High speed temperature, pressure, and water vapor concentration measurement in explosive fireballs using tunable diode laser absorption spectroscopy

Results from the design, development, and testing of a probe capable of making quantitative measurements of temperature, pressure, and water vapor concentration in near field explosive detonations are presented. This work extends established tunable diode laser absorption techniques to the field of explosive and energetic materials diagnostics with improved temporal resolution. Simultaneous measurement of temperature, pressure, and water vapor concentration were successfully measured at 30 kHz in a constant volume explosion at a standoff distance of 52 cm from 40 g of PBXN-5. Explosive testing was conducted in the 1.81 m³ blast chamber at the University of Illinois at Urbana-Champaign Energetic Materials Diagnostics Lab. Measured values compared very well to theoretical calculations for shocked air during the blast phase as well as late-time quasi static conditions. Data show a discrepancy between pressure and temperature equilibration times. This observation is attributed to comparatively slow mass diffusion of explosive products and thermal diffusion of heat relative to pressure equilibration through shock reflections.