Have an idea for a woodgas stove that I want to make but before I do I have a question about the bushbuddy... what's with the double layer can thing? You could cut weight and have more room for wood if you used just one can with holes in it hobo style? But I don't know much about this stuff. Someone learn me a thing or two!

In interviews with Fritz Handel, inventor and builder of the Bushbuddy, he explains how at first he wanted a cool 'jacket' around the firebox so he could set the stove on a combustible surface without damaging the surface. He noticed secondary combustion of smoke gasses as a result of the airflow through the double wall. This made the stove more efficient and led to the current design.

You can find an interview at hikeitlikeit.com.
Scroll down to the question:
"Can you tell us a little about the beginnings of the Bushbuddy stove and how you arrived at the current design?"

Another interview is at hikingfinland.com

Both interviews are very good.

Hope this helps.

Edited by Lancem on 01/17/2012 22:12:23 MST.

The double wall is to create a draft to feed the secondary air holes with fresh air.

IMO, the bushbuddy is a very poor example of a wood gas stove, or a really well constructed hobo stove. A true wood gas fire burns a clean blue flame similar to your natural gas stove in your kitchen. In WWII they used to run cars on wood gas. Google it.

Here's a good link if you are intrested...
http://journeytoforever.org/biofuel_library/WoodgasStove.pdf

BM

I made and tested a few a while back.
Heat rises so the hot chamber around the sides pulls in air from the bottom
which goes into the combustion chamber up top and basically provides a cleaner hotter
burn. I suppose since it burns from the top down it also pulls some wood gas into the side chambers too, but thats a guess.

One decent one I built was a 12 oz Heiniken can outer with a sardine can inner.

IF you want to try it go here and it will show you how to make one.
http://www.hobohilton.com/hwgs1.html

The holes have to be just right and this particular one was a bit hard to start, but
burned hot and consumed the wood down to white ash.

I never used it enough to see how long it would last but it is light.

Burns about 15-20 minutes.

I think it could be vastly improved on with Titanium
and more experimentation for a more permanent solution.

I ended up going alcohol since it takes a good bit just to light off the above wood stove. Probably the wrong proportions, IE too tall per diam or the hole area is off etc.

You could also check out weber fire starters from Ace hardware. Same as wetfire cubes. They will boil water but they do smoke your pot. I carry a couple for emergencies

Here is a link to Tom Reed's commercial wood gas stove. http://www.woodgas-stove.com/catalog.php

Notice it is made of stainless steel, double walled, has primary and secondary air, and an electric fan.

I just really LAUGH at all of the homemade stoves without a Fan. They are very inefficient. The fan does many things. It mixes the fuel, it makes enough air flow for a usable cooking fire with limited fuel, it eliminates the need for a stove pipe to pull the air across the fuel. And most importantly it forces a much better transfer of the heat energy to the cooking vessel.

I've made 3 meter wood gas stoves, but a hair dryer on it instead of a DC fan and boiled gallons of water much faster than with my kitchen stove.

Think about it, the Mega Stove puts out 55,000 btus. My residential natural gas stove puts out 10,000 BTU's on HIGH.

Look at the picture of the flame coming to the center of the Mega Stove. 55,000 BTU's.

Here is a link to a diagram of how it works. http://bioenergylists.org/node/2560

EPA wood burning stoves for homes are very similar in design. Primary air comes into the fuel below and "cracks" the hydrocarbons i.e. making them into wood gas. These EPA gasifing stoves use one half the amount of wood as regular stoves. I assume the same is true of the commercial wood gas stove. It probably uses 1/2 the fuel of a hobo stove to cook the same amount of food. Secondary air that has come up the side (in the camp stove) between the walls comes out. The air is super heated and if operating properly should give a blue flame much like a petrol or propane stove. There should be very little smoke.

The double wall provide VERY LITTLE draft. There is an equation for how much of a pipe you need for draw, but suffice it to say 8 inches does more to hurt the flow of air than help.

If you want to make a better HOBO stove make one like this.

1) Take a large coffee can and poke holes in the top and bottom of the sides in a 1-3 area ratio. Since you are not putting a fan in there, put some holes in the bottom also. Without forced air, you need more space for air to come in.

2) Fill it with fuel.

3) Put it on a few rocks so air can come up from below. You probably want to cut the top or put up 3 or 4 pot poles to make a 2-3 inch space between the top of the can and the cooking vessel. you can also feed more fuel in this space. This is not how the stove is supposed to be fired for best performance, but the reality is in this configuration this is how it is done.

