Infrared Fiber Optic Diagnostic for Solid Propellant Combustion

We report on a program to develop and demonstrate a diagnostic technique using infrared fiber optics to probe the decomposition processes in burning gun propellant strands. The present experimental configuration involves measuring the absorption through a small gap between two embedded fibers. The gap can be filled with propellant, or left open to fill with gaseous decomposition products. Spectroscopic detection is presently achieved using pairs of bandpass filters. The absorption record can be correlated with readings from an embedded thermocouple and with a high resolution video recording of the bum. We also report on preliminary experiments in which an electrically heated filament is used to melt the infrared fiber as its transmission and physical appearance are monitored.The goal of this program is to develop a fast-response probe of solid phase processes which can support the development of a predictive modeling capability for gun propellant combustion. We present examples of data for the atmospheric pressure burning now under investigation. A full assessment of the usefulness of this technique will require further observations and analysis.