Help a newbie out!

Im having some trouble understanding some stuff, specially on downdraft reactors.

Since gas passes directly trough the combustion zone, how does it not light on fire?
I Know im wrong because obviously it works, if someone can explain that it would probably help me lots.

Also, some more things im probably wrong about :

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first pic: external heat, gas will be liquids, vapor, up to a certain temp that the gas will be clean and burnable…

second pic: the gasifier / combustion zone , gets only about half of the oxygen needed to burn… hence C+ 1/2 O2 = CO

Mixing the CO with O2, and you’l free the energy and get CO2


Short answer is: A lot of it does burn, just doesn’t have enough o2 to burn completely. Also, burning (actually, “heating” since it’s not all about rapid oxiation) is actually necessary to crack many of the larger “gooeyer” molecules. Some of the tars and oils get broken down into safer/more usefull gasses. Some water too.
Obviously just a nutshell answer.

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Thanks a lot! that clicked now in my head, now i also get why downdraft reactors are supposed to create cleaner gas, since the tars and oils that would just go trough the output in an updraft have to go trough a higher temperature zone.