4) Now make ANOTHER metal sheet to put around the coffee can. This screen is in place to keep cold air off the burn chamber and also to help to keep the combustion air heated before it reaches the fuel. Same ideas as the electric wood gas stove, but without the tight tolerances.

5) In addition you can attach a metal pot skirt around the pot. Make sure the heated air can scrape up the sides of the pot.

All of that said, either make your own, or buy one of these stoves for best performance: http://www.woodgas-stove.com/catalog.php

You can take a large coffee can, put a small one in it... to make one. The make a "fan assembly" out of a cookie can.. put a 1.5 volt fan or 9 volt computer fan or something similar. I take the fan off a 3 inch computer fan and put it on the 1.5 volt motor and make a little mount for it. Then I use a rechargeable battery. when the cans burn out, just replace them. You can make 2 sets of the cans.. load both up and cook continuously.

"I just really LAUGH at all of the homemade stoves without a Fan. They are very inefficient. The fan does many things. It mixes the fuel, it makes enough air flow for a usable cooking fire with limited fuel, it eliminates the need for a stove pipe to pull the air across the fuel. And most importantly it forces a much better transfer of the heat energy to the cooking vessel. "

That's a touch harsh, but I personally have to laugh when someone calls their stove a "wood gas" stove when it's got big floppy yellow flames akin to an open campfire. Here's a pic of my wood gas stove running at it's peak efficiency-This is what it looks like just after coming up to temperature-I think more than anything what most diy backpacking wood gas suffer from are two things- #1) heat loss and #2) poor mixing of air and fuel.

If you look at that diagram you posted, which coincidentally is taken from the pdf that I posted, the stove body is made from a heat insulating material. Efficient pyrolysis needs to occur at high temperatures. Tin can stoves lose a lot of heat. I haven't had time to play with my wood gas stove projects lately, but I have been trying to figure out how to make a light weight compact insulated pyrolysis chamber.

Now if you think alcohol stoves are slow and finicky- wood gas is a bunch worse. Proper preparation and loading of wood takes time, and then with my stove it needs to run for about 3mins before it's up to temperature and running well. Then you can stick the pot on and start boiling, and it'll take about 10 mins to get a rolling boil, but will continue to burn for about 25mins on one 60g load of fuel.

BM

"I just really LAUGH at all of the homemade stoves without a Fan. They are very inefficient. The fan does many things. It mixes the fuel, it makes enough air flow for a usable cooking fire with limited fuel, it eliminates the need for a stove pipe to pull the air across the fuel. And most importantly it forces a much better transfer of the heat energy to the cooking vessel. "

I actually have a quiet chuckle to myself when I see a stove WITH a fan.

How efficient does your backpacking woodstove need to be?

Put wood in - Get fire out...

I have read so much "scientific" debate on the subject that is conflicting. How can forcing air through a small stack of wood be More efficient? It seems like it would burn your fuel up in no time at all. Through practice and testing done over literally thousands of these small personal campfires I have gone to smaller and fewer holes to keep the fire manageable and to maintain a consistent flame longer when lit from the top.



With a single or double walled stove (no fans) you can bring 2 cups of water to a boil in 6-7 minutes all day long from the time it is LIT without adding any wood. It takes a couple of minutes to load the stove but as soon as the fire is lit you can place the pot on. The one below fits in an Evernew 640 and weighs 2.5 oz but has a large enough firebox to do the job.





single wall vs double wall? As far as burning wood goes it makes no difference at all. I owned a bushbuddy but sold it because even though it worked just as well as the other double walled stoves I have made, it had a fantastic resale value too. It is probably more important is to practice making many fires in whatever stove you choose so that you learn how to get the most out of it.

Edited by cadyak on 01/19/2012 21:38:13 MST.

"I actually have a quiet chuckle to myself when I see a stove WITH a fan.

How efficient does your backpacking woodstove need to be?

Put wood in - Get fire out...

I have read so much "scientific" debate on the subject that is conflicting. How can forcing air through a small stack of wood be More efficient? It seems like it would burn your fuel up in no time at all. Through practice and testing done over literally thousands of these small personal campfires my stoves have evolved to have smaller and fewer holes to keep the fire more manageable and to maintain a consistent flame longer when lit from the top."

That's a very valid point. If all you want to do is cook your dinner, what do you really need? Heat... and that's about it. For me, the wood gas stove project is in of itself a hobby. I'm a closet pyro (responsible pyro, at least now that I'm an adult) and trying to get a nice clean burning flame from a few twigs on the ground is fascinating to me. So, if you just want to build a hobo stove, or a slight more sophisticated TLUD stove, that's fantastic. It'll get the job done more than adequately.

