Black pizza oven: rocket vs fire in the dome

[jody]

Hi there, 

I don't know if my title makes sense, basically I'm trying to work out what the advantages are of using a rocket stove to heat a large domed clay pizza oven over simply building a fire in the oven. I'm really curious to know if anyone has tried both and what differences they've observed.

I realise that using a rocket stove would mean much higher temperatures, but i can't work out if this advantage would be offset by the fact that the oven itself is no longer the combustion chamber. 

And if a rocket stove is better at heating a pizza oven, does anyone have any advise on the best size and type of rocket stove to heat a 100cm diameter pizza oven?

Thanks for reading,

Jody

[satamax]

The only advantage to me, is less smoke, to no smoke.

I want to try a pocket rocket pizza oven. But haven't had time at all for the moment.

I have a rather crude drawing.

www.permies.com/forums/posts/list/38661#301667

The chimney should go lower inside the oven.

[patamos]

For a pizza aven i would go rocket because it warms up fast. The convection of the gasses will cook a pizza in minutes.
If you want to bake bread the dome fire oven is the winner because it can hold the moisture in when you seal it up.

Long roasting dishes can be done with either, but i think the rocket 'fire as you cook' better utilizes the available heat

[jody]

Nov 4, 2015 23:36:33 GMT -8 satamax said:

The only advantage to me, is less smoke, to no smoke.

I wasn't expecting that answer on this forum satamax, does that mean you don't think a rocket stove would heat it any faster or more efficiently than a fire in the dome?

i had a read through the thread you linked to on permies where you describe a design where you integrate a batchbox or pocket rocket into the actual oven. I couldn't quite get my head around it, was the idea to use the oven as the combustion chamber and the heat riser as the flu?

[jody]

Hi patamos, just to clarify are you saying that a rocket stove would be ideal for a pizza oven with minimal thermal mass where you simply heat the air?

The moisture issue is interesting, thanks for pointing that out. I just asked my partner about it and she said she often puts soup in our fan oven while baking bread, this keeps the crust nice and soft. Would the gasses from a rocket stove be passing through too quickly to keep any moisture in? Could this issue be overcome by putting a bowl of water in the oven while baking bread?"

[patamos]

The rocket fired oven will heat by a combination of hot convection gasses and conduction and radiating of warmed mass.
At first the convection will provide most of the heat, but the on-going rocket fire will gradually heat up whatever mass is in walls and base of the dome. How dense you form said mass determines how quickly it starts giving that back and for how long. There is much room for versatility here.

Interesting idea about including a bowl of water while baking. My guess is it will not work as well as in house ovens because more gasses are escaping during combustion.

I think once you have determined your main cooking intentions you can combine rocket fire with a mass dome.
I built one last year with 3.5" of mass in the dome because the client wanted at least 4 hours of flywheel at fairly high temps. It works 'okay' but not the greatest in that the rocket (6" L feed - not so powerful) takes a lot of feeding to get the dome up to radiating temperature. It still cooks okay due to the convection, but is a hybrid that compromises the rapid heat up that one can achieve with less dense mass.
Other rockets ovens I and others have built point to a 1" or 2" thick mass in the dome as closer to ideal… One i built for a community kitchen had 1.5" of mass in the dome and a kiln shelf for the base. It reaches 700f in less than 20 minutes, but can also bake and roast all kinds of things during and after the fire burning….


my two cents

[satamax]

Well Jody, i've had a restaurant and pizzeria when i was younger, with my father and grandmother. I was doing the pizzas. So i vaguely know what i'm talking about.

A pizza oven, with the fire inside is tried and proven technology. Tho i hated the smoke.

The pocket rocket oven, i've thought about, and think it could be a good system. You keep the fire inside, but might have a cleaner combustion.

My later thoughts on the subject, carefull if you try that not to fit the heat riser too far from the fire, otherwise the reburn in there might not happen. And this way, you're taking away a lot of heat from inside the oven. Tho, when you see the bottom of a pocket rocket, that might not be that much of a concern

In the case of a pocket rocket oven, i would use a "plunging" heat riser, which would go down to the floor of the oven, with the apropriate gap. Insulated, unkike the pocket rocket. And the exhaust gases from the heat riser would be directed back, on top of the dome, to heat it more. With an insulated second skin. Which make things more complicated.

