Coupled effects of ammonia addition proportions and pipeline diameter on self-ignition in high-pressure hydrogen leakageOA

Hydrogen''s intrinsic flammability and explosiveness pose serious safety hazards.This study systematically investigates the coupled effects of pipe diameter and ammonia addition proportions on self-ignition during high-pressure hydrogen leaks.Utilizing computational fluid dynamics(CFD)techniques integrated with the Large Eddy Simulation(LES)and the Eddy Dissipation Concept(EDC)combustion model,the effects of ammonia addition proportions(0%∼15%)on shockwave propagation characteristics and critical self-ignition conditions are analyzed for a range of pipeline diameters(5 mm,10 mm,and 15 mm).A constant volume zero-dimensional homogeneous adiabatic reactor model in Chemkin-Pro was utilized to analyze the generation and consumption rates of H_(2)and O_(2),together with the corresponding elementary reaction kinetics.Principal findings indicate that increasing the ammonia mixing ratio significantly reduces the generation and consumption rates of H_(2)and O_(2),suppresses elementary reaction intensities,and elevates the threshold for self-ignition.Notably,mild ammonia blending produces suppression effects comparable to pipeline diameter expansion.A 5%NH_(3)mixture decreases the critical release pressure for a 5 mm pipeline from 1.61 MPa to 1.42 MPa,equivalent to the suppression efficacy of increasing the pipeline to 15 mm in pure air conditions.Furthermore,the combined chemical-physical synergistic mechanism between ammonia addition and diameter scaling amplifies ignition inhibition.In a 15 mm pipeline with 15%NH_(3)blending,the intensity of the leading shockwave after hydrogen leakage decreases by 23.18%compared to a 5 mm pure-air pipeline,while the critical release pressure for ignition increases by a factor of 2.57.This study clarifies the chemical-physical coupling mechanisms of ammonia and pipeline diameter in mitigating self-ignition caused by high-pressure hydrogen leakage,providing theoretical foundations for the safety design and risk assessment of hydrogen energy transport systems.