Exhaust Gas for Charcoal Production?

This has most likely been tried before, but i was wondering if we could use the exhaust gas for making charcoal as we run. My thinking was to run the exhaust into a vessel which is filled with wood chips to see if the exhaust gas was hot enough to form charcoal whilst running. Then divert some of the Gas/ Wood smoke to the EGR on Charcoal gasifier. It has been stated on the internet that small engine exhaust gas under load could reach temperatures as high as 420 degress celcuis.

I am in the process of making up a test container and plumbing to exit exhaust gas through a bed of wood chips, small pieces etc.

Some thoughts or input into the idea would be helpful, thanks Roscoe.


It’s been done, but will be messy as well as a fire hazard.

You have to wait for charcoal to cool down after it’s been made, if it’s reintroduced to oxygen too soon it’ll spontaneously combust at once. There’s a polish guy on YouTube that has done this in small sub 5 gallon batches. Anything bigger it will only somewhat dry the fuel and not carbonize it.


Thanks Cody, Do you possibly remember the Youtube link? I would like to see his video.

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Also,I forgot to say thank you for the warning.

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Cody is right, but fuel drying this way could be also helpful. I saw a photo of a tractor during WW2 with a device like that: Drums on the rear fender, in which the exhaust gases were routed in order to pre dry the wood, was stated below. If I remember right, it was a DEUTZ tractor especially built for woodgas.


Til, any update on the LandRover?


He’s speaking more on the terms of using exhaust to make the chips into charcoal, which takes a lot longer and can get messy.

I do like using exhaust to dry the fuel for reloading the hopper. NHHobbyLoggr on YouTube has done this.


I can add some input into this.
Engine exhaust temperature out of a close coupled electrical generator set will be in the 400-500 Fahrenheit temperature. NOT 500 Centigrade.

So it can easily dry wood chips with allowed air ventilation circulation to remove the water moisture.
Once dried down it can also easily ignite those dried wood chips using that air circulation as the oxygen source. You must closely monitor and either remove the wood from the exhaust heat. Or divert by-pass the engine exhaust to save your chips.

True dedicated charcoal making you first you allow the moisture to be driven off; then use much of the woods volatiles driven off as a heating fuel to save the carbons structures for you desired charcoal. So only somewhat building up coating messy.

Now an intended wood cooker system for tars and condensable volatiles is diffnertly controlled; some what using up the charcoal as the heating fuel source and is internally VERY gooey, sticky messy.

Then there is normally open wood Torrification. Surface charring. Moisture reducing. Semi-converting. Not so messy just very rising driven off stinky and air polluting.

So what you propose Roscoe is certainly possible.
I’ll bet you $150. USD ( the value of a DOW Lifetime upgrade) that if you set ups for this you will quit it fairly quickly as just to hard to keep stabilized controlled.
And a horrendous internal cleaning up mess to keep functioning for batch cycling.
You SHMBO; your friends and family, will be shunning skin stained stinking you. No one will want to handle your clothes. Or allow your clothes into “their” washing machines.

In the past fellows in certain needed basic trades became the village pariah outcasts.
Today modern; then just have to shops setup their own old washing machines and clothes driers. So factor that as an added expense into your process. Once you are making black tars and concentrated volitials you will have to pre-soak you clothes in bought out solvents.

Steve Unruh


Thanks for the link Cody of NHHobbyLoggr, he seems like a very interesting fellow. I am presuming that the wood chips in his drier are green? At least it can be used to dry wood.

Steve, You and Cody are more than likely correct and like you said the product at the end would not justify the mess of tars that would accumulate.

The other thing was to use the hot exhaust gas for heating water. I just don’t like seeing all that energy wasted, especially as we work hard enough to make our charcoal.

Thanks for everyones suggestions and advise, Roscoe


Exhaust drier-charcoal16072023.pdf (89.2 KB)
This is a drawing of my thoughts and a experimental nozzle i will try shortly.


I think water heating is much more feasible.

Chasing efficiencies can sometimes turn into an ouroborous, the snake eating its tail.

As far as funneling any pyrolysis gasses to the charcoal gasifier, you run the risk of the gasses entering at a rate faster than the charcoal gasifier’s active zone can handle.

At that rate I think it would be easier to just make a wood gasifier, then the drying mantle from the generator’s exhaust could be used for refueling instantly. Make the heater as big as your hopper, and when the hopper runs empty you have fuel that’s more dry than it would have been. Wire baskets or metal mesh trash cans are good, so moisture can sweat out.


