"Fire" zone and fuel?

I didn’t want to hi-jack a great post going on, so figured I’d ask here.
What keeps the fire at the nozzle and not rising up into the fuel? Is it that we want to use 100% of the intake air that we let into the burn chamber while it’s still at the nozzle? If so that helps me better understand why sizing charcoal is so important.
Simple question of the day(LOL)…on burning charcoal, is there actually “fire” going on or is it more of a bed of coals that’s continuously being fed as it burns down and more fuel drops into the zone?
Thanks guys.


Hi Allan,
it is the fact that the nozzle is embedded in the fuel. Much more fuel than available oxygen. So, the oxygen is consumed near the nozzle and after a short distance, there is no oxygen left to spread the fire further away.
So you are right, 100% of the intake air is used. First the char is burnt with the oxygen to CO2 (and heat released) and after that reduced with more char to CO (and heat consumed).
How far this is spread out is dependent on the fuel size: Big chunks have little surface compared to the volume, so the reaction zone need to be larger. Small pieces are vice versa, but the flow resistance increases if they are too small.
So for your imagination of the interior of a simple fire gasifier: It is a glowing ball of coals starting at the nozzle surrounded by more coals. As they are consumed, the surrounding coals drop in the glowing zone.
Hope that is a bit helpful for you.


Here is a video I took of my charcoal powered Geo Tracker with a mirror in the ash box looking up at the nozzle. If you look closely you can see the pieces of charcoal bouncing around in the nozzle air stream and gradually getting smaller and disappearing into gas and ash.


Neat videos, Don, like the muffler burner.


Thanks guys. I’d looked around a bit and pretty much figured it, but it’s good to see someone else confirm ones thinking.
Part of my asking is for anyone else wondering the same thing.