Effects of Oxygen Concentration on Soot Formation in Ethylene and Ethane Fuel Laminar Diffusion Flames

In studying the effects of oxygen concentration and molecular structure on the morphologies of the soot particles produced by hydrocarbon fuels, ethylene and ethane were chosen as experimental fuels. With a Gülde laminar coaxial diffusion flame device, a soot particle device was used to sample soot particles at different oxygen concentrations (21%, 24%, 26%, 28%, and 31%) and at different heights above a burner (HABs = 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm). High-resolution transmission electron microscopy (HRTEM) was used to scrutinize and analyze the soot particles at varying oxygen concentrations. The findings suggest that at the same oxygen concentration, ethylene produces brighter and taller flames. With an increase in the oxygen concentration, ethylene flames and ethane flames gradually decrease in height and become brighter. With an increase in the HAB, the average primary soot particle diameter ( D p ) increases initially and then decreases, the fractal dimension ( D f ) increases, and the aggregates transition from strips and chains to clusters. At the same flame height (HAB = 30 mm), the D p decreases, the D f increases, the carbon layer torsion resistance ( T f ) and the carbon layer spacing ( D s ) increase, and the carbon layer changes from a parallel arrangement to a curved arrangement to form denser network aggregations.