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

One turbine - gear set that might be considered is the Solar APU . it runs
at
higher pressure and higher flow, but at the lower exhaust pressure it
might be a passable match, and the reduction gear is there .
(I still think the recovery turbo electric Hybrid has a better chance for
automotive use) - Vance

 
The Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2004 All world wide rights reserved.