Tomoyuki Wakisaka

A numerical study of the effects of boost pressure and exhaust gas recirculation ratio on the combustion process and exhaust emissions in a diesel engine

Abstract Experimental studies carried out at the New ACE Institute revealed that a combination of high-pressure fuel injection, high-pressure supercharging, and high exhaust gas recirculation (EGR) ratio was very effective in reducing both emissions of NO x and soot in a heavy-duty diesel engine. However, it is difficult to clarify the mechanisms of emission reduction under such operating conditions by experiments alone because the mixture formation and combustion processes are very complicated. The main purpose of this study was to investigate the effects of boost pressure and EGR ratio on the combustion process and exhaust emissions in a direct injection diesel engine by means of a three-dimensional numerical analysis. The combustion processes under various conditions of boost pressure and EGR ratio in a research diesel engine have been numerically simulated using the authors engine computational fluid dynamics code (GTT code). By comparing the calculated results with the experimental ones, it has been confirmed that the cylinder gas pressure, the rate of heat release, and the NO emission can be predicted reasonably well and the soot emission tendency can be predicted qualitatively. Furthermore, soot and NO formation characteristics have been examined under various EGR ratio and boost pressure conditions on the basis of φ-T (equivalence ratio-temperature) maps where the calculated local gas states in the combustion regions and the soot and NO peninsulas obtained by zero-dimensional numerical simulation have been plotted.

Evaluation of Artificial Caudal Fin for Fish Robot with Two Joints by Using Three-Dimensional Fluid-Structure Simulation

A fish robot with image sensors is useful to research for underwater creatures such as fish. However, the propulsion velocity of a fish robot is very slow compared with live fish. It is necessary to swim at a speed several times faster than the speed of the current robots for various usages. Therefore, we are searching for the method of making the robot swim fast. The simulation before making the robot is important. We have made the computational simulation program of three-dimensional fluid-structure analysis. The flow around the caudal fin can be examined by analyzing the fin as an elastic body. We compared the results of numerical analysis with the results of PIV measurement. Both were agreed well. Because the performance of a fish robot with two joints is better than that of a fish robot with one joint, we searched for an excellent fin for the fish robot with two joints by using CFD. We confirmed that the swimming performance of a fish robot becomes very good when the caudal fin is rigid except for the root of the fin which is comparatively flexible.

Development of Fish Robots Powered by Fuel Cells: Improvement of Swimming Ability by a Genetic Algorithm and Flow Analysis by Computational Fluid Dynamics

A fish robot with image sensors is useful to seek disaster victims in flood areas. In order to perform rescue operation for long time, the method of supplying electric power is important. The purpose of this study is to develop fish robots powered by polymer electrolyte fuel cells (PEFCs).

A numerical study of the effects of piston head configurations on stratified mixture formation in gasoline direct-injection engines

In this paper, the characteristics of flow and spray motions affected by from piston head configurations were investigated numerically. Calculations were carried out from intake process to the end of compression. GTT (Generalized Tank and Tube method) code, which includes a third order upwind Chakravarthy-Osher TVD scheme andk-ε turbulence model with fuel spray analysis was used for the calculations. As a results, piston heads with smaller radii of curvature were found to give stronger reverse tumble than those with larger radii of curvature. Similar results are shown in the convection and diffusion of fuel sprays.