Experimental and simulation studies on flame characteristics and soot formation of C₂H₂ jet flames

This work aims to identify the relationship between the temperature and soot formation in the C₂H₂ laminar flames. The effects of flow rates and equivalence ratios on the flame temperatures and structures were investigated. The flame length increases with the increase of the equivalence ratio. Meanwhile, the flame color changes from pale blue to bright green from the fuel-lean to stoichiometric condition, and further to bright yellow under the ultra-rich conditions. By sampling and observing the morphology of soot at different heights of the flame, we reveal the factors affecting the size of soot. As the flame height increases, the growth rate of soot agglomerates becomes faster. The contribution of surface growth to the soot particle size decreases gradually. The collision and aggregation predominate the soot growth. To uncover the soot formation mechanism, the average particle size and particle distribution as a function of height above burner were correlated with flame temperatures. Furthermore, the underlying mechanisms behind the nucleation and growth of nascent soot particles from polycyclic aromatic hydrocarbons (PAHs) were reveal via ReaxFF molecular dynamics simulations. The results show that the aggregation ability of PAHs decreases as the temperature increases. The aggregation ability of PAHs is also affected by size, and the larger the size, the stronger the aggregation ability of PAHs. Both the experimental and simulation results provide novel insights into the development of combustion kinetic model for soot formation in sooting fuels.