AFRL-AFOSR-VA-TR-2016-0301 Nonequilibrium Molecular Energy Coupling and Conversion Mechanisms

The report presents results of development of an accurate, physics-based model of vibrational androtational energy transfer in three-dimensional collisions of rotating diatomic molecules, applicable over awide range of collision energies and vibrational / rotational quantum numbers, and results of detailedkinetic modeling studies of state-to-state molecular energy transfer processes, including excitation ofvibrational and electronic states by electron impact, collisional quenching of excited electronic states,vibration-vibration (V-V) energy transfer, vibration-rotation-translation (V-R-T) relaxation, internal modeenergy thermalization, molecular dissociation (both by electron impact and during quenching of excitedelectronic state), and plasma chemical reactions. The kinetic modeling prediction are compared with recenttime-resolved, spatially resolved measurements of vibrational level populations, gas temperature, andatomic species and radical number densities in the afterglow of a ns pulse discharge generating stronginternal energy mode disequilibrium in air and fuel-air mixtures. The present results provide newquantitative insight into kinetics of molecular energy transfer and plasma chemical reactions in air and fuel-air mixtures, at the conditions of strong internal energy mode disequilibrium. Closed-form, physics-based,DISTRIBUTION A: Distribution approved for public release. analytic expressions for state-to-state rotational and vibrational energy transfer transition probabilities lend themselves to straightforward incorporation into state-of-the-art DSMC nonequilibrium flow codes. Understanding kinetics of energy thermalization and chemical reactions in ns pulse discharges considerably improves predictive capability of kinetic models, which has major implications for plasma assisted combustion and high-speed plasma flow control, where these discharges are used increasingly