Chemical, Dilutive, and Radiative Effects of Simultaneous CO2 Addition to the Fuel and Oxidizer Streams on Soot Formation in a Co-Flow Diffusion Ethylene Flame

In this study, the chemical (CE-CO2), dilutive (DE-CO2), and radiative (RE-CO2) effects of simultaneous addition of CO2 to fuel and oxidizer streams (CO2–F/O) on the soot formation in a co-flow diffusion C2H4 flame were experimentally and numerically investigated. A detailed soot sectional model, including soot inception, soot condensation, H-abstraction-C2H2-addition (HACA), and oxidation processes, was adopted. The CO2–F/O showed an effective suppression on the soot formation, with the maximum soot volume fraction (SVF) decreasing from 5.46 to 3.42 ppm. The DE-CO2 contributed the most to the soot suppression, followed by the CE-CO2, and the RE-CO2 resulted in the smallest drop in the peak SVF. The CE-CO2 initially suppressed the reaction rate of C2H4 + H = C2H3 + H2 and then decreased the benzene (A1) concentration through 2C3H3 = A1 and iC4H5 + C2H2 = A1 + H. Both the CE-CO2 and DE-CO2 dominated the decrease of the soot condensation rate. The decrease of five-ring polycyclic aromatic hydrocarbon (A5) concentration caused by the CE-CO2 contributed the most to the decline of the soot condensation rate. While the DE-CO2 suppressed the soot condensation rate by lowering the temperature of the flame. The decreasing amounts of C2H2 and H radicals caused by the CE-CO2 accounted for the lower HACA surface growth rate. The DE-CO2 showed an obvious suppression effect on the formations of O2 and OH radicals and then lowered the O2 and OH oxidation rates.