Mike, here is a walk around video of my charcoal lawn tractor project 3 or 4 years ago.
The 12 hp engine was seized so I put a 10 hp
in it. I have a mower deck for it but I don’t use it much because it only has a 32 inch cut. I don’t want to cut grass all afternoon when my 60 inch mower lets me do it in less than hour.
How did I miss this one Don… Such a complete efficient build as usual.
Hey Mike, I did some fuel consumption testing on my little generator project, and I what I came up with was about 3 lbs of charcoal plus maybe 350 ml of water gave me about a quarts worth of gas. The density of charcoal varies quite a bit depending on tree species, and how its being made, but the numbers I have seen posted here seem to fall in the 1.3 - 2 lbs/gallon range. The water is not strictly necessary when you start out, but i have found it makes for considerably more powerful gas.
Bear in mind too that you will invariably wind up with quite a bit of charcoal left in your tank at the end of your run, probably around half. Heat tends to build up in the hoppers on simple fire setups, but since the charcoal is so light, oversizing the fuel hopper is not really much of an issue.
I have never tried to refill my system when it was hot - maybe someone else can chime in on their experiences with that. Refilling with the engine running is going to be a problem with an updraft design, but you do shut the engine off when you refill your gas engine, dont you ? 
I also highly recommend the “leitinger nozzle” that Kristijan devised, but I suspect that any nozzle design that includes a large chunk of steel is going to do pretty well. The nozzle area gets very hot, but with enough mass the heat can be dissipated fast enough to keep it from melting down.
There is a dizzying amount of reading to do on this site - and even after thinking I have read all of the threads on charcoal, something new pops up (I also missed that build somehow, Don!)
Have you developed your charcoal production capacity yet?
Wow, thanks for all the great info guys!!! It will take me a day or two to go through it all. Not because I’m slow but because there’s so much to see 
David, thanks for bringing me back to the Simple Fire. I had seen that first video of Gary in front of the wood pile and didn’t realize so much development had continued with the design. I’m working through that long thread first to get educated.
Don, that is a great, compact build! It’s cool to be able to talk to you about it. Do you still use popcorn as the filter? What is your reactor tank made from and how many gallons does it hold? How long a run could you get from it if you were mowing your lawn (while upgrading your 60" mower to wood gas)?
Hi Carl, thanks for confirming the approximate 3 gallon equivalent to a quart of gasoline. Water sounds nifty but that would definitely be a future upgrade. When you say I’d end up with half the charcoal in the tank at the end, why is that? I’ve seen these units run on youtube but I haven’t seen them shut down or run out of gas before so I’m probably missing some obvious operational things…
As I learn more about this system (Simple Fire) I realize that the fan is to draw all the air out of the system. So I see that refilling would undo that. But if the engine is off and you dump more charcoal in, I’m assuming you’d just run the fan for a bit (or crank the engine) until that new air is evacuated and you’re back in business. Maybe?
That Leitinger nozzle sounds perfect. Seems like you could just take a big chunk of steel roundstock, drill down the center 90% of the way, drill the air ports in from the side and pipe tap thread the one end and you have a super massive nozzle.
I produce charcoal currently in my wood stove in the house. One small batch at a time. Without trying too hard last spring I made two chicken food sacks of charcoal. I’d need to make a better grinder and sifter. That production was for biochar for the garden. But to run the tractor, I think I can make enough during a heating season.
You guys are the best!
Never had a reason to refuel while running. The producer is on a hitch so that it can be placed on the front or rear. Rotatory mowers tend to need more power than ground engagement chores.
The simple answer is heat. As you read some of the old posts, you will no doubt come across a bunch of the theory of charcoal gasification, but its fairly spread around. Essentially there are 4 reactions happening, 2 of which you can ignore if you dont add any water. The first and most obvious one is just combustion of solid carbon C + O2 → CO2 which is exothermic. With the high airspeed at the nozzle, you can easily get temperatures of 1200-1300 C - hot enough to melt the ashes into glassy slag (also hot enough to melt just about anything else i.e. nozzles). This forms a lobe of heat, much like the flame on an oxy-acetylene torch. As the oxygen is consumed a reduction zone forms, where essentially the high temperature CO2 and the carbon that is heated from below undergoes the boudouard’s reaction C + CO2 → 2CO - this is endothermic, and requires temps of like 700C to convert the CO2 entirely to CO (I think).
Okay, so without writing you a book about it 
you have competing exothermic and endothermic reactions that it seems unlikely that we will ever really truly balance, and you also have a really hot lobe of gas forming at the nozzle. If you keep that lobe buried in charcoal, the heat is trapped - charcoal is good insulator. But as you consume the char in your hopper, the level drops, and eventually you expose the top of the lobe, and things start to warm up. Once the char-gas reaches a certain temperature its expansion will dilute it to the point it wont run an engine (if it hasnt melted anything in your system by then - like plastic sump hoses). Koen, who’s work you will be sure to see, swears by 20" of charcoal covering the nozzle, and has designed some pretty cool reactor designs that have a long tube on the bottom of the hopper. If you just have a bucket-o-charcoal, you will really only be able to burn about half of it before you start to overheat.
