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Post by Vortex on May 4, 2020 9:36:21 GMT -8
Hi Trev, I'm thinking about how much control it's possible to have over the hot plate. As I'm scaling down your dimensions to fit a 130mm chimney I plan to have a 40mm thick shelf and and a 60mm depth of the top chamber and then to adjust the height of the restriction to achieve the most balanced burn. I'm assuming that it's also possible to adjust the depth of the top chamber in order to tune the heating of the top plate. Does that sound reasonable? Which are the hottest areas of the hotplate, above and in front of the exit port? How hot do these and other areas get? Is it possible to place pans in different positions for simmering for example? How long does it take to boil water? Can you use two pans at the same time? How long does the hotplate stay hot for? Hi fishalive, Sounds OK. If you reduce the distance the gasses travel under the hotplate you'll reduce the amount of heat available there. If you want to be able to direct it into mass instead you could use one of those cooktop insulators like they use on aga's and Rayburn ranges. A thick steel cooktop is slower to heat up but holds the heat longer. If I wanted it primarily as a cookstove I would use a ceramic cooktop, that would increase the speed it heated up and amount of heat available. I used 15mm thick steel because I wanted to get as much mass as possible in the small space I had available, and heating was my main goal. Mine usually takes about 20 or 25 minutes from cold startup to boil a full kettle of water, but only a few minutes once it's up to temperature. It can still boil water for about 20 or 25 minutes after flame has stopped in the afterburner though, a ceramic top wouldn't have that long lag time. The hottest part of the hotplate is middle front, temps get lower towards the edges which simmer nicely. I usually keep 3 kettles on the stove for hot water as it's free. I have an instantaneous gas water heater but in the fire season I only use it for the shower. |
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Post by fishalive12345 on May 4, 2020 22:59:06 GMT -8
As always thanks for the answers.
My name's Brian by the way.
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Post by Vortex on May 5, 2020 10:40:35 GMT -8
yasin asked recently about what my graphs are like when the stove is fired from cold, here it is today after not being lit for a few weeks. 3/4 load of crappy pine, lit from on top. Note the lower stack temps. Also the 16 minute mark spike due to the O2 dropping below 8%. Mean C* Stack 112.6C. %O2 10.9. ppm CO 348. % Eff. 92.8 
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Post by Jura on May 5, 2020 13:57:00 GMT -8
Do yo maybe know what causes such fall of O2?
Sudden ignition of bunch of lower placed slivers??
I'm very eager to get know CO concentration later on during "coaling phase" (annealing phase - is that proper locution?)
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Post by Vortex on May 5, 2020 14:47:49 GMT -8
There was a strong wind today, that creates more draw and even with the Draft Regulator it drives the fire a bit faster, which means it wants more air, and soon as O2 drops below 8% carbon monoxide goes straight up. I wasn't watching the stove so didn't notice till I heard the Testo start diluting. I just open the door a crack and it goes back to being happy again.
The coaling phase is almost pure carbon monoxide. Once the flames stop in the afterburner there's nothing to burn it with. That's going to be the case no matter what kind of stove you have. I can keep the afterburner going quite a bit longer by gradually reducing the primary air, opening the bottom air a little, and making sure the embers are all together over the ash-trap.
The Testo starts diluting at 2000ppm carbon monoxide to protect the sensor, so if you leave it to run till the embers are out, all you'll see on the graph is a load of zigzag lines as the dilution cuts in and out.
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Post by Jura on May 6, 2020 4:55:00 GMT -8
There was a strong wind today... Got it The coaling phase is almost pure carbon monoxide. I'm just pondering whether adding more air in the coaling phase would help to lower emissions. C + O 2 <-> CO 2. if there is enough oxygen and proper mixing the combustion shall follow stoichiometry. CO is a combustible gas. And the reaction has a high entalpy. I'm worrying as the EU ecoproject norm requires average emissions from the whole process.. I can not afford buying the EU norm (and Polish Masonry Association is kinda unwilling to do so..) Hope Yasin will come up with some solution as he obtained the EU norm and is playing with certifications procedures. |
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Post by Vortex on May 6, 2020 7:07:07 GMT -8
From observation it seems that during the flame phase the carbon monoxide is burned with the rest of the wood-gases in the afterburner, but as the flame phase comes to an end and the coaling phase begins the gas/air mix in the afterburner gradually gets weaker until it goes out. Reducing the primary air keeps the wood-gas/air mix in the correct range for combustion to continue until there is not enough wood-gas left to ignite in the afterburner, at which point any carbon monoxide not burned directly above the coals leaves unburnt in the exhaust gasses. Adding a little bottom air during the coaling phase seems to help in the combustion of carbon monoxide directly above the coal bed, but even though carbon monoxide is a flammable gas it seems there is not enough produced from the coals to facilitate normal combustion in the afterburner. This graph shows what happens to the carbon monoxide level if I add more primary air at the end of the burn during the coaling phase.  |
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Post by Jura on May 8, 2020 2:09:17 GMT -8
Reducing the primary air keeps the wood-gas/air mix in the correct range for combustion to continue until there is not enough wood-gas left to ignite in the afterburner, at which point any carbon monoxide not burned directly above the coals leaves unburnt in the exhaust gasses. I went to the cellar and found (pretty dust covered )notebook with lectures on combustion of solid fuels: Combustion reaction of C is flameless. I found the part I thought about and it said that in annealing phase of "element C" oxidation reaction the ratio of CO/CO 2 is highly dependent of the reaction temp. And the higher it is the more CO in a flue gases.in temp range 1000 K- 2000K it will be predominantly CO. The endothermic reaction of C+CO2 -> 2 CO is the main culprit of that state of affairs. In short words: During the reaction there is not enough oxygen in the proximity of the C element surface, as it is surrounded by the reaction products ie CO 2. Thus the bolded above reaction takes place. BTW. I never thought I would read the kinetic-diffusive model of an reaction with such profound interest. Trying to figure out why adding air during the coaling phase causes such a dramatic increase in CO concentration. It seems a bit a bit counter intuitive to me . So the only occlusion I may come up with is : While allowing more air enter the firebox "normal combustion" (ie. resulting in CO 2) increases so the temp above the coal bed increases proportionally, which according to the theory turns product's stream to contain more CO ) |
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Post by Vortex on May 8, 2020 9:12:53 GMT -8
There is plenty of O2, and more makes the CO go higher. The temperature in the afterburner during the coaling phase is falling rapidly and would usually be 1000K or lower.
