compressed air engine is notg new. We run a model steam engine on compressed air. There is a company in the US that makes "air hogs" and you can buy their model planes in SM and they use compressed air. A pump is used to compress air.
Now, getting compressed air from nowhere is something else. It takes power to produce compressed air.
You can connect a tube to your biyenan's mouth when she is talking. That is compressed air, free perhaps.