Kristijan, I follow you to a point, but we need the charcoal for our hot gas to go thought so it will convert to CO, methane, and H2, CO2 Any time you clean out the ash, charcoal pieces, and fine carbon, you can sift the ash and fine out and replace the charcoal in the hopper. It will be consumed advenually. It just can’t keep going though with out being changed into CO, Methane, H2, CO2 sooner or later. The proof is you never have any clinkers in the bottom of your wood gasifier, like you do in the Charcoal gasifiers. That is because of the char is slipping through, and ash. I picture it like molten lava moving, except it is charcoal in all sizes becoming ash once the gas are extracted. Even in a Charcoal gasifier you need the charcoal for the conversion. The only difference I see is the ash just sits there and fuses into a clunkers right by the nozzle holes.
In a wood gasifier there is a lot of moving , swirling, flowing, from the nozzles area and on down past the grate, to where the air slows down in the drop box if you have one or hot gas filtering area, or slyclone filters, usually you do not see char pass this point.
As far as I see the best thing to help when the gasifier is at the 1450 plus *f range at the grate, is to add dry cold air if you have it to add, it’s dense not expanded like hot air, it will help with the moisture going though the fire tube, causing more H2 to be formed by cracking the H2O. It will also help start to cool the gasifier down a little if running hard and if you are not over pulling it.
This is a something I would like add on my gasifier, a cold air add after my muffler preheated air.
I think everyone has said it " The Big Balance " inside the gasifier.
Bob
Bob,
My statement was we need to capture as much charcoal in the firetube as possible while it operates. It doesent matter if you put it back in later, yes, it will burn and get gasified, but it will loose some of the potential to crack steam. We need it there when it gets made, this is the lmbert self adjustment principal.
There is no need for sliping char. My gasifier slips a teacup of char per month, lets say 500 miles. Never got clinkers. The bigest differences between wood and charcoal gasifier are the different temperatures and the fact that the direction of flow of ash is pointed away from the air nozzles for wood gasifir, but toward the air nozzles for charcoal gasifiers. This means ash accumulates near the chargas nozzles.
Edit: l just reread your post, we basicly ment the same thing. Sory if l look liked like a smartass 
Okay I hear what you are saying, Kristen. How do you keep so little char from slipping, I would like to slow mine down some. I know my gasifier is bigger , but I slipping a hole lot of char. Maybe Chris is right, my Right foot has alot to do with it. Lol
It is the difference in our gasifier’s in design, WK verses Imbert and size.
Bob
I think its the grate. Mine is fixed and has narrow slots with surface area about 150% of the restriction. But, l allso have a very " cilindrical" reduction. This alows me to have good gas velocityin the reduction, sweeping it of any ash, while the grate doesent alow char to slip.
There is a scetch l posted in TomCs gasifier thread recently, you can look at what l mean if you like.
Bob, I think it’s also possible we, with our tiny charbeds, are pulling through from time to time - oxygene down into the dump area consuming the char.
Kristijan, what do you think?
Hmm l dont know… but we can test that! Ill empty the ashpit today and put one big photografed peace of charcoal in. Well see if it changes in shape after a feew hard pull drives.
Wayne use to put a newspaper in the dump to check for airleaks. Survives if there’s no oxygene present. I don’t know if it’ll fit in my dump. Maybe stamps
Hi guys,
I think this the answer por the 10% that Mikkonen states:
Dry wood: 59% final
“Wet” wood: 53% final
59 - 53 = 6%;
6% is “almost by a fraction” 10% of 59%.
I think that that´s what he means by a gain of 10%, comparing dry against “wet” wood.
Hi Abner,
It beats me how people interpret numbers, i can’t find the relevance 
“59 - 53 = 6%;
6% is “almost by a fraction” 10% of 59%”
Fact is; changing the temperature for the incoming air, for the gasification/oxydation process, does changes the gas contents, for better or for worse… it all depends the build of the interna from the gasifier.
Changing the gas contents also does changes the pressure from the combustion mixture…
Playing with data, comparing temperatures vs gas contents, reveals that, the colder the gas enters the engine, the better/more gas can enter the engine. This colder gas/air mixture benefits the power more then a change in the gascontent.
