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Cooking on a 4 inch batch rocket stove  RSS feed

 
gardener
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So far, only a few guys have used rigidiser.
 
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I couldn't resist mucking around on this spring day while I'm waiting for my ceramic fibre  blanket insulation to arrive.



And yes, it doesn't follow any measurements from the published double shoe box trials, and the upper box is squashed.  I just wanted to get something up to play with.
And final cooking plate temperature was 300 deg C before I ran out of things to cook.

It did seem rather hard to keep the fire going though.  
 
pollinator
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Graham. where is your newly obtained ceramic blanket? I might be able to help in the informal freight department via some of my mates around the country.
 
Graham Chiu
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Thanks Phil but I've already paid for delivery ... 10 boxes of 7m length 25 mm thick ceramic blanket.
I'll use one small piece for the test riser, and I guess the others I can make into duvets!
 
Phil Stevens
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Whoa. Let me know if you want to sell any of it!
 
Graham Chiu
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Sure, I've messaged you.  I can't use 70 m of ceramic fibre blanket right now!
 
Graham Chiu
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I'm still cycling through all the variations I've seen.  I just tried a standard J tube (1:2:3) but I've never had much luck with those as this one again started to burn back up the feed tube. So, I modified it into a hybrid J/L rocket stove.  I don't recall where I saw this ..  but I think it was on this board.

 
Satamax Antone
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Well, this is along f styles mag rocket.

But you need to seal things up. I can't even heat a rocket going on.   And stop using so much mass.

Put some of your insulation  on the ground.

A layer of bricks flat on this. Then bricks on edge, to make a burn tunnel.  Bricks flat above the ceiling of the burn tunnel. Few bricks on edge to form the feed.  You stick all of this with mud. Then make a heat riser with a piece of tube and your blanket insulation,  mud that above your brick core.  This should work.
 
Graham Chiu
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I've got so much stuff there it's hard to see.  There is a layer of firebrick under all of that on top of the gravel to form the stable base.   On top of those are the new thinner grey coloured light weight firebricks which are on edge to form the burn tunnel with one on top.  They also form the riser.

But the other bricks are just there to hold the clay pipe (feed tube) over the burn chamber, and to form the first half of the burn chamber.  I ran out of the new light weight bricks.  I only had 12 recently bought in auction and shipped from another city.

But this design looks good for a mass heater and still doesn't suit me for cooking as I really need to enclose it with a bell, and a chimney so I don't breath in the combustion fumes, especially after lining the riser with a ceramic blanket.
 
Graham Chiu
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Can I call this a double shoe box rocket stove if I have brought back the riser ( i.e. it's not a riserless core ).



Getting 300 deg C on the cooking plate but needed a lot of wood to get there.  I guess what that means is, you can get to any temperature given enough fuel.
 
Satamax Antone
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Graham Chiu
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Don't know about Black except my cooking plate ended up looking like that but at 4:05 the mass of the flame vortex ascending the riser was white indicating a temperature of about 1300 deg C was being reached.



The ceramic blanket I bought is only rated for 1260 deg C.  I haven't installed it yet.  But what happens if you exceed the blanket specs?  Does it just crumble?
 
Graham Chiu
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I saw something which I thought was pretty amazing.  I lifted the top of my riser and observed the flame turning 90 degrees under the cooking plate instead of shooting straight into the open air.
I had two bricks over the top of the riser, and only lifted one.  Perhaps the other half was dragging the flames from the unconstrained side with it, and/or the draft was strong enough to bend the flames towards it.
 
Graham Chiu
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So, at 3:28 in this video https://youtu.be/veg3FYyE4Rs you see the dual ram's horns vortex rising vertically and then ducking sideways under the cooking plate presumably being drawn by the draft.

What I should try next time is removing both top bricks to see if the flame is still pulled 90 deg from the vertical.
 
Satamax Antone
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So this seems better than what you have done before.

i like the passing under the grill and all. Now, what i sugest you do, go there

http://donkey32.proboards.com/thread/734/peterberg-batch-box-dimensions

Take the proper measurements for your build. Draw a bit what you want to do, and start building,  sticking those bleemin bricks with mud!    I can tell your heat riser is too small. Or it seems very small. It is better if you use insulated firebricks or ceramic blanket for the heat riser.  And keep heavy firebricks for the  grill chamber. As having mass there would be interesting for taming the  temperature spikes.

