Woodgas Stove

What the hell you talking about?

Do you really want to know?

Decomposing wood gives of a flammable gas.

Not as whacky as HHO, but..........................................

I vaguely remember an elementary school experiment doing something like that, but if I remember right, it took quiet a few wood chips and a hot flame under the can to produce enough flammable gas to ignite and produce a flame. And to use a 20lb propane tank to hold the burner too?

In these the flame burns from the top down. As the wood is heated the gases are released and come out of orrifices around the top of the burn area called jets. In use they resemble a natural gas stove and burn very efficiently.

You are doing a very poor job of explaining the situation. Don't worry, this is quite common. Instead of spilling your thoughts as quickly as you can, try this:

Put yourself in the position of hearer while you are speaking. You have never seen this contraption. Without ever having seen your setup, does what you are saying make sense to you? If not, edit the post until it does.

In these times of great technological wonders, you can use a cell phone or digital camera to take photographs of what you are talking about, and insert the photos into your post.

Soup-can wood-gas stove? What!?

Half a helium tank? Cut in half how?

Jets? From what?

Heat exchanger? What type? Configuration? MOC?

Do you see why pictures, or at least sketches, are a requirement here?

It makes sense to anyone with an understanding of woodgas stoves and that was my target audience!

If you look around enough, you can probably find articles and pictures of cars that used heated wood chips to generate combustible gas. They typically involve a funky tank toward the rear.

So why not just burn the wood the old fashioned and simple way?

Over the years I have talked with enough people and read enough stories about other people who tried to make burning wood as complicated as they can in order to gain some apparent efficiency or something or other out of it only to at some point only find out that to do so ends up being a lot of hard work and fuss for whe ends up being very little gain.

Thanks, tcm!

Good application of experience, though it will fall on deaf ears if OP doesn't return.

GA

Perhaps but l'm not content to rely on stories of others who have failed at something that I know works! I've simply ran into a snag related to the units size.

That's what they all said and believed. Still didn't happen.

Personally I see no point in the concept when it gets to a point that the only way it will work is with specific woods preconditioned to very specific moisture/age/grain/particle size and so on tolerances which makes the fuel source itself less than simple cheap and easy to produce.

As for myself about 12 - 13 years ago I went the other way and built a incinerator type boiler system that rather than being highly fussy about its fuel source and tolerances literally burns anything that can hold a flame ranging from green wood of any variety to rotten punky moldy junk, wood pallets, garbage, cardboard, old hay, tires, coal of any grade, railroad ties, plastics, and for the last 4 years now used oils of any grade too.

Sure it might not be 99% efficient but really when I can use anything that's combustible and that does not need to be processed down to any form other than small and light enough for me to physically handle for fuel my options to use most anything combustable I can get for free and handle easily more than makeup for it.

In my smaller camp stove I have burned everything from used oil filter cartridges to leaves and sticks and everything else that would burn with no processing other than to cram it into the stove and it works perfectly every time so I'm stumped as to why scaling it up should present a problem and yet it seems to. The fire burns longer and hotter than if it was just thrown into a pile and burned but it acts more like a rocket stove than a gasifier.

..."gain some apparent efficiency or something or other out of it only to at some point only find out that to do so ends up being a lot of hard work and fuss for whe what ends up being very little no gain". Editorial remarks inserted for clarity.

The only reason to pyrolyze wood for the production of combustible gases (possibly by adding small amounts of steam at high temperature also), is to provide a gaseous fuel to an engine downstream of the device. On the other hand, wood meal (or even large chunks) can be burned and with a properly designed heat exchange produce useful temperatures at the inlet of a gas turbine. This idea cannot work (for long)with an internal combustion engine, hence the need for gaseous (or liquid) fuel.

I don't agree with some points, simply wrongly orientated I feel.

You said "The only reason to pyrolyze wood for the production of combustible gases (possibly by adding small amounts of steam at high temperature also), is to provide a gaseous fuel to an engine downstream of the device."

That is simply wrong, of course you can go this way, but there are simpler methods as well.

I agree that to achieve a wood burn really well, usually needs a complicated system, with computer control, fans and and and is needed. My wood Pellets stove for one.

But actually making a small fire so efficient so as to basically not emit CO when burning wood (thats what it mostly burns in the gas produced) and to be basically CO2 neutral, without needing complex control mechanisms, is actually a very nice achievement I find, many achieve it, thousands of DIYers......

Making it portable is even finer....many do that as well....

You said "This idea cannot work (for long)with an internal combustion engine, hence the need for gaseous (or liquid) fuel."

Look on the internet as to how in WW2 (and before), many countries had cars, buses and even locos running on wood gas, because there was a lack of fuels in liquid forms.

They ran for years and years.

Some are STILL running.

Some have been built recently.

