[Gasification] thermoacoutics, rijke tubes, sondhauss tubes, pulse jets-- how do we make them not work?

[Pete&Sheri]

Why not just put the swirl burner up as high as you need it?

Pete Stanaitis
-------------------

doug brethower wrote:

> Tune it with an expansion chamber patterned after two stroke exhaust. 
> Many  innovative designs to increase flow/power back in the day.  
> Newer designs  focus on the sound quality aspects as well.
> On Wed, 16 Feb 2011 01:11:42 -0600, jim mason <jim at allpowerlabs.org> 
> wrote:
>
>> any ideas out there for how to make a pulse jet robustly not work?
>>
>> we're having lots of problems with thermoacoustics now that we've put
>> a tall stack on our gasifier swirl burner.  we're using a tall stack
>> now to keep startup gasses away from the operator.   the swirl burner
>> is 5" in diameter, 10" tall.  we've added a 4 foot or so stack of the
>> same 5" diameter.   it looks like this
>> http://www.gekgasifier.com/forums/showthread.php?t=501  (though this
>> one without the joint at 10")
>>
>> when run under high load, it howls rather loudly.  if art, it would be
>> fabulous.  if a genset, not so good.
>>
>> darrel tonight explained that we have made a rijke or sondhauss tube.
>> or really, an unintentional pulse jet.  read about them here.
>> http://en.wikipedia.org/wiki/Rijke_tube.   scroll down 3/4 to see
>> sondhauss close bottom tube, exactly as we have.
>>
>> this apparently can happen with any pipe of one or two open ends, with
>> a big temp difference between the ends.  a great enough temp diff
>> between the ends alone will set up the standing wave.  you can make
>> the effect more pronounced with heat exchange meshes inside that
>> augment the pulse in one direction, but not the other.
>>
>> turns out the best place to site a mesh, or apply your heat source is
>> about 1/4 length of the tube. (at least with the two end open type)
>> hmmm, we put our always on silcone nitride igniter right about the 1/4
>> length point.  didn't think of that one.  no idea if it is enough heat
>> to be making a difference in the resonance though.  we should try
>> turning it off and seeing if the resonance changes.
>>
>> an important thing that makes them work is the push and pull against
>> atmosphere.  this suggests that one way to "detune" the tube would be
>> to put holes in the sides around the top portion of the tube.  make
>> the pulse hit atm at difference lengths, and thus scatter the wave,
>> like one does in a car muffler.
>>
>> or, maybe a flare outward would work?  but that seems to only help
>> impedence matching, and make the trombone louder.
>>
>> we put criss-cross baffles down the tube tonight.  that helped quite a
>> bit, but didn't solve it fully.  also made more higher pitched tones.
>>
>> this pulsing is also likely why we have flame backing up into the
>> mixing section/blower/etc in manners we never have before.  i we did
>> most our testing on the blower and flame arrester, integrated
>> flare/exhaust with just the short stack.  the big resonance problem
>> did not start until we put on the 4' extension.
>>
>> i wonder if we could insulate our way out of this problem.  insulate
>> the stack from bottom to top, even out the temp differentials so it
>> can generate less sharp thermal pulses.
>>
>> any other ideas or experience for how to make your pulse jet not work
>> under any circumstance?
>>
>> jim
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> -- 
>> ------------------------------------------------------------------------------ 
>>
>> Jim Mason
>> Website: http://www.whatiamupto.com
>> Current Projects:
>>    - Gasifier Experimenters Kit (the GEK): http://www.gekgasifier.com
>>    - Escape from Berkeley alt fuels vehicle race:  
>> www.escapefromberkeley.com
>>    - ALL Power Labs on Twitter: http://twitter.com/allpowerlabs
>>    - Shipyard Announce list:
>> http://lists.spaceship.com/listinfo.cgi/icp-spaceship.com
>>
>>
>
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