Top loading highbred?

Hi guys, I am thinking about building a new fire, my own fire is still working fine but I feel I can make a better version.
So just getting back to basic design......why does the fire box have to be the same dimensions as the rest of the system?

Well in fact it does not because mine is not and other folk have built successful fires with big fire box capacity and an opening lid.
I would like to understand more about this because on the forum it has been stated many hundreds of times how important it is to keep system size throughout.

Perhaps my present fire is not actuality performing as well as I think? I have no way to measure any pollutants coming out of the chimney but my fire seem to work extremely well.
I know it has been discussed before but what about a highbred between a batchbox and a J tube = big fire box, top loading and shorter riser.
I am sure most of you will have seen this guys videos but he seems to be on the right track for such a design.
https://m.youtube.com/watch?v=KGKIcxxRo6g&t=344s

Hey Fox,    I don't know if I'll be able to give the answer your looking for but this is just my take on it and certainly open to input or corrections.

From my understanding, keeping the csa size the same throughout the system has been directed towards the J tube design with a piped heat exchanger which was the go-to rocket stove design for many years. This generic rule made sense as it allowed an even flow of heat to provide the necessary draft without restrictions. You could certainly fudge on it here and there but for the average person building their first rocket, the rules were kept simple and straight forward.

The batch box and bell systems on the other hand opened up a whole other take on this rule. The size of the box and bell are still governed by a certain proportional csa size but certainly don't need to be the same csa size.  

Peter van den Berg, Matt Walker, Kirk Mobert and rocket scientist all over the world (including you!), have done lots of work on stretching those boundaries. Not a lot of people have a Testo gas analyzer though to really see whats going on inside whenever changes or modifications are made so the evidence of producing a better stove is not always very clear or reliable. Just because there is no smoke, doesn't necessarily mean its burning clean, or as clean as it could be. Not that we are trying to get to achieve stoichiometric combustion, but at least these pros can verify our tinkerings and come up with something that is proven to work very well and in a lot of situations.

Peter has said to me once that he would like someone to further develop a hybrid between a batch and a J but that he was not the person to do so.
So I guess the point is, there's always more room for improvement and innovation. As long as we are not perpetually passing along outdated or proven to not work information, the faster the growth of clean burning stoves can be utilized by everyone who needs them.

Thanks Gerry, development is an expensive and risky business, in this instance I have a friend who is very keen to own and use a smokeless, radiant heating cook stove.
It will be housed outside under a open sided shelter come man cave, party house type thing!
I could just duplicate my own stove with a few basic improvements but there are a couple of factors that I would like to change such as the height of the riser.

I will draw a few sketches of what I have in mind but I want to maintain the top loading facility and supply pre heated primarily air as well as secondary  air or at least look into the pros and cons.

One feature that I really wish I had, would be a choice of radiant heat or no radiant heat ...or if you like ...the ability to use the hot plate without heating the barrel.

With my own fire, I have found the actual hotplate height is ok for cooking but is a very inconvenient height for looking across when sat down. What I mean is if we have guess in the winter who want to sit around the fire the plate is just at eye level and you can’t see the person opposite you!
Then in the summer I can’t cook around the fire without pouring with perspiration.
I have some answers but more questions.

I have a few vids of the vertical batch.



Mind you, it's not tested completely.

Hey Satamax,   When the wood is loaded vertically into the firebox, what is to keep it from leaning up against the glass or more importantly, up against the port and block the air flow?

Also, I guess the floor is flat with no angled bricks?

Fox,   Its been a while since I last saw your cook stove. Could you post another picture of it when you send your sketches so we can compare them?
As for the heat from the barrel, couldn't you just put a heat shield of some sort around it or cover it with brick or cob?

Gerry Parent wrote:Hey Satamax,   When the wood is loaded vertically into the firebox, what is to keep it from leaning up against the glass or more importantly, up against the port and block the air flow?

Also, I guess the floor is flat with no angled bricks?

