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Characteristics of compressed natural gas (CNG) direct injection auto-ignition were investigated experimentally. A rapid compression machine (RCM) with the compression ratio of 10 was used. The diameter and thickness of the combustion chamber are 80 mm and 20 mm, respectively. After the compression start, fuel was directly injected with a single hole injector at the injection pressure of 7.0 MPa, and auto-ignition takes place. The fuel injection timing was varied from 50 ms to 60 ms from the compression start. Two kinds of natural gasses were tested; 12A (CH4: 99.1 %) and 13A (CH4: 86.3 %, C2H6: 5.2 %, C3H8: 1.9 % and others). A glow plug was installed in the cylinder in order to assist the ignition, which was set at 30 mm downstream from the fuel injector nozzle exit. Two kinds of auto-ignition processes were observed. For CNG 12A, auto-ignition always takes place after the end of the fuel injection. The ignition delay is relatively long (40 to 80 ms) and the fluctuation is large.

Easiness in closing a vehicle door has been often evaluated on a physical vehicle body, and in most cases, has not been fully studied by computer-aided engineering (CAE) in an earlier developing stage. The authors have developed a numerical method for reproducing the behavior of a closing door with a high fidelity. Characteristics of this method are that moving grid is used to reproduce the unsteady air motion caused by closing the door, and that external reaction forces including cabin pressure are coupled with the equation of the door motion to achieve a high fidelity. This method has made it possible to quantitatively evaluate cabin pressure rise and determine minimum door closing velocity, and the method has turned out to be effective.

The flow structures about a car-like bluff body with a variety of after-body configurations are numerically studied based on a finite-volume solution method with the sub-grid scale turbulence model. The numerical calculations are compared with the experiments in both the water basin and wind tunnel. Different detachment features are demonstrated in the case of different after-body configuration by the numerical analysis and the computer-graphics visualization. Some critical features such as high and low drag states are revealed in the numerical simulation in the case of critical-angle configuration and their mechanism are discussed.

A numerical analysis method is developed for predicting the pressure fluctuations on the front side window surface, aiming at the elucidation of the external aerodynamic flow structure about the front pillar of a road vehicle. The simulated results are assessed by comparison with the acoustic theory and reveal fairly well the dependence of the predicted surface pressure fluctuations upon the vehicle cruising speed with the sixth power law. The features of three dimensional vortical flow are clarified from the analysis of the simulated results, indicating the strong relationship between the vortical formation and the external pressure fluctuations on the front side window surface. The external pressure fluctuations seem to be strongly related to the vortex breakdown during its interaction with the front side window and the roof-side window junction.

An experimental technique is developed for a vehicle moving steadily in the vicinity of the ground. A towing tank with a steadily advancing carriage is used and the unfavorable effects of the boundary layer on the ground which is inevitable in the case of a wind tunnel are fully removed. Experiments with a box-shaped model and a car model revealed some interesting features of lift, drag and side force at various clearances from the ground. Lift force is the most sensitive to the boundary layer and the lift measured in a wind tunnel may not completely represent lift on the road. The flow with vortices near the bottom surface of the body has one of the most important effects on the forces.

A newly developed finite-difference solution method TUMMAC-VII is applied to the flow about a road vehicle. It is a time-marching solution method for the Navier-Stokes equation in the framework of a fixed rectangular coordinate system. The no-slip boundary conditions are implemented in the body boundary cells. The use of a subgrid-scale turbulence model enables us to resolve the structure of the 3D vortical flows past road vehicles. Simulation is performed for the Ahmed model as well as the GEOSTORM model with a quarter and a half-million grid points, respectively, and the results are compared with experimental results.

Negative pressure around the front pillar of a vehicle travelling at high speed deforms the door frame in the outward direction. This causes the aspiration noise. Finding a method for the reduction of the resulting air aspiration noise is a goal of this study which analyzes this phenomenon. The method proposed here can be applied to find effective measures to reduce aspiration noise at the early stages of vehicle development.

Numerical analysis of flow around the front end and in the engine compartment of FWD vehicles in three-dimension is presented. Finite - Volume Method is used for numerical integration of Navier-Stokes equations, incorporating k-ε model for turbulence. This method proved to be effective tool, showing good agreement of volume flow rate through radiator with experiments. Application of this method from the early stage of vehicle development contributed to significant saving of development term.