Bubbles are steam. Yes, the fire would need to heat the water to 2000C before it would start to crack into hydrogen and oxygen.
So, maybe high temp “pure carbon” charcoal is making gasifiers harder to restart or moisture or dust/ashes or “other gases.” I’m interested in the “pure carbon” idea, but I have used high temperature (electrically conductive) charcoal in my gasifiers with no problem getting good gas very quickly. I have sometimes noticed a lot of steam at the flare when trying to restart. In the past, I have assumed that the restart problem was ash coated charcoal. I’m surprised that we have not come across this issue in the old literature. Wait, I just remembered something in the Kalle gasifier document.
I found it:
“Apart from the reoccuring event of taking out the slag, the car was nice for long drives. But it was also my opinion that it ought to be possible to improve its accessibility. In other words: make it start easier and faster from cold condition or after a longer pause in the driving. What more precisely gave me the impulse of this possibility was that when the gasifier was freshly de-slagged and serviced, thus new fresh charcoals were in place in front of the nozzle, the car started significantly faster, maybe in just 5 minutes rather than the normal 10–15 minutes for a car that has cooled down. So I begun studying the reasons for this. The explanation was simple. The fresher, ash-free and cleaner surfaces were more reactive. I also found out that the size of the fuel were of great importance; particularly if the smaller charcoals had clean (new) fractures; a certain amount of moisture also appeared to be beneficial.”
Like using a water drip, moisture is beneficial because hydrogen is released when the hungry glowing charcoal reacts with the oxygen in water. Although the reaction temperature is high, it is still far too low to actually crack water if carbon was not present.