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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