Hi Dean,
I'm a bit confused by your first sentence. You seem to be suggesting
that there is a blue flame before the bottom is bright orange.
Tell me if this makes any sense.
In a TLUD the bio-char doesn't start to burn until the pyrolysis front
reaches the bottom. At that time the bottom is glowing bright orange and
char oxidation is taking place. The hot CO2 formed at the bottom then
may reduce to CO as it passes hot carbon above the bottom layer. This CO
can then burn with additional air in a blue flame above.
This is somewhat stove dependent but there can be some tar condensation
on the fuel chamber walls during pyrolysis. During the char burning
phase and perhaps in this case at the end when the top of the char pile
is radiant orange, this layer of tar could re-volatize and mix with the
CO to form a higher energy flame with a reddish component. It would also
be helpful if we knew what the excess air values were during these phases.
My two sense,
Alex
On 23/09/2012 8:10 PM, Dean Still wrote:
Hi Stovers!
I've been noticing a shift from blue flames above the burning bio-char
in a TLUD to purple flames nearer the end of the burn when the bottom
of the pile is glowing bright orange. I suppose that the blue flame is
caused by burning CO but I wonder why the purple forms after the blue?
The blue self sustaining flame doesn't heat the water in the pot as
well as the purple flame phase although the pile of bio-char is fully
ignited at that time and may account for the more rapid rise in water
temperature.
Any ideas?
Best,
Dean
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