Paul,


The same dialog comes up time and again with turbo-compounding.


Everyone agrees, I believes that an axial turbine is more efficient and
would be the theoretically best way to go with a turbo compounding system.
However the costs of designing one or even getting it right, are formidable.
And then we would still need a gear down mechanism and a  complicated
housing casting out of $$$ material. In short we would be turbines design
business not sourcing them. This applies to a directly mounted turbine
running at e-shaft speeds as well.  Great looking idea but how big? I think
it was Gordon who calculated the turbine diameter would have to be about
three feet to provide the torque to put back 30 or more horses into the
system. That causes many obvious problems.

So step down gearing is a must,  and this has pretty much been known since
the  the R3350 was created, and more recently proved again in slower running
diesels.  "Turbines like to run fast, just not too fast," said a wise
contributor of this forum once. We are lucky with the Wankle in that we
don't have to gear down as much to get to a decent cruise speed of 6,000rpm.

Perhaps we could say that well designed turbines like to run at speeds that
cause little restriction to the gas flow that drives them. Obviously with no
lift the blades are not going to turn the shaft at all so there will be some
restriction in proportion to how much power it can output and the blade
design efficiency. The least drag design would probably be an axial turbine
within a narrow band of operation but I am not going stay awake at night
worrying about that small percent difference between the perfect axial and a
off the shelf VGT radial.

For myself I have finished up a lot of projects in the last year so that I
can finally devote more time to the engine project. I now have two engines
(one a junker, in pieces) and I am sourcing an Renesis now.

Still finding a good turbo-charger is not easy. I still have to get a hold
of Francioas about selling me a turbo.  I'm having no luck  finding info
about a Garret VGT unit based on a T4 housing.

One question.  On the Renesis housing, are those two oil injection ports
above the P-port? In my second test engine I would like to duplicate your
work and see if the turbo compound output would have a  similar output to a
13B output.  I would therefore like to enlarge those ports and use them  to
insert the fuel injectors.  Sure it will lower the compression ratio but I
think we can agree that is a good thing for a slightly boosted Renesis.

Doug

Above the P-ports.