I watched your video several times and spotted a few things. At 1:04 you turn on your fan, however at 1:28 to 1:30 I see some smoke coming UP through the fire tube instead of being drawn down. This tells me that your fan is not powerful enough. Also locate your fan as far as possible AWAY from any heat that might melt your wires or motor parts.
I agree with Andrew and Koen, the wood as you show it isn’t quite loaded correctly for start up. You need to develop a bed of charcoal that the gas passes through to do the chemistry to produce the flammable gases.
This is the start up procedure I used and my grate. For meaningful results you must use DRY wood. Wet wood loads the smoke up with steam and you will never get it to sustain a flame. You can hold a torch to it and see that there is burnable gas there, but move the torch away and the flame will not sustain by itself. If you try to start an engine with wet gas, the spark plug immediately fouls with water and will never start. Now how did I find that out?!
I included this video to show what the start up flame should look and sound like before you load it up with fuel.
@ 1:18 this shows the fully loaded firetube. The fire burns up the tube and the CO2 and H2O (products of complete combustion) are drawn down through the the red hot coals and the C, H, and O atoms reunite to become the gaseous fuels, carbon monoxide CO, methane CH4 and hydrogen H. As it stands now you have incomplete combustion that is loaded with steam.
I never ran an engine off my FEMA because I started my work on the imbert gasifier, a superior design for sure, albeit more complex to build. The results, however, far out weigh the hassle of the build. I realize you’re working on a proof of concept for now, but the bug will get you. I used an air ejector system, but a fan will work fine also.
Hope this helps.