I have installed the Aslan core and sealed everything up with high temp silicone for testing and in prep for cob.
It fires great. Plenty of draw, never any issues with that, just throw some kindling in, torch it, and off to the races.
However, the main issue I'm seeing is it's running cold. Remember, outside test firing yielded 2500 degrees. Inside, the best I've been able to do is 1400 and most of the time it stays around 900-1100.
So I started playing with it. Turns out when I close off the P-channel, the temperature goes up, and not a small amount, 100 degrees or more. It will go from dropping 2 degrees a second to jumping 2 degrees a second.
Another thing I have noticed with this core design is the feed tube is much too small for the nominal size of the core (8"). The CSA is only about 42 square inches.
I think what is happening is that it is sucking through a lot of air and there isn't enough wood burning at once to consume enough of the air for the mixtures to get right. It's not getting hot enough for much of an afterburner effect. The flames are short and fast.
So I'm going to widen the feed tube by an inch, at least, to get the CSA closer to 50. It's too bad the feed tube is going to look a bit bodged, it's so pretty in virgin steel. But it's a consumable part anyway.
No more riser cracking, it's not getting nearly hot enough.
Try closing down the main air side and leave the p channel open yet?
Yes, doesn't seem to help much.
Since I posted this, I enlarged the feed tube, it's now 6.5" by 7.75" including the P channel. The feed tube from the brick to the top rim is 18". The total heat riser from the floor to top is around 5 feet.
I don't know if it helped, I can get the temp higher now up to 1600, for instance burning bark.
I am very happy with being able to burn larger wood though.
This really proves the concept of split barrels for me (really helps if you can weld) because I have so much draw I can put the wood in the feed tube and then start the fire with kindling ON TOP of the wood and there is enough draw to suck the fire straight downward. (Not a good idea though because it makes smoke. Breaks cardinal rule of rocket stoves, keep the wood cool until it's actually on fire.)
Last Edit: Mar 21, 2021 20:56:55 GMT -8 by Solomon
I think it's looking great Solomon. There is somewhat of an issue when scaling up it that they can flow so much air that the three T's ( Time, Turbulence, Temperature ), need some help. With that much air flowing through the Time factor is almost nil. So in the chimney you'll need a damper that can almost shut down the flow to zero. Most of the commercial ones have enough openings for the axel that they work just fine without being able to stall the flow completely. The flames should be at least six inches long and even long enough to get to the riser early in the burn. If not the mass flow will cool the inside of the stove as well as carry the smoke away from the critical zone before it can super heat enough to combust.
Edit to add: There is a need to be able to close off the feed port to leave just about 1/8" gap for primary air, (I have a 3/16" thick steel plate and it gets to about 350*f and adds some preheat to the air flow.) If not, when it starts to get rolling there is too much air and it dilutes the smoke column before it gets down to the flame boundary.
Last Edit: Mar 21, 2021 10:08:10 GMT -8 by pigbuttons
Good info. I designed the exhaust so I could take the cleanout cap off and obstruct the exhaust if necessary. Maybe I'll stick a brick in there.
This is a good example of what I talked about a few months ago about adding oxygen sensing. I'm sure a lot of these run just fine, maybe too rich, maybe too lean, but you don't know unless you have instrumentation (or smoke).
I have discovered scraps of ceramic fiber board make excellent dampers. Way better than brick. They never get hot enough to burn you except on the face facing the fire. The bricks seem to get quite warm. I use two of slightly different sizes, they can damp down all except 3/4" and then turn them 90 degrees and they close it off completely.
It is neat to see firing from cold, the exhaust will put out a nice plume of water vapor, until the chimney is heated, then nothing but a little heat shimmer. I'm going to try to record the whole process from cold in the morning.
Well the thing is, you will probably want to alter the flow from both ends during the course of a burn; wide open to light, 3/4 open coming up to full speed, 1/4 open during most of the burn, fully closed during coaling. Dampers are cheap and easy to install. Plus they cut about 95% of the cold air from dropping down the chimney or warm air escaping your thermal mass when the stove is turned off. Or with your skills you could make a true butterfly valve and completely close off the system from the outside influences.
Last Edit: Mar 22, 2021 3:41:42 GMT -8 by pigbuttons
"it's not getting nearly hot enough" the uncovered bench is a giant radiator.
The thermocouple is in the core, directly in the gas flow near the bottom of the heat riser. Depending on the flame characteristics it should be around the hottest part of the entire stove irrespective of the bench.
The same way that a radiator works ? maybe like a water cooled internal combustion engine ? I think that the uncovered bench is stripping a large amount of heat from the entire system & if covered with mass would slow down this rate of loss and have a corresponding effect on the core.Think about what happens to an engine of you loose the coolant .
I think what Soloman is suggesting is that there is no physical mechanism by which more than a minute amount of heat can flow back from the barrels to the core.
What I'm saying is that what Fuegos is suggesting is impossible or at least there is no physical mechanism that explains his assertion.
The core is the hottest part of the system.
The vertical barrels are the next hottest part of the system.
The vertical barrels are the hottest at the top, and get colder as gas travels down.
Heated gases flow in one direction through the system.
No part of the system is stealing heat from another part of the system.
There is no forced fluid movement like in a car engine or a radiator.
How does a cooler section of a plug flow system strip heat from a much much hotter part of the system?
How is assertion consistent with the fact that when this core was testing without barrels or mass, it reached temperatures of over 2450F? Wouldn't all of nature be "stripping heat" from the core? How did the open air allow heat to "back up" back into the core to make it hotter?
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Mar 11, 2019 18:56:41 GMT -8
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deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
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Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
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