Some are in the Himalayas for example....

Look here:-

Wood+Gas+Powered+Cars

I saw a German guy here in our village (visiting) a few years ago, with a big old 3 liter Mercedes car, with a small trailer and a gasification unit on it. He had been using it for over 20 years.....it simply ran and ran, provided you threw wood in occasionally...... No electronics, no electrics and the Mercedes ran beautifully once the fire was producing. he used a tiny amount of petrol to run the engine to "get the fire going enough".....

When fossil fuels run out, such conversions will come back........let us make ourselves "clever" today......

Maybe you meant to say something different?

Uh......I believe that's exactly what James said.....you can inject fuel gas into an internal combustion engine.....but not SOLID FUEL for very long. Long dissertation just to repeat what James Stewart just said............

You could be right, but for clarity, please explain this comment:-

On the other hand, wood meal (or even large chunks) can be burned and with a properly designed heat exchange produce useful temperatures at the inlet of a gas turbine. This idea cannot work (for long)with an internal combustion engine, hence the need for gaseous (or liquid) fuel.

I cannot make sense from it, hopefully you can!

Thanks in advance.

No one in their right mind would attempt to inject wood meal into burner can of gas turbine, but gas from wood pyrolysis is probably OK and is done. Same thing with ICE, one could inject the wood gas into the intake.

On the other hand, wood pyrolysis could be coupled with compressed air heat exchange upstream of the burner cans on gas turbine to get more of the BTU value overall.

We are getting there slowly, BUT:-

On the other hand, wood pyrolysis could be coupled with compressed air heat exchange upstream of the burner cans on gas turbine to get more of the BTU value overall.

Did you not just mean wood gas instead of wood pyrolysis? Or would you be somehow heating the biomass on/in/near to the turbine to produce the gas?

In most "engine" situations, you have the pyrolysis-gasification/filtering, separate from the engine itself....perhaps you can paint the picture a bit better please!

Thanks in advance.

I think I got carried away in the moment. What I meant was by using an inter-cooler on the gas turbine compressor (if staged), one could preheat some of the air normally routed to wood pyrolysis, to attempt to gain more yield of gas, support faster pyrolysis and combustion of the wood fuel. The wood gas product from pyrolysis would have to be under pressure in order to admit this to the GT burner cans. I have not quite figured this part out. I suppose the wood gas reactor would have to be a special design, with advanced eductors drawing the wood gas into a compressed air stream. Sounds pretty hazardous based on temperatures, since autoignition needs to be avoided. I suspect this would be a more touchy operation than simply admitting preheated natural gas to the burners.

You'll see there are several video's on construction and operation of wood gas stoves here.....

https://www.youtube.com/watch?v=5ZPvLpexXFw

Budget-sensitive rednecks probably can't afford these gaudy examples, unless their stills are efficient.

As I said I can build a smaller scale one and it works perfectly! The larger size however seems to pose a challenge however as it does not generate the same type of combustion.

Well without pictures and detailed drawings with accurate measurements and detailed info about materials used, this is pretty much just a guessing game.....OK I'll guess it has something to do with the airflow....or lack of control of airflow...or both....

Exactly! Woodgas Can Stove - Instructables

It's like the one lyn's posting only difference is I'm using a much larger scale. A picture of it would look almost identical. In the smaller scale it works exactly as it should however in the 30 gallon drum size it reacts differntly! I'm going to cut the drum down in height as I'm thinking it may not be creating enough vacuum to draw the woodgas from the bottom of the burner and back up to the jets. I can see the flames and smoke being drawn downwards. Mine has the holes in the bottom of burn area, putting the holes in the side like it shows in the instructables proved less than satisfactory.

Ok, thank you! That makes sense to me now.

Your larger design may need to be annular. This keeps the distance to the centre of the wood small. Also you could look at multiple tubes/burners. It would sort of look like a steam engine boiler.

Like others i don't see what you see. I can only see an overall LOSS of efficiency. Gas producers were used during the war to power cars because petrol was rationed. You couldn't burn wood in the IC engine but you could use wood gas. Despite there being lots of these gas producers lying around after the war none were pressed into service heating homes.

Homework for you. Find out how these gas producers worked and see if you can work out for yourself why they didn't get used for the sort of purpose you are looking at.

Jim

From all I have read the units of which you mention fell out of favor after gasoline became availale again there were also relatively large. Also I'd think storage of the gas produced could present a whe new problem to figure out as the woodgas was used as it was produced no storage was needed however in home heating the gas couldn't burn non stop and I belive there would need to be some sort of pump involved, the engine would have created vacuum to pull fuel in, in home heating that could be an issue.

