The present study applying a plasma jet to activate water in a controllable environment is aimed to investigate the effect of a combination of (working/ chamber gas) on the properties of plasma-activated water. After 10 min of activation, results reveal that a significant decrease in solution pH is observed with the presence of N 2 . Hydrogen peroxide appears to be the major species for most gas mixtures, except [Ar + air/Ar] and [Ar + air/ air], where nitrite and nitrate dominate. A gas mixture of [Ar + air/Ar] produces the maximum concentration of NO 2 − , while the maximum NO 3 − and H 2 O 2 are observed for [Ar + air/air] and (Ar/Ar), respectively. Overall, the antibacterial efficacy correlates well with NO 2 − concentration. K E Y W O R D S plasma jet, plasma-activated water, reactive nitrogen species, reactive oxygen species, sterilization F I G U R E 1 A schematic of the experimental setup 2 of 7 | LAI ET AL.

The adiabatic, laminar flame speeds of gasoline surrogates at atmospheric pressure over a range of equivalence ratios of Φ = 0.8–1.3 and unburned gas temperatures of 298–400 K are measured with the flat flame method, which produces a one-dimensional flat flame free of stretch. Surrogates used in the current work are the primary reference fuels (PRFs, mixtures of n-heptane and isooctane), the toluene reference fuels (TRFs, mixtures of toluene and PRFs), and the ethanol reference fuels (ERFs, mixtures of ethanol and PRFs). In general, there is good agreement between the present work and the literature data for single-component fuel and PRF mixtures. Surrogates of TRF mixtures are found to exhibit comparable flame speeds to a real gasoline, while there is discrepancy observed between isooctane and gasoline. Moreover, the laminar flame speeds of TRF mixtures with similar fractions of n-heptane are found to be insensitive to the quantity of toluene in the mixture. Mixtures of ERFs exhibit comparable flame speeds to those of TRFs with similar mole fractions of n-heptane and isooctane.

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This study is to investigate the role of O3 on NO and NO2 oxidations to selective formations of NO2 − and NO3 − in plasma-treated water. Two plasma reactors, a surface dielectric-barrier discharge (DBD) and a coaxial DBD jet, are employed to water treatment with a working gas primarily consisting of N2 and O2. Results of surface DBD show that O3 first is increased with plasma treatment time, reaching a maximum, and then decreased. NO takes time to grow and the grow of NO is accompanied by O3 decrease. Formations of NO2 − and NO3 − are associated with gas-phase nitrogen oxides while the presence of O3 has a critical influence on a selective formation of NO2 − and NO3 −. The strong oxidation of O3 favors the formation of NO3 − while inhibits NO2 − formation. O3 serving as an inhibitor of NO2 − is confirmed with the DBD jet experiment where O3 is admixed in the downstream of the post discharge. O3 enhancement on NO3 − formation is demonstrated by exposing water to a synthetic NO gas with and without O3. In addition to O3, the presence of water vapor in the working gas, presumably facilitating formation of HNO2 and HNO3, greatly promotes NO2 − and NO3 − concentrations in solution. This is thought to be due to the stronger dissolution susceptibility and the relatively larger rate constant of HNO2 and HNO3 than those of N2O3 and N2O5. Finally, based on observations obtained here, a schematic roadmap of selective NO2 − and NO3 − formations is presented.

The present study experimentally investigates the effects of plasma discharges on the stabilization of lifted non-premixed jet flames in a stream of co-flow air. The plasma discharge is produced on the sharp edge of the fuel nozzle exit, facilitating its impact on flame stabilization. It is observed that the application of plasma discharges has an impact on the enhancement of flame lift-off velocity, lift-off height, and hysteresis phenomenon and leads to plasma-attached flames, plasma-enhanced lifted flames, and plasma-ineffective lifted flames, depending on flame lift-off conditions. A maximum enhancement of approximately 84% is observed for the flame lift-off velocity when the co-flow velocity is sufficiently low. As the co-flow velocity or the jet Reynolds number is low, the flame is anchored at the nozzle by the discharge. As the co-flow velocity or the jet Reynolds number is increased, the flame detaches but with a decrease in lift-off height compared to the flame without the discharge. If the co-flow velocity of the jet Reynolds number is continuously increased such that the flame lift-off height is beyond a critical value, the effect of plasma discharges diminishes and the flame lift-off height becomes comparable to that without plasma discharges. In flame hysteresis studies, both of the flame lift-off and reattachment velocities are increased with 2-fold enhancement when the discharge is present. Spectroscopic study shows that the emission characteristics, particularly for those between 400 and 800 nm, in flames are intensified with the presence of plasma discharge, consistent with the flame luminosity visualization, probably due to the reduced lift-off height that leads to reduced air premixing, resulting in increased soot formation.