Investigation on the lower flammability limit and critical inhibition concentration of hydrogen under the influence of inhibitors

Hydrogen is considered a leading clean energy carrier and versatile industrial raw material, playing a crucial role in driving down greenhouse gas emissions. Ensuring the safe utilization of hydrogen holds paramount significance. The present study investigated the variation law of the lower flammability limit of hydrogen under the influence of inhibitors (carbon dioxide, nitrogen, and heptafluoropropane) through experimental testing. The critical inhibitory concentration required for complete suppression was determined. Additionally, the explosive characteristics under the influence of inhibitors were evaluated, and the inhibitory mechanism was analyzed in conjunction with chemical kinetics. With an increase in the quantity of inhibitors added, there was a corresponding increase in the lower flammability limit of hydrogen, as demonstrated by the results. When 10% volume fraction of heptafluoropropane was added, the lower flammability limit of hydrogen increased by 94.74%. At lean Burn conditions, the inhibitory effect of carbon dioxide on the maximum explosion pressure, adiabatic flame temperature, and heat release rate of hydrogen was higher than that of nitrogen. When the heptafluoropropane inhibitor was added, the explosion pressure, adiabatic flame temperature, and heat release rate of Hydrogen-Air flame showed an increasing trend followed by a significant decrease. As the addition of heptafluoropropane inhibitor increased, the consumption of active free radicals such as hydrogen radicals and hydroxyl by fluorine-containing free radicals interrupted the chain reaction, thus inhibiting the combustion reaction process. Additionally, it was determined that the critical inhibitory concentrations of the three inhibitors for hydrogen with different volume fractions are ranked in order from low to high as heptafluoropropane < carbon dioxide < nitrogen. The research results can promote the safe utilization of hydrogen energy.