Effects of hydrogen doping ratio and CO₂ on the explosion characteristics of hydrogen-doped natural gas

Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is suspectible to leakage and explosion accidents. The study used a 20-L spherical device to investigate the effects of hydrogen doping ratio and CO₂ addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyze the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the pressure parameters of hydrogen-doped natural gas explosion and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, while both the rapid burn time and sustained burn time decrease progressively. The maximum rise rate of explosion pressure and flame propagation speed gradually increase when the hydrogen doping ratio is lower than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum rise rate of explosion pressure and flame propagation speed rise rapidly. The addition of CO₂ has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is weak. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase. Meanwhile the concentration of active free radicals and the product formation rate increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO₂ can reduce the laminar burning velocity, adiabatic flame temperature, active free radical concentration and product formation raten of the mixed gas, but adding CO₂ does not change the reaction path of methane.Hydrogen-doped natural gas technology has been gradually used in pipeline transportation, but hydrogen-doped natural gas is prone to leakage and explosion accidents. The study used a 20L spherical device to investigate the effects of hydrogen blending ratio and CO₂ addition on the explosion pressure and flame propagation characteristics of hydrogen-doped natural gas, and the chemical reaction kinetics method was used to analyse the explosion mechanism. The results showed that the hydrogen doping ratio has a promoting effect on the hydrogen-doped natural gas explosion pressure parameters and flame propagation speed. As the hydrogen doping ratio increases, the maximum explosion pressure gradually increases, the rapid burn time and sustained burn time are gradually decreasing. The maximum explosion pressure rise rate and flame propagation speed gradually increase when the hydrogen doping ratio is less than 0.5. When the hydrogen doping ratio is greater than 0.5, the maximum explosion pressure rise rate and flame propagation speed rise rapidly. The addition of CO₂ has an inhibitory effect on the explosion pressure and flame propagation speed of the mixed gas, but the suppression effect on pressure parameters with high hydrogen doping ratio is poor. Through reaction kinetic analysis, it can be seen that as the hydrogen doping ratio increases, the laminar burning velocity and adiabatic flame temperature gradually increase, the mole fraction of active free radicals and the rate of product increase significantly, and the mixing of hydrogen changes the reaction path of methane. When the hydrogen doping ratio is greater than 0.5, reactions R84, R46 and R3 enter the top ten steps of the reaction, producing H and OH radicals, which promotes the reaction. CO₂ can reduce the laminar burning velocity, adiabatic flame temperature, active free radical mole fraction and rate of production of the mixed gas, but adding CO₂ does not change the reaction path of methane.