23. of November 2016
The inside of the air-nozzle-tip is best, if it is made with trumpet-profile to accelerate the air progressively.
Pressure difference over the nozzle ~2 -- 10" H2O makes good to start with...
The bottleneck is like the female nozzle in an injector, there is only speed, the pressure builds up lower down.
Also, the bottleneck surface is O-rich, reduction takes mainly place lower down and in the bottle sides, where the char is tighter.
Yes, the "doghouse" or "birdhouse" was completely dribbled away; the roof-edge was never out enough or broad enough to hinder the "back-rush" of char, assisted by the return loop gases.
Then the roof-edge was glowing away too...
The intension was to have a cutting-in sharp beam, but you saw it!