Category: build

In the continuing saga off no-smoke charcoal making, I’ve added air injection to the system.

In recent runs, I could tell the fire wasn’t getting enough oxygen. There were a couple reasons I knew this.

1. when running just the stove, I got a red jet flame out of the top. A picture from a previous post:

   If everything were running optimially, there’d be enough oxygen inside the stove that all combustion can happen inside the stove. Said another way, volitile gases waited til being exposed to outside air before doing their thing.

2. another reason; pretty much the same as #1, when making charcoal, I got a red flame around the paint can. I want it to be a nice bright flame under the can.

So I’ve added a supercharger.It’s kinda hard to see in the thumbnail, I drilled four small holes in the length of pipe between the cap and the coupling (actually, it’s called a nipple… heh heh, he said nipple ;-)). The other end of the pipe, but the valve is a connector that allows me to hook it to my air compressor.

Air flows from the compressor through the valve (the throttle), through the pipe that runs through the middle of the combustion chamber when I get the side benefit if heating the air, and then it’s injected into the flow of gases coming off the fire.

(check me out, using all this technical sounding language. you’d think I’m a rocket scientist. I’ll have to mail my fried Jose who actually IS a rocket scientist. literally)

Well, it worked quite nicely. I now get only a little bit of smoke right at the beginning of the burn. Best of all, it’s starting to SOUND like a rocket!!! I need to find a microphone so you all can hear it. Very cool.

One by product of it all is that it burns to completion much quicker. I haven’t opened the paint can yet so I’m not sure if I got charcoal through out. If not, I’m gonna try adding a thermal mass to the upper section like I already have with the stove itself. Might make it a bit top heavy.

My friends out there are probably starting to think that I’m losing my mind. Hopefully, the cool factor of it all compensates. I trust you’ll let me know.

I’ll close with something this all makes me think of, the guys at Purdue that lit charcoal in a bbq using liquid oxygen.

actually this is take four.

1. exit hole on top. Mistake. lots of uncombusted smoke
2. exit hole on bottom. Better, but still lots of smoke
3. pipe extention to inject smoke into the heart of fire. That worked, but the ducting I was using still leaked smoke.
4. today’s experiment

Somehow, the thought of using an old paint can came to mind. I looked at my collection of paint and I found two that were bad. I took the old primer can with thick yogurt consistency. Plus there was only 1.5″ left.

I cleaned it out and drilled a 1/2″ hole in the bottom for the pipe. Notice the elbow to reduce the chance of stuff getting in there. Also the small hardware cloth cage to ensure a clear path to the pipe. The outside of the can is a 3/4″ wash with threads cut into it using the pipe thread cutter I got from Harbor Freight.

Here, you can kinda see the pipe extending down into the fire.

The first batch had some smoke, but I suspected that’s the coating on the can burning off.

The results are pretty good, though not very much of it. Need to find a larger paint can. Somehow I remember the existence of 2.5 gallon containers.

When wood burns, what’s really going on?

As I understand it, it’s a 2.5 step process.

1) Heating the wood causes it to vaporize into its component molecules.

1.5) depending on the temperature, the longer, more complex molecules decompose into simpler molecules. Larger molecules don’t burn as well. Axle grease doesn’t really burn. Gasoline does. If you heat up axle grease enough, it will break down to something that will burn.

2) The simpler molecules burn and the larger ones got up in smoke.

The point of my rocket stove is that the fire happens in a hot space and I get more complete combustion due to that concentration. That’s been working pretty well.

Over the last year or two, I’ve read a couple times about Terra Preta and how it can be used to help revitalize farming soil and also serve as carbon sequestration. After I hear about it again on Science Friday. In the story, the guest described the charcoal making process as simply heating wood to about 400 or 450 degress F in an oxygen poor environment. This was also something that I’d read and thought about before due to this site

So I figured, why not try it myself? My results have been good so far, but the process makes too much smoke.

First, I took some left over ducting and, together with two end caps, I make a canister about 10" diameter and 16" long. I suspended this canister inside a piece of 12" diameter ducting. I suspended them with screws similar to how I did the rocket stove.

