limits are also found to trigger aggressive driving behavior. In terms of vehicle occupants, the safest situation from a driver injury standpoint is when there are 2 or more passengers in the vehicle, at least one of whom is above the age of 20 years. These and many other results are discussed, along with implications of the result for graduated driving licensing (GDL) programs. / text

Many modeling studies have been carried out to simulate the current distribution across the channel and shoulder direction in a proton exchange membrane (PEM) fuel cell. However the modeling results do not show agreement on the current density distribution. At the same time, no experimental measurement result of current density distribution across the channel and the shoulder direction is available to testify the modeling studies. Hence in this work, an experiment was conducted to separately measure the current densities under the channel and the shoulder in a PEM fuel cell by using the specially designed membrane electrode assemblies. The experimental results show that the current density under the channel is lower than that under the shoulder except when the fuel cell load is high. Afterwards two more experiments were carried out to find out the reason causing the higher current density under the shoulder. The effects of the electric resistance of gas diffusion layer (GDL) in the lateral and through-plane directions on the current density distribution were studied respectively. The experimental results show that it is the through-plane electric resistance that leads to the higher current density under the shoulder. Moreover, a three-dimensional fuel cell model is developed using FORTRAN. A new method of combining the thin-film model and homogeneous model is utilized to model the catalyst layer. The model is validated by the experimental data. The distribution of current density, oxygen concentration, membrane phase potential, solid phase potential and overpotential in a PEM fuel cell have been studied by the model. The modeling results show that the new modeling method provides better simulations to the actual transport processes and chemical reaction in the catalyst layer of a PEM fuel cell.

Due to escalating energy costs and limited fossil fuel resources, much attention has been given to polymer electrolyte membrane (PEM) fuel cells. Gas diffusion layers (GDLs) play a vital role in a fuel cell such as (1) water removal, (2) cooling, (3) structural backing, (4) electrical conduction and (5) transporting gases towards the active catalyst sites where the reactions take place. The power density of a PEM fuel cell in part is dependent upon how uniform the gases are distributed to the active sites. To this end, research is being conducted to understand the mechanisms that influence gas distribution across the fuel cell. Emerging PEM fuel cell designs have shown that higher power density can be achieved; however this requires significant changes to existing components, particularly the GDL. For instance, some emerging concepts require higher through-plane gas permeability than in-plane gas permeability (i.e., anisotropic resistance) which is contrary to conventional GDLs (e.g., carbon paper and carbon cloth), to obtain a uniform gas distribution across the active sites. This is the foundation on which this thesis is centered. A numerical study is conducted in order to investigate the effect of the gas permeability profile on the expected current density in the catalyst layer. An experimental study is done to characterize the effects of the weave structure on gas permeability in woven GDLs. Numerical simulations are developed using Fluent version 6.3.26 and COMSOL Multiphysics version 3.5 to create an anisotropic resistance profile in the unconventional GDL, while maintaining similar performance to conventional GDL designs. The effects of (1) changing the permeability profile in the in-plane and through-plane direction, (2) changing the thickness of the unconventional GDL and (3) changing the gas stoichiometry on the current density and pressure drop through the unconventional GDL are investigated. It is found that the permeability profile and thickness of the unconventional GDL have a minimal effect on the average current density and current density distribution. As a tradeoff, an unconventional GDL with a lower permeability will exhibit a higher pressure drop. Once the fuel cell has a sufficient amount of oxygen to sustain reactions, the gas stoichiometry has a minimal effect on increases in performance. Woven GDL samples with varying tightness and weave patterns are made on a hand loom, and their in-plane and through-plane permeability are measured using in-house test equipment. The porosity of the samples is measured using mercury intrusion porosimetry. It is found that the in-plane permeability is higher than the through-plane permeability for all weave patterns tested, except for the twill weave with 8 tows/cm in the warp direction and 4 tows/cm in the weft direction, which exhibited a through-plane permeability which was 20% higher than the in-plane permeability. It is also concluded that the permeability of twill woven fabrics is higher than the permeability of plain woven fabrics, and that the percentage of macropores, ranging in size from 50-400 µm, is a driving force in determining the through-plane permeability of a woven GDL. From these studies, it was found that the graduated permeability profile in the unconventional GDL had a minimal effect on gas flow. However, a graduated permeability may have an impact on liquid water transport. In addition, it was found that graduating the catalyst loading, thereby employing a non-uniform catalyst loading has a greater effect on creating a uniform current density than graduating the permeability profile.

