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Post by martyn on Mar 2, 2023 11:23:12 GMT -8
I was wondering why my 6” J tube seems to peak its top temperature on the hotplate, directly above the riser, very near the beginning of the burn.
So here is what I have found to be the same over many years and hundreds of fires.
I light the stove with the same fuel I use all the time which is offcuts of mixed wood from my workshop, within 10-15 minutes the top is registering 475-550c.
After about 20-30 minutes the top is running at around 350-400c and stays like that as long as I feed the fire.
So why does the temperature drop when the stove get hot?
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Post by Dan (Upstate NY, USA) on Mar 2, 2023 15:59:59 GMT -8
I think your stove pipe gets heated up and the velocity of the whole system gets going until it reaches peck temp, then it cools the exhaust gasses by drawing excess incoming air.
I think...
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Post by martyn on Mar 3, 2023 4:58:53 GMT -8
Yes maybe, I just wondered if anyone else has noticed a similar situation?
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Post by peterberg on Mar 4, 2023 3:01:03 GMT -8
Yes, I did. Measuring the temperatures inside the riser of my batchrocket development model back in 2012 I found out the hottest spot tended to shift up and down during any run. At first, the highest temp was measured right opposite the port and at full bore this shifted upwards to come down again during the tailout.
A J-tube might be somewhat different in this respect, but it seems to be a general characteristic as you put it. During earlier experiments with small J-tubes I found out that when running at full bore the afterburner flames were confined to the very bottom of the riser only. While starting up, however, flames tended to come out of the riser altough not all the time. I assume that the temperature of the burn tunnel in different stages is responsible for this phenomenon.
My opinion, others are free to cherish their own.
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Post by martyn on Mar 4, 2023 4:24:01 GMT -8
I thought it might have something to do with air temperature, at the beginning of the burn, perhaps the air supply is cooler and maybe it supplies more oxogen, but once the stove has been running for 20 minutes the air is being super heated and contains less oxogen?
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Post by Vortex on Mar 4, 2023 5:52:26 GMT -8
Maybe it could be a lack of air at startup - as you've seen with the Vortex stove, when there's not enough air the flames stream out of the afterburner up into the top chamber. The more air you give it the shorter the flame path as all the gases are burning up and most of the heat is absorbed into the walls there, but when there is not enough the unburned gases travel farther through the system before being burned, so heat gets produced farther down the system and heats the mass there more.
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Post by martyn on Mar 4, 2023 6:23:51 GMT -8
Yes that sounds reasonable!
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Post by Dan (Upstate NY, USA) on Mar 4, 2023 12:14:59 GMT -8
Its funny, fire is old as civilization, yet we push science to go to dead planets, instead pushing it to improve the most renewable source of energy.
While science tries to shut down wood burning for cooking and heating instead of using that capital, time and energy to make it even more sustainable.
Instead a bunch of amateur's make new discoveries and improvements while poking around in our backyards...
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Post by martyn on Mar 7, 2023 12:38:39 GMT -8
Yes quire bazaar but to be fair a lot of the wood burners in my locale shop are getting pretty advanced with an insulated fire box, secondary air and lots of adjustments!
Anyway here is the stove from last nights stat up …..
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