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Post by Jura on Feb 6, 2020 10:28:48 GMT -8
Dear Trev
have you got some more charts and observations to share?
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Post by Vortex on Feb 6, 2020 11:00:03 GMT -8
Hi Rafał, Slowly making progress, hope to do an update on my afterburner experiments soon. Hi Trev, In reducing the gap between shelf top of the after burner and the hot plate above was the restriction added on the shelf or to the hot plate? I assume the measurements down stream of this are flexible. Hi James, Make the shelf so the front edge is 4.5" back from the inside of the afterburner window. Ive found that greatly reduces the etching of the glass. The restriction (afterburner exit port) sitting on top of the shelf, couple of inches back from the front edge. Make it so it's easily adjustable from 1 to 1.5 times the firebox port size. If it overfuels make the restriction smaller, if the fire is too slow make it bigger. I'm still working on finalising these parts so will update the thread with them when I'm finished. |
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Post by peterberg on Feb 6, 2020 11:44:03 GMT -8
The right size of the end port is probably the same as I've found out a year ago in the Double Shoebox mk2 development, 105% of the firebox port. Maybe a little bit more in order to compensate for the restrictive channels in your heater.
It's all done before, no need to invent it again.
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Post by patamos on Feb 7, 2020 17:40:26 GMT -8
Hey Pat, Good to hear from you  Are you running the same stove setup this winter? What do you use for tinder? I had a load of wood shavings which were brilliant but I've run out now. When lighting from on top with paper and cardboard it seems to smother the kindling in a thick layer of ash. I think traditional tinder was dried moss, we have tons of that here but I've never tried it. Ya, same triple shoe box with inverse aryan. I took out the sloping firebox roof and replaced with a corbelled brick and CFB lay up. Presently have bottom air feed spanning the width of the last (deeper) third of the firebox floor. I got into burning top down after a few good exchanges with Norbert over at MHA, whose Condar PM analyzer has been indicating much the same improvements with that kind of burn strategy as your testo has. For tinder and fine kindling i use a stash of shredded scotch broom. Last summer i built a light clay cabin using that as the fibre. My neighbour runs a business clearing it from the land under hydro lines. Brought me 4 yards of chipped broom which i then ran through a 5hp shredder. Then sifted through 1/2" screen to get the size i needed for mixing with clay. The bigger stuff that wouldn't get through the screen (about 5% of total) has made awesome tinder. Kind of like twigs coated in lighter fluid |
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Post by esbjornaneer on Feb 13, 2020 10:32:31 GMT -8
Hi Trev, Looking forward to when 'soon' arrives  Paper and card board are not what they used to be... lots more clay in it nowadays. I have stopped using it for starting fires altogether. Better to go with small sticks if you can make sure they are dry, or splitting wood small enough to take from a lighter if you can't get hold of more shavings. |
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Post by Jura on Feb 13, 2020 12:00:44 GMT -8
Paper and card board are not what they used to be... lots more clay in it nowadays. Clay = glue ? |
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Post by esbjornaneer on Feb 14, 2020 11:43:56 GMT -8
Clay is not equal to glue... but it may be glue rather than clay. In my childhood in the '80s-'90s I was told that colour printed glossy paper was not good to burn as it contained clay. So naturally it had to be tried. It left a lot of ash of a similar type I get when burning most paper nowadays. The type that seems to still stick together and smother whatever is underneath it. I get the same from a lot of card & cardboard too. It may not be clay as I don't remember who it was that told me back then and don't know how likely it is that (s/)he knew what it was talking about... like me |
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Post by Jura on Feb 14, 2020 13:33:29 GMT -8
In my childhood in the '80s-'90s I was told that colour printed glossy paper was not good to burn as it contained clay. What u meant was probably ash..it was/is still used as a filling agents of the mass. in ol'good days they Kaolin clay was used, now is talc, and CaCO3 Nowadays the trouble in "paper" are chem additives (waxes, resins, organic emulsifiers, ). "paper" also contains hydrocarbons in form of fibers which are not similar in their structure to cellulose (that's why it gives smell of burning plastic while incinerated). As to heavy metals: zinc sulfide is frequently used so ash obtained from incinerating such paper is a serious contaminant. I'm afraid we are detouring from main topic in Trev's thread and becoming spammers. So .. Trev...maybe its better to delete our posts? |
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Post by Vortex on Feb 14, 2020 15:41:25 GMT -8
No, you're fine, I started the discussion on paper and kindling, glad you guys chimed in. There seems to be all sorts of crap used in paper and cardboard these days: en.wikipedia.org/wiki/Coated_paperI started chopping up kindling into large matchstick sizes after I ran out of wood-shavings, it works really well but is a bit time consuming. We don't have much Scotch broom here, Gorse seems to take that niche and is too prickly to use easily, plenty of other pyrophytic plants so I'm sure I can find something suitable. Sorry for the delay Esbjorn, hopefully the suspense isn't too much for you I can only have one good fire a day so it's slow progress. For every change you make you really need to repeat the test 3 times to make sure the results are indicative and not just one-offs. Will write up my results soon. |
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Post by patamos on Feb 17, 2020 10:35:07 GMT -8
Trev, do you know about the chopping in a car tire trick? Pack the sticks (vertically) pretty tight, and whack away at them...