Otherwise, use a big batch and a raised oven above the heat riser, that would aleviate all the problems above. Still use a plunger tube for the chimney, so the oven acts as a bell. Two problems of that technology, kneeling to feed the batch! I can tell you that i hate this. Been there done that. (on a stove or two) And you loose the fire in the oven. Which means on a pizza, you might not have that fast browning crust on the bubbles.

Remember, i'm vaguely seasoned in stoves. Tried one oven in the batch rocket range retrofit. Which didn't work. But i have not done any oven as of yet. So take all this with a grain of salt.

[patamos]

Ya, that makes sense too.
if you are making pizzas all day like Max was doing, or baking a whole lot of bread... then a big chamber with lots of mass makes sense. Helps to keep the flywheel steady. And the crust sounds divine…

But if it just a few pizzas or this and that for an hour or so, then no point warming up a whole bunch of mass that is going to stay warm well after you have finished using it.

I've never tried a pocket rocket in the dome, so can only guess that the greater the mass the more powerful it will need to be.

The batch box under the dome would be a good way to warm up a lot of mass.
For lower mass ovens i'd be more inclined to place a J and L feed under it. So that the convection temperature can be moderated by the amount of fuel you are adding as you go.

[alanloy]

I wonder if using a standard J tube (or even an L) into the bottom of your oven would work?  Similar to what Tim Barker has done here permaculturenews.org/2012/10/16/rocket-oven-a-permanent-wall-mounted-kitchen-oven/

[patamos]

yes, that is what i have been doing and advocating for.
Only with refractory casts and bricks and cob instead of metal...

Ls and Js each have their advantages. Ls are more fool proof, although for a longer burn oven the J's require less tending.

[flavius76]

Hello! Im from Romania, i built such a roket mass dome oven, with a diameter at the base of 50cm and height 35 cm, the dome is 12cm thick and 5cm insulation with 2cm clay plaster. It need just 1 hour of intense fire with about 4 kg of wood, to heat de mass at cooking point. The only bad thing is that it need continuous feeding when is fired.

My model is a hybrid, the base are made from a cast plate for cooking , but the base could be made only from bricks. www.dropbox.com/s/sfn4k4n8daya0kf/roket%20oven%20pt%20donkey%20forum.skp?dl=0


Here is a video link.
www.youtube.com/watch?v=R4fofWdCn7g
www.youtube.com/watch?v=7e6vd2KMZps

[patamos]

Nice oven Flavius,

Is it entirely a pre fired oven?

Or do you also use a deck plate?

[flavius76]

Tanks Patamos, is not so beautiful outside, i used scrap bricks from demolition of a wall, but it works ok.


Now I use only pre fired oven, but my model allows the maintenance of fire during baking, but in my case it is not necessary, i think products are more delicious in a preheated mass oven. The cooktop plate I used for frying potatoes, fish, etc, in oven mode i use three bricks placed on the cooktop, which heat up and use them like oven base.
In the back of cooktop is a removable metal piece, in oven mode i remove the piece and gases go down from oven to exit, is a bell configuration.

If I bake bread, heat the oven to 220-240 Celsius(from cold mass), bread baking lasts 45 minutes, after baking the temperature drops at 170 Celsius, it takes 20minutes of fire to bring back at 240 degrees.


The roket sistem is small(5" / 12cm), at the beginning failed to achieve a high flames in the oven, after 2,5 hours of fire the temperature inside the oven was only 150 C. After several measurements i noticed that the oxygen level in the flue was too high(12-15%). After that I installed a chimney damper, to adjust excess air. When you see that flame like a volcano in the second link video, the oxigen level is 5-8%, maybe i'm in overfueling zone, but in this way obtain high temperatures in the oven, stack temperature reaches up to 400 degrees C,  is the only way to heat fast the mass oven. And during this time the feed should be kept full with wood, unfortunately the wood does not simply slide down the slope 45 degrees, i must put directly inside the mouth.