Effect of orifice plate spacing on detonation propagation

Experiments were carried out to measure the detonation propagation limits in a 10 cm inner-diameter tube equipped with equally spaced orifice plates. The limits were established based on the successful transmission of a detonation wave from the obstacle-free first-half into the obstacle-filled second-half of the tube. The effect of the orifice plate spacing was studied for hydrogen, ethylene and acetylene-air mixtures at atmospheric pressure and temperature. Experiments were carried out with 63.5 mm and 76.2 mm diameter orifice plates, spaced at 1.5 and 2 times the tube inner-diameter. The results were compared to previously reported data obtained at a plate spacing equal to one-tube inner-diameter. By increasing the plate spacing the quasi-steady detonation velocity, measured at the end of the orifice plate filled section, approached the theoretical Chapman-Jouguet detonation velocity. The results show that for the 76.2 mm orifice plates, with 1.5 and 2 tube diameter spacing, the detonation propagation limits correspond to the condition d/λ > 1, where d is the orifice plate diameter and λ is the detonation cell width. The same correlation was found for the larger blockage 63.5 mm orifice plates with 1.5 and 2 tube diameter spacing. This is in contrast to previous results obtained by Cross and Ciccarelli (2015) for the same 63.5 mm orifice plates at one tube inner-diameter spacing that correlated the propagation limits with d/λ > 2. Large wave velocity fluctuations were observed for the two-diameter orifice plate spacing for mixtures near the propagation limits. These velocity fluctuations, measured by ion probes spaced at a distance larger than the orifice plate spacing, are indicative of a galloping detonation wave.