snipss...
Doug,
I would suggest you start from scratch on the turbine. As Monty has
pointed
out, this will be far more likely to to bear fruit. There are at
least three
persons/firms making small production runs of vaccuum cast superalloy
turbine blisks for the model gas turbine world. The standard 66mm
turbine
for most model engines costs about $120. Join the gas turbine
builders
association or the yahoo group
http://groups.yahoo.com/group/homebuildturbines/
I suspect that automotive turbo's survive the high EGT's because they
are
only exposed to a relatively small mass flow and therefore low heat
flow.
They are able to reject this heat flow fast enough. As you up the
duty
cycle, although the EGT is not increasing, you are flowing more heat
than
the turbine can reject. Thus the need for Inconel or superalloy
(MAR-M,
RENE... etc). The combination of Wankel EGT's, a high duty cycle, and
manned
aircraft expected TBO and reliablity may well exceed the material
capabilities of the super alloys and drive you to a cooled turbine
(thus
ending the project). Gas turbine engines only combust a fraction of
the
cycle air, and cool the cumbustion products significantly before they
are
passed across the first stage nozzle. We are not afforded that
luxury.
Replacing the shaft on an off the shelf turbo is not trivial. The
turbine
wheel is normally shrunk onto the shaft, and it's removal damages the
wheel.
Calculate the energy stored in a heavy radial inflow turbine at
100000 rpm,
and the velocity/ inertia of the parts if it lets go as two even
parts. Bad
idea using a damaged turbine.
For a given mass flow and fresh gas temperature (which you have) ,
you have
a single optimum nozzle throat area. Work out what that is and you
can play
around with the turbine diameter and blade length. Too large a
diameter and
the blades are too short and the tip losses dominate, too small and
RPM is
excessive.
If you design to a single point, you will still have to go through a
few
iterations to optimise it, and that will be at your test altitude.
For your design point I would see if Tracy could provide the
following:
At sea level, 65% RPM, the OAT, density, fuel mass flow, and air flow
ratio.
With this you can work out your mass airflow, and thus the HP the
turbine
delivers. You can then optimise the trade off between increasing
turbine
diameter simplifying it's design (and increasing it's cost) or higher
speed
gearbox (with higher cost).
Why not separate the tasks and use an aircraft turbo, and an axial
flow free
power turbine?
Regards,
Mark Wrathall
Thanks Mark
Yes you certainly have a good point. At least on the bench test it
makes a
lot of sense to use two turbos. It would speed up the testing a give us
some target data to shoot for. lt certainly makes turbo rpm balancing a
little easier because it is a simpler act of controlling the intake
throttle
valves. The response won't be very quick but for dialing in the economy
cruise rpms is doesn't have to be. In application it gives us an ability
to
send the kinetic exhaust energy to the boost turbine or power turbine or
combination thereof.
Eventually we will have to go to an aircraft turbo or turbos? and they
will
need some special order parts for the power turbine side. That phase of
the
program is down the road a bit. Before designing any new equipment and
(thanks for the tip on the turbine club) I need to have a through
understanding of what is happening with some standard equipment. I am
still
a complete greenhorn when it comes to turbos. Paul seemed to have
identified an old/new compressor Paxton that may be a good starting
point
for the power turbine side of it. I have to study it. Since we are
still
in the bench test mode I am interested in looking anywhere for ideas. I
appreciate yours. And also Daniel's . I did look into the Tesla turbine
concept early on. Vance said it well about skin friction. My concern
was
more about accumulating particulate matter from the waste stream. I do
share
Vance's admiration for Tesla as well. The significance of this great
inventor's work have yet to be fully discovered.
For those of you already flying rotaries please wait until I can get
some
hard data on what is happening. This idea is going to be a show stopper
for
my own plane and purposes unless I do one or all of the following;
1. Simplify the components
2. Make the components have multi-functions
3. Go with a smaller higher performing powerplant.
4. Find other ways to lighten the planes gross weight. ("Sorry honey, no
baggage and BTW we are going to have to fly in our underwear")
Two turbos are heavy but then again so are the magnetic or mechanical
clutches, a toroid CVT, or planetary gear sets with one turbo.
For the two turbo bench test delivering power to the rear of the engine
gives us the advantage of replacing the heavy steel flywheel with an
aluminum toothed wheel thus giving us at least 10:1 reduction from the
power
turbine. In this configuration we need a larger exhaust manifold with
twin
valves (of undetermined design at the present) on which two turbos will
be
directly connected. Exhaust can be separate or go to a common outlet.