If the C is surrounded by CO2, then maybe it is not coming into contact with enough O2.
A little air up through the ash-trap forces the O2 through the coals and burns with a bright mustard yellow flame - which does lower the CO - but if a hole burns through the embers so air can pass easily then the CO spikes back up. A very steep sided V shaped firebox would help with that.
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Post by peterberg on May 8, 2020 12:49:56 GMT -8
The Austrian way to avoid lots of CO in the coaling stage is shutting down air supply. I've seen it happen, it works, within minutes the coal fire is starved of oxygen and the CO goes down rather quickly. The reasoning is this: a layer of coal under the next morning fire will help to burn through the fuel pile easily. Ignition temperature of charcoal is quite a bit lower as compared to the wood itself. I've done this for a couple of winters now, I let the coal bed deminish somewhat before shutting down so there won't be a huge pile of coal left.
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cork
New Member
Posts: 23
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Post by cork on May 8, 2020 13:03:30 GMT -8
Hi Trev,
James here, my stove is still in the making. While the essence is the same as yours as I have had to fit it into an inglenook so it has a different footprint. It is deeper and narrower with a dog leg. The exit port in the top chamber is above the back of the fire box I hope this will not affect it too much. Also I remember you noting that your flue temperature was a little high at 150 oC. With the dog leg the mass on my stove is adjustable so I was wondering how much to add. The path for gasses will have less turns with less restriction but a longer distance to travel. I could email you a couple of photos as I have no idea how to post them here.
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Post by Vortex on May 8, 2020 14:34:35 GMT -8
The Austrian way to avoid lots of CO in the coaling stage is shutting down air supply. I've seen it happen, it works, within minutes the coal fire is starved of oxygen and the CO goes down rather quickly. The reasoning is this: a layer of coal under the next morning fire will help to burn through the fuel pile easily. Ignition temperature of charcoal is quite a bit lower as compared to the wood itself. I've done this for a couple of winters now, I let the coal bed deminish somewhat before shutting down so there won't be a huge pile of coal left. Hi Peter, Does that work ok with top lit fires? I wondered if you'd just end up with more coals, as the fire might not get down to burning them till the coaling phase again. I guess the lower ignition temperature means they burn along with the wood above them? |
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Post by Pablo Crespo on May 9, 2020 1:27:58 GMT -8
Finally got some time to start putting together the new stove today. It will eventually go on top of the 2" concrete slab which is the base of the existing stove. The frame is made from 2" (50 X 50 x 6mm) angle steel, with a 6mm thick sheet of steel in the center of the angle and then a 2mm sheet on top of that.  I was planning to use the 2" storage heater bricks I have as the inside base layer, but I don't have enough. I'm going to need all the ones I have farther up in the stove, so I think I will cast a slab in a few pieces to put in the bottom. On the right below is a storage heater brick (9" x 7.5" x 2"). They're made of Magnetite, which is basically iron ore. They're incredibly heavy (7.5KG / 16.5Lbs) and very effective at storing heat. The rock on the left is a piece of naturally occurring magnetite I found on a beach about 15 miles away from me. I eventually found lots including the seam of ore in the cliffs where they had come from. I'm thinking of going back to collect more to break up to use as the aggregate to cast the inner base from.  Hello from the north of Spain. I would like to know if anyone has results on how magnetite bricks behave in the firebox. I wanted to build the entire core and channels of a masonry kitchen with them. |
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Post by peterberg on May 9, 2020 2:22:13 GMT -8
Hi Peter, Does that work ok with top lit fires? I wondered if you'd just end up with more coals, as the fire might not get down to burning them till the coaling phase again. I guess the lower ignition temperature means they burn along with the wood above them? Yes, it works with top lit fires, I've done it like that for 4 years now and I didn't get stuck with a firebox full of coal. The overall effect is when the fire is on its way it burns through under the remainder of the pile that isn't burning yet. This is a consequence of the charcoal igniting at a lower temperature. And as I said, I tend to let the glowing bed go down for some minutes before closing the air inlet. In Austria it is standard procedure to close the heater down well before the coals are gone. In the end its better to burn the coals while there's a healthy flame phase going on above it, as you found out yourself. Less CO means efficiency is higher as well, oxydising CO generates heat. |
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Post by Pablo Crespo on May 9, 2020 3:03:30 GMT -8
.... Would love to see any pics you have of those stoves. Current state of affairs in the vortex cook stove world :-) :  Hello from the north of Spain. I would like to know if the water exchanger shown in the image is for domestic water or for a central radiator stove. In Spain, stoves of this type manufactured in the Lacunza or Hergon type, the heat exchanger for water is located in the firebox and generates a lot of creosote and bad combustion. Do you know if it is possible to put the exchanger somewhere else to avoid cold burning in the firebox and to be able to heat water for central heating? Thank you |
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