Bushwalk Australia

I’m trying to get my head around what features make a gasifier twig stove work.

I was quite happy with my previous twig stove attempt, made from a cut down ikea cutlery holder - base removed, and sliced vertically, then held in a circle by bits of wire, which left a 4-5cm vertical opening in the side to poke twigs in. I wanted it to fit inside my billy, hence the cuts. The downside was that everything got covered in soot, and it needed reloading with twigs during the burn to boil a billy of water.

My understanding of gasifier twig stoves is that they are double walled. My question relates to the positioning of the holes in the walls….I’m presuming the outer wall has holes around the bottom to allow air in, and that’s it. And the inner has holes at a similar level to the outer at the bottom to allow air in. The question is, do I then put 1 or 2 rows of holes further up the inner to get the gasifier effect? I’m presuming one row near the top is needed, but, does another row halfway up the inner add anything further?

Also, does the inner need to extend further up than the outer? I’m thinking of making one out of old tin cans for practice, and then maybe aluminium flashing/thin brass sheet for the end product…

Any thoughts would be appreciated.

Will try to upload 2 photos relevant to my post, but internet is useless where I am atm.

And, yes, I can then add a battery operated fan to improve things further!

Andrew

I believe you want the inner wall holes only along the top, as you want the air drawn in from the bottom outside to preheat / draw up the gap before coming out above the burn chamber. There's a picture of the 'top lit up draft' here: https://energypedia.info/wiki/Gasifier_Stoves

I bought a cheap one from aliexpress many years ago and it works surprisingly well, I imagine you'd only have to scale the air draw height and cross sectional size in relation to the burn chamber to make sure you were getting the right amount of air. The aliexpress one burns with a very defined secondary gas burn at the top, you can see the flames swirling with the air draw. I might be able to find mine and take some measurements. I've been meaning to build a scaled up version in like a 10 or 20 litre metal bucket size for car camping.

For camping they seem kind of impractical as they need constant feeding with small timber to keep burning, which would be a bit of work if you wanted to cook on.

Thanks for that. I really only boil water on it, so not fussed about feeding more twigs in.

A

Done some more reading, and now have a better idea of what I’m aiming for. I need a design that will fit in my squat Evernew 1l billy, and it seems that gasifiers are better if taller, so will look at a stackable version to get the height. Will be searching supermarket for things in cans of useful proportion for this!

Heinz stew!

Hi andrewa, I've got one I never use and happy to post out to you if you want, just PM me your address. I know you want to make your own, but I think it would be good to see how one works to help in designing your own. The hardest part about the construction, is the need to seal the top join where the outer shell joins the inner. Unless you can weld, you'll need to crimp and seal the join.

The reason I don't walk with one is because they aren't particularly light, due the fact they are double walled metal. Plus you need dry twigs, which can be hard to find when it's wet/raining.

While I don't use one, they are an amazing bit of kit.
You only need little twigs around 1-3mm thick which you'll find at any camp spot, no need to walk distance to find wood.
Once the gasifier starts working, which doesn't take long, they give off extreme amounts of heat, problematic cooking food but unreal for boiling water.
Bushcrafting or for longer walks in dry country, they're definitely worth considering and a lot fun to use.

Pm sent. Thank you

andrewa wrote:I’m trying to get my head around what features make a gasifier twig stove work.

I was quite happy with my previous twig stove attempt, made from a cut down ikea cutlery holder - base removed, and sliced vertically, then held in a circle by bits of wire, which left a 4-5cm vertical opening in the side to poke twigs in. I wanted it to fit inside my billy, hence the cuts. The downside was that everything got covered in soot, and it needed reloading with twigs during the burn to boil a billy of water.

My understanding of gasifier twig stoves is that they are double walled. My question relates to the positioning of the holes in the walls….I’m presuming the outer wall has holes around the bottom to allow air in, and that’s it. And the inner has holes at a similar level to the outer at the bottom to allow air in. The question is, do I then put 1 or 2 rows of holes further up the inner to get the gasifier effect? I’m presuming one row near the top is needed, but, does another row halfway up the inner add anything further?

Also, does the inner need to extend further up than the outer? I’m thinking of making one out of old tin cans for practice, and then maybe aluminium flashing/thin brass sheet for the end product…

Any thoughts would be appreciated.

Will try to upload 2 photos relevant to my post, but internet is useless where I am atm.

And, yes, I can then add a battery operated fan to improve things further!

Andrew

Hi Andew, Do I have your stove design correct in my head? Is it an open-ended cylinder with a vertical slot in the side? If so, your stove design sounds as though it is just ideal once you add the blower to it. It will have powerful heat, no smoke with dry sticks, a little start-up smoke with wet wood and your fuel sticks can be a meter long if needed, but don't trip on the sticks in the darkness and spill your coffee.

To be able to burn wet wood (even in the rain) is very good. On the other hand, simmering and gentle cooking and slow water heating can be done with dry sticks without the fan running for most of the time. With dry sticks we cooked for two and sterilized water for four people using only one 18650 Lithium-ion battery for a week of a three-week walk. Also, a bed of residual charcoal in the stove is excellent for simmering with the fan switched off.

The stove can be as light as a feather if made of roll up titanium foil or as cheap as chips from any modified tin can. This 35g 'poor student stove' (Made from a tuna tin) is an example:


I have found that having a bottom to the stove is most convenient as it means that the stove can be picked up with pot grippers to move it to a more convenient place or to empty it sensitively to pack it up quickly. It also makes it easy to point the stove optimally into the wind when cooking without the fan running.

I have many simple design options including two pot stoves on my website and these include stoves without a stove body, just a hole in the ground or a few rocks. They all burn wet wood with little smoke and the fuel stick amount and preparation are absolutely minimal.
https://timtinker.com/blower-stoves-gallery-index/

It gets away from carrying the weight and bulk of a double-skin true gasifier stove and it is still a gasifier stove even if it has no stove body that you carry. I hope this helps and encourages you to take the next step.

Tim

Very late to the thread, just seen it
I will post some details, instructions and photos to show you how to make a cheap and light gasifying stove
See https://bushwalk.com/forum/viewtopic.php?f=53&t=41081

The design is an evolution of one I saw on YT with adjustments through trial and testing
I actually used to make these and give them away to people - they cost about $6 for the cans
They are light and actually as light (and often lighter) than most professional ones - it’s all in choosing the right cans (trial and testing - I can help short circuit this )
The trick is to find cans with thinnest walls, and the right sizes that maximise fire box volume - plus the right height to diameter ratio (again, trial and testing and theory)
The downside is, being tin, they rust after use (you carry them in a plastic freezer bag anyway to avoid gunk on your gear just like expensive ones, and they last at least a season, and unlike my expensive Ti ones I do not clean them ever, which kinda appeals to me). Not really a throw away, more like a DIY reuse of otherwise landfill material and after finally killing them through extensive use (at zero manufacturing cost !!!) they rust back to core ferrous materials much more quickly in landfill.