Analysis of the Onset of Detonation in the DDT Process for Combustible Mixture

For comparison with several methods used to define the location of the onset of detonation, several of experiments were performed to study on the deflagration to detonation transition (DDT) for premixed C2H2+2.5O2 mixture in a shock tube. A high-speed digital camera was used to track the velocities of flame, shock, or detonation wave. In this work, six methods were used to define the location of the onset of detonation, and six different results of the DDT run-up distance (LDDT) and the time of the detonation onset (tDDT) were obtained. It is found that the methods based on the flame emission radiation and the growth trajectory of flame, shock, or detonation wave can accurately define tDDT and LDDT. The onset of detonation defined by the other methods based on the speed of detonation wave might result in some error or underestimated values due to the localized explosion taking place just prior to the generation of detonation.