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Post by Vortex on Mar 15, 2020 12:26:57 GMT -8
Hello yasin Well done, that was quick work! My firebox is smaller now I'm using the sloped sides: 310 x 335 (300 middle 230 edges) x 380. so yours is about 20% bigger. The size of the afterburner exit port depends on the amount of draft the system has, more draft = smaller port. My afterburner exit port is: 48 x 230 (90mm back from the front edge of the shelf top, under the hotplate). In strong wind 40 x 230 is OK, even though I have a draft regulator set to 13pa. The afterburner really needs to be made of all insulating refractories. The sooner it's glowing red hot the better. You are burning a lot of small sticks which will make a lot of wood-gas very quickly. I use a mix of sizes - large at the bottom, small at top - like this: www.vftshop.com/images/others/Stove/toplitstack.jpgThe secret seems to be in keeping the gas to air ratio within the range that the afterburner can cope with. Optimal O2 is between 8% & 12%. 10% O2 seems optimum. The stove runs out of air /overfuels below 8% 02: www.vftshop.com/images/others/Stove/testo/testo56.jpgKeeping the fire from falling down between the firewood is important especially at the beginning. It's hard if you don't have very straight wood. Larger splits are better for the top lit fires as they interlock and form a layer the embers cant fall through. I also have some difficulties with this as I live by the sea and all the firewood here is very knotty, bent and twisted. When you can see the double vortex it's a lot easier to diagnose problems: If the double vortex is just shaped like a fountain then it'll be above 12% O2, and needs less air (this is normal at startup though). If flame is going around the edge of the afterburner shelf towards the exit port then it's around 8% O2, and needs more air. Hope that's some help. Trev
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yasin
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Post by yasin on Mar 16, 2020 8:07:56 GMT -8
Hello Vortex Thanks for your answer ! I tried this configuration once again this morning and it failed again ! The limit of stability was reached at 16,0%, just like yesterday. After that it ran very dirty. Yet I amended the firebox with two large "V" to mimic your setup. I also reduced the air intake to approximately 5000 sq. mm to be closer to your setup. On the previous burn I used 7500 sq. mm, which was my classic setup for this heater. My draft too is regulated to 12-14 Pa and the after burner exit port was 50x230 mm. The thing stopped to smoke when I took off this afterburner to have an empty volume of 610x410x200 mm (WxDxH).. and it was stable up to 13,0% O2 ! Really strange but interesting ! It can't be the wood that I'm using : small wood produce intense fires with a O2 that drop rapidly. Then it is easy to see the stability level of the core. On your graph the stability limit seems to be 8% as you noticed already, which is excellent. Hot cores or insulated cores gain approximately 2% O2 stability in my experience. So on your core with my uninsulated refractory concrete I was expecting a stability around 10% O2.. not 16% ! I'm wondering some things : - how old are your testo cells and when was the testo last calibrated ? Electrochemical cells used by testo don't live more than 3-4 years. After that the readings are completely wrong. It happened to my old testo 330-2LL. You can check it directly on your testo. - did you set an automatic dilution above a certain CO threshold ? Like 2000 ppm or something else ? Because too much CO can destroy your cell in one firing. - maybe my downdraft setup interfere with the core ? I need to check that tomorrow. Regards,
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Post by Vortex on Mar 16, 2020 15:13:22 GMT -8
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yasin
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Post by yasin on Mar 17, 2020 2:15:59 GMT -8
Thank you again for the reply !
OK so that can't be the analyser givin wrong results ! I don't have a testo 330-2LL anymore, I have the new version -- the testo 300-LL. The guys of testo came with it when I explain my project to them. They didn't tell me about the solid fuel measurement adapter and I checked the manual, there is no mention of it. But my probe is of a new version too.. maybe the adapter is not needed anymore ?
If your system is stable at 8,0% O2, then if I replicate your setup I should obtain a system that has the same stability, regardless of the fuel I use. Small sticks or small pallet wood like peterberg just make the fire develop quicker.
This morning I tried a similar setup, but with cold air (5500 mm2) coming from the bottom of the door, just as your heater. I modified the top box to make it a little bit bigger (280 W x 410 D x 140 H). Then I added a second port just as in the DSR2 (not directly against the front of the heater, a little bit backward). The second port was 280x35 mm (1,1x the section of the first port).
