A couple of gasifying “scientific” questions

Well, I am still working on getting the gremlins out of my project and I will continue to update that thread if I have any progress, but in the meantime I thought I would start a new thread if anyone wants to tackle one or both of these two questions. In an attempt to understand gasification much better I have been spending a lot of time reading up in the DOW library, and I came across a couple of questions that I wanted to ask - the first one will probably be pretty simple the second one might need a little more explanation - so here goes….

Question 1. Relates to charcoal in the gasification process. Prior to coming to DOW I did not even know that there was such a thing as charcoal gasification, but now with this new knowledge that seems so popular with many my question is this:

So gasification requires 4 processes Drying, Pyrolysis, Combustion and Reduction - however that is based on wood gasification if I am correct - so if this is the case, which of these processes does charcoal gasification skip or bypass? I am thinking obviously it has skipped the drying process, and it would seem that it would also have to go through combustion and reduction - but I am wondering is pyrolysis already completed when charcoal is made? Anyway, any of you charcoal guys that want to chime in , I would really like to understand charcoal better as it relates to the 4 processes and if it “skipping” a couple of steps or bypassing part of the process that wood would normally have to go through.

Question 2. This one might be a little more complex - I am trying to learn the relationship with oxygen better. So far I have learned that smoke passing over hot coal strips the oxygen molecules off CO2 and H2O leaving behind CO and H2. I have also learned that this makes a clear gas that you see above the head of a match before it combines with oxygen and turns into a flame. So far so good, I understand the relationship prior to making syngas and the process required to make that reaction happen. So the question I guess I have is the relationship of oxygen post syngas production - since it seems like we are stripping away something that we will again use or need again later. Does the oxygen in the environment create the combustion? I would not think this is the case or else flare gas would spontaneously combust - so then is it ambient air plus heat that equals combustion which I guess would be the conditions of a match head?

I am trying to learn more about the process by which smoke passes through the coals, gets converted into usable syngas and then eventually combusts and turns back to smoke.
Here is how I am currently understanding it - the basic match head example, there is the match, the clear syngas, then combined with oxygen near the hot match head becomes flame, and then smoke is produced. Specifically I am trying to learn this process better so that I will be able to better understand and troubleshoot my project.

My understanding so far is that a gasifier, when it is first started, produces only smoke for a few minutes - because the coal bed is not hot enough. But then presuming the coal bed is hot enough, how would an air leak also produce smoke? Does it combust inside the gasifier and come out as smoke? Sorry if this second question sounds stupid, I am just trying to understand the process much better so that I can figure out which gremlin to continue to chase in my project - to go down the trail of “my hearth isn’t getting hot enough” or to keep chasing down the trail of “I must have an undetected air leak”. My thinking is if I can understand the process better, perhaps I can isolate down to just one cause to start looking into instead of chasing down multiple things that could be giving me problems.

For anyone unfamiliar with my project it is on another thread with pictures of it and my progress, that thread is called “New gasifier project giving me troubles”


Here’s my answers but backwards.

#2 yes oxygen from atmosphere is reintroduced to make it flammable again, and an ignition source sets it off.

#1 Charcoal is wood that’s been through Pyrolysis. In a charcoal gasifier it’s also robbing oxygen molecules to make CO and if there’s moisture, Hydrogen. There’s some other gasses that a charcoal gasifier doesn’t make, like Methane, that a plain wood system does produce.
With a charcoal gasifier you’re doing all the hard work for the reactor ahead of time. So sensitive engines, smaller engines, and other uses are easier with charcoal gas. I consider charcoal gasifiers as a sort of Training Wheels because it lets you not worry as much about the reactor itself but how you’re interacting with the engine, eg how good is your filter, is the gas and air being mixed correctly etc
For travelling I do think the raw wood system is superior. To travel long distances beyond work commute you’d either have to pre make all of your charcoal ahead of time, in sealable bags, or bring your apparatus for making the charcoal. Charcoal also isn’t ideal for people that live in states with frequent burn bans, or live in cities.
With wood you can use salvage, or limbs, or firewood from a gas station. Bring a power inverter from your vehicle battery and a chop saw you’re golden.
But also, a raw wood system could run wet charcoal. And others have seen benefits of adding a percentage of dry charcoal to their wood fuel to absorb the moisture in a usable way, Bobmac and Kristijan call it Rocket Fuel.


