Abstract: A combustion chamber assembly for use in a diesel engine includes a combustion chamber being defined in a crown of a piston, the piston having a central axis, the combustion chamber having a center portion being elevated relative to a bottom plane of the combustion chamber. The center portion is defined in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the combustion chamber central axis. The combustion chamber further has an outer margin, the outer margin being defined in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the combustion chamber central axis and being greater than the center portion radius. The spherical center portion and the spherical outer margin are connected by an annular surface.