Hi,
TRY, You heel my wounds ...
Year 2002. That time I was at sea. I sailed on a commercial ship and found one dutch magazine, (probably "Panorama") and there was an article abt compressed-air-driven-car, developed in France.
With one air charge that car could make 500-600 km.
Is it, what You meant / developed ?
I was so sticked with that idea, that started to draw / build my own "air-engine".
I used 1 empty vessel (30 bars allowed), 1 very old 2 cyl. gas engine, 1 air reducer...
Well, that thing worked. Of course, not efficently as I wanted, but it worked.
I'm not sure, how You transfer air pressure into rotating movement (I think - reciprocationaly), but :
1. with a good timing of inlet / outlet valves (probably - electronic timing could be considered),
2. with a very good lubrication of parts,
3. may be double expansion should be considered ?
4. and may be some parts need to be warmed up ?
this engine will have efficiency.
But, "efficient" means what it means.
Compressed air has to be produced.
By compressors.
And here is the point ! ...
If we going to use ENVIROMENTALY FRIENDLY ELECTRICITY (to drive compressors), then, congradulations, we will have a clean engine ...
So, I doubt in very high efficiency, but, because of enviroment, this concept is great.
It is more safe, more simple than hydro-engines.
I'm not sure, who will strive to buy patents...
Oh, yes, still same names (as usual)

...: B*, SHE**, TEXA**, AGI*, TOTA*, STATO**, ...
There is a problem, not engines.
TRY, I will support this concept as much as I can.
Will be happy to help / support / develop / calculate / mount / pack / weld / cut / carry / check / etc.
Please, contact me, if necessary.
Kind regards and respects,
Andrei