Vortex Stove

[matthewwalker]

Thanks for the response Trev. I'm genuinely interested in digging deeper into this topic. One of my favorite aspects of all of this is the many tools we have in our kit, and understanding them better moves us all forward.

I have built the exact same fireboxes using both dense and light brick, insulated castings and heavy castings, and I've tested them with the Testo, over and over again. I've also tested other builder's builds, always heavy materials.

I do not believe that insulated materials in the firebox or flame path are some magic bullet, appropriate or best in every situation. I do however challenge the idea that heavy materials can extend the clean burn, or help the combustion be more complete. Wouldn't an insulated firebox heat the combustion to clean temperatures more quickly? Why would the heat, from the fuel and air combusting, gain momentum from dense material rather than the additional mass to heat being a constant drag?

Those are serious questions, I don't know if I'm right or wrong.......It makes sense to me that in a rocket where we want complete combustion in one area of the heater and all heat extraction in another, we would want to minimize heat loss in the combustion area. This particularly applies to the many rocket enthusiasts who like to talk about how little fuel they use. Why spend the first part of the burn heating the firebox? I do think that in constant burn appliances, the advantages start to wane, depending on the combustion design.

Might be time for a new thread!

[Vortex]

Thanks, Matt. If you want to fork this discussion off to another thread please do. It's an interesting topic that I'd very much like to get to the bottom of.

[patamos]

Hi Guys,

Just before the thread forks off, i feel impelled to share a bit. I too have been pondering the most appropriate combination of materials in the core. This topic is showing up more and more often in the Masonry heater world as well. I believe the Austrian 'eco box' guidelines are also now advocating for less mass in the core.
I've no doubt that the lower mass firebox better concentrates the heat into the fire itself. Matt's testo comparisons are consistent with those coming from many other studies.  The thermal energy that goes into heating the core's mass early in the burn simply does not offer the same amount of payback during the coaling stage.
That said, it probably offers more of a return when reloading, in that it serves as a searing external heat source that speeds up combustion of the initially cold fuel.  The high mass core also offers good return for baking post-fire.  Of course, this is only useful to the extent that when we apply that function.

This much to say, with a small fire box like this vortex, in which the low profile of the stove makes it suitable for baking/cooking functions... and multiple reloads might be common (eg. over-firing for larger heating application)… the qualities of a heavier core offer value that is less pertinent in other comparisons.

That said, i've been experimenting a fair bit with sodium silicate and sand skim plasters over ceramic fibreboard and IFBs. Lots to learn there…

[DCish]

Feb 5, 2017 12:51:58 GMT -8 patamos said:

Hi Guys,

...
That said, i've been experimenting a fair bit with sodium silicate and sand skim plasters over ceramic fibreboard and IFBs. Lots to learn there…
...

Been having similar thoughts. If you start a thread on this I would gratefully follow it.

[patamos]

Feb 5, 2017 17:48:15 GMT -8 DCish said:

Feb 5, 2017 12:51:58 GMT -8 patamos said:

Hi Guys,

...
That said, i've been experimenting a fair bit with sodium silicate and sand skim plasters over ceramic fibreboard and IFBs. Lots to learn there…
...

Been having similar thoughts. If you start a thread on this I would gratefully follow it.

Ya will do.  Wanting to put them through a fair bit of rigorous abuse before commenting much.  

[patamos]

On another note, Trev, assuming you get around to secondary air experiments before i do, i have been considering how your core relates to the Austrian eco firebox approach. They talk about side and rear air feed starting 2/3rds of the way up the walls. But most of those builds have walls at least 5 bricks high. This vortex being roughly 3 bricks high (4.5" x 3 in N.A. sizing) the stove has more of a U-shape burn pattern. running lower front to upper back and forward along the top plate.

With these things in mind i am inclined to focus more of the secondary air in through the top plate - ala so many of the gassifiers out there.
I've been casting the whole top deck in separate pieces so that this central top plate can be removeable.

Another consideration. Whereas Peter and Matt's experiments have shown that air supply at roughly 25% of CSA with roughly half and half ratios of primary and secondary air delivery… we have to consider that the vortex is more of a masonry fire box, in that the whole load will be alight at once and wanting to go full tilt. During this stage we had best ensure there is enough oxygen to prevent 'over-fueling'. Looking at the eco box, they seem to accept that there will be excess oxygen during earlier and later stages of the burn, so long as there is enough during this peak in pyrolysis and ignition.

The primary air port down low in front is still a superb means of ramping things up quickly, but i wonder if we ought to boost the secondary %?

Either that or rework the pre or post throat configuration to achieve the titrations that the batch boxes are getting.

I recently met a fellow on one of the nearby islands who builds Finnish contraflow heaters. He also does research for the MHA and has a testo that he is willing to lend… so there could be some numbers on the horizon. I will not be surprised if they are 'okay' to 'pretty good', but I certainly do not expect the results Matt's set up is achieving.

[Vortex]

Hi Pat, I really hope to get down to some experimenting soon. I had hoped to have half of the new stove built by now, but life just keeps getting in the way...

