The reaction zone structure of cylindrical detonations in monodisperse sprays

Abstract

Schlieren framing and streak photographs, and pressure transducer traces describing thedetailed structure of detonations propagating through low and high vapor pressure sprays are presented. The experiments were performed using a pie shaped test chamber with an included angle of 20°, a length of 140 cm and a width of 5.2 cm. Detonations were initiated with a small explosive charge at the vertex of the tube and propagated through a monodisperse spray of 400 μm decane and heptane droplets generated by 322 hypodermic needles fed by an oscillating pressure supply. The structure of low vapor pressure decane sprays in oxygen is driven by droplet shatteringand by the sudden explosion of fuel entrapped in the droplet wake after a certain ignition delay period t ig . The blast waves generated by these wake explosions are clearly shown in both the framing and streak photographs. Superposition of a pressure trace and streak photograph indicates the source of the pressure oscillations usually observed in the reaction zone of spray detonations. Values of ignition delay time and wake blast wave parameters derived from the streak photographs are presented. Different results are obtained for high vapor pressure heptane sprays in oxygen. A gaseous detonation propagates through the already vaporized fuel with properties determined by the vapor. Droplet breakup, shattering, and explosion follows at a considerable distance behind this front and does not appear to affect the detonation velocity. The structure of such “Hybrid” detonations is clearly illustrated by schlieren framing photographs.