[Stoves] Stoves and STEM education

Tue Feb 26 14:00:15 CST 2013

Dear Jock

Great picture.

Something try: put a fat nail into the smaller holes and twist them to the
right to make the hole such that it forces the air to flow right, not
straight in. Don't do this for the large holes.

The result is a strong tendency to form a vortex which is continuously
disrupted by the large jest pointing in, giving great turbulence.

The tall pillar of sooty flame you mentioned is caused, ultimately, by the
pack of penetrating power of the air entering the holes. If they are larger
and fewer, the inrushing air can reach the centre. If the penetration is
good, the soot disappears. 

The idea of allowing secondary to enter is widely known, but good
implementations of it are few. The concentration disk somewhat compensates
for this lack of penetration but it still has issues (on the same count).
There has to be enough draft above the secondary air entry point to pull the
secondary air into the middle.

Some have realised the problem but not the cause, and added a central hollow
pillar with holes in it attempting to get the air into the middle of the gas
stream. Again, the disk can help, but it insulates/isolates the fire from
the top of the fuel bed which causes additional problems related to
maintaining the gasification. It also increases ignition emissions, in my
view.

Although we speak of a flame burning section above the secondary air
entrance, it is not only for burning the gases, it is to provide sufficient
draft to get the mixing right. When failing to get the draft right (pushing
the flame out to burn against the pot bottom) people have added fans to
compensate for the lack of draft. A fan is just a predictable source of
draft and you can get the same result with a chimney (section).

Regards

Crispin

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