[Stoves] Model II iCan -- update

[Crispin Pemberton-Pigott]

Dear Jock

>I find it fascinating that much of the time most of the flames appear to go
DOWN into the iCan towards the fuel load.

The downward flame may be caused by air entering the can at the top edge and
travelling down the outer edge to the secondary air port region. This
indicates you have a good draft in the system because it would not do that
if there was an unsealed bottom to the stove.

It is probably not the best way to feed air into a fire because it gets
mixed with the combustion products from the fire if there is a pot on.
Usually a stove will burn like that when the pot is off. Once there is a
plate on top, or a donut-like flat ring, the air can't get in and the
combustion characteristics change, sometimes a lot.

It is probably wisest to put a pot on when making observations, to see if
you have cold, fresh air entering the combustion chamber from above,
ostensibly the exit. What you make notice is that flames which used to be
burning well, and short, start to emerge from the side of the top of the
stove, passing along the bottom of the pot. This is a sign that the air
supply is inadequate. If you cut off the abnormal air needed, the gas fails
to burn completely and emerges looking for additional O2.

It may be that the air supply into the open stove is far more than it needs,
and it perfect with the pot on. Hard to say without measuring. The point is
that stoves should be tested with a pot on if they are intended to be used
for cooking.

Placing a ring on top, a 'concentrator ring' or a 'donut' or a cone (which
changes the draft so be careful) or a perforated plate, can prevent fresh
air entering the flame zone from above. The behaviour of the flame changes
dramatically. I will send you a video of this effect directly because it
won't get through the chat system.

Regards
Crispin