Animated Engines

CO₂ Motor

This style engine could be powered by steam (I’ve heard of at least one), 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 downward.

Exhaust

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

Completion

Flywheel (or propeller) momentum carries the piston upward to complete the cycle.

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This animation also illustrates the CO₂ reservoir. Compressed CO₂ is a liquid and becomes a gas as the pressure is released. In other words, the liquid CO₂ boils at normal atmospheric temperature and pressure, so one might say this engine runs on CO₂ steam.