Laser absorption measurements of temperature, pressure, CO, and CO2 at near-MHz rates in post-detonation fireballs with comparison to synthetic measurements

Abstract

A laser absorption spectroscopy (LAS) diagnostic was used to obtain measurements of temperature, pressure, CO, and CO2 at 500 kHz or 1 MHz in post-detonation fireballs produced by hemispherical samples of pentaerythritol tetranitrate (PETN). A quantum-cascade laser was scanned over multiple CO absorption transitions near 2008.5 cm−1 at 1 MHz, while an interband-cascade laser was scanned over a CO2 absorption transition near 2394.8 cm−1 at 500 kHz. Light from each laser was combined onto a single path and passed through a detonation chamber approximately 83 mm above the 12-mm diameter hemispherical PETN charge. The CO and CO2 absorption signals were post-processed to obtain time histories of temperature, pressure, species column pressures (PCOL, PCO2L), and species column mole fractions (XCOL, XCO2L). Additionally, schlieren imaging was performed simultaneously at 500 kHz to aid interpretation of the LAS measurements. Experimental and synthetic (i.e., CFD based) LAS measurements were compared to evaluate the accuracy of the CFD model and its ability to model the turbulent afterburning of the detonation products in air. In general, the experimental measurements exhibit reasonable agreement with the synthetic measurements at early times; thereby supporting the accuracy of the CFD model. Periods of disagreement between experimental and synthetic measurements at later times are most likely due to a reflected shock and detonator cavity jetting, which are not accounted for in the CFD model.