Having good flow and knocking down
pulses is what I had in mind with my tangential muffler. The pipes from the
ports enter as close to tangential as possible, which I think is important for
swirl flow. On the inside wall opposite the ports are a series of vanes welded
at an angle to the flow to assist in breaking up pulses, and direct the flow
toward the exit end of the 5” diameter muffler. There is a conical
truncation to the exit pipe of 2 ¾” dia. which also has internal vanes to
“straighten” the flow into the exit pipe. It is all made out of inconel.
It seems to be reasonably effective at cutting
the noise level.
In addition; I added a small muffler,
or resonator, of my own design, which is simply a 5” dia tube (this one
321 SS) surrounding the inner 2 ¾” tube which is drilled full of holes. At
the center of the muffler is a single orifice plate which reduces the flow area
by about half. This unit allows further expansion of the pulses through the
holes and some of the flow bypasses the orifice, while some just goes straight
through. Very little back pressure, but further knocks the peaks off the
pulses. On the dyno we measured that this secondary muffler knocked the level
down another 6 db.
The exhaust is not quiet, but it is not
really offensive. You can listen at http://members.cox.net/alg3/Runclip.wmv
I’ve attached an old photo which
gives you an idea of what it looks like.
Even on the ground runs I have not noted
excessive in-cowl heating; and my system is not coated. I’d say that
coating the inside could help by reducing the emissivity (absorbtivity) of the
inside surface, but on the outside it would make very little difference. You’re
talking about coating thickness of less than .010”, so the conductive drop
through that is very little.
Al
P.S. Dave Atkins also runs an inconel
tangential muffler which seems to work OK. His first one made from SS disintegrated
after awhile due to stress corrosion; which will happen to SS at these temperatures
if stress is present.
Just to stir things up... It
seems that with exhaust systems, the exhaust consists of two parts which should
be handled differently. Part 1 is the exhaust gas flow which
we want to flow out with little restriction. Part 2 is the
exhaust pulse which we try to attenuate, breakup,
etc. These two are like the difference between
wind and sound-waves. In the past 24
hours or so, I've been wondering about using anechoic chamber principles
to attenuate the pulse. I have a specific layout in mind
which should tend to attenuate the pulses while not interfering with
exhaust gas flow. Anybody hear of such a thing?
Tom (looking for project sponsors or a job)
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