Saturday, February 21, 2009

Wood powered Camping Stove (updated)

I enjoy the outdoors, camping, hiking and I like to prepare food in the outdoors, just a quick boil-up for a cup-a-tea or a full meal. I have owned two camp stoves, I chose to purchase multi-fuel stoves as they are cheap to run and fuel is easy to find.

Recently I have started wondering about the logic of enjoying the outdoors while contributing to it's destruction with the use of non-renewable resources and the production of greenhouse gases. Obviously a camp stove is not making a significant contribution to the problem, but it got me thinking of alternatives.

I had read wood gasification and seen engines running of wood gas. I wondered if this could be applied to cooking. Wood gas is produced by heating wood and driving off the volatile components, this produces a mixture of gases, including Methane, Hydrogen Carbon Monoxide and some others. A conventional camp fire produces these gases, but much of them are lost in the smoke because the is insufficient Oxygen in the fire to burn the gasses. A camp fire requires a large amount of wood to cook a small amount of food due to the incomplete and inefficient combustion of the fuel. Sure enough there are lots of people making gasifier stoves of various types, however many of them seem rather complicated to make, or expensive to buy, or not piratical for camping. I decided to try and build one out of common materials using simple tools and techniques.

Below is a simplified diagram of how my gasifier camp stove works...

Somehow it seems to have gone in as a negative.

The basic idea is that the wood burns at the base of the stove, aided by air forced in by a small fan. The stove consists of two chambers, one holds the fire, the other acts as an air duct. The heat from the wood burning at the bottom of the inner chamber heats the wood above, driving off gases that are then burned at the top of the inner chamber aided by a supply of hot, fresh air that has passed up inside the outer chamber.

The idea is all very well, but how can this be easily built out of everyday materials?

Below are a series of images showing how I built my stove.

1. Here I have 3 cans, A tomato can, a pineapple can, that fits in the tomato can and a 35mm movie film can that is large enough that the tomato can can sit in it's lid. Any 3 cans that will fit into each other this way will work. Paint cans, food cans, travel sweet cans... collect your cans and experiment.
I also have a computer power supply fan.

2. Using a small, sharp, but not favorite knife I cut a hole in the bottom of the tomato can, slightly smaller than the pineapple can.

** Be careful, both the Knife and the edges of the can are sharp!!**

After cutting the hole use the back of the knife blade to smooth the cut edge of the can. be sure there are no pointy bits or splits.

3. The pineapple can needs to fit tightly inside the tomato can. To do this hole the pineapple can at about 45deg, push it into the hole in the tomato can and rotate it to push down the cut edge of the tomato can. as the hole gets larger the pineapple can will start to fit in the hole. be careful not to push the pineapple can in at 45deg as this will split the tomato can.

4. Place the pineapple can in the hole, hold it in place and give it a good smack with a heavy, but fairly soft object, I find a size 9 hiking shoe works well.

5. If the shoe does the job you should get something like this... the pineapple can should fit snugly in the tomato can and should rest in the beveled edge made by rotating the two cans together.

6. Holes need to be drilled to direct the air flow from the outer chamber into the inner chamber. I still haven't figured out the best location for the holed, or the best ratio of holes at the top to holes at the bottom. I tested this stove and I think there are two many holes at the bottom as the fuel burned too fast and I don't think all the gasses were burned.

7. Next I used the 35mm film can to make a base/fan housing. Find the center of the lid, place it on the bottom and drill a hole through both. I used a short piece of copper water pipe as a rivet by placing it through the hole and hammering it flat to fix the lid to the bottom of the can.

8. Using a hole saw and a drill cut some holes through the up-turned lid into the bottom of the up-turned can. You could use a knife or rotary tool to cut holes if you don't have a hole saw. Just make sure that there is plenty holes for the air to move through.

9. Now to install the fan. For this fan to fit well I had to cut off the corner tabs on the top side of the fan. Be sure to note the direction of rotation - this type of fan is designed to push air in one direction only, it can't be reversed by changing the polarity.

10. Mark where the corners of the fan will meet the sides of the can. Use a pair of pliers to make corners for the corners of the fan to fit into. Sorry for the poor quality of this image.

11. Here you can see the fan fitted into the film can. It can take a bit of manipulation of the can to get the fan in, but once in it fits well.

12. Cut slits into the rim of the film can to give tabs that can be folded down, holding the fan in place and allowing air to flow to the fan. This also makes the legs for the base.

13. Here it is, the stove fully assembled. The tomato can sits nicely inside the film can. I haven't bothered making it air tight. I did add some tape on the join between the film can and lid.

14. All the stove needs now it a pot stand. This could be as simple as a pair of nails placed over the top all it needs to do is allow the air/fire to escape pot and the top of the stove (you don't want to plug the stove with your kettle). This pot stand was made out of the top of a bean can, the tabs fold down at about 45 degrees. It is stronger that it looks, it will easily support a pot containing 2l of water.

15. Here it is in action. You can see it is flaming a lot. I am working on a modification to reduce this flaming as it wastes heat.

Here the fan is running of a 12v battery charger. The idea is that it can be run off a small battery pack consisting of 10 AAA. alternatively it could be run from a small solar panel, or a crank generator.

Future plans...
*I hope to figure out, by experimentation, the best layout of holed for optimal combustion and burning time.
*I also need to control the flaming.
*I would like to run this without external power, but all I can think of at present is some sort of turbo system and I think that might be a bit complicated to build out of cans.


Joc said...

If I tried to make one It would not work, seem a lot of effot

I am thinking of getting a Fire-Spout
has any one used one

Tom said...

That looks like a neat little rig, I like how it packs down.

This differs from my stove in that it is not a gasifier stove, it is more like a fire in a box, which is a simpler design that I am sure works great. I have a tendency to find the most complex solution to simple problems. What I am trying to build is a wood burning stove that gives heat like a gas burning camp stove. I am not quite there yet, but I have a few ideas I am working on. I'll post them once I finish this article.