Radiation-Induced Structural Modifications and Soot Evolution in Microgravity Laminar Flames at Elevated Pressure

Microgravity environments significantly impact soot formation and flame stability in laminar diffusion flames, yet the underlying mechanisms remain poorly understood, especially in high-pressure combustion systems. This study utilizes a hybrid moment method (HMOM) coupled with P1 radiation modeling to investigate the radiation-induced modifications to temperature fields, flow structures, and soot evolution in ethylene-air co-flow flames under elevated pressures (1–8 bar), comparing normal gravity and microgravity conditions. Results show that microgravity environments amplify soot volume fractions by 200–300% compared to normal gravity, due to extended reactant residence times. Radiative heat losses lower peak flame temperatures by 20–150 K, with this reduction becoming more pronounced at higher pressures due to increased radiation from both gases and soot. At critical pressure thresholds in microgravity, a transition from closed-tip to open-tip flame structures occurs in co-flow laminar diffusion flames, driven by radiative heat losses approaching 45%–60% of total chemical energy. Unlike spherical flame extinction, laminar diffusion flames experience local extinction triggered by heat release rate (HRR) decay at the flame tip, followed by the opening of the hydroxyl radical (OH) zone. This structural modification creates an oxidative boundary discontinuity, preventing the OH zone from fully encapsulating soot particles, thus allowing soot to escape oxidation pathways.