Piston for an internal combustion engine

Claim 1

An internal combustion engine including a cylinder in which is mounted a reciprocable piston, said piston having a combustion chamber formed in its head, the combustion chamber having an inlet orifice in the top surface of the head, a flat bottom wall, and a side wall which includes a plurality of concave recesses which intersect to define cusps directed towards a central zone of the combustion chamber, said cusps including concavely curved portions which extend upwardly from the flat bottom wall and inclined portions which extend between the curved portions and the surface of the head along the surface of an imaginary cone having its apex above said top surface, the portions of the recesses which intersect to define the inclined portions of the cusps forming scallops around the inlet orifice, the scallops being contained within an imaginary circle on which lies the radial extremity of each scallop, and the diameter of said imaginary circle defining an overall diameter of said inlet orifice equal to 50% to 60% of the diameter of the piston, the cylinder including an elongate inlet nozzle for liquid fuel inclined with respect to the main axis of the combustion chamber and positioned in the cylinder so that the axis of the inlet nozzle, when the piston occupies its top-dead-centre position in the cylinder, intersects the flat bottom wall of the combustion chamber at a point spaced from the main axis of the combustion chamber by a distance no greater than 4% of the overall diameter of the inlet orifice.