I’ve been thinking about a small, updraft, charcoal gasifier. I scrounged an old galvanized garden sprayer. It has a nice fill door that will work for loading, and a few small holes for an outlet. There’s a larger hole, about 1.5 inches, say 3.5 cm, where there was a pump. I was thinking about how to plug it, and the thought overlapped with an idea I had about a safety shut off. If I were to put a coolant thermostat in that hole, with some grease or a gasket where 'stat closes, it would create a leak when the internal temperature reached the opening temperature for the thermostat, maybe 160 F/70C. This would lean out the engine when the char runs low, protecting the rest of the system. Do you think this would work? Am I asking for puffs and flames? I haven’t had problems, at least not flaming ones, with previous leaks, but I’ve never made any on purpose.
Leaking air with hot gas will usually make it burn at that spot. Not sure how hot it has to be, but I’d maybe set up a kill switch connected to the temp probe to shut down the engine.
You should just build a simple unit and get it working first. Then let the ideas come. Your perception will not be accurate and will change, once you build something and get to work. You are trying to solve something you have not even created yet.