Two-stroke internal combustion engine

摘要

There is provided a reverse scavenged two-stroke internal combustion engine that is capable of effectively suppressing the short-circuiting of fresh charge (unburnt air-fuel mixture), while at the same time being capable of further improving scavenging efficiency, combustion efficiency, etc. The horizontal sectional shape of at least one pair of scavenging passages (31, 31 and 32, 32) is closer to a triangle than a parallelogram along substantially the entire lengths of the at least one pair of scavenging passages, where a cylinder outer circumferential side of the horizontal sectional shape is narrowest and a cylinder bore wall surface (10a) side of the horizontal sectional shape is wide. Further, horizontal scavenging angles (α, β), which are angles of intersection formed between lines (Ea, Ea and Eb, Eb) extended towards an intake port (33) from guide wall surfaces (31c, 31c and 32c, 32c) that define the scavenging passages (31, 31 and 32, 32), are acute.