Editing Piston (section)

====Deflector pistons====
[[File:Two-stroke deflector piston (Autocar Handbook, 13th ed, 1935).jpg|thumb|left|upright|[[Two-stroke engine|Two-stroke]] deflector piston]]
Deflector pistons are used in [[two-stroke engine]]s with crankcase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient [[scavenging (automotive)|scavenging]]. With [[cross scavenging]], the transfer (inlet to the cylinder) and exhaust ports are on directly facing sides of the cylinder wall. To prevent the incoming mixture passing straight across from one port to the other, the piston has a raised rib on its crown. This is intended to deflect the incoming mixture upwards, around the [[combustion chamber]].{{sfn|Irving, Two stroke power units|pages=13–15}}

Much effort, and many different designs of piston crown, went into developing improved scavenging. The crowns developed from a simple rib to a large asymmetric bulge, usually with a steep face on the inlet side and a gentle curve on the exhaust. Despite this, cross scavenging was never as effective as hoped. Most engines today use [[Schnuerle porting]] instead. This places a pair of transfer ports in the sides of the cylinder and encourages gas flow to rotate around a vertical axis, rather than a horizontal axis.{{sfn|Irving, Two stroke power units|pages=15–16}}

{{Commons category-inline|Deflector pistons}}