How does charcoal perform in a wood gasifier?

Hi All,

I’ve been a long time lurker and just completed a build of a down draft gasifier. I sized it to produce gas for a 3500 w generator. I intended to use use wood from the get go, but decided to try charcoal. I get a nice stable flare on wood but nothing on charcoal. I almost got it to flare, but that’s about it.

So I was wondering if this is normal or not given that the charcoal was bone dry and there was no water drip. Shouldn’t I get some flare even without water? If I should be getting a flare on charcoal, then that will point me towards looking for a problem in the gasifier.

Thanks in advance for any advice,


Are you sure the flame wasn’t invisible? If I can’t see the flame I will hold a piece of paper or a leaf to see if it catches fire.

Charcoal should work just fine, maybe wet the charcoal a bit. The water is mostly to ensure the reaction temperatures aren’t too high. You’re using wood charcoal and not briquettes, right?


Thanks for finally posting Marty. You have a nice looking build there. We need a little more information about your fuel in order to diagnose your problem. The flare looks nice on wood so what are you using - chunks or chips? And what did you use for charcoal size wise. If the charcoal is too big it might cause weak gas that won’t flare. What blower are you using?
Don M


Thanks for the quick replies. As to your questions, I’m sure it wasn’t lit as I used my hand (probably not the best practice :wink:) to feel for heat. Also, I had a propane torch and when I applied the flame to the gas I would get an orange flame. Once, when it flared for a second or so, I could see the flame, so I’m certain there wasn’t any flare the rest of the time.

I used chunk charcoal from where I burn brush, so I had a variety of sizes from 1/2 inch up to around 2 inches. On wood, I was running rounds cut from 1 to 1-1/2 inch diameter dried branches about 1-1/2 inch long.

The blower was something I welded up. I live in Chile and there isn’t much in the way of auto recycling yards like in the States so I just made the fan casing myself. I used an impeller out of a dead leaf blower driven by a 12v motor from China. The white square thing at the bottom left of the photo is a simple rheostat. I found that the lowest setting worked best on wood. The motor I got was rated 3000 rpm at 12V. I figure I’m running closer to 1000 rpm now. No idea what cfm I’m getting.

After trying to get a flare for half an hour, I peeked inside the hopper. I saw a partially glowing mass of charcoal - about 4 inches above the air inlets. I threw some wood on top and minutes later had a flare. Maybe the charcoal was too hot?

Thanks again for the help!


You won’t see anyone here begrudge you about a lack of materials. Sometimes the best resources are in your skills and not in materials.

On charcoal gasifiers they typically do not have a
restriction. If you plan to use wood then you should leave the restriction in but if it is removable easily then I would take it out when running only on charcoal.

It could be your gas isn’t mixing with enough air. Try to drill air holes in the flaring pipe to let it mix a bit.

Are you using the blower to push the gas or to pull the gas?

I find it’s easier to flare when pushing from the air inlet sometimes. For this video I was using two bilge blowers, not as strong as a snail blower like you built. Bear in mind this gasifier is super simple and actually was undersized for this truck. All it has is a single nozzle and a grate about 12" down only ever meant for charcoal.

For fuel size I would see about using pieces 1" down to 1/4". You could make a screen or buy one maybe to sort it out faster.

Charcoal gasifiers typically are ready to flare instantly.

I would try to run an engine with the charcoal, perhaps your blower is too strong and is blowing out the charcoal flare? Hard to tell.


Holy Moly, Cody! That is impressive.

I have an approximately 2-1/2 inch restriction as seen in the reaction vessel photo below. Unfortunately, as you can see, it is not easily changed.

I am pulling gas and flaring at the outlet of the fan. The roar from your setup would indicate to me that you are really pulling some serious cfm’s through there. I don’t get any sound like that. But I assume your gasifier is for a much larger engine than mine


Very nice workmanship on the gasifier. Is the nozzle in side the yellow tank and the restriction is the bottom pipe?
If you have a drawing cross section of the build it will help a lot.
Welcome Martin to this DOW site.


I initially thought this gasifier would work for the 4.3L V6 on that GMC Sierra, and while it did power the engine I think it was pulling on it too hard. I’ll have to see if it works for my 2L Mazda truck.

By the way, when you added wood to the hopper how clean was the gas before lighting it? You might be ready to run an engine on wood pieces.


hello marty, on my cooker experiments , when the gas speed on the burners was too fast because of small tube diameter, i could not flare the gas, or only flare it for some moments, how also cody mentioned…
maybee a solution is if you build for charcoal another inner vessel instead of the yellow one, so you can change easily the one or the other, depends what you use, wood or charcoal…
nice build!


Welcome Marty. I agree that the fabrication of your reactor section shows real skill. I think giorgio’s advise about building a separate charcoal reactor is very good. It’s obvious that you are already making way more gas from your wood chunks than you really need to run that small engine. If making charcoal is not a problem for you then a simple fire updraft is definitely easier to run and maintain. Anyway good job on all you have built so-far.


