In-cylinder direct-injection spark-ignition engine

摘要

An in-cylinder direct-injection spark-ignition engine operable in at least a stratified charge combustion mode where fuel injection is executed on a compression stroke while introducing a normal tumble flow created on an intake stroke to an induced air drawn into a combustion chamber through an intake port, includes a piston movable through a stroke in a cylinder, and having a cavity combustion chamber recessed in a piston crown and formed into a circular-arc shape in a flow direction of the normal tumble flow. The cavity combustion chamber is formed in the piston crown so that the cavity combustion chamber extends from an intake valve side to an exhaust valve side. As seen from a cross-sectional view from a direction perpendicular to the flow direction of the normal tumble flow, a recess of the cavity combustion chamber is circular-arc shaped in cross section by two different curved surfaces being continuous with each other, namely a first curved surface located at the exhaust valve side and having a first predetermined radius of curvature and a second curved surface located at the intake valve side and having a second predetermined radius of curvature greater than the first predetermined radius of curvature. <IMAGE>