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

Localized arc filament plasma actuators for noise mitigation and mixing enhancement

A device for controlling fluid flow. The device includes an arc generator coupled to electrodes. The electrodes are placed adjacent a fluid flowpath such that upon being energized by the arc generator, an arc filament plasma adjacent the electrodes is formed. In turn, this plasma forms a localized high temperature, high pressure perturbation in the adjacent fluid flowpath. The perturbations can be arranged to produce vortices, such as streamwise vortices, in the flowing fluid to control mixing and noise in such flows. The electrodes can further be arranged within a conduit configured to contain the flowing fluid such that when energized in a particular frequency and sequence, can excite flow instabilities in the flowing fluid. The placement of the electrodes is such that they are unobtrusive relative to the fluid flowpath being controlled

Localized arc filament plasma actuators for noise mitigation and mixing enhancement

A device for controlling fluid flow. The device includes an arc generator coupled to electrodes. The electrodes are placed adjacent a fluid flowpath such that upon being energized by the arc generator, an arc filament plasma adjacent the electrodes is formed. In turn, this plasma forms a localized high temperature, high pressure perturbation in the adjacent fluid flowpath. The perturbations can be arranged to produce vortices, such as streamwise vortices, in the flowing fluid to control mixing and noise in such flows. The electrodes can further be arranged within a conduit configured to contain the flowing fluid such that when energized in a particular frequency and sequence, can excite flow instabilities in the flowing fluid. The placement of the electrodes is such that they are unobtrusive relative to the fluid flowpath being controlled

Mixing and flameholding in supersonic combustor by electrical discharge

Compared to a basic scramjet design, operation of scramjet combustors using plasma assisted ignition and flameholding offers considerably more flexibility over the choice of its geometry, due to replacing mechanical flameholders with a highly effective electrically driven apparatus. The articlce presents the results of an experimental study of supersonic combustor operation enhanced by an electrical discharge. A novel scheme of plasma assisted mixing, ignition, and flameholding is demonstrated, which combines a wall fuel injector and a high-voltage electric discharge into a single module. The experimental combustor with the cross-section of 72 mm (width) ´ 60 mm (height) and length of 600 mm operates at a Mach number of M = 2, initial stagnation temperature of airflow of T0 = 290–300 K, and stagnation pressure of P0 = 1.3–2.0 Bar. The combustor is equipped with four plasma ignition modules, flush-mounted side-by-side on the plane wall of the combustion chamber. The combustion tests were performed using ethylene injection with a total mass flow rate of GC2H4 \u3c 10 g/s and discharge power in the range of Wpl = 3 – 24 kW. The scope of the experiments includes characterization of the discharge interacting with the main flow and fuel injection jet, parametric study of ignition and flame front dynamics, and comparison of this scheme to earlier tested configuration. This approach demonstrates a significant advantage in terms of flameholding limits. An operation mode with strong combustion oscillations was observed at high fuel injection flow rates. Methods of flame front stabilization based on plasma application are discussed. The technique studied in this study may have significant potential for high-speed combustion applications, including cold start/restart of scramjet engines and support of transition regime in dual-mode and off-design operation

Analysis of Fast Ionization Wave Discharge Propagation in a Rectangular Geometry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90689/1/AIAA-2011-3449-301.pd

The 2022 plasma roadmap: low temperature plasma science and technology

The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years

The 2022 Plasma Roadmap: low temperature plasma science and technology

The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5–10 years.Peer ReviewedPostprint (published version

Kinetics of Аdsorption of nickel(II) Ions by Zeolite with Immobilized Thiosemicarbazide

