Mechanisms of detonation initiation in multi-focusing systems

The work is dedicated to the experimental and numerical study of the mechanisms of gaseous detonation initiation in a stoichiometric hydrogen–oxygen mixture due to the reflection of a shock wave from a complex-shaped end wall. Several elliptic surfaces of different geometries, including distributed ones, were considered. We refer to such reflectors with multiple elliptical surfaces as multi-focusing systems. The experiments were carried out in a shock tube. Visualization of the process was carried out with a high-speed schlieren system. In the experiments, the ignition delay times and the critical incident shock wave Mach number for detonation initiation were measured. Two-dimensional Euler simulations, on a fully unstructured computational grid, were carried out to determine the mechanism of detonation initiation. The numerical approach was verified using the experimentally measured ignition delay times. Reasonable agreement between the simulations and experiments for the critical Mach number of detonation initiation and for the efficiency of various multi-focusing systems for detonation initiation was achieved. Different regimes of detonation initiation depending on the incident shock wave Mach number were observed.