CO₂ Motor

This style engine could be powered by steam, but is more commonly seen in small model airplane engines powered by compressed air or CO₂ (carbon dioxide) gas. The popular Air Hogs toy airplanes are propelled by this style motor.

INTAKE : At the top of the stroke, the pin on the piston presses the ball valve upward, admitting high pressure gas into the cylinder.

POWER: The gas expands, driving the piston downwards.

EXHAUST: When the piston advances past the exhaust port, the high-pressure gas is released.

COMPLETION: Flywheel momentum carries the piston upwards to complete the cycle.

I found this information and pictures alongside with an animation that shows  how this engine works 

on the same web-page there are also different diagrams that show how different kinds of engines work.

BY: Ana Martinez