Insulating the firebox could be good too.

Have you read this whole thread?

http://donkey32.proboards.com/thread/511/adventures-horizontal-feed

Seen this one?

https://permies.com/t/71700/Tiny-House-Cook-Stove-Heater

Or this one

https://permies.com/t/35569/Range-retrofit

This one?

http://donkey32.proboards.com/thread/703/vortex-stove?page=1&scrollTo=6299





 
Graham Chiu
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That's a lot of information to absorb ... I doubt I managed to even get 5%     The thread by Vortex seemed to relate mainly to the construction of masonry stoves.  What I can take from his $10k build vs my 15 minute stack a few bricks to build a stove is that I need to insulate my burn chamber more (in addition to the riser).  I can't put ceramic fibre blanket on the inside as the wood will just tear it apart.  Perhaps I can first coat it with that mix of liquid glass and sand?  Or just wrap the outside of the burn chamber with the ceramic blanket, and then stack more bricks to hide it.

But what I found interesting is that the wood pellets I chucked in were still there in shape but crumbled when touched as though they had just gasified.

The problem I have with such a small stove is the scaling.  Such a small fire is dominated at present by the size of the fire bricks I'm using.  And when I start adding 1" insulation inside, I'm significantly dropping the CSA.

What I was originally planning to do was encase the sides in sheets of Ytong to try and create a nice outdoor box stove.  Ytong is insulative, and I've seen people drill holes into it to make a temporary rocket stove.  But now I'm getting all sorts of odd shapes sticking out of my basic box

PS: The riser is 18 inches tall which is two 9 inch bricks.  I believe I have seen figures of 16-24 inches being found to be satisfactory.
 
Satamax Antone
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Ytong cracks badly with heat.
 
Graham Chiu
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Satamax Antone wrote:Ytong cracks badly with heat.



My temperature probe says the bricks on the exterior don't reach more than 80 deg C.  Ytong should easily cope with that.
 
Satamax Antone
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It cracked in exactly the same position, on the batch core you can see above.

Obviously the heat will be retained by ytong. But it is perfectly usable, if it's held by another layer.
 
Graham Chiu
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I did a rebuild seeing if I could create a side port so that I could more closely form a box but that didn't work the one time I tried it.  The flames didn't to really climb the riser.
Perhaps not enough fuel.  So, gave up on that configuration.

I then rebuilt it to what was working, and the box is very close to the 4" parameters as per the spreadsheet.  However, the port is a little high since it goes all the way to the top of the firebox, and the riser is 18 inches vs the  suggested 28 inches.   But the DSR has no riser.  I'm picking up secondary air from all the poorly fitting bricks in the riser.

I doubled the height of the black oven under the cooking plate, and didn't reach 300 deg anymore, but got to 240 deg C.  But then I gained a decent oven for potatoes, and kumara.  And tonight I managed to burn some decent sized branches that were lying on the property,

I noticed Matt's batch box rocket stove is lined with ceramic board but he has fire brick on the bottom and along half the height of the two sides which seems a reasonable compromise.  I need a door for feeding fuel in ( going the scour the charity shops to find a rectangular ceramic glass lid ), and a better way to secure the chimney.  Looks like I'm settling on this design.
 
Satamax Antone
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Careful with the DSR, it doesn't have a heat riser per se, but has a chimney.
 
Graham Chiu
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Mine isn't a DSR since I do have a short riser. It just has the oven over the batch box's fire box. So the fire makes a 360 degree turn.

I wonder if I have enough space to fit in a white oven there.
 
Graham Chiu
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Since I now have a black oven under the cooking plate which is about 9 inches high, I wonder if I can construct a white oven using unglazed ceramic tiles.  Make a mini pizza oven as it were.
I would have it suspended in the gas stream, or maybe, have a way of deflecting the gases to the cooking plate or to the white oven.  I saw someone post their experiment here using ceramic tiles and he stated that they cracked in the burn chamber but survived in the riser.


 
Graham Chiu
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Just a question about insulation.  Has anyone tried using natural sheep wool to seal any cracks and crevices on the outside eg. around one's casserole lid door, or under cooking plates.
I see sheep wool has an ignition temperature of 600 deg C but I wonder what repeated exposure to high heat will do to it.
 
