Thanks. =)

What would be the point of fitting a larger compressor to slow down
the turbo? Larger compressors have a higher "comfortable" flow rate
and function very poorly if this rate isn't carefully matched to the
engine it is supplying. A bigger compressor would allow the turbine to
extract more work from the exhaust gas, but the extra airflow this
generated would have to be wasted or it would literally back up and
flow out the compressor inlet several times per second. This "surge"
really beats up the turbo and just means you're asking the compressor
to operate in a pressure-flow regime it is incapable of.

One thing they did in the F1 turbo era was to use very large
compressors to circumvent the poppet-valve release used to control
boost pressures. The story as I remember it is that at some maximum
permitted pressure, a valve on the intake would open and vent charge
air to the atmosphere until pressure dropped below the max allowed
value. Teams selected turbos that would outflow the poppet valve,
which would have looked rather something like you described: a big
compressor wheel fitted to a smaller exhaust wheel, possibly lacking a
wastegate altogether. Naturally this uses ALL of the exhaust energy
the turbine is able to reclaim, but the extra work is still being
wasted.

If you wanted to use an air motor to drive the crank, you could use an
exhaust-driven turbo to supply it for some Rube Goldberg-style turbo
compounding. The frictional losses would likely be obscene. =D


I have a PDF version of the 2nd edition of that book. I have not
exactly read it cover-to-cover though.

-Chris.

Our biggest problem is the turbine blows up after a few hours.
The built in waste gate is too small. Even when wide open.
True the heat is high but the excessive RPM is the main culprit as
the load on the blades is m*V^2/r. A pop off valve on the intake manifold
would be no problem. So far a bigger compressor seems to be working almost fine
on Dave Leonard's turbo 13B in his RV6. My guess is the turbine is three or four
times more powerful than needed for continuous operation. The excess power is
there to accelerate the compressor as quickly as possible.

Dang now you tell me :) Can you email me the pdf?

Paul Lamar

Paul,


I believe Dave Parks uses a pop-off valve in his TE-06 turbo set up.  It
makes sense to control surge.  I will install one for safety purposes
even though I have a bypass valve to unload the  supercharger or
completely bypass it.

Chris,

Thanks for the input and link to the Nye company.  They may be just the
people we are looking for.  A turbo gen set has always been a passion
for me but I don't see it in turbo compounding a aircraft engine
because of the downstream component weights.  Power generation at a
fixed base or large truck, running on biofuels, yes definitely.

Where are you located by the way? I am in the midst of trying to identify
a candidate for some turbocompounding proof of concept testing and I'll
be in the states for the next week on the West Coast of USA.  Have plane
can travel.... well  a little ways a least:).

I would appreciate your observations on trying to ball park a turbine.
Reeves Callaway gave us some good advice about picking a turbine that
can swallow the whole gas flow of our engine as a starting point.
Probably in a T4 size shell. Problem is we don't really know how to
measure the exhaust gas flow yet, and that is something I would be
interested to know.   I know how to measure air flow  on the intake side
with a variety of techniques including ultrasonics.

It has been suggested before that we roll our own axial turbine but that
step is down the road a bit and has its merits and demerits.  In the
end,  perhaps a hybrid enhanced guided flow radial turbine would be most
compact, and easy to install unit at the expense of some loss in
efficiency.

From Garrett's website I picked up three possible candidates to try and
JUST DO IT, though I admit these choices could be laughable unsuitable
and a waste of time and money.  I am only interested in the turbine side
and fitting a traction drive where the compressor normally resides.
First tests  the turbo/traction drive is connected to a small dyno.
Design goal is 80 hp output and turbine operating at some point between
75K and 90K rpm.   Your comments would be appreciated.

The turbines are from smallest to biggest:
Model            Wheel dia.        Trim               A/R
GT3571            68                 84                 1.18
GT3582R          68                 84                 1.06
GT4508R          87                 86                 1.01  to 1.44

Doug in Japan

Paul,


It is worth contacting this company.  Check this out.

http://www.nyethermodynamics.com/nt-rt30/index.html

Doug in Japan

I did. It is vapor wear so far. I sent the following questions
on Tue, 23 Sep 2008 05:31:31 and I did not receive an answer yet.

What is the operating temperature of the magnet?
What is the tensile strength of the magnet material?
Is the bearing assemble water cooled?
How much electrical power can one extract from a 200 HP
2.6 liter engine?

Paul Lamar

Paul,

I am not speaking about the turbo charger radial gen set. That obviously
is a high rpm unit and is a challenging project.

I was speaking about the axial turbine design which is labeled "NT-RT30
(Low Speed Radial Turbine)"  How low of rpms is the question.  As a
final design something like this could be a candidate.  I thought you
would appreciate the design of the shroud, elliptical cross section
diffuser, central exhaust, and of course the axial turbine.  Mounted on
the pulley side of the engine and the recovered torque brought in either
via a belt or direct soft couple would be sweet.

Doug

You have got to be kidding. As far as I can tell it is a totally unique
concept. There would be tremendous heat lost in the axial diffuser.
The stress on the blades would be complex and problematic.
It looks like something you would see in a Hydroelectric station.

The elliptical part is the collector. The gas or water must enter axially
judging by the blades shapes.

What time is it over there?

Paul Lamar

Paul,

Yes it is unique, but I am not experienced enough to judge if it will
work or not.
As for the time it is now  Wed. 21:12.  I'll be here for another 19
hours.

Doug in Japan