Vortex Stove

[peterberg]

Jun 16, 2024 2:31:42 GMT -8 martyn said:

However for my own use, I need to be able to re load when the vortex dies, the only way I have found how to do this so far, is by removing all the coals and re staking fresh wood.
I think this issue applies to all the riser-less cores and even batch box designs, it is just more obvious with the vortex stove because you have a viewing window.

The batch box designs are prone to overfueling while reloaded, that's true. Only to be avoided by letting the fire die down, adding some small pieces on top of that so that the flames are raging again and adding large logs on top of that. The trick is to keep the flames going, a lot of fuel on top of glowing coals won't work.

In summer of 2017, the Double Shoebox Rocket #1 employed a venturi in the ceiling which core had the same habit of overfueling as you are seeing now. At the time, I couldn't get it right while coupled to a decent chimney so I discontinued the design.

However, there are two batchrocket designs to date that employ a trick that will slow the fire down when a certain level is reached. One of those is the Double Shoebox Rocket #3, what has been done in this one might be helping or it might not, it's up to you.

The following is how it could be tried in your situation: nothing is changed from the afterburner space down. Above it, there's a space that's 160% to 180% (not critical) cross section area compared to the chimney, so it's probably quite high. Through this, the stream switch from front to the rear where at the end is a slit in the ceiling. As wide as the whole of the space but sporting a csa that's 100% again.

To recap: a firebox with a port in the ceiling, an afterburner space above that where the double vortex is spinning, a somewhat larger opening at the front side that leads to the expansion chamber with a narrow(ish) slit at the rear end of the ceiling.

The upshot of this: in the afterburner the gases get mighty hot. The space above is larger, so there's plenty of room to expand. All these expanded gases are forced to go through the narrower top exit. In effect, the DSR3 is VERY reluctant to go into thermal runaway, it works as if it has a maximum burn rate. Before it is reaching this state, there's no restriction at all. It speaks for itself that the rest of the cooking or heating device need to be virtually frictionless.

To round it off, the DSR3 design doesn't have a separate secondary air provision. Instead, all the air is supplied through the top half of the door frame, nothing lower in the firebox while there's a space above the fuel at all times.


Good luck!

[fruitbat]

Hope you're feeling better soon martyn , and not just because I'm keen to see what you try next!

[martyn]

Thanks Peter, I understand what you are saying and will have a go at implementing that aspect.
Thanks Fruitbat, I only have one kidney and only 75% of my remaining kidney that is left  and that has two tumors growing on it! So I wont actually be getting better but, I have good and bad days.

[Vortex]

Sorry to hear that, martyn. I wish you the best of health, and may all your days be good ones. Trev

[fruitbat]

I'll echo Trev's comments and wish you all the best, keep busy but look after yourself and don't overdo it! I've also been through the mill health wise, but put an 18-month layup waiting for an op to good use catching up on all the content of this site, and semi-delirious daydreaming of various heater designs!

[martyn]

Right we might be getting somewhere …. as we know I have been using a large top box and finding some benefits but still not quite what I wanted.
So after reading Peters post, the one thing I changed was the outlet from the top box, I adjusted it from a 10cm square to a full length 500mm x 15mm right at the back.
This really has made a difference to my over fueling issue, however all is not good as the long thin outlet would not evenly heat the hotplate.
So I made a return counterflow that comes back towards the front and down underneath the fire box and back up the chimney!
Now this does work as you can see in the video but … the vortex is not the best and it was not happy to get going so I would need a start up bypass.
So progress but not quite there as yet…..

[Vortex]

That looks great. Your exit port was 1.33 csa before, now its 1.0, but by changing from a 100mm square hole to 500mm x 15mm, you've also increased the surface area of the exit port by 2.5 times, now you have some back pressure in the system to resist the overfueling.

[martyn]

Yes but I think I have a little too much back pressure now…
I think there is a little bit more to it than that though, I only video a limited amount of the testing I have done, I have tested dozens of exits shapes and sizes.
Today alone I lit 5 fires all with different settings, I tried the slot without the counterflow and although it did not heat the top plate very well it resisted the over fueling and produced a magical vortex! Unfortunately it also sent most of the heat up the chimney.
I think we are getting closer to my goals though….

