Mechanisms of detonation initiation in multi-focusing systems
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ORIGINAL ARTICLE
Mechanisms of detonation initiation in multi-focusing systems P. S. Utkin1
· A. I. Lopato1
· A. A. Vasil’ev2
Received: 27 November 2019 / Revised: 9 August 2020 / Accepted: 23 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Keywords Detonation initiation · Multiple reflections · Shock wave · Schlieren visualization · Unstructured grids
1 Introduction Detonation initiation, and its optimization, is one of the most important research areas in combustion. It was shown experimentally [1] that the critical energy of initiation is the sole governing parameter of the mixture if the initiating discharge duration does not exceed a certain critical value. Otherwise, for a longer discharge duration, a larger amount of energy is required for detonation wave (DW) initiation. In [2], an attempt was made to explain this result in simulations. The spatial factor was studied experimentally in [3]. Detonation was initiated as a result of the passage of DW from two narrow planar channels into a wider channel. The relative channel separation was varied by using a baffle. The initiation data
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P. S. Utkin [email protected] A. I. Lopato [email protected] A. A. Vasil’ev [email protected]
1
Institute for Computer Aided Design RAS, 19/18 2nd Brestskaya, Moscow, Russia 123056
2
Lavrentyev Institute of Hydrodynamics SB RAS, 15 Lavrent’ev pr., Novosibirsk, Russia 630090
were correlated by plotting the ratio of the baffle and narrow channel width versus the critical pressure for detonation initiation. It was concluded that a spatially inhomogeneous source distribution under certain conditions could be more effective in detonation initiation than a single charge that was the algebraic sum of individual initiators in a spatially distributed scheme of DW initiation.
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