RE: WW II gasifier vehicles. You Tube has at least 2 first hand videos on the subject. One is a German truck, converted for the war and still running, the second is Australian; a pickup (ute) made by a outback settler. Both burn any type of wood and/or other soi\lid fuel. The guy in OZ has a series on what he did and also cd's.

I find that an interesting subject and may try my hand at building one someday. Thank you!

The scale up answer then becomes one of modular air flow chambers, where the diameter of each chamber within the gasifier section is right, and the induced gas/air flow of each is also right, this means each (round ??) section must transfer gas to the annular space of the outer diameter hull. The jets have to be the same size, maybe a bit less, but there again, no one seems to have worked out the flow velocities, and how to induce the off-gases most efficiently from various posted videos on the net. Looking down, I see circles within circles, maybe even with insulation between the inner circles, but there has to be a series of at least a few transfer tubes from each to the periphery.

Could that help?

Take two Ex-Lax and come back tomorrow.

Woodgas Can Stove - Instructables

Clearly most of the replies so far are from members who are not familiar with wood gas stoves. The design allows for re-ignition of un-combusted gas that is entrained within the smoke plume. This makes them typically 8-10 as efficient in converting timber to heat than a camp fire and about 3 times as efficient as clay stoves. As a result of the secondary combustion the smoke plume contains very few particulates and, once full output is establish, almost invisible. A successful design relies on using the heat if the initial combustion to create a forced air draft that is introduced into the exhaust plume just above the primary combustion zone. A mixing chamber of the correct proportions allows the smoke and air to fully combine and a secondary hot blue flame is ignited above the mixing zone.

Some possible problems with your scaled up design. The walls of your primary combustion chamber may not be getting hot enough to create the required convection. Make sure that the fire in the primary combustion zone (PCZ) is evenly distributed. A layer of expanded metal fitted 20mm above the primary combustion air intake (PAI) holes allows air to reach all of the underside of the wood and prevents PAI from blocking. If you can easily lift it out while keeping it horizontal it makes cleaning out easier. The distance between the inner and outer containers may be too large, so the air is not heating enough and moving fast enough to produce an air jet from the secondary air intake (SAI) holes. Without an air jet mixing will be poor and efficiency is much lower. The SAI holes may be too high or too low above the PCZ or they may be too large/too many. The amount of air that passes through the PAI determines the height of the SAI above the PCZ. Attach with a single central bolt a secondary plate with the same hole pattern as the PAI. Rotating this plate by a few degrees partially blocks the PAI holes and gives you control over the air flow. Attach a band drilled with the SAI hole pattern around the area of the SAI holes. By rotating this band slightly the SAI holes become partially blocked and so this air flow can also be controlled. Make your heat exchanger vertically adjustable so that you can position it extract the maximum amount of heat from the stove. Insulate the outside of your outer chamber to improve both convection flow and personnel safety. It should get too hot to touch.

Responding to, "a subject they have no knowledge of" never inhibits many of us here.

Hey, it goes with the territory. Get used to it.

Merry Christmas.

I was going to ignore this but, since most long time, active members easily recognize the difference between someone with "a genuine thirst for knowledge" and someone who is just lazy and wants a quick answer for their homework (or work) assignment, you might want save the rebukes.

Your reference to Tesla or Eddison (it's Edison, by the way) are completely irrelevant. They knew how to find the answers for themselves, a quality that seems to have fallen into disuse since the invention of the internet, and forums like CR4. Tesla or Edison would certainly have used search engines where the material could have at least been validated if they wanted technical help.

Frankly, I thought you were given lots of constructive help, and if your feelings were hurt by any of the answers you received, you may want to search for a kinder, gentler forum and recommend it to those others whom you feel were slighted by some responses given here.

I believe that CR4 is, for the most part, more civil than 99% of the anonymous, public forums available on the internet.

Maybe you just haven't gotten used to it yet.

Because, when a topic is deemed OT by the admins, it is counted as 5.

Anyone who then responds to it is also automatically assessed 5 OT points, as well. It's automatic.

The responder can uncheck the "Yes, this comment is very likely to be considered to be 'off-topic'" and avoid the assessment, unless admin judges it OT, again.

I think.

I have not seen the insulation idea mentioned anywhere else, but I find it to be fairly obvious that you want the gas/air mix to get as hot as possible and to help it force its way upward by convection, sucking more air/gas from the bottom.....

Its also a safety concern for a user....Fiber glass or rock wool should be good.....

Try the insulation idea first before making the gap smaller as it might deliver enough convection on its own, who knows?

Best of luck and again, thanks for the ideas etc...

I do believe you are making a few fundamental errors.

1) The smoke (flame) outlets must be larger than the inlets.

2) The fire must be below the level of the outlets, so that the heat goes into the inner side walls, heating the air there and using convection, force the air to rise and to blow out of the outlets. So a "Taller" stove will burn better to my mind.