Good explanation Cody.
As for pyrolyzis it was in old times often called “dry distillation”, i don’t know if anyone use that term today, but i think it describes it good, you distill the wood when making charcoal. :smiley:


On its most basic level we burn some of the fuel in the gasification reactor to create heat.
This heat is used to convert carbon or biomass into gasses that in the absence of enough oxygen are themselves combustable.

CO carbon monoxide the the inclomplete product of carbon combustion.

Heat drives this remember that.
The heat cooks the material inside the device ( reactor gasfier chose your term ) to break up the bonds of carbon and oxygen and hydrogen to make a gas fuel we can burn.

When done corectly you get mostly CO, H2, light hydrocarbons.
This is the fuel.

You also get unreacted water ( heat in these devices can split the water into fuel as well [email protected] and Oxegen that combines with carbon to make CO ) Nitrogen from the air that does not burn, CO2 that did not crack to CO in the heat and sometimes TAR and heavier oily materials that did no crack in the heat.

Acids are created as well and other minor chemical reactions that create things that burn, but we want to avoid these because they can plug up the pipes.

The idea to keep in mind this is a heat driven process.

Charcoal gasification starts with wood or biomass that has already had the tars and most of the water cooked out
there is very little that can cause you trouble with a refined fuel


basically, with the charcoal process, you are pyrolizing the wood, this removes the tars and water leaving ideally pure carbon. Instead of doing it inside the gasifier, you are doing it outside the gasifier. The char bed inside the gasifier ideally helps break down the tars which are big and sometimes complex molecules, into more usable chemicals. Because you aren’t dealing with trying to break down the tars inside the reactor with charcoal, it can be a much simpler, lighter design to get fuel grade gas, and it isn’t as suspectible to getting tar in your engine.

Basically, all you have done is shrunk the fuel down to what you actually want which is the pure carbon.

The other half of it is what tools you need to produce fuel as Cody mentions. But travelling, you could buy lump charcoal (not the pressed briquets those have additives you don’t want), and use that. Or if you just want to try it, you can buy a bag of lump charcoal.

A lot of what you do depends on what you have for a wood supply, tools and time you wish to pursue it with. Even the gasifier design will depend a bit on what size fuel you have to run optimally.


Sean my only issue with store bought charcoal is it typically isnt fully carbonized. I got some to lay in the bottom of my grate to hold up my smaller bits, mostly Brands. Also expensive.

Even though I’ve only ran charcoal vehicles thus far my end goal is a raw wood system. It takes me hours of waiting to make about 30 gallons to 50 gallons of charcoal, which after grinding is really about 20 gallons.

With wood in those same hours I could fill up bags of chunks and set them aside to dry


DerrickD on your question #2 when the oxegen is stripped off of the “smoke” CO2 and hot H2O vapor, “where does it go?”
The hot woodchar carbons are given up binding to the stripped free oxygen to make more CO fuel gases. The H2’s left de-oxygenated as fuel gas.
Yes in woodgasifer under some variable conditions some percentage of CH4 wood-methane fuel gas will be made.

Perhaps a better way to visualize it is in energies. Potential in the solid wood fuels. To active-made in the wood using gasifier off the end of the air restricting-directing nozzles. It is that ONLY source of active internally made HEAT energy in a wood gasifier made doing the pyrolysis cooking, and above that wood drying.
And ONLY that made-active HEAT energy in the oxidization zone being hot gases sucked and falling made hot wood char transferred down into the HEAT absorbing reduction zone.
The reduction word here being used properly in the chemical sense of making more complex molecules into simpler ones. Takes a heat energy input to do this.
It is those made simpiler molecules of H2. CO, and CH4 that want to with new air oxygen and an ignition source turn back into complex CO2 and H2O.
Giving back that originally gasifer made heat in this secondary combustion.