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Post by Vortex on Apr 21, 2020 14:39:47 GMT -8
Observations from the winters experiments. I never got around to many of the things I wanted to try out, I could easily do another whole winter of experiments with the Testo just on the afterburner, but the experience taught me a lot. They took longer than I had expected due to the limitations of only being able to have one fire a day and the variables of wind and fuel. The draft regulator wasn't able to adequately limit the draft in strong wind, and most of my firewood was not straight or of the correct length best suited for top down fires. This meant I had to repeat most experiments several times at least to get a clear picture of the results. I also made the mistake of experimenting with different thresholds at the same time. I later realised the threshold size has a relationship to the afterburner exit port size. The experiments really highlighted the importance of the 3 T's (Time, Temperature & Turbulence): The hotter, faster and longer the double vortex can be kept spinning in the afterburner, the cleaner the burn. The exit port helps keep the double vortex spinning in the afterburner. It seems to work by creating a bit of a bottleneck in the gas-flow, so the rapidly expanding gases in the firebox forcing themselves through the firebox port into the afterburner are then directed more into spinning the gasses in place rather than driving the system faster, which improves mixing and combustion and lowers exhaust Carbon Monoxide. The size of the afterburner exit port also determines the amount of resistance to gas flow there is in the system, and so regulates how much gas can move through the system in a given time. The smaller the exit port, the more restricted the gas flow, the more air the fire requires - as a slower gas-flow delivers less air than a faster one. Too small an exit port makes the stove slow to start and sluggish, but harder to overfuel. Too large an exit port makes is easy to start, faster burning and overfuel more easily: - Smaller exit port (More resistance): harder startup, slower burn and vortex, so less mixing and more CO, but less prone to overfuelling - Larger exit port (Less resistance): easier startup, faster burn and vortex, so better mixing and less CO, but more prone to overfuelling Without a threshold the exit port can be a little smaller, as the primary air blows directly on the fire, producing more hot gases, which drives the stove a bit harder via the expansion of the gases in the firebox. The correct gas to air ratio is crucial. Too much air prevents the double vortex from forming properly and lowers the temperature in the afterburner. Too little air causes the double vortex flame to exit the afterburner, both of which leads to more unburned Carbon Monoxide in the exhaust gases. Of all the different configurations I tried I got the best results with the Afterburner exit port on top of the shelf, approx 75mm back from the front edge: 230mm X 40mm (1.05x firebox port):   |
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Post by fishalive12345 on Apr 22, 2020 23:21:48 GMT -8
Hi Trevor,
not sure what I'm looking at in the photo. Could you give a guided tour?
Also, the 'the exit port is 75mm back from the front edge' of the shelf that separates the secondary burn chamber into two sections?
So you're describing the size and exact location of the exit port on the roof of the secondary burn chamber, right?
Thanks
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Post by Vortex on Apr 23, 2020 10:31:02 GMT -8
Hi Trevor, not sure what I'm looking at in the photo. Could you give a guided tour? That picture is looking into the top chamber from above with the hotplate removed. The bottom of the hotplate forms the top of the exit port. That's correct. I refer to the part of the secondary burn chamber where the double vortex forms as the Afterburner, and the area above the shelf and under the hotplate as the Top Chamber. This picture shows it looking up through the afterburner window:  |
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Post by fishalive12345 on Apr 23, 2020 20:47:07 GMT -8
Thanks Trev.
Going back through your thread I see that the shelf is made of 1" ceramic fibre board and 1" cf wool so a total of just over 5cm thick.
The shelf is optimally 75mm back from the front of the afterburner window and 230mm is the width of the Afterburner and Top Chamber so the 40mm is the height between the shelf and the roof of the Top Chamber, visible, seen from above, in a photo on page 36 where you removed the cooktop plate.
In the same photo on page 36 we can see the exit from the Top Chamber into the cooktop plenum so the area where heat becomes usable for cooking.
Hope I've got that right.
In your last photo, looking through the afterburner window, it looks like the the afterburner is narrower at the back, but maybe this is just an illusion?
One last thing, the various additions of, I guess CFB or CF wool are to shape the gas path. The function of most is pretty clear but what about the triangular shaped one sitting towards the front of the shelf and across its width. It must have the effect of slightly narrowing the 40mm between the shelf and the roof of the Top Chamber. Is that correct?
Hope I'm not being annoying by asking so many questions and, as always, thanks for generously sharing your design and findings.
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Post by Jura on Apr 24, 2020 3:57:40 GMT -8
Are those corrugations on side walls applied intentionally to add more turbulence or you just happened to have such piece of material?
Seeing the chart my blance weighting DSR II and Vortex cores leans towards the last one.
Have you ever tried to continue measurements till the end of coaling phase?
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