3) The larger outlets letting out the heated air and any smoke that EVENTUALLY gets sucked down from the fire inside, which then travels up the sides and is blown across the top of the fire and gets ignited. This will NOT happen if the outlets are smaller than the inlets, though it might happen if they are about the same total area, due to the heating/thinning of the air.

You need to get/achieve a slight vacuum in the side walls somehow, due to convection/chimney effect, hot air rising and jetting across the top of the fire, so that once the walls are hot, hot smoke is sucked downwards from the fire through the holes under the fire and then upwards through the sidewalls, mixed with air sucked in from outside. The direction of the fire is therefore "reversed" and will/should burn downwards in the middle from the top. This why it is SO important to have the inside and outside walls really well sealed together, the second video mentions this as well...

I have to admit I have never made one, so this info is actually gleaned only from several Youtube videos, some of which did not work as wished and it appears to be that they also tried opening up the lower holes to the outside, which did not help.....

If I was making one, I would make a sliding "restrictor" around the lower outside holes, that once the fire had heated the side walls, I could control just how much air was entering those holes, watching the effects on the burning gas and the speed of burning. Too little air through the lower outside walls may consume the wood far faster than you wish....due to too large amount of air being sucked down though the fire.

Also, as you (and the others on YouTube) are looking for wood gas being burnt as a ring of jets at the top, to reduce smoke to a minimum, adjusting the air supply should allow you to "tune" this perfectly.....

This was one of the best videos that I saw:-

Wood Gas Stove 1

and this:-

Wood Gas Stove 2

or this:-

Wood Gas Stove 3

Maybe when the weather is warmer, I will try and also make one (if I don't forget about the idea before then!!)

I hope this helps you further.....

The first video is similar to one that I own and what I modeled my larger version on I've found in the smaller versions I've built that smaller jets result in a longer burn time. I'm sure at some point that may not work due to jets being to smal or other factors I've not yet encountered. My air intake is 1/2" holes roughly 6" apart all along the bottom, the floor of the fire pit is also drilled out to 1/2" and covers the whole area. My jets are now drilled out to 3/8" and I did get some gas to ignite through the jets for awhile today although most of the gas ignited on the top ring of the stove. I will try making a sleeve to fit inside outter barrel and cut down on area to heat in hopes of getting more of a chimney affect, there is currently about a 4" gap between the inner and outter walls. The fire burns from top to bottom as it should but gas production or perhaps flow is insufficient. I like the idea of adjusting air flow and will try that as well as making the jets adjustable. I may well scrap my current prototype and start again with a smaller version and tinker with upsizing a little at a time until I find a size that suits my needs.

A few further thoughts:-

Making the whole construction higher than its width, should make operation better as convection will be improved due to a longer chimney effect.

Wide and short may be more difficult to get working I feel....all the ones I saw on YouTube, were higher than they were wide....

The seal between the two cans at the top must not allow any leaks or efficiency will suffer.

Some simple insulation around the outside, placed above any "side" holes, right up to the top of the sides, should speed up the fire working properly, especially on a cold, windy day, by increasing the convected air/wood gas temperature dramatically....

It might even be good enough to allow the fire to be moved without getting burnt....though not a good idea, unless some danger is noted in the position where it was fired up - too close to a house or a tree for example...... Fireproof gloves should be available, or cool handles.....or both!!

Removing the base of the outer can is a waste of time and effort I feel, though many do it, assuming that you have the intake holes around the bottom of the base on the side. Because when it sits on the ground, the hole in the bottom is mostly closed off anyway....I would leave it on....

Having the base still on is why the BushBuddy can be held on the palm of the hand while in use......

BUT!!! this does mean that the air sucked in at the base must make a rapid 90° change of direction....so it may be a good idea to NOT pierce the sides of the outer can, but to make the holes in the base and of course add some (adjustable) feet to allow the air easily in, so the 90° direction change can be smoother, the higher the feet are.

This means that the air has effectively a straighter path.

If the "gas" holes in the inner can are NOT in the bottom, as many do, but say a cm or two above the bottom, in the sides, also angled upwards as either in the excellent "instructable" or one of the videos (I forget which), so that the gas is partially "aimed" upwards in the wall space, I feel that too could have some possible beneficial effects.

This would also make it easier to add a variable "choke" to the bottom, to control just how much gas is made/burnt and how much outside air is added....

Furthermore, to smooth out the change of direction of the incoming air, some fins, in the space between the inner and outer walls, angled to twist the gas flow upwards slightly, would allow that gas to reach a higher temperature, it having a longer path next to the hot inner wall to pick up heat....

I find this whole article to be very interesting for many here and quite useful as a camping or even garden heater for cool evenings....it would be great if all the interested parties here to all work together so that we end up understanding the "science" of how such a burner is made far better than seems to be the case at this time...whoever is making one it would seem.

