COMBUSTION CHAMBER STRUCTURE FOR DIESEL ENGINE

A piston (4) of a direct injection type diesel engine (1) has a re-entrant type cavity (6), and a fuel injection nozzle (7) with multiple nozzle holes is arranged on the center line thereof. The cavity (6) has a lip portion (42), which is the portion thereof having the smallest diameter, positioned below a piston crown surface (43) and a pocket portion (44) formed above the lip portion (42). The pocket portion (44) is positioned at a height to which a pilot injection injected prior to the top dead center under engine idling is directed, and the position of a wall surface (45) is so set that a leading part of the injection spray does not collide strongly therewith. The fuel from the pilot injection temporarily stays in the pocket portion (44) and moves into the cavity (6) by means of a subsequent squish flow. Accordingly, an increase in unburned hydrocarbons (HC) is suppressed.