Che-Wun Hong

Molecular Analysis on Methanol Diffusion in a Model Nafion Membrane

Methanol crossover, mainly due to diffusion mechanism, deteriorates the performance of direct methanol fuel cells. Using a molecular simulation technique, we try to reproduce the methanol diffusion event in a model Nafion membrane with an atomistic resolution. The simulation system comprises molecules of the Nafion-water-methanol-hydronium ions at four different concentrations of methanol. Molecular simulation results show that methanol molecules migrate with water clusters and hydronium ions via the sulfonic acid groups of the side chains of the electrolyte. Electro-osmotic drag coefficients and diffusion coefficients of methanol were evaluated at varied methanol concentration and compared to reported experimental results. The thermal effect on the methanol diffusion was also investigated using this molecular analysis technique.

In-Cylinder Tumble Flow Field Measurements and Predictions

This paper presents the comparison between measured and predicted results of the in-cylinder tumble flow generated by a port-valve-liner assembly on a steady-flow test bench. The purpose was to advance the understanding of the stationary turbulence process via experimental and computational techniques in the same time. A baseline single-cylinder 4-stroke motorcycle engine was chosen. Its liner was replaced by a transparent acrylic-plastic tube and the piston was removed. This was to focus the research on the tumble flow generated by the geometry of its port, the passage of the canted inlet valve, and a dome-shaped combustion chamber. The in-cylinder turbulent flow field was measured via a 3-component laser Doppler velocimeter (LDV) point by point. A simultaneous computer simulation was carried out to predict the in-cylinder flow field of the same engine under the same operating condition, using KIVA3V-the most recent version of the KIVA code. The mean speed, turbulence intensity, tumble ratio, swirl ratio, and voriex circulation from both skills were all compared. A reasonably good level of agreement has been achieved. Both modern techniques are also validated.

Ionic Dynamics of an Intermediate-Temperature Yttria-Doped-Ceria Electrolyte

This paper presents the ionic dynamics simulation of an intermediate-temperature solid oxide fuel cell electrolyte. The example electrolyte is a yttria-doped ceria which was proved experimentally to have better performance than the traditional yttria-stabilized zirconia in the intermediate-temperature operation range (below 1073 K). This paper employs the molecular dynamics technique to analyze the oxygen-ion transportation from a nanoscale aspect. The simulation reveals that the oxygen vacancy tends to be constrained near the Y 3+ ions in the crystalline lattice. The influence of different operation temperatures and various Y 2 O 3 concentrations on the ionic conductivity was studied. The results show that 10.1 mol % of Y 2 O 3 doping concentration tends to have the optimal ionic conductivity, while the system temperature tends to increase the ionic conductivity proportionally. The simulation has been compared with published experimental data and shows reasonable agreement in both trend and order of magnitude.

Computer simulation of hydrogen proton exchange membrane and direct methanol fuel cells

This paper describes the computer simulation of electrochemical flow phenomena to predict the performance of proton exchange membrane fuel cells (PEMFCs), which include hydrogen and direct methanol fuel cells (DMFCs). To study the transport phenomena inside the low temperature fuel cells, the mass, the momentum, and the species equations are required. Darcy laws were employed to simplify the momentum equations in the porous diffusion layers and also to linearize the conservation equation set. That reduces the computational load significantly without losing the generality of the flow field. Performance simulation results were validated with some published experimental data. The comparison shows satisfactory agreement between them. This virtual performance test bench plays an important role in the prototype fuel cell design. The computer aided design tool is able to provide detailed information on the transport phenomena of the fuel cells, in which the flow visualization is not easy to carry out by experiments.

Bond graph modelling of fuel cell and engine hybrid electric scooters

This paper presents the modelling technique and dynamic simulation results of fuel cell and engine Hybrid Electric Scooters (HES) using the bond graph approach. The first example is on a fuel cell-battery hybrid scooter, in which the zero pollution fuel cell is the major powerplant, also acts as the battery charger. The second case study is on a typical engine-motor-regenerator-battery HES. It mainly consists of a brush-less direct current motor/regenerator and a 4-stroke direct injection spark ignition engine. They are interconnected in parallel by a continuously variable transmission. Detailed differential equation sets as well as simulation results are presented. A fuzzy auto-pilot control rule was employed to simulate the vehicle performance under typical driving pattern conditions.

