CO2 motors are quite old and have been around for a long time. The CO2 cyclinder is connected to the place glo head would normally go. When the piston reachs TDC, a pin taps a ball check valve, and CO2 enters the cyclinder and pushes it down. The prop creates a flywheel that swings the piston around and back to TDC where the cycle starts over again. This continues until the CO2 cylinder is empty.

These motors can be very small or rather large, depending on the application. There are even multi-cylinder motors, in-line, V-8s, radials and rotary engines. Here's a ******* link to Sam's Models in the UK. Click on 'Gasparin CO2 motors' for a page showing some of the available CO2 motors: http://*******.com/4ywr