Influence of potassium chloride on PAH concentration during soot formation studied using laser-induced fluorescence

Abstract Previous studies have shown that addition of potassium chloride (KCl) reduces soot concentration and primary particle size. To improve the understanding of this phenomenon, this work focuses on investigating the influence of KCl addition on formation of polycyclic aromatic hydrocarbons (PAHs), assumed to be precursors of soot. The method used is laser-induced fluorescence (LIF), for which different size classes of PAHs can be probed using selected combinations of excitation and detection wavelengths. KCl solutions of different concentrations were aspirated into premixed ethylene-air flames, and spectral and 2D imaging PAH-LIF measurements were performed using laser excitation at 266 nm and 532 nm. PAH-LIF spectra using 266 nm excitation showed a peak in the UV region at around 350 nm and a peak at around 550 nm in visible region, where the latter peak intensity increased strongly with flame height. The normalised PAH-LIF spectra obtained using 532 nm excitation showed no spectral change with flame height. The main results from this study showed that KCl addition, firstly, had negligible influence on the formation of smaller PAHs (measured using excitation at 266 nm and detection at ∼ 320 nm), and secondly, decreased the formation of larger PAHs at increasing flame heights (measured using excitation at 532 nm and detection in the visible region).