Cylinder structure of internal combustion engine

A cylinder structure of an internal combustion engine comprising:

• a body having a combustion chamber surrounded by an external fence and a cylinder head, an air inlet defined on a first side of the combustion chamber, an air outlet formed on a second side of the combustion chamber, and two scavenging units formed on the combustion chamber and intersecting with the air inlet and the air outlet, wherein a respective scavenging unit has a first scavenging orifice, a second scavenging orifice, a first fringe and a second fringe which are configured to surround the first scavenging orifice and the second scavenging orifice, a first engagement portion arranged between the first fringe and the second fringe, and a first fixing orifice defined on the first fringe;
• two lids covering the two scavenging units so as to close the first scavenging orifice and the second scavenging orifice, and an air conduit being defined between a respective lid and the external fence, such that when the internal combustion engine scavenges exhaust airs, the exhaust airs are drawn into the first scavenging orifice and are discharged out of the air outlet via the air conduit and the second scavenging orifice, and the respective lid has multiple second fixing orifices located on an internal wall thereof;
• and
• multiple positioning elements, wherein a respective positioning element has a stem and at least one hook which extends from a first end of the stem, the stem extends into the first engagement portion along the first fixing orifice and a respective second fixing orifice, and the stem is rotated so that the at least one hook contacts with the respective lid, and the respective lid is connected with the body.