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The Mitsubishi GDI engine has adopted a pair of upright intake ports, to induce a rotating in-cylinder flow, reverse tumble, and control air fuel mixing with this flow. The port design of the GDI engine was optimized for achieving a high intensity of the reverse tumble while maintaining a high charge coefficient, by means of modeling of in-cylinder flow and experiment with a steady flow rig. First of all, the ideal design of the upright ports was discussed. It was found that for enhancing the reverse tumble, it is more effective to arrange a pair of the ports parallel, than to arrange them convergent. The parallel arrangement leads to the smoother flows passing through the intake sides of the intake valves, and then descending on the cylinder liner, that is turning toward the rotation direction of the reverse tumble, because of less impingement of the flows through a pair of the valves.

Flow and flame structure visualization and modeling were performed to clarify the characteristics of bulk flow, turbulence and mixing in a four-valve engine to adopt the lean combustion concept named “Barrel-Stratification” to the larger displacement center-spark four-valve engine. It was found that the partitions provided in the intake port and the tumble-control piston with a curved-top configuration were effective to enhance the lean combustion of such an engine. By these methods, the fuel distribution in the intake port and the in-cylinder bulk flow structure are optimized, so that the relatively rich mixture zone is arranged around the spark plug. The tumble-control piston also contributes to optimize the flow field structure after the distortion of tumble and to enable stable lean combustion.

This paper describes a new grid generating system particularly designed for automobile external flow analyses. The system consists of three major parts as follows: Part I collects the geometrical data of the automobile surface and develops an intermediate grid. Part II generates the surface grid on the surface of the automobile. The surface grid is used as the boundary condition for generating the three-dimensional grid for the flow space. Part III generates the three-dimensional grid for external flow analyses. In generating the surface grid, a new approach of generating grid has been developed, in which two elliptic grid generation equations are solved directly on the physical domain. The three-dimensional grid is generated by the elliptic grid generation method blended with the hyperbolic method. An iterative solution algorithm based on the approximate factorization scheme has been developed.