Laser Absorption Spectroscopy Measurements of High Pressure and Temperature Aluminum Combustion in a Shock Tube

This study presents measurements on the combustion of nominally 20 micron diameter particles burning in air at elevated temperature (3600 +/- 150K) and pressures (8 – 63 atm) in Sandia’s High-Temperature Shock Tube (HST) facility. Measurements were made using a suite of advanced diagnostics that coupled laser absorption spectroscopy (LAS) measurements of the temperature and column density of aluminum monoxide (AlO) with either digital in-line holography (DIH) or nitric oxide (NO) laser absorption. DIH measurements were made within the AlO LAS laser probe volume and provided a measure of the diameter and number of particles. This enabled a comparison of the particle density in the AlO measurement volume between cases. In a separate case, the NO laser absorption probe was overlapped with the AlO laser absorption diagnostic, enabling simultaneous measures of the bath gas and AlO temperatures. Results show that the energy addition by a combusting particle field with densities less than ~0.1 particle/mm^3 will not increase the bath temperature. Further, measurements indicate that AlO production is decreased at elevated pressure conditions. This suggests a shift to heterogeneous surface combustion or a large increase in the ignition delay with increasing pressure.