Unravelling the regulatory role of supercritical CO₂ in CH₄/O₂ combustion: Linking reaction pathways to performance

Abstract

In the context of global energy transition and net-zero emission goals, supercritical carbon dioxide (sCO₂) technology has emerged as a core solution for next-generation low-carbon energy conversion systems. However, the combustion characteristics of fuel/oxidizer in sCO₂ environments remain underexplored. To better understand the fuel performance under sCO₂ conditions, this study takes methane combustion (CH₄) as an example, employing reactive force field (ReaxFF) molecular dynamics method, to examine the combustion performance of CH₄/O₂ under varying gas blend ratios, α (the ratio of number of sCO₂ molecules to the number of CH₄ molecules). At a representative pressure of 200 atm, the results show that when a small amount of sCO₂ is introduced (0 < α ≤ 1), the consumption rate of CH₄ is markedly accelerated, as sCO₂ lowers the activation energy for CH₄ decomposition and shortens the initial decomposition time. However, when the amount of sCO₂ exceeds that of CH₄, the system exhibits an inhibitory effect on CH₄ combustion. Notably, sCO₂ addition can reduce the net formation of CO₂ in the system, contributing to emission reduction. This work elucidates the critical pathways through which sCO₂ affects CH₄ combustion reactions and intermediate product conversion. To further investigate the dependence of pressure, simulations are extended to 100 atm - 250 atm, revealing that the optimal α range varies with pressure. This study, for the first time, clarifies the mechanism by which sCO₂ concentration regulates the CH₄/O₂ combustion, provides valuable insights for optimizing combustion chamber design in sCO₂ atmospheres.