Mechanistic insights into real-gas effects on methane–oxygen autoignition via a multi-fluid-mixing model

In this study, the real-gas effects on the autoignition process of supercritical methane–oxygen mixtures have been systematically investigated through detailed kinetics simulations. The real-gas equation of state together with the multi-fluid-mixing (MFM) model are employed to evaluate various thermophysical properties, including density, specific heat, and enthalpy. By adopting the MFM model, real-gas corrections can be selectively applied to individual thermophysical properties and individual species to quantify their independent and combined contributions to the global responses. Six key species (O 2 , H 2 O, H 2 O 2 , CH 4 , CO, and CH 2 O) are identified as important for the real-gas effects either due to their high concentrations or kinetic relevance. The results show that real-gas effects lead to a reduction in ignition delay time under supercritical conditions. Among different thermophysical properties, density corrections exert the most essential influence, while specific heat and enthalpy corrections of some species also contribute markedly. Sensitivity analysis has been uniquely tailored to quantify the nuanced real-gas effects stemming from diverse system parameters. It further identifies the relative importance of different corrections and interprets their effects. The real-gas effects under different initial temperatures, pressures, and equivalence ratios have also been investigated. The present work provides a mechanistic understanding of how real-gas thermophysical properties influence ignition behavior in supercritical methane–oxygen combustion, offering insights that may serve as a useful reference for studying real-gas effects in other fuels and operating conditions.