aha, i was wondering how that worked. Creating pure sodium using the Downs process requires a lot of electricity and I doubt this engine would be economic if that was required. But it looks really promising, >= 40% efficiency is a great goal.

If such a generator were powered by nat gas rather than being a battery of sorts, then even being a bit less efficient than an ICE would be attractive if the generator were simpler and had a lower TCO than the ICE equivalent.