Patent ID: 8646428

Claim:
A piston positioned for reciprocal movement in a combustion engine cylinder between a bottom dead center position and a top dead center position, the piston including a piston crown comprising an upper surface facing a combustion chamber, the piston crown containing a piston bowl formed by an outwardly opening cavity, the piston bowl comprising an outwardly flared outer bowl section haying a concave curvilinear shape in cross section, at least one intake port arranged to provide the combustion chamber with intake air substantially without swirl, an injector arranged to inject fuel into the combustion chamber from a position adjacent a geometrical centre of the combustion chamber and having an impingement area of a progressing flame plume in the outer bowl section, and where substantially half way between the impingement areas and in a plane substantially perpendicular to the reciprocal movement are arranged a first type of protrusions protruding into the combustion chamber from the outer bowl section and having a smooth form shaped for preserving kinetic energy in a flame plume and where each of the first type of protrusions has a shape of a longitudinal ridge that extends only in the outer bowl section, and where the first type of protrusions having a left side flank and a right side flank of the ridge when seen from the injector, and where the left side flank is formed differently compared to the right side flank in order to redirect the movement of a flame plume progressing towards the left side flank in a plane perpendicular to the reciprocal movement differently compared to a corresponding flame plume progressing towards the right side flank, wherein an upper part of the ridge, positioned away from a bottom of the piston bowl, having a form that is swept in one first direction in a plane perpendicular to an axis of reciprocation of the piston and when seen from the injector, and a lower part of the ridge, positioned close to the bottom of the piston bowl, having a form that is swept in an opposite direction to the first direction when seen from the injector and in another plane perpendicular to the axis of reciprocation of the piston, and where a distance parallel to an axis of reciprocation of the piston and between the planes is at least half of a total length of the ridge.