Vortex Stove

[martyn]

I had some fun this afternoon 

[solobird]

Quoting a peterberg comment over from permies forum regarding DSR3, but I think it could also apply here

The idea is that at the very moment the gases are coming out of the tube, room to expand is available. Shortly after that expansion has happened, the whole kaboozle need to exit through a slit that's system size again. That won't be a restriction during most of the burn, only at the point that a thermal runaway is imminent it will be. As such, it's an automatic self-regulating system that won't kick into an overfuel situation that easily. And beleive me, a full-scale overfuel situation (or thermal runaway, same thing) is as scary as a chimney fire.

Not sure what your chimney size is, but if it's bigger than 4", maybe you could have the restriction there.

On a different note, was thinking of ordering a vermiculite board for a project later this year, but seeing it crack so easily makes me wonder. The one I could find is rated 1100C max.

[victorlt]

I had some fun this afternoon

Hi martyn ,

Thank you for posting your experiments results! When adding fresh wood in a burning hot firebox, try to block primary air till the minimum - 10-15% CSA let say. Blocking primary air gives air deficit in the system and burning in the firebox will go not so fast and produce less gasses passing to the afterburner. But as chimney is hot the chimney traction then sucks more air through the secondary air holes. In my stove when adding fresh wood this gives feeling that stove is starting to run on a propane gas instead of wood - no visual flames or smoke is seen passing the port - just crazy jet flames are blown from the secondary air holes which gives feeling there is somewhere hidden blow fan with propane tank in the system

Crazy burn

[martyn]

Solobird, vermiculite is fantastic for certain parts of the stove and to be fair it will last very well in most circumstances.
Most rigid refractory products will crack under extreme conditions, vermiculite is no different.
Small non structural cracks are to be expected, as a rule the smaller components can last for years but the bigger pieces are prone to cracking.
It has its uses and nothing else comes close when experimenting due to how easy it is to work with.

[martyn]

Thanks Victor, that would be easy for me to try out next time!

[victorlt]

Jan 26, 2023 0:18:17 GMT -8 martyn said:

Thanks Victor, that would be easy for me to try out next time!

Thank you martyn for sharing your experience. By the theory of biomass burning when you have sufficient starting heat source (glowing charcoal) in the firebox, actually you can close primary air at all to the 0% and pyrolysis will still go ahead producing pyrolysis gasses needed for burning in afterburner. This is because wood has trapped oxygen inside its structure and pyrolysis can be absolutely self-sustaining and ultimately exothermic till the charcoal stage. But this is theory - in real environment you need to play with primary/secondary air balance in order to get somewhere in between the gasification and standard burning modes.
Also if you have another piece of pipe try to extend your chimney at least 1m. In order to get this effect you need to have good chimney draft and I'm afraid the piece you are using is to short to get this.

[Vortex]

martyn, as you noticed when you removed the restriction of the top chamber it immediately started overfueling. The resistance / back pressure of the system and correct air control are the way to avoid it. Mid burn reloads are the most challenging for batch stoves and to cope with that extreme example it would really need the resistance of the side channels and a full mass.

[Karl L]

Jan 25, 2023 14:02:22 GMT -8 solobird said:

On a different note, was thinking of ordering a vermiculite board for a project later this year, but seeing it crack so easily makes me wonder. The one I could find is rated 1100C max.

I've used Vermiculite board a lot, rated at 1100C.

One thing to bear in mind is that its coefficient of thermal expansion is similar to steel - i.e. not negligible.
So if it's very hot on one face and cold on another it will bend. And if it's a big piece and it's restrained from bending then it will break.

I never have a problem with this because I divide large surfaces into smaller pieces and allow them to move a little.

[martyn]

Experiment number four…

[victorlt]

Jan 28, 2023 7:54:23 GMT -8 martyn said:

Experiment number four…



Hi martyn. Directing gasses down from afterburner area - bad idea. I tried it with no success too. If you just put the chimney directly on the afterburner roof this would reveal real system power. I see you tried to block primary air to test if secondary is working - but this is far away how it would work if you give it a freedom to move up instead of forcing down.  

[Vortex]

That's looking good martyn, I find after mid burn I can reduce the primary and add the secondary air up through the ash trap, it seems to work as well as adding it through the sides of the port, but with the added bonus of burning up the embers nicely at the end.

[martyn]

Jan 28, 2023 10:00:33 GMT -8 victorlt said:

Jan 28, 2023 7:54:23 GMT -8 martyn said:

Experiment number four…

   

Hi martyn . Directing gasses down from afterburner area - bad idea. I tried it with no success too. If you just put the chimney directly on the afterburner roof this would reveal real system power. I see you tried to block primary air to test if secondary is working - but this is far away how it would work if you give it a freedom to move up instead of forcing down.  






Hi Victor, don't most vortex stoves direct the gasses down?

[martyn]

I found that last years vortex cook stove with the large top box and cast iron plate under the glass, worked extremely well with no issues on start up and a long clean burn.
I dont really need to improve on that aspect but being able to add fuel to keep temperatures consistent was not so easy.

With yesterdays experiment, with the flow now going down and heating the space around the core, it was obvious from the start, it was not going to instantly burst into life like last years stove.
There was also quite a bit of chimney smoke on start up although that might of been because of damp cement board.

It seems the afterburner on my last years stove would run at 700- 750c and the top of the afterburner vermiculite would be 350c, on that basis I though that by resting the glass on top of the afterburner and running the gasses down each side, that would give me a nice even 300-350 over the cooking plate.
However the center would not go much over 200 and the sides were 350c.

I think I am running about 15% secondary air, I will increase this to 20% for next time and I think I will raise the top box height too.

I am working towards sitting the vortex stove where my J tube is and pushing it through the mass of the concrete base.

[Vortex]

The slower startups always showed as cleaner on the testo for me. If you still have those open holes into the flue channel under the V-shaped floor it's possible the startup smoke is coming from them.

[martyn]

Yes interesting how the triangular holes worked, I in fact did initially had them open to the exhaust but once the fire was going strong I tried unblocking one then both, with one open and one blocked, the open one was pulling quite hard and even sucking some black smoke out during an over fueling period.
So they definatily have an influence!
If I did not have other commitments and I had a lot more money, then I would be experimenting every day, it is something I enjoy but very time consuming too.
I was thinking yesterday that I could do with two stoves running as the same time so adjustments could be compared while running in tandem, or ….. even better four or five stoves ha ha ….