Questions re Modified Riser on Batch Rocket for Bread Oven

[tcb]

I am thinking of building a Bread Oven using a Batch Rocket.  

My idea is based on the French gueulard-bread-oven (Google "four à gueulard" and you will get plenty of information  in french - unfortunately there are not many finds in english).

The main feature of the gueulard oven is that it has a fire chamber underneath the main cooking chamber.  It uses a "gueulard" to redirect the heat by about 90 degrees into the chamber so it flows horizontally towards the back of the chamber (unfortunately the forum will not me upload attachments or I would post a picture, but if you check YouTube you will see that the gueulard projects quite a nice hot flame into the oven).  

Basically the gueulard itself is a hollow round elbow made out of cast iron that fits into the hole coming from the firebox which swivels so it can be pointed in any direction.  When the oven gets hot enough you take the gueulard out and replace it with a "gamelle", which is basically a cast iron cup which fits into the same space.  It holds water and so provides steam for the bread.

So my idea is to put a batch rocket under the main chamber.  This has been discussed on the forum and I think the consensus was that it should work.  But ( there's always a but isn't there) I see from Peter's notes that the riser dimensions are critical.  So my questions are related to the gueulard essentially adding an extension to the riser tube: Specifically - Does the gueulard need to be taken into account when designing the length of the riser and if so how?

In operation when the oven comes to temperature the gueulard is removed  and replaced it with the gammele (shortening the riser?).  The gammele will essentially block the riser presumably stalling the batch rocket.  This should not matter as it has already done its job and can always be re-fired if required.  So in this phase of operation I am thinking I will just redirect the heat from the batch riser with some sort of damper so it just exhausts outside the oven or back into the oven.  Any thoughts? Specifically am I correct in assuming that the batch rocket will no longer be operating in rocket mode?

Finally are there any rules of thumb for calculating the size of rocket based on the cooking chamber size/surface area or thermal characteristics? 

Thanks for any guidance that anybody can provide.

Cheers

[Pascal from Ivrea]

This is what you want to make?

[satamax]

TCB, make your riser as per Peter's dimensions, and add the gueullard. If that's possible. The problem being, usualy; that you have to shorten the heat riser, for coocking apparatuses. With Indipendenteenergy, we're both working on a vertical batch box. He's a bit ahead of me. As i have a shop to run, a flat to finish. A gen set to repair, and a sawmill to finish. So, rockets are not realy my priority untill the autumn.

[satamax]

Thinking of it; it would may be ; be intresting to make the "ouras" not only flaps which open or close. But two plunger tubes with flaps above. So that even when they are opened, the oven acts as a bell, in conjuction with the closed door. And have a third full CSA normal oura, for when you open the door. That would be needed just in case of a smoky burn.

By the way, TCB, where you located? Me south east france, on the italian border.

[tcb]

Pascal

That picture is where I got the idea.

Satamax

I am in regional Western Australia about 139 km East of Perth.

If I understand you correctly about the Ouras ->.  In pictures I have seen the oven has two vents (Ouras) at the back.  I think you are suggesting that these vents have a tube going down to near the bottom of the oven so that the oven acts as a bell chamber. If so I think that is a good idea.

Not sure I understand what you mean when you say 'have a third full CSA normal oura, for when you open the door.'.  Do you mean have a third vent (say on the center line) WITHOUT a tube so that you can exhaust smoke from oven for when the batch rocket starts to smoke. 


In any event I guess i am going to have to build one to see  what works. This might take a while.

BTW the difficulty I foresee is interfacing the gueulard to the riser and also switching the riser output to somewhere other than into the oven.  Need to research flaps and the like.


Cheers and thanks to both of you

Tom

[satamax]

Tom, the part about plunger tube, you got perfectly.

The third one, i thought, would closed all the time, except when the door is opened. And with no plunger tube. So you do'nt have a blast of smoke back into your face. Tho, i open my batch rocket top door all the time, and you rarely see smoke. Or smell anything.

I had imagined a simpler oven for myself, a pocket rocket oven. www.permies.com/t/38661/rocket-stoves/rocket-powered-pizza-oven The latest idea, would be to make both feed tube, and heat riser, plunge tubes. make a kind of insulating firebrick bed below the feed tube, and some around, as a removable wall. So the embers don't come to the pizzas, and this would rise the temp, to get a better burn.

FFS, i need to try this one. Sooo little time!

[Deleted]

The only reason for the hood is that it compensates the eccentric fire entrance.
I have seen a video of such an french oven with the entrance in the center.
The fire hit the center of the dome.
After firing a pot with water was placed in the hole.
With a batchbox the entrance will move inwards.

Wikipedia gives the Higher (HHV) and lower (LHV) heating values for wood as MJ/kg:
HHV 21.20
LHV 17.0

By calculating with the LHV value you are on the safe side.
Only woods with large amounts of lignin and resin may have significantly higher values.

[docbb]

there are few exemples but you will find some paths in this thread

rocket oven

and here

just search a little

And find the tags



and Building