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Cylinder and ports, viewed from above. Schnuerle porting [1] [2] is a system to improve efficiency of a valveless two-stroke engine by giving better scavenging.The intake and exhaust ports cut in the cylinder wall are shaped to give a more efficient transfer of intake and exhaust gases.
For normal automotive design this point is almost always between 69 and 79 degrees ATDC, with higher rod ratios favoring the later position. It only occurs at 1/2 stroke (90 degrees) with a connecting rod of infinite length. The wave/flow activity in a real engine is vastly more complex than this but the principle is the same.
Animation of a two-stroke engine. A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston (one up and one down movement) in one revolution of the crankshaft in contrast to a four-stroke engine which requires four strokes of the piston in two crankshaft revolutions to complete a power cycle.
A stroke is the action of a piston travelling the full length of its cylinder.In a two-stroke engine, one of the two strokes combines primarily the intake stroke and the combustion stroke, while the other stroke primarily combines the compression stroke and the exhaust stroke, though technically since both ports are exposed during both the combustion and compression strokes, some reversion ...
A port-map can be useful to determine opening/closing-timing and the area of specific ports. These diagrams are usually represented as a rolled out cylinder where the width equals the circumference and the height equals the stroke plus the cylinder skirt, the ports are outlined.
For two-stroke engines, crossflow scavenging was used in early crankcase-compression engines, such as used by small motorcycles. The transfer port (where the fuel/air mixture enters the combustion chamber) and the exhaust port were located on opposite sides of the combustion chamber. This arrangement had the advantage of simplicity, but it also ...
The advantage of the split-single engine compared to a conventional two-stroke engine is that the split-single can give better exhaust scavenging while minimizing the loss of fresh fuel/air charge through the exhaust port. As a consequence, a split-single engine can deliver better economy, and may run better at small throttle openings.
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