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. However, transporting hydrogen via the natural gas pipeline network poses significant explosion safety challenges. To address these concerns, 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 initiated prior to ignition, creating 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 dynamics of explosion flame propagation 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 accelerate flame propagation and enhance 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, with 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 higher injection pressures correspond to shorter injection time. Meanwhile, the maximum explosion pressure at larger injection pressures is more sensitive to changes in injection time. Injection pressure and injection time are the key parameters governing the impact of CO₂ injection on 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.