Abstract: A vertical vortex, namely, a reverse tumble flow is formed inside a cylinder of an internal combustion engine to form an intake air flow for smooth intake and exhaust in the internal combustion engine and also to promote atomization of fuel and mixing of air and fuel in a combustion chamber. To form this reverse tumble flow, a downstream portion of an intake passage is formed extending toward a central axis of the cylinder. To promote the formation of the swirl and further to form the combustion chamber as an efficient compact combustion chamber, a recessed portion is formed in a top wall of a piston. The top wall of the piston is provided with a raised portion at a location adjacent to the recessed portion, whereby, in the vicinity of top dead center of the piston, a squish is produced in a direction flowing toward a side of a spark plug in the efficient combustion chamber.

Abstract: A vertical vortex, namely, a reverse tumble flow is formed inside a cylinder of an internal combustion engine to form an intake air flow for smooth intake and exhaust in the internal combustion engine and also to promote atomization of fuel and mixing of air and fuel in a combustion chamber. To form this reverse tumble flow, a downstream portion of an intake passage is formed extending toward a central axis of the cylinder. To promote the formation of the swirl and further to form the combustion chamber as an efficient compact combustion chamber, a recessed portion is formed in a top wall of a piston. The top wall of the piston is provided with a raised portion at a location adjacent to the recessed portion, whereby, in the vicinity of top dead center of the piston, a squish is produced in a direction flowing toward a side of a spark plug in the efficient combustion chamber.