Quad Core Pizza Oven

[kishatic]

Hi all,

here I present another idea for the illusive rocket stove-powered pizza oven I had and I would be very pleased if you tried to shoot holes in it.

Please see attached drawing.

I have been experimenting with clay pizza ovens and the possibility to power them with a rocket stove for some time now.
Why? Why not? ;-)

I will gladly explain my previous experiences and how I come to this particular idea in detail but first allow me to explain the current plan.

My main question to you wise people is:

1. Can you run multiple rocket stoves which (sort of) get their air from one large container?

2. Would the cooling effect from the inflowing air actually prevent the floor from heating up?

3. Could this design, in a reasonably short time (1 hour), transfer enough heat (500 C) into the dome and floor, while at the same time provide radiant heat from the fire and embers to cook a pizza in 90 seconds?

4. Or is there something else fundamentally wrong with this idea?

The primary goal of this oven is to be effective, and not so much efficient . In other words: I don't mind burning through two boxes of kindling if it means getting the whole thing up to temperature.
(that's why I threw my hair loose, as we would say, and went for 4 rocket stoves firing at the same time)


So, I hope the drawing explains the idea well enough but the idea is to :
- make a normal, small (60cm dia) clay pizza oven dome, about 8cm in width
- leave 4 openings at the base, lined with a strip of stainless stove pipe
- build 4 rocket stoves in front of these openings, with their insulated chimneys running along the outside of the dome. (I would flatten the cross section of the channels to get as much contact with the dome as possible.
- every rocket stove has its own chimney so as to not disrupt the airflow-pressure-convection-thingy
- the feed tubes to the stoves would be long enough to take the full length of the 30cm clean pine kindling sticks they sell here in the supermarket in boxes for cheap.
- the feed tubes would have a lid with a hinge that closes the air supply from this side
- all air would be sucked in through the opening in the dome


My assumptions (hopes and dreams)
- by using 15cm feeder tubes I can burn a lot of wood at he same time (= lots of heat)
- the fire will heat up the dome and the fire brick floor
- the combined conductive and radiant heat will be enough to heat the entire cooking floor (the oven is going to be smallish, only three fire bricks wide)
- the radiant heat will help char and cook the pizza, similarly how a live fire in a traditional pizza oven would
- while the dome heats up, it might pre-heat the inflowing air and help combustion even more.

Modifications:
- It might be better and easier to construct vertical feeder tubes and a short horizontal burn channel. Why yes/no?
- I could see laying 4 separate air ducts on the oven floor during warm up to allow a higher intake speed of air and to be able to close the oven door and trap in the heat.

Thoughts?


Cheers,

Thijs

Attachments:

[Deleted]

One big rocket will create a lot more heat than four smaller ones, which have together the same cross sectional area. A lot more convenient to operate too.

In my experience a vertical downfeed downdraft stove burns several hundred degrees hotter.

[kishatic]

Thanks Karl,

one single stove might still be a option, the problem with that is is that all the heat will need to 'travel' through contact heat to the far, opposite side of the oven.

that would make one side to hot and the other side not hot enough.

Is a rocket stove with a 15cm diameter pipe system considered small?

Also, great that you recommend the vertical feed.
I will re-read some of the other threads as to why these burn hotter. Is it because of the horizontal burn chamber?

Cheers,

Thijs

[Deleted]

Posted by thijsatteiltje on Yesterday at 3:49pm

Is a rocket stove with a 15cm diameter pipe system considered small?

No, not for an oven.
My pizza oven with an inner diameter of 650 mm is powered by a single 160 mm rocket
an can reach 400°C within a short time.

However you cannot build a completely closed white oven with an inner dome made of clay, neither with one rocket nor with four.
The thermal conductivity is far to low.

Something on this line has been tried by Aprovecho and failed.
To get it hot enough they had finally to allow the combustion gases to enter the chamber.
www.aprovecho.org/lab/pubs/rl/reg-rep/doc/83/raw

Without heat from below, as in your design it becomes far worse.

A completely closed white oven could maybe work with an inner dome made of 90% alumina (korund).
Would require at least three different sieve lines of appropriate size.
Rather expensive stuff.
With a friend I have tried to get the highest possible thermal conductivity
from electrical non conductive and non poisonous stuff, therefore I know exactly what is posibble.

By definition a two chamber oven (separate firebox) qualifies as a "White Oven" even if the
combustion gases do enter the baking chamber.

Classical "White Oven" design
brickovendiaries.wordpress.com/2011/04/01/initial-white-oven-design-for-mobile-truck/

By this definition my pizza oven is a "white" one too. ;D

I did a fair amount of research before I have build my oven and have burried the idea
of a completely closed "white oven" made of clay or any othe non metal material.

