[Stoves] Purple flame

[Dean Still]

Hi Alex,

I experience that if there is the right amount of secondary air the flame
above the pile is sustained during the switch from burning wood to burning
bio-char even though the bottom of the pile is not yet glowing orange.
Maybe you're right that the tar is burning later when the bottom has fully
caught fire that gives the blue flame a reddish tinge. Good idea!

Ron: Maybe we have to burn the bio-char to get above 45% thermal efficiency
which is Tier 4 in the IWA metrics? I think it's great that a TLUD can be
tuned to either save or burn the bio-char to meet the needs of the
consumer, say urban vs rural?

Best,

Dean

On Sun, Sep 23, 2012 at 6:29 PM, Alex English <english at kingston.net> wrote:

>  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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