Piston for a direct-injection spark-ignition engine and a direct-injection spark-ignition engine equipped with the piston

To provide a simple piston structure for a direct-injection spark-ignition engine which can properly stratify the mixture in the proximity of the spark plug in the stratified-combustion operation, without impairing the reliable ignition of the spark plug. In the direct-injection spark-ignition engine (1), the central portion of the roof of the combustion chamber (6) is located at the higher level than its peripheral portion, the spark plug (16) is disposed in the central portion, the fuel injector (18) is disposed on the left side of the central portion, and the fuel injector (18) injects fuel so that the fuel confronts against the tumble flow produced in the combustion chamber (6) in such a manner that the mixture is concentrated in the proximity of the spark plug (16) and ignited, in the cross-section in which the tumble flow turns clockwise. On the piston (5), a cavity (27) having the bottom surface along which the tumble flow flows and extending to both sides of the cylinder axis (Z) is formed, and a step (28) is formed on the left side of the cylinder axis (Z) on the bottom surface of the cavity (27) for guiding the tumble flow upwardly, in the cross-section above.