An element-oriented model simplification algorithm based on dynamic similarity

This paper presents an element-oriented model simplification algorithm (EO-MSA) in multi-physical domains. It aims to generate a simplified model to release computational loading while maintaining model fidelity. The dynamics of the multi-physical system can be constructed based on a unified bond graph approach. This EO-MSA approach eliminates those bond graph elements which influence the system behaviour insignificantly in the mathematical model. This study proposes two newly-defined indices, dynamic similarity (DS), and model similarity index (MSI), to evaluate the similarity of candidates which are order reduced. Ten error-dynamics modules are mathematically constructed and structurally classified for both the DS and the MSI. The reduced model with minimum MSI can be determined using this approach. Quarter-car simulation results demonstrate that this EO-MSA approach is capable of reducing system complexity while maintaining fidelity with satisfactory tolerance.

On the study of energy-based control strategy for a lithium battery/supercapacitor hybrid energy storage system

This paper develops an energy-based control strategy for a lithium battery/supercapacitor hybrid energy storage system. The lithium battery set is interconnected in parallel with the supercapacitor module which is linked with a buck-boost converter downstream. The performance maps measured from experiments are utilized to form a control-based nonlinear system model. The control modes can be separated into the hybrid mode and the charging mode. Using. global explorative approach, under various conditions of battery state-or-charge, supercapacitor state-of-charge and loading power, the energy distribution (power split) control can be derived in these two modes. With such energy management, the consumed energy of this hybrid energy storage system is minimized.

Multi-Scale Analysis of Transport Phenomenon Inside the SOFC Using MD and CFD Techniques

This paper analyzes the transport phenomenon of a solid oxide fuel cell (SOFC) from micro and macro aspects. The micro-scale model focuses on the ion hopping transportation inside the solid electrolyte and the macro-scale model aims at the flow phenomenon and thermal management inside the diffusion layers and the flow channel. In SOFCs, oxygen ions are conducted through the ceramic membrane of Yttria-Stablized Ziconia (YSZ), which is composed of ZrO2 and Y2 O3 . This paper uses molecular dynamics (MD) method to evaluate the ion conductivity of the solid electrolyte. Doping with different percentage of Y2 O3 , the ion hopping simulation shows that about 8 mole % gives the optimal performance. Also the higher the operation temperature, the better the ion conduction. Temperature field management is also a critical issue in the SOFC design. A set of three-dimensional computational fluid dynamics (CFD) model (including mass, momentum, energy and concentration equations) inside the porous diffusion layers and the flow channel of the SOFC were employed to estimate the cooling effect under different pattern of flow channel designs. All simulation results were validated with experiments reported from other literatures. The integration of the micro and macro-scale analyses proves to be versatile in the SOFC prototype design.Copyright

Bond graph dynamics of a rubber-belt continuously variable transmission

This paper analyses the system dynamics of a rubber-belt continuously variable transmission (CVT), which is widely adopted in the modern scooter powertrain systems. Dynamic mathematical models were derived from the physical configuration of the CVT directly via a bond graph approach. The CVT mainly consists of a varying-diameter driving pulley and another flange-moveable driven pulley, interconnected by a V-shaped rubber belt. Effective belt diameters of both driving and driven pulleys are controlled by a speed governor and a torque regulator, respectively. Each component was functionally analysed, employing the field theory in the bond graph technique. Mathematical equations were derived and then solved on a Matlab platform. Both static and dynamic performance simulations were examined for future electronic control implementation.

Atomistic Analysis of Proton Diffusivity at Enzymatic Biofuel Cell Anode

This paper investigates the proton diffusion phenomenon between the anode catalyst and the electrode in an enzymatic bio-fuel cell. The bio-fuel cell uses enzymatic organism as the catalyst instead of the traditional noble metal, like platinum. The fuel is normally the glucose solution. The fuel cell is membrane-less and produces electricity from the reaction taken place in the organism. When the biochemical reaction occurs, the protons and electrons are released in the solution. The electrons are collected by the electrode plate and are transported to the cathode through an external circuit, while the protons migrate to the cathode by the way of diffusion. Unfortunately, protons are easy to dissipate in the solution because the enzyme is immersed in the neutral electrolyte. It is an important issue of how to collect the protons effectively. In order to investigate the diffusion process of the protons, a molecular dynamics simulation technique was developed. The simulation results track the transfer motion of the protons near the anode. The diffusivity was evaluated from the trajectory. The research concludes that the higher the glucose concentration, the better the proton diffusivity. The enzyme promotes the electrochemical reaction; however, it also plays an obstacle in the proton diffusion path.Copyright