On the theoretical analysis of hydrogen-oxygen explosion limits

Hydrogen, as a clean and renewable energy source, has attracted significant attentions due to its potential to address global energy demands and environmental concerns. However, its high reactivity poses challenges for safe and efficient utilizations. In this study, the radical and thermal runaway explosion characteristics of the H2/O2 system were investigated by Jacobian matrix analysis and chemical kinetics calculations, respectively. The results indicate that the explosion mode of this system can be represented by the signs of eigenvalues of the full Jacobian matrix across the entire pressure-temperature domain. Furthermore, the explosion limits can be predicted by a reduced 5-by-5 radicals’ matrix, which are in excellent agreements with those obtained using full Jacobian matrix and chemical kinetic simulations. By using the reciprocal of the maximum eigenvalue of the matrix as the characteristic time, the ignition delay time (IDT) of the H2/O2 mixture can be accurately predicted under various conditions. Additionally, the analyzation reveals that only H, HO2, and H2O2 radicals play the dominant roles in determining the explosion limits. Therefore, the explosion system can be further reduced to a 3 by 3 matrix, and three single expressions were derived for each explosion limit. Finally, the effects of equivalence ratio on the explosion limit were investigated, and the reasons for the rotating and shifting trend are revealed. These findings demonstrate the effectiveness of matrix-based methods for predicting the explosion limits of premixed gases and offers a valuable tool for safety assessments and process optimization in various industrial applications involving hydrogen.