My posts are "observed theory", that I would hope to test out myself in the spring time......possibly in stainless steel......

I will continue to follow this blog in the future, thanks to the OP and to all others who have posted as well......

Removing the bottom of the outside can actually helps in ash removal. Same with having the holes in the burner at the bottom help with combustion not to mention if your making one from an old can more than likely the one end will have been opened to remove contents. If the vent holes are on the sides the bottom will fill with ash and choke out the fire eventually. With the holes in burner on the bottom you can give stove a little tap, ashes fall down and you can ad more wood. You can pick up a small unit on ebay and study it in use and learn much about how they work. I've built about five so far trying to improve my design for a longer burn time. It's been the lager version that has been giving me problems but I made a slight modifacition and saw an improvment so I believe I'm on the right path. I'll share an update once I figure out how to make it better. Thank you for your input and Merry Christmas to all!

A u-tuber by the name of Mr tesalonian does a lot of wood gassafiers, even goes as far as driving his truck off of wood gas / syngas. Good luck Sir,

I have watched several of his videos including the one with the gasifier truck. He shares some good information. I've only found one video that comes close to what I'm trying to do. The poster had converted a wood stove to be a woodgas burner. Sadly they didn't share any hints or tips on it's construction or things to avoid. The fire box was rectangular instead of round but I'm not sure that would matter. Thank you!

Isn't it marvellous the way that Mechanical Engineers do Process Engineering?

Recently home wood burners have come under EPA rules, and some will be discontinued. Only efficient burners will be allowed to be sold in the USA, apparently. So it behooves us to learn from this thread. Many good posts, I liked Hi-tek-Rednecks one the best. Like he said a simple double drum wood burner works just fine, has secondary burn. That is what I presume the EPA wants, a good burn. The catalytic burner add-ons seem to work, too. They may make bad burners pass the new rules.

Personally, I am concerned about anything that makes flammable gas, it may pop.

Basically, all these wood-gas stoves are just glorified Bunsen burners modified to burn solid fuel.

With good air flow, one can get wood to burn very efficiently. Based on this theme, the old blacksmiths used to use wood to forge metal, and better blacksmiths actually used iron ore to make steel. Their "furnaces" used a bellows to increase air (oxygen) flow to the solid fuel, be it coal or wood.

The old steam engine locomotives and steam tractors used the exact air flow designs that you see for these wood-gas stoves. They also fed the exhausted steam up through the stack to increase the "chimney effect" or air "multiplier" effect to make efficient use of solid fuel. Early on, one would see black smoke pouring from coal-fired steam locomotives. By the Second World War, it was most common (in the U. S.) to see steam only coming from the stack of locomotives, due to efficient burning of coal and much better air flow.

So, for the originator of this topic, your design does not cause enough air to be used for primary heat (wood combustion) and therefore, not enough heat is generated to cause secondary air to be pulled up through the outer wall and out the secondary air holes. Width-to-height ratio is important in building air velocity out the secondary burn holes.

For anyone interested the following link may prove useful. You may have to copy and paste if it's not live.

http://www.build-a-gasifier.com/gasifier-history

The "BOOM" is imminent! Abandon ship! Abandon Ship!

It actually sounds like the heater is not drafting well enough to maintain the fuel-to-air combustion ratio properly.

Maybe adding a small adjustable speed blower to maintain air flow would help.

I get a complete burn even lots of woodgas, you can watch as it spins around in the barrel before doing a long drawn out dance around the top of the stove. In all honesty I think the air gap inbetween the inner and outter barrel is to large for the chimney affect to work correctly. If you watch the fire you can see the flames and smoke being drawn to the bottom of the burner keeping it cherry red till the wood is all but gone. I'm scrapping this prototype, it was not very well thought out. I've decided to start from scratch and build several more stoves starting from the soup can size and working my way up paying better attention to detail as I go. As I look at my manufactured stove the air gap is around 1/4" or so. Probably should be about that regardless of stove size. Not having any real luck finding information relating to the scale I'm looking to build in.

What is the size of the gap right now?

If you are right, and I feel that there is a very strong possibility that you are, you need to try a few things before you give up on this attempt:-

1. Insulate the outside to maintain the temperature of the "convected" air and gas mixture

and/or

2. reduce the width of the gap by adding something to the inside of the outside can to make the gap smaller...or finding a middle can that is wider, making a larger fire and a smaller gap, probably the best way....

and/or

3. Ducting more heat into that gap, some sort of heat pipe arrangement maybe?

Of course, if the holes at the base of the outside can are simply too big, there may simply be too much air in the mixture and it does not burn well. Block some up.

If they are too small, then too much air may be drawn down through the fire, possibly making a lot of gas, but using up the fuel too quickly. Open some out. Variable may be better....

