Effects of pressure and CO2 dilution on soot formation in coflow ethylene/air laminar diffusion flames by numerical simulation

Abstract

Numerical simulations were conducted to investigate the effects of CO2 addition to the fuel side, ranging from 0 to 0.2 mole fractions, on soot formation and the flame structure in ethylene/air laminar diffusion flames at 1, 5, and 9 atm. The object is to lay a foundation for future research on the generation characteristics of soot under actual operating conditions. The soot inception steps were considered as polycyclic aromatic hydrocarbon (PAH) collided with benzo(ghi)fluoranthene (BGHIF), benzo(a)pyrene (BAPYR) and benzo(a)pyrenyl (BAPYR*S) (5-Ring structure) as soot inception steps, while surface growth via hydrogen-abstraction-acetylene-addition (HACA) and PAH condensation, and oxidation via OH/O2 processes. The results showed that elevated pressure changed the flame structure and increased soot loading significantly, which decreased the peak mole fractions of H, O and OH radicals and soot precursors, then concluded that PAH condensation and OH oxidation under high pressure were the important mechanisms for the soot formation. The addition of CO2 at 1, 5 and 9 atm significantly reduced the soot volume fraction, while the addition of CO2 at 5 and 9 atm led to an increase in the peak OH mole fraction in the flame, which led to an increase in the peak OH oxidation rate, and further reduced the PAH inception, HACA, and PAH condensation rates, and this trend became more pronounced with the increasing addition of CO2.