Then above there was a big volume of 610 W x 410 D x 130 H mm) and then the two downdraft channels.
The fire was more stable ! Stability was around 12 % O2, but the combustion was mediocre.. 1800 ppm of average CO. Surely the pre-heating of the primairy air leads to a lot more of excess air with this setup.
Maybe the firebox size is important too.. maybe I should start by replicating exactly your core and then move on slowly..
Regards,
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yasin
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Post by yasin on Mar 17, 2020 2:27:19 GMT -8
Vortex , I have made a sketchup file, could you check it to tell me if I understood the design of your heater properly ?
Thanks !!
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Post by Vortex on Mar 17, 2020 4:01:08 GMT -8
Hi yasin If I burn a full load of small sticks or pallet wood in my setup it will overfuel, so if you are trying to recreate how mine is working, you'll not be able to do it like that. You need a large afterburner for that much gas. I've found the larger I make it the less well it seems to be able to burn small amounts of gas cleanly. I do not have room in my stove for a large afterburner, and I do not have access to lots of small sticks, so this is ideal for me. I only have Sketchup Viewer and that doesn't seem to show the dimensions. There are 2 differences I can see in your model. The main one is the top chamber exit is not at the front, it is on top about 75mm back from the edge of the shelf, between the shelf and the underside of the hotplate. Gap from glass to front edge of the shelf is 110mm: The firebox sloped sides are like this: Trev
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Post by Vortex on Mar 18, 2020 13:05:53 GMT -8
I don't have a testo 330-2LL anymore, I have the new version -- the testo 300-LL. The guys of testo came with it when I explain my project to them. They didn't tell me about the solid fuel measurement adapter and I checked the manual, there is no mention of it. But my probe is of a new version too.. maybe the adapter is not needed anymore ? It's easy to miss in the manual. static-int.testo.com/media/19/b2/9d1cfff0a18c/testo-330_Instruction-Manual.pdfPage 9:
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yasin
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Post by yasin on Mar 18, 2020 23:02:26 GMT -8
Hello Vortex , Thanks again for everything ! Your help is very useful to me ! My testo is the 300, the new version of the 330, so here is the right manual : static-int.testo.com/media/ee/b3/a3d865ba93ef/testo-300-Instruction-Manual.pdfI searched again with keywords and everything, there is no mention of this adapter. Concerning the tests with small wood, it is my goal to make the core overfuel ! Then I see what the O2 level are at the time of the overfuelling. The higher that level of O2, the more unstable (thus polluting) the core is. It is a very pragmatic method to test any modification of a core. The lower the O2 level at the moment of overfueling, the better the core. I found this during the experiments of the batchblock V1 in 2017. That threshold is not very sensitive to the size of wood. I use wood of 40-45 mm average diameter and it's excellent to push the core to its limit. There are some things I just realized about your core : experiments are done daily with a firebox insulated from the outside and the afterburner is fully made of insulating materials. So the whole burning area must be really hot when the tests start. In my testing setup I cool the heater so that the inside temperature of the heater is equal to the outside temperature. Theses days the testing are done with a heater at 10°C the morning and around 18°C the afternoon. If the tests are made on a hot heater, the results are much better, but not comparable. The testing for the norm ask for cool heaters. Then if the whole afterburner area is made of insulating materials, that may also explain the good results of your setup and the average results of mine. My configuration was very similar to your drawing in the thread "vortex stove". I don't want to use insulating materials because of their price and the dust they put of food (when they are used in direct contact to flames). So yesterday I took off this configuration and put back the batchblock V2. Regards,
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Post by esbjornaneer on Mar 20, 2020 7:27:33 GMT -8
Hi Yasin, good to see your thread and hear that there is a brand new testo on the scene. I have looked through the manual you posted and there is no mention of the extra filter as you say... as the flue gas socket is the same as on the 330-2LL, would it be prudent to ask testo of the solid fuel adapter is needed? It would only be in order that your instrument does not fail prematurely.
I am pleased to see that you are talking about the measurement methods for EN15250. How can one get access to those norms and procedures?
All the best in your testing and development. Esbjorn
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Post by Vortex on Mar 20, 2020 12:12:23 GMT -8
Hi Yasin,
Thanks for explaining your method, I don't want to be overfuelling my stove all the time so tend to run it on the edge, so it overfuels just at the very peak of the burn, that way I can try different configurations to see how it responds.