If the holes in the top inside of the inside can are too large, the worse effect should be that the jets of flame will be shorter and maybe the possibility of "blow-back" or small explosions in the gap, which will be very annoying.

Too small and the gas being burnt, depending on the pressure difference (convection) between the top and the bottom of the "gap", if good, will "shoot" gas jets too far across the burning fuel, maybe removing too much air from the actual fire......

What I do not understand is why hasn't anyone used variable air control on these little fires? Or at least, I haven't been able to find such a fire online with variable air control is probably more accurate..

I did find one that recommended insulation, but only the one.....its obviously an underused method of improving efficiency.

Its important that as much heat as possible be transferred into the gas and air to improve the convection, therefore "gasification" and the overall efficiency of the stove.

There is a nice well made and cheap wood gas stove available from China on ebay that should be a good starting point for anyone wanting to experiment with small changes and see the effects. It appears to work well in its delivered format according to people on the net, so starting from a known position should be easier...

It appears to be delivered here in Germany for under US$20. If you value your time, it costs basically less than an hour of work for many!!

EUR 15,66 with free delivery here....

Set up for use:-

Packed:-

I find that it even looks good too!! But be careful, its lightly built for back packers, easily damaged, but also easily re-worked!! A similar one is here:-

http://www.youtube.com/watch?v=eK9paoZ98Kk

I checked the melting point of some metals, ones that conduct heat well, but did not either cost too much or melt at too low a temperature. There are several that may prove interesting, Aluminium (but probably only as cladding on the outside of the inside pot, without direct fire contact as it melts a little bit too low for fire contact), Copper, Brass.

My personal "best" choice was I feel copper, that it conducts heat many times better than most steels and melts at above 1000°C. I do not know if any bad chemicals are released from copper when hot, but it is very easy to work and could also maybe used to "clad" the outside of the inner pot, for example.....

You may have better ideas than I, but I feel a thin steel tube on the fire side, stainless maybe? and a thick copper cladding may be a way to go......plenty of that heat transfer grease between the two or similar....or lots of copper rivets to keep good contact between the two maybe?

Just a thought or two......

I don't have time to touch on all of the points you raise as I must get to work but the stove you shared is ok. I have one but the jets are too large and give a shorter burn time than perhaps some of the higher quality stoves might.

One could possibly fabricate a slider ring of sorts with holes to adjust air flow and jet size to tune in a fire they liked. I have a stove like this and can testify it does work. I however find my soup can version I built using information from a youtube video is superior in performance. It did give off some rather noxious odors the first firing or so so if you build one from used or even new cans like the ones they show from paint cans outdoors would be best even after well used plenty of ventalation is advisable. My current prototype produces enough heat to melt aluminum so perhaps as an outter covering with a small air gap for insulative purpose might work. Have a great day Andy!

Happy new year to you as well.

Andy

Have you considered tapering the stove walls so that the base is larger than the exhaust exit?

This would allow the combustion gas flow speed to naturally accelerate with temperature increase(s) thereby increasing the chimney effect.

The reaction temperature could be controlled by regulating the inlet air at the base with a simple adjustable damper assembly.

I would think the temperature could also be automatically controlled by utilizing exhaust gas temperature feedback to a mechanical or electrical damper position controller. (Direct reacting Temperature Control Valve/TXV ? Or RTD or TC with electronic controller?)

I had not thought about tappering to be honest. It very well could be helpful, seems there is much yet to be learned about the use of woodgas which seems odd for something discovered in the 1600's

The damper idea I've considered and thought a simple sheet metal ring with holes the same size as intake holes could be attached with some sheet metal screws and tightened once the operator felt they had the right setting. Same with jets.

Not sure about the automatic controls, I must confess I don't have that much knowledge of temp controls and what little I do have is on my solar heater and house heater.

Could they be ran from voltage produced by peltier modules to keep the portability in tact or would 120V be needed?

If you are going to investigate temperature control, a bi-metal strip that closes the dampers as it gets hot and bends and then reopens them as it cools would be simpler than electrics. KISS. Mount the strip fixed at the bottom and oriented so that the top is free to move at a tangent to the outer container. An adjusting screw moving the strip mounting back or forwards could be used as a regulator (or see below). The damper would have to rotate freely but a ring resting on three rollers with a cutout in the lower edge to engage the top of the bi-metal strip would possibly work. For the super dooper all bells and whistles model (+$49.99) you could have three cutouts in the lower edge of the ring all slightly differently oriented to the hole pattern so that the holes start at different levels of closure. Stamp letters into the metal next to each cutout; C for cooking temperature, E for economy burning, and S for smoldering. Fix a shield round the strip for mechanical protection and to stop any wind disrupting operation.

