A diesel combustion system including a piston, an annular impinging block, and a combustion chamber. The combustion chamber is divided by the annular impinging block into an upper chamber and a lower chamber. The annular impinging block includes a lower guide surface that is adjacent to the lower chamber and that extends from a trough line connected to the piston to a crest line. The ratios among the inner diameter of the top of the piston, the outer diameter of the top of the piston, the diameter of the trough line, and the diameter of the crest line define the shape of the combustion chamber which leads to increased rate of combustion, reduced soot emission, and increased fuel efficiency.