Abstract: A combustion chamber of an in-cylinder direct fuel injection spark ignition engine having a pentroof composed of an intake side roof and an exhaust side roof, a piston, and a cylinder. The combustion chamber has a fuel injector provided between the intake side roof and the exhaust side roof inclined toward the exhaust side port, an intake port provided on the intake port side roof at an acute angle with respect to an extended line from the exhaust side roof so as to form a tumble flow of intake air along the exhaust side roof, a piston cavity with a curved surface formed on the top surface of the piston so as to reflect a fuel spray injected from the fuel injector together with that tumble flow in the direction of the intake side roof, and an electrode of a spark plug projected from the intake side roof so as just to collide with the tumble flow.

Abstract: Disclosed is an apparatus for generating a tumble in a cylinder of a fuel injection engine in order to improve combustion. The apparatus comprises an air intake passage having a straight portion whose center line is approximately in parallel with a roof face of the combustion chamber on the exhaust valve side and a tumble control valve for generating a tumble in the cylinder. The tumble control valve is a flap valve or a butterfly valve for closing a second air intake passage and for opening a first air intake passage.