Monday, 25 May 2009

Woodgas camp stove demo

You may have noticed in some recent posts that we've got a fancy new stove to use at the wood - well, here's a demo video of how it works. (Still pictures and a text explanation are below)



It's a WoodGas CampStove XL. What it does is "gasify" the wood, burning the gas produced in an efficient manner right under the cooking pot. Basically there's a cylinder inside it that you fill with small sticks:
If you look carefully you'll see some small holes at the base of this cylinder - these allow in a small amount of air to gasify the wood. Gasification means allowing the wood to partially burn, resulting in a mixture of gases, including hydrogen, methane and carbon monoxide (so don't use it indoors). These are all flammable gases, and as they rise up the inside of the stove they meet with more air injected through a ring of holes at the top of it:
The gas mixes with this additional air and burns. Right above it sits your cooking pot, resting on a simple but effective pot stand:
The air is drawn in through holes around the the outside of the base of the stove, which encloses a small fan. In the picture below you can see the two power sockets for the fan (high and low speed), and the air inlet holes:
The battery pack contains two AA rechargeable batteries (I reckon my 3200mAh batteries will run it for over 15 hours), and you plug it into the high or low speed socket depending on how much heat you want out of the stove:

Mike

8 comments:

Anonymous said...

Your missing the whole point of the gasifer design. You are supposed to light it from the bottom because the gassification process is optimum under LOW OXYGEN conditions. Lighting from the top you are just fanning the wood with the blower and decreasing the stove maximum efficiency significantly.

What you want to do is get a good ember going and drop it in the bottom and then pile your wood on top of it. Leave the blower on high for about a minute until the ember is good and hot then reduce the fan to low so there is just enough O2 to keep the coal going and push move the C0 and H2 to the upper vents where they can combust.

Mike Pepler said...

Actually, I do know about gasifier design, that the stove is based on an updraft gasifier, and therefore should be burning at the bottom (in theory).

However, the instructions that came with it say to light it from the top, so in the interest of doing a demo of the stove as the manufacturer intends it to be used, this is what I did.

In practice it actually works very well, and after a few minutes getting going, where the secondary airflow IS just fanning the flames, the wood lower down starts gasifying, and you can see the woodgas burning as it mixes with the jets of secondary air.

I think the important difference is that this isn't a gasifier as such, but a stove (that happens to use gasification), so the design and use may have to be a bit different.

Having said that, I've been meaning to try lighting it at the bottom and then adding fuel, but haven't got round to it yet. When I eventually do (perhaps in a couple of months), I'll make a video and put it on this blog.

Cheers, Mike

Anonymous said...

Mike I think the first guy may be wrong about lighting it from the bottom. I believe this design is called a inverted downdraft gasifier and lighting it from the top is correct, but when adding more wood ideally it should be added to the bottom.

Mike Pepler said...

Adding wood at the bottom might be a bit tricky!

I think you're right about it being an inverted downdraught - it's a counter-intuitive name though, isn't it! :-)

Mike

jerome said...

Great pic you have there.
I'm planning to built one of these. What's the size and number of the inner holes, at the top and at the bottom?

Mike Pepler said...

@Jerome. I've not got one with me right now, but I think there's about 10 holes at the bottom, about 2mm diameter. The holes at the top are about 4mm, and probably 25-30 of them.

Cheers, Mike

jerome said...

Thanks a lot Mike!
Also, I concur about the lighting at the top. This kind of stove are meant to be fill with wood and burn from the top down. You can always had a few pieces of wood at as time to prolong the burning.
For the science behind it; Here's a link to a presentation by the designer, Tom Reed.
http://www.vrac.iastate.edu/ethos/ethos05/proceedings2004/presentations/reeddasandersongasification.pdf

Daniel Rustad said...

This is a top load up draft stove (TLUD)and they are designed to burn top down. Theoretically, if you were to burn it from the bottom you would be allowing the wood gas to escape out the top without burning it and essentially lose the gasifier effect. In other gasification processes the gas is captured to use later. This design uses the wood gas immediately after it is available.