[martyn]

Wow I am pulling my hair out trying to get my stove to work as I want!
One day i can get fantastic results, quick start up, no smoke on glass, beautiful vortex shape and even the ability to re load for a continuous fire!
Then the next day, with the same setting it all goes wrong.

Different weather conditions, air temp, wind, different wood, differently stacked wood, different amounts of wood?
I mean most times it all comes good and the glass will clear and the stove will calm down after reloading but if I could only just get it to be consistent ….
It could be the vermiculite fire box gets to hot or the ceramic glass lets out to much heat but I must of tried hundreds of variations so far.
Not giving up quite yet but I fear I am getting obsessed!
I am going to increase the height of my chimney next…….

[patamos]

Reminds me of something Norbert Senf once mentioned: 'It's not rocket science - it's actually way more complicated than that'

[martyn]

So over the last two days I have been using a top box 175% of the vortex chamber with a slot in the top.
I have tried many sizes and positions of the slot, long thin, square, ranging from 80% to 150% etc, many variations of down-flow to straight into the chimney.
My conclusion is … yes, the big box resist overfuelling , best I found was 110% CSA with 75mm gap above the exit to under the cooktop.
The flow was coming out of the slot, hitting the cooktop and traveling down 250mm to exit out the chimney.
Temperature was quite even over the top and it was possible to almost feed the fire like a J tube but…… the vortex flame was rather red in colour and generally a bit smoky even with no door in place.
I feel there is some potential with this expansion idea but I cant get it to work as well as my original big top box of 100mm x 550 x 350 top box.
That worked very well apart from I could not refuel.
I have one or two changes to try tommorow but my wife is complaining she wants the patio back neat and tidy! ….

[martyn]

I have found a better setting that really does resist over fuelling!
I resized the top box and took away the space alongside the afterburner so the box is only above the afterburner rather than surrounding it.
I think it has about twice the space as the inner afterburner space, 31 x 34 x 8.5 cm. The exit is 2.5 x 31cm
The flow now exits right out the bottom of the stove.
It is quite possible to feed the fire at any time without it going in to melt down mode but, the vortex is a bit lazy and red, not bad and better than a few days agp.
The fire needs more oxygen even with no door, I tried opening up exit from the top box but that allows the stove to smoke when refuelled.
I think a better chimney would help a lot but in the meantime I will reduce the down flow for the next burn and try moving the top box exit a bit closer to the front.

[martyn]

I was talking to the guys who work in my local stove store, some of them are, not surprisingly, very clued up especially the guys who have been on training courses  and factory visits.
These insulated high tech stoves are really interesting and lovely to look at too….

[fruitbat]

Well done for bringing this up martyn- modern European woodburning stoves are getting very efficient and ever closer to an internal design we would recognise as rocket enthusiasts.

Without wanting to be overly negative, this is one reason I struggle to engage with the world of permaculture which seems somewhat stuck in the past with J tubes and piped benches. Time and again I read opinions online regurgitated from Ianto Evans' book about the wonders of the RMH over the useless metal box stoves... which have in fact now moved on to the point where a recent model is likely more clean-burning and long lasting than a J-tube made out of scrap and found materials!

The missing piece of the puzzle is of course mass to extract all possible heat. But as a core, these stoves are getting close to ideal, and there will be interesting developments over the next few years!

[martyn]

In the rocket mass heater world we have a bunch of enthusiasts trying to build heaters on a limited budget as a hobby.
The bigger commercial stove companies have huge budgets trained engineers and real scientists to develop very efficient new designs!
Virtually all the latest models have a large burn chamber with lots of space around the wood, a slopping roof with secondary air, a restriction followed by an expansion area under the chimney.
There are three air supplies, bottom air, hot secondary air and third, very hot air.
The third air supply, I find particularly interesting as it is sucked or pulled down over the glass and through the burning wood!
I just wonder what we can take from that to use to our benefit on the vortex stove?
I have been trying to burn off excess smoke inside the vortex chamber but burning off all the wood gas before it reaches the vortex chamber will be my next approach…..