Batch cookstove with a small riser

[Deleted]

OK Peter, that's very good news !

This afternoon I came back to the bell setup and I tried to push it to its limits.. I added small wood three times during the pic of the burn, I played with the door and the bypass to speed the fire and... nothing ! At the end of the analysis I even made coals fall inside the port and the CO only showed a negligible pic..

The whole thing is just so very very stable as long as you don't cross the fatidic 8.5% O2 tipping point.

Exact Sketchup plan : uzume-asso.org/assets/docs/experiences/cuisiniere_donkey/batch165_sidewinder_cuisiniere_121617.skp

Combustion analysis :


I'll only do two more tests :
- a true square instead of the half octagon
- using insulating bricks inside the riser

Then I'll settle to this core and go back to a more normal lifestyle.

Regards,

[matthewwalker]

This is an interesting approach Yasin, very informative testing in a short time. I suspect that the shorter cores will never reach the low O2 stability that the riser versions do. I agree with Peter that stable in the 9% range is doing very well for these types.

[Deleted]

Hi everyone,

Two more runs this morning. I tried the square riser with two full firings one after the other.

In terms of CO that is a failure. More CO overall and it seems like the O2 tipping point is higher (between 9,5 and 10% O2). So the core is less stable.

Visually the double vortex is struggling to appear. The thing seems more chaotic but maybe too much chaos is not good neither ?

The results of the first firing :


Some Hi-speed pictures taken 5-10 minutes after the beginning of the fire :







It makes me wonder if a fully octagonal riser wouldn't be better..


Regards,

[peterberg]

An octagonal riser is probably better to form the double vortex, yes. But is a smooth vertical path a good combination with a short riser?

That brings me to another old idea: up till now all risers has been straight.
We know that even with a long riser the flames will come out of the top sometimes, yes? When that happens combustion goes over the "tipping point" and it starts smoking, sometimes like mad.
What if a tapered riser is employed, wider at the top? It would slow down the velocity of the gases so there would be a longer stay in the riser, I'd think. Actually, your small bell downstream the riser could be acting as such. Harder to construct such a tapered riser but maybe it doesn't need to be smooth. Making it wider in steps would create ridges at the inside which in turn could provide for additional small eddies along the walls, much like the trip wire effect.

Together this feels like a possibility to create a short riser in a simple way, don't you think?

[Deleted]

Hi Peter,

I have observed in the standard batch configuration that the double vortex is forming very well at the bottom of the riser BUT just a little bit higher it's becoming only a straigth vertical flow of flames with (I think) very little turbulences. I think that is the reason why the riser of the standard batch is so long.
In fact I have seen this effect also in this configuration here with the riser being only 4.2B (formerly it was 5B but before the testo experiments I took some part off to shorten it because I saw this).

The idea of the bell above the short riser is to keep what I think is the best part of the riser and then to force the gaz to mix thanks to the bell effect.

So I'm thinking that a clean double vortex could help a longer and more turbulent stay in the riser (while keeping velocity high) before the flames enter the bell. The little triangles are ready so I'll try a full octagonal shape this afternoon.

Now I'm not sure I understood properly your idea. You mean to restrict that vertical flow of flames just at the end of the small riser ? For example I may taper the top of that riser to a square of 120x120 mm to force a better bell effect.

Is that what you mean ? If not, could you provide me a drawing ?

Regards,

[matthewwalker]

How about the opposite? Cover the "riser" and put a fire fountain port there like Peter's DSR.

[peterberg]

Dec 17, 2017 3:47:01 GMT -8 @yasintoda said:

Now I'm not sure I understood properly your idea. You mean to restrict that vertical flow of flames just at the end of the small riser ? For example I may taper the top of that riser to a square of 120x120 mm to force a better bell effect.

What I meant was the riser a the bottom the normal size and than gradually wider when stepping up. Not restricting the flames but providing more room higher up in the riser itself instead.

But the other way around, also brought forward by Matt, is probably worth to investigate.

[Deleted]

Geopolymers allow freestyle forms with only one limit, the whole surface must be accessible for coating.

[Deleted]

I tried the fully octagonal core this afternoon and it's impressive how this modification changed the behaviour of the core !

Visually the flames are much faster and it seems that the flames go much more out on the top of the riser.

In terms of combustion it went as low as before (around 90 ppm CO diluted at best) BUT during the last experiments the plancha changed it's shape because of the heat and the intense testing so I see now that there are air coming in..

During the analysis I see that the "tipping point" is higher (around 9.5% O2) but I don't believe it. The fire seems more intense than that.

I need to find a workaround for measures or to re-flatten the plancha and to add joints for air-tightness.


I like the idea of a DSR setup ! I'll try that !



Regards,

[Vortex]

What thickness is the steel you used to make the plancha? On my original stove I used 5mm and it changed shape, I now use 10mm steel with a slightly larger 5mm piece welded on top, so it can sit in the hole and expand without warping.

Do you have any kind of seal around the edges of the plancha? I use the flat sticky fire-rope that's made for sealing the edges of stove glass, and I stick it underneath the bottom edges.

[wiscojames]

If you get a chance to post a picture, I'd love to see how it's welded, etc. Is it in your build thread? I have access to steel and welder, and it is more durable than a glass top.

[travis]

What is a DSR?

[josephcrawley]

Double shoebox keep up with times man

[manU]

Hello. Nice work Yasintoda!
Thanks for sharing, very interesting.
To me it would be interesting to see how this affects combustion: a flat deflector plate right over the riser that creates a "second port like" opening to The side, maybe 5 to 7 cm high. Also could distribute The flames in a way it doesn't warp the plancha. It could be a refractory slate, but maybe a piece of vitroceramic could work and the inside of the riser would still be visible.
Just a thought, cheers

[Deleted]

Hi everyone,

Vortex the plancha is 8 mm steel. I've made something similar than you to deal with the dilatation. I think I've just been too high during the "hard testing" and the outside temp of the plancha was 550°C at max which is very high.. For the next plancha we'll use steel angles welded under it to prevent wraping, but if you have another idea, that's welcomed !
I'll use that joint yes for under the plancha. It's the same we use for the glasses and the doors.

wiscojames you can have a look at the sketchup plan, it's described there.

manu thanks, your idea is very close to the DSR one and I tought about something along those lines too. I'll try it. Right now with the plancha being bent the air coming in makes the O2 levels higher than they should be so I can't really test anything more before I reaflatten the plancha and add an air-tightness joint between the plancha and its support.

Regards,