Graham Chiu
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I turned my 4" batch box black oven into a mini pizza oven!



Although the firebox was over 800 deg C at times, the pizza "stone" didn't go over 200 deg C.
Need to do some cutting to resize the stone to the right size, and add a door somehow.

PS: This was my most successful burn ever.  It was basically smoke free from start to finish except for when I put in an overly large "log".  I moved things around, and suspended the log in the fire using my go to piece of rebar, and the smoke went away.
 
Graham Chiu
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Rather than resizing the pizza "stone" which is 30 x 30 cm, I think I'm going to try an aluminium sheet under it to try and spread the heat more evenly to prevent cracking.
And I'm going to try enlarging the oven so I can get a whole ( 30 cm ) pizza in there rather than only cooking 1/4s at a time.

 
Graham Chiu
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So, a question for the experts.  Is it better for a black oven to be closed ended, or, to have the gases flow over the food instead of under?
 
Graham Chiu
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More successes today. Roasted belly pork with totally crisp skin, and juicy meat. I covered the pizza stone with tin foil to protect it from the oils being released from the pork. And then I cooked 4 pizzas to perfection.

Several times my oven started to smoke when I overloaded the burn chamber, so I just lifted the brick capping the riser so it vented straight up and not into the oven. And when I managed to stop the smoke, I then covered it again.

Who needs an electric oven?
 
Graham Chiu
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Having a black oven is a god send when you've left your firewood out in the rain

I'm doing another roast pork belly today and left my kiln dried firewood outside overnight, and it's pouring down right now.
I can't leave the meat till tomorrow as the recipe says don't marinate for more than 24 hours.  Yes, I could just stick it in the electric oven but that's defeatism.
So, the wet firewood goes into the black oven until I'm ready to burn it.  And any soot that gets deposited on the drying wood I get a chance to reburn again
 
Graham Chiu
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Not quite as good as my first try as I didn't quite have enough fuel to get the oven hot enough.
I had to use the grill to get the skin to crackle, and you can see from the cuts that the skin could use a bit longer cooking.
Still I guess it means it's not a fluke, and it's semi-reproduceable - smoked as well using Manuka firewood.
 
Graham Chiu
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From posts here and elsewhere it's clear that the only way you get stone or brick hot enough to cook pizza rapidly is to have the fire in camera you're going to cook the pizza. Sure you can vent heat in or around a metal container but those contraptions only reach 250 deg C so your pizza isn't going to cook in 30 seconds.

But the issue with a traditional pizza oven is that you have a dirty burn which you need to keep going for over an hour to get the mass to heat up sufficiently.

I wonder if a DSR2 would work if you used a cast iron plate separating the boxes? When you want to cook, you divert the secondary burn to a different riser, and cook directly in the second box. I'm suggesting cast iron instead of fire brick since other experimenters have shown a fire brick floor won't heat up sufficiently when heated by a J tube.

See http://donkey32.proboards.com/thread/2257/show-rocket-pizza-oven regarding a L tube unable to give adequate heating by grga
 
Graham Chiu
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Well, I cobbled something together along these lines.  And I hit 380 deg C on the pizza stone!
But the top of the oven, since I was using a metal plate, wasn't hot enough and I didn't get any browning of the pizza bread on the edges.
But the bottom crust burned in patches.  When I took it out, I managed to drop the thing topping sides down on the ground
Oh well, we still ate the experiment.
So, it seems I need to lower the height of the oven and use bricks instead of cast iron.
 
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I think I may of explained this before but the principle of a wood burning pizza oven is very basic
The oven needs to retain heat to create optimum cooking temperatures long after the fire has gone out. A well designed oven will retain its heat evenly between the temperatures of  300-400 C for long periods.
To heat the oven quickly you need a good air flow in and out of the oven and use really good dry hardwood.
The larger the oven the longer it will take to heat and stop smoking, lots of folk build massive ovens that take 3-4 hours to heat but it is really skillfull to cook more than one pizza at a time, so In my mind a one pizza sized dome is far more sensible to own and enjoy.
A 75cm dome is still quite a chunk of material but it will heat quickly and retain the heat perfectly for hours of enjoyment and easy cooking.

Re burn and smokeless chimney takes around 15 mins in the summer months.