Fox,   Its been a while since I last saw your cook stove. Could you post another picture of it when you send your sketches so we can compare them?
As for the heat from the barrel, couldn't you just put a heat shield of some sort around it or cover it with brick or cob?

Hi Gerry.


Well, leaning against the glass, ney bother, it doesn't matter much. As only a small portion will touch at any given time. But a grid of some kind could be inserted there too.

Angled bricks could be used at the bottom, but it would be a pain for loading wood, which would need to be far shorter than firebox length. Mind you, it could prove interesting to light the stove.

The port doesn't go all the way down, so it doesn't get blocked by embers. On top, a wide  "P channel" out of thick steel could be implemented. Onto which the lid could hinge.

But i need proper materials, not salvaged heat riser and ultra thick bread oven bricks.

Thanks for sharing that Mr. Fox!

Really cool build. Super interested to see what you put together. Good luck!

Peter🔥🧱🔥

I would love to use my fire as a base to experiment with but my wife has put her foot down about more work in our finished  Party house!

So I have to work on paper for now, it’s just that my minds works much better with real life 3d models.

I am still studying the form but it seems one way to get more from the J tube design is by pre heating the air.

One thing I am thinking about is using a double glazed window and feeding the primary air between the glass so it gets pre heated.
I can easily form a secondary air channel into the top of the burn chamber if I mould it with refractory cement.

I am thinking about a 8x12” x 12” deep slopped bottom firebox on a 6” system.
My own fire uses a 8x8” x 12” with a flat bottom.

Starting with the fire box basics...

Fox, put a cooking plate on that firebox!

Interesting design Fox.
I know Matt Walker has tried quite a few rockets with viewing windows in his early developments which has made the fire visible and very enjoyable for viewing pleasure. They do however throw off a lot of heat from the combustion chamber where temps are needed to be kept as high as possible for best combustion. A trade off that may be worth it depending on your goals.

Not sure how the secondary air system will work with your idea as it seems to be introduced far down the burn tunnel?  but it will be interesting to follow your creation as it develops.

Only the front and top of the fire box would be double glass but I could add insulation to the front if necessary it is more about preheating the air than viewing and glass seems an easy material to use for such a job.. however this is just my ideas and any criticism is very welcome the more we talk and discuss the better.

I made this model a few years back that is based around a vortex design and big fire box, i know some folk dont think a vortex is a very good method but it remains one the most popular designs on some of the forums?
What do you think?

Back in 2012, during the 9 months' development of what was later dubbed as batchrocket I did some measurements on vortexes and their relative performance characteristics. In short, a single vortex works although clean burning was induced somewhat later in the combustion process and the riser should be at operating temperature. A double vortex device isn't any more complicated to build but can be run clean much earlier in the process.

In fact, the moment the roaring sound starts, the CO level drops down, even in a stone cold core. This wasn't the case with a single vortex so I concentrated on its double counterpart which looked like to have the best papers to a succesful and simple to build core. A single vortex device might be persuaded into comparable behaviour but in order to do that one need lots of time and a calibrated gas analiser. The chance to hit the right proportions and shapes by sheer accident and first time is actually equal to zero.

Thank you for your input Peter, i read all your post i can find and i know you prefer the double vortex.

When I first built my stove it ran as a pretty standard J tube with very good insulation and a one piece cast core, after a few months of use  the max temp i saw on the top was  around 500c
There was no restrictions other than a barrel and I used a well insulated chimney and to be honest i was very pleased with its performance.

Over the last year or so I have made a few modifications, each one added a bit more heat to the top plate.

I increase the fire box size from 6x6 x 8 to 8x8 x12 inches deep and added a P plate. This made the fire much better for me to use and increased the temp to 517c

Next I added a small triangle restriction at the end of the tunnel to resize it from 6x6’’ to 6’’high and 5’’ wide  This forced a vortex to form.
I also added a glass lid and a ajustable vent for the primary air supply.

With the glass lid fitted and restricted primary air the P plate really pulls in air and once the fire is hot, the top plate will go well over 600c and glows bright red!