You ever see the comic movie Mouse Hunt?
The scene of the painstaking spring set hundreds of set mouse traps?
Trip on in and trigger releasing back those preset springs no matter which way you turn. Ouch! Ouch! And ouch-ouch!

The woodgas pyrolysis was obtaining the many new mouse traps. The oxidization and reduction zones the time frame engry investment; storage setting the springs and triggers on all of those mouse traps.
You fueling in the hair trigger mouse traps into your engine then igniting triggering them the useable enrgy release goal.

Be very careful with the four zone concepts. The zones in real gasifier usages float, blend, transition change a lot.
The WK gasifier and others could easily be considered three zone. Some raw wood systems effectively blending, seamless two zones. Member Joni and Larry Dobson blend so well they think in one continuous zone.

Nope. Nope. You cannot suck me into a wood versus charcoal debate.
Steve unruh


Hello Derrick, a carburetor is a device for gasification of liquid fuel, which is gasified due to negative pressure and hot heated surfaces, that is, a change of aggregate state from liquid to gaseous state occurs, which requires a certain amount of energy, which is obtained from the waste heat of the engine. in the creation of vacuum and heat during compression. Combustion requires a gaseous state of fuel and oxygen. A gasifier is a device that gasifies fuel from a solid state, even for this process it is necessary to invest a certain amount of energy, which is obtained by burning part of the fuel in the gasifier, for this we supply oxygen or air. If we talk about the gasification of wood, this process starts at a temperature of about 250°C, where hydrogen and oxygen gas begin to be released, which may or may not burn immediately, depending on the temperature. If they burn, water vapor and heat are produced, which greatly raises the temperature in this part, which also causes gasification of carbon, which binds with hydrogen,… CHX - tar gas is produced. As I said, carbon is gasified at higher temperatures, higher than 650°C, which is achieved by burning part of the coal, well, if this happens in an area where there is an excess of coal, the combustion will not be complete, but incomplete, so gas will be produced CO and possibly gaseous carbon, which will form soot or coal dust after it cools down. .,…:thinking:


yes. but you need less charcoal off the top of my head it is 2:1 ratio. Now where I actually proposed it wasn’t for a vehicle, although it works. It was the 2 cylinder genset he was running, which wood has an issue because you need to maintain a high temperature to break down the tars and boil the water off, which is where the more constant air draw comes into play, and it isn’t needed for char. :slight_smile:

I didn’t know that, but it actually makes sense since a lot of the smokey flavor actually comes from chemicals in lignin. I haven’t ever purchased it. My wood source is brush, so charcoal makes a lot more sense in MY case. It isn’t everyones.


Thanks for the answers everyone, they help me a lot. So what happens inside the gasifier if you have a leak of outside air? Does the mix combust inside the gasifier past the choke and just come through the system as smoke? Or does the oxygen just bind to the other elements and make smoke without combustion, just like spoiling the mix?

By the way, my latest test yielded no results I used a thermal gun to take a couple of readings where I could so I could further diagnose and I took a couple of videos - if I can figure out how to post them directly to my other post I will, I don’t have a YouTube account so ill see if I can upload them.


Derrick you’ll need to upload them to a video hosting website and link it. Videos don’t upload directly to the forum.


