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Paul,
I thought we talked about a larger diameter, slower turning turbine some
time ago. This looks very good! I need one for around 5500 continuous
engine rpm.
Steve Brazil
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I think we finally have a handle good enough to recommend a direct drive
turbine
diameter and blade configuration as a starting point.
I'll run through the numbers for you. Such a low engine RPM may not be
practical
for a direct drive turbine. So don't get your hopes up too high.
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To get closer in I need the exhaust pipe diameter and a measurement of the
dynamic pressure in the pipe using a SS pito tube.
The dynamic pressure will be in the range of 500 to 1000 pounds per square
foot or 3 to 7 pounds per square inch.
Paul Lamar
--
Paul
In measuring the dynamic pressure via a stainless pito tube does the pito
tube itself introduce an error in the reading? I was under the
impression Mazda used some type of high temp. piezo electric sensor
inserted into a bung welded on the manifold before the turbine.
Doug in Japan
Not significantly. I think Mazda was measuring static pressure in the
exhaust.
It is the combination of exhaust gas density and exhaust gas velocity you
are
after. That is what generates dynamic pressure. Dynamic pressure is what
generates lift on a wing or a turbine blade. As you climb and the air
density is
reduced you have to fly faster to get the same lift on the wing. If you heat
the
air the density also goes down. That is were the term density altitude comes
into play.
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I am just thinking out loud here. Given the dynamic pressure (we can measure
that) and exhaust gas temperature (we can measure that too) what is the gas
velocity? Anybody have any ideas on how to calculate this?
I suspect. It has something to do with the ratio of the temperature
expressed
in Kelivin. 100 F is 311 K. 1700 F is 1200 K or four times higher.
Does that mean air density at 1700 F is one quarter of what it is at 100 F?
Dynamic pressure in pounds per square foot at sea level density
and standard temperature is .0026 (AD) time velocity squared.
D.P. = A.D. X V^2
Paul Lamar
Paul,
Thermodynamic problems are almost always based on temperature change with
respect to absolute zero.
Steve Brazil
Is that rankin or kelvin? I forget.
Do you have data on that engine?
Paul Lamar
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