Quenching char for fuel

I notice a lot of folks that make charcoal for biochar quench their char with water to stop the process.

For people making charcoal for fuel, though, this is not a good idea, because this you have to dry it before use.

Covering it with soil is another technique and another big no for fuel char.

So, how do fuel makers quench their char? Do you just close up the retort real tight?


It depends on gasifier design. A downdraft charcoal gasifier works best on slightly moist charcoal.

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Aren’t most folks using the updraft design, like a simple fire?

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Yes, I shovel it into a 55 gal. barrel with a tight fitting lid and don’t open it till the next day.


“So, how do fuel makers quench their char? Do you just close up the retort real tight?”:
I let the process do the “quenching”:

—Makes good blacksmith forging fuel, too.

Pete Stanaitis


If you are making fuel for an engine a little bit of moisture in the charcoal is actually helpful. Sometimes we actually feed a little water through the gasifier’s air intake nozzle. This produces a richer gas and the engine will make more power.
What happens is the water, H2O, cracks into hydrogen and oxygen. The hydrogen is good fuel. It passes through to the engine unchanged. The oxygen reacts with the hot charcoal to produce carbon monoxide, which is also a good fuel for the engine.
When the water cracks it absorbs heat and cools the burning charcoal down. This is a good thing because the temperatures we often see in the reaction zone are often so high the ashes will melt and stick together. When these stuck together ashes cool they form a hard, stone like material that we call clinker. Clinker causes problems. It doesn’t go through the fire grate, and it sticks to parts inside the apparatus.
See minute 15:05 of this video for an example of a clinkered fire.

As Kristijan noted above, this only works if you are doing a downdraft. As Abe correctly notes, most designs people have built on this site use an updraft. The problem with an updraft is that the hot gasses move up through the fuel hopper and evaporates the moisture. You end up with a bunch of steam in the gas at a point where the reaction cannot crack it. The result is poor engine performance and condensation in the filter.

It sounds like the method of biochar production you are talking about is just burning wood in a pit. To make engine grade fuel, most people use steel drums or some other sort of retort that can be sealed up. You can shovel the coals into a container and snuff it out with a tight-fitting lid, but it is very hot if you have a big pile. Also, you want “tight-fitting” not “air-tight.” An airtight container filled with red hot coals will turn into an airtight container full of charcoal under a pretty serious vacuum. It does not take many PSI to make a 30" diameter lid impossible to remove. Those galvanized steel garbage cans work well, though.

I have been meaning to try using a sheet of metal roofing to snuff out charcoal that was done in a pit. If you line the sides of the pit with some cob before you burn, you will be less likely to get a bunch of little dirt clods in the fuel. Dirt is not the end of the world, though, it will just bake into ceramic and wind up with the ashes in the gasifier.


I messed around for years with steel plates, weights, clay, dirt, rocks, and every once in a while got a barrel that stayed warm overnight which wasted some of the charcoal. After accumulating hundreds of containers of ground, sorted, dry engine grade charcoal, I realized I could quench the barrel with about 20 gallons of pond water, and the next day, dump it out into a pile. Eventually the contents of that pile would make it to the screening table, the grinder, and back to the screening table. This August (last month) we had about 25 days over 100° F, lots near 110° F, and any charcoal on the screening table was guaranteed DRY. All my extra drums and plastic barrels with lids are in use, so now I just transfer the charcoal to a feed sack or dog food bag and put it in the barn. If I ever get around to using it, it will have the same water content as any of the hundreds of bags in storage. I used to label the bags as to type of wood, and put the date on the tag, but now I just try to find a place to put it. Last week while out shredding pastures, I found two dead trees and used a front-end loader to move the wood to my charcoal making area. The wife asks why I keep making charcoal, and the answer is that I am attempting to slow global warming. (She buys that!)
So, just make a whole bunch of engine grade charcoal, and use the stuff you made years ago. Quenching with rain water works well, because as soon as mosquitoes appear in the collected water, it needs to be covered or dumped. Because of our coal-fired power plants, the rainwater has a pH of 3. (Carbon Dioxide to Carbolic Acid makes acid rain?) The acid water washed fines under the screening table go into the compost and end up in the garden. Good Stuff!


That’s a good point, Ray. I am also in Texas, and we have hot, dry summers. Everything dries in a few days around here.

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Here is my tlud charcoal maker and char gasifier/genset. I have about 180 hours runtime. I haven’t had any tar in my engine. My bucket filter collects a little water, perhaps a cup during a two hour run. I get about 1200 watts with water drip, about 8-900 without. I make a 1 by 3 inch clinker without water drip, petty nuisance in my case but can see how it might become a problem in a larger system.
Water quenched charcoal.

50 gallon tlud made from a water heater tank. You can see how far the burn has progressed by where the top third of the tank has turned black.

4-3/4" pipe gasifier with water drip.


I am curious how much water there is in your finished charcoal. Would you be willing to do a moisture test? In the past I weighed out 100 grams, then dried it in the oven untill the mass stabilized. I found even 5% moisture caused condensation in my filter and poor performance, but this was also during the dead of winter with 40 degree temps and probably 80-90% relative humidity in the outside air.

I also found I got better performance with water drip - but the steam needs to be cracked - and clearly it is not if it winds up in the filter. That being said, doesnt slightly damp air boost engine performance a little bit? Clearly there are a lot of factors here. It would be interesting if you could contribute some more data on what is working for you.


