Importance

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Abstract

A piston is arranged within a cylinder so as to be movable upwardly and downwardly, a fuel injector is provided at a cylinder head of the cylinder to directly inject fuel into a combustion chamber in the cylinder, and mixture of fuel and air in the combustion chamber is ignited by a spark plug provided at the cylinder head. Scavenging paths and an exhaust port are provided in the cylinder so as to perform scavenging of the combustion chamber and perform exhausting when the piston is moved downwardly by combustion of the mixture. A top portion of the piston is provided with a convex portion with an inclination surface of which inclination extends in a direction of the top portion of the cylinder from an outer periphery of the piston towards a central portion side. The inclination surface of the convex portion is provided as a linear inclination surface of which vertical section contour is linear such that scavenging air from outlet openings of the respective scavenging paths is blown directly on the inclination surface. An angle .theta. between a ceiling surface at each of the outlet openings of the respective scavenging paths and a perpendicularly crossing surface perpendicularly crossing the axial line of the cylinder is made smaller than an angle .alpha. between the linear inclination surface on the top portion of the piston and a perpendicularly crossing surface perpendicularly crossing the axial line of the piston.

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First Claim