Vortex Stove

[whitebramble]

this posting has become my stove bible ---built a number of welded steel wood burning stoves over the years to heat my old cottage and improved on each one a little but they just dont muti task /purpose that well so i have been reading up on stoves for sometime ---and i have been wanting to build something better for awhile now and your vortex stove is just what i think would be perfect for me to start out with.I burn turf mostly as good hardwood is not cheap as , and i have my own turbury rights to bog---whilest i do have some trees on my property theres not enough to go and just use timber .Besides most of my planting out has only been growing for about 5 years, i have increased the amount of tree planting  only in last 3 years and with my hempcrete insulation of the cottage coming along i am hoping to be better prepared for the years ahead .Thanks for the inspiration  

[Vortex]

Sounds like you're in Ireland as well? I used to cut and burn some turf mixed with the firewood. I got fed up with having to empty the ashes so often though, with just wood I only empty them 3 times a year. Not many people still cutting turf now. I'd recommend planting some Eucalyptus for quick firewood crops. I planted a few when I first came here and harvested them 6 years later when they were 30 foot high and a foot thick.

[whitebramble]

hello, sorry to have just arrived here , my first post introducing myself has been lost ---due to my own mistake ---i am a one letter at a time computer expert, yes  i am in ireland --north kerry ---not much eucalypt around my way , i have seen a few trees planted in gardens but looking into it a bit more and they just dont do that well around here,our soils are heavy clays and bog cutaways mostly. I have planted out some grey alder and black birch -also called cherry birch ---but most of my trees are only a foot to 2 feet high so a long way to go and some free self seeding polar ,ash beech and sycamore around the property,but the bulk of my planted up stuff are walnuts ,chestnut ,hazel,bellota oak,apple ,pear and so on --part of my other long term food forest type plan ,so wont be burning many of them yet. Turf is the old standby - i do my cut every year and 6 bins does the year plus some left over , yes lots of ash to clear out ,but i have a couple of uses for it which are on going ---apart from the soap making disaster which i wont be repeating to soon. Been collecting materials to build a new stove for heating ,cooking and hot water , but looking at this type of stove ,i will have to include firebrick and such onto my list , i do have an old induction hob stove --a very expensive one that would take another small fortune to repair even though these would be minor. Actually i will have to build a rocket water heater stove as well for my hot tub project --and after seeing a masonry type stove in use ---one of those would be very nice in the remodeled kitchen ---but small steps first.

[Vortex]

Today's test run. Ash, Holly Willow and Monterey Pine. 2 large pieces stood vertically in the back of the firebox, the rest laid horizontally width-ways with 3 sticks of pine kindling on top. Lit from on top in the middle with the bypass closed.

[Vortex]

For this mornings test burn I made a steep 45 degree sided grate out of some old pieces of firebrick. I've noticed CO seems lower in the coaling phase when there is air up through the ash-trap, but as soon as a hole burns through the coals the CO spikes back up. My grate is quite shallow so the embers don't fall in on themselves, so I wanted to test how it would behave with steeper sides.

Ash, Willow, Holly & Monterey Pine, laid horizontal length-ways. Because of the higher level of the grate the usual half load about three quarters filled the firebox. Lit from on top with the bypass closed. I added another 5 smallish pieces of wood at 9:47. The temperature in the afterburner broke my previous record of 921.2*C and went up to 938.7*C. The previous record was set on a windy day with a full load of fuel, today was very still so I was surprise it went so high.

The normal rise in CO at the start of the coaling phase never arrived and instead kept getting lower. It dipped down to 32ppm at it's lowest point.

[peterberg]

Trevor,
It's evident that a Testo is a nice tool to tune one's heater. You've found out a wood fire in general and yours specifically don't like under air, it generates far too much combustible gases in a short time frame. The only situation under air is beneficial seems to be in the coaling stage. The Austrians avoid the CO peak at the end of the burn by closing the air inlets completely so the coal fire dies down by itself and leave a coal bed to start the next burn on.

Also, letting the fire develop by itself without the assistance of a bypass is much better. The switch from burning fiercely to slowed down by closing the bypass is too abrupt most of the time, resulting in an overload of combustible gases again. The fire will adapt in due cource but it'll take some time in the order of 5 to 10 minutes.

The effect of flames that are coming out of the afterburner area means the combustion isn't complete anymore. This effect is evident in most afterburner constructions I've tested which could mean it is a universal thing.

Maybe you found out by yourself, but I mention it here just for good measure. Efficiency is calculated using end temperature and O² residue in the exhaust gases. CO is diluted by O², so low CO numbers and high O² numbers aren't as good as it looks like. In a "normal" box stove the CO goes up when O² comes down, in an afterburner construction both go down the same time provided combustion is commencing the right way.

That said, your diagram above is a very good one, almost as good as it gets. The end temp could be considered on the high side and as a consequence efficiency could be higher. But then, the thing is running very nice, reflected by the new temperature record. O² is as low as I would consider being still safe, CO is most of the time lower than 500 ppm at the same time which I would consider excellent.

