CARS Diagnostics for Solid Propellant Combustion Investigations

The specific technical achievements of this Army Research Office contract are as follows. Coherent anti-Stokes Raman Spectroscopy (CARS) was first successfully applied to solid propellant combustion at elevated pressure (up to 35 atm) under this project. The high pressure equilibrium chemistry (temperature and multiple species concentration) of nitramine combustion was verified with the CARS measurements. The use of a high pressure, motorized combustion vessel allowed control of the spatial location of the burning propellant surface and data acquisition from the thin (100 micron), near-surface reaction zone. Dual broadband CARS of HCN, H2CO and CH4 was utilized to observe the competition between two major reaction mechanisms; they determine the speed of the overall reaction. Resolution of the temperature and species profiles in the reaction zone, required for further insight, was provided by a major advance, the implementation of Line CARS, a 1-D imaging geometry, that allows single shot (10 nsec) measurement of the large temperature and concentration gradients near the surface with a spatial resolution of 25 microns. These milestones have expanded the database of propellant combustion knowledge and provided valuable information for future formulations of energetic materials.