Plasma-assisted combustion has been demonstrated as a promising technology to improve combustion performance in gas phase systems. Recently, sodium dopant in solid propellants serving as an electron donor has been utilized with microwave energy deposition to enhance burning rates. The local structure of the propellant flame is likely important in determining the efficacy of energy absorption, but the multiphase combustion environment presents a complicated system. These systems exhibit significant particle scattering and high sodium atomic density, leading to complications in single photon fluorescence detection. In this work, a two-photon excitation scheme at 685 nm (3s-3d) is used to investigate sodium distributions in 2.46GHz continuous microwave assisted propellant flames at three different sodium-dopant levels. The nanosecond excitation at 685 nm is examined with detection at 589 nm and 818 nm. The structure of the propellant flame is characterized with synchronous backlit imaging and laser-induced fluorescence of atomic sodium.
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