Flame propagation characteristics and thermal radiation hazards of methane-hydrogen-mixed cloud explosion in unconfined area: Experiment research and theoretical modeling

Under an equivalency ratio of 1.1, this manuscript studies the fireballs of methane-combustible gas clouds with varying hydrogen doping ratios (5 %, 10 %, 20 %, 30 %, 50 %, and 75 %). It then modifies the semiempirical-theoretical fireball heat radiation model based on flame size. Under 5%–30 % mixing ratio, flame growth characteristics are more comparable, and peak flame propagation speed is 18 m/s, whereas the mixing ratios of 50 % and 75 % are higher, take 0.1s to complete the accelerated process, and reach 26.7 and 36.7 m/s, respectively. In flames including methane hydrogen-doped mixtures, thermal diffusion instability and hydrodynamic instability are common. With an increase in the hydrogen doping ratio, the flame self-acceleration index shows a steady rising trend. Additionally, heat flux meter peak heat radiation values increase with hydrogen blending ratio, while the time to peak decreases. These findings align with the developmental process of flame morphology. Based on the observed flame development characteristics, a semi-empirical-theoretical model of heat radiation from the fireball is simplified. The results show that as the hydrogen doping ratio increases, the safety zone must be moved further away.