Tinkering again

[swright81076]

I have decided that I want to tinker more with stoves, I already have a box full of pressurized side jet alcohol can stoves I've made, these work really well, so long as you have meths in your kit. So this time I wanted something that could burn something that is easily accessible. Wood.
I've made several hobo stoves in the past, but this time wanted a wood gas stove. I've seen various ones on YouTube again made from tin cans, and seen the wild stoves ones, but I wanted something that looked.... elegant, and after reading several articles on inverted downdraft gasifiers. I came up with a design which is one piece, portable, and fits in a billy.

I ended up with a stainless steel double walled vessel or 6, and have made my prototype (5 vessels left to play with).

There are a series of air holes in the outer base and in the inner base too, with air inlet holes around the side. The gas jets are an inch down the inner lip.

I didn't have a lot of time to test it out, but added a little kindling and used some biomass pellets. (Our house uses a biomass boiler for heating and hot water so I have a plentiful supply).
One it ignited it burned really well, and once the wood gas kicked in it was a joy to watch. Like I say I didn't have time to use more than a hand full of pellets so didn't do a burn time or boil time, but I'll update later.

Here are a couple of pictures and a YouTube video.

http://www.youtube.com/watch?v=SCJwaZ3LaMc

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[spandit]

How did you drill the internal holes? I was thinking of doing something similar with an old insulated mug

 

[swright81076]

the internal holes are only about an inch down, so it wasn't too bad. I put masking tape an inch down, marked the holes 10mm apart, and used a centre punch and a good blow to get a divot. then a 3mm hss hex bit, in the end of a screwdriver bit extension so i could get a decent angle. the holes in the base were the hardest, I had to use a pilot, then build up gradually to 12mm.

 

[spandit]

I was thinking of cutting a large hole in the base of mine and attaching a small fan to force the air up and out of the holes. I'm intending in putting a lever in the holes at the top and angling them down, if that makes any sense

 

[swright81076]

My plan was to use a fan but the way mine is made, the bottom gets quite hot so not sure how long the fan would last.
When you say levering down, I would say its not necessary from what I've seen of mine. The flames jet up anyway, plus I noticed a layer of smoke above the biomass, so I'm gonna make air holes midway down the inner chamber, this will improve the gasification. I'll have to cut small horizontal slits with a dremel as theres now way you could drill holes there.



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[ged]

That looks great! Where did the double-walled vessel come from?

 

[swright81076]

Its actually a wine cooler. Looked everywhere for something that would do the job. Ended up at homebase, they are half price at £6.99, so bought them all from castleford store.

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[Biker]

Mental note to self - "visit homebase when in the UK next Thursday."

Been faffing about with tin cans trying some woodgas stoves but that has to be the best looking one I've yet seen. I like your way of thinking about it being "elegant" ... a man after my own heart with that sort of idea in mind.

Really like that a lot. I'm going to be following your progress on the various prototypes before even touching my homebase wine cooler so I don't bollox it up.

Just wondering if the wood gas would burn better if the were allowed to premix with the air so you get a blue flame, or am I talking out of my ar$e? Think of the way a bunsen burner works. If you close the air hole at the base the gas burns yellow and wavey, but open that air hole and allow the air into the pipe to mix with the gas and bingo you get a blue flame jet, the same amount of fuel is being burnt, just more efficiently. Anyway tis just a thought. I'll leave that to better minds than mine to dwell upon.

 

[swright81076]

Thank you. I do like things to work and look nice. I know exactly what you mean about the blue flame, I'm hoping the slots I'm gonna cut half way down the inner chamber should help with the mixing and air flow.
I've been umming and arghing about the blue flame. I'm pretty sure when the mix is right, there's an awful lot of carbon monoxide released. Not too worried as the stove will be outdoors. But. To get the blue efficient flame I'd need another inverted container inside the mouth as a flame wick forcing gas into the outer chamber. I might use a stainless insulated mug to experiment.

This picture should show what I'm trying to get at.

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[spandit]

Right, made a similar stove, fan assisted. I'm sure the one I'd borrowed before (http://www.woodgascampstove.com/) only had air holes inside at the top so all the air was sucked in the bottom, passed up the sides & out through the top holes - yours seems to have lower air holes too, or am I reading it wrong?

