COMBUSTION CHAMBER OF SUBCHAMBER TYPE IN DIESEL ENGINE

PURPOSE:To improve a combustion characteristic at low speed high load operation of an engine, by communicating main and subcombustion chambers through a communication hole, speading sectional area of its passage from the main chamger side to the subchamber side further setting area ratios of both end openings of the communication hole for area of a piston top to within a specific range. CONSTITUTION:The captioned engine is formed such that a main combustion chamber 4, formed by a piston 1, cylinder liner 2 and cylinder head 3, and a subcombustion chamber 9, constituted with a lower part by a cap 5, are communicted by a communication hole 6 drilled in the cap 5. In this case, the communication hole 6 is formed with its sectional passage to oval shape, simultaneously its sectional area is arrnged with a side of the subcombustion chamber 9 winder further with a side of the main combustion chamber 4 narrower. While ratio of area in an opening at the side of the subchamber 9 of the communication hole 6 to area of a top of the piston 1 is st to within a range of 1.6-2.5%, further raio of area in an opening at the side of the main chamber 4 to the area of the top of the piston 1 is similarly set to within a range of 0.7-1.6%. In this way, smoke concentration at low speed high load operation can be decreased to attain the desired end.