Influence of Different Frequency Power Generators on Plasma Temperatures in the Ammonia Decomposition Process: OES-Based Temperature Profiling in a Gliding Arc.

A gliding arc plasma reactor operated with highly concentrated ammonia (90 vol % NH3 in N2) was investigated using spatially resolved optical emission spectroscopy, electrical diagnostics, and gas chromatography. Fitting the N2 second positive system (310-360 nm) yielded rotational and vibrational temperature profiles along the arc for 50 Hz and Bipolar HV high-frequency (25-35 kHz) excitation. Results indicate local thermal equilibrium near ignition and a transition to nonequilibrium along the arc, which is a typical characteristic of a gliding arc. Bipolar HV kHz excitation produced higher vibrational temperatures, enhanced N2 + emission downstream, and substantially increased reaction rates localized in the discharge channel. It demonstrates improved energy concentration and higher ammonia conversion compared to 50 Hz, and promising potential for energy-efficient hydrogen recovery from ammonia.