Lots of working paper engine models on the web, but this builder, Aliaksei Zholner, is really prolific on YouTube. Some short videos, including a rotary and Stirling engine made out of paper. These engines run on air, and you can see them run in the videos, often from air supplied from an inflated balloon.
All of these videos are under 2 minutes long, except the last one at 3:02.
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