Chemical Kinetics and Energy Budget Analysis in Streamer and Nanosecond Spark Plasma at Ammonia – Air Flame Conditions

This study presents chemical kinetic and energy budgets analysis using 1D simulations of streamer and spark phases of nanosecond pulsed non-equilibrium plasma in combustible NH3 / O2 / N2/ H2O mixtures. Spatiotemporal evolution of important radicals such as O, OH, H, NH2, and NO, which affect ignition, flame stability, and emission of ammonia flames are shown. Chemical pathways obtained using our unique plasma global pathway analysis (pGPA) algorithm provide insight into the dominant modes of electron energy transfer which directly and indirectly affect gas heating and radical production at various thermochemical states. Conditions in unburnt reactants, pre-heat zone, reaction zone, and burnt products are chosen for self-consistent modeling of avalanche to streamer to spark transitions. The dissociative quenching of singlet oxygen atom (O(¹D)) with NH3 and H2O plays an important role in the production of OH and NH2, whereas the quenching of the electronic excited states of NH3 results in the formation of H radicals. Fractions of all the inelastic and elastic collision losses with the total electron Joule heating have been used to predict values of operating parameters such as the applied voltage and pulse duration to efficaciously channelize the electron kinetic energy during the streamer formation and propagation phases. Fractions of the plasma energy used in fast gas heating, radical generation and vibrational energy rise during the streamer and nanosecond spark phases have also been quantified.