Real-gas effects on explosion limits of hydrogen–oxygen and methane–oxygen mixtures at elevated pressures

Abstract

The explosion limits of hydrogen–oxygen (H₂–O₂) and methane–oxygen (CH₄–O₂) mixtures under high-pressure, supercritical conditions are analyzed computationally. It is shown that the non-ideal effects of the ignition delay time (IDT) occur at pressures above 100 atm, with the extent enhanced with increasing pressure. This causes the third limit for the H₂–O₂ mixture to move towards lower temperatures. Sensitivity analysis then identifies the reaction mechanisms responsible for the observed behavior. It is further shown that the main species, namely fuel and oxidant as well as H₂O₂ radical, affecting the explosion limit of real-gas properties are determined by perturbing the attraction parameter ($a$) and repulsive volume correction parameter ($b$) of each species in the Redlich–Kwong equation of state. It is shown that fuel and oxidant play essential roles in the triggering the non-ideal effects in the system, and H₂O₂-related reactions are important at high pressures. Furthermore, the parameters $a$ and $b$ have different behaviors on the third explosion limit. The latter has a stronger influence on the explosion limit than the former, on account of the temperature of the explosion boundary decreases with increasing pressure. Moreover, the deviation tendency of the explosion limit of H₂–O₂ and CH₄–O₂ mixtures is also applicable to different equivalent ratios and dilutions with the real-gas effects. Results of this study are expected to provide new guidance for future investigations of explosion limits at high pressures.