Near-limit detonation in long spiral tube: An improved experimental methodology and frequency analysis

Abstract

In the present work, near-limit detonations in near stoichiometric propane-oxygen mixtures were investigated using a long spiral tube facility. Compared to previous studies, our improvements in the tube length, framing rate and resolution, image processing methods for distortion correction and detonation front detection, allow for a significant increase of the amount and quality of data obtained. As the initial pressure was decreased, stable, stuttering, and galloping regimes of detonation propagation were successively observed. The use of wavelet transform made it possible for the first time to visualize the change of the intrinsic frequency of the oscillation of the detonation front velocity during the highly unstable propagation in the stuttering and galloping regimes. The failure/re-initiation cycles produce the highest power density at frequencies in the range of 500–1000 Hz. In the stuttering regime, additional velocity fluctuations were observed in the range 2000–12000 Hz during the re-initiation events. In the galloping regime, velocity fluctuations took place during the low-velocity periods, with characteristic frequencies in the range of 2000–2500 Hz. The dynamics of the failure and re-initiation events were characterized in terms of induction length normalized wavelength. It was shown that in the stuttering regime, the detonation failure events occur after a quite random length, whereas the detonation re-initiation events appear to occur after a rather constant length. In the galloping regime, less variability was observed, and failure and re-initiation events occur at a rather well defined frequency.Novelty and Significance Statement1. Improved experimental facility and techniques to study near-limit detonations in long spiral tube2. First application of wavelet transform to study near-limit detonations3. Detailed study of the frequency of failure and re-initiation events in the stuttering and galloping regimes