COMBUSTION CHAMBER STRUCTURE FOR DIESEL ENGINE

A direct injection diesel engine (1) includes a piston (4) having a reentrant cavity (6) and a multi-hole fuel injection nozzle (7) disposed on a center line of the cavity. The cavity (6) is formed by a lip portion (42) defining a smallest diameter at a position below a piston crown surface (43) and a raised portion (41) formed at a center of the bottom and shaped like a frustum of a cone. A conical surface (41a) of the raised portion (41) is formed to have an angle pointing to a spray point (FP) of the fuel injection nozzle (7) at a piston top dead center position. The height position of a top surface (41b) is substantially equal to the height position of the lip portion (42). This structure is to promote the oxidation of soot by utilizing the air in the central part of the cavity (6).