Membranas hidrocarbônicas não fluoradas têm sido desenvolvidas para uso em substituição as membranas fluoradas (Nafion®) em células a combustível de eletrólito polimérico (PEMFC), ou em temperaturas superiores a 80 °C, ou em células com adição direta de álcool. Este trabalho teve como objetivo avaliar o desempenho de membranas hidrocarbônicas catiônicas, desenvolvidas para uso em célula a combustível alimentada com etanol (DEFC), e de camadas de difusão gasosa (GDL – Gas Difusion Layer) e eletrodos (GDE – Gas Difusion electrode) preparados para uso com as mesmas. Duas membranas hidrocarbônicas (E-750 e P-730) da empresa FuMATech®/GR foram avaliadas quanto à capacidade de troca iônica e grau de inchamento em água/etanol, quanto a composição química, morfologia, comportamento térmico e visoelástico e condutividade por impedância. As GDLs foram preparadas a partir de uma emulsão aquosa de Teflon® e pó de carbono Vulcan XC-72R®, com e sem agente emulsificante (resina sulfonada), dispersa em ambas as faces do tecido de carbono pelo método de aspersão. Os GDEs foram preparados pela deposição de emulsão catalítica de diferentes eletrocatalisadores sobre as respectivas GDLs do ânodo e catodo. Os GDEs anódico e catódico foram preparados com 1 mg.cm-2 do eletrocatalisador de PtSn/C 20% (75:15) e de Pt/C (20:80), respectivamente, e caracterizados por MEV-EDS. As características fisico-químicas das membranas hidrocarbônicas foram similares às apresentadas pela membrana Nafion®. O desempenho do protótipo de célula unitária DEFC com as membranas FuMATech® foi inferior ao obtido com a membrana Nafion® usando-se GDE comercial. Por outro lado, ensaios com a membrana Nafion® utilizando-se os eletrodos preparados neste trabalho e eletrodos comerciais apresentaram valores de potencial similares. / Non-fluorinated hydrocarbon cationic membranes have been developed for use instead of Nafion® in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), or at higher temperatures than 80 ºC, or in fuel cells fed with alcohol. The aim of this work was to evaluate the performance of commercial non-fluorinated hydrocarbon cationic membranes with potential use in direct ethanol fuel cell (DEFC), and also evaluate the Gas Difusion Layer (GDL) and Gas Difusion electrode (GDE) prepared for use with them. Two hydrocarbon membranes (E-750 and P-730) produced by FuMATech®/GR were analyzed according to their ion exchange capacity, water uptake in water/alcohol solution, morphology, chemical composition, thermal and viscoelastic behaviour, and conductivity by impedance. The GDLs were prepared by spraying an aqueous emulsion of Vulcan carbon/Teflon®, with and without emulsifier agent (sulfonated hydrocarbon resin), in both sides of a carbon fabric. The electrodes were prepared by the respective deposition of the electrocatalysts emulsions on the cathode and anode GDLs. The anodic and cathodic GDEs were prepared with 1 mg.cm-2 of the electrocatalyst of PtSn/C 20% (75:15) and of Pt/C (20:80), respectively, which were characterized by SEM-EDS. The physicochemical properties of the hydrocarbon membranes were similar to the Nafion® membrane ones. The potential values obtained in a DEFC prototype unit cell with FuMATech® membranes were lower than those with Nafion-117 membrane. On the other hand, the performance of the DEFC prototype with Nafion-117 membrane was the same if used GDEs commercial or here prepared.

