You’re right, even the best filter won’t make a bad gasifier good.
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I think I have one of the best design builds a WK Gasifier and believe me, I can easly make tar gases in it. But I make sure the gases have to pass through the really hot charcoal bed and the tars are changed into good burning woodgases. Running a gasifier hot and passing all the air and gases through the supper hot lobe and through the proper sized restriction plate or hole makes sure the tars are burned up and changed. The other 75 % of operation of the gasifier.
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i can promise this. by the end of my first gasifier, i WILL NOT consider it a sucess until i get all tars out. even if i have to make a modular multistage filter that uses cyclones, media filters, water/oil scrubbers, or any other type of filter i can find. being able to burn it up would be best, but i dont think i have found a wood gasifier that can get rid of all the tar. im sure there are plenty of steps i can take to reduce it from the offset.
start with charcoal, good dry hardwoods, good down draft design that cooks it away as much as possible. but there is an itch in the back of my mind that doesn’t want to hope for the best case scenarios. it may be misguided, but i want to plan for failures. nothing in my life has ever …just worked. and if i can plan for the failure ahead of time, maybe i can stop it from happening lol.
NOW THE HARD PART
I need to figure out what kind of gasifier design is best for wood pellets. i know thats not the best fuel, but if i can get pellets to work well, then i can make my own and store them en masse
any suggestions? there are so many designs out there. and im almost to the point of ignoring YouTube altogether. nearly every video on YouTube seems like click bait, and you only ever see the units they use works once then never again. makes me feel like a loit of them were just making videos for the views and that irritates me because its potentially passing out bad information that will destroy peoples motors because they trusted some kid on youtube that tells them to use a bee smoker to pump tar filled gas into a 2-stroke motor (if you seen the video, you know what i mean)
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Hi Thomas, your thinking is right, building a good functioning gasifier, with good filtration is the way to go. Aiming at filtering tars out is more of trouble/impossible, maybe useful at big, stationary applications, where lots of fresh, running water are available.
As others have said: filtering tars out are almost impossible, but can somewhat be done with lots of work.
Only working filters for tars i’ve heard about are from historical aspects, before the downdraft gasifier was invented, often looked like this: a wet scrubber, filled with coke, with continous showers of water (a lot) “washed” and cooled the gas, after that multiple “floors” with first 3 of planer shawings, then 6 floors of sawdust, the gas passing from down to up, filtered, and sawdust absorbed tars, needed lots of maintenance, the filter arrangement took up 4 times the space of the gasifier itself.
Another historical option was the rotating Linderoth filter, which i cant find any pic’s of at the moment (like a fast spinning centrifuge for gasses)
The modern options should be the electrostatic precipitator just as Kristijan mentions, but for tars it needs a battery of them, they can easily clog from tars.
Not my meaning to bring you down, more like encourage, much nice ideas and inventions show up on this fantastic forum 
About making charcoal and collecting tars i’ve posted some sketches somewhere, i don’t remember where right now, i can post a sketch if you’re interested? Or if someone else remember where they was posted?
In the case of making charcoal and tar (and turpentine, methyl alcohol, creosote, the “un-condensable” gasses are best used for heating the retort.
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Well then that concerns me greatly. If it’s essentially impossible to be rid of the tars, then would it not be reasonable to assume that the engine would be destined to fail? Maybe I’m misunderstanding something, I truly hope I misunderstanding something.
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All about temperature. Each wood no matter the moisture content or species has the ability to make tar. BUT. The whole goal to me is to thermally crack that tar in the fire, break it down into more energy dense fuel. If the tar is consumed we get a more calorific powerful gas. If the gasifier does not reach the correct temperatures the Tars will not be cracked, and they will pass through the system and end up causing any number of problems. This alone is one reason many start with a charcoal gasifier where the Tars have already been baked out by the charcoal making process. It’s very forgiving for a first timer to run on charcoal,vs glueing up an engine with Tars running on raw wood. The other big option is a condensing hopper,which will get rid of a TON of tar before it every reaches the super heated char bed. This can consume a lot of energy to crack the Tars cooling the fire lobe down, where some gasifiers get rid of most the tar in the hopper and let the fire consume the rest
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Okay let me explain here, and clear things up. Above the nozzles in the hopper area where the wood pyrolysis is taking place, turning the wood to charcoal tar is also being produced with moisture. We drain off the tars and moisture and into the tar /water condensation tank it does. Some of the moisture and tar go on through the gasifier past the nozzles into the hot lobe charcoal 2000 to 3000 decrees temperature.
The restriction opening makes sure moisture and tars do not by pass this area. The moisture turns into Hydrogen and the tars turn into Carbon Monoxide and Methane gases going through the hot charcoal bed on down to the grate carring moisture that is still not changed. The temperature at the grate is around 1500 f. to 1700 f. decrees in temperature. Soot and ash is also carried through. By the time it gets to the drop box cross over it is cool down to 800 f. decrees and it is a wet hot gases now. There should be no tars left now by going through the hot charcoal bed temperatures.
We just need to cool the gases to drop out the moisture and clean the soot and ash out of the good wood gases, then up the to engine to be remixed with air at a 1 to 1 ratio and burned into the engine.
The key is a very hot charcoal bed temperatures to do this and keeping it hot while in use.
Edit: And yes to what Marcus said.
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You know what the best feeling in the world is? Ending the day a little smarter than I started. Thanks for the comprehensive response
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Hi Thomas,
I think I know where you are coming from. I’m an engineer too. You seem to be trying to get modern reliability out of an art that mankind has not yet fully understood. If you want to completely eliminate all possibility of tar you will have to go the charcoal route. Then there’s the issue of sulfur, H2S that combines with condensate water to form H2SO4. And then there will be the problem of premature thickening of engine oil. Join the merry ride. 
However, I think that Tone’s tractor gasifier comes the closest to what you want.
Tractor with gas?
Rindert
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thats the plight of engineering though innit?
“can it be done?”
not sure…BUT WE ARE GONNA FIND OUT
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Thomas,
Don’t set the bar so high, that you get discouraged when the real world of physics and unforeseen circumstances smack you around. Have fun with this and learn as you go! Yes, you will be able to innovate. There is always room for improvement. Keep in mind this is essentially a mature, antique technology. It is the modern tight-tolerance, multi-valve, computer-controlled engines that are the problem, the old designs are more forgiving of error, or of less than perfect gas (whatever that is).
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Good advice for all new comers into the world of Gasification, Mike.
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Shoot for the moon. Even if you miss, you’ll land among the stars.
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Very true, but it’s a long way to that first star–take extra food. 
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my old man always said i was nothing if not determined…or hard headed…either way, the results are the same!
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