Effect of external cylindrical obstacles on the structure and overpressure characteristics of spontaneously ignited hydrogen jet flames

The spontaneous ignition of high-pressure hydrogen jets produces intense jet flames and strong overpressure, posing significant safety concerns for hydrogen energy facilities. This study examines the effect of external cylindrical obstacles, characterized by their diameter (D) and distance from the tube exit (L), on the structure and overpressure characteristics of spontaneously ignited hydrogen jet flames. The experiments were conducted using a high-pressure hydrogen injection system, and high-speed cameras and pressure sensors were employed to capture flame evolution and pressure variations. The results show that obstacle geometry significantly influences the near-field flame structure and flame angle (θ). Increasing the obstacle diameter enhances radial expansion and deformation of the Mach disk, while a larger distance from the tube exit promotes axial flame development. The maximum external overpressure decreases with increasing obstacle diameter and rises with increasing distance, which exhibits a clear negative correlation with the flame angle. Regression models were established to quantify the relationships between geometric parameters, flame angle, and mean overpressure. The findings demonstrate that both D and L play decisive roles in regulating the interaction between jet flame evolution and overpressure behavior. This work provides theoretical insights and experimental evidence for the safety design and risk assessment of hydrogen leakage scenarios in energy systems.