An experimental study of different obstacle types for flame acceleration and DDT

Abstract

Harnessing detonations for energy conversion and transport applications requires methods for efficient deflagration-to-detonation transition (DDT) over short distances. The results of three different experiments, characterizing different types of obstacles for flame acceleration and DDT are reported in this work. Flame acceleration by obstacles with identical blockage ratio but different geometric details is investigated using light-sheet tomography. Small but distinct differences in propagation speeds are identified, which correspond to the various obstacle geometries. DDT experiments are carried out to investigate these configurations beyond initial flame acceleration observable with highspeed imagery. A strong effect of obstacle spacing on DDT success is observed, indicating an optimal spacing of slightly larger than two tube diameters. A so-called pseudo-orifice is considered in order to recreate the flow behind a mechanical orifice with the same blockage ratio considered in the previous experiments (0.43). The pseudo-orifice injects fluid perpendicular to the flow, creating a circumferential jet-in-crossflow configuration. Particle image velocimetry is conducted in an acrylic water test-rig in order to measure the flow field in several planes in the acrylic combustion chamber model to assess the effect of the pseudo-orifice on the flow.