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Post by Vortex on Jun 29, 2019 10:21:55 GMT -8
The bypass and kindling really help with the quick heating of the afterburner at startup, but the combustion keeps improving right up until the afterburner chamber is glowing orange, so any way you can make that happen sooner should help. Though if the startup burn is too fast it smokes up the afterburner glass, a gradual start doesn't do that. I don't think lining the afterburner chamber with ceramic blanket will help, as it seems to need some mass to hold a bit of heat to radiate back. The IFB is the best I've found so far.
I tried many different pre-heated secondary air supplies directly into the afterburner. Most seemed to disturb the double vortex in some way without any noticeable improvement in combustion. A small amount introduced into either side of the front of the port was nice as it gave good definition to the double vortex spirals. My secondary air is up through the ash-trap, so it gets heated as it travels through the ash-box, ash-trap and up through the embers before mixing with the hot gasses going into the port.
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Post by fishalive12345 on Jun 30, 2019 7:39:18 GMT -8
What effect do you think insulating the inside of the firebox would have on getting up to temperature quickly, with ceramic fibre board as in Matt Walker's latest stoves or with insulating castable refractory cement? I think I remember your firebox is made of castable refractory and is insulated externally with CFB.
When I looked into this recently I visited a place where they sell refractory materials and the owner showed me a whole series of castables, less resistant more insulating, the other way round and everything in between. He also had ceramic fibre board, both the bio soluble and non bio soluble versions. The limitations of the bio soluble version, apart from fragility is that it has a maximum temperature of 1050 degrees centigrade. He really didn't think it would stand up to being used in the firebox because it's not tough enough. I did say that people have used it successfully but he was thinking about people throwing logs into fires.
I was thinking about trying your design but using more insulative materials so your comment about insulating firebrick in preference to CFB in the secondary burn chamber is really interesting. I imagine the IFB would have similar characteristics to insulative refractory cement and it would also be more resistant to knocks in the firebox than CFB.
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Post by gadget on Jun 30, 2019 8:58:28 GMT -8
Better yet, how about rigidizing the ceramic fiber board/blanket and adding a face coat? It would add a little bit of mass and add lots of abrasion resistance.
That is what the forge DIYers do. They rigidize the fibers then add a hot face. If done right, it keeps the insulating value of the fiber.
Their formula is typically:
fumed/colloidal silica rigidizer
satanite face coat
ITC-100 kiln wash
The reflective kiln wash could be skipped
I have been testing homemade face coats with lots of success.
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Post by marcios on Jun 30, 2019 9:41:29 GMT -8
I've read that some refractory ceramics would be the best for the parts in contact with fire: abrasion resistance, high reflectivity with heat storage at surface and low thermal conductivity and expansion. (Which kind of ceramics is the one we see in modern fireboxes? based on cordierite?)
Other way could be a coat like that (how thick?) or a castable mix or an advanced IFB (radiant at the surface, medium density?) that come close to all that properties. In this case, IFB, CFB or vermiculite board would work the same way?
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Post by gadget on Jun 30, 2019 10:53:17 GMT -8
The only way to really get any insulation out of ceramics is by having air pockets within the material. This is done either through ceramic fibers or trapped air pockets like in IFB. There is also bubble alumina but it is pricy stuff. Bubble alumina is much stronger if done right.
The forge builders have a good solution. Build a hard shell around an insulated base. They have high fuel cost and abrasion from working with metal so there is a motive there. They are seeing much higher temps and their system works good.
cordierite is an excellent ceramic choice and I suspect very common in high quality brick. Its common in kiln furniture and those ceramic honey comb grids used on IR heaters. It has a kind of yellow sandy color to it. I have a couple dozen of those rectangle honeycomb cordierite grids I'm using for secondary air diffusers on a heater I am building this winter. It is a strong ceramic but I'm not sure how reflective it is.
I would think mullite would be a good choice if you wanted more reflectivity and it is also a very strong ceramic and very white (reflective?). Its not as conductive as 99.5% alumina ceramics. Its used in spark plug ceramics.
Good old fire brick works pretty well as is, especially compared to a steel stove. I've done it in a rocket with no insulation and it did great but we want to take it to the next level so its insulate to the max. Matt Walker has shown how well ceramic fibers work. He has come up with a thin high temp metal shell for dealing with abrasion that is working out well. I'm going a different route and am covering my fibers with a patchable ceramic hot face for wood abrasion.
I have not seen the numbers but I think the ceramic fiber blanket and board out perform IFB. I don't know about vermiculite board, I don't think it will last as long.
