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
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