To be honest the thought or controls does interest me but I don't think they would be very practical in my current project and might even present a problem.

In order to have true control one would also need to control the woodgas production which would presumably continue to be produced from the wood being heated.

Since gasifier explosions are not unheard of and there are too many variables that are unknown to me at this time I think I will stick with trying to use the gas as it is produced, at least for now. Thank you for your insight!

How about using batteries? The stove should be able to keep them warm enough to function....Better yet, once I have perfected my thermally re-charged batteries that operate mainly from 45-85 C degrees, I will send you one for a nominal donation.

Seriously, I am working on that project, and it may change how low grade "waste" heat is viewed across the globe.

I made a comment previously about making the jets smaller, that is a really wrong idea.

What you want is narrowed channels at the bottom (you can use vanes in alignment with the flow that taper toward a slight restriction), couple the openings to the inside pyrolysis section(s) of the burn so that wood gas is induced by having that inlet at the most restricted point in the air flow. Make the jets larger by 200% (twice the area, not the diameter) than the area of each flow restriction around the periphery.

At that point what you will have is accelerating air at the point where wood gas is admitted to the jet channels. I think each jet should have its own channel of flow by using essentially baffles from inner to outer diameter, taper from bottom to slightly more narrow at top could possibly help (as stated by SHOCKISCAN), and with the baffles this might help cut down on wind effect on burner.

I think I want one of these for re-melting aluminum scrap so that I have more to tinker with in my shop. I would also like to make a couple of brass parts to an old wood vise I have that appears to be worn out. Now I have all the silicone molding rubber I need, also have Insta-mold. I also have some casting wax additive (made this at another job).

Now if I could just figure out a way to get all the flood water in St. Louis area to be in a gigantic lake in West Texas / Eastern New Mexico, we could re-write the food production books in this part of the world.

Here is a link that will help somewhat.

I will send more info shortly.

http://www.boilersupplies.com/temperature-control-pressure-valves/trerice-91000-series

I found a website with some good drawings that may be helpful. I found it very interesting to see that its quite a narrow gap between the inner and outer Pots....

diy-wood-gas-stove-instructions

Thank you, I'll look into that.

On your other comment copper could be an option although where I am it's expensive or was last time I looked at buying some for a project I was working. Also while making cylinders from copper would be rather easy attaching everything together may be a hassle for a do it yourselfer.

It may be abled to be tig welded but not sure. I have read it can be brazed or soldered, the last not being an option due to heat. Maybe it could be bolted or put together with copper rivets. Stainless seems to be a better option but would still need to be welded or bolted together unless the maker had good fabrication skills and tools to form the the need parts to fit together. I guess the same would go for copper.

I am glad to find others with an interest in the woodgas stoves!

Firstly, you did not tell us where you are. Copper transfers heat many times faster than most other metals....

Secondly, if cost is a factor, search for an old scrap immersion heater cylinder, they are sometimes made of quite thick copper.

Using the right tools and leaning how to soften & shape copper with heat and water makes it very malleable/useful.

Hard Brazing using brass spelter should be good enough for the temperatures reached. Riveting will also be good and easy, as will nuts and bolts.

I have decided to make my next one in stainless, provided I can get the sizes of metal needed.....then add copper in certain areas....

If you go with copper, who says it has to be welded? Why not just roll form the inner and outer cans so that the difference in radius is about 1-2 mm (at the narrowest point) with fins fixed to the inner cylinder's outside to hole position or the outer, and to channel the air/gas mixture to each jet. I bet you can cut the copper sheeting precisely enough to form its own rolled edge hinge. Then you can pin that with heavy gauge copper wire (or steel coat hanger??)

Why use copper when you can buy carbon steel much cheaper?

Who says the stove has to be round. I can be a polygonal cylinder just as easy (for the inner and outer cylinders, with close fitting parts made to cover the top air/gas channel thus directing the mixture to the jets. The close fitting parts might have to sealed with high temperature insulation?

Make your own damper slides for each facet of the polygon. (Octagon is about as high as I would take this.) Pentagon is easy to brace internally for strength. Rivets are a cool way to make stuff also.

You could also make an outer sheath from Aluminum sheet (and even insulate this from the hot outer polygon with Fiber Frax high temp oven insulation or other suitable rock wool). This outer sheath could be designed to allow ash removal, and also to be an upwind "air scoop" to assist with air flow during stove start-up. Add a couple of wood handles on some brackets, and you have a stove you can move around as needed.

The idea for possibly using copper is that it conducts heat so well, but does not melt at such a low temperature as Aluminium, and is cheaper than silver.....

With these styles of wood burner, you need to get as much heat as you can into the air convection, so as to "suck" the burning downwards at the top of the fire.

Which will also suck in air from above and down through the fire.

