DIRECT FUEL-INJECTION ENGINE

摘要

In a direct fuel-injection engine including a pent roof type piston having, at any position in the circumferential direction, a cavity with a uniform cross sectional shape including the central axis (Lp) of the piston, the cavity (25) being depressed in a central part of the piston (13) the height of the top surface of which varies in the circumferential direction, a lip (26) is provided in a protruding manner in the inward radial direction at an opening edge of the cavity (25), the cross sectional shape of the lip (26) being uniform at any position in the circumferential direction to prevent spillover of fuel from the cavity (25). Due to the configuration, inconsistency of any cross-sectional shape of the cavity (25) including the central axis (Lip) of the piston can be prevented, and uniform mixing of the fuel inside the cavity can be secured by providing the lip (26). Further, the durability can be strengthened by making the thermal load to be applied to the lip (26) at a time of combustion of air-fuel mixture in the circumferential direction uniform, and the casting accuracy can be enhanced by making the cooling speed of molten metal at the lip (26) at a time of casting of the piston (13) uniform.