A combustion chamber in an engine includes a piston and an injector with plurality of orifices arranged to inject spray/flame plumes, which impinge on a piston outer bowl section during most of the injection. Between spray/flame plume impingement areas and in a plane substantially perpendicular to reciprocal piston movement are arranged a first type of protrusions protruding into the combustion chamber, having a smooth form for preserving kinetic energy in the flame and for redirecting circumferential flame progress mainly towards a center axis of the piston with minimal flame-to-flame interaction. A second type of protrusions are arranged in the impingement areas, being adapted for redirecting flame progress into a circumferential flame progress direction in a plane substantially perpendicular to the reciprocal piston movement and with minimal flame-to-piston wall interaction and minimal kinetic energy loss.