[Stoves] Re: Blue Flame: was Re: Tom's WoodgasCampstove

[Crispin at newdawn.sz]

Dear Friends

Sorry for pressing "Reply to all" as I usually avoid that bu the topic is 
significant.

Dr Tom wrote:

+++++++++++++++
Three separate factors will make the flame blue:

1)  Burning fuels low in lignin (the precursor to tars) such as corn and 
paper
2)  Burning very wet fuels (the charcoal is consumed to dry each layer
3)  Burning the resulting charcoal (but this needs more primrary air and can 
result in lots of CO if the flame goes out)
For most purposes the flame color is not important.
+++++++++++++++

I want to confirm from a large number of tests with paraffin using an FSP 
stove (and encouragement from Alex English to explore this possibility) that 
the colour of the flame is not much of an indicator of a highly efficient 
burn or of CO.  I was otherwise convinced for some time.

Alex's point was that a flame can be quite smokey and still have a very low 
CO content.  This was not strictly about combustion efficiency, but about 
low CO.  I always equated the blue flame of the FSP stove to a low CO 
believing that it was the CO burning that was the blue colour.  Well this is 
partly true: it is the CO burning, but that doesn't mean all the CO burns. 
Raising the ignitor plate on the FSP stove ' too high' gives a noisy erratic 
flame with a lightning-like luminescent flame edge and a very high CO level. 
I have equated the strange flame edge with high CO.  A partially yellow 
flame does not mean high CO though it does mean a lower flame temperature 
(800 v.s. 1000 C).

On the other hand, testing a paraffin lamp for CO can be surprising: very 
low CO in certain cases, no blue flame.

I tested an FSP stove on high (about 2 kw) and low (about 500 watts) during 
a boil and simmer of 5.8 litres.  The emission of CO was very low all the 
time (typically 0.03% of CO2 emitted on high) and it still burned very 
cleanly on low.  Even when there was considerable buildup of black carbon in 
the stove (running a smokey paraffin fire) the CO remained low _on condition 
that_ the air was preheated.  The black carbon emitted obviously varied all 
over the place, but that only proves CO and BC are not really related (kudos 
to Dr Tami).

The low combustion efficiency of the low power simmer led to the buildup of 
BC on the stove parts, resulting in a lowering of the overall performance. 
Both boiling and simmering were about 57% eff. though the simmer should have 
been 65-70% if the carbon had burned.  It used 110 gm of paraffin (1/2 a 
cup) for the whole test which took about 75 minutes.  That is 22 cc per 
litre boiled and simmered (alu. pot, no heat shield).

I have on occasion exceeded 80% PHU with an FSP stove but I am concerned by 
output figures that high.  They look too good!  I will write more later on 
how that was achieved.  I think we are safe to say it is as efficient as a 
propane stove with similar emissions and about 1/2 the running cost.  The 
first ones will be on sale for $25 this weekend at the Rand Show in 
Johannesburg to gauge public reaction.

Best regards
Crispin



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