According to law of conservation of energy.

If I have closed, thermally isolated box.

In there, there is a device, which converts thermal energy to mechanical and blows a fan there.

Let's say that box is donut.

What will hapen? Will box move?

Potentinally propelant less space drive.

If you put something really heavy and utilize that work can be bigger to go in unstraight direction, you don't have to have propelant.

Warped motion could provide innertia drive...