Combustion chamber structure for diesel engine

Abstract

In the present invention, the piston (4) of this direct injection type diesel engine (1) has a re-entrant 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 the piston crown surface (43) and a pocket portion (44) formed above the lip portion (42). The pocket portion (44) is positioned at a height at which a pilot injection injected before top dead center during engine idling is oriented, and the position of the wall surface (45) is set such that the tip of injection spray does not collide strongly therewith. The fuel from the pilot injection temporarily stays in the pocket portion (44) and moves inside the cavity (6) by means of a subsequent squish flow. Accordingly, an increase in unburned hydrocarbons (HC) is suppressed.

Description

technical field [0001] The present invention relates to a combustion chamber structure of a direct-injection diesel engine. The direct-injection diesel engine is constituted to have a reentrant type cavity on the top surface of the piston crown, and multiple Fuel injection nozzles for injection holes. Background technique [0002] In a direct-injection diesel engine, a technique is known in which a small amount of fuel is injected before the top dead center as a so-called pilot injection in the main injection which injects earlier than the predetermined injection timing after the top dead center. In recent years, attempts have been made to further multistage the pilot injection for the purpose of reducing noise (so-called diesel knock) in the low-load region and improving combustion stability. [0003] As described above, when the pilot injection is injected in multiple stages in a low load region such as at idle, the first injection is performed at a stage when the in-cyli...

AI Technical Summary

Problems solved by technology

If it is a large-diameter cavity combustion chamber in which the inlet diameter of the cavity is set to be large, the cavity will inevitably be flattened, so the swirl velocity and extrusion velocity in the cavity after the top dead center will decrease, and the In the medium to high load area, the deterioration of soot is prone to occur due to insufficient mixing in the cavity

[0005] In addition, Patent Document 1 discloses a structure in which a "cutout" is provided at the opening edge of the cavity, and an inlet lip is formed at a position next to the top surface of the piston, but this Patent Document 1 actively uses the The technique in which the spray collides with the "digging" above the lip and faces upward is not a technique that can improve the deterioration of unburned HC caused by the above-mentioned pilot injection before top dead center.

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