Membranas hidrocarbônicas não fluoradas têm sido desenvolvidas para uso em substituição as membranas fluoradas (Nafion®) em células a combustível de eletrólito polimérico (PEMFC), ou em temperaturas superiores a 80 °C, ou em células com adição direta de álcool. Este trabalho teve como objetivo avaliar o desempenho de membranas hidrocarbônicas catiônicas, desenvolvidas para uso em célula a combustível alimentada com etanol (DEFC), e de camadas de difusão gasosa (GDL – Gas Difusion Layer) e eletrodos (GDE – Gas Difusion electrode) preparados para uso com as mesmas. Duas membranas hidrocarbônicas (E-750 e P-730) da empresa FuMATech®/GR foram avaliadas quanto à capacidade de troca iônica e grau de inchamento em água/etanol, quanto a composição química, morfologia, comportamento térmico e visoelástico e condutividade por impedância. As GDLs foram preparadas a partir de uma emulsão aquosa de Teflon® e pó de carbono Vulcan XC-72R®, com e sem agente emulsificante (resina sulfonada), dispersa em ambas as faces do tecido de carbono pelo método de aspersão. Os GDEs foram preparados pela deposição de emulsão catalítica de diferentes eletrocatalisadores sobre as respectivas GDLs do ânodo e catodo. Os GDEs anódico e catódico foram preparados com 1 mg.cm-2 do eletrocatalisador de PtSn/C 20% (75:15) e de Pt/C (20:80), respectivamente, e caracterizados por MEV-EDS. As características fisico-químicas das membranas hidrocarbônicas foram similares às apresentadas pela membrana Nafion®. O desempenho do protótipo de célula unitária DEFC com as membranas FuMATech® foi inferior ao obtido com a membrana Nafion® usando-se GDE comercial. Por outro lado, ensaios com a membrana Nafion® utilizando-se os eletrodos preparados neste trabalho e eletrodos comerciais apresentaram valores de potencial similares. / Non-fluorinated hydrocarbon cationic membranes have been developed for use instead of Nafion® in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), or at higher temperatures than 80 ºC, or in fuel cells fed with alcohol. The aim of this work was to evaluate the performance of commercial non-fluorinated hydrocarbon cationic membranes with potential use in direct ethanol fuel cell (DEFC), and also evaluate the Gas Difusion Layer (GDL) and Gas Difusion electrode (GDE) prepared for use with them. Two hydrocarbon membranes (E-750 and P-730) produced by FuMATech®/GR were analyzed according to their ion exchange capacity, water uptake in water/alcohol solution, morphology, chemical composition, thermal and viscoelastic behaviour, and conductivity by impedance. The GDLs were prepared by spraying an aqueous emulsion of Vulcan carbon/Teflon®, with and without emulsifier agent (sulfonated hydrocarbon resin), in both sides of a carbon fabric. The electrodes were prepared by the respective deposition of the electrocatalysts emulsions on the cathode and anode GDLs. The anodic and cathodic GDEs were prepared with 1 mg.cm-2 of the electrocatalyst of PtSn/C 20% (75:15) and of Pt/C (20:80), respectively, which were characterized by SEM-EDS. The physicochemical properties of the hydrocarbon membranes were similar to the Nafion® membrane ones. The potential values obtained in a DEFC prototype unit cell with FuMATech® membranes were lower than those with Nafion-117 membrane. On the other hand, the performance of the DEFC prototype with Nafion-117 membrane was the same if used GDEs commercial or here prepared.

