A piston crown for a diesel engine in which the crown has an annular recess coaxial with an injector injecting fuel in a radiated, non-swirl pattern. The recess has an internal central crown portion approximately parallel to the angle of the fuel injected and a curved outer section to curve air compressed by the piston significantly enough that it is directed back toward the central axis and mixes with the fuel injected along the internal central crown portion to promote mixing and reduction in soot formation.