Lego compatible compressed air engine

I wanted to make a smaller engine, someone said it would be nice if we could power lego with it.
so, it had to
- be small
- fit lego
- not be to powerful
- run on not too much pressure
- be self starting

so it's just that, a small simple self-starting lego compatible engine :)

short clip..
https://www.youtube.com/watch?v=YkbbkBF4Dc8