This is just the passive rotor part.
It would be mounted in a round shaped holder that supplied compressed air, or one that had hemi heads and combustion chambers, or magnetic coils or whatever.
If it was used in an engine design, you might have say 3 pistons per rotor. You could then have three combustion chambers external to the rotor.
Then you could idle on one chamber, cruise on two chambers, pass or go uphill on three, whatever you want.
And firing timing would not be much of an issue, because as the piston itself rotated under the combustion chamber, it would be activated.
Really, it’s a very simple idea.