Effect of Ultrafine Water Mist with K2CO3 Additives on the Combustion and Explosion Characteristics of Methane/Hydrogen/Air Premixed Flames

To ensure the safe utilization of hydrogen-enriched natural gas (HENG), it is essential to explore effective explosion suppressants to prevent and mitigate potential explosions. This study experimentally investigates the impact of ultrafine water mist containing K2CO3 additives on the explosion characteristics of methane/hydrogen/air premixed combustion. The influence of varying K2CO3 concentrations on pressure rise rates and flame propagation was analyzed across different hydrogen blending ratios. The results demonstrate that the addition of K2CO3 to ultrafine water mist significantly enhances its suppression effects. The peak overpressure decreased by 41.60%, 56.15%, 64.94%, and 72.98%, the flame speed decreased by 30.66%, 70.56%, 46.72%, and 65.65%, and the flame propagation time was prolonged by 25%, 20.83%, 22.92%, and 18.75%, respectively, for different hydrogen blending ratios, showing a similar trend. However, the suppression effectiveness diminishes under high hydrogen blending ratios and low K2CO3 concentrations. Further analysis using thermogravimetric infrared spectroscopy and chemical kinetics simulations revealed that the heat release rate and the generation rate of active free radicals significantly decrease after the addition of K2CO3 to the ultrafine water mist. The recombination cycle of KOH → K → KOH, formed by reactions (R211: K + OH + M = KOH + M) and (R259: H + KOH = K + H2O), continuously combines active free radicals (·O, ·OH) into stable product molecules, such as H2O. However, at low K2CO3 concentrations, reaction R211, which suppresses laminar combustion sensitivity and consumes a larger quantity of active free radicals, does not dominate, leading to a reduced suppression effect of K2CO3 ultrafine water mist. Several factors during the reaction process also adversely affect the performance of K2CO3-containing ultrafine water mist. These factors include the premature onset of laminar flame instability at low K2CO3 concentrations, the increased flame-front propagation speed due to the addition of hydrogen to methane, which shortens the residence time of K2CO3 in the reaction zone, and the turbulence caused by unvaporized droplets.