morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on May 20, 2012 7:17:56 GMT -8
Peter,
Firstly thanks for your posts - they have been very interesting.
My tests, although not very scientific, look promising. I made a simple tripwire from steel and a ceramic fibre gasket for my 8" diameter test stove. I don't have a Testo or similiar flue gas analyser but judging from the exhaust it did appear to burn cleaner. The exhaust flue temperature probe showed it did get up to temperature faster too.
Unfortunately the ceramic fibre gasket wasn't up to the job and burnt out after the third test. I'll see if I can get some higher temp paper to build a new one and post some photos too. I also need to check ebay for a flue gas analyser!
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Post by peterberg on May 20, 2012 23:54:50 GMT -8
My tests, although not very scientific, look promising. I made a simple tripwire from steel and a ceramic fibre gasket for my 8" diameter test stove. I don't have a Testo or similiar flue gas analyser but judging from the exhaust it did appear to burn cleaner. The exhaust flue temperature probe showed it did get up to temperature faster too. Hi morticcio, Yes, this small ridge can make a surprisingly difference. Coming up to temp faster is another signal. More of the hydrocarbons are being oxidized, so more heat is produced. Consequently, the metal trip wire will burn out in a couple of burns, so it isn't useful in a permanent appliance. Looking forward to your photos! |
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Post by morbius on Jul 19, 2012 17:02:45 GMT -8
Excellent explanation of valveless pulsejets: www.pulse-jets.com/valveless/index.htmen.wikipedia.org/wiki/Valveless_pulse_jetNote that many valveless pulsejets are very similar in shape to the standard j tube of a rocket stove. Much information about jets in general are at the home site of the first link above: www.pulse-jets.com/However, the mother load of info on jets in general and valveless pulsejets in particular is the same site's forum: www.pulse-jets.com/phpbb3/Going by gut instinct, I think Peterberg is right: his 4" stove is running as a badly tuned pulse jet. Tuning it may become a problem. But since the tuning, in a large part, has to do with the volume ratios of the exhaust and intake "tubes" compared to the combustion chamber --the exhaust chimney and wood holder compared to the flame chamber (I'm forgetting the terminology)-- it should be possible to tune it correctly, and by ear. Note the cone-shaped end to the exhausts. This may be important even to a rocket stove's burn tube.....And remember: a rocket stove with thrust is probably a bad idea!! |
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Post by morbius on Jul 19, 2012 17:51:37 GMT -8
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Post by lostsoul on Jul 21, 2012 14:53:29 GMT -8
No the burnout problem is still there, but the bottom of the feed tube is made of refractory now. And surrounded by insulation, only the top end of the feed is cooled. So, the bottom of the feed is red hot, the top end is cooled and creeping up of the fire is history, none of the six testruns showed any sign of that problem. I'm sorry if this has already been covered in other posts, I'm still new and haven't had a chance to read as much as I would have liked to as of yet. If memory serves some people have mentioned not liking the idea of using fans and such as it is another potential point of failure, not to mention requiring a power source. That being said I'm wondering if any tests have been done with a passive cooling system, perhaps using attaching a heatsink to the feed tube so it can dissipate the heat at a faster rate perhaps eliminating the need for a fan? I realize that with the high temperatures copper would likely be the only option, with the high price of copper these days it would certainly be an investment, however if it eliminates a potential failure point it might be worth it? |
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Post by Donkey on Jul 21, 2012 15:06:12 GMT -8
The P-Channel seemed to have solved the issue pretty well.
I think copper would melt away, the temperatures are way too high. My steel P-channels warp pretty bad every so often (I bend 'em back) and are showing signs of burning, the metal is getting thin and pocked.
Seems to me, something a little more heat resistant than mild steel is best, stainless might be the ticket.
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Post by mintcake on Sept 5, 2012 12:45:26 GMT -8
I've just been reading all about those J-tube shaped pulse jets... One disturbing thing (for a stove) is that they do eject some of their exhaust out of the short end. Not sure I'd want CO ejected into my living room....
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Post by satamax on Sept 5, 2012 13:25:16 GMT -8
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Post by peterberg on Sept 6, 2012 0:54:01 GMT -8
I've just been reading all about those J-tube shaped pulse jets... One disturbing thing (for a stove) is that they do eject some of their exhaust out of the short end. Not sure I'd want CO ejected into my living room.... This thought has crossed my mind about a year ago. At the time, just to be sure, I've bought a CO-sensor and installed that in the workshop. That went off only once: this happened when the chimney temperature dropped too much so the smoke came out of the stove. During the sessions with the stove in pulse mode the sensor didn't even flinch. |
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Post by peterberg on Sept 6, 2012 0:58:57 GMT -8
You wouldn't want the noise nor the speed or fuel consumption either  The sound of the stove in pulse mode isn't comparable at all with a real pulse jet, decibel-wise. The speed of fuel consumption is in tandem with a higher yield, which can be desirable in itself. |
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Post by Donkey on Sept 6, 2012 6:55:31 GMT -8
And if you're storing heat in a mass, short term (on a burn by burn basis) consumption doesn't matter.
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Post by kirkerik on Nov 3, 2012 11:02:05 GMT -8
Thank you for the idea of the Peter-channel! I have been considering modifying my RMH just because when the stove gets very hot after a few hours of burning, the fire creeps up the feed tube. Especially with punky or soft woods. The way i have dealt with it so far is by placing some fire bricks at the back wall of the feed tube (no mortar) there by increasing the velocity of the incoming air and reducing or eliminating smoke in to the house. My exhaust is "equivalent" to at least 50' horizontal (with all the elbows) and the chimney exits under the eave so my draft is decent but could be better. I will be exiting the chimney vertically now, as there is now an addition where the old chimney exit was, so my draft should be much better.  I can not wait to try the Peter-channel! |
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Post by kirkerik on Nov 3, 2012 11:41:45 GMT -8
Peter,
i had a theory on why you may be seeing more stable results with your castable refractory unit when compared to your designs made with metal. Have you considered the thermal mass of the refractory burn tunnel creating a more stable combustion environment?
You said that the CO would spike every time you added fuel to the previous designs. Right? Perhaps the steel having so little thermal storage could create unfavorable conditions every time you add or shift the fuel source. Even if backed by insulation, the influx of fresh fuel could lower the temperature of the burn tunnel very quickly since there is little storage of heat in the pipe itself even though it is very hot.
Your latest design is cast refractory having much more thermal storage potential. Once up to temperature, any change coming in to the burn tunnel is easily stabilized by the thermal energy stored in the heavy burn tunnel. Yes?
i like your trip-wire idea as well and it is encouraging to hear it makes a measurable difference! Keep up the good fun! i dream of having a workshop and test some stoves someday as well. ;D
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Post by peterberg on Feb 14, 2021 8:53:39 GMT -8
The design of the optimized J-tube is open source for a long time now. It's availability slipped my mind and is long overdue, so here it is. It's SketchUp file version 8 of a 150 mm (6") design. Mark when scaling up or down, the height of the trip wire should stay the same. pberg0.home.xs4all.nl/Bestanden/J-tube/6inch-Jtube.skp |
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