Experimental and numerical investigation on flame propagation and transition to detonation in curved channel

The Deflagration to Detonation Transition (DDT) process in a curved channel was numerically and experimentally investigated for stoichiometric ethylene/oxygen and acetylene/oxygen/argon mixtures. The numerical method was based on the two-dimensional Navier–Stokes equations with detailed chemical mechanisms. Flame propagation through the curved channel was observed using a high-speed camera. Four distinctive flame patterns were identified, appearing in the following order: spherical flame, finger flame, tongue-like flame, and detonation. The development of the tongue-like flame occupied most of time of the DDT process and played an important role in the onset of detonation. The formation of the tongue-like flame was analyzed in detail and its interactions with boundary layers enhanced the flame surface as well as the flame velocity. The modes of detonation initiation in irregular and regular cellular detonation systems were compared. Although the local explosion always occurred at the outer wall regardless of the mixture type, the detonation was caused by the amplification of instabilities for irregular system at the outer region of the tongue-like flame, whereas shock focusing-ignition occurred at the outer wall for regular system. Furthermore, the DDT run-up distance LDDT was shorter for the irregular system than for the regular system with the same detonation sensitivity.