Aslan Core, Update!

[Solomon]

Hey all, I haven't posted in a while, but I'm still around.

Just wanted to post an update on how the Aslan Core is performing in the midst of our second full winter.

The short answer is, too well.

So, what's been happening is I cleaned up an old weed growing operation where they used 5" 2x4 and 2x3 blocks as spacers for the racks to dry the weed. They gave me about a cord of these, maybe more, and me, never being one to turn down free firewood, (cured and pre-cut even), took it home and threw it in my wood shed and have been burning it this year.

The problem is, it burns way too fast and hot and since my thermocouple has been malfunctioning, I didn't catch it. So the inside of the core has been melting away, turning to glass and dripping down. All the ash (yes I mean all) has been getting sucked into the mass.

On the upside, heating has been great, we have heated the whole house almost exclusively with this stove. Pretty standard operation, once or twice a day burn for a couple hours, and it heats the whole house, with the help of some blowers and fans to move air around.

I have pictures of all this but I don't remember how to post them unless the system has changed. They're too big. Has that changed? Has the size limit changed?


So, what to do.

I was already planning on replacing the J-Tube core with a batch box core this coming spring/summer. So I'm not worried about that. I have put a couple things in the system this week to slow down the gas flow and put a throttle on this thing. It seems to have worked, so I hope that holds together for the rest of the winter. If it doesn't, then I buy some more heater buddies and heat with propane until I can get the new stove rebuilt.

Given how it turned out, which you've seen in my other threads, I'm thinking instead of just replacing the core, I'm going to tear down the whole thing and start from scratch and build a large masonry heater with a batchbox core. I want it to fit in the corner better since sitting on the bench never really worked. It would be much better for the floor space in the room and would look more conventional and presentable. This will give me the opportunity to make some adjustments using the experience I now have, to build a machine which is more serviceable, more durable, and easier to operate.

I haven't figured out the design yet, other than the approximate size and location of it. I need to work on the gas flow paths, construction materials and methods, and I still havent decided how to build the core, either out of brick or cast. I really like the idea of cast, but it introduces a further element of complexity and materials aquisition.

And I still haven't found any solid information on how to build and more importantly, attach, a door.

[Dan (Upstate NY, USA)]

You posted the links from your google drive account for the photos last time

[fiedia]

Hello, have you seen this for your door? donkey32.proboards.com/thread/2464/door

[Solomon]

Well, my attempts to throttle this thing down were only resulting in more overheating episodes and black smoke. I was rolling coal like I was burning plastic, but it was just wood.

The problem is, the core has melted out more like a 9" than an 8". In fact some spots it is fully a 10" core because of the loss of ceramic fiber board. The fiberboard has melted down into glass, warped, fell out, etc. It was rated at 2300F, but surely it doesn't turn to glass until 3000 or more? I don't know. I do know that my ash was becoming clinker. Looks like a'a lava from Hawai'i.

So I put two layers of split bricks on the bottom of the burn tunnel and feed tube, as well as returning the P-channel to the setup. I'm burning my first test load right now, but it is definitely acting more sedate.

All I need is for this thing to last the rest of the winter. I just want it to burn clean and provide heat. I'm not trying to get the most performance out of it anymore, I've obviously pushed it well past its limits.

So, what would I do differently? (Even though I'm not building another J tube). I would reduce the height of the burn tunnel in the design I received. As I discussed previously, the plans I received and worked with had not been properly sized and vetted, they were upsized from a 6" CFB core and there were some issues that I worked out, but it ended up with a burn tunnel that was 3" too tall. So the stove probably burned most correctly when it was full of ash, when it slowed down quite a bit.

I don't know if some of you remember when we talked about temps experienced in a RMH. Reading some of Peter Van Den Berg's work, he expects temps of 1400F. Even when this unit was functioning correctly, I was easily able to overheat it if I wanted to, and by overheat, I mean 2300F. It should never have been allowed to reach those temps. 1800 should have been a more appropriate speed limit.

Owing to the limited abrasion resistance of the CFB, I would line the entire bottom and sides with brick splits. I would even put them in the roof if I weren't concerned about them cracking and falling down, but that's much less of a concern. I would also do a full brick feed tube. Heck, probably just go with the standard brick firebox, but maybe go with something extra special for the first brick over the burn tunnel, you know the one I'm talking about. I was once very interested in the cast J tubes from Peter's design and I'd love to try one of those. But at least maybe cast that one brick or the whole feed tube from an extremely tough high temp castable, just make it bullet proof.

As far as the heat riser, I have loved the CFB riser tubes that I have used, except the fact that they are melting. For my money, forget the square brick stuff, go with something round and well insulated and long term durable.

Overall, the Wisner design is very good. I did it all differently and look where it got me. Make sure you have a good draft, I have 28 feet of vertical chimney, and make sure your manifold is open. It will make your system more forgiving.

[gadget]

Dec 15, 2022 17:56:32 GMT -8 Solomon said:

The problem is, the core has melted out more like a 9" than an 8". In fact some spots it is fully a 10" core because of the loss of ceramic fiber board. The fiberboard has melted down into glass, warped, fell out, etc. It was rated at 2300F, but surely it doesn't turn to glass until 3000 or more? I don't know. I do know that my ash was becoming clinker. Looks like a'a lava from Hawai'i.

There are fluxes when burning wood. I've seen melted ash in good old fashioned metal box low temp wood stoves. It's fun to scrape off firebrick. I no longer use ceramic fiber blanket in any really hot areas due to rapid damage. It's a bummer cause it works so well.

Best refractory I have ever used was made from clay I refined from my back yard, go figure.

By the way, the temperature rating has more to due with temp cycle rating in that range then melting point. The cycling really should be the only issue with an intended application but it sounds like you got some hot fires going on there.

[Solomon]

Okay, I found an easier way to post pictures. Before I was copying and pasting some code and whatnot, but I found a site that you can just paste the link from Google drive in and it gives you an embedding link.  www.labnol.org/embed/google/drive/

So here is the lower two foot section of riser. It is completely glassed. I'm not saying it can't be reused, I might still reuse it. It was only about 7.5" to begin with so now with the melting and added roughness, maybe it's 8" equivalent.


Here is the upper two foot section of riser, not glassed, but definitely overheated. Remember, this stuff was rated to 2300 and on my first test, I tested it to probably 2400F.


Here is the rear section of the burn tunnel and the manifold:

You can see booger colored chunks of melted riser glass around the edges.

Next is the view of down the bench. All of the ash was being converted to clinker or being sucked down into the bench. Previously, about half the ash was staying in the burn tunnel, about half in the manifold and just a little bit was ending up in the bench. This deposition that you see here is only from THIS WINTER'S burns. I cleaned all of this out before the heating season. The whole of last winter only deposited ~1 inch of ash in the bench.


This ash almost looks like volcanic ash more than wood ash.

Finally, this is the top fuel that I've been burning that caused all this damage, 5 inch chunks of 2x2, 2x3, and 2x4. Now we have switched back to mostly cord wood with smaller supplements of the blocks. I also added firebrick splits to the bottom of the burn chamber to tighten up the cross section and reduce the throttle, temps, and burn rate.

I do remove the screws before burning. I've collected about 5 pounds so far, good quality star drive 3 inch construction screws. It's fantastic because it was free.