Soot emissions of steady and oscillatory candle flames

Soot particle emissions from steady flames have been extensively studied; however, less attention has been given to oscillating flames. This study aims to characterize the emission of soot particles from oscillatory flames generated by burning two bundles of candles (four candles per bundle) and compare them with a steady flame case. When two oscillating flames interact at varying separation distances, they exhibit two oscillatory modes and one steady mode, namely, in-phase (IP) oscillating flame, oscillation suppression (OS) flame, and anti-phase (AP) oscillating flame. Time-resolved flame images were captured using a digital camera, revealing that the OS mode represents steady flames, while the IP and AP modes represent symmetric and asymmetric oscillating flames, respectively. The flame height and the area were measured for both steady and oscillatory flames. The mean flame height remained nearly constant across all flame modes, whereas the mean flame area exhibited significant variations among each flame mode. Additionally, the diameter of soot particles was measured using the dynamic light scattering technique. The results indicate that steady flames produced the smallest soot particles (78 nm) compared to their counterparts in oscillatory flames. Furthermore, within the oscillatory flames, the symmetrically oscillating IP mode generated larger-sized soot particles (129 nm) compared to the asymmetrically oscillating AP mode (102 nm).