Hi Phil,
Everytime energy is converted from one form to another, there is a loss. A steam cycle suffers from weight, complexity and efficiency problems. I know Mercedes made an announcement about it but that approach is nuts.

It is simpler to take the hot, rapid exhaust gas and pass it through a turbine to extract the latent heat energy with an alternator conversion to electricity. Then dump the electricity into the battery bus, after suitable rectification and noise removal, and voila, just what MG2 needs.

I've been under my Prius and it looks like it might fit in the space of the existing muffler. It is not a trival problem but it is doable. But this is beyond the scope of this forum and thread.

Bob Wilson