Abstract: A piston is arranged for reciprocal movement in a combustion engine cylinder. Protrusions are or a ridge is arranged half way between flame plume impingement areas in a plane perpendicular to the reciprocal movement and protrude to the combustion chamber having a smooth form adapted for preserving kinetic energy in a flame plume. The protrusion or ridge includes a left side flank, a top section and a right side flank, and a transition section between each of the side flanks and the top section, the transition section including a deflection edge in order to minimize flow losses.

Abstract: A piston is positioned for reciprocal movement in a combustion engine cylinder. Half way between flame plume impingement areas are arranged a first type of protrusions protruding into the combustion chamber and having a smooth form adapted for preserving kinetic energy in a flame plume. Each of the first type of protrusions has a shape of a longitudinal ridge that extends only in the outer bowl area. The first type of protrusions have a left side flank and a right side flank of the ridge when seen from the injector. 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 corresponding flame plume progressing, towards the right side flank.