I did some riser temps recording way back in 2012, 2.5 cm from the rear wall and roughly halfway the height of the port. My record stands on 1172 ºC, absolutely tops and never repeated again. In the end nobody is served by one-time records, so I consider 1000 ºC or quite close to it as normally achievable.

Playing with such a device is tantalising, don't you think? There's so much to be learn from it.

[rakettimuurari]

Nov 23, 2019 10:01:05 GMT -8 Vortex said:

For this mornings test burn I made a steep 45 degree sided grate out of some old pieces of firebrick. I've noticed CO seems lower in the coaling phase when there is air up through the ash-trap, but as soon as a hole burns through the coals the CO spikes back up. My grate is quite shallow so the embers don't fall in on themselves, so I wanted to test how it would behave with steeper sides.

Ash, Willow, Holly & Monterey Pine, laid horizontal length-ways. Because of the higher level of the grate the usual half load about three quarters filled the firebox. Lit from on top with the bypass closed. I added another 5 smallish pieces of wood at 9:47. The temperature in the afterburner broke my previous record of 921.2*C and went up to 938.7*C. The previous record was set on a windy day with a full load of fuel, today was very still so I was surprise it went so high.

The normal rise in CO at the start of the coaling phase never arrived and instead kept getting lower. It dipped down to 32ppm at it's lowest point.

Thx for this inspirational thread Vortex. I Re- read now after a while... I feel the urge to build some "stove- stuff" accumulating - grrrr I' ve been planning couple of years to build a cooking stove next and your build is most temptating; especially due the streamlined and solid design. I might end up dismantling my J- tube in sauna dressing room and replacing it with this design. Actually only (1st) half of it would do as I could leave the bell on that old one standing! J- tube is not really easy lover, if the usage is once a week in -5'C  -- -30'C temperature range. Needs some prework always in the beginning as I have no bypass. I could build (half of) your model, combine that with the existing small bell + add the bypass hatch... 

To this: 


What do u think? As I uderstand it should be enough if I just make 1 st half of your build all the way to the opening (1 x CSA) after the afterburner box and the route it with low connection in to the bell on the right ...?


Sláinte!

-Antti-

Ps. My sauna stove configuration (in the actual sauna room) is now very close to your build - especially the upper chamber and it works wonders. When the burn gets to the speed, the glass is clean and no visible smoke or steam from chimney.

[Vortex]

Nov 24, 2019 1:50:52 GMT -8 peterberg said:

Trevor,
It's evident that a Testo is a nice tool to tune one's heater. You've found out a wood fire in general and yours specifically don't like under air, it generates far too much combustible gases in a short time frame. The only situation under air is beneficial seems to be in the coaling stage. The Austrians avoid the CO peak at the end of the burn by closing the air inlets completely so the coal fire dies down by itself and leave a coal bed to start the next burn on.

Also, letting the fire develop by itself without the assistance of a bypass is much better. The switch from burning fiercely to slowed down by closing the bypass is too abrupt most of the time, resulting in an overload of combustible gases again. The fire will adapt in due cource but it'll take some time in the order of 5 to 10 minutes.

The effect of flames that are coming out of the afterburner area means the combustion isn't complete anymore. This effect is evident in most afterburner constructions I've tested which could mean it is a universal thing.

Maybe you found out by yourself, but I mention it here just for good measure. Efficiency is calculated using end temperature and O² residue in the exhaust gases. CO is diluted by O², so low CO numbers and high O² numbers aren't as good as it looks like. In a "normal" box stove the CO goes up when O² comes down, in an afterburner construction both go down the same time provided combustion is commencing the right way.

That said, your diagram above is a very good one, almost as good as it gets. The end temp could be considered on the high side and as a consequence efficiency could be higher. But then, the thing is running very nice, reflected by the new temperature record. O² is as low as I would consider being still safe, CO is most of the time lower than 500 ppm at the same time which I would consider excellent.

I did some riser temps recording way back in 2012, 2.5 cm from the rear wall and roughly halfway the height of the port. My record stands on 1172 ºC, absolutely tops and never repeated again. In the end nobody is served by one-time records, so I consider 1000 ºC or quite close to it as normally achievable.

Playing with such a device is tantalising, don't you think? There's so much to be learn from it.

Hi Peter. Thanks for your comments. Yes I'm enjoying experimenting with the testo, never thought I would get the chance, it's taught me a lot. My neighbours son saw my stove when he was over on holiday from Germany this summer. He has the idea to get some made to sell as a kit, but wanted to see some test results first. He got hold of the testo and sent it to me, I'm very grateful to him.

Yes, I was aware the high O² with low CO was not as good as it looks. The O² seemed to be getting gradually higher each burn, until I changed to a new clean filter and then it went back to normal range. Have you ever noticed that happening? I couldn't think how a clogged filter would make O² higher.

