Direct-injection spark-ignition engine

A direct-injection spark-ignition engine having an intake air system which is so constructed as to produce a tumble in a combustion chamber whose ceiling is higher at a central part than at a peripheral part as seen in a cross section viewed from a direction from which the tumble seems to be turning clockwise, said engine comprising:

• a spark plug;
• an injector provided at the central part and the peripheral part of the ceiling, respectively;
• said injector injects fuel into the combustion chamber in a direction opposite to a flow of the tumble to produce a stratified combustible mixture around the spark plug at an ignition point during stratified charge combustion operation;
• and
• a piston formed with a cavity on the top surface of thereof, said cavity is in a form of an upper opening being elongated to both the left and right sides of a cylinder axis the a distance between the ceiling of the combustion chamber and a bottom surface of the cavity as measured parallel to the cylinder axis being smaller on the right side of the cylinder axis than on the left side of the cylinder axis and largest at least at a point where the cylinder axis crosses the bottom surface of the cavity, a portion of the cavity to the left of the cylinder axis has a larger volumetric capacity than a portion of the cavity to the right of the cylinder axis, as seen in said cross section;
• and the upper opening of the cavity extends approximately equally to the left and right sides of the cylinder axis as soon in top view along the cylinder axis.