> Hi Bill,
 > There may be a potential pitfall to your idea. The axial flow blade
 > shape (twist, airfoil shape, length) would have to be optimized for a
 > particular gas flow. That would mean a bell curve for efficiency. (There
 > would be down slopes either side of a particular point.) As you go to
 > altitude, less and less gas would be produced so a design optimizing the
 > bell curve high point that works well at sea level will not be the
 > optimum at altitude. Some compromise would have to be allowed for. The
 > most logical scenario would be to design for 8000 feet at whatever gas
 > pressure is available from the engine at that altitude. Above 8000
 > you're WOT and nature will decrease gas flow as you go higher , and
 > below that level the pilot can maintain gas flow if
 > the additional performance is required. The downside here is that to
 > receive 'compound'  fuel efficiency benefits at say 3000 ft the aircraft
 > has to be operated at WOT which may not always fit the flight
 > mission.    Dave M

 All the more reason to put a turbo charger after the turbo-compound
 turbine so that you turbo normalize the engine. Who doesn't want their
 available power at altitude to be close to full?

 -dave

 The ideal configuration is have the turbine and the compressor on the
 same shaft. That minimizes heat and kinetic energy loses.


 Paul Lamar

Is that right (ideal configuration)?  It sounds like you are saying a
single stage turbine is more efficient than a multi-stage turbine.
That's not true for jet engines..  Maybe that's an apples to oranges
comparison..


Matt-

What I am trying to say is there are heat loses and kinetic energy loses
in the plumbing on the typical dual turbine, turbo compound installation such
as DD, Scania and Caterpillar.

Some multistage turbines are on the same shaft.
Perhaps the best configuration is have the blow down turbine
on one shaft and the compressor turbine on another both turbines
in the same housing to minimize heat loses. Perhaps coaxial shafts
can be used. This is done in turbo fans. The first smaller turbine
drives the compressor and the larger diameter second turbine drives
the fan.  In our case the second turbine could be the power turbine
for the turbo compound part. Power for the TC could be taken from
the center of the turbo charger so to speak. Much like the Napier Nomad.

Obviously an engine years ahead of its time :)

All this is moving further and further away from Bill Jepson's KIS.