Also, colder air inlet, combined with more moisture in the wood does make better/stronger/cleaner gas, in a good gasifier offcourse, compared with preheated air and dryer wood.
The benefit lays in , in this case, in the hydrogen content, that increases the fuel reactivity in the combustion chamber of the engine.
Resulting in, better energy efficiency, more torque vs energy consumption.
Working with a “hotter” reduction zone, reduces the amount of Co2 leaving the gasifier, hence less losses from the energy input vs power on the wheels.
Edit: the most important zone is; the transition between oxydation zone and reduction zone, it is at that point that a good gasifier makes or breaks…
Not to look like I’m preaching from the gospal and again this is my interpretation but…
In Mikkonen’s book he argues that in a wood gasifier, wood 100% dry contains enough oxygen and hydrogen “chemically” bound within the wood that additional oxygen and hydrogen in the form of water/humidity is not needed and only disturbs the gasification process. Temperatures must exceed 800C for water to be transformed to hydrogen and CO and excessive water can steal the heat away from the reduction zone by having to transform the water through it’s different physical states i.e liquid to gas. If you can’t keep the fire hot due to vaporizing excessive moisture than the transformation of water to hydrogen will be stifled. Gasifier design or not if things are too wet and cold I can’t see high quality woodgas being made, I am open to being wrong however.
I don’t argue that IF the excess water could be converted to hydrogen and CO if would provide a more energy dense gas but without using external energy input the wood containing this excessive moisture would not be able to reach and maintain appropriate temperatures for this process to unfold.
Personally I’ve experienced this on my gasifier when using excessively wet wood, just didn’t have the power that it normally did on “dry” wood. Best driving i’ve experienced was with 2 yr old seasoned hardwood stored in a barn (felt very dry).
Hi Dustin,
Nope you’r not preaching, you’r correct in your understandings of Mikkonen’s book.
The only thing i wanted to point out is: find the balance between cold air/humidity and learn how to observe and understand each ones your gasifier and with that gathered knowledge being able to control.
Trying to put it in 2 words:
Wet wood likes cold air inlet / heat transfer to the hopper, maximum condensate drain above the oxydation zone.
Cold air contains more oxygen per volume and it is the keyphrase in gasification: control your oxygen flow… balance the oxygen with the fuel you are using…
Dustin, What is your experience with the ceramic insulation versus your earlier metal fire tube as far as temperatures are concerned. Do you think the zone between oxidation and reduction is hotter by keeping the heat in that zone rather than using some of that heat to heat incoming air and then re-introducing some of it back through the nozzles? (saves the firetube) My ceramic blanket is 2 inches thick so I am thinking that most of the heat will stay in the hot zone. I am also thinking of not having any air preheat tubes before the nozzles to keep it light and simple - hence the original question for this topic. I appreciate all the feedback so far.
I just saw this paper* It is Dr. Shu’s how to make char in 10 minutes using molten salts, because you heat up a salt (it isn’t table salt) up to like 300C and dump the liquid salt in, and it pyrolyzes the material into char and you can capture all the pyrolysis oils, and such that come off it… But then he ran a test at 500C with a more corrosive salt and added an oxident to the mixture, and he got no tars. The paper doesn’t say exactly what they are using. However, it is pretty common to use alumna-silicate or there are a few others as a catalyst, and some of them are found naturally in clays. The result tables are fairly interesting to look at, because there isn’t much for tars and yields went up.
Thanks for bringing this topic up Don, I have often wondered about this! I built mine as Wayne was putting out the build videos and if I remember correctly I put 5 ea 1/2 inch nozzle holes in and I think that worked out great for my size engine! I noticed as time went on we started using bigger holes and then more and more of them!
I thought the idea was to “starve” the system of oxygen but it seems now we are giving it all it wants and maybe “flooding” the reaction zone! Please correct me if I’m on the wrong tract, Herb
Herb, I don’t consider myself an expert on this but I think you just brought up the big difference between the Imbert and the WK gasifiers. On the Imbert with the relatively small char bed you have to stick pretty close to the sizing chart for the nozzle sizing and diameters and more parameters such as engine sizing and velocities in order to stay within the narrower range to make good gas. The WK with the large char bed is much more forgiving and has a large turn down ratio. The nozzles “pour” in air for oxidation where the Imbert “blasts” in air.
