Oxygen

[DevilsBrew]

Is air ever added at the bottom of the burn tunnel in front of the base of the feed tube on a J rocket stove? I am up late thinking about combustion and wondering why you guys do the things you do. I would appreciate any help with this.

[mannytheseacow]

I was thinking that same thing watching that brick oven stove that Hagrid just posted. I'm more of an implementer than an experimenter so I don't have any answers for ya. I like that idea of a tall feed with a cover, and letting the primary air come from the front... seems like it would be good to inject that air right where it is needed, though it might mess up the draw if the top feed isnt covered or at least reduced to make up for the extra air going in.

[DevilsBrew]

About the cover - There needs to be a 2:1 ratio between hydrogen/carbon and oxygen? Is that correct?

[matt walker]

If we are talking about an insulated J of proper proportions, it won't be improved by adding secondary air anywhere, at least with regards to cleanliness/efficiency. That said, it really all depends on what results one is trying to achieve and what materials/design are being used. It's up to the builder/designer to decide what direction to take to achieve their desired results, and there's a million ways to build a fire. So, in other words, build it however you want to. Have fun!

[colin saengdara]

If you do decide to build it, keep in mind a couple of things. Keep the feed tube a good deal shorter than the heat riser. Make your cover air tight, and don't insulate the feed. This will assure that your feed does not become a better chimney than your riser. The fuel will start to pyrolize in the feed, so you will find that you have to be careful when opening the cover to add more fuel to avoid getting smoke and flames in your room. You may even want to block the primary air when opening the feed so that it works like a normal J when the feed cover is off.

I've built a couple temporary outdoor stoves this way and don't really like it. I prefer the simplicity of either the J, or the batch box. Getting the design right in terms of primary air, and feed size will require some experimentation. I always got flames up out of the feed, but admittedly, I did not put any effort into designing the opening to be the proper size for the stove.

One of the big hassles was that the length of my fuel never seemed to be just right, due to the fuel below not being completely combusted, so with wood sticking out the top, I couldn't close the feed completely, and if I waited for the coals to go down, then i was underfeeding the stove. Not a favorite design of mine to say the least.

[DevilsBrew]

I am floored by the "no secondary air to a J tube" fact. I am going to have to mull that over.

Colin, excellent post. I would love to see pictures of your temporary cookers and will have to do some searching on here. If you haven't post pictures, then please do.

All of my stoves and ovens have been outside cookers. I honestly think the J is the best for cooking. BUT I had one problem. It was so windy here that I had a problem with the reverse draft. I had flames shoot back up when the wind turned. I was like "Oh Sh**, not doing that again". Ah, maybe I will try it again.

[whitefire]

I was considering doing just this with an extended feed tube that could be covered just so I could feed it outside air. I decided not to because the risk of blow back.

[DevilsBrew]

I should add that I didn't have the j hooked up to an oven/bell at the time. The oven would have prevented the backdraft.

One of the themes of the moment seems to be secondary air - How much and where to add it. I myself have been looking up old models of furnaces and boilers. That is where the question came from. Secondary air is a requirement unless it is a j tube. Very puzzling.

[colin saengdara]

Devil, I haven't posted and most of my cookers are lost to the sands of time. I had been a lone experimenter for years and just made em', used em', realized they could be better, and took em' apart to reuse my materials. I started out after seeing a youtube video and I got hooked right away. I made my first stoves with stove pipe and old 5 gallon paint containers. I configured them every which way and learned a lot about what burned well and what didn't. But of course, when something burned very well, it didn't last very long. Later, I found a source for used fire brick, and I started stacking. This was a much better material. Safe, long lasting, and although it was slow to really heat up, once hot, it stayed hot for a long time. It was soon after this that I finally checked out the permies.com website and found a whole new world of other people interested in rocket stoves and sustainability in general. I "met" Matt over there on the permies site and then checked out his videos and was very impressed and inspired by his attitude, his designs, and his ability to share what he's doing for others. One of the things he's inspired me to do is to join the conversation. I still only post infrequently. My tendency, as I'm sure you've noticed, is to give lots of information that I think will be useful. It's just easier for me to try to anticipate the next logical questions and offer up the answers, than to carry on conversations that I might not be able to respond to given my time constraints. After all, I do have to process wood about every 2 or 3 days to stay ahead of the weather here.

Looking outside now, I'm trying to see if I've still got an example of one of those primary air in front types... It's not set up. The surrounding masonry is still there, the stove was made from 8 inch stovepipe. 1 tee, 1 90 opened to about 45 degrees for the feed, 1 8 inch end cap to cover the feed, another 90 to turn the gases upward into the heat riser, and a heat riser made from an 8" x 24" stovepipe wrapped with 1"kaowool squeezed into a10" diameter shell made from an old chicken feeder. I still use the riser for almost every impromptu build. even for an open barbecue, it takes the smoke right out of your face and drafts it up the tube. Pretty neat really! The inner tube is mostly gone from the heat now, but the concept worked pretty well for a movable heat riser. I'm pretty sure that the stove core is sitting on my pile of stove parts, but that's under the snow right now. I mostly used this for outdoor winter instant heat, cooking in the summer sometimes, and occasionally just for the heck of it. I'll take some pictures of what I've got laying around.

This is the heat riser:


This is the inside showing the deterioration of the inner pipe and the kaowool interior insulation:


If you want me to I probably have enough materials onhand to show you exactly how I set up the 8 inch top feed. But like I posted earlier. I don't suggest you build it this way. If you are dead set on doing it, and you want it to be a permanent stove, then I will be happy to assist you in the design so you can at least avoid some problems that I have already experienced.
-Colin

[DevilsBrew]

My interest lies in the experimental stuff and cooking stoves/ovens. I will build a temporary masonry cook stove and tear it down the next day. That is fun to me. I get a kick out of watching the "crazy" stuff people come up with. I became hooked on the European and Russian metal and masonry stove youtube videos and websites. That is where this all started for me. They have always seemed to be a step ahead of what is going on in America.

I appreciate your help and posts, Colin. Know that I do absorb it all. I request pictures and video a lot because it is easier for me to catch on when I see the visual representation of a build. Also know that I ask these questions because I am trying to understand the science behind a build. Why it works and why it doesn't. Maybe it doesn't always come across online but I am constantly trying to learn.

My long term goal isn't a permanent stove. I get too much enjoyment out of experimenting.