This is so that the gasification can take place with the un-burnt wood and the gas produced exits at the bottom of the fire and then can get mixed with the air entering from the outside holes in the skirt, and to burn it above the fire......

This diagram may allow you to envisage it easier. Its from Wiki:-

While copper may sound attractive and would potentially be aesthetically pleasing the VOC's contained within wood smoke would seem to rule it out. At least one VOC is known to be deleterious to copper.

And with at least 100 VOC's known to be in wood smoke there may well be others that could interact with the copper, perhaps in a manner that's hazardous to ones health.

I think it would be prudent to thoroughly reasearch the potential affects of the known VOC's in wood smoke on metals before investing the time and money to build an appliance meant to use it.

GA

Like it.

How about using copper as the "pie sections" of each polygon, thus allowing a bit more overall stove radius? Copper as you have pointed out, would assist with the needed heat transfer from core to periphery.

I should think that it might be possible to incorporate a burner ring or set of rings just under the pot support in larger versions of this. A mutation of this idea: instead of using copper pie pieces as just sheet metal, make those pieces as a spaced envelope of two sheets of copper, with a rolled joint at the top (and bottom it needed), and set up the wood gas/air mixture in these sections, and have burner holes at the top, so the actual flame pattern is a complex star pattern.

Of course as Luke pointed out, one needs to be careful not to eliminate the smoke and volatile organic compounds, but then introduce a reaction product of copper (vapor) and VOC. I think the likelihood is minimal, but there again, I am just a lumberjack.

Http://chemistry.about.com//od/firecombustionchemstry/a/smoke-chemistry.htm

If anyone is seriously considering building a woodgas stove and curious about the chemicals involved the above could prove at least somewhat helpful.

Since it's been brought up so many times I'm going on record and saying IMO using copper for any purpose involving a natural gas is not such a great idea due to potential for corrosion and other unknown possible side affects.

I found an interesting .pdf from east Africa and wood gas stoves and stove design, particularly the links at the end of the information.

There are also the sizes for a simple design that may point you better in the right direction.

factsheet_gasifier_web_final

I have also decided to have a go, so I have started to look around for parts.....

That is interesting information. Thank you for sharing! Most of the information I've ran across has been from others trying to figure things out as well, or so it would seem. I'll be starting in on another attempt this coming weekend. I wish you luck with your stove!

Thanks.

If you posted some pictures of your problem stove, particularly the inside design, maybe we can fix it together here?

We are not alone!!!

I still believe (I just read your original post again!) that the air holes along the bottom outside edge, are too large and too much "suction" is being lost. It fits with your original description well.

The"real" problem might still be that the gap between both "walls" is too wide, but think "too wide for the air hole size".

Its easier to block up say every second hole with a ball of silver foil for testing and see if it improves....or not!!

....and/or add some thick insulation to the inside of the outer wall, to help temperature and reduce the gap.

Fiberglass matting comes to mind. But a few balls of aluminium foil would be easier and quicker....

Hi Luke,

any news for us?

i am planning to buy some components to make my own, I am looking around on ebay to find stuff that will fit together with minimal work (not outside in the garage, its too cold!!).

Not any new news, we have been raising our grandsons for the last 8 months so time to myself is a rare commodity... I will be back after it here in a week or so I think. I'll also try to post the pics you asked for. Have not been able to do so from my mobile phone but not sure why. I read an article that said the popcorn tins work nicely. You could probably find some Christmas ones left over on the cheap someplace. Just need one larger and one smaller to start and see what it's all about. I'm hooked on the idea of a larger stove and I will get one to work sooner or later. Good luck!

I am going to try using stove chimney parts, all in black!! 2mm Steel.

One of the important aspects of how well the stove eventually works, is how the gas nd air are convected, or so I thought.

But I my have been using the wrong wording, I looked up "chimney effect" and found this, which says it far better than I could, from Wiki:-

http://en.wikipedia.org/wiki/Stack_effect

Stack effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect is also referred to as the "chimney effect", and it helps drive natural ventilation, infiltration, and fires (see Kaprun disaster and King's Cross fire).

It certainly improved my understanding of the effect!!

This is sounding more and more like a challenge for a gas flow engineer. To get the draft right, there should be an optimum ratio between can height, gap spacing between inner/outer wall, and bottom orifice size and number, along with top hole size and number. I suppose one does not want to create a bottleneck by having too few, too small holes on the top "burner" outlet. Actually the "bottleneck" should be on the bottom, and having an adjustable damper at the bottom should really help set up the ideal drafting. I see this as a ring with slots in it, or holes that line up with the bottom induction holes when fully open, and will close back to say 20% of full open.

Good post, makes a lot of sense, I think!!

I suppose too bad there is not an easy way to adjust wall gap (or wall area/volume). Too many degrees of freedom leaves the average operator out in the cold?