Hi all, Doug + Paul,

I snipped most of it to make it short...

BTW I forgot to mention this Doug. An RX8 with 30 MPG  in the EPA

highway

driving cycle would make a monumental impact in the automotive world.
Currently the RX8 is rated at 25 MPG. 20% better would put it over
the magic 30 MPG. The shock wave would be heard in every major auto
manufacturers board room around the world. A 20% improvement in fuel
consumption is totally unheard of in the automotive industry.
Automotive engineers would sell their grandmothers for only a 2%

improvement.

This would be easy to achieve with 60 year old turbo compound

technology.

So why not use the 60 year old and modernize it! See below.....

I'll explain it another way. A small turbine is chosen to optimize
the exhaust power available when the engine is generating HP below

4000 RPM

and partial power. We are looking for only six to eight HP here or 20%

of

the engines 30 to 40 HP with commensurate torque. Typical of the RX8

cruising

down
the highway at 80 MPH in sixth gear. At 3000 RPM the RX8 is doing 60
MPH in sixth gear. So from 3000 to 4000 RPM is the range we are

interested

in improving the MPG. We don't really care what it does WOT.

This tiny turbine would be rapidly destroyed by over speed and/or

excess heat

if we increased the power of the engine by running it WOT above 4000

RPM.

Therefore the waste gate is opened by the computer at anything above
4000 RPM and moderate intake manifold pressure (partial throttle).
If necessary the passage to the turbine can be blocked as well.
I hope this clarifies the situation.

Mazda has already quite a bit experience with sequential turbos so why not:

a) Use a sequential twin turbo with a freewheel unit between them. This way,
one can spool up fast, the other can kick in later. To avoid overspeed use
the drive from a CVT as Mazda must have some somewhere too, out of some
small city econobox. According to your calculations the single turbo will
only make some 8-12 hp more. So even if the twin turbo runs all the way to
max hp, lets say at 9000rpm, they would not put out more than lets say 50
hp. A CVT should be able to take that easy. Besides it only has to stay
constant from your suggested 4000rpm to max - control should be simple as
there is no need for powermanagement via CVT just constant rpm above
4000rpm.
Though it should be possible to incorporate some electronic control to spin
the turbo at the optimum speed even below 4000rpm.

b) To avoid a freewheel unit between the turbos you could use to complete
units as in your drawing. One boosting, while the other is coming online
later, as more power is blasting down the exhaust!

c) With full turbo speed control via electronic CVT drive, you might even be
able to get away without the twin-turbo - as long as the single turbowheel
can thake the "heat" :). At least rpm wouldn't be any concern above 4000
rpm - just heat.

d) Additionally I would explore to still have some intercooled turbocharging
to fill the chambers! With little boost (7-8 psi), but electric booster!!

This is of course strictly earthbound, as we would not need all this in an
aircraft with near constant rpm...

Thomas J.  :)

 
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