Paul,


Some more thoughts on turbo compounding.  Reading the NACA. report No 822
again it was revealed the blowdown turbines were calculated to be 85%
efficient.  Total reduction in BSFC at sealevel was 9% and  21% at
30,000  Mentioned throughout the text are the words "gear turbine and
supercharger."  In other words, both objects were geared to the engine
shaft and that for calculation purposes it should be assumed they are
gear to the same shaft.

The first paragraph of the INTRODUCTION states that  "The use of an
exhaust gas turbine to drive a supercharger at high altitudes is an
effective method of maintaining sea level engine power at altitude.
Talking about a turbocharger here.  Next line.  "Analysis has shown
however that the waste energy of the exhaust gases is recovered more
effectively by maintaining an engine exhaust pressure higher than the
minimum required for turbosupercharging.
Next paragraph.
"The purpose of the analysis reported is to determine the improvement in
net brake specific fuel consumption that can be obtained if an engine is
equipped with a geared turbine and [geared] supercharger as compared
with the engine using a standard turbosupercharger.

Note this means it is inherently more efficient to use a supercharger to
boost the engine to higher exhaust pressures than required for to run a
turbocharger.Hence all exhaust energy at a higher potential level
goes through a highly efficient blowdown turbine.

This is a important concept.
Yes the rotary wankel has a more powerful exhaust then the old [radial]
piston engines but the operating efficiencies of  centfrigical turbines
found in mass produced turbochargers are only about 50%.  Operating
efficiency of the compressor are about 70%.  Total power extraction
efficiency therefore is about  35%.  Actually lower if the an
intercooler has to be used.  I have heard about 1/3 of exhaust energy
extraction numerous times so this estimate is probably correct.

As you and others have mentioned many times the rotary has exhaust energy
in excess of the 30 or so hp needed to operate the turbo attached
compressor.  Less energy loss in the compressing system is required for
the Rotrex  supercharger.  Don't want to fool with superchargers or
large blow down turbines?  Here is a solution.

If there is indeed another 50hp ready to be captured beyond the needs of
the turbo-charger requirements a quick and dirty test will reveal if
this is true or not.  I am advocating connecting the standard Hitachi
turbo up to one exhaust port and seeing  if it will supply the necessary
air flow to normalize the engine at 18,000 feet.  At 15 psi this is at
least 35lbs per minute at 200hp power settings.

Two possibilities.  It performs as expected or it doesn't perform as
expected.

1.  It doesn't perform?  OK so there is not as much recoverable energy
in the exhaust as we originally thought...  Aw Darn! Forget about TC
systems.  Good news is: Attach a  turbocharger and get on with other
testing.

2.  No problem?  It works  Great!  Continue to test the torque on the
turbine to verify the maximize horsepower output of one port. Perhaps
the turbine can be upsized to normalize the airplane at an even higher
altitudes.  Bad news: Aw Darn!  More work to design a TC turbine:)

For tractor configurations  mount the  turbo-charger on the PSRU side
with the compressor facing into the wind for some free rammed enhanced
boost and/or turbo cooling if needed.  Yes the turbine and compressor
sections can be rotated into other positions. Oversized? No problem.
Waste gate and blow off valve decrease turbine power and airflow.  Down
low waste is acceptable for short term.  Either that or increase fuel
flow and use the extra HP to get out of town fast.The cooling system
needs to be sized properly or the flight will be short lived.

For the other free exhaust port/s whether 13B or 20B,  use them for a
turbine compound system to bring power into the accessory side.  50 hp
available?  Another plate and bearing will be needed to support the
overhanging loads applied to the e-shaft.  Suggest an early 13B housing
or custom  CNC housing.

Doug in Japan


You are forgetting one thing. Rotaries have been boosted to extraordinary
manifold pressures. Take a gander at the size of the turbo charger on this 1200
HP 3 rotor engine. I am willing to bet the turbine in this turbo charger is
generating as much as 300 HP. Here too is a HP curve of a 1996 700 HP 2 rotor
side port engine. The dyno sheet was given to me by Abel Ibarra hisself :)
Yes the engine was using alcohol and NOS but it still takes a lot of air to make
this kind of HP.

Paul Lamar

Paul,

Yes they have been boosted to high levels but all this tells us is that
the block and cooling systems are robust and the run duration is a very
short time.  More air requires more fuel and waste more hot gases that
can drive a bigger turbine.  This also indicates the ports are large
enough to be able to pass more gas.  Both are beside the point I am
trying to make.  Your statement that the turbine is  generating 300 hp
is misleading.That  potential may be passing through the port or even
the turbine it surely isn't capturing or even needs to capture it to
drive the compressor of that size.


