The Kneeslider just posted this article about a new type of 2-stroke engine that is under development. The Kossack engine uses the same rotating assembly as a standard engine, but the piston and combustion chamber have a rectangular cross section. There’s also no wrist pin between the piston and connecting rod. This means the piston and connecting rod can be made lighter and simpler. The Kossack engine can improve 2-stroke efficiency by up to 30 percent by providing better control over intake and exhaust overlap. Head over to the full article on The Kneeslider site for a lot more details and videos of an engine model and the prototype running.