ICOPE-15-C116 Role of CO_2 in the CH_4 oxidation during fuel-rich combustion in O_2/CO_2 environments

Abstract

The effect of CO_2 reactivity on CH_4 oxidation in fuel-rich O_2/CO_2 combustion where the concentrations of reactants were high was studied by using the reactive molecular dynamics (ReaxFF-MD) simulation. The results showed that the reaction rate of CH_4 in fuel-rich O_2/CO_2 combustion compared to that in air combustion was significantly lower under low temperatures, but it was higher under high temperatures. The amount of CO molecules and OH radicals formed in fuel-rich O_2/CO_2 combustion were noticeably higher than that in air combustion which proved that CO_2 participates in chemical reactions primarily through the reaction CO_2 + H = CO + OH (R1). R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO_2 inhibited the oxidation of CH_4 in low temperature but advanced the oxidation of CH_4 in high temperature. Under fuel-rich combustion, H_2 was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H_2O production. These hydrocarbon reactions were competitive. CO_2 reactivity reduced the H/OH ratio by converting H to OH which enhanced H_2O production but inhibited H_2 formation.