Effects of non-premixed CO2 injection pressure on the premixed explosion characteristics of hydrogen-doped natural gas

Coal-to-hydrogen is an effective solution for the low-carbon transformation of coal energy. To address the explosion safety issues during coal-to-hydrogen transportation via the natural gas pipeline network, the effect of non-premixed CO2 injection on the explosion characteristics of hydrogen-doped natural gas was investigated. An experimental explosion platform was independently designed and constructed to actively release CO2 into the hydrogen-doped methane explosion via a high-pressure gas injection device. The CO2 injection was turned on earlier than ignition to create a non-premixed turbulent atmosphere. The volume of CO2 injection was controlled by injection pressure (0, 0.5, 0.75, and 1.00 MPa) and injection time (0, 60, 120, and 180 ms). The explosion flame propagation dynamics and pressure behavior under non-premixed CO2 injection were analyzed. Results showed that injection pressure and injection time significantly influence the premixed explosion process. The injection of non-premixed CO2 into the premixed explosion induces turbulence, causing flame wrinkling. Structural changes in wrinkled flames increase the flame surface area, leading to accelerated flame propagation and enhanced explosion intensity. For a given injected time (e.g., 0 or 120 ms), increasing the injection pressure introduces more CO2, which enhances localized turbulence and disturbance in the flame, leading to further flame acceleration and more severe explosion consequences. As the injection time increases, the maximum explosion pressure of different injection pressures increases and then decreases. CO2 injection in the explosion plays a competitive relationship between turbulence promotion and dilution effect, and there is a critical injection time. Excessive CO2 injection can enhance its dilution effect, weakening the CO2 injection on the explosion of turbulence perturbation ability, which reduces the explosion intensity. Moreover, a larger injection pressure has a smaller critical injection time. Meanwhile, the maximum explosion pressure at larger injection pressures has a higher sensitivity to changes in injection time. Injection pressure and injection time are the key parameters of CO2 injection affecting the explosion hazard of hydrogen-doped natural gas. The findings provide fundamental guidelines for the safety prevention and control strategy of hydrogen transportation in the natural gas pipeline network.