Effects of NaHCO3 thermal decomposition characteristics on variable-pressure methane/air flames

NaHCO₃ is widely used for flame inhibition due to its efficient heat absorption ability. However, the coupling effect between the powder particle size and initial pressure on the decomposition efficiency of NaHCO₃ at the flame front remains unclear. To further investigate the interaction mechanism between variable-particle-size powders and variable-pressure flames, experiments were conducted using NaHCO₃ with four particle sizes (median diameters D₅₀ of 40.36, 18.36, 16.23, and 9.29 μm) and three initial pressures of premixed gas (0.8, 1.0, and 1.4 atm) in a 36 L spherical vessel. The thermal decomposition model of NaHCO₃ suggested that a higher initial pressure shortens the residence time of particles in the flame front, thereby hindering NaHCO₃ decomposition. Moreover, with increasing initial pressure, the flame temperature gradually decreases. Besides, we propose a dimensionless concentration parameter to characterize the coupling effect of the initial pressure and powder particle size quantitatively. The results revealed that the sensitivity of the explosion suppression efficiency to the particle size decreased with increasing initial pressure; the reduction in the explosion induction time and pressure peak arrival time caused by smaller NaHCO₃ particles was more significantly affected by the initial pressure. Finally, the LBVs obtained via the confined spherical flame method were compared for the inhibited and uninhibited flames, and the most recent kinetic mechanisms for inhibited flames were discussed. This study provides a theoretical basis for effectively preventing and reducing the risk of methane explosion accidents.