Check out the world of industrial compressors and blowers and you can see
for the same SCFM  requirements Hp inputs are tiny.

http://www.hsiblowers.com/products/high-speed-turbo-blowers.html


Doug in Japan.

I guess I am missing your point. For the most comprehensive study on the turbo
compound rotary and all its variations read Appendix 17 of this strangely named
202 page paper.

NASA Contractor Report 189106
Stratified Charge Rotary Engine
Critical Technology Enablement [buzz word :)]
Volume II - Appendixes
C.E. Irion  and R.E. Mount
Rotary Power International, Inc.
Wood-Ridge, New Jersey

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

Page 201
"The dual stage turbocharging  configuration with an upstream
turbo compounding (power) turbine is preferred for its high equivalent power,
good off-design operating performance range, and reasonable simplicity.  The
recovery of pulse power leads to substantial increases in power turbine
output, so the system should be designed to fully utilize this power.  The
power turbine can provide at least 60 to 80 hp, while keeping the engine
back pressure between 30.6 psia and 34.9 psia."

Paul Lamar



Paul,

Yes I have this paper and read it several times.  That is why I being
such a hard ass on the subject:)  60-80 recoverable Hp  are the upper
limits assuming that the pulse effects of exhaust modeling had been
proven out as predicted.   I agree with them and you that the pulsing
effects are valuable.

"Additional analytical efforts are needed to better quantify exhaust pulse
effects which apparently will significantly affect turbomachinery sizing and
power output.  Additionally, an off-design system analysis should be
performed to learn how the proposed system configuration performs at lower
altitudes and lower throttle settings.  These conditions will determine
control schedules and may have an impact on proper turbomachinery matching."

Lots of variables here.  For one, the engine is direct injection which
may increase its tolerance for higher operating back pressures. For the
model of one power turbine and one turbo-charger here are the proposed
specs on  the power turbine.  What are your thoughts on the meaning of
VOLUME listed below?  It appears they are speaking about turbine volume
but they must have gotten a decimal place wrong. 2196 cubic inches would
mean the turbine is 48.8 inches long.  4.88" perhaps.  I suspect they
didn't know about traction drives when this research was done.


POWER TURBINE
PRESSURE RATIO-1.24
SPEED (RPM)-24227
SPECIFIC SPEED-0.6000
DIAMETER (IN)-7.576
WEIGHT (LBM)32.25
VOLUME (IN3)- 2196.


Doug in Japan

It is just a paper study and I think it was based on a fictitious engine of only
80 cubic inches. A 13B is about 160 cubic inches so perhaps they are incorrectly
rating the engine based on the displacement of only one chamber. The same thing
Mazda does when they say the 13B is 1.3 liter.  It could in fact have been based
on a 13B.

I  have no idea what they mean by volume of a power power turbine. That could be
the length (36") and diameter (?) volume of the exhaust duct. If it is that the
area of the exhaust duct is 61 square inches which does not make sense. Could be
6.1 square inches which is 2 3/4 inch diameter. Makes more sense. Why it is so
long is a mystery. Perhaps they were looking for a tuned organ pipe effect.The
32 pound weight is rather high for an 8 inch diameter turbine. That sounds like
the weight of a complete turbo charger and more.


I get the impression that the people that did this study had no experience with
actual engines let alone turbo charged rotary engines.

Lots of strange stuff in here like; why is the charge air duct five feet long
yet no diameter is given?

The sad part about the whole situation is they never built any hardware to get
some kind of practical handle on the performance.


Paul Lamar

--

Paul,

Oh I mistakenly believed this was based one of the SCORE engines.  Say on
the inlet and outlets is is stated half angle degree =  ten.  What does
this mean?

Doug in Japan.


I don't think it was. By this point in time RPI, I suspect, was using Mazda 13B
engines to do what little applied research they were doing.


"stated half angle degree =  ten"

Fancy way of stating the sharpness of the trailing edge on a compressor blade.
In this case it is Delta.

----------------------------------------------------------------
Doug,

I highly recommend a book called Fundamentals of Gas Turbines 2nd edition by
William W. Bath  1996 ...John Wiley


Paul Lamar

Paul,

Thanks for  the info.  Actually I do have a good book Gordon recommended
called "Elements of Gas Turbine Propulsion" by Jack D Mattingly, 960
pages.  Most of it is Greek to me though:)
It is more concerned with designing jet engines but does have 7 pages on
the formulae required to design a centrifigal-flow vaned turbine with
fixed vane stators.  I'll have to scan these pages and send them to you.

Doug in Japan

Thanks Doug. If it is promising I'll have to get it and take a look at it.

Paul Lamar