Membranas hidrocarbônicas não fluoradas têm sido desenvolvidas para uso em substituição as membranas fluoradas (Nafion®) em células a combustível de eletrólito polimérico (PEMFC), ou em temperaturas superiores a 80 °C, ou em células com adição direta de álcool. Este trabalho teve como objetivo avaliar o desempenho de membranas hidrocarbônicas catiônicas, desenvolvidas para uso em célula a combustível alimentada com etanol (DEFC), e de camadas de difusão gasosa (GDL – Gas Difusion Layer) e eletrodos (GDE – Gas Difusion electrode) preparados para uso com as mesmas. Duas membranas hidrocarbônicas (E-750 e P-730) da empresa FuMATech®/GR foram avaliadas quanto à capacidade de troca iônica e grau de inchamento em água/etanol, quanto a composição química, morfologia, comportamento térmico e visoelástico e condutividade por impedância. As GDLs foram preparadas a partir de uma emulsão aquosa de Teflon® e pó de carbono Vulcan XC-72R®, com e sem agente emulsificante (resina sulfonada), dispersa em ambas as faces do tecido de carbono pelo método de aspersão. Os GDEs foram preparados pela deposição de emulsão catalítica de diferentes eletrocatalisadores sobre as respectivas GDLs do ânodo e catodo. Os GDEs anódico e catódico foram preparados com 1 mg.cm-2 do eletrocatalisador de PtSn/C 20% (75:15) e de Pt/C (20:80), respectivamente, e caracterizados por MEV-EDS. As características fisico-químicas das membranas hidrocarbônicas foram similares às apresentadas pela membrana Nafion®. O desempenho do protótipo de célula unitária DEFC com as membranas FuMATech® foi inferior ao obtido com a membrana Nafion® usando-se GDE comercial. Por outro lado, ensaios com a membrana Nafion® utilizando-se os eletrodos preparados neste trabalho e eletrodos comerciais apresentaram valores de potencial similares. / Non-fluorinated hydrocarbon cationic membranes have been developed for use instead of Nafion® in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), or at higher temperatures than 80 ºC, or in fuel cells fed with alcohol. The aim of this work was to evaluate the performance of commercial non-fluorinated hydrocarbon cationic membranes with potential use in direct ethanol fuel cell (DEFC), and also evaluate the Gas Difusion Layer (GDL) and Gas Difusion electrode (GDE) prepared for use with them. Two hydrocarbon membranes (E-750 and P-730) produced by FuMATech®/GR were analyzed according to their ion exchange capacity, water uptake in water/alcohol solution, morphology, chemical composition, thermal and viscoelastic behaviour, and conductivity by impedance. The GDLs were prepared by spraying an aqueous emulsion of Vulcan carbon/Teflon®, with and without emulsifier agent (sulfonated hydrocarbon resin), in both sides of a carbon fabric. The electrodes were prepared by the respective deposition of the electrocatalysts emulsions on the cathode and anode GDLs. The anodic and cathodic GDEs were prepared with 1 mg.cm-2 of the electrocatalyst of PtSn/C 20% (75:15) and of Pt/C (20:80), respectively, which were characterized by SEM-EDS. The physicochemical properties of the hydrocarbon membranes were similar to the Nafion® membrane ones. The potential values obtained in a DEFC prototype unit cell with FuMATech® membranes were lower than those with Nafion-117 membrane. On the other hand, the performance of the DEFC prototype with Nafion-117 membrane was the same if used GDEs commercial or here prepared.

No description available.

Die konstruktive Gestaltung des Flussfeldlayouts und der Kanalquerschnittsparameter einer Bipolarplatte kann maßgeblichen Einfluss auf die Leistungsfähigkeit einer Brennstoffzelle haben. Insbesondere die Intrusionswirkung von Gasdiffusionslagen (GDL) infolge einer mechanischen Vorspannung auf die Aktivfläche führt zu einer Verengung des effektiv durchströmten Kanalquerschnittes. In dieser Arbeit wird angenommen, dass die Intrusionswirkung in direkter Abhängigkeit von Kanalparametern metallischer Kanalplatten steht, dies wird experimentell untersucht. Die hierbei zur Anwendung kommende Prüfmethode sowie der zugehöriger Prüfstandsaufbau wurden bereits in [1] aufgeführt und erste experimentelle Ergebnisse präsentiert. In dieser Arbeit wird der betrachtete Parameterraum erweitert, indem zusätzliche Kanalquerschnittsproben experimentell untersucht werden und das jeweilige Intrusionsverhalten ermittelt wird.

