Experimental study on correlation between PAHs and soot in laminar co-flow diffusion flames of n-heptane at elevated pressure

As Polycyclic Aromatic Hydrocarbons (PAHs) are the main precursors of soot formation, the investigation of PAHs formation and PAHs transforming to soot is essential for understanding the soot formation and soot reduction in combustion. This study investigated PAHs and soot formation in laminar co-flow diffusion flames fueled by n-heptane at elevated pressures. By using the combination of Laser-induced Incandescence (LII) and Laser-induced Fluorescence (LIF) techniques, the distributions of PAHs and soot concentration in flames were obtained with the energy of 6 and 48 mJ at various detection times. The flame stability at different pressures was analyzed, and the relationship between the integrated signal intensities of Soot-LII and PAHs-LIF in the region near the flame centerline was discussed. The results revealed that, with the increase of pressure, the flame stability becomes worse and both the soot and PAHs concentrations are increased. The integrated intensities of Soot-LII and PAHs-LIF in the region near the centerline of the flame scale with pn. In addition, the integrated signal intensity of Soot-LII has a good linear correlation with that of the PAHs-LIF, and the slopes of correlations are 0.33 and 1.81 at the laser energy of 6 and 48 mJ respectively.