Single-shot, mid-infrared ultrafast-laser-absorption-spectroscopy measurements of temperature, CO, NO and H2O in HMX combustion gases

This article describes the development of the first single-shot ultrafast-laser-absorption-spectroscopy (ULAS) diagnostic for simultaneous measurements of temperature and concentrations of CO, NO and H2O in flames and aluminized fireballs of HMX (C4H8N8O8). Ultrashort (55 fs) pulses from a Ti:Sapphire oscillator emitting near 800 nm were amplified and converted into the mid-infrared through optical parametric amplification (OPA) at a repetition rate of 5 kHz. Ultimately, pulses with a spectral bandwidth of approximate to 600 cm(-1) centered near 4.9 mu m were utilized in combination with a mid-infrared spectrograph to measure absorbance spectra of CO, NO, and H2O across a 30 nm bandwidth with a spectral resolution of 0.3 nm. The gas temperature and species concentrations were determined by least-squares fitting simulated absorbance spectra to measured absorbance spectra. Measurements of temperature, CO, NO and -H2O were acquired in a HMX flame burning in air at atmospheric pressure and the measurements agree well with previously published results. Measurements were also acquired in fireballs of HMX with and without 16.7 wt% H-5 micro-aluminum. Time histories of temperature and species column densities are reported with a 1 - sigma precision of 0.4% for temperature and 0.3% (CO), 0.6% (NO), and 0.5% (H2O), and 95% confidence intervals (CI) of 2.5% for temperature and 2.5% (CO), 11% (NO), and 7% (H2O), thereby demonstrating the ability of ULAS to provide high-fidelity, multi-parameter measurements in harsh combustion environments. The results indicate that the addition of the micron-aluminum increases the fireball peak temperature by approximate to 100 K and leads to larger concentrations of CO. The addition of aluminum also increases the duration fireballs remain at elevated temperatures above 2000 K.