I've seen that before. I think he's being too optimistic about the fuel savings. I haven't seen any test results so far. BMW was experimenting with using a steam engine (the Turbosteamer) to use the waste heat of a gasoline engine and they said that the efficiency would be up to 15% better. It seems wasteful to allow the exhaust gas to escape and then use just the heated combustion chamber to generate steam. I wonder if it would be better to inject water into cylinder during the power stroke and keep the engine running as a four stroke.
http://en.wikipedia.org/wiki/Turbosteamer