Chemical effects of natural gas components on polycyclic aromatic hydrocarbons and soot formation in inverse diffusion flames

Abstract

This work investigates the chemical effects of ethane, propane, and butane substitution for methane on flame properties and sooting behaviors in inverse diffusion flames of natural gas in different ratios by a decoupling method. Results show that the influences of varying natural gas ratios on the concentration distributions of soot particles and soot gaseous precursors are greater than on temperature. After a certain amount of methane is replaced by C2–C4 alkanes, the soot volume fraction (SVF) becomes more centerline-dominated. Meanwhile, the average primary particle diameter increases while the number density of primary particles and the average number of primary particles per aggregate decrease. Due to their chemical effects, C2–C4 alkanes not only promote the formation of H2, C2H2, and C4H4 but also contribute to an increase in A2, A3, and A4 formation. As for the soot formation reaction rates, the condensation rates are promoted. However, under varying ratios, C2–C4 alkanes demonstrate diverse chemical effects on the coagulation rates. Among three alkanes, ethane has the most pronounced chemical suppression effect on soot inception, HACA surface growth, and oxidation process rates. The combined effects of increased condensation and delayed oxidation rates result in elevated SVF in natural gas flames.

Keywords

• Inverse diffusion flames
• Soot formation
• Chemical effect
• Natural gas