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Post by Donkey on Apr 13, 2012 10:43:44 GMT -8
I've been wondering: Is it possible to build a stove that doesn't rely on convection for draft? A stove that can run in any orientation, one that you can flip upside down and it would STILL WORK? Can a stove be designed to work in a weightless environment?
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JBW
New Member
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Post by JBW on Apr 13, 2012 15:11:07 GMT -8
I think you would need at a minimum some sort of air flow. Compressed air, electric fan, flatulent fat man (me  ), or my favorite - jet engine. Maybe a heater that uses a liquid fuel sprayed at high pressure to move the air by venturi effect? |
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Post by Donkey on Apr 13, 2012 15:36:42 GMT -8
As always, I'm looking for a solution through passive design.. Of course, using fans, etc. would work.. But for the sake of THIS conversation, let's consider them to be cheating.. I think it would be fair to allow the user to blow on the fire to get it started..  I imagine that expansion of the heated gasses would be our sole motive force.. Could some kind of pressure differential be generated by shape alone? |
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Post by sierramog on Apr 13, 2012 21:09:43 GMT -8
From my research on the 'net, there is a long development history of pulse resonant heaters going back to the thirties. Some are in commercial use but they tend to be noisy. This link is to a fairly recent patent on an industrial pulse heater for an assembly line. www.google.com/patents/US6210149?printsec=drawing#v=onepage&q&f=falseI don't think anyone has developed a wood powered pulse heater, they tend to be propane powered. From what I have read they are very similar to valveless pulse jet engines in principle. Jam jar jets are a homebuilt example of an alcohol powered heater that 'could' generate its draft when oriented any direction but because it is liquid powered is always seen upright. www.youtube.com/watch?v=W7k0xh8ezgQI wonder if the 'rocket' sound of your heaters is a resonance that can be exploited to add more draft in the same way the above devices operate? If so, it might improve reliability but add some noise. |
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Post by peterberg on Apr 14, 2012 10:36:46 GMT -8
Interesting thought. I'm quite convinced it can be done with an acoustically resonant exhaust pipe. Like the pulse jet, as sierramog suggest. It will pose some difficulties not seen before, like a very noisy stove, vibrating like hell. And only working when the fuel is superheated.
The normal rocket stove isn't self-starting, but it can brought up to running temps in mere minutes. The small rocket stove I have here do need at least 40 minutes of very careful feeding and nursing in order to get it up to the required temperature for something which I would call pulse jet mode, or whatever it is. This could be cut down to, say, 10 minutes with the help of compressed air or an electrical paint stripper. Would that also count as cheating?
One of these days I have to run the small scale experiment up to maximum temperature and shoot a short film complete with sound. That would be a very interesting movie to see. ;D
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Post by Donkey on Apr 16, 2012 7:20:28 GMT -8
I would very much like to see that movie.
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Post by peterberg on Apr 17, 2012 3:59:10 GMT -8
Today, I've shot two video-clips, using my wife's mobile phone. The clips are low-res, but the sound is about right.
During the first clip there's a very audible metal-like clattering, caused by the bung hole which wasn't screwed down at the top of the uppermost oil drum. I've tried to shorten the start-up time with a paint stripper, but that wouldn't work. After I've changed it for a very antique hair dryer, blowing cold air only, things went a lot smoother. Total start-up time up to the required temperature went down from 40 minutes to 15 minutes.
The second attempt took a while longer to my surprise to get it up to the desired mode.
Nothing more to tell, really. It kept on going this way as long as it has been forced fed using very thin pieces.
I'll post these links also to the "small scale development" thread.
Donkey, given a short start-up time without additional means and the possibility of a random orientation, could this be the stove you are looking for?
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Post by Donkey on Apr 17, 2012 8:24:33 GMT -8
Peter..
Once your stove is making the pulse jet sound, can it be turned on it's side or upside down and still work?
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Post by peterberg on Apr 17, 2012 11:34:53 GMT -8
Once your stove is making the pulse jet sound, can it be turned on it's side or upside down and still work? I honestly don't know. Because of two main problems: the stove is coupled to a chimney and it is gravity fed. Turning it upside down, all the fuel will fall out. Two smaller problems: all the vermiculite will drop on the floor as well and the darn thing is awfully hot. ;D |
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Post by Donkey on Apr 17, 2012 15:40:28 GMT -8
Actually, from the pictures, I figured.
Perhaps a twin to your stove could be built with the insulation trapped in, a grate on the feed to hold the wood and no chimney.
The thing could be mounted on gimbals or something.. Set up so that it can be rotated upside down when it's up to heat.
For a test of this type, the barrels are probably unnecessary. Hmm.. I'll think about that.. I've been meaning to do a stove with a cast burn tunnel/feed anyway..