Of course none of that proves anything apart from the top gets hotter!
However it is interesting that all the mods seem to have a positive effect for own personal goals which were to be able to load more wood and achieve a higher temperature in the centre of my hotplate.

I am keen to listen to any input from anybody and only to happy to use a double rams horn or consider any other ideas but my main goal is to maintain similar performance but with a max 28’’ high riser.  

I have been busy studying various rocket stove designs.

Facebook offers some incredibly innovative designs, largely based on metal cook stoves but there are plenty of super insulated high temperature builds too.

I got diverted to log burning stoves and found some interesting seemingly smokeless designs but funny enough the log burning discussion finally  lead me back to this forum and F Styles build here https://permies.com/t/54074/Rocket-Mag-heater-Rocket-Mag

I have read through the thread and find it very interesting.
However unless I missed a few bits of conversation, it seems the design works best or perhaps ‘only’ with large logs?

It looks to me like the 6” half circle in the burn chamber needs to be covered by the flat base of a large log and smaller diameter fuel might not work?

Apart from the slightly scary ‘flash back’  risk this seems to be to be a fantastic design!
He talks about 1000f on top of the barrel with what must be a short riser and using quite basic materials.

Well, not having seen one in real life, i can't  really comment.

I argued with F styles, that this wasn't a "rocket stove" I'm not that sure anymore. It can work with wrist size fuel, even smaller, i think.  There might be an use for a stove like this. But this is not documented, over the course of several years, with measurements, follow ups on the mods etc. I would have loved to see "testo" graphs of this. And less bragging. I think there is a real risk of flashback. It could be interesting if someone with a few builds behind him, would make on of those, to see if it's worth pursuing. To get a more "sensible" evaluation of the thing.

Yes there are some crucial measurements missing and none of the photos  are very clear but fundamentally he has made a simple design that appeared to work extremely well!

I realise that lot of guys who post on this forum are understandably very interested in numbers and proven statistics  none of which are available however just the concept of completely burning a log inside a drum without smoke is a hugely interesting  in my book.

I would be concerned about the hot gas build up and also I do wonder about consistency when used with different sized logs.

He seems to imply the air flow is always strong and available due the sunken tunnel under the log and more air flowing around the log and then all mixing together on the other side.
I can see that but only if there is one large piece of wood that is suspended over the channel, if there were small pieces they would sit in the channel and the air would flow through the wood rather than around it?

Fox James.

Well, i would be afraid of the wood deprivation. I mean, if there is only one log in there, and it doesn't burn fast enough. And there is not enough embers underneath. This cools the fire. And kils efficiency, up to the point the fire stalls. Or stops.

You know, along the top load vertical batch. There is another solution, top load horizontal batch. Exactly a per the book batch. With a metal cookplate  hinged on top. With a handle. You would load from the top. Instead of the front, but it is exactly the same. I think with a strong draft, may be the firebox could be extended upwards a smidge, over Peter's designs.

But the problem, is the full burn. In a batch, it starts somewhat tame, and then the full dragon breath comes in, where all the logs are on fire. And if you have too many logs, stacked in the top extension,  this would overload.

What are you trying to achieve, being interested by the magazine rocket?

The air going through the wood is one of the principles of good rocketry.

Basically, you're reducing the free air circulation area, with burning wood, so the air velocity increases, augmenting turbulence and thus mixing. The port in a batch is there to increase the turbulence, but wood, either in batch or J tube is responsible for  the turbulence too. Hot burning gases take some room to, so the air intake gets faster. Well you see what i mean?  

HTH.

I just have a general interest in all forms of rocket stoves as I gain more info for my next build that is all.
I am half way through an outdoor kitchen build for a friend (customer) and I want to build a top loading cook stove but I have not decided on the design a yet.

Well, my take on this.

We already have plenty of tools, J tubes, Batch, DSR Radiators, accumulators cooking plates, ovens etc. To fit most of our needs.