On the nozzle, you can see the one i built here 2000 watt charcoal generator project - #24 by oregoncarl
My wall thickness is not huge, less than 1/4" if I recall correctly, but the whole section of pipe weighed like 7lbs. I have thought that a big block of steel with a hole drilled in it could also work, it seems like the mass is the key. Don Mannes build a nozzle with a big steel puck in his Geo Tracker, which I believe also held up well. The nozzle is really the heart of the system, and there are 2 really interesting thread about what people have tried so far. Tungsten carbide seems like it might be another contender for indestructible nozzles.
I thought Torsten Källe’s 1942 article was inspiring.
Rindert
Mike you are going to love charcoal gasification. I don’t fully understand the attraction, but this stuff really flips my switches.
Drill your air ports in from the top of the pipe for better protection against catastrophic oxidation and at 45 degrees to allow easy nozzle clearing (use bent poking rod) without emptying the reactor.
You’ll find loads of other very clever tips as you wade through old posts.
Phew, I just read through Gary’s full Simple Fire thread, Carl’s generator thread and Torsten Kalle’s article. And watched a dozen videos that were included in those threads and side tracked down a few more rabbit holes. In doing so I’ve answered half of my own questions from above. Thanks for the links, now that I’m looking at the right stuff, it’s making more sense.
My new novice questions are:
It sounds like taller is better and narrower is ok but it limits overall charcoal capacity. What’s the minimum diameter of a reactor that would still have enough charcoal insulation to keep the sides from getting too hot for my backside?
After mowing the lawn, I’d close the inlet port to starve the reaction of air and shut down. Next time I start it up, do I have to clean anything out or would I just add more charcoal and light it up? How often would slag or other stuff need to be removed from the unit?
If I’m hauling firewood and need to stop for 15 minutes to unload, would I have to leave the tractor idling or can I shut it off and then restart without going through a whole ignition process?
Assuming exhaust gas recirculation, I think there would be two adjustment valves - Air into engine and Exhaust back into reactor. I can see that the air into engine needs to be fiddled with until the system heats up (kind of like the choke on the tractor now). Does the exhaust recirculation valve need to be fiddled with or can it stay locked in one position week after week?
Thanks everyone, the information here is wonderful and the people are even better. Trying to understand it without being pointed somewhat in the right direction was quite daunting!
Hi Mike, Well, welcome to the dark side!!! (yes, another one) Kind of interesting that seven or so years ago only a few of us here were interested in charcoal gasification. My how times have changed. But Hey, as Bruce says, “it really flips my switches” and we welcome another convert. OK, all kidding aside charcoal makes an easy fuel to gasifiy for small engines. The gasifier is light weight, the chargas is easy to clean and you have quick start up times. Generally within two minutes. The down side is fuel preparation and a dusty fuel.
I’ll kick in here to answer your questions. Taller is better, yes. You need that depth of charcoal over the oxidation zone/reduction zone that Carl did so well at explaining. The gasifier on my8hp walk behind Gravely is a milk can about 12 inches in diameter and 24 inches high. I get about 45 minutes of run time before refilling. (refilling happens when the charcoal bed has only dropped 8 inches.) Let me recommend you use a vessel 12 to 14 inches in diameter.
Shut down is as simple as capping the air inlet and walk away. Start up may require you to run a poker into the nozzle thereby knocking any ash away and allowing fresh charcoal to take its place. If you have done this say 5 times, there will be a point where the contents of the gasifier will need dumped to remove the ash. To date, all my ash has been very easily broken and not formed into slag. Keep the ash and use it with water to clean your greasy hands. Works amazingly well!
If you stop for a legnth of time. Just cap off the air inlet to keep the fire from consuming more charcoal while you do other chores. When you are ready to go again, unscrew the cap, turn on the start up fan and as soon as the chargas can sustain a flare, fire up your engine. The charcoal will stay lit for hours, depending on how hot the oxidation lobe was when you shut it down. If the fire went out, you only have to give it a quick light with a torch to get it going again. The Exhaust return valve can be fixed. As you watch the glowing charcoal in the nozzle, open the exhaust valve until the glow goes from a bright yellow to a bright red. At a bright red, you will be able to easily see individual particles of charcoal as they burn.
You can also refill your gasifier when the unit is hot. Shut off the engine, open the gasifier and keep your head back. If the carbon monoxide is hot enough, it will “poof” when the oxygen hits it. then the flames will settle down and you simply dump more charcoal on top, refill the gasifier, put the lid back on (air tight) run the start up fan until the gas is flareable then start your engine and keep working. Maybe 5 minutes to do this.
