Jim Brewer wrote:

Paul,
I'm not an engineer so help me out here.  I get some junk mail from an
Army-Navy surplus type that sells guns, parts and books.  One of the manuals
they sell is a study done on the fabrication of silencers for guns by some
government arsenal.

Now my question; How does the detonation of a gun and the detonation of an
engine differ other than in the sound wave speed and frequency?  If one can
silence a gun can't we do the the same with the rotary?   Do you think any
of the techniques of gun silencers would be applicable to silencing of our
Mazda rotaries?  Wasn't some Detroit grad student on the list going to help
us make the rotary purr like a kitten?

Jim Brewer
Albemarle, NC

There are some similarities that's for sure.

Paul Lamar

In the olden days of automobiles (no I am not quite that old) before there was a
Midas muffler shop - engines were fitted with "Maxim silencers" - as in Hiram
Maxim the gun designer. They are indeed from the same family, and the larger the
silencer, the more effective it will be (within reason). However for the gun you
have to use a subsonic load, or all the silencing you do for the gases will be
undone by the sonic boom (if you ever "pulled targets on a riffle range, you will
know what I mean - Vance

Yes riffle bullets travel at supersonic speeds and there is a sonic boom.
As I recall we are dealing with supersonic exhaust gas velocities leaving
the exhaust port. The new side exhaust port should mitigate the noise as
the port opens and closes more slowly.

Paul Lamar

Touché  - Doctors can't write legibly, and engineers can't spell :-)
I had not considered supersonic flow in the exhaust - but it is probably at required
critical pressure ratio (around 2 to 1) when the valve initially opens, and this may
well be a significant portion of the noise signature. But it should rapidly drop below
that value, or the back pressure would be intolerable.  Mufflers and silencers work on
a combination of dissonant tuning and absorption, turning some sonic energy back into
heat.
Vance

 
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