In the 6 stroke Crower cycle water is injected for another power stroke and to cool the engine but CO2 + steam causes an acid build up problem if the exhaust steam is condensed and recycled.
In conventional 4-stroke CO2 would come from the exhaust that always remains in the head space.
What they need is a spring mounted piston head -- a few psi retracts the piston. It bottoms out under the pressure of compression/power strokes and provides the usual head space and compression ratio. On the 4th stroke it extends from lack of back pressure and exhausts _all_ the gas and all the CO2 from the cylinder.
Then inject the water on the 5th stroke.
In 2 stroke most of the CO2 comes from the difficulty of precisely charging the cylinder. The goal is for the entire interface to reach the exhaust port at the same time. Either too much exhaust remains in the engine or too much fuel goes out with the exhaust or both.
I'm just thinking out loud.
Bret Cahill