Anyway, it burnt fairly well. Sides were too hot to touch whilst bottom, with fan attached, remained quite cool. The inner holes were punched through with a thin centre punch (which made things much easier) then drilled to 3mm. There's a nice vortex effect once it's going, which didn't come off that well in the video (to come) - I could relight the gas with a lit spill when it went out so it works OK. Need to make a pan support for some test boils

 

[swright81076]

The lower air holes you are talking about are in the diagram (I think), I haven't done these yet. Still experimenting as it is at the moment with different fuels.

So. I tested it a few times today. First with small pieces of hard and softwood,about the size of your little finger. This went really well, nice even burn, I filled it half way. Lots of jets and quite a low flame height from the burning wood. Run time approx 38 minutes. Boil time 500ml a shade under 3:20 minutes.

Same test with larger pieces again filled half way. Roughly size of a decent sausage. Run time 19 minutes boil time 4:30

Third test with wood pellets. These were a real swine to get going, eventually they began burning with very low flame. No smoke, it was just swirling above the flames. I was about to leave this, when the jets fired. All jets burning with very little flames from the pellets. Boil time again same as small pieces at about 3:20, burn time. Well over 40 minutes, until jets went out. (These could be relit by a flame) there were still smouldering charcoal in the base, and after dropping a handful of chopped pine, the stove instantly sprang back to life.

So far the pellets were the best, however because its so damn difficult to light them I'd say small pieces of wood are the way to go, so far.

Tomorrow I'll experiment with more air holes in the side to see if I can get it more efficient, maybe a blue flame, doubtful it'll happen but I'm more than chuffed with burn time and boil time.

This burn time can be increased just by adding more fuel (obviously). Also after every experiment , except large pieces, nothing was left in base but white ash.

I shall update again once I've tried it with side air holes.

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[Chiseller]

Good elth, tip my hat to yer Capn

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[swright81076]

Right then. Firstly I think the latest modifications to this stove deserve a thread of its own, but for the time being I'm updating this one.
After countless changes to the air intake holes I believe I have come up with the perfect woodgas stove bar none.

The modifications are. 1 inch of celotex foiled backed insulation then silver foil covered plaster board on top of this in the base of the inner chamber. This seals the air holes in the base and creates insulation and reflects the heat upwards to cooking area. A row of holes drilled through the side, about 10mm above this layer of insulation. (I drilled through from outside but covers holes on outside with aluminium tape) the base has been cut away for a 12v CPU fan to be fitted. (Fan blows air into the burning fuel and forces air and gas out of top jets) the increase in power is astonishing.
Bear in mind this is still a prototype. The final version will have fan installed within the base, along with feet on bottom for air flow into fan. I also need to find better insulation for the base. I will also fit a thermoelectric generator in the base of combustion chamber which will power the fan optimally, alleviating the need for external power.
If any of you guys have any suggestions for insulation I am all ears.
Here's a couple of pictures and a YouTube video.
Oh, one last thing. Boil test. 500ml cold water in uncovered container. Just under 2 minutes.

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https://www.youtube.com/watch?v=HFaoRVkHj9E&feature=youtube_gdata_player

 

[swright81076]

Once I get a final version made I think I might whack it on evil bay see what it does.

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[swright81076]

Oh I forgot thanks to spandit. I put a nail in top jets and angled downwards, also did same with bottom jets, hopefully create a fire vortex in base. This worked a treat. Cheers for the tip.

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[Dannytsg]

Some very good craftsmanship

 

[swright81076]

Thank you. The final version should look more "finished"

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[spandit]

Glad my idea worked. I'm thinking about angling mine so they swirl, which would be cool

Tried running the CPU fan from a wind-up mp3 player/phone charger - only worked when the handle was being turned. When I test ran mine it was hooked up to a 12V battery charger but it's not portable...

 

[swright81076]

It swirls anyway mate,

you could fit pipes to the jets to truly control them but then that's far too over engineered and all the while I'm considering the weight.
Think I've solved the insulation issue. A disc of aluminium or steel on top of a layer of rock wool or ceramic wool.

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[Chiseller]

Looking fierce :thumbup: put me down for one ;-), can you get a simmer?

...... Failed dogger and alleged bigot!