Agreed Cody, I will make up a water heating system first. Any how, i have enough on my to do list all ready. Just waiting for a few fittings to arrive to finish my new gasifier and then onto the water heater.


I’ve noodled on this a ton. Random thoughts:

At least for direct heating of wood/wood chips, you don’t want the temperature to drop below 220F and drop out all that “water of combustion”.

Any condensate is going to be acidic and nasty if/when it does drop out

This makes any heat exchanger dealing with condensate vulnerable to degrading or expensive (stainless / maybe aluminum) if it isn’t. Invariably some condensate will drop out.

Indirect heating of wood is hard because it conducts heat poorly. Even with indirect heating you’ll want gas circulating through the chips for any meaningful heat transfer, even if that gas is held separate from the exhaust. Also you now have a heat exchanger, maybe two. Also you now have wood vinegar condensate to deal with.

You can dry wood chips with a simple solar heater assisted by a counter flow heat exchanger. Because the temperatures never get above 180F or so, you can use plastics in the heat exchanger that are tolerant of the wood vinegar. You won’t torrefy the wood but you’ll get it bone dry because of the ultra low relative humidity of ambient air heated heated to 140F-180F. That doesn’t make use of exhaust heat but it does get wood dry?

Consider pre-heating your combustion air with exhaust gases. That’s still heat economizing and it may be easier than a gas to solids system. Hotter combustion air is less dense so you’ll need more of it by volume but it can drive the gasification reaction harder/hotter. On charcoal you will certainly be able to use more water drip.

Water heating from exhaust, yes! The heat transfer of gas to liquid can be very high. For that reason a stainless exchanger may be in budget. Aluminum might work as well. 400-500F is decently high grade heat so it’s a little sad to use for water heating but lets not let the perfect get in the way of the good.

For water heating… you probably don’t want to directly heat exchange the hot exhaust gas with the domestic/potable hot water (lots of reasons). My best thought is an unpressurized but insulated pre-heat water tank. The exhaust warmed water loop and cold water inflow for the regular hot water heater get plumbed into separate loops immersed in the same hot unpressured tank. Free preheating for the domestic hot water and double buffered from exhaust to potable water.

I’ll stop there - every path I’ve explored has its issues. (edit: doesn’t->does)


I am attaching a video below that relates to this topic, otherwise I first cool the exhaust gases with water to heat the house, well, I use the remaining heat to dry the wood chips, this works pretty well. I have temporarily abandoned this project, as I plan to build a smaller building on this site, and install a more powerful generator inside,… the waste heat will be used for heating and for drying wood chips,…


Cody, where do you come up with all these words? I have to keep a dictionary handy to read your posts. :grinning:


I read so far ahead in class that I’d read other books. Loved Greek epics and mythology when I was in school.


Tone, you have a tidy setup there and thanks for posting the video of it. It is good to see people coming up with all these solutions to the wasted heat from exhaust. Heating the house with it also is taking it to the next level, good idea.

I will draw up a plan of the water heater and would much appreciated postive or negitive feed back of design.
Thanks everyone for your input and opinions. Although my orignal intentions have changed, i have gain much in other areas.


Tone, I could help but notice your running a diesel engine. Would be interesting maybe in another topic if you could shed some more light on your setup, thanks Roscoe.


Hi Roscoe, below is a thread where you can read some thoughts and review sketches and pictures,…


The exhaust contains water. The result is that when the system is cold there will be condensation.

When Mike Larosa and I were at APL some 12 years ago they received a load of wood chips that the wonderful state government required be soaked with water for transport. That made for very significant challenges to use them for the weekend demonstrations. We ended up spreading them out on tarps in the sunlight on the hot asphalt to accelerate their drying.

Mike and I were there and during a demonstration run I came up with the idea of directing the exhaust from the Lister into a gabage can and burying the exhaust outlet under the chips to try accelerating the drying process and to muffle the exhaust sound.

At first the chips seemed to actually become more wet. Then as the chips warmed up they appeared to start drying. The same process as can be seen with the exhaust from an automobile. The water condenses inside the cold pipe and muffler and the water runs out. Once the exhaust components are warmed, then the water no longer condenses out. The water is still there - it just does not condense.

Due to this water being present I don’t believe the process will work to actually produce charcoal. I certainly am not saying it won’t work. There are some thermochemical processes involved that I do not claim to understand. I do believe using the gasses to heat a chamber that contained the wood feed stock could work to dry and begin to torrefy the wood. There have been folks who tried this using a wide range of methods. I know the late Andy Scofield made an exhaust heated auger for aiding in drying cherry pits.