Ed Huntress wrote:

FWIW, there was an engine of similar concept built in the 1920s. At least a
couple of them wound up in marine installations. Fuel was cheaper then and
they proved not to be worth the complication.

I only mention that because the idea of a two-stage engine producing steam
is really an old one. There were a number of two-stage transportation
engines (trucks or cars) built by the major manufacturers, as prototypes, in
the 1970s.

I found that 1920s engine somewhere on the Web the last time this was
discussed, within the past year.

On a different tack, the current record holder for efficiency is a two-stage
stationary turbine built by GE this year. It ran at 51% thermal efficiency.
These prime movers are one of the two types of gas/steam turbines that are
being built in some new generating-plant installations. The other
technology, which produces efficiency in the 42% - 47% range, is
supercritical steam.

Thanks, Ed.

R,
Tom Q.