Carbon blackening pots

[hpmer]

I have built a rocket stove similar to that shown in the above post that works great, but get a build up of soot on the bottom of the pot when cooking with it.

Is this just a fact of life with wood burning stoves, or is there something I can change to get the heat without the mess?

My stove is made from a 6 gallon metal trash can and insulated with perlite, and uses 4 inch pipe with an elbow for the joint.

[Donkey]

Sounds to me like you have incomplete combustion.
Could be not enough air..
Could be not enough turbulence for complete fuel/air mixing.. (I doubt this, the Aprovecho style feed provides plenty of turbulence)
Could be wet wood.. (though it would make more tars and creosote rather than carbon/soot)

In the aprovecho cook stove design the shelf is pretty important, make sure you have it installed properly. Try adjusting the pot height, it's easy to choke the flow from above. You want it as close as possible without slowing the flame even a little bit.

After all is said and done... Yes, cooking with wood can be a bit sooty/smoky either way. Shouldn't be OVERLY so, but you will likely have to put up with a certain amount. It's worth it though.

[hpmer]

Thanks for your thoughts, Donkey.

I've been toying with buyilding a new stove to further experiment with and you've given me some good suggestions. It's good to know that I can at least reduce the carbon buildup.

Yes, wet wood could be the issue, as well as the pot too close to the top. Perhaps also the stove isn't getting hot enough given the elbow design. I plan to replace the elbow with a "T" to allow more coals to build up and improve air flow.

I also plan to experiment with some of the "turbulators" presented in the heating section.

I built my stove with my 11 yr old son to boil down maple sap into syrup - a good father/son project with a tasty reward at the end. We've been impressed, but think there's room for improvement.

[Donkey]

Welcome to the boards.
IF you want to build a stove for long boiling projects, I recommend the down draft feeder box. Actually.. I've pretty well switched to the down feeder method for all my projects.
Rocket stoves are quite fiddly.. The down feeder helps with that a bit, as gravity does the job of pushing the wood in as it burns. It eliminates the shelf entirely, and goes a long way on it's own toward a good fuel/air mix.

You know, besides encouraging laminar flow, the elbow itself shouldn't really be the problem in your stove. I've got a cooking rocket in my house made from six inch pipe. It's got an elbow and was originally set up in the Aprovecho style. I have switched to feeding it through the top which is generally NOT recommended, though in my case it works quite well. Anyhow, the elbow seems fine.

Try building your next stove from six inch pipe. Also a taller heat riser will add remarkable pep. Add in the down feed box, insulate to the gills and SHAZAM!! check it out..

[Teach]

Hi there, when it comes to cooking with wood I highly doubt you will ever get a flame that comes into direct contact with your cooking pots that does not blacken your pots no matter how clean burning the stove is!!!! The good news is this, blackened pots heat their contents quicker than unblackened pots! And not just by a small amount either. Pre-blackened pots (fire seasoned) will boil water considerably quicker!

So even though your stove may not be perfectly clean burning, it's not entirely a bad thing! However, keep striving for the cleanest burn!!!

Ian....

[Donkey]

That's probably a good point..
I build my cookers taller than the Aprovecho style.. Their design was originally intended for cultures that cook on the ground, so they are built short.
Actually, it was key to rocket stove (cooker) success in being accepted all over the world, where others were not. Not only are they efficient, they are culturally appropriate in most of the right places.

Anyhow, in my culture folks cook standing up, so taller heat risers.. The taller heat riser pipe (like 2 1/2 to 3 feet) draws better, and tends to keep the pot off the flames. I think that the taller pipe (as long as turbulence and insulation is high) burns more completely as well. I see little to no blacking on the models I've made in some time..

[Teach]

So the secret then is...............make your riser tube taller AFTER you blacken your pots on the shorter one first! Big Grin.

That makes perfect sense Donkey. Being a tall person I have always looked at people cooking on the ground thinking.......man that looks uncomfortable......hard on the knees etc. By making your riser taller you affectively allow more time for the burn to complete before it hits your pots. What happens though when the stove has not yet come up to temperature? Same affect or does it still push a little suit?

Did you just use a cheap metal pipe for the combustion chamber as well as the heat riser and insulate them both well? (perilite or wood ash perhaps)? Or did you use insulating fire brick with added insulation?

[Donkey]

Ive done steel, brick, cob, woodchip/clay, etc,etc...
All will varying levels of insulation.. Often, I'll go to this friend of mine's place for BBQ.. I'll grab a few bricks out of his pile, build a stove and cook something.. Though every time I go back, I gotta re-build it.. He takes em apart or backs into em with his car...

[efficacy]

A simple way is to coat the bottom and sides of the pot with thin layer of sticky mud. It will eventually bake off, and being so thin it won't be too much of an insulator.

Some people rub dish soap over their pots. While this does indeed work, i do not care for the idea of smelly burnt chemicals in my food.

Pomolive scented tea.. EWWWW.

Also it does depends on flu height . I made Vavreks (Aprovecho) oil can rocket stove.

I did notice that there is a significant space between the top of the flu and the grill where the pot sits. Gives a little more draft and protection from the wind.

There was a little more sooting with greener wood. However not as bad as with the much shorter coffee can rocket stove.

[canyon]

I like the mud smear method! How many firings do you get usually or is it a fresh mud every time? Just curious.

[Donkey]

Now.. I know it's a nit-pick an' all.. But, wouldn't the clay soak up and or deflect heat from the pot, reducing it's conduction efficiency??

(propeller head alert)

Seems to me that blacking on the pots is a sign of unburnt fuel. Sure, there will be carbon unburnt in the mix that will deposit on pots. It should never be greasy, creosote black. You want a dry, powdery carbon if any.

[efficacy]

canyon.

It would have to be each time. All i do afterward is tap the pot with a piece of wood and the remainder falls off. Washes off with relative ease.


@donkey.

Unless your caking on 1/4" or more of mud. A paper or even hair thin stain of mud won't even register on the insulation scale.

I find it odd that so many on these forums can always find 100% dry kindling in the woods. Even with a powered woodgas stove there will be sooting.

I am not quite certain what a " propeller head " refers to in this instance. However i get the feeling it can't mean anything good for me.

Bye.

[ernie]

its long hand for pyrogeek questions. lol

[Donkey]

Actually," propeller head" was referring to myself.. Pyrogeek etc.
Nth degree efficiency is really not my primary concern..
It was meant more tongue-in-cheek, poorly delivered.

[hpmer]

Dry, powdery carbon is indeed what I get, so at least it is not the greasy, creosote black stuff. So that's something, I guess.

And I did take Donkey's suggestion about the down feed method, changed the elbow to a "T", and have added an adapter box to the front end of the stove. Looking forward to firing it up since it is soon to be maple sugarin' time and that is the reason the stove was built in the first place. I'll know within the next week or two how the new setup works.