… all transformations take place in the gaseous state, the shape of the area, the density of the pieces of fuel, the temperature and the supplied oxygen to a certain area,… the quality of the gas results, if the gas is not combustible, the resulting gas burns inside the gasifier, that is fact, most good gasifiers produce good gas and some carbon soot, they work in a safe way, where there is always enough coal, which consumes all the oxygen far from the exit, but in your case, the oxygen penetrates all the way to the exit and beyond, probably a void is created in in this area, the fuel does not flow and does not fill the space, I guess…


I want you to try this please Derrick , Go to your machine don’t light it just close the hopper lid go to the flare tube and place a small blower , be that a mattress fan or even a hair dryer so now it is blowing air through your whole system with a hand held spray bottle filled with a few drops of dish washing up liquid and some water start spraying all your pipes fan body tank everything all the way to the lid , that s all that is needed , once your at that end and you had no soapy little bubbles showing then you have a good air tight system , then its something else causing the issue , even the style of the flare tube can cause the flare not to stay lit , does your stay alight if you hold a flame torch under it ? some times after pulling with a high speed fan try slowing down the fan a little .
That’s about all the advice i can give you , i really want you to get that first flare soon before it does your head in .
All the best Dave


We the answer is it depends.

Wayne posted something a few days ago about leaks on the premium side but I will restate a few things.
If the leaks are before the reduction zone. They don’t make much difference until they get really big.
If it is when the gas is still hot enough to combust. It will actually burn up the gas and come out as CO2 (smoke). That is what we call a hot leak.
If it is in the filters and pipes after the gas is cooled down it just weakens the mixture. Most systems you have some adjustments to an extent. But once you get to a point where the air intake valve to your engine won’t turn off any more. Then they have to be fixed.


Case in point the carb I just put on the Toyota I tore the air clean to carb gaskets badly, but I wanted to drive the truck so the mixer body went back on with no gasket. My air mix valve is now closed half way what it was before when it had the gasket, big air leak enough to see woodgas rolling out from under the mixer when I shut the motor off. Other then air adjustment, this additional oxygen does nothing. Now if that leak was further back in the system weakening the woodgas mixture it could be less controllable. Yet Wayne drove his v10 dodge not only with Leatherman pliers size holes in the hopper, but no hopper lid at all, down right fema mode. Truck still produced clean gas that ran the motor. I believe Jan at one time had his hopper lid come flying off while going down the road and truck still ran! I think a passerby pointed it out to him his truck was billowing amoke if I recall correctly


True. My hoppers like to puff now and then if the filler gaskets don’t seal. Other than that a small leak into the hopper doesn’t hurt anything.

Derrek, read @JocundJake’s post above. I doubt your problems are leaks. The charbed is the key. As long as your charbed is in good shape you should be able to make burnable gas (even if you still have small leaks).
The charbed should not be too tight or too coarse. You can feel it with your poker, but that can be tricky without a reference. That’s why we use vacuum guages. One way of telling if the charbed is too tight is to listen to the vaccum blower. There should not be much difference in the sound of it with the filler lid open or closed.

About smoke. In the world of gasification it means tar. Thick white smoke in the hopper is normal. Any of it passing the charbed is bad. Wayne often refers to a light haze coming out of the blowers as being OK. Smoke at that stage often means a too coarse charbed or raw wood too far below nozzle level. In my opinion it’s actually easier to determine tary gas with no flaring.
I have no doubt you at some point aready made good gas. If you like to flare, depending on the size of your blower, try increase the diameter of the flare tube. Most likely the gas speed is just too high.


Thanks Dave, now that my lid is (relatively) air tight I will try this as you suggested when I have a little more time this weekend and see what it shows.


Just wanted to give a general big THANK YOU to all of the replies above since they have really helped me to understand the process much much better - you guys are the best!


Air leaks above the combustion zone like an open top can lead to your hopper contents catching fire if you shut down with it like that

If air can get into the system in such a way that your burn out empty then you have a potential fire hazard

Smoke will try and puff out leaks on shut down

Look for them and try and seal them up
This is not a safe condition because gasses can find there way into the cab of a truck or car
They can collect in places and that can lead to fires, explosive mixtures and gasses dangerous to your health and life threatoning

On start up I like to purge the system with engine exhaust to avoid pockets of combustible gas that may ignite and pop or blow up damage the fire later plant

Leak controls reduce the possibilities of these things


Tom that is a pathway in your PC it won’t link to anything.

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