Kazushige Kikuta

Measurement of Water Production Behavior, Temperature, and Current Density Distributions in a Polymer Electrolyte Fuel Cell

This paper observes phenomena related to water production behavior inside a fuel cell and analyzes the effect on the current and temperature distribution across the reaction area. A fuel cell permitting direct observation of the phenomena in the cell, 2-D temperature measurements in the cathode channels, and local current density measurements on the anode side was manufactured. The experimental results showed the production and flow of liquid water in the cell, and there were good correlations among the distributions of current density, temperature, and water amounts in the channels. The behavior of current, voltage, water distribution, and pressure differences in the cathode channels were used to hypothesize about the possibility of gas paths deep in the gas diffusion layer in the flooded condition and a positive feedback mechanism in the drying-out condition.© 2006 ASME

Numerical Simulation of Liquid Water Behavior in Separator-Channels in PEMFC Using LBM

In a polymer electrolyte membrane fuel cell, the condensed water in the separator-channel prevents the supply of reactants to electrodes, which deteriorates the cell performance. The Lattice Boltzmann simulation has been conducted to understand the behavior of condensed water in the separator-channels. The scheme for the two-phase flow with large density difference was applied and the boundary condition for wettability at the corner inside the channel was examined. The present simulation demonstrates the effects of the cross-sectional shape, the wettability of channel and the volume of condensed water on the liquid water behavior. In the hydrophilic separator-channels, the liquid water spreads along the channel wall to form film and, in a specific condition, the water draws away from the gas diffusion layer, which suppresses the flooding. On the other hand, the liquid water forms sphere, covering larger area of the surface of gas diffusion layer in the hydrophobic separator-channels, but the drain performance of liquid water is superior.Copyright

Study on Simple and High-Speed Diesel Combustion Model for Driving Mode Simulator Available for Premixed and Diffusion Combustion of Sprays

To design a diesel engine adapting to future exhaust gas regulation, it is important to develop a driving mode simulator which can simulate vehicle performance and exhaust emissions including after-treatment system. The combustion model for this objective must be able to simulate heat release rate, variety of emissions necessary for after-treatment simulation, and exhaust gas temperature in very short computational time. The authors have developed a diesel combustion model based on the Hiroyasu model by adding variety of modifications to minimize optimization process of the empirical constants. It was shown that the simulation results with the improvement model were in good agreement with the experimental results. By adding Tsurushima model consisting of nine reaction steps with several intermediate species, the model became available for the both combustions of spray diffusion flame and of homogeneous charge compression ignition.Copyright

Conditions for Homogeneous and Rapid Deposition of Si Film on Semiconductor Wafers

The paper investigates the method of improving deposition rate in semiconductor deposition process, while maintaining film thickness uniformity and step coverage in a vertical LPCVD (Low-Pressure Chemical Vapor Deposition) system. In general increasing pressure improves deposition rate, but it decreases uniformity of thickness. The result of experiment and the numerical simulation showed that the non-uniformity of film thickness in high-pressure condition can be improved by controlling flow patterns in the space between wafers. In the molecular flow region (low pressure), the deposition rate and the step coverage were not influenced by the source gas flow rate. In the viscous flow region (high pressure), the step coverage can be improved by increasing source gas flow rate. For the flow the nozzle design and exhaust port location are important. Installation of rings outside of wafers is also effective for the improvement of thickness uniformity.

Study on Microsocopic Diffusion Structure in Diesel Flame Affecting on NOx Emissions and Their Reduction Method

Experiment and numerical simulation indicated that the large NOx formation in diesel engine is due to the weak mixing intensity in the spray tip region, where the flow and turbulence structure is quite different from the continuous jet flames. The fact indicates that there is a possibility of reducing NOx, from diesel engines by enhancing mixing intensity at the spray tip region to the level of continuous jet flame. As one of the attempts to make the velocity profile of diesel spray similar to the steady jet, an inert gas was injected prior to the fuel injection. With the pre-injection of inert gases, the flame apparently became less luminous, and the NOx emission index decreased to two-thirds of the non pre-injection case. Numerical simulation showed that NO decreases with the increase of the pre-injection period, although the maximum temperatures are almost constant in all cases. This suggests that the NOx reduction is not due to the temperature difference but due to the enhanced mixing and decreased time at high temperature by the pre-injection. The report presents the above results together with photographic analysis of enhanced mixing of spray tip region by pre-injection of water.