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Post by Vortex on Jun 30, 2019 11:47:15 GMT -8
What effect do you think insulating the inside of the firebox would have on getting up to temperature quickly, with ceramic fibre board as in Matt Walker's latest stoves or with insulating castable refractory cement? I think I remember your firebox is made of castable refractory and is insulated externally with CFB. When I looked into this recently I visited a place where they sell refractory materials and the owner showed me a whole series of castables, less resistant more insulating, the other way round and everything in between. He also had ceramic fibre board, both the bio soluble and non bio soluble versions. The limitations of the bio soluble version, apart from fragility is that it has a maximum temperature of 1050 degrees centigrade. He really didn't think it would stand up to being used in the firebox because it's not tough enough. I did say that people have used it successfully but he was thinking about people throwing logs into fires. I was thinking about trying your design but using more insulative materials so your comment about insulating firebrick in preference to CFB in the secondary burn chamber is really interesting. I imagine the IFB would have similar characteristics to insulative refractory cement and it would also be more resistant to knocks in the firebox than CFB. It seems to be a bit of a trade off. A low mass CFB firebox will get up to temp quick but it can only reflect back the heat present, so the temp drops just as quick towards the end of the burn. A dense firebrick firebox will take a long time to get up to temp but will give back that stored heat right to the end of the burn, so it's one end of the burn or the other. That's why I went for a compromise of 1-3/4" / 45mm dense cast with 1" / 25mm ceramic insulation on the outside. An Insulating castable refractory mix would probably be roughly equivalent, as it has some mass and is insulating to a degree, the downside would be that it wouldn't be as resistant to abrasion as a dense layer backed by CFB. Personally I'm very wary of ceramic fibre products in the firebox. As a child I watched my father suffocate to death slowly from industrial caused lung cancer, and later my step father was diagnosed with asbestosis, mercifully something else killed him before it progressed to far. If you want to try the super insulated firebox, one idea I had that would make CFB fireboxes more durable and safe is to line them with ceramic cooktop glass. Pat made a heated secondary air plenum below his firebox roof using it that has apparently survived OK. |
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Post by marcios on Jun 30, 2019 15:42:48 GMT -8
The bypass and kindling really help with the quick heating of the afterburner at startup, but the combustion keeps improving right up until the afterburner chamber is glowing orange, so any way you can make that happen sooner should help. Though if the startup burn is too fast it smokes up the afterburner glass, a gradual start doesn't do that. I don't think lining the afterburner chamber with ceramic blanket will help, as it seems to need some mass to hold a bit of heat to radiate back. The IFB is the best I've found so far. I tried many different pre-heated secondary air supplies directly into the afterburner. Most seemed to disturb the double vortex in some way without any noticeable improvement in combustion. A small amount introduced into either side of the front of the port was nice as it gave good definition to the double vortex spirals. My secondary air is up through the ash-trap, so it gets heated as it travels through the ash-box, ash-trap and up through the embers before mixing with the hot gasses going into the port. I was thinking in low dense and low conductive ceramic tiles/plates to line or to be the roof of firebox, and secondary chamber walls by extension, with a proper tickness to start irradiating fast. In addition to winning in reflectivity, wouldn't it be good to have a little mass to soften fuel variations? After the initial burn stage, have you ever tried left open only door side air inlet (with enough gap)? |
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Post by marcios on Jun 30, 2019 20:58:56 GMT -8
The only way to really get any insulation out of ceramics is by having air pockets within the material. This is done either through ceramic fibers or trapped air pockets like in IFB. There is also bubble alumina but it is pricy stuff. Bubble alumina is much stronger if done right. The forge builders have a good solution. Build a hard shell around an insulated base. They have high fuel cost and abrasion from working with metal so there is a motive there. They are seeing much higher temps and their system works good. cordierite is an excellent ceramic choice and I suspect very common in high quality brick. Its common in kiln furniture and those ceramic honey comb grids used on IR heaters. It has a kind of yellow sandy color to it. I have a couple dozen of those rectangle honeycomb cordierite grids I'm using for secondary air diffusers on a heater I am building this winter. It is a strong ceramic but I'm not sure how reflective it is. I would think mullite would be a good choice if you wanted more reflectivity and it is also a very strong ceramic and very white (reflective?). Its not as conductive as 99.5% alumina ceramics. Its used in spark plug ceramics. Good old fire brick works pretty well as is, especially compared to a steel stove. I've done it in a rocket with no insulation and it did great but we want to take it to the next level so its insulate to the max. Matt Walker has shown how well ceramic fibers work. He has come up with a thin high temp metal shell for dealing with abrasion that is working out well. I'm going a different route and am covering my fibers with a patchable ceramic hot face for wood abrasion. I have not seen the numbers but I think the ceramic fiber blanket and board out perform IFB. I don't know about vermiculite board, I don't think it will last as long. Bubble alumina as well as alumina aerogel insulation composites are really fabulous things, but unfortunately it seems they're a little far away from us. On the other hand, fortunately, we have several other options. All firebox ceramic wall in www.brunner.eu/en/ is a cream to yellow sandy color, as well other centenary leading producers. Do you have anybody who could say about such ceramics? I'm curious about how you're going to implement cordierite grids for secondary air diffuser. Good old dense firebricks: from now on I only think of using them as heat storage, taking advantage of delay in getting warm. Yeah, I'd seen Walker crazy anti-mass design and A330 alloy riser. I'm inclined to high mass with visual Aryan fontain, firebox sized to the limit that it is no longer possible to avoid loss of efficiency, insulating castable mix with sodium silicate and, just like you, hot faces coated or lined. In relation to back insulation function (without contact with hot gasses), for which it would be enough to consider the equivalent thickness of the materials if not structurally applied, there seems to be no substantial difference, so vermiculite plate won't perform and last equally? |
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Post by Vortex on Jul 1, 2019 0:49:22 GMT -8
Some mass is good, yes. As I said it was a compromise, 45mm thick dense cast plates with 25mm of ceramic insulation on the outside. That gives enough mass to smooth out any dips in the burn and retain enough heat for the end of the burn, so there's nothing left but fine white ash.
