Two-stroke internal combustion engine

A two-stroke internal combustion engine comprising:

• a piston disposed in a cylinder, reciprocating between a top dead center and a bottom dead center, and defining a combustion chamber;
• an exhaust port opening in the cylinder and opened and closed by the piston for discharging a burnt gas in the combustion chamber;
• a crank chamber receiving a fresh gas and pre-compressing the fresh gas by a descending movement of the piston;
• and
• a plurality of scavenging passages including scavenging ports for communicating with the combustion chamber and the crank chamber in the scavenging stroke and discharging the fresh gas pre-compressed in the crank chamber as a scavenging gas to the combustion chamber, the scavenging port opened and closed by the piston, wherein
• the scavenging passage included in the plurality of scavenging passages and connected to at least one of the scavenging ports constitutes a variable scavenging passage, wherein
• an upper end portion of the variable scavenging passage has a guide surface being constituted by a side wall surface of the variable scavenging passage on a cylinder intake side and defining a discharge direction of the scavenging gas discharged from a variable scavenging port connected thereto on a horizontal plane, wherein
• the guide surface includes at least a first guide portion defining a first discharge direction of the scavenging gas and a second guide portion defining a second discharge direction of the scavenging gas, and wherein
• the discharge direction of the scavenging gas is changed horizontally, orthogonal to a vertical movement of the piston, from the first discharge direction to the second discharge direction by the first and second guide portions in the scavenging stroke.