Influence of Hydrodynamics on Soot Process in Laminar Jet Diffusion Flame

The mechanism controlling the soot process of a laminar jet diffusion flame is investigated through experiments and theoretical analyses. The effect of hydrodynamic characteristics on the soot volume fraction and smoke point of jet flames is focused on. The luminous flame height at smoke point under normal gravity and microgravity environment were compared. The soot concentration and temperature distributions of laminar ethylene diffusion flames with different co-flow air velocities and fuel nozzle diameters are measured by light extinction method and RGB two-color pyrometry method, respectively. High co-flow air velocity and small nozzle diameter can reduce the soot content in the flame, resulting in a higher smoke point, which is related to the increase in flame temperature caused by a shorter residence time and better fuel–air mixing conditions. The simple prediction of the theoretical oxidation zone shows that decreasing the nozzle diameter may make the oxidation zone longer, favouring the oxidation of soot in the flame tip region. Furthermore, a brief theoretical analysis of the contributions of fuel exit momentum and buoyancy in residence time during fuel combustion is presented. It is considered that when the fuel outlet diameter is small, the nozzle diameter may affect the residence time and hence the smoke point to a greater extent. This work provides new insights into the influence of hydrodynamics on soot process in laminar jet diffusion flame.