Detonation re-initiation mechanism following the Mach reflection of a quenched detonation

TL;DR

This study investigates how detonations re-initiate after Mach reflection by combining advanced experimental techniques and simulations to observe shock interactions, hot spot formation, and detonation development in methane-oxygen.

Contribution

It introduces a novel experimental setup for high-resolution observation of detonation re-initiation mechanisms and provides new insights into the sequence of ignition events post-Mach reflection.

Findings

Hot reaction products are entrained into a vortex behind the Mach stem.

Detonation first appears along the Mach stem, then hot spots form in the unburned tongue.

Numerical simulations confirm experimental ignition sequences.

Abstract

This experimental study addresses the re-initiation mechanism of detonation waves following the Mach reflection of a shock-flame complex. The detonation diffraction around a cylinder is used to reproducibly generate the shock-flame complex of interest. The experiments are performed in methane-oxygen. We use a novel experimental technique of coupling a two-in-line-spark flash system with a double-frame camera in order to obtain microsecond time resolution permitting accurate schlieren velocimetry. The first series of experiments compares the non-reactive sequence of shock reflections with the reflection over a rough wall under identical conditions. It was found that the hot reaction products generated along the rough wall are entrained by the wall jet into a large vortex structure behind the Mach stem. The second series of experiments performed in more sensitive mixtures addressed the sequence of events leading to the detonation establishment along the Mach and transverse waves. Following ignition and jet entrainment, a detonation first appears along the Mach stem while the transverse wave remains non-reactive. The structure of the unburned tongue however indicates local instabilities and hot spot formation, leading to the rapid reaction of this gas. Numerical simulations are also reported, confirming the sequence of ignition events obtained experimentally.