The top lit horizontally laid fires seem to produce very low CO, but make huge amounts of coals and so high CO at the end. Whereas the 45 degree laid and lit from the front fires that I was doing before, seem to produce a bit higher CO through the burn but make a lot less coals so less CO at the end. I think I'll do some measurements from lighting to completely out and see what the CO averages are.

I've heard of the Austrian way for dealing with the coals but have never tried it. I would think a flat bottomed firebox would be better for that, as they'd be more spread out and would cool quicker - I'll have to give it a try.

The exit temp is a little high, but my whole stove including mass and firebox is only a little over half a cubic meter in size, and it's usually still warm when I light it the next day. I'm amazed it's able to take up and store as much heat as it does. What would be the optimum O² level to aim for, and if it is above or below that would you adjust it via the primary air?

[peterberg]

Hi Trevor, keep in mind that in the last stage of the burn, being coaling phase, it's nearly all pure CO that's produced. In sharp contrast with the flame phase where besides CO all sorts of complicated tars are formed and broken up to form other, simpler ones. The CO is only a tell-tale sign of combustion quality since it's one of the last large molecules being cracked.

In my experience, an O² level of 6% is the lowest achievable in the combustion cores we are playing with. It could be lower, yes, but chances of overfuelling and creating a dirty burn rises exponentionally. Best bet is to aim for lowest O² around 8%, which is already extremely good. It's only 10 years ago that stove constructors wanted to keep O² above 10% and temperature above 250 ºC just for safety.

In case you would like to try what could be achieved, stay around the heater and deminish primary air a bit at the time. Listen to and view the fire, when the flames are turning angry red and sound is muffled you are on the wrong track.

[Vortex]

Nov 25, 2019 1:32:25 GMT -8 rakettimuurari said:

Thx for this inspirational thread Vortex. I Re- read now after a while... I feel the urge to build some "stove- stuff" accumulating - grrrr I' ve been planning couple of years to build a cooking stove next and your build is most temptating; especially due the streamlined and solid design. I might end up dismantling my J- tube in sauna dressing room and replacing it with this design. Actually only (1st) half of it would do as I could leave the bell on that old one standing! J- tube is not really easy lover, if the usage is once a week in -5'C  -- -30'C temperature range. Needs some prework always in the beginning as I have no bypass. I could build (half of) your model, combine that with the existing small bell + add the bypass hatch... 

To this: 


What do u think? As I uderstand it should be enough if I just make 1 st half of your build all the way to the opening (1 x CSA) after the afterburner box and the route it with low connection in to the bell on the right ...?

I cant see any problems with that so long as you have a good chimney. I would definitely put in a bypass, even if you dont need it for lighting it's useful when adding fuel during the burn. I presume you're not thinking of using steel for the outside skin like I did? It doesn't cope with getting wet very well. A ceramic cooktop would work better in the steamy environment of a sauna. Post some pics if you build it

[rakettimuurari]

All true. No metal for that one; will get insta- corroded. Basically I could utilize all the solid firebricks from the J- tube core, although castable enables to make bit thinner elements (will make burnchambers floors and roofs out of that anyway). Yes, have to think about this... it could be a better project in summer. Probably I will just update my J- tube with a bypass at this point. Thanks for the experimental work and the dimensions/ measurements; your double ram-horn looks very convincing One of these days I'll add some new pictures about the "aryan sauna stove's" latest configuration + burn to that thread. Afterburner chamber is smaller now and bottom corners are camfered & bottom insulated.

[Vortex]

I've been continuing with using the testo every day when running the stove. I've settled on horizontally laid top lit fires as that gives the lowest overall CO.

I can get about 8 out of 10 like this now.



Stacking the wood so there are no gaps for the burning embers to fall down really helps avoid large CO spikes at startup.



Best air ratios seem to be full primary and secondary (each 10% CSA) up until the flue temperature peaks and starts to fall, then 50% primary, close secondary and open tertiary (through ashbox) about a quarter (1% CSA).

Next I plan on making slight changes to the afterburner everyday to see if and how it effects the results. Will let you know how that goes.

[Jura]

My Lord!

Not so long ago I have learned the word "impeccable" - and I may use it with regards to your last chart- I believe


After I got know You got the Testo I was almost sure I'd see this statement : "Next I plan on making slight changes to the afterburner everyday to see if and how it effects the results. Will let you know how that goes" one day.

You have joined the "experiment upper Circle" .



I wish I had testo, too..



Thanks for being the cutting edge.

[wisc0james]

Nice Ram's Horns, too! I suspected top lit was better, but hadn't thought about no gaps.

[Dan (Upstate NY, USA)]

Best air ratios seem to be full primary and secondary (each 10% CSA) up until the flue temperature peaks and starts to fall, then 50% primary, close secondary and open tertiary (through ashbox) about a quarter (1% CSA).

That seems like a lot of baby sitting.

Any way to get the same results without all the fiddling?