Effects of Carbon Dioxide and Water Vapor Addition on Benzene and PAH Formation in a Laminar Premixed CH4/O2/Ar Flame

Abstract

ABSTRACTThe effects of CO2 and H2O addition on benzene and PAH formation in a laminar premixed CH4/O2/Ar flame at atmospheric pressure were numerically investigated using two recently developed kinetic mechanisms with PAH formation up to at least benzopyrene. To distinguish the chemical effects of CO2 and H2O addition through partial replacement of Ar from their thermal effects, additional calculations were performed with fictitious carbon dioxide (FCO2) and fictitious water vapor (FH2O) addition. Both PAH kinetic mechanisms predicted that the formation of benzene and PAHs are promoted by the thermal effects of CO2 and H2O but are more significantly suppressed by their chemical effects. The pathway analyses revealed that the reduction of benzene concentration due to the chemical effects of CO2 and H2O is attributed to the following two aspects: (i) through the reduced concentration of propargyl radical or propyne and (ii) through the promoted oxidation and hydrogen abstraction reactions of benzene caused by increased OH concentration. The reduction of the overall PAH formation can be explained as the consequence of benzene reduction. Although there are quantitative differences in the predicted flame structure in terms of temperature and mole fractions of benzene and PAHs, overall qualitatively similar effects of CO2 and H2O addition on benzene and PAH formation are predicted by the two reaction mechanisms.