Design and Simulation of Two Stroke Engines

Chapter 1 - Introduction to the Two-Stroke Engine
enge process in a ported cylinder with two or more scavenge ports directed toward that side of
the cylinder away from the exhaust port, but across a piston with essentially a flat top. The
invention was designed to eliminate the hot-running characteristics of the piston crown used
in the original method of scavenging devised by Sir Dugald Clerk, namely the deflector piston
employed in the cross scavenging method discussed in Sec. 1.2.2. Although Schnurle was
credited with the invention of loop scavenging, there is no doubt that patents taken out by
Schmidt and by Kind fifteen years earlier look uncannily similar, and it is my understanding
that considerable litigation regarding patent ownership ensued in Germany in the 1920s and
1930s. In Fig. 1.2, the various layouts observed in loop-scavenged engines are shown. These
are plan sections through the scavenge ports and the exhaust port, and the selection shown is
far from an exhaustive sample of the infinite variety of designs seen in two-stroke engines.
The common element is the sweep back angle for the "main" transfer port, away from the
exhaust port; the "main" transfer port is the port next to the exhaust port. Another advantage
of the loop scavenge design is the availability of a compact combustion chamber above the
flat-topped piston which permits a rapid and efficient combustion process. A piston for such
an engine is shown in Plate 1.6. The type of scavenging used in the engine in Plate 1.5 is loop
scavenging.
Fig. 1.2 Various scavenge port plan layouts found in loop scavenging.
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