Hey BrianW
A few very operator engine running experienced points.
Screw that first Blue flare for IC pistion engine running!! IF you were to IC piston engine adjust for that crap gas it will not have very good power; and will not want to run on any other more energy dense woodgas.
Your #2 flare is great engine power gas. Your #3 will work but be an ignition timing bugger.
You DO NOT filter into good engine gas. Cooling only de-humidifies, Some; condensate washes, But especially DENSIFIES the engine fuel gas.
Untimate test before engine of woodgas usibilty is will it spark ignite and stay lit. Use a flint tipped welders striker for this. The engine does NOT have an open continious flame inside of it.
Your problem is still in that hearth core!!
Your jets to restriction out to the grate is too shallow resulting too small of an active volume with huge gaps between the air nozzles effective HOT spews.
For a low internal velocity system you’d want to raise the jets 3X the hight. ADD more jets to a 4" perimeter spacing and tighten up the diameter to ~12".
For a High Velocity system, raise the jets 2X. Again, add more jets to a 4" perimeter spacing. Tighten up your diameter to ~10".
Your sucsess will not be determined by your air/gas preheating. Many successful with direct to the outside, vertually unpre-heated air. THEN you must use very dry wood. For your current build style just go the Imbert/Hessleman way and manifold connect the jets within the gas space. Let in air flanged out the side into this manifold tube like it appears you are doing with your liting port.
This individual air tubes originated in the 40’s for below deck Baltic sea marine systems to COOL things with no outside air exposure and should have been left there. Hard to build. Hard to seal. Only so-so effective. PITA.
Get your hearth sorted first. THEN filter and cool just to protect and give engine power.
Don’t want to use a WK hearth . . . . then look at Stigg Erik Werners tank built hearths - they work. Or Mike LaRosa’s brake rotor hearths: LaRosafiers - they work.
Both of these searchable here and out on the Net.
Regards
Steve Unruh