COMBUSTION CHAMBER STRUCTURE FOR INTERNAL COMBUSTION ENGINE

A combustion chamber structure for an internal combustion engine includes, in a piston top part, a concave portion (12) formed eccentrically with respect to a cylinder center axis (C1), and a tapered portion (20) that connects an upper end face (22) of the piston top part and a side face (18) of the concave portion (12). The tapered portion (20) is formed so that a tapered portion volume (volume of a space formed between the tapered portion (20) and an upper wall surface of the combustion chamber) in a first portion of the piston top part is greater than a tapered portion volume in a second portion that is nearer than the first portion to an eccentric direction of the concave portion (12) from the cylinder center axis C1.