Experimental Study on the Deflagration-to-Detonation Transition Distance in Millimeter-Scale Smooth Tubes

Abstract

The deflagration-to-detonation (DDT) run-up distance for small-sized tubes is an important parameter for determining the position of a detonation initiation in the pulse detonation propulsion device as well as industrial safety. However, its variation tendency is insufficiently clarified, owing to complex multiple competing mechanisms between the properties of mixtures and the negative displacement effect of the boundary layer (the heat and momentum losses from wall). In this paper, the authors assess the of a stoichiometric ethylene/oxygen mixture in four capillary tubes based on high-speed photography measurements. Compared with macrotubes, the experimental results indicate that the area divergence induced by the boundary layer causes the relationship between and and/or to vary. Further comparative analysis suggests that a critical value of about can be employed to distinguish between microtube and macrotube behavior. As such, microtube behavior is defined according to the area divergence , and not only based on the tube diameter. Finally, a theoretical model is introduced to predict the and is reliable for a stoichiometric ethylene/oxygen mixture in micro- and macrotubes. The conclusions in this study can provide potential applications for practical predetonator and micropulse detonation engines.