Constitutive relationships are developed to describe the water transport characteristics of the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). Additionally, experimental fixtures and procedures for the determination of the constitutive relationships are presented. The water transport relationships are incorporated into analytical models that assess the impact of the water transport relations and that make PEMFC performance predictions. The predicted performance is then compared to experimental results. The new constitutive relationships are significantly different than the currently popular relationships used in PEMFC modeling because they are derived from experiments on actual PEMFC gas diffusion layer materials. In prior work, properties of the GDL materials such as absolute permeability, liquid water relative permeability, porosity, and capillary behavior are often assumed or used as adjustment parameters in PEMFC models to simplify the model or to achieve good fits with polarization data. In this work, the constitutive relations are not assumed but are determined via newly developed experimental techniques. The experimental fixtures and procedures were used to characterize common GDL materials including carbon papers and carbon cloths, and to investigate common treatments applied to these materials such as the bulk application of a hydrophobic polymer within the porous structure. A one-dimensional model is developed to contrast results based on the new constitutive relations with results based on commonly used relationships from the PEMFC literature. The comparison reveals that water transport relationships can have a substantial impact on predicted GDL saturation, and consequently a significant impact on cell performance. The discrepancy in saturation between cases can be nearly an order of magnitude. A two-dimensional model is also presented that includes the impact of the compressed GDL region under the shoulder of a bipolar plate. Results show that the compression due to the bipolar plate shoulder causes a significant increase in liquid saturation, and a significant reduction in oxygen concentration and current density for the paper GDL. In contrast, compression under the shoulder has a minimal impact on the cloth GDL. Experimental inputs to the 2-D model include: absolute permeability, liquid water relative permeability, the slope of the capillary pressure function with saturation, total porosity, GDL thickness, high frequency resistance, and appropriate Tafel parameters. Computational polarization curve results are compared to experimental polarization behavior and good agreement is achieved. / Ph. D.

The Polymer Electrolyte Membrane (PEM) fuel cell has a great potential in leading the future energy generation due to its advantages of zero emissions, higher power density and efficiency. For a PEM fuel cell, the Membrane-Electrode Assembly (MEA) is the key component which consists of a membrane, two catalyst layers and two gas diffusion layers (GDL). The success of optimum PEM fuel cell power output relies on the mass transport to the electrode especially on the cathode side. The carbon based GDL is one of the most important components in the fuel cell since it has one of the basic roles of providing path ways for reactant gases transport to the catalyst layer as well as excess water removal. A detailed understanding and visualization of the GDL from micro-scale level is limited by traditional numerical tool such as CFD and experimental methods due to the complex geometry of the porous GDL structural. In order to take the actual geometry information of the porous GDL into consideration, the x-ray tomography technique is employed which is able to reconstructed the actual structure of the carbon paper or carbon cloth GDLs to three-dimensional digital binary image which can be read directly by the LB model to carry out the simulation. This research work contributes to develop the combined methodology of x-ray tomography based the three-dimensional single phase Lattice Boltzmann (LB) simulation. This newly developed methodology demonstrates its capacity of simulating the flow characteristics and transport phenomena in the porous media by dealing with collision of the particles at pore-scale. The results reveal the heterogeneous nature of the GDL structures which influence the transportation of the reactants in terms of physical parameters of the GDLs such as porosity, permeability and tortuosity. The compression effects on the carbon cloth GDLs have been investigated. The results show that the c applied compression pressure on the GDLs will have negative effects on average pore size, porosity as well as through-plane permeability. A compression pressure range is suggested by the results which gives optimum in-plane permeability to through-plane permeability. The compression effects on one-dimensional water and oxygen partial pressures in the main flow direction have been studied at low, medium and high current densities. It s been observed that the water and oxygen pressure drop across the GDL increase with increasing the compression pressure. Key Words: PEM fuel cell, GDL, LB simulation, SPSC, SPMC, x-ray tomography, carbon paper, carbon cloth, porosity, permeability, degree of anisotropy, tortuosity, flow transport.