I've tried all the different air combinations. best I've found is full primary and secondary through the whole burn, and door open a crack until my back kettle boils. When all the embers are burned out I close the primary and secondary air ports and the chimney damper.
Vermiculite board is fine in small pieces even right in the afterburner, but anything big enough to have a temperature gradient across it cracks from the differential expansion. So it would be fine for backing insulation, though I don't know how good it is compared to ceramic fibre.
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Post by fishalive12345 on Jul 1, 2019 2:58:43 GMT -8
Does anyone have any experience with soapstone? I was thinking of it as facing material and/or as a heat storage material.
The problem with facing materials and using multiple materials in general is that they're going to complicate a build that is already going to be complicated for me.
First I was thinking of ceramic fibre but also worried about the health aspects. I mean wood smoke is already carcinogenic. Then I thought about dense firebrick with some kind of facing. Now I'm thinking about castable and that's only the combustion part of the system.
On the previous page Patamos talks about Matt Walker's stove; refuelling, the cooktop, the oven. I have been following stove developments on proboards for years but have only recently realised that different stove uses require different burning and fuelling patterns, so basically different stove designs. I used to think the aim was to have the best, the most efficient stove but now see that you need the best stove for this or that combination of uses (including fire gazing).
It's a real pity that instrument testing requires expensive equipment.
Trevor, has the way you use your cooktop changed as you moved away from open fires, to a closed firebox that you refuelled (not sure if that's right), to a kind of batch situation where you burn a full load and don't need to burn again till the next day?
If you wanted to use your stove to cook twice a day, morning and evening, would that be doable? Does it just depend on how efficient your heat recovery system is?
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Post by Vortex on Jul 1, 2019 4:24:11 GMT -8
I pretty much stopped using my original stove for open fires after the first winter. I love open fires but they eat through the fuel so fast. My aim is to only use the wood I collect from normal maintenance around the farm. I don't want to be cutting down trees just for firewood, there are not enough here as it is.
Before I put in the Aryan afterburner I was cooking twice a day on the stove when I fired it, breakfast in the morning, dinner in the evening, but since changing over I have mostly only been lighting the stove once a day around midday, and cooking my lunch on it. If the weather is unusually cold I go back to twice a day. If I'm cooking and the stove is hot I use it, if not I use the gas.
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Post by fishalive12345 on Jul 1, 2019 4:38:16 GMT -8
I guess if you open the bypass you can heat the cooktop and .... trying to answer my own question, if you burn when your cooktop and heat recovery system are saturated you risk damaging them and you also waste heat up the chimney.
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Post by Vortex on Jul 1, 2019 8:21:58 GMT -8
I occasionally do a small burn with the bypass open, when I just want to warm the house a little on a spring or autumn evening, but don't want the house to be to warm overnight. Also I've got distracted and done the whole burn with it open a few times and it never did any harm. The stove only stays hot for a few hours after though, so you could use it as a cookstove that way if that was what you wanted.
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Post by fishalive12345 on Jul 30, 2019 23:48:54 GMT -8
More questions...
Trevor, have you ever experimented with scaling your design down? Do you think it would be possible?
I seem to remember that it was discussed and got a negative response. I'm thinking of trying to buid an outdoor experimental setup.
I plan to try a four inch/10cm chimney system like the roquetinho which is a 4" system with heat riser built in Portugal mostly for quick heating rather than heat storage. The firebox is 16x22x33cm. Peter Van De Bergh developed it or was involved in the development.
There are similarities between the climate in Portugal and the Ligurian coast in Italy that would probably make this size more suitable for our needs.
I'd like to see if it's possible to experiment with this kind of system size but change secondary combustion and the layout for heat recovery, lower and longer, and to incorporate an oven as well as a cooktop. That's seems to be the kind of layout that has lead some people to come up with or develop afterburners other than heat risers. Your vortex stove, Matt Walker's cookstoves and Uzume in France for example.
As far as the cooking, heat recovery side is concerned, I kind of envisage a system with half of the top surface as cooktop and the other half insulated with the (black) oven immediately under it. It would have two bypasses. One which would help at startup if necessary and would enable the use of the cooktop without heating the oven or heat storage and one that would allow the use of the cooktop and the oven but would bypass the (small) heat storage element.
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Post by Vortex on Jul 31, 2019 8:55:03 GMT -8
I haven't experimented with scaling yet but it's next on my list, hopefully sometime this summer. 4" is challenging in almost any style, I'm planning to try a 5" first, if that goes OK then I'll probably try a 4".
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