[kishatic]

Thanks Karl!!

great, great answer.

Although of course a little disappointed about my not-so-brilliant idea now :-) I appreciate you clearly explaining the fundamental problem with heat transfer through conductivity to me.

So to summarise for myself: Clay/Sand and Firebrick have a high Thermal Capacity (so they can potentially CONTAIN a lot of heat, but they have a (very?) low conductivity .

So you can not expect to heat one side of a 7,5cm dome shell (or one end of a fire brick) with 900c degrees gasses and expect the other end to reach 400c + in any reasonable time.

Correct?

I have been reading more of your posts and will go back to the drawing board. I still like the idea of inventing something new or improving on earlier designs.


Is this the oven you mention in your post?

donkey32.proboards.com/index.cgi?action=display&board=cooking&thread=508&page=1#4556

Is there a lot of difference in the heat of the cooking floor vs the heat of the dome?

I wanted to do something similar to your design first but read on other forums people having troubles with making the floor to hot while the dome was not hot enough. How do you handle this?

Thanks again,

Thijs

[kishatic]

Hi Karl,

here is a picture of a previous rocket stove oven I build. Not so effective as yours, I'm afraid. Although it does allow me to pre-heat it and build a smokeless, normal wood fire on the cooking surface.

The idea is similar to yours, although it is much more massive (my first mistake)

You say your oven reached 400C quickly.

Does that include the top of the dome?
What is quickly?

I was thinking that a fundamental problem with my oven was that although the rocket stove get very hot, air/gas is both a (relativly) bad conductor and container of heat and by the time the gasses reach the top of the dome they have lost a lot of heat already.

Plus, they rush as quickly as they can out the chimney.

I see you design has large bottom plate and a narrow gap between the plate and the dome. Is this key to get as much heat into the dome?

Still very interested to know the surface temperature of the dome your oven can reach.

thanks!

Attachments:

[Deleted]

Posted by thijsatteiltje on Yesterday at 2:52pm

So to summarise for myself: Clay/Sand and Firebrick have a high Thermal Capacity (so they can potentially CONTAIN a lot of heat, but they have a (very?) low conductivity .

So you can not expect to heat one side of a 7,5cm dome shell (or one end of a fire brick) with 900c degrees gasses and expect the other end to reach 400c + in any reasonable time.

Correct?

Yes.

Is this the oven you mention in your post?

donkey32.proboards.com/index.cgi?....508&page=1#4556

Yes.

Is there a lot of difference in the heat of the cooking floor vs the heat of the dome?

The temperature is distributed quite evenly.
My infrared thermometer with laser pointer did not show significant differences between baking floor and dome.
Even though the baking plate is directly hit by the flame there is no hotspot in the center of the plate. To low heat conductivity.
The star, which allows the flow of the combustion gases below the plate makes the center a bit thicker.

[Deleted]

Posted by thijsatteiltje on Yesterday at 3:03pm

You say your oven reached 400C quickly.

Does that include the top of the dome?

Yes.

What is quickly?

With the rotten and wet wood there less than half an hour.
Ten cm walls add up to a lot mass.
With dry hardwood it would be faster.

Plus, they rush as quickly as they can out the chimney.

You could lower the exhaust or prevent a straight exit in many ways.
picasaweb.google.com/Jonnygms/RocketOven#slideshow/5600380213232462402

I see you design has large bottom plate and a narrow gap between the plate and the dome. Is this key to get as much heat into the dome?

Yes.

Still very interested to know the surface temperature of the dome your oven can reach.

It could become hot enough to be used as a kiln.

Jed Guinto has build a big one and (mis) used it to burn clay rockets.
holeyroket.files.wordpress.com/2011/11/the-stoves-prototype-development-project-pdf-version.pdf

[kishatic]

Thanks Karl,

that is an awesome document that Joshua wrote (I have friends who went to that same university, Wageningen in the Netherlands)

and yes, I was aware of Jonnygms's oven, it was actually part of what inspired me to make my pizza oven.

But I had read mixed experiences from other sources plus had troubles deciding how to make the construction work with the materials I had. Also, the hotspot on the baking plate worried me, but I see now that the thickness can solve that problem.

Now I wished I had stuck to your idea. ;-))

So, you would recommend making a oven similar to yours, right?


Thanks a million.

Thijs

[Deleted]

Posted by thijsatteiltje on Today at 3:40am

So, you would recommend making a oven similar to yours, right?

It's a pretty simple and very effective solution.