A study on detonation-diffraction reflection point distances in H2/O2, C2H2/O2, and C2H4/O2 systems

Recently, Kawasaki and Kasahara (2019) reported that reflection point distance , which is a detonation characteristic length relevant to the diffraction process, is a useful measure; i.e., the critical condition for detonation diffraction can be universally expressed in terms of the diffraction point distance, independent of mixture stability. However, their findings were limited to their experimental conditions only. In this study, we performed high-speed visualization of processes of cylindrical (line-symmetric) detonation diffraction around a 90-degree corner for two series of experiments to obtained reflection point distances, l(r), as a novel characteristic length, and examined critical conditions of reinitiation expressed in terms of the reflection point distance. In the first experimental series, stoichiometric C2H2/O-2 mixtures with 50% Ar dilution were employed, and the channel width l(c) was varied to 5, 10, 15, and 20 mm to investigate the influences of the boundary condition of the flow field. In the second experimental series, H-2/O-2, C2H2/O-2, or C2H4/O-2 mixtures with different equivalence ratios were employed to investigate influences of the reaction systems. Our results confirmed that the channel width does not affect the reflection point distance or the critical condition. The critical condition was also independent of fuel species and equivalence ratio, and can be uniquely expressed as l(r)/l(c) = 4.0 +/- 0.6 in terms of the reflection point distance. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Through experimental study on detonation diffraction, we found that the reflection point distance can serve as a new characteristic length, and the critical condition can be expressed using it; the results show that the reflection point distance and critical condition are not affected by channel width, fuel species, or equivalence ratio.