Here are some images that will probably give you a better idea of what I constructed:

I gathered from following this forum that fuel bridging is a common problem. So I wanted as few projections into the hopper as possible. The air nozzles are simply holes drilled into the hopper just over the restriction. This required an air plenum which I figured could do double duty: it cools the hearth area and preheats the air.

I have run my generator but only to see if the gas was good enough. I don’t have any filters besides the cyclone. The second barrel was meant to be a cooler and a hot filter. I have a filter element cage built that screws into the bottom of the barrel, but I need some heat resistant cloth to cover it. However, after running the gasifier I think the incoming temps are low enough that a simple cotton cloth would work.

I became interested in charcoal as I am still concerned about tars. It seems like if operation of the gasifier goes off spec, tars could become an issue. But the other reason is fuel preparation. I have an abundance of firewood. We heat here exclusively with it. But when I used some wood that has sat in the wood shed for over a year and is dry enough for stove use, it produced a ton of water. “Dry” wood with ten percent moisture is still a lot of water!

I baked some chunks on top of my wood stove and that solved that issue, but I can’t imaging doing that when I get to running regularly. Even if I prepped wood over time that way, I would have to store it so it wouldn’t reabsorb moisture from the ambient air. I guess I could build a drier using heat from the generator exhaust …

The other issue is chunking the wood. I am using a chop saw and that would have to change. I have already come close to loosing appendages over the years and despite being old (68) I think I would like to keep all ten till the end. :wink: That means another build.

So in the end charcoal started looking attractive. I think Giorgio’s advice is good too. All I need is another barrel top and propane cylinder. :slightly_smiling_face:


Good morning Marty .

Just one small item I happen to notice . There seem to be a lot of area for gas to be stored which could create a problem in certain conditions .


Hi Wayne,

Could you please elaborate on what problems could occur in which conditions? Thanks!


Hello Marty .

The gasifier system is being operated under negative pressure which means if a small air leak happens in the system fresh air will be drawn in and mixed with the gas . if enough air leaks in to reach the proper fuel /air mix a spark in the system could ex-night the mix.

If the ignition happens in an area with little volume it will be a belch , burp or fart . If it happens to an area where there is a huge area it is an explosion .

Somewhere on the DOW is a thread from Wayne Baker that was building a stationary gasifier . The best I can remember it ended up on the top of his house :frowning_face:


Hi Wayne,

Good point!


One good way to check for air leaks would be to spray soapy water while blowing air into the system. If you see any bubbles, weld or silicone patch it. But yes large collection areas can go off instead of it travelling back to the puffer lid.


Hi, i agree with Wayne about that big volume of gas can be a danger, the best way probably would be to make a blow- off valve, intead of rebuilding the gasifier totally, could be a fairly big, 6-8 inches lid, with good sealing, and pretty heavy spring load, as long it’s the “weakest link” opens easier than the gasifier ruptures, place it somewhere with lower temp, maybe in upper part of gasifier, opposite side from gas outlet?
Just some suggestions, anyway: very nice build :smiley: :+1:


Marty, the spring loaded lid you built looks good in the hopper design. After the filter container where your hot filter is, there should be a pop off valve like the tennis ball pop off valves that Wayne designed. Simple to make. Having a couple of them in the cool gases piping of the system will help if this puff event ever happens.
Having cool gas piping that is connect with rubber couplings help too they will just come apart in case the pop off valve a not enough to handle the puff event.


I just ran some more tests on charcoal. I moved the fan to the outlet of the cyclone. Since I would be running charcoal, I figured I didn’t need all the cooling to protect the fan. The first test was with unscreened charcoal straight from a fire pit - 2" and smaller. I did have a problem with water as I had doused the brush fire with water to save the charcoal from going to ash. I had a ton of water in the exhaust and until the load dried out a bit, I couldn’t get a flare going.

I ran a second test on the remnants of the first test later on after everything cooled down. Unlike Cody’s machine, it took about 10 minutes before I could get a sustainable flare. Until that point I got an orange flame when I applied a propane torch to the gas flow. When the gasifier outlet pipe and cyclone warmed up, then I got a sustainable flare.

The flare isn’t as long as on wood, but I am happy with the outcome. One thing I noticed is that I don’t seem to get any bridging. I was always shaking the gasifier with a vibration motor while on wood, but not with the charcoal. :slightly_smiling_face:

I am getting sparks in the flare every so often - stuff that makes it past the cyclone. So a filter is next on the list to make and then hooking up the radiator to get as dense a fuel gas as possible.

Thanks to everyone with their suggestions - this forum rocks!


Looks great Marty. That’s the first home build fan I’ve seen since the GEK gasifier. That’s pretty impressive in itself.