The failure and re-initiation of quasi-detonations in stoichiometric acetylene-oxygen mixtures diluted by nitrogen

Abstract

In this study, the failure and re-initiation of quasi-detonations are investigated systematically in stoichiometric acetylene-oxygen mixtures diluted by nitrogen, and the nitrogen dilution range of 10–45 % is considered. Photodiodes are introduced to obtain the average velocity by recording the detonation time-of-arrival. The smoked foil technique is performed to register the detonation cellular structures, and a high-speed schlieren system is used to observe the propagation processes. Three propagation modes are defined based on nine repeated experiments, i.e., Go, No-go and Critical regimes. For the “go” regime, the exiting detonation all successfully evolves into a spherical detonation in nine repetitions of the experiments. For the “no-go” case, the detonation all fails upon exit and becomes a deflagration. The case between the Go and No-go is called as the critical mode. Near the limits, the critical pressure of successful evolution into a spherical detonation is obtained, and the data indicates that the critical pressure is approximately independent of the wall roughness. But the critical pressure can increase obviously by introducing the nitrogen dilution. The cell sizes for quasi-detonations are measured, and the ratio of the critical tube diameter (dc) to the cell size (λ) is considered to quantify the critical criterion of detonation re-initiation. Note that the previous criterion of dc/λ ≥ 13 about normal detonation re-initiation cannot be applied to the quasi-detonation, and the re-initiation condition for quasi-detonations can be nearly quantified as dc/λ ≥ 8. The results are consistent with those obtained in our previous study (Xuxu Sun et al., Combustion and Flame, 112280). Corresponding to the normal detonation in a smooth tube, the critical value of dc/λ is always lower for quasi-detonations, which indicates a favorable effect on the detonation transmission is verified.