Direct observations of reaction zone structure in propagating detonations
We report experimental observations of the reaction zone structure of self-sustaining, cellular detonations propagating near the Chapman-Jouguet state in hydrogen-oxygen-argon/nitrogen mixtures. Two-dimensional cross sections perpendicular to the propagation direction were imaged using the technique of planar laser induced fluorescence (PLIF) and, in some cases, compared to simultaneously acquired schlieren images. Images are obtained which clearly show the nature of the disturbances in an intermediate chemical species (OH) created by the variations in the strength of the leading shock front associated with the transverse wave instability of a propagating detonation. The images are compared to 2-D, unsteady simulations with a reduced model of the chemical reaction processes in the hydrogen-oxygen-argon system. We interpret the experimental and numerical images using simple models of the detonation front structure based on the "weak" version of the flow near the triple point or intersection of three shock waves, two of which make up the shock front and the third corresponding to the wave propagating transversely to the front. Both the unsteady simulations and the triple point calculations are consistent with the creation of keystone-shaped regions of low reactivity behind the incident shock near the end of the oscillation cycle within the "cell."
Copyright © 2003 The Combustion Institute. Published by Elsevier. Received 4 February 2002; received in revised form 16 July 2002; accepted 6 August 2002. The development of the detonation facility and imaging experiments has occupied several generations of students and technicians who have worked in the Explosion Dynamics Laboratory at Caltech over the last decade. The authors thank R. Akbar, M. J. Kaneshige, E. Schultz, and P. Svitek for their invaluable contributions. The simulations were carried out with J. J. Quirk's Amrita computational system. Portions of this work were supported by the ONR and the DOE.
Accepted Version - PintgenCF2002.pdf