Oxy-Fuel Combustion Mechanism of Fushun Oil Shale Kerogen: A ReaxFF Molecular Dynamics Study

To elucidate the combustion behavior and molecular-scale reaction mechanisms of Fushun oil shale kerogen under oxy-fuel atmospheres, ReaxFF molecular dynamics simulations were performed based on a previously constructed kerogen model. Five reaction systems were established: 21% O2/79% N2, 21% O2/79% CO2, 35% O2/65% CO2, 55% O2/45% CO2, and 75% O2/25% CO2. Under programmed heating, the evolution of chemical bonds, gaseous products, char, tar and gas transformation, and system potential energy was systematically analyzed. The results show that, at the same O2 concentration, CO2 delays low-temperature oxidation, shifting C–C and C–H bond cleavage and O2 consumption to higher temperatures. At elevated temperatures, however, CO2-related pathways promote carbon skeleton fragmentation and CO formation. Increasing O2 concentration from 21% to 75% advances O2 participation and H2O formation, suppresses low-temperature CO accumulation, accelerates char consumption, and drives the system toward complete oxidation dominated by small-molecule gases. Potential energy analysis further indicates that higher O2 concentrations advance the intense exothermic oxidation stage. A four-stage oxy-fuel combustion mechanism is proposed, providing molecular-level insight into the coupled effects of CO2 and O2 concentration.