The first thing I'm going to try is a highly insulated secondary burn chamber above the firebox - so the burn pattern will be shaped more like a W on it's side.

The way I load the stove now I never get runaway / full-tilt / all-fuel-burning-at-once problems. The firebox on a vortex is a dead end - like a TLUD on it's side - in fact that's often how I think of it. If you stand up large pieces of wood in the back, medium at the front sides, with the kindling in the middle front, once the startup phase is over the burn is up the face of the large pieces, and gradually works backwards through them, so there's no chance of a runaway burn.

I plan to try a sealed door with secondary air around the throat or roof of the firebox. There are a few small leaks in the sides and back of my present firebox and I only see jets of burning gas there at the height of a very hot burn, so I'm not inclined to try it there. The best position I've found for secondary air, is up through the ash-trap, but then all other gasifying stoves I've seen do that (except downdraft's). In fact whenever I notice the stove isn't gasifying right it'll be because the ashbox is full and blocking the secondary air.

I look forward to those testo results. I doubt very much they'll be in Peter or Matt's range but that's never been my sole motivation, aesthetics are just as important to me, so I'm looking for the happy medium.

[patamos]

Ya i hear you about the aesthetics. Nothing like a good view of the primordial television
Loading and cleaning ergonomics are small factors as well…


Ya i think you have have a good point about the all at once light up. I can get things going all out, but that is only with a high proportion of smaller pieces (construction offcuts…). Could be i've also had my head a little too far down the MHA eco-box rabbit hole lately.

Regarding secondary burn. I have been wondering about adding another course of brick above the throat deck. But 6" or so rearward of the throat suspend a slab of refractory across the cavity with a thin CSA sized exit port down low. The secondary air feeding into the throat from a plenum between two layers of fire chamber top-plate. Hopefully this will create a highly turbulent secondary burn chamber ala some of the old contraflow designs.

Lots of ideas to play with

[Vortex]

Sounds like we're thinking along the same lines for the secondary burn chamber, Pat.
The new stove design is 7 full bricks (7 X 4.5") high - two full bricks above the top of the firebox - so I've got a little extra room to play with there. Was also planing to try out a 'port' into various shaped chambers to see how the extra turbulence affects the burn.

[patamos]

Sounds interesting.

There might be some information to glean from Peter's older 'rocket syphon' experiments. I know he steered away from it once he started getting better results with the batch box port into riser configuration. But he did notice differences in the various little features he played with. Perhaps variations of vermiculite board lining the secondary burn chamber will be a good way to experiment.

[Vortex]

Finally got some time to start putting together the new stove today. It will eventually go on top of the 2" concrete slab which is the base of the existing stove.

The frame is made from 2" (50 X 50 x 6mm) angle steel, with a 6mm thick sheet of steel in the center of the angle and then a 2mm sheet on top of that.



I was planning to use the 2" storage heater bricks I have as the inside base layer, but I don't have enough. I'm going to need all the ones I have farther up in the stove, so I think I will cast a slab in a few pieces to put in the bottom.

On the right below is a storage heater brick (9" x 7.5" x 2"). They're made of Magnetite, which is basically iron ore. They're incredibly heavy (7.5KG / 16.5Lbs) and very effective at storing heat. The rock on the left is a piece of naturally occurring magnetite I found on a beach about 15 miles away from me. I eventually found lots including the seam of ore in the cliffs where they had come from. I'm thinking of going back to collect more to break up to use as the aggregate to cast the inner base from.

[drooster]

"Channelling your inner bottom".

I love my magnetite bricks (storage heater) and actually used them on really cold nights as a kind of foot-warmer, taken fully heated from my Rayburn oven. Good for drying paint on small items too.
A seam of the stuff sounds like a medieval smelters dream!

I'm thinking of laying them on the top of my upcoming project to collect heat, and maybe for the structure of the firebox.
I think I have ten of them.

[Vortex]

I have 30 of them and I'm still searching for more. Don't know how long they would last in a rocket stove firebox, but I've heard of people using them inside metal box stoves ok.

Got the side and back steel plates in today, and made a form to cast the inner base. I'd still rather use storage heater bricks for the base if I can get them. I just found a for sale ad for 10 old storage heaters, would be loads in those.

[ilpiccolo]

this thread is encyclopedic ... good job guys! I am going to cut off the secondary air control plate (in the ashtray drawer and goes on the fire from below) and I came to doubt of what would be the right proportions between this air and the preheated coming in at 2/3 of the fireplace (this should mix with the pyrolysis gas and give a second combustion)

20 cm forward and 20 back should be enough to find the right setting ... (it said so does not look professional)

suggestions or empirical experiences?

[Vortex]

You're ahead of me there, ilpiccolo! I haven't experimented with heated secondary air in through the firebox walls yet.

The secondary air up through the ashbox on my present stove was an unintentional discovery, so it's just what leaks in between the steel side panels - it's hard to say what area hole that equals.

You'll just have to experiment and see what works best, I'd be very interested to hear what results you get though.