Paul,

Can you direct me to the article or post on turbo compounding using
electric generator to drive a DC motor connected to the E-shaft method.
While the conversion losses may be higher then that of a direct
drive via speed reduction unit, it would appear that the electric
method would be fairly easy for the home builder to put together.

Thank you
Rick.


Here are a couple of papers from the DOE on
the Caterpillar program.

Paul Lamar


Paul,

Thank you for the documents on electric turbo compounding.  Of course my interest
is in Turbo Compounding a 13b.

Given the available exhaust heat/pressure in on a 13BT what size generator
and what size crankshaft motor would you suppose is needed to recover any excess energy?
What would you guess the mechanical/electrical/thermo losses might one
see a rotary setup? (in terms of %)

What sort fuel efficiancy would you guess/estimate can be realisticly
gained from such a setup on a 13BT?  I know that these are all very
vague questions but I'd like to get an idea of the "ballpark" figures.

Do you have any off-the-shelf turbos that would be suitiable to modify
and incorporate into a turbo-compund application?

Overall I can see why you are so passionate about turbo-compounding,
I too ask myself if it such a great thing then why
hasn't anyone put
it into wider use? --Although I am guessing that the answer to this
question is more complicated then the technical challege of putting
together a practical Turbo Coumpound system together.

Thank you
Rick.

50 HP recovered is about doable on a two rotor. However an electric solution
means you will throw away about 10 HP of that or 20% not to mention the severe
weight penalty.

I think a 15% improvement in BSFC right off the bat with an all mechanical system
is very doable.

As development progressed we might see as much as a 25% improvement down
the road.  It also depends on the altitude and the duty cycle.
Aircraft engines will see the most benefit.

We just can't go on throwing away 50% of our gasoline out the exhaust
pipe of our internal combustion engines.

The turbo with the most potential is a Borg Warner used on Porsche's
with a variable area
nozzle.

Paul Lamar


Paul,

I see your point, The weight penalty of an electric system capable
of transferring 50HP to the crankshaft does seem to be a bit much.

It would appear that a mechanical system would be the best design,
I suppose that the challenge then becomes gearing down from a
turbine speeds down to crankshaft speeds.

I noticed the Wankel-axial turbine concept on your website....
http://www.rotaryeng.net/Turbo-compound2-3D.jpg .  Is this only
a concept or is there someone working on a actual prototype?
Have their been any discussions/posts/web links on this design
that you can direct me to?  What are the pros and cons of the
Wankel/axial turbine design?

Also, in one of your online video's you had made mention of NASA
recovering 80HP out of a Turbo compound Wankel back in 81' or
91'.
What sort of set up did they have?  is there any info available on
their efforts?

Thanks much,

Rick.

As far as I know nobody is working on that concept but it is the
simplest. The trick is to get the blades up to 300 or 400 MPH at 7500 RPM.
That is were you get max HP from the  600 or 800 MPH exhaust gas.

Yes. Download this paper.

http://www.rotaryeng.net\NASA-Paper-turbo-compound-rotary.pdf

Paul Lamar

Paul,

Thank you for the link to the NASA paper... it's 200 page PDF chuck full
of high level data so it will take me a while to go over it... should
make some interesting reading.

Who came up with this rotory axial turbine layout/design?

You wrote;
"The trick is to get the blades up to 300 or 400 MPH at 7500 RPM. That
is were you get max HP from the  600 or 800 MPH exhaust gas."

Can you expand on this a little for me... I'm not quite following
what you are saying.

Also, in looking at this design I would imagine that a high
temp/high wear seal between the shaft and the turbine would be
required.  I can also see that cooling the turbine shaft would
be an issue.  What are your thoughts on these as it pertains to
the large diameter axial turbine design?

Rick.

A little turbine theory.
When the blades are stationary and the gas velocity flowing through
the blades is high torque is a max but HP is zero. When the blades are
going as fast as the gas the torque is also zero as well as the HP.

Right around 50% blade velocity to gas velocity HP is a max
and torque is half of what it is a zero blade velocity.

