Critical energy for direct initiation of spherical detonations in C₂H₂-O₂-Ar and C₂H₂-N₂O-Ar mixtures

Direct initiation was achieved via a high-voltage capacitor spark discharge and the critical energy was accurately estimated from the analysis of the current output. Experiments were carried out to measure the critical energies of C₂H₂-O₂-Ar and C₂H₂-N₂O-Ar mixtures under different initial conditions. The critical energies for C₂H₂-N₂O-Ar mixtures are significantly higher than those for C₂H₂-O₂-Ar mixtures under the same initial conditions. The relation between explosion length and critical tube diameter was analyzed to explore the large discrepancy of the critical energy between those mixtures. The critical tube diameter measurement in C₂H₂-N₂O-Ar mixtures was further investigated, and based on the critical tube diameter correlation, the relationship between explosion length and critical tube diameter for C₂H₂-O₂-Ar mixtures was found to be r₀=2.5d_c. And the corresponding relationship is r₀=2d_c for C₂H₂-O₂-Ar mixtures. It displays that the proportional factor between explosion length and critical tube diameter will increase if N₂O is used as an oxidizer, which results in more initiation energy per unit required for initiating the mixture to achieve a direct detonation. Thus the critical energy of direct initiation tends to be higher.