Hello Giorgio,
That was my first successful project, though I made so many mistakes. I learned a lot. You can read here.
Now I have started to make a wood gasifier for small engines, based on Joni’s instructions for a small engine gasifier.
Rindert
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I made one like that using 20lb propane tanks if anyone wants to see the build, I scaled it up somewhat since the diameter of the tank was scaled larger than his schematic.
I think this would be very good in stainless steel.
With Joni’s drawing he says it will run a 300-500cc engine, I think mine could power a 400-700cc engine.
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Difficulties in ensuring a good mixture of gas and air:
- pressure resistances or negative pressure on the gas line
- intermittent overpressure on the gas line
- pulsating engine suction
- changing the quality of the gas
Vacuum on the gas line:
To a large extent, this would be solved by a diaphragm, which actually transfers the pressure conditions from the gas line to the air line, there is also a lever with which we adjust the tension of the auxiliary spring, thus enriching the combustible mixture.
Gas line overpressure:
The moving element in the mixer tightly closes the gas supply to the intake manifold until the engine starts the intake cycle, at which time air also enters in addition to the gas, because the gas overpressure also loosens the spring on the air valve and thus almost equalizes the conditions in the mixer work and the mixture is good
Pulsating engine suction:
The moving element will be made of light plastic, which will ensure a quick, easy opening and just as quick closing of the mixture, which will allow a good filling of the engine. The leading axle will have a small diameter, which allows easy movement and jams are almost impossible.
Changing gas quality:
The driver or operator has the option of “damping” the air by increasing the spring tension behind the air flap, thus enriching the mixture.
Please alert me to any other problems that I have not taken into account.
A little more physics to spice it up, the definition of pressure is the force on the surface and if we study the mixing of two gases in the same ratio and this ratio is maintained from the min flow to the max flow, the cross-section between the inlet opening of the gas and the air at the point of mixing should be the same, no depending on the size of the flow. At the same time, it is necessary to maintain the same pressure of both gases at this point, this is partly done during the preparation with a throttle valve and membrane for equalization, and the greater part is provided by the moving element, which is affected by the pressure and gas flow, and this determines the size of the offset and with this the size of the cross-section of the openings of the two gases and if you imagine, you can find that the pressure of the two gases will also be relatively equal at the point of mixing.
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That looks really interesting Tone, for the air, is there a “ring” of holes, or a slit all around?
Should a spring from an old SU or Stromberg carburetor work for this?
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I wind the springs in the lathe, and I get the wire for making the springs nearby from a craftsman who makes springs.
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Goran, I owe you one more answer. How to determine the mixing ratio? If you imagine a conical bed, where the moving element closes both the gas and the air… the vacuum of the engine overcomes the small force of the spring and the moving element moves away from the wall and the layer of gas flows to the place where the air holes are, and here is the cross section of the holes the air occupies the same share as the gas, so the gas only gets half of the cross-section, and so does the air. If you imagine the situation, you can also find out that the gas and air will already be effectively mixed at this point, which is also a condition for a good ignition. Below is a sketch for the show.
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Then i understand, that is really innovative, looking forward to follow this build 
And as you say, i can imagine the gas and air would be very well mixed/blended in this, which is important.
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I like how the fuel gas flows past the air inlets creating a venturi in TS’s mixer. The Venturi pulls air through the inlets based on fuel gas velocity. That should be more stable than balancing the mix with pressure alone.
I also like how the check valve aspect of the mixer has a large area. Small pressure differences acting on a large surface still generate a good amount of force. This will make the valve act under very small pressure differences which makes it easier for the engine to pull in its fuel-air charge.
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I find the idea of an enriching pipe very interesting for a gas mixer.
It would certainly help ensure a healthy curb idle. Has anyone tried this? Pictures from the Handbook of Biomass Downdraft Gasifier Engine Systems.
Obviously this drawing is an abstract but it could be adapted very easily.
I still need to do a complete cleaning of my Quadrajet but I could utilize the old Brake Booster port to add an enrichment circuit.
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Hi Cody, I installed a gas inrichment valve on my auto mixer set up if I need it. I use it when I need more gas flow when going up hill because my two 2" gas lines into the engine compartment become one 2" line and going through the Ford throttle body it is 1 7/8" port line into my auto mixer bowl so the 3/4" valve line was add and is operated from the cab of the truck. It works great, very noticeable when opening it up.
Bob
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I have. Twice. The Mercedes had a litle port right under the tb. Hooked the woodgas there, but it was too small to realy do much. Better thain blinding it thugh…
The Škoda has a biger port, half " or so on the manifold and l hooked woodgas there (restricted). Problem is this port is located at the side of the manifold and it seems that way only the woodgas isnt mixed propperly, one cyl gets the woodgas and the other less so it idled rough.
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The weather is quite rainy here, but I’m spending a little time working on the lathe, I managed to make a few basic pieces,… but there is still some precise work to be done… so that the wood gas mixer will be created.
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Very interesting! Please make a schema so we can understand.
Rindert
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Rindert, there is a sketch above in contribution 103, I intend to make something similar 
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You are an artist when it comes to fabrication Tone. My stuff is hiding behind the barn already!
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Not really Marcus, my had of for the both of you. I wish I had some of your skills.
A piece of art Tone. I have two lathes overhere but cant get any of those out of it.
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this mixer could be built by a 3d printer if an autoCAD plan existed
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You would need good heat and chemical resistant filament.
Carbon Fiber Nylon would be close but it becomes brittle as it absorbs moisture from even atmospheric air.
I know some have printed in PTFE for car parts but I think it’s on the weaker side of temperature resistance.
PLA is chemical resistant but also weak to heat
ABS you wouldn’t be able to use any cleaning solvents or it would melt.
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