Abstract
Previous studies have shown that alkali salts influence combustion processes and soot formation, although the effects seem to vary across systems. Moreover, fundamental studies on the effect of potassium and sodium salts on formation of polycyclic aromatic hydrocarbons (PAH), which are precursors in soot formation, are scarce. Here, we report a study in which the effects on PAH formation due to the addition of alkali metal salts (KCl, KOH, K2CO3, NaCl and NaOH) to premixed ethylene–air flames were investigated. Different size classes of PAHs were probed using both spectral and 2D measurements of laser-induced fluorescence (PAH-LIF) using the excitation wavelengths 266 nm and 532 nm, while detecting the fluorescence emission at selected wavelength ranges. Elastic light scattering (ELS) measurements were also used to complement the fluorescence data. It was found that potassium and sodium salts do not significantly influence the formation of small PAHs (2–3 rings), while decreasing the concentration of larger PAHs at higher heights above burner (HAB). Another important result was that the anion in the salt (Cl−, OH−, CO32−) negligibly influences the PAH and soot formation processes after dissociation of the salts.
Highlights
The scientific community has been in the quest to decipher soot formation for several decades [1–3]
The laser-induced fluorescence (LIF) signal intensity is detected in two different spectral regions corresponding to different size classes of polycyclic aromatic hydrocarbons (PAH), and the signal intensity in each region is related to the PAH concentration
5 mm all signal profiles overlap within the experimental uncertainties, both salts at all three concentrations negligibly influence the formation of small PAHs at higher heights above burner (HAB) in comparison with the reference case
Summary
The scientific community has been in the quest to decipher soot formation for several decades [1–3]. Soot formation related to biomass combustion and. There have been several studies on the influence of potassium and sodium on soot formation in applied systems, such as biomass and coal combustion systems [7, 10–18]. Addition of potassium has been found to reduce soot concentration [7], diminish particulate matter emissions [10] and improve catalytic activity in soot oxidation process [10–13]. Sodium addition showed catalytic activity for soot oxidation [14, 15], and an increase in soot yield [15]. The effects of addition of potassium or sodium are found to vary across systems. Potassium chloride (KCl) impregnation of birch wood in a wood stove increased the emission of larger particles (size ~ 200–500 nm) while reducing the emission of
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