Anyway forget about 30 second cooking time, a better bet is to look for 350c base and 400c air space above the pizza, you can then manage the pizza a lot easier and cook it in around 3-4 minutes.
Also rember that shop bought pizzas are not designed to be heated at above 250c and just burn up at hight temps.
Perhaps looking at how a modern pizza oven is designed will help you design what you are looking for....
F69EF0A6-698F-48F3-A5BB-62568C7D38AA.jpeg
[Thumbnail for F69EF0A6-698F-48F3-A5BB-62568C7D38AA.jpeg]
 
Graham Chiu
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I think I've seen those diagrams before.  The obstacle that was facing all rocket stove based pizza ovens was reaching a floor temperature of 500 deg C.  Most I've seen are only hitting about half that.
So, now I've hit 380 deg C for the floor, I just now need to get the top hot enough, which I think means lowering the height of the oven.  380 deg is not 500 but it's getting very usable.

Now I didn't know that store pizzas are only supposed to be cooked at 250 deg C   But my pizza base was a little charred.  It wasn't burnt
i guess I have to now learn how to make pizza dough.

Anyway, one obstacle down, another two to go!  Now where's the pizza dough recipe
 
Fox James
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It is recommended to get the pizza oven brick surface to around 500c but that is a guide to show you have saturated the brick mass to around 350-400c.
So the brick is not 500 all the way through, it has been heated to around 350c on the cold side, about 400 in the middle and 500 on the hot face.
At that stage you can push the fire away from the cooking spot and allow the brick temperature to equalise and stabilise to around 400c
However the dome itself will be saturated right through with 500c and will hold that higher temp as the small fire is still supplying heat at the top of the dome.

After a few years!! Your get to know your oven and it’s best cooking temps.

There are loads of pizza oven forums and I can tell you that only a fraction of the builders on the forums get it right first time!
Just like rocket stoves there are certain facts that must be adhered too and so many people don’t want to except that, they become very disappointed with their new smoky, low tem ovens that go cold in a few hours.
Re making dough ... good luck it is not easy, at least not until you have mastered the art.


I had a fantastic pizza at a little place on the lake side in Tekopo, the oven was not lit but still warm from the night before. The guy put in a couple of pieces of wood and we had pizza within ten mins. The owner told us he has had that same oven warm for 3 years without it ever getting to ambient temperature!
 
Graham Chiu
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Never been to Tekapo but I'll watch out for the pizza oven if I ever do

My pizza stone is primarily being heated from below as it's sitting on the firebox top. I didn't think it would survive without intervening steel to disperse the heat more evenly. I don't know what the differences are in thermal lag between these substances so loss of heat is a concern. The two in combination are not as thick as a brick but hopefully the fire below will keep up with the heat loss.

I've not yet seen a successful dry stack pizza oven with a clean burning fire.  I have seen dry stacked brick ovens in a rectangular shape with bed angle iron used to support the roof of bricks but the burns are dirty.
It does make good pizza though they claim.

Maybe it's impossible to get both a clean burn and use a dry stack but I'm going to try a bit longer before I give up and build a more traditional one.
 
Graham Chiu
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I made my own dough this morning following  perfect pizza dough recipe

and then used the residual heat from the rocket stove in the secondary burn chamber.






I'm burning or toasting the bottom before I can get the sides to crisp up still so I had to pull these pizzas out at 5 minutes of cooking time.

I just used a tomato paste, with shredded asparagus, then button mushrooms covered with mozarella cheese.  The mushrooms were moist so when I bite into them it releases its retained fluids

Not sure how I can toast the sides ... but currently this oven is working for my peasant tastes
 
Graham Chiu
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As I comment, you'd think this would work!

 
Fox James
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Good effort!
Perhaps you could pre heat a pizza stone and surport it in the chamber and slide in the pizza between the base and the stone.
Even with a full on pizza over you need to raise the cooked pizza base to just under the dome top to get the real burnt melted cheese effect.

 
Graham Chiu
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The oven top is reading 300 deg on the brick but I guess it's possible the air is hotter.  I've seen people lift their pizzas using the peel to the roof of the oven but I didn't realize that it was to burn the cheese!

I've got a stainless steel rack with 3 legs that I am going to use to raise it up a bit.  At present the pizza base is cooking in about 4 minutes.
 
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