Chemical Effects of CO2 and H2O Addition on Aromatic Species in Ethanol/Air Diffusion Flame

Abstract

ABSTRACT Exhaust gas recirculation (EGR) is an effective technique used widely to meet current emission regulations. In this work, the mechanism of H2O and CO2 addition (a main component of exhaust gas) on polycyclic aromatic hydrocarbons (PAHs, the precursor of soot) formation was investigated numerically in ethanol diffusion flames, motivated by current concerns on particulate matter (PM) emissions when ethanol is applied to modern gasoline engines, especially under high load and temperature. To understanding the underlying mechanisms of H2O and CO2 on ethanol flame, a comprehensive chemical kinetic analysis was performed by modeling gas-phase chemistry with PAHs formation up to pyrene. In order to distinguish the important chemical role of H2O and CO2 addition through partial replacement of N2 from their thermal effects, additional calculations were performed with two fictitious species. The numerical results show that the thermal effect of H2O and CO2 reduces the peak flame temperature, but their chemical effect influences the peak flame temperature differently. The results also showed that the addition of either H2O or CO2 led to a significant reduction of PAHs via thermal and chemical effects. The chemical suppressing effect of H2O and CO2 addition on PAHs formation was identified and attributed to reduced PAHs precursor species and slow of PAH growth process. However, reaction pathway analysis showed that the chemical effects of H2O and CO2 influence the PAHs chemistry differently.