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Post by sierramog on Apr 18, 2012 0:29:48 GMT -8
Peter, thanks so much for posting the video. Very encouraging! I am wondering if a Honda or Toyota resonator could be used for a resonating chamber like this fellow (accidentally) discovered? www.youtube.com/watch?v=Ir4ppXXtR2w&feature=channel&list=ULA night run starts after about 3:42 minutes showing the internal flame. I am not experienced at all so I can only speculate but suppose one were to use propane to get it to pulse, then add wood gradually and subtract propane gradually. Use best known rocket stove experience, construction and orientation (none of which I have) to achieve draft, then pulsation, then gradually rotate it to see if pulsation would drive the flow at various angles in spite of the loss of gravity induced draft. The French scientist FH Reynst who developed pulse combustors in the mid 20th century proved that very high acoustic energy dramatically improved efficency. The pulse frequencies I saw most reported were in the range 50-200hz. To my untrained ear the muffler and Peter's run both sounded similar. Maybe 25hz for the lowest tone and some harmonics? |
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Post by peterberg on Apr 18, 2012 1:16:50 GMT -8
This is what I've come to understand: the proportions of the pulse-jet, in the sense of length and cross sectional areas are very important. Altering the length could kill off the effect altogether, or the frequency could change at a higher or lower value. So, the fact that this small critter is able to reach pulse mode is astonishingly, it's also purely by accident.
By the way, the muffler jet frequency is definitely lower than what my stove is producing. The V-1 frequency (43Hz) is a little bit higher compared to the stove. So, the stove's frequency is probably somewhere between 30Hz and 40Hz.
Edit:
Come to think about it: I'll have to try pulse jet mode with a shorter heat riser. For one of the experiments I've cut off a length of about 10", and attached it back again later. I could take that piece off and try again.
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Post by peterberg on Apr 18, 2012 7:50:36 GMT -8
Today, I've shot two more clips. The first was running inside the same drums, only the heat riser has been shortened by 12". So the end of the riser has been 3' away from the top of the drum. To my surprise, it kicked in pulse mode within the same parameters as before. Even the frequency of the pulse seemed to be the same.
Lifting the plug of the bung hole on top killed the effect almost instantly. Closing it started the pulse again.
The second clip is done with the same riser length, the only difference is there's only one oil drum instead of two. Same frequency again, heating up time equal. Lifting the plug killed the pulse, but sometimes the drum was shaken so bad it lifted sometimes a bit on one side. That did shut off the pulse as well for a second or less. The drum is probably part of the jet length?
To hear it run and trying to have it continued is real fun!
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Post by peterberg on Apr 19, 2012 4:13:12 GMT -8
Again, I've tried another option. I've extended the heat riser, enough to bring the end of the riser 2" from the top of the single drum. I'd need the best part of an hour to get it up to a state favorable to pulse jet mode. Even then, it proved to be difficult to get it to stay in that mode, every 20 seconds or so it wanted to drop off to normal running mode. While fiddling and prodding, I've been able to keep it running like that for about 10 minutes.
Clearly, all the other configurations were more or less alike in its ability to reach the noisy mode. The top of the drum has been away from the riser at 2, 3 and 1 foot, no problem with coming up to acoustical resonance. Possible conclusion: the recommended gap will prevent the super mode, more or less. Probably caused by too much resistance in the drum. It needed the drum however, lifting the bung hole plug killed the sound immediately.
Donkey, if and when you are going to try and repeat the test, it's good to know this rocket has been equipped with P-channel, trip wire, rounded tunnel end and a tunnel ceiling slightly like a tile roof shape. The drum is a normal 15 or 16 gallon one, the riser consisted of 1" vermiculite board and the space around the riser was plentiful. And last but not least: this "thing" has been connected to a rather tall masonry chimney.
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Post by Donkey on Apr 19, 2012 8:27:17 GMT -8
Peter, What do you mean by a "tile roof shape"? When I finally get to do this test, (it's like to be a while, my workshop schedule is heating up) there will not be a tall masonry chimney involved. I'm not sure how I would attach a chimney to a stove that I intend to rotate upside-down... Have you tried running your stove without a chimney? I expect that doing that inside your shop could be problematic, smoking yourself out would be a poor outcome.  It's interesting that pulse-mode only works with an extra large barrel gap, also interesting that the barrel is important to the action. I wouldn't have guessed that outcome, though somehow, it rings true. I'll have to show this thread to my brother (who studies rocket science) and see what he thinks. |
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), or my favorite - jet engine. Maybe a heater that uses a liquid fuel sprayed at high pressure to move the air by venturi effect? 
