Description
Recent experimental studies of repetitive nanosecond pulse discharges demonstrate their significant potential for plasma assisted combustion, high-speed flow control, and low-temperature plasma chemistry. The main advantage of using these discharges for ignition is efficient generation of electronically excited and radical species. In the experiments, time-resolved temperature, N2 vibrational level populations, absolute O, H, and OH number densities, and ignition delay time are measured in premixed hydrocarbon–air, hydrogen–air, and hydrogen–oxygen–argon flows excited by repetitive nanosecond pulse discharges in plane-to-plane and point-to-point geometries. Time-resolved temperature and OH number density in lean H2–air, CH4–air, C2H4–air, and C3H8–air mixtures are measured by picosecond, broadband Coherent Antistokes Raman Spectroscopy (CARS) and by OH Laser-Induced Fluorescence (LIF). Time-resolved, spatially resolved temperature and absolute number densities of OH and H in Ar–O2–H2 mixtures are measured by UV Rayleigh scattering, LIF, and Two-Photon Absorption LIF (TALIF), respectively. The results demonstrate that ignition occurs due to efficient generation of radicals in the discharge and provide insight into the kinetic mechanism of low-temperature plasma assisted ignition. Time-resolved electron density, electron temperature, and electric filed in transient nanosecond pulse discharges are measured by Thomson scattering and picosecond CARS/4-wave mixing. Comparison with kinetic modeling calculations shows the need for development of a predictive low-temperature plasma/fuel chemistry model applicable to fuels C3 and higher. Kinetics of nanosecond pulse nonequilibrium electric discharges in liquids and at liquid–vapor interfaces is of great interest for applications such as reactive nitrogen/oxygen species generation, plasma activation of water, removal of volatile organic compounds from aqueous solutions, and plasma chemical reforming of liquid hydrocarbons and oxygenates. One of the main difficulties in studies of liquid/vapor phase plasma chemistry is sustaining the plasma at controlled, reproducible conditions which would lend themselves to in situ optical diagnostics. Dynamics of discharge development and kinetics of energy coupling in liquid–vapor interface plasmas remains poorly understood. Plasmachemical reactions near the vapor–surface interface may occur at high peak electric fields and low temperatures, due to rapid evaporative cooling of the liquid. Surface ionization wave discharges generated by high-voltage nanosecond pulses are studied over liquid–vapor surfaces (water and alcohols). Over a wide range of conditions, surface plasma “sheet” remains diffuse. No perturbation of the liquid surface by the discharge was detected. Products of plasma chemical reaction accumulated in the ionization wave discharge over liquid butanol/saturated butanol vapor interface are detected ex situ, using FTIR absorption spectroscopy. Reaction products identified include CO, alkanes, alkynes, aldehydes, and lighter alcohols. In situ laser diagnostics are used to measure radical species concentrations (OH LIF and H TALIF). Absolute, two-dimensional distributions of [OH] and [H] have been measured in a repetitively pulsed nanosecond discharge sustained near liquid water/saturated water vapor interface. The results suggest significant potential of this approach for near-surface plasmachemical reforming of evaporating liquid reactants.
Recommended Citation
Adamovich, I. (2014). Nanosecond pulse discharges for plasma assisted combustion and low-temperature plasma chemistry. In A. Bajaj, P. Zavattieri, M. Koslowski, & T. Siegmund (Eds.). Proceedings of the Society of Engineering Science 51st Annual Technical Meeting, October 1-3, 2014 , West Lafayette: Purdue University Libraries Scholarly Publishing Services, 2014. https://docs.lib.purdue.edu/ses2014/mfts/pst/2
Nanosecond pulse discharges for plasma assisted combustion and low-temperature plasma chemistry
Recent experimental studies of repetitive nanosecond pulse discharges demonstrate their significant potential for plasma assisted combustion, high-speed flow control, and low-temperature plasma chemistry. The main advantage of using these discharges for ignition is efficient generation of electronically excited and radical species. In the experiments, time-resolved temperature, N2 vibrational level populations, absolute O, H, and OH number densities, and ignition delay time are measured in premixed hydrocarbon–air, hydrogen–air, and hydrogen–oxygen–argon flows excited by repetitive nanosecond pulse discharges in plane-to-plane and point-to-point geometries. Time-resolved temperature and OH number density in lean H2–air, CH4–air, C2H4–air, and C3H8–air mixtures are measured by picosecond, broadband Coherent Antistokes Raman Spectroscopy (CARS) and by OH Laser-Induced Fluorescence (LIF). Time-resolved, spatially resolved temperature and absolute number densities of OH and H in Ar–O2–H2 mixtures are measured by UV Rayleigh scattering, LIF, and Two-Photon Absorption LIF (TALIF), respectively. The results demonstrate that ignition occurs due to efficient generation of radicals in the discharge and provide insight into the kinetic mechanism of low-temperature plasma assisted ignition. Time-resolved electron density, electron temperature, and electric filed in transient nanosecond pulse discharges are measured by Thomson scattering and picosecond CARS/4-wave mixing. Comparison with kinetic modeling calculations shows the need for development of a predictive low-temperature plasma/fuel chemistry model applicable to fuels C3 and higher. Kinetics of nanosecond pulse nonequilibrium electric discharges in liquids and at liquid–vapor interfaces is of great interest for applications such as reactive nitrogen/oxygen species generation, plasma activation of water, removal of volatile organic compounds from aqueous solutions, and plasma chemical reforming of liquid hydrocarbons and oxygenates. One of the main difficulties in studies of liquid/vapor phase plasma chemistry is sustaining the plasma at controlled, reproducible conditions which would lend themselves to in situ optical diagnostics. Dynamics of discharge development and kinetics of energy coupling in liquid–vapor interface plasmas remains poorly understood. Plasmachemical reactions near the vapor–surface interface may occur at high peak electric fields and low temperatures, due to rapid evaporative cooling of the liquid. Surface ionization wave discharges generated by high-voltage nanosecond pulses are studied over liquid–vapor surfaces (water and alcohols). Over a wide range of conditions, surface plasma “sheet” remains diffuse. No perturbation of the liquid surface by the discharge was detected. Products of plasma chemical reaction accumulated in the ionization wave discharge over liquid butanol/saturated butanol vapor interface are detected ex situ, using FTIR absorption spectroscopy. Reaction products identified include CO, alkanes, alkynes, aldehydes, and lighter alcohols. In situ laser diagnostics are used to measure radical species concentrations (OH LIF and H TALIF). Absolute, two-dimensional distributions of [OH] and [H] have been measured in a repetitively pulsed nanosecond discharge sustained near liquid water/saturated water vapor interface. The results suggest significant potential of this approach for near-surface plasmachemical reforming of evaporating liquid reactants.