I can see the appeal to à stove which wouldn't need to be stoked every now and then, and burn for a fair length of time, without needing attention.

But, this comes at a cost. The fact that the chances of it burning badly are far greater.

Plus, since the mass is recovering the heat which would be otherwise  wasted, and redistributes it inside afterwards.  The need for long burns is mitigated. Well, in the alps, at 1500m altitude, in a ski resort. I do mostly three loads a day, when it's cold. Two in October/November, and 2 End of march/ April. May be 3  in the evening, and one relit, in the morning on the embers, when it reaches around -20c° But i spend may be 1/2 an hour, between startup, and the three loads. May be if i pass nearby, i would stoke it once or twice an evening. The stove is downstairs, in the workshop. So, i don't see that much of a need for long burns. I startup around 6pm, and it burns full blast till 10ish. Usually, by midnight i can close the chimney flap (20% of airflow remaining)

Yes there is quite a bit of choice from tried and tested designs but it is fun to adapt or design your own version and i certainly dont need the ultimate burn just a smokeless outdoor cooking stove.
I notice that when the Dragon core was available it had what looks like a metal cap on the burn chamber, i guess that is to prevent abrasion and help pre heat the air?

That's à P channel.

I think it served those functions that you mentioned as well Fox along with a built in P Channel as Satamax pointed out.

Yes it looks like a multi function object but it is difficult to see exactly how it fits in place from the photo.
I assume Peter Had a lot to do with the design ?
The actual casting looks to be a work of art and built to a high standard, I dont think it is still in production and might even be outdated now with ceramic fibre board and ceramic fibre being readily available!

Yes, Peter was the designer of the core. He is a man of perfection and very good at what he does. His development thread is here: small scale development
One of his photos shows exactly how this P channel fits to the core.

As far as cf board, not everyone has access to it or is out of their price range whereas casting can be more appealing to some. Hard to make a trip wire or backsweep from cf board than it is to cast but also much more of a learning curve with casting too. Nice there are options, each with their own inherent benefits and drawbacks.

I made up a ‘one off mould’ this morning for the fire box using foam and wood, I did not make anything fancy or re usable as I don’t know how my ideas will work out.
What is annoying though is my vibrating table stopped working ! It is quite a few years old and has done a lot of work but I was still surprised to see it fail.
I filled my mould switched on the table, it worked for about 5 seconds and just stopped dead!
So I had to revert to more unconventional ways using a concrete poker all around the wood base.
Refactory cement is best mixed very dry and you really need a vibrating table to get it to settle without any voids so I am not completely convinced if it will come out perfect.

Hi Fox;  
Your form looks good but sure is a bad deal your shaker table died.
What poor timing on its part.
We can only hope you got enough mixing done to get it to settle.
Good Luck on stripping the form... It will be like Christmas opening an unknown present.  
Will you like it.... or is it back to the drawing board/ repaired vibrating table.

Could of been worse I suppose but it seems to be void free and structurally sound just not as pretty as I would of liked.
I used stainless pins and burn out fibres so I hope it won’t crack for at least a few years...

Next problem is that my locale supplier has no ceramic fibre board in stock and they can’t get any more from the wholesaler!
I had a long look on line and I could only find one U.K. outlet selling any and they want ridiculous money for it but I can’t import it anyway.

I live on a small island, nice in lots of ways and we don’t even have any  covid19 over here so no lock down or local restrictions apart from our ports are closed!
Meaning ... basically I can’t but any ceramic fibre board.
I have lots of ceramic matting and tones of refactory cement so I might have to give my design some more thought.

Good save Fox!
Might not be as pretty as you would like, but looks solid.
Wonderful your island has no health concerns, but sure is inconvenient you can't get any cf board.
In time Europe will  open up and things will be available again.
Meanwhile keep innovating, I like seeing your stoves, they are always a work of art!

Yes indeed, a very nice stove body Fox! Look forward to see how it holds up.

