INFRARED FIBEROPTIC DIAGNOSTIC OBSERVATIONS OF SOLID-PROPELLANT COMBUSTION

This article reports on work to develop and demonstrate a diagnostic t echnique using infrared fiber optics to probe the decomposition proces ses in burning gun propellant strands. The experiments reported here i nvolve measuring the absorption across an open gap between two embedde d fibers as it fills with gaseous decomposition products. Spectroscopi c detection is achieved using pairs of bandpass filters. The absorptio n record can be correlated with readings from embedded thermocouples a nd with a high-resolution video recording of the burn. We have observe d N2O, a decomposition product of hexahydro-1,3,5-trinitro-1,3,5-triaz ine (RDX) evolving into the observation volume. The N2O appearance is often an abrupt event. Coupled with evidence that it can occur while t he observation region is relatively cool and far from the burning surf ace (observed in cases involving burning at 6 atm pressure), these obs ervations suggest hypotheses concerning the physical processes in the condensed phases of this propellant, hypotheses including the developm ent of pressurized voids or matrix-trapped bubbles, which can release decomposition gases into the unburnt propellant through cracks that su ddenly open. The appearance of N2O after the temperature record sugges ts that melting and decomposition of RDX have begun (observed in I-atm cases), implies that N2O formation is indeed not an initial step in R DX decomposition under our conditions. Copyright (C) 1997 by The Combu stion Institute