Combustion chamber for an internal combustion engine of direct injection type

In an internal combustion engine of the direct injection type including combustion chambers each defined by a cylinder head, a cylinder liner, and a piston head having a wall defining a cavity therein, means for producing air swirl in said cavity and fuel injection means each having a plurality of fuel injection nozzles, said nozzles being arranged to inject jets of fuel into said cavity radially against said cavity wall, the improvement wherein said cavity wall is constructed to define a generally equilateral polygonal cavity formed in the upper part thereof and a generally toroidal cavity formed in the lower part thereof, the ratio of the depth of said equilateral polygonal cavity to that of said toroidal cavity being about 0.3 to about 1.2, and wherein said equilateral polygonal cavity has rounded corners formed therein, the ratio of the radius of said rounded corners to that of an inscribed circle of said equilateral polygonal cavity being from about 0.05 to about 0.8.