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N2 oxidation kinetics in a ns-pulsed discharge above a liquid electrode

Tijdschriftbijdrage - Tijdschriftartikel

Ondertitel:N-2 oxidation kinetics in a ns-pulsed discharge above a liquid electrode
In this work, the kinetics of nitrogen fixation via plasma-induced N-2 oxidation in a 10 ns pulsed atmospheric pressure water-contacting discharge sustained in air is investigated. Two pulse regimes, a single pulse and a three-pulse burst of 100 kHz, are considered. The densities of relevant radicals (NO, O) are studied by time- and space-resolved laser-induced fluorescence spectroscopy. It is concluded that in a single pulse mode, O atoms are mainly generated by O-2 reacting with electronically excited states of N-2 (A(3)Sigma(+)(u), B-3 Pi(g), C-3 Pi(u)) and are primarily reduced as a result of O-3 formation. The O density shows a maximum at similar to 100 ns after the plasma pulse with number density of similar to 10(23) m(-3). NO radicals, on the other hand, are primarily formed by reacting with the N-2(A(3)Sigma(+)(u)) state (up to similar to 1 mu s after the pulse) and with OH radicals (up to similar to 10's of mu s), peaking at approximately 60 mu s with a peak density of similar to 10(21) m(-3). The NO loss pathway is represented by the reversed Zeldovich mechanism at short time delays (similar to 10's mu s), whereas at longer delays (>100's of mu s) HNO2 and NO2 formation causing NO loss start to be dominant. In the burst mode, the energy efficiency of NO formation decreases despite higher N-2 conversion, for which three reasons are suggested: (1) NO removal by the generated O(D-1) after the discharge pulse through the reverse Zeldovich mechanism, (2) NO oxidation via the accumulated O-3, (3) pre-ionization induced by high pulse repetition rate (100 kHz) leading to shrinkage of the plasma bulk.
ISSN: 1361-6595
Issue: 6
Volume: 30
Jaar van publicatie:2021