I have never noticed any difference in performance based on the starting temperature of the stove, and it occasionally goes 48 hours between firings if I'm out working all day and get home late. I normally do one burn a day unless the weather is unusually cold. The firebox & afterburner of my stove is insulated from the mass so cools down quicker. Usually after 24 hours the mass is 35C to 45C. I measured the temp of the mass, firebox and afterburner this morning before lighting, the mass was 40C, afterburner was 30C, Firebox 32C.
The white disc filters in the testo probe are very good, but they get wet from condensate and the water carries a little of the carbon black through the tubes into the testo. The filter part of the solid fuel adapter kit is very good at catching that before it gets into the testo.
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yasin
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Post by yasin on Mar 20, 2020 22:51:19 GMT -8
Hello esbjornaneer Thanks for your kinds comments ! Unfortunately the norms are costly : www.boutique.afnor.org/norme/nf-en-15250/appareils-de-chauffage-domestique-a-combustible-solide-a-liberation-lente-de-chaleur-exigences-et-methodes-d-essai/article/721565/fa139422You need to buy them even thought as a manufacturer you must follow them..
Regarding the combustion, it is a bit different from everyday testing since :
- the heater must be cold - draft is mechanically controlled with a fan and a regulator to 12-14 Pa (the bypass must be closed all the time)
- the analysis must be quite longer than what Peter usually does. The testing can stop at 16.8% O2 only if the O2 level went down as low as 4.4% (ie 16,0% CO2). Otherwise you need to stop a long time after 16.8% O2.. usually I have to go until 18.5% O2. - the results have to be brought to 13%O2, which means that if your average O2 is 14%, the CO13%=(21-14)*CO/(21-13). So if you are making a slow burn your results will be less good.
Vortex thanks for the details.. it looks like I had greatly underestimated the importance of the insulation in the afterburning area !
Regards,
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Post by Jura on Mar 23, 2020 0:52:12 GMT -8
it looks like I had greatly underestimated the importance of the insulation in the afterburning area ! Not only you! I also built an DSR2 core with normal bricks and it can hardly heat a "plancha". The firebox type from below's photo is said to burn as clean and efficient as DSR2. (but I have not seen a proof for that statement.) (I do remember you dislike this kind of secondary air provision. Once I have occasion I'll peep into the firebox to check the state of those air inlet bricks). (photos from Piece Artura)
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Post by esbjornaneer on Apr 3, 2020 6:49:57 GMT -8
yasin Thank you for your last comment and details about the test reading procedure. I hope you don't mind me asking some questions...?
The time for ending the test: is it at 25%of CO2max that the test should end? That is what beReal testing methods state.
Adjustment to 13%O2 equivalent: When I have a test result with mean figures of 952ppmCO, 16.7%O2, 83%Effn, and 121degC, with your formula I get an adjusted CO@13%O2 of 511.7ppm. Which sounds to me as if it would be a cleaner burn than if I had had 952ppmCO (or even 600ppmCO) with 13%O2 and not been able to adjust it... In which case it sounds as if the EN norms think it is better to have unburned CO and higher O2, than a lower CO and 13% or lower O2. Is my logic totally wrong here?
I am aware that the higher O2 lowers the %Effn, but Effn can also be improved by more heat extraction (within limits). So as long as Effn is acceptable a higher O2 seems to be a cleaner burn?!?
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yasin
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Post by yasin on Apr 3, 2020 23:50:44 GMT -8
Hello esbjornaneer You're absolutely right, my calculation is not correct ! I inverted the formula by mistake, sorry ! In your case, CO13%=(21-13)*CO/(21-16.7). So if you have 952 ppm of CO @16.7% O2, it gets adjusted to 1550 ppm CO 13% O2. So that would be above the 2022 EU norm.
Thanks for those details. I am pretty sure the DSR2 will work correctly without any insulation. In my BatchblockV2 core there is no insulation at all, and the results are now pretty good :
I think the problem in your build was the fact that the plancha is not directly above the riser. If you look at the designs of my cookstoves, the plancha is always directly above the riser. Like that it works fantastic. But if I was to put something in between the riser and the plancha, the heat would not be strong enough.
Concerning the guy who said his core was performing as well as the DSR2, well... that is very easy to say !
Regards,
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