I then crimped the end of the 12" ducting so I would fit snugly on the stove.

On the first try, I put a vent hole on the top, but this was not such a good idea because it produced a LOT of smoke. I removed it from the stove and let it cool off. I sealed the hole with a bolt and drilled a hole on the bottom. This worked better, but still had more smoke than I cared for.

Since smoke means incomplete combustion, I need to channel the smoke into the heart of the fire, so I took a piece of iron pipe I had around and had it extend from the bottom of the canister down into the fire.

This helped things a bit, but the canister itself wasn’t sealed all the well. Smoke was escaping through the seams. Not realy sure how to fix that. The whole thing heats up enough that solder will melt. to attach the iron pipe, I used a ring bolt from my box of electrical parts. It’s from one of those things that hold wires onto a metal junction box. Anyway, it melted off!

so the experiment hasn’t quite panned out. If I were living in the country, it’d be good enough, but here in the city,… not so much.

Here’s the first batch. Charcoal. If you take a piece of it and break it, it’s consistent throughout.

So the next step will be to figure out a way to seal the canister or to make another one that doesn’t have these issues. Maybe #10 food cans. I’ve also thought about some sort of shroud to expose the smoke to more heat. will hvae to think about it some more.

Here are some more cool fire pictures. 😉 Oh. One thing I forgot to mention. I added more holes inside the rocket stove, so there more airflow. It doesn’t burn like this for very long, but it’s pretty spectacular.

I took some more pics of my stove in operation. I just love how the flame jets around. I also have some pictures with Grady for scale.

Recently, I’ve been thinking about how wood burns. It started when I read a post on the blog The Oil Drum when someone posted an opinion that instead of turning celulose into alchohol, we should just burn it by gasifying. As I understand it, when you heat wood, it gives off gases that will burn. It you make it hot enough, the carbon chains in the gases will reduce to simpler modecules that burn well and this is the key to a clean burn.

This prompted me to do a bit of googling and that brought me to the WoodGas website which goes into more detail about how it works as well as information on how to make simple cookstoves, particularly for use in less developed countries. More googling and I arrived at a description of the MIDGE stove.

Since I’ve been on sabatical, the last couple weeks, I’ve had some free time and I decided to build a stove out of ducting. I also have a big pile of woodchips that I got for free from a friend whose an arborist. The stove is composed of three lengths of ducting 6", 8" and 10" in diameter, two reducer flanges and mesh.

The 6" duct holds the woodchips. The screen is to allow plenty of air to come through. Note the 4"x4". This is not a part of the stove, it’s only to hold the duct, so I can drill holes. When the stoves is running, the chips burn from the top down giving off fumes. The ring of holes at the top of the duct injects more air into the stream of gases for combustion. One of the keys is to have it all happen in a hot, contained space. This is one of the main differences between a woodstove or fireplace insert and a basic fireplace. In a fireplace, it’s difficult to maintain a sufficient heat density.

Once I had the center duct with plenty of holes (I actually want to add more, but that’ll require me to take the whole thing apart), I put it inside the next larger duct (8") using a reducer flange and some sheet metal screws. Hopefully, the pictures illustrate it better than I can in words. The purpose of this is to guide heated air up and out of the holes using the chimney effect. Warm air rises.

Now I have a duct that holds the chips and serves as a firebox. I have a mechanism for heating air and injecting it into the volotile gases. On it’s own, this works ok. Knowing that maintaining a hot space is key, I added a third duct (10") to shroud the rest of this stove. The space between the 8" and the 10" is filled with sand. From reading around a bit, wood ashes serve as a good insulator, so maybe I’ll try that, but right now, I don’t have enough ashes. I did have sand though.

I fired the stove up a couple times and it’s pretty cool to watch. I’m using green woodchips, but it only takes about 5 min for it to get going and stop smoking. Through experimenation, I’ve found that if the flame goes out, you get a LOT of smoke. The neighbors were probably wondering if I’d planning on burning down the house. This means you can’t realy add fuel to the fire once it’s going. Maybe using dry wood would change this dynamic, but for now, I’ll have to do it in batches.

Here are some pics of the flame. Notice how it jets out from the air holes.