Correlation between the critical tube diameter and annular interval for detonation wave in high-concentration argon diluted mixtures

Detonation tube including driver section and test section was built to investigate the failure mechanism of detonation wave near the limits. The mixture of C₂H₂+2.5O₂+70%Ar was investigated experimentally. Fiber optics was used to measure detonation velocity. Smocked foils were used to record the detonation cellular structure. The results show that, with the initial pressure far lager than the critical pressure, detonation wave propagates at a constant value in the tubes. Detonation velocity decreases with the decreasing initial pressure. With a given initial pressure, the detonation velocity decreased as the tube diameter (or channel interval) decreased. Under the critical pressure, the detonation velocity propagated a short distance in the tubes and then decreased gradually until complete failure. For different geometries tubes and channels, by introducing dimensionless parameter d /λ and w/λ (d the dameter of the round tube, w the interval of the annular channel and λ the size of detonation cellular), the results show that the critical thickness is half of the critical diameter. Good agreement is found between the experimental measurements in both geometries which supports this conclusion and theoretical mode. The failure mechanisms based on the detonation front curvature for stable detonation in mixtures that are highly argon diluted are well defined.