Investigation of the physical and chemical effects of fire suppression powder NaHCO3 addition on methane-air flames

In this study, the influence of fire suppression powder NaHCO3 on premixed flames was investigated experimentally and numerically. To better understand the suppression mechanism of the powder, the physical heat sink and chemical reaction contributions of the addition of the powder on the laminar burning velocity of methane-air flames were analyzed. An improved model was developed to predict the influence of the physical heat sink effect on burning velocity, and the model aligned well with the experiment. The results demonstrated that the physical effect had a non-negligible impact on flame suppression. Thereafter, the chemical reaction effect of NaHCO3 powder was investigated, and the results showed that the chemical effect suppressed flames by scavenging free radicals. When a large quantity of agent was added, the equivalence levels of the free radical concentration resulted in the saturation of the chemical effect. The influence of the initial temperature and pressure on the chemical effect was also studied. Finally, the exact contributions of the two effects were compared under different sizes of the powder particles. The results indicated that the suppression mechanism was under the thermodynamic control when the particle size was large, as that the physical heat sink effect played a more important role than the chemical effect. Conversely, the suppression mechanism was under the kinetic control when the particle size was small, as the chemical reaction effect occupied the dominant position.