Propagation and structure of laminar methane-air flames under supergravity conditions

This study investigates the effects of supergravity on the propagation and structure of one-dimensional premixed methane/air flames using detailed chemical kinetics and fully compressible reactive Navier-Stokes simulations. The results demonstrate that positive gravity accelerates flame propagation and increases flame speed, while negative gravity decelerates propagation and reduces flame speed. The primary mechanism is identified as gravity's modification of the momentum field (flow velocity and pressure distribution) through the body force term in the momentum equation. Analysis of flame structure reveals that positive gravity leads to a broader, less intense flame with lower peak temperatures, reduced heat release rates, more gradual species gradients, and altered radical distributions. Negative gravity leads to the opposite trend. Detailed kinetic analysis shows that key elementary reaction rates (e.g., H + O₂ = O + OH, CO + OH = H + CO₂) are enhanced under negative gravity and suppressed under positive gravity. Furthermore, the effects of both pressure and flame stretch under different gravity levels are investigated. These findings provide critical insights for combustion modeling in extreme environments, with implications for high-performance propulsion systems and astrophysical phenomena. Novelty and significance statement For novelty, this study presents the first comprehensive numerical investigation of laminar methane/air flame propagation under supergravity conditions, systematically revealing the acceleration effects of positive/negative gravity on flame dynamics. The research innovatively demonstrates that gravity's impact on flame speed is primarily mediated through momentum field modifications (body force term) rather than direct energy equation influences, while also uncovering gravity-induced restructuring of flame thermal/chemical profiles—particularly the intensified production of key radicals (H, CH₃) under supergravity. For significance, the findings provide fundamental insights into flame behavior under extreme gravitational environments, addressing critical knowledge gaps in combustion science. The acceleration mechanism and gravity-pressure coupling effects have direct implications for optimizing high-performance propulsion systems operating in supergravity conditions. The identified restructuring of flame thermal/chemical profiles under supergravity also offers new perspectives for modeling astrophysical combustion phenomena. This research establishes a theoretical foundation for future studies and technological applications in extreme environment combustion.