As far as a fan is concerned- I've had more burner configurations have problems getting enough secondary air to feed the amount of wood gas being released, causing it to run "rich". That's pretty easy to verify. Running a fan is a simple solution to the problem, though I don't like it. I feel it ruins the elegant simplicity of the stove.

BM

Edited by Ultra_Magnus on 01/19/2012 14:58:38 MST.

Let's talk woodgas.

quoting Fritz: "The next development in the Bushbuddy saga came when Ryan Jordan at BackpackingLight purchased one of the new Bushbuddy stoves. He was impressed enough with the secondary combustion to ask me if I could make him a 6 ounce version of the stove. How could I reduce the weight? The obvious place to save a lot of weight, and a lot of work too, and potential problems of fit, would be to eliminate the base that the firebox sat on. By rearranging the internal construction of the stove to allow eliminating the base section, and by using even thinner metal for most of the stove, I was able to achieve this goal. Soon afterward, just before his upcoming Arctic 1000 trip in 2006, he asked me if I could make an even smaller stove that would fit inside his Snow Peak .9L titanium pot. I built for Ryan what turned out to be the prototype for the Bushbuddy Ultra.
As they say, "the rest is history". Ryan ordered a hundred Bushbuddy Ultra stoves from me, and popularized the stove. I discontinued the larger model Bushbuddy, and started making a new "redesigned regular model" that was the same size as the Ultra.
"

Ryan Jordan received the untested prototype that Fritz made and took it on his Arctic trip. Came back and ordered 100. As the original design got smaller and smaller, the problems got bigger and bigger. Ryans prototype design sold like hotcakes. Anything that Ryan used sold like hotcakes.

The current BB can only accept 1.5 inch length twigs, anything longer than that will block incoming air from within the double wall. Blocking those holes negates the function of the double wall. If you fill the stove with twigs to overflowing, which most people do, the double wall is not necessary.

Addison, I suggest you make a single wall stove. Let the folks in the 3rd world countries make the double walled so called woodgas stoves with their electric fans. There is no such thing as a woodgas stove in the backpacking world. Even Fritz made a comment that there is no woodgas coming up the double wall. It's just warm air. It's in the interview that we were given links to. I repeat, no wood gas in the double wall, just warm air. Fritz has been making wood stoves for a long time and knows what he's talking about.

I purchased a Bushbuddy stove used on ebay. I did extensive testing and found it lacking in many respects. The results of those tests are located at my website, www.bplite.com in the "wood Stove" forum. After tests were complete, I sold the Bushbuddy, resale values hold high.

Brent driggers had a bushbuddy and sold it. Brent has logged in many many hours of wood stove testing and is conidered an expert in my eyes. When you burn cords of wood, you get a good undertanding of how wood stoves work. (mini cord) ;-) Thanks Troy for all that you've done for the wood burning community.

Edited by zelph on 01/24/2012 20:00:47 MST.

Hi there Lance. Interesting interview with Fritz Handel especially what he says about the air going up the double wall, that it is not woodgas. Here is a quote from the interview you linked us to:

Can you tell us a little about the beginnings of the Bushbuddy stove and how you arrived at the current design?
FH
I had been using the Sierra Stove. The fuel efficiency was inspirational, but the need for a battery was a drawback.
I experimented with a number of different wood burning stoves for my own use, which didn’t have a fan. They worked pretty well, but they all had a bad habit of igniting any flammable surface they were set up on. This seriously limited the places the stove could be safely used.
I was trying to find a way to keep the bottom of my stove cool enough that it could be placed directly on flammable surfaces without charring them. Thinking that more cooling air drawn through the bottom of the stove might be a solution to this problem, I put a double shell around the firebox to create an additional draft through the base of the stove. The warmed exhaust air was routed into the firebox near it’s top. When I saw what appeared to be jets of flame entering the firebox, and very little smoke, I knew this was something special. (The phenomena is called “secondary combustion”. The apparent “jets” of flame entering the firebox are not, as some people mistakenly claim, “wood gas” entering the firebox, but warm air, which combines with the invisible, rising, unburned gasses in the firebox). This first experimental stove evolved into what today is the Bushbuddy.

I just came by to view the link that was given concerning the interview with Fritz.

We are having a discussion about double walled stoves over at bplite.com and I needed a quote from this thread. thank you!!!

"The apparent “jets” of flame entering the firebox are not, as some people mistakenly claim, “wood gas” entering the firebox, but warm air, which combines with the invisible, rising, unburned gasses in the firebox)."