Combustion produces water, and there will always be some water in the wood or char gas you make. If your filter is becoming restricted when water gets in it then I would guess you need to make a hay filter like Wayne’s, or maybe wood chips or something else. I don’t know your system. I just have a plastic pipe with a lot of holes drilled in it and four socks covering up the holes.
I don’t know the moisture content of my char, but I know there is some because when I use some for the bbq I can see the steam come out of it at first. I read somewhere, I think form Garry Gilmore, that charcoal naturally absorbs moisture from the air. I’ll see if I can weigh, bake, and reweigh some charcoal this week.

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Combustion of hydrocarbons produces water. If the char is fully cooked, it should be just carbon, and hence, only capable of burning to CO or CO2. :grinning:

The water problems I had came entirely from the char absorbing moisture from the air. Clearly water vapor in the gas stream does not have to be an engine-stopping problem. It could be that you built a system that works because the water is able to drop out, or it could be that a certain amount of water vapor does no harm. It does make me wonder if damp charcoal would work in someone elses gasifier, or in a different climate, etc. I hope you dont take my comments as argumentativeness, I really am just curious, and interested in advancing the communities knowledge on what is actually going on in our gasifiers.

If you run a moisture test, maybe also try some of the charcoal left in the top of your hopper after a run. My hunch would be that the stuff in the hopper would be bone dry, but I also remember that my attempts at drying charcoal once it was wet were less than successful…


Don’t know squat about charcoal for fuel but I have used a lot of it as bio-char. Bio-char will suck up a lot of moisture. It has to be charged before mixed into soil or else it will suck up the nutrients from the soil and they won’t be available to the plant for at least a year or more. I can take a five gallon bucket of ground char and mix in about a gallon and a half of worm casting tea and it will soak it all up in a couple days.


OregonCarl you make an excellent point about the relative air humidity affecting results.
Look at you and I.
Just one week ago, and for the previous 4 weeks we were 20% and less RH with 80’s, 90’s F sunny days. Interior continental air.
EASY to dry anything. Too easy to promote combustions!! One spark. One ember. And Poof! On fire and racing.
Now . . . .40’s-60’s F and 90-100% air RH after days raining. Continuous mid-Pacific Ocean air now. Lazy starting combustions. Have to really work at it.
You know we will not see dry, drying now unless a long mid-winter freeze down. Not really be dry until at least next mid-July now.
So you and I just learn to burn, combust, gasify around a fuels at 20% moisture; and air-in 60-80% RH.

Plainsman Canadian Greg Manning woodgasing had 10 months year of super low humidity air and fuels he developed around. He found to get the same results he had to gasifier air-in refrigerate and de-humidify for his systems to produce his expected results.

So really no way to compare results from these two extremes.
Compare West Texas to green wet Pennsylvania? Ha!

Scientists compare using declared standardized testing conditions.
DIY’ers must DO to get results to their own varying conditions.
We, each of us: must slave away to our most prevalent conditions.



Hi Abe,
Regarding your question on using water to snuff out the combustion of charcoal, I’ll reply “Don’t do it.” You can make good chargas with bone dry charcoal, BUT you may not be able to make good chargas with damp charcoal. The charcoal does adsorb some moisture from the air and if you live in an area with high humidity you need to store your engine grade charcoal in sealed containers. A little moisture in the charcoal is only good when the moisture is directed into the oxidation zone of the gasifier. This is the only place where injecting water into the gasifier will help boost the hydrogen content of the chargas. If the moisture is in the charcoal located outside this oxidation zone, then it will only be evaporated and condense somewhere else.
Some others, like Ray, can get away with using water to quench their charcoal because in a hot, dry cliimate, they can lay it out in the sun and dry it. I live a humid area and do not have that ability. With that said, I find no problem snuffing out a batch of freshly made charcoal. Pete provided a good link for the method I use Charcoal for my Gasifiers, How I make it
with an important part being to cover the holes at the bottom of the barrel, make sure to stomp on them to pack the dirt tightly over the holes and place a flat piece of sheet metal or tight lid across the top of the barrel. By next morning, the barrel is usually cold, but if not, it still gets dumped into my special barrel that has an air tight lid. It is dumped into there to continue to cool while another batch of char is started.
Moisture in engine grade charcoal should be keep to a bare minimum. Adding water to quench the char creates a wild card that can affect the quality of the char and add another variable that can cause problems.
My 2 cents.
Gary in PA


Gary, thank you for the input.

I live kinda in the middle. Part of the year it is hot and bone dry here. Part of the year it is wet and high humidity.

It seems like if you have a good setup with a retort you can close, that would also be the easiest way to quench.

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No worries Carl. I get a little ‘hot under the collar’ when I’m trying to learn too. Seems to me that its just part of the deal.

“During the second World War, fighter pilots could push a button and inject a stream of water into the turbochargers of their monstrous powerplants…” MEN link

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Mostly drawing leaking air got engine running on charcoal gasifier

disconnected condenser disconnected sock filter started engine while pulling with shop vac .
ran engine for some five minutes . no air mix all leak air . built with parts on hand .


Rindert; Reminds me of how we put a qt jar of water under the hood with two hoses running into the cap of the jar. One hose went from atmosphere to the bottom of the jar. The other hose went from a vacuum tap on the intake manifold to above the water in the jar. The vacuum line pulled from the top of the jar, making the air come in from the atmosphere to the bottom of the water, which bubbled up and caused water vapor to go into the intake manifold. Not very sufisticated but in our minds it helped gas mileage. ( like at $0.29 a gallon I really worried about gas mileage.) TomC