I am now communicating with these people.
http://www.land-and-sea.com/dyno/dyno-price.html
"Dynamometer package contains components for testing many automotive
engines
up to 800 Hp.* Includes: shaft mount 13î toroid water brake absorber,
strain
gauge equipped torque arm, DYNOmite Pro data acquisition computer,
manual
load valve, full function data acquisition wiring harness, mobile engine
stand, bell-housing adapter plate, 1-3/8î x 10 splined clutch
input-shaft,
mounting hardware, stainless braided hoses with aircraft fittings, and
instruction manual." Cost about $10,000.
All I really need is the water brake absorber, strain gauge equipped
torque
arm and their software. Don't know if they will sell just those. If
not I
would appreciate anyone's' advise on how to make or purchase the first
two
items. I already have the stand finished and am now upgrading an old
computer to run Windows XP. And yes Paul it will run Rhino as well:)
The cart when complete will have rain proofed sound deadening panels
installed. With a forklift we can put the whole unit on a small truck
and
take it anywhere to demonstrate.
Doug in Japan
Doug, do you have access to a well equipped machine shop? At the very least,
you are planning to replace the shaft in a standard turbo-charger with a
longer shaft (which is not a good idea as detailed above). Can you machine
to a tenth or two? If you are equipped to make this shaft, then you are
probably equiped to make your own design from scratch.
Take a look at the Swedes write up of making his model turbo prop to get a
feel for the machining required of a free power turbine and high ratio
reduction drive.
http://www.5bears.com/tprop.htm
Ragrds,
Mark.
No shaft replacement required. The torque through a coupling is 2 foot pounds
or less. Why make a new shaft when all is needed is a coupling? I am all for
making a new custom turbine but the optimum design is far from
my capabilities. Since the efficiency of radial inflow turbine (turbo charger
turbine)
is currently 70% or better over a fair range I think it would be hardly worth
the
cost and extra weight to build a axial flow turbine. You might at best achieve
another
10% turbine efficiency. Why reinvent the wheel when there are so many out
there to
choose from.
BTW Scania apparently thought axial flow turbines were not worth the expense
although they
did use a separate power turbine. They did not however use a CVT which is a
large
difference in matching the power out of the turbo charger to a form the
e-shaft
can accept. Even if the CVT is only used as a quick way to determine the best
point design gearing for aircraft use. What Scania also had to deal with was
the
smoke limit. See the attached front page of a IMECH technical paper on the
subject.
They could not let the turbo charger section be bogged down by the power
section.
That would cause black smoke. I have addressed that by incorporating a
disengagement
clutch. The purposes of the clutch is to disengage the power out of the
turbocharger
during acceleration to allow the turbocharger to spool up unimpeded. In fact
when
combined with an electric assisted turbo and computer control of the clutch
and CVT lots of flexibility is afforded to deal with any transient modes.
In the mean time we don't need computer control as we can control both the
clutch and the CVT ratio manually for test purposes.
Paul Lamar
Paul I wonder if the downstream turbo rpms in Scania's design was
controlled through the fluid connection. It would be easy for them to by-
pass fluid to increase slippage. It would make sense that they would be at
least be thinking of the possibilities. However I agree with you that the
toroid wheel should be more efficient and more precise, but more importantly
it can change the gear ratios and be slipped as well.
By the way I moved my schedule up because of a sudden business meeting in
Chicago on Oct. 7th. I will miss Tracy's get together on the Oct 28th and I
was really looking forward to seeing a bunch of rotary ethusiasts in one
place at the same time. I will drop in and say hi a couple of weeks earlier,
that is; if will still have me:)
My flying route will be along the coast from Florida to New Orleans, and
then up to through Texas, across New Mexico and at this point Tucson,
Phoenix, Flagstaff and Prescott Ariz. to see friends.
In California I will be going to San Diego, LA area, and after that I go
north. By route and final destination is not determined at this point.
If their is a chance to met Monty or Mark lets do it. Where do either of you
live? Bob Darrah in Texas, I would love to see your SeaWind and speak to
you as well. How far from Austin are you? Anyone else working on rotary
powered aircraft that wouldn't mind if I fly in to say hello in mid to late
October can contact me at <fir@gol.com>
Doug in Japan
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