Divided chamber type diesel engine

Claim 1

A divided chamber type of diesel engine including a block containing a cylinder; a cylinder head mounted on the block; a piston in the cylinder; a main combustion chamber defined between the piston and the cylinder head; a cavity formed in the cylinder head and opening into the main combustion chamber; and an insert member rigidly fitted into the opening of the cavity provided in said cylinder head, the insert member having a cavity facing the cavity in the cylinder head to define a pre-combustion chamber and a port connecting the pre-combustion chamber to the main combustion chamber, wherein the improvement comprises: the cross-sectional configuration of said pre-combustion chamber is substantially circular, and the radius R of the cross-sectional portion of said pre-combustion chamber formed by the cavity in said cylinder head is slightly smaller than the radius R' of the cross-sectional portion formed by the cavity in said insert member (R < R'), whereby a step portion is formed on the inner circumferential wall of said pre-combustion chamber for controlling the swirl generated in said pre-combustion chamber during the compression stroke of the diesel engine in order to reduce the NO x emissions in the exhaust gases.