I had to explain this to all the phd's in charge of Formula One
R&D at the World MotorSports symposium :)

It is
in my video.
http://www.rotaryeng.net/Oxford-640-4802.wmv

Shaft seals made from Teflon would work. SS hubs will transfer
less heat to the shaft. Also the blades are self cooling as they
are hollow and pump cooling air through them. A feature of all
early GE aircraft turbo chargers starting back in WW I.

Paul Lamar


Paul,

Thank you for the clarification... its seems obvious now that you have explained it.

Some rough calculations for 350mph blade velocity at 7500rpm put
the direct drive turbine diameter at about 1.35 ft... not too
unreasonable.  do you see a problem with incorporating a second
stage turbine to recoup the an additional 25% from the exhaust flow?

Does anyone produce 'off the shelf' axial turbines  that are
suitable for this design?

I am trying to envision the concept of air flowing threw the
vanes of the turbine.  I can see how air would be forced
threw by way of centrifugal force but how does this cooling
air exit the system??

The only way I can see this at the moment is if exhaust
ported out to the atmosphere immediately after hitting
the turbine.  Would you happen to have any
detailed pictures of this type of system... perhaps one
of the earlier GE systems you made mention of?


Thanks much

No and in fact that is a good idea. That is a relatively cheap
and technical risk free way of doing it as turbine technology is off the shelf
from Barber Nichols.

   http://www.barber-nichols.com/

Here are some pictures of the R3350TC housings.

Paul Lamar




    Again thank you for the info and the pictures.  I was up into
the wee hours last night scething, drawing and coming up with
new questions. -In short, desktop experimenting.

I mention off the shelf turbines because hobbyist need to remain
as practical as possible.  Would you happen to know of a
Barber-Nichols turbine model/part number suitable for what we
are talking about?  Also would you have a ballpark idea of their
cost?

Also... something else that I can not pin down in my head...
Considering that it is being propelled by the motor, does a the
compounded turbine develop PEAK HP at 50% flow rate ?  I guess
this question comes to mind because in my visualizationson of
the system, I see the the exhaust flow 'chasingin a moving
target' thus closing/widing the speed gap between the exhaust
flow and the turbine. -or- does the fact that the exhaust flow
is perpendicular to the rotation of the turbine make this a
non-issue.............. I am starting to think that RPM should
be determined by the flow to the turbine with the engine
throttle being second.  Are my assumptions on on the right track
or am I missing something?

My mind is spinning faster then the turbine.

Rick.

Other than a R3350 turbine I know of no other parts numbers but
I am not into turbo jet engines. I'll bet there are a bunch
of used turbo jet turbines out there that will work.

Here are the pictures Rick is referring to.

It develops PEAK HP at 50% no load peak FREE to turn turbine RPM.
Not shown in the pictures.
Lets say the exhaust flow is 800 MPH. If the blades are going
800 MPH on a free turbine then there is no load on the turbine.

In the pictures the turbine is fixed to the e-shaft and cannot exceed
the RPM of the engine therefore the blade diameter is sized to go half
exhaust gas velocity.

At 50% exhaust flow rate the turbine HP would be way down.

The exhaust flow to the turbine will be max at wide open throttle
at the engine red line. In the case of a P-port rotary that
will be around 10,000 engine and turbine RPM with this configuration.

At wide open throttle at less than red line the flow to the turbine
will be a max FOR THAT ENGINE and TURBINE RPM!

This remains the easiest and lowest cost way to build a turbo compound
rotary to demonstrate the fuel burn advantages and HP increase. No high
reduction ratio gear box required. All that is required is a little
Inconel or SS sheet metal fabrication and an off the shelf turbine.

Paul Lamar


Paul,

I absolutely agree that this is the most straight forward method to Turbo compound.
After countless hours of trying to identify the variables (turbine dia,
flow rate, RPM, ducting.. etc) it would appear to me that what is needed
is a variable pitch turbine.

Now the question is this... is it easier to vary the pitch of the turbine
or is it better to vary the flow rate?  I"m thinking that varying the
exhaust flow rate would present efficiency losses and some exhaust
back pressure.  What are your thoughts on a variable pitch turbine?
Does one even exist?

Also,  what are your thoughts with regards to controlling engine
RPM by variing the exaust flow to the turbine.?

Rick.

Borg Warner makes a turbo charger Porsche uses with a variable
area nozzle. In effect almost the same thing as variable pitch turbine.


Paul Lamar