Good morning Jan
I think yes . More open nozzles , less velocity and heat near nozzles allowing the reaction further down in the fire tube .
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Is there any difference between making an Imbert type, or making one more similar to Fema?
Does the heat increase caused by restriction have any significance other than removing the tar?
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Jan, the second drawing is more like a WK thain a FEMA. FEMA lacks any restriction at all.
But its the gradual taper of the conical charbed and heat being pumped via finned firetube/air preheat at the nozzles that boosts the temps and make a WK work so well. Also longer contact time with the charcoal
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Ok, thanks for answering. I have taken down my unit, the car is broken.
Would you recommend what I do to the image on the right instead?
I think it feels strange that the heat increase should go down in the ashes, or am I thinking wrong?
Oh no! Whats wrong with the car?
If you go the WK way you need to go all the way. Problem is you might have heat damage without any way to sufficiantly cool the firetube.
The heat concentrates above the restriction in this style gasifier. At the restriction its all more or less over, in contrast with an lmbert where its hottest at the restriction.
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The pipes for the nozzles are broken on my car.
It was fun to hear that you found the fault in your car. Now I do not understand again.
Do you mean that
there will not be a heat increase in a choke?
Most of the heat is concentrated above the restriction in such a sistem yes
Jan, Iāve mentioned before but Iāll say it again - I all depends on gas demand. And that goes for any gasifier. As long as thereās oxygen present - thereās heat made.
At idle you will run out of oxygene already in the nozzle area. In the other end of the spectrum - running WOT uphill - oxygen will reach all the way down to the grate.
Thereās no way of telling how a gasifier works without specifying what kind of work youāre asking from it.
Restriction: I would say itās mostly about sizing the gasifier internals. The smaller the restriction - the more dead ash-cone space.
At idle thereās probably not much happening at the restriction at all. Just a slow flow of gas, made right below the nozzles, finding itās way down through the char. At WOT you could almost do without the restriction.
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Ok so an Imbert works as a dual unit, really.
If there is a small need for gas, does the oxygen reach down to the restriction, if there is a large need, does the heat increase under the restrixtion so it gives gas even under the restriction?
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Jan, I donāt know what you mean by a dual unit.
All we know is char lumps will be consumed as long as thereās oxygen present, and when they run out of it they make gas as long as the temp stays above 600C. The char lumps donāt know if they are above or under the restriction or what kind of housing we put them in. They only care about oxygen and temperature.
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I agree with everithing JO nicely described. Except its not just oxigen that āeatsā char. As long as there is enaugh energy (read above 600c) water steam and CO2 will consume charcoal just the same.
Ha, but in a way JO IS right. Ith the oxigen atom in those two that does itā¦
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Why did my coal in the unit look white when I emptied it?
I also have a hard edge of carbon after the entire top edge of the fire tube, above the nozzles?
(I have abstinence without a wood car)
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Jan, 5 minutes ago I volontered to give wife a lift for an errand, but I canāt make up my mind which one of the woodburners to choose 
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Is there no not like button?
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Oh, and the carbon buildup at the firetube top is normal - baked tar and debrie.
Your char looks normal too.
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