A Numerical Study on the Influence of CO₂ Addition on Soot Formation in an Ethylene/Air Diffusion Flame

Abstract

Earlier studies have confirmed that the addition of CO₂ to a diffusion flame suppresses the formation of soot. However, a consensus has not been reached on the fundamental mechanisms of the suppression. In this paper, the influence of CO₂ addition on soot formation in an ethylene/air diffusion flame is investigated by numerical simulation, with focus on the fundamental mechanism of the suppression effect on soot formation. A special strategy is employed to separate the chemical effect from the thermal and dilution effects. The simulation results confirm that the addition of CO₂ suppresses soot formation through not only the thermal and dilution effects, but also the chemical effect. The chemical effect of CO₂ addition is primarily caused by the reduced concentration of radical H due to the reaction CO + OH ⇐ CO₂ + H, which suppresses the soot inception and surface growth rate. The chemical effect of CO₂ addition has negligible effect on soot oxidation process.

Keywords:

• Carbon dioxide
• Laminar diffusion flame
• Soot