RFC for my compact core design.

I'm assuming I came up with something new but let me know if someone already had a similar idea.

While I really like rocket heaters everything I've seen so far is very "stretched" in one dimension and wouldn't fit where I want to. I want something more cube-like that still achieves as clean combustion as possible. I came up with this. I'm temptatively calling it a N-core or I guess an upwinder? anyhoo let me explain. my drawing is lacking a lot of areas that would need to be sealed but hopefully it's obvious where.

- fresh air from the bottom.
- a "grill" of refractory brick long cuts transversely over the wood. Under it a steel spiral (no need for welding if using thin enough steel and a tube bender), doesn't need to be perfect as long as the final vertical tube is as straight as possible and can spin.
- steel is heated via radiation downwards from the main fire. I believe downward radiation is wasted in most designs
- the spiral spins via a magnet, I think this is called a curie wheel. I hope a strong enough magnet would work even behind refractory brick but there are obvious workarounds if it doesn't. failing that by adjusting the height of the spiral it should be far enough to not break the steel main idea is by rotating the steel should never get hot enough to fail. while also distributing as much radiation heat as possible over the long distance of the spiral. worse case scenario the spiral fails but then only secondary air is cut everything should be sealed enough to not let gases inside. (I really don't want to die of CO poisoning in my sleep)
- the main firebox is a simple a box as it can be but on top a shape similar to the port in a standard batchbox pointing sideways to a secondary chamber. This is just theory but I assume an ideal geometry could be achieved.
- the primary combustion gases meet as soon as possible with the heated air from the steel tube. Hopefully creating good secondary combustion
- Obviously I'd protect the spinning tube with refractory brick.  I have a few ideas how to make the hot secondary air blow downwards a little to help with the draft. But failing that a side opening would do.
- Finally I should have clean and hot enough gases to be harvested via a bell/bench/etc. the drawing shows in red the ideal N path

let me recap benefits:
cube like design so potentially quite more compact.
secondary air is heated more . I have read pyrolisis gases need 300°C to 500°C (572°F to 932°F) to self combust but spiral can be made as long and wide as needed.
space on top of main fire could be turned into an oven/cooking area? not my priority right now but obvious to think about.
I believe the fabrication should be simple? all straight cuts, a tube bender is not that expensive I think making a "spiraling steel piramid" and squashing it should do the trick?
no metal parts in direct contact with the main fire, or if they do it will be only briefly.

my concerns:
spiral probably too long? rotating mechanism could fail? I only have a 1/2 inch tube bender that is probably too narrow.

what do you guys think, is there any obvious points of failure I'm missing? why haven't I seen wood boxes where the wood is on top of a refractory grill? is that prone to failure. any idea how much volume of secondary air is needed?

thanks for reading this far any input is more than welcomed.

Interesting. A few observations.

1. Energy radiated towards an insulated firebox floor is not wasted - it's accumulated and will be radiated back towards the door, walls, and then to the room. Changing this flow will not produce anything extra.

2. Stoves with ceiling port are built by Kuznetsov. Making the port horizontally at the top side to force the secondary combustion to happen when gases are descending may not work. In both rocket, Kuznetsov and in other designs from 100 years ago, combustion chamber is on the ascending path. Ascending hot gases want to flow in one stream, descending fill all openings creating multiple streams - lowering heat density and thus impairing combustion.

You would need to build a prototype. I would focus on a proper port placement to see if it works at all.

Hi Crist!
Thanks for making me realize there was an elephant in the room. I see now that forcing fire downward will prove a challenge. I still think it can be done or at least workaround it but I rather redesign to avoid the issue altogether.
I will post here if anything new and worthwhile occurs to me

The fire will travel down but because descending gases evenly fill spaces, the energy may get de-intensified and impair combustion, but if a descending channel was narrow enough and shaped correctly it could work as combustion chamber. You have to experiment.

There have been experiments with compact batch box cores, notably the Double Shoebox Rocket. There have been several distinct variations over the years (DSR1, DSR2 and DSR3). Fox James who posts here has also developed compact cores.