Hi, Don, All!
We repeatedly hear curious statements about the oxygen content of air at different temperatures:
The ratio between oxygen and nitrogen in air does not change by changeing the temperature of the mix!
The expansion coefficient of these two does not differ radically.
Once air is taken in, one component cannot push annother component “into hiding”, or anything like that…
When a white-glowing charbed under succing produces a certain amount of CO molecules per second, it needs a certain number of oxygen atoms, and that the process “grabbs” from the incomming air-stream both at 0 and say 273 degrees Celsius.
The 273 C degree air has just to flow at double rate as the
0 C degree air.
The air (as a whole) is just thinner at higher temperatures, and provision for the flow-area has to be concidered at the construction board! (drawing table)
…
The other side of the matter is that preheating the primary air will raise the operating temperature, fulfill the oxidation part faster, and deliver a hotter gas for reduction.
Hi Max,
Correct statement and:
This is the part where as i consider not to be correct.
or to difer from opinion …
at 0 degree, the air will poor in ( startup ) and at 273, the air will blast in ( normal condition )
The only time that the oxidation will be faster is if the combustion material is been preheated.
It is the heat transfer rate from the combustible that is to consider, hence, the whole gasifier design is depending the fuel caracteristic period
Try the test with a blowtorch on a frozen piece of wood… you can speedup the gasflow but can not increase the oxygen content…
My statement: if you create a sufficient “preheating zone” above the nozzles, well balanced with preheating air/devices, the “plank” , then you can play, far less cumbersome, with a steady airflow on your nozzlesize, hence better anticipate the whole process.
You want to create a “steady” fuel flow, going down stream to the char bed, a sufficient temperature in the reduction zone, with a sufficient dwell time to do the job of converting al into good gas.
For all processes involved, its the combination of dwelltime + one mole to connect with another mole @ the correct timing / condition…
Its to the builders to make that happen 
keep the problem as simple as it gets, and play one parameter by the time… work gradualy to the solution…
At least 2 persons here on DOW are admirable funny to learn from :twinky:
one thinks for he does, not following the paved path and teaching us how it can be done ( WK )
one does before he thinks, also not following the paved road and also teaching us how it can be done ( Kristijan )
And so many more builders where i enjoy reading their endavours, their perspectives…
each off you deserving, imho, the same acknowledgement as an Imbert or any other builder before…
Hi, Koen!
31.10.2016
to mess. 37
Sometimes I just discuss a single item, assuming adjacent details being in tune with the one of interest.
It’s alright that a gasifier generating preheated air also provides preheated fuel when in full operating condition.
At least after a while with a plank helping.
Hopefully this is correct.
Hello Don
as far as temperatures I can only speak subjectively and hypothetically and have no objective numbers to give you. I do not use grate thermocouples and my temperature probes are located in different locations on the two gasifiers. Now subjectively I would say that the ceramic insulation (CS) firetube heats up quicker than the metal gasifier from start up. My standard operating temp on the CS firetube is 350-400C on the crossover pipe with the max temp i’ve reached being 500C. My original thought on the insulation was exactly as you stated, keep the heat where the reaction/gas production is happening. The blanket I used was 1 inch and I have had no issues so 2inch should be adequate.
With this first unit I did incorporate some preheating but less than a traditional WK. I definitely see the draw to have a preheatless air intake, less construction, less restriction. As Koen has stated perhaps a refocus of preheating the hopper and use of a “tuned” (appropriately sized nozzles) ambient temperature intake air. Only experimentation will tell
My 2 cents. I feel certain that at start-up, and for as much as 30 minutes after, the steel fire tube (3/8" in my case) is acting like a heat sink for oxidation/reduction. With steady highway driving, it takes that long for the nozzle TC to reach a steady state of 800-1000F. Am I right to assume that if oxidation temps suffer, reduction will suffer too? I’m guessing a blanket lined fire tube would reduce the heat sink effect at start up, and maybe during the run, keeping more heat inside, thus allowing higher internal temps in the right places?? Hopefully continued experimentation (like Dustin said) will give a better understanding.