Mercury Outboards has a two stroke wth a sealed crankcase as with a four stroke, and with the air-fuel mixture (without an oil component) inected into the cylinder, like fuel injection in four stroke engines. Black Twingle and another poster and I were discussing this as part of another topic earlier, but I thoght it might interest some of the technicians here.
I think an improvement could be made by injecting air during the power downstroke, the air completely pushing the exhaust gas out the exhaust port, and then, with the piston coming back up, inject fuel, the air and fuel would mix, and then at the top of the stroke the spark would ignite the mix. Seems simple to me .. no valves needed .. the crank and rings lubricated as in a conventional four stroke. ANyone want to invest a couple hundred thosand in development?