Numerical study of the spontaneous ignition mechanisms of pressurized hydrogen released inside pipes with different structures

Hydrogen is considered a key clean energy carrier to achieve the global goal of carbon neutrality. But spontaneous ignition can occur when pressurized hydrogen is released into pipes, and the presence of different pipe structures will significantly affect the ignition mechanism. In this work, the effects of varied pipe structures on the shock wave propagation and spontaneous ignition characteristics are investigated by numerical simulation with the DNS-like approach, EDC combustion model, and 21-step detailed hydrogen combustion mechanism. Results show that the simulation is in well agreement with the experimental data. Five dominant spontaneous ignition mechanisms are provided depending on different pipe structures. Among all types of pipe structures investigated, contraction structures can lead to a greater increase in shock wave pressure due to more severe shock wave reflection and convergence. While enlargement structures can contribute to more mixing of hydrogen and air, causing more sufficient combustion. This study provides a comprehensive understanding and clear safety guidance to inform the practical application of hydrogen energy.