Thanks guys it is a start but a bit frustrating, I have this idea about cutting out a quite complex  vortex shape from a solid block of stacked 2” CFB and using a fairly short riser as I want the fire (when pushed)  to spread out of the riser top so it can be seen through four windows .
I was building this for a friend but I don’t know if he has the patience to wait as I have pretty much finished his outdoor kitchen area including a pizza oven, sink and BBQ.
I have found some 1460c board for sale at a reasonable price in the U.K. and it may be possible to get a friend to collect it and cut it up so it can be posted via standard mail in several pieces... but it is a lot of trouble.
I have left one end of the fire box open as I plan to use double glass and feed the air in between the panes but I will have to test it out to see if air coming in the top or bottom works best.

I managed to find a single 25mm sheet for sale on eBay.... at more than double my normal cost and it has to be cut into quarters so it can be posted!
Well that is not quite correct as I normally buy the 50mm unbranded sheets from my local supplier at £97 per sheet so way more than double!
Anyway one 25mm sheet will get me back on track, hopefully early next week.

The more I study the form the more open the design potential seems to be.
I an no expert and have very little experience with building or designing rocket stoves but I see many different designs with quite a lot of variation between them!
It seems the common ground is to produce a very hot fire inside an insulated box and then manipulate the hot gasses to suit your needs.
Certainly facebook and YouTube have lots of ideas and although virtually none of the examples have been tested with a gas analyser, many seem to satisfy the high efficiency and smokeless goals of their owners.  
Unfortunately I simply have to many other priority interests to dedicate my spare time to test out many of my ideas but it seems to me that there is huge scope to develop the concept.
In my eyes there are a few things that people would like to experience and really expect from a living fire and the main one not surprisingly, is the flame.
I think Peters double shoe box with a top window is pretty interesting to watch and definitely one of my favourite designs, however the few examples you can find that show the flame burning  sideways are super cool.

Well said Fox!  Variety is the spice of life even when it comes to rocket stoves!  

On the other hand, I have heard Matt say that just because a stove produces no smoke doesn't necessarily mean that its burning clean.
So who would I put more of my attention following? - a You Tube first time burn video or someone with years of experience and a gas analyser?

Quite right Gerry although there are also many other very capable and clued up folk out there, you can find some beautiful and impressive stoves on the FB pages.

I have spent the last four years experimenting and developing my pizza ovens to work as efficiently  as possible and believe me i have had my critics!
However I now have a design that seems (no gas analyser ) to work far better than the standard base design.

It is quite interesting to think that dome shaped wood fired ovens have hardly changed in design since the Roman times and in fact the same formulas and dimensions are still being successfully used to this day. In other words they got it right a long time ago.

All I have done is make use of modern materials and tweaked the gallery design, so nothing radically different  however my latest build will heat up and become smokeless in just over half the time of the first one i built.
I looked really hard at the air flow and redesigned the the gallery (air in air out) but i suspect  the use of modern insulating materials has made the most différence .

This guy has developed a fantastic cook stove!
He has quite a few videos based around the cyclone but this one has some great effects near the end.
I have seen his work discussed a few times on FB but I was not paying attention at the time so I cant remember much of the talk. I think the air flow forms an air barrier between the flame and the metal, working to both insulate and prolong the life of the metal?

Insulate, or cools the flame?

The design looks well thought out and I believe it has taken him many years of experiments to get this far.

I am particularly interested in the fact that secondary air is fed in to the heat riser rather  than before it.

Obviously  the use of metal allows the secondary air to be heated up to very high températures and that might not be easy with insulating materials.

I think the opposing air flow Is what causes the cyclone to form within the air barrier and i suspect that hole size and spacing must of taken a lot of expérimentation   to get working so well!

I would like to see what effect injecting secondary air Into the center of a vortex as this would be relatively easy to manipulate.

I have been asking question, watching videos and generally trying to gain information ... there so many opinions and designs with no real standards hence the problems with house Insurance.
It seems every country has its own version of a rocket stove and even what the term defines !
Anyway i have ordered some Ceramic paper as this seems to be the in thing for smooth and flexible lining ....