Abstract: A projection positioned in the center of a concave section of a toroidal combustion chamber is divided into a section with a steep slope extending from the bottom to the head surface and a section with a gentle slope. The head surface is in the form of a flattened conical trapezoid. Because of its shape, the projection makes it possible for the air which is close to the center section to flow close to the surface of a side wall of the concave section. The air which had been at the center section is added to the amount of air supplied for combustion and is mixed with the fuel in the vicinity of the surface of the side wall of the concave section. By setting the angle at which the air flows along the side wall surface (re-entrant angle) in the combustion chamber, the flow of the air close to the side wall surface is made turbulent, which improves the agitation of the fuel.

Abstract: Variable swirl intake apparatus (24) controls a swirl of intake air in cylinder chamber (22) of an engine.

Abstract: Variable swirl intake apparatus 24 controls a swirl of intake air in cylinder chamber 22 of an engine. Variable swirl intake apparatus 24 has intake port 25 which has entrance portion 25a formed on cylinder head 23 of the engine and extending from the side surface of cylinder head 23 and swirl chamber 25b which communicates with entrance portion 25a and is formed to provide a swirl to a gas flow flowing from entrance portion 25a, intake valve 26, arranged on the lower surface of cylinder head 23, for opening/closing between swirl chamber 25b and cylinder chamber 22 of the engine, swirl control path 28, one end of which is open to swirl chamber 25a on the side of entrance portion 25a with respect to a line connecting the axis along a piston sliding direction at the center of cylinder chamber 22 and the axis of the intake valve, and the other end of which is open to the side surface of cylinder head 23, and a control apparatus 29 for controlling a gas flow into swirl control path 28.