Rocket stove cooker

Hi
I recently got interested in all of this rocket stove buisness and thought I might try making one myself to be able to cook outside in the summer without using the barbecue.

If you take a look at the pic attached, thats the sort of thing I'm looking at building; not the type with flames coming out of the top. My main aim is to make it as compact as possible( roughly 1 metre high) , hence the shared wall between exhaust and cooling chamber.

I would like to make it out of brick. Given it's usage (cooking and therefore no need for heat storage or long burning periods), is it necessary to insulate the combustion chamber or can it just be made from brick ?

Cheers

Seb

You're still going to have to make it out of firebrick, as that design will probably still get very, very hot.  Normal brick will crack.

I've been thinking of the same type of cooker.

I want to minimize smoke (I have a boy with mild ashma) and am thinking that the butt warming notion of drawing the gasses back down again  - i.e. lengthening the chimney bit - will help.

The big question I have is this:  the black line you show represents a hot plate. 
The normal "cooking" rocket stove has this open - i.e. a grill - the fire is touching the pan.

Not much heat is lost from the pan in your diagram when the pan is not in direct contact with the fire?  Is it alot?  to much to make the down draft worthwhile?  Does the draft action actually steal heat from the "hot plate"?

In the butt warmer - it's ok for this downstream gas to be hot/warm - that's GOOD heat going through the system - still being absorbed by the cob bench - etc.

In the stove, I'm worried it might be wasted heat...

Scott911 wrote:
In the butt warmer - it's ok for this downstream gas to be hot/warm - that's GOOD heat going through the system - still being absorbed by the cob bench - etc.

In the stove, I'm worried it might be wasted heat...

There will be some wasted heat. The rocket stove (whichever way) is trying to do two things:
1) burn the wood more completely so as to cause less health problems.

2) burn less wood than the standard (in many parts of the world) three stone fire.

I don't think that much is gained by exhausting from the bottom of the barrel (try and see I guess). Some of the rocket stoves look very much like the picture above, but with a hole that the pot sits in so that the flue gas hits the side of the pot too. i think the pot could be sealed to the barrel easy enough. Then the flue gas is exhausted through the side of the barrel fairly high up. Unless you have a use for the flue gas (small oven or warm bench) the least complex solution is to exhaust as soon as you are finished with the heat. I think the testing they did showed that when you use a rocket stove to just heat the bottom of the pot, it's efficiency falls a lot... not much better than a well done open fire. Efficiency is amount of food cooked for amount of wood.... normally measured by time to boil a known amount of water.... or maybe that is end temp of a known amount of water with the same amount of fuel. It has been a while since I read this stuff.

hey sebgreen -

One thing to keep in mind is that if you use heavy brick means without insulation, you'll have to be heating up all that mass in addition to your cookpot. 

Your quart of water for tea may require just abit of fuel.  BUT, now remember that you also have to heat up the mass of all that brick each and every time you want to cook something.    That adds to the time and amount of food needed, probabaly several times over.