Исследовано влияние температуры на кинетику адсорбции ионов никеля(II) цеолитом с иммобилизованным тиосемикарбазидом. В рамках диффузионных моделей Бойда и Морриса-Вебера использован количественный подход для первичного разграничения внешне и внутри диффузионного лимитирования адсорбции. Показано, что диффузия ионов через пленку раствора и диффузия в зерне цеолита вносят свой вклад в общую скорость процесса, и адсорбция протекает в смешанно-диффузионном режиме. Вклад химической стадии в кинетику гетерогенного процесса адсорбции был охарактеризован в рамках кинетических моделей Лагергрена, Хо и Маккея и Еловича. Наиболее применимой для описания исследуемых процессов является модель псевдо-второго порядка. Модель предполагает, что скорость процесса адсорбции ионов никеля(II) лимитирует химическая реакция, которая в случае рассматриваемых цеолитов сопровождается образованием хелатных комплексов (состава 1:1) за счет донорно-акцепторного взаимодействия ионов металла с атомами азота и серы тиосемикарбазидного фрагмента. Такой тип взаимодействия характерен как для материалов функционализированных тиосемикарбазидом, так и в целом для органических адсорбентов, содержащих N- и S‑активные группировкиThe effect of temperature on the adsorption kinetics of nickel(II) ions by zeolite with immobilized thiosemicarbazide has been studied. Within the framework of the diffusion models of Boyd and Morris-Weber, a quantitative approach was used for the primary distinction between external and internal diffusion limitation of adsorption. It is shown that the diffusion of ions through the solution membrane and diffusion in the zeolite grain contribute to the overall rate of the process, and adsorption proceeds in a mixed diffusion mode. The contribution of the chemical stage to the kinetics of the heterogeneous adsorption process was characterized in terms of the kinetic models of Lagergren, Ho, and McKay and Elovich. The most applicable for describing explored the processes is the pseudo-second order model. The model assumes that the rate of adsorption of nickel(II) ions is limited by a chemical reaction, which, in the case of the zeolites under consideration, is accompanied by the formation of chelate complexes (composition 1:1) due to the donor-acceptor interaction of metal ions with nitrogen and sulfur atoms of the thiosemicarbazide fragment. This type of interaction is typical both for materials functionalized with thiosemicarbazide and, in general, for organic adsorbents containing N- and S‑active group

Correction to: Two years later: Is the SARS-CoV-2 pandemic still having an impact on emergency surgery? An international cross-sectional survey among WSES members

Background: The SARS-CoV-2 pandemic is still ongoing and a major challenge for health care services worldwide. In the first WSES COVID-19 emergency surgery survey, a strong negative impact on emergency surgery (ES) had been described already early in the pandemic situation. However, the knowledge is limited about current effects of the pandemic on patient flow through emergency rooms, daily routine and decision making in ES as well as their changes over time during the last two pandemic years. This second WSES COVID-19 emergency surgery survey investigates the impact of the SARS-CoV-2 pandemic on ES during the course of the pandemic. Methods: A web survey had been distributed to medical specialists in ES during a four-week period from January 2022, investigating the impact of the pandemic on patients and septic diseases both requiring ES, structural problems due to the pandemic and time-to-intervention in ES routine. Results: 367 collaborators from 59 countries responded to the survey. The majority indicated that the pandemic still significantly impacts on treatment and outcome of surgical emergency patients (83.1% and 78.5%, respectively). As reasons, the collaborators reported decreased case load in ES (44.7%), but patients presenting with more prolonged and severe diseases, especially concerning perforated appendicitis (62.1%) and diverticulitis (57.5%). Otherwise, approximately 50% of the participants still observe a delay in time-to-intervention in ES compared with the situation before the pandemic. Relevant causes leading to enlarged time-to-intervention in ES during the pandemic are persistent problems with in-hospital logistics, lacks in medical staff as well as operating room and intensive care capacities during the pandemic. This leads not only to the need for triage or transferring of ES patients to other hospitals, reported by 64.0% and 48.8% of the collaborators, respectively, but also to paradigm shifts in treatment modalities to non-operative approaches reported by 67.3% of the participants, especially in uncomplicated appendicitis, cholecystitis and multiple-recurrent diverticulitis. Conclusions: The SARS-CoV-2 pandemic still significantly impacts on care and outcome of patients in ES. Well-known problems with in-hospital logistics are not sufficiently resolved by now; however, medical staff shortages and reduced capacities have been dramatically aggravated over last two pandemic years