Hopefully I won't need a monster muffler.
Paul Lamar
What will be the affect on efficiency of the long pipe between the
engine and the turbine?
Cooler exhaust=denser gas, but cooler exhaust=lower velocity.
My gut-feeling is that closer is better ... ??????
If my guess is correct, I guess one could turn the turbine around and
come up with a more complex drive-train. But I suppose
max-efficiency is
really beyond the goals of your experiment at this stage, huh?
RBerglund
Here is the effect of the gas temperature on the TC HP recovered.
From a SAE paper on TC published in 1945 by C.F. Bachle
"Turbo Compounding the Piston Engine".
On the other hand cooler temps are easier on the turbine blades.
Paul Lamar
OK ... If I read the graph correctly... and if I remember my physics
correctly ... Work is calculated as the integral of P x dv ( ie the
area beneath the curve on the pressure vs volume graph) so obviously
there is more area beneath the high-temp curve than beneath the
low-temp
curve. But the curves for various operating temps are fairly close
together, and even with one-thousand degrees of cooling there is a
surprising amount of energy remaining in the exhaust gas.
Take all you can get! :)
RBerglund
The trouble is turbine strength is a steep slope :). Just like exhaust
valves.
Where temperature and centrifugal force converge failure occurs.
I think the limit in commercial jet engines is 1300 F long term.
Maybe military jets use unobtanium :)
Paul Lamar
Looking at that bellows section just before the turbine, it seems like
you're picking up some cooling as the exhaust expands into the larger
diameter turbine inlet. Given that the bellows is probably inducing a
little bit of drag anyway, I wonder whether it would buy you
anything to
eliminate the bellows and turn that section into a short expansion
chamber (with the decrease in turbulence compensating for some of the
cooling loss), depending on what the exhaust temperature is at that
point. I can't tell whether you have a means of picking up the
turbine
inlet temperature. Of course, if it's cool enough, it's not an issue.
You're probably eating, sleeping and breathing this thing right
now, so
maybe you've considered all of this stuff already.
Dave Klingler
It has a smooth, smaller diameter liner that is only attached at the
input end. I am sure DD considered the heat transfer carefully.
That DD part cost over $100.
Paul Lamar
That thing's a work of art. If I owned one I'm not sure I'd do anything
with it other than pick it up and admire it every day.
The DD inlet temperatures are much lower, aren't they? Yes, I guess I
could go back through the emails and figure that out…
Dave Klingler
Paul,
Regarding potential power loss issues attributable to exhaust radiation
heat loss prior to the DD15 compound turbine, you may wish to consider
an appropriate ceramic coating on the exterior of the exhaust piping as
well as on the turbine components themselves. These efficient thin
thermal barrier coatings would carry a minimum weight penalty.
This would additionally be a personnel safety measure.
Best Regards, FParker
I am worried it will be too hot for the turbine. A little heat loss
might be a good thing. I have an infra red hand held thermometer. I'll
know more after it runs.
Paul Lamar
Okay, I went back and looked through the emails. You had part of this
conversation with Philippe Dejean back on June 20. Well, not much to do
but try it out and see what happens.
It's a proof-of-concept anyway. If it works at all, you've passed a big
milestone.
Dave Klingler