Just a heads up here. Gasoline is a very efficient and easy fuel to use whereas charcoal takes work. However, a big part of the satisfaction for me comes from knowing I can make my own fuel. And there is also a HUGE amount of satisfaction you can get when you finally drive around on charcoal. In fact, we recommend you buy 5 lemons before driving around to help dim the big smile that happens when it works.
Gary in PA
Thanks Gary for the reply! I’m intrigued by this technology. Fueling my garden tractor, maybe a wood chipper and maybe a generator with homemade fuel would be wonderful. Knowing I only need one of the valves to be adjustable is a relief. If I’m really crafty, I can use the tractors choke lever to adjust the air valve. Now I just need a heated shop and some time and I can get going on this.
I’ll just keep more questions coming while I’m at it 
Do people make chambers with two diameters and a gradual taper between them? Say 10-12" wide down in the oxidation/reduction zone, flaring open to 18-24" about 20" up. Then you could have more capacity before your charcoal gets low without having as tall a unit or as much charcoal down below the 20" mark.
Is there a grass fire risk with one of these? Or if there is, can it be resolved?
I saw a thread by a wonderful gent who used a 5 gallon metal can that seemed to buckle after a few uses. Does the system create a strong vacuum when shut down and capped off?
Has anyone found or used a start up fan that is in-line between the engine and the gas generator? So that you run the fan to get a flare and then turn it off and let the engine suck gas through the fan during operation? Not sure if that would make things easier but the flare tee could be closer to the engine intake and maybe make starting the engine easier. Or maybe I’m just getting way to creative already. Damn newbies…
One of those air mattress pumps wouuld do that nicely.
Thanks Andrew, those could do the trick.
Maybe I’m imagining a problem that doesn’t exist but it seems like if the fan was inline to the engine and the flare tee was right by the carb, the changeover from flaring to running would be slicker. As long as the fan/pump didn’t block the flow of gas through it when it was turned off.
And then you could just use one valve on the flare pipe to simultaneously turn off the flare and allow the engine to run. IE no valve to turn between the flare tee and the engine intake.
You would have to close the air mixture valve while flaring so you would not push gas out of the air mix valve?
At the end of a run the temperature spikes so I wouldn’t want the gas going through the fan and possibly warp it. That has always been my thinking. If your engine has a starter it doesn’t matter if its a pull cord then for sure get the gas as close to the engine as possible to make cranking easier.
Ahh, thanks guys for straightening me back out. Looks like I had a solution in search of a problem 
I don’t want to divert you from your noble gasifier quest, but if you live in a cold climate you need heat in your shop.
Rindert
Thanks Rindert! I love permies.com and those types of heaters. I have a relatively large greenhouse that I’m hoping to heat with compost but if that fails, I’m dreaming about a charcoal generating batch box heater of some sort.
I should have been a bit more clear about my needs though. First I need a shop , THEN I need some time or heat. If I have heat I can work in the winter when I have more time.
You’re going to end being like Wayne. He built a bulldozer, a sawmill, a house, … and finally a bunch of gasification stuff. 
But hey! Nothin wrong with that at all.
Rindert
I have never seen a gradual taper as you describe, probably just because of the technical challenge of building it that way. Here is a design that Koen in Thailand came up with
Gilmore style? - #1019 by k_vanlooken
I think his bottom reactor tubes are only 5 or 6 inches in diameter. His nozzle points upwards, so that helps prevent a hot spot forming on the opposite side. I have always really wanted to build something in that configuration, but I have never been able to find a good thin-walled tube in that dimension.
As others noted an inline blower isnt needed, but If you look around, there are people that have done it with the bigger bilge blowers. I have never really had a problem with getting the char-gas close enough to the intake. Your engine is displacing a lot of gas with each pull, and you can get rich gas through a couple feet of hose in 2 or 3 pulls.
This depends on how you orient your nozzle. A lot of guys now run the air in vertically, instead of straight through the side. My first design basically just had a hole in the bottom of the reactor, and every hiccup in the engine would scatter some burning coals on the ground. Using a leitinger nozzle really eliminates that problem, as anything that falls down stays in the tube. A fine wire mesh cap would also help. Some designs use a nozzle over an ash-pit, but then you need to have some arrangement to light it up at the start.
Cooling large quantities of charcoal in a sealed barrel is a very bad idea. the vacuum it creates is capable of crushing a 55 gallon drum, or at least clamping the lid on so tight you have to drill or smash it open. In hindsight, drilling a hole would have been better than just hammering on the rim out of frustration - so learn from my mistake if you ever do that 
it was a brand new barrel too. Shouldnt be a problem with the gasifier, though, it will find some tiny little leak to equalize the pressure as it cools off.
I am in a similar situation, in that I need to build a shop before I can get too much more done on my woodgas setup. Hopefully it will stop raining soon…
