[Stoves] Inverse Diffusion Flames in TLUDs

Julien Winter winter.julien at gmail.com
Mon Mar 7 16:19:04 CST 2016


Hi all;

Here is an interesting article about inverse diffusion flames IDF similar
to what we see in many TLUDs:

Blevins, L. G., Yang, N. Y., Mulholland, G. W., Davis, R. W., & Steel, E.
B. 2002. Early soot from inverse diffusion flames. Prepr. Pap.-Amer. Chem.
Soc., DiV. Fuel Chem, 47(2), 740-741.

https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/47_2_Boston_10-02_0236.pdf

I have attached a photo of standard diffusion flame and an IDF of ethylene
flames near their sooting limits. (Kumfer, BM; Skeen, SA; Axelbaum, RL.
2008.  Soot inception limits in laminar diffusion flames with application
to oxy-fuel combustion.  Combustion and Flame 154; 546-556)
[image: Inline image 1]




In her article, Linda Blevins argues that soot forms on the outside edge of
an IDF, then follows a trajectory away from the flame, and escapes
oxidation.  In a standard diffusion flame, soot tends to be oxidized in the
tip of the flame.

One common type of syngas burner for TLUDs has secondary air entering the
gas burner through small holes.  The flamelets arrising from these holes
start out as a type of IDF.  Syngas rises from below, so the underside of
the flamelets should be more fuel rich than the top side (which may be
lean).  Therefore, soot production in a TLUD burner should be greatest on
the underside of the flamelets.  If the flamlets coaless to form a sheet of
flame across the width of the gas burner, then (most?) soot particles will
have to pass through this flame and oxidized to varying degrees.

However, if we turn down the gasification rate in the TLUD, so there is not
a continuous sheet of flame across the width of the burner, is there a
change in the nature of soot particles in the exhause gas from the stove?
Will there be a higher proportion of polycyclic aromatic hydrocarbons vs
black carbon from a turned down TLUD?  Of course, when turned down the mass
of soot emitted may not be very high.  All the same, this is an example of
why we should characterize emissions from stoves over a wide range of power
levels when assessing health risks.

Cheers,
Julien.



-- 
Julien Winter
Cobourg, ON, CANADA
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