Thoughts on a wood stove which leaves pots clean/ peanut woodgas Magic Stove Video 1

I am hopeful that this is the solution to the quest for a simple blue flame natural draft TLUD camping/hiking woodgas stove that does not blacken pots.

What's different:
- bigger secondary air holes but not too big
- some height but not too much height between the secondary air holes and the top of the stove
- smaller primary air holes on the bottom surface, but not too small
- updraft flow resistance provided by the size, quantity and quality of hard wood pellets allows the pellets to pyrolysize at the required rate for the stove to burn a blue flame

Further experiments showed the concentrator ring causes blackening of the bottom of the pot. I don't use the ring anymore.

Additional Thoughts:
- observation from my other wood gas stoves is that when the yellow flame hits the bottom of a pot containing cold water, the pot will blacken
- hypothesis: flame venting above the top edge of a natural draft wood gas stove will turn yellow and/or give off smoke
- design goal: maximizing percentage occupation of the blue flame within the burn chamber
- turbulent air flow will lead to more random instances of small puffs of smoke leaving the stove which, over time, blackens the pot. The alternative laminar flow design is preferred.
- too much updraft above secondary air holes will allow too much air to enter the stove and increase amount of yellow flame exiting above the stove. To prevent this, minimize the height of the chimney above the secondary airhole but maintain the amount required to allow the blue flame to burn off all smoke
- if the relatative combustible heat content of the smoke to the volume of the rising gas flow is low then it will be harder to meet goal. Maybe keeping the fuel and smoke cool is one solution because cooler smoke should be denser and hence have higher heat content.
- the diameter of the stove should match the size of the pot. Whatever the size of the pot, if fill 3/4 full, the content should boil in 5 to 10 minutes for fast boil then the stove should flame out without smoke. For a stove designed for slow simmering, the stove should allow a boiling pot of water to maintain a slight boil for at least 40 minutes.

Stove dimensions:
Peanut can - from dollar store - height 70mm diameter 85mm. 8 holes 3mm.17 mm from edge. Bottom of can has an edge of 3mm. A 19oz vegetable can has the same diameter.
RIng cylinder - height 60mm - top diameter 89mm with curled edge. bottom diameter 87mm straight cut. 7 holes 16 mm diameter, 33mm apart centre to centre. Height from centre to top edge is 31.5mm. I am guessing if the #holes is odd then the secondary air will flows better.
Combined measurement of peanut can with added ring cylinder height 118mm,
Top plate - diameter 97mm, hole diameter 44mm.

Space below the air holes is part of the combustion chamber. Based on 3 burns I would guess the optimal for blue flame is around 32mm +/- 5mm to the bottom of the air holes. If using fuel other than pellets, perhaps a flame arrestor screen could be used to maintain this optimal distance.

Extra holes needed to increase pyrolysis at the bottom outer edge near the end of the burn to reduce smoke at flame out.

Category:

Science & Technology

Tags:

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• TLUD
• woodgas
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• stove

[wheelnutt]

@jw934 Hi again, like I said in my first comment to you, Id be very impressed if youd get no soot with wood. Major manufacturers struggle with that even when using refractory insulations, fans, microprocessors etc. Good luck with experiments

[jw934]

@wheelnutt For a wood stick stove that does not leave soot and is 6-8 in. tall, I need to have low updraft from primary air holes. One problem is sustaining the flame after the alcohol burned off and the burning sticks not transfer enough heat downwards. To overcome that I will need to preheat the fuel sticks, perhaps over a small fire like the way you heat the charcoal to threshold temp. Perhaps a grill bucket of stick cut to dowel size. If it works I might use that for camping. Would you?

[wheelnutt]

@jw934 Yes the briquetes are garbage. I make my own from oak ,ash or best of all willow, thats the one for gunpowder:-)

[jw934]

@wheelnutt I do appreciate your insight and experience on charcoal. Last year I tried it 3 times and give up because of the smoke. Perhaps it was because I used charcoal briquettes which are tightly compressed mixture of charcoal and sand. I'll go buy a bag of real charcoal and give it a go. I am sure it will work just as you described. Thanks.

[wheelnutt]

@jw934 I have lit hundreds of charcoal fires. You just place a few small pieces on the sticks first so as not to smother the kindling. When that is alight more charcoal can be added. I cant believe I have to explain how to burn charcoal, its very simple, ave a go. Charcoal is like your pellets but with the crap taken out of them.

[jw934]

@wheelnutt When the charcoal is placed on top of the lit sticks, lots of smoke would be generated since the charcoal is cold and will extinguish the flame. Smoke will only stop once all the sticks have turned to charcoal. To prevent that smoke, you could start with a bigger fire - one that is significantly greater than the volume of charcoal. Would you agree? Could you tell me if you are speaking from experience?

[wheelnutt]

@jw934 The way to use charcoal is to put some sticks in the can, light them then put in some charcoal. It burns clean and hot for a given mass of fuel because the crappy tars and creosote is allready distilled out of it.

[jw934]

@wheelnutt I should have said that the sticks I picked up from beside my house filled to the same level as that of the pellets in my stove in the way I packed it weighed only 30% as much as the stove filled to the same level with pellets. But I would have thought you could have figured out what I meant.

I don't know of a way to use charcoal to provide adequate performance with the typical hiking water boil test. Assuming you don't either, I don't know where are you going with this suggestion.

[wheelnutt]

@jw934 How can you say Sticks are only 30% the density of pellets. It depends what wood the sticks are, balsa or ebony or anywhere in between, and their moisture content.

Try charcoal, that will have a higher calorific value than pellets and burn cleaner.

[jw934]

@wheelnutt My stove takes 65g of pellets to boil 1 litre of water (or 35g for 500ml). It is probably comparable to hexane or liquid fuels on short trips. Pellets are eco friendly and not restricted for air travel.

Sticks are only 30% the density of pellets. This means I will need a stove at least 3 times the size.

Sticks are usually moist unless you are hiking in a desert. I think what might work is to use a small stove to dry and heat the sticks then use the sticks to cook. Will try.