Analysis of chemical kinetic characteristics for autoignition of ammonia-hydrogen blended fuel under different leakage pressures

Objective Autoignition induced by high-pressure hydrogen leakage is a critical hazard in the safe utilization of hydrogen energy. Ammonia blending serves as a promising suppression strategy for this hazard, while leakage pressure serves as a key parameter governing autoignition behaviors. Therefore, exploring how leakage pressure chemically regulates the autoignition characteristics of ammonia-hydrogen blended fuel is of vital significance.

Methods Using Ansys Chemkin-Pro software and the Otomo chemical reaction mechanism, simulations are performed at initial temperatures ranging from 1 000 K to 1 600 K and an equivalence ratio of 1. The influences of leakage pressure (6 MPa, 8 MPa, 10 MPa, and 12 MPa) are examined. These include effects on IDT sensitivity, radical concentrations, radical formation rates, and chemical reaction pathways of the ammonia-hydrogen blended fuel.

Results IDT shortens remarkably as leakage pressure rises from 6 MPa to 12 MPa, with a reduction of approximately 44.2％ at 1 000 K. Sensitivity analysis reveals that the chain-branching reaction H+O₂ = O+OH (R1) consistently exerts the strongest promoting effect. In contrast, the three-body reaction H+O₂(+M) = HO₂(+M) (R13) (where M denotes the third body in the reaction) plays an inhibitory role. Elevated leakage pressure increases the absolute sensitivity coefficients of all critical reactions. Since the overall contribution of dominant ignition-promoting reactions outweighs that of inhibitory reactions, the global reactivity of the system improves. Further analysis of radical concentrations indicates that, with rising leakage pressure, the mole fractions of highly reactive radicals H, O, and OH increase by roughly 47.72％, 66.33％, and 17.05％, respectively. Meanwhile, the mole fraction of the intermediate radical HO₂ decreases by about 41.40％. Chemical pathway analysis demonstrates that higher leakage pressure enlarges the proportion of OH radicals in most nitrogen-containing pathways and reduces the contribution ratios of H and O radicals. Consequently, the system relies more on oxidation processes dominated by OH radicals to drive autoignition.

Conclusion Increased leakage pressure improves the reactivity of the H/O subsystem, elevates radical production, and optimizes radical distribution pathways. These variations markedly reduce the IDT of ammonia-hydrogen blended fuel and increase its autoignition propensity. The research findings provide theoretical guidance for the safe storage, transportation, and leakage protection design of ammonia-hydrogen blended fuels under variable pressure operating conditions.