| 摘要 |
By setting the configuration of a cavity (25) of a piston (5) appropriately, tumble is produced in air that is aspirated into a combustion chamber (6) inside a cylinder (3) from an intake port (8), and by means of this tumble, the spray of fuel injected by a fuel injector (12) is caused to gather around the periphery of a spark plug (7). A predetermined tumble in the form of an upright ellipse is set in the longitudinal cross section of the cylinder (3) which includes an injection point (I) of the fuel injector (12) and an ignition point (T) of the spark plug (7). The bottom surface (26) of the cavity (25) is curved so as to conform to the radius of curvature (R1) of the lower end of the elliptical tumble, thereby advancing the formation of elliptical tumble which is unlikely to interfere with the cylinder wall surfaces.
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