An engine includes a combustion chamber including a cylinder wall defining a cylinder, a fuel injector disposed in a first opening in the cylinder wall and a piston head disposed in the cylinder. A piston bowl at least partially defined by a wall having a generally spiral shape is provided in a top of the piston head.

A combustion chamber for an opposed-piston engine has a rotationally skewed shape in a longitudinal section that is orthogonal to a chamber centerline, between diametrically-opposed openings of the combustion chamber through which fuel is injected. The rotationally skewed shape interacts with swirl to generate a tumble bulk charge air motion structure that increases turbulence.

A direct-injected compression ignition internal combustion engine includes an engine housing having a cylinder and a piston movable within the cylinder and including a piston end face forming a combustion bowl. The piston end face has an annular piston rim with a rounded inner rim surface that extends radially inward and axially downward from a planar outer rim surface to a combustion bowl edge. An antebowl is defined by the rounded inner rim surface and has an antebowl volume that is about 0.8% or greater of a total volume of the combustion bowl and the antebowl together. A configuration and dimensional attributes of the antebowl is associated with reduced smoke production during operation, particularly for low to mid-load transients.

A piston for engine may include an annular body including a combustion bowl defining a volume and surrounded on a top side thereof by an annular crown portion defining a top squish surface with include an inner edge defining an opening to the combustion bowl. The opening may include an area for combustion gases to enter the bowl during a compression stroke of the piston. The combustion bowl may include a reentrant surface that defines a tangent that forms a reentrant angle with the top squish surface. The reentrant angle may range from 28.0 degrees to 32.0 degrees. A ratio of a bowl volume to an area of the entry opening may ranges from 45 mm to 52 mm. A ratio of a bowl volume to the reentrant angle may range from 12 cc/deg to 15 cc/deg.