This work presents the development and application of a novel laser-absorption-spectroscopy diagnostic capable of providing quantitative, time-resolved measurements of gas temperature and HCl concentration in flames of metallized composite propellants containing ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene (HTPB). This diagnostic utilizes a quantum-well tunable-diode laser emitting near 3.27 μm to measure the absorbance spectra of two adjacent HCl lines using a scanned-wavelength-modulation-spectroscopy technique which is insensitive to non-absorbing transmission losses. This diagnostic was applied to characterize the spatial and temporal evolution of temperature and HCl mole fraction in flames of AP-HTPB composite propellants containing either an aluminum-lithium alloy or micron-scale aluminum. In the aluminum-lithium-propellant flame on a time-averaged basis, the flame temperature was ≈80 to 200 K higher (depending on location in the flame) indicating a more complete combustion and the mole fraction of HCl was nearly 70% lower compared to the conventional aluminum-propellant flame. The results further suggest that lithium is effective at scavenging the chlorine from AP and reducing HCl formation, however, significant time and space is required to reach equilibrium levels of HCl at the conditions studied here.
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