Characterizing the Interactions Between Flow Dynamics and Soot Production in Ethylene Non-Premixed Pulsed Flames

Abstract

This study investigates the effect of flow dynamics on the soot temperature and volume fraction fields in a non-premixed pulsed ethylene flame generated on a Yale burner. Soot properties were characterized through absorption/emission techniques, while Particle Image Velocimetry with zirconium dioxide tracer particles was applied to the entire flame. The resulting velocity fields were used to calculate shear strain rates in different regions of the flame. The results showed that modulation significantly affected the soot distribution, with a variation of \(\sim\)12% in the soot volume fraction between consecutive phases of the cycle. During certain phases a higher injection flow rate is favored by the acoustic pulse, leading to an increased amount of fuel being burned and a higher soot formation. This behavior is related to the flow expansion in the upper regions of the flame, where high velocity zones coincide with an increment in soot temperature due to particle transport and accumulation. Also, areas exhibiting heightened strain rates are linked to elevated levels of mixing and oxidation. These regions are associated with a low soot volume fraction. This is likely due to enhanced mixing and oxidation under elevated strain rates, as suggested by previous numerical work, highlighting the suppression of soot inception and the predominance of oxidation processes during specific phases of the forcing cycle. The interactions between fluid structures and soot-rich zones were identified as a crucial aspect of overall combustion dynamics, with a direct impact on efficiency and emissions.