Effect of hydrogen fraction and initial pressure on the inhibition of methane/hydrogen/air explosions by NaHCO3

Abstract

To explore the effects of the hydrogen fraction and initial pressure on the inhibition of methane/hydrogen/air explosions, the inhibition of stoichiometric methane/hydrogen/air explosions (hydrogen fraction ranging from 0 to 0.8) by NaHCO3 at various initial pressures (0.8 atm, 1.0 atm, 1.4 atm) was investigated in a 36 L spherical vessel. The experimental findings indicate that the effectiveness of NaHCO3 in suppressing methane/hydrogen/air explosions is significantly influenced by the hydrogen fraction and initial pressure. For a given hydrogen fraction, higher initial pressures weaken the inhibitory effect of a given NaHCO3 concentration on explosions. The drop ratios in the maximum explosion pressure for initial pressures of 0.8 atm, 1.0 atm, and 1.4 atm are 41.2 %, 19.7 %, and 15 %, respectively, at a hydrogen fraction of 0.8 and a NaHCO3 concentration of 400 g/m3. Additionally, the inhibitory impact of a given NaHCO3 concentration diminishes as the hydrogen fraction increases at the given initial pressure. An increasing hydrogen fraction decreases the drop ratio of the maximum explosion pressure while simultaneously increasing the maximum pressure rise rate and deflagration index. A thermodynamic equilibrium model for the endothermic decomposition of NaHCO3 particles was built to explore the impact of the hydrogen fraction and initial pressure on the decomposition characteristics of NaHCO3 particles of different sizes. The laminar burning velocity was derived using a theoretical model through the experimental pressure history and was calculated through detailed chemical kinetic modeling. The effect of the hydrogen fraction on the suppression mechanisms of NaHCO3 was evaluated by using the normalized laminar burning velocity. The dominant inhibition mechanism of NaHCO3 on the laminar burning velocity changes from physical inhibition to chemical inhibition with increasing hydrogen fraction.