Species and Temperature Characterization of Ammonia/Air Mixtures in a Nanosecond-Pulsed High-Frequency Plasma-stirred Reactor*

Plasma and composition parameters were varied to determine the effects on the plasma temperature and output species. Using a nanosecond-pulsed high-frequency plasma pulse generator, a dielectric barrier discharge ammonia/air plasma was generated to study plasma-assisted ammonia cracking. Optical emission spectroscopy (OES) was used to validate nitrogen species' rotational and vibrational temperatures by targeting the N₂ (𝐶³Π_𝑢 -> 𝐵³Π_g) transition, or the second positive system. An in-house fitting software was used to fit the observed spectra to determine the temperature, assuming that the N₂ ground state projects the N₂ (C) rotational state. It was observed that the rotational temperature, which represents the gas temperature within the plasma reactor, increases with increasing specific energy input (SEI); however vibrational temperature does not. Thus, preliminary results indicate that excitation and dissociation of NH₃ is a significant pathway for energy input compared to N₂ molecular vibration within an NH₃-containing plasma. Fourier transform infrared spectroscopy (FTIR) will be used to quantify water and ammonia output under various conditions. The overall ammonia left in the exhaust will give insight into the total ammonia decomposed and compared with the H₂ output already validated by Faingold and Lefkowitz, will offer insight to the dominant reaction pathways in plasma-assisted ammonia cracking.