Direct fuel injection diesel engine

In a direct fuel injection diesel engine having a piston with a pentroof-shaped top face, with regard to a pentroof-shaped piston with a cavity recessed in a central part of the top face, a radial width S of a squish area formed between an outer peripheral part of the top face and a lower face of a cylinder head changes in the circumferential direction of the piston. By setting a squish clearance H large for a portion where the radial width S of the squish area is large and setting the squish clearance H small for a portion where the radial width S of the squish area is small, more specifically, by setting S/H so that it is constant in the circumferential direction, it is possible to make the strength of the squish flow uniform in the circumferential direction of the piston, thus promoting the mixing of air and fuel and reducing harmful exhaust components.