Wenting Sun

Genetic effects of radio-frequency, atmospheric-pressure glow discharges with helium

Due to low gas temperatures and high densities of active species, atmospheric-pressure glow discharges (APGDs) would have potential applications in the fields of plasma-based sterilization, gene mutation, etc. In this letter, the genetic effects of helium radio-frequency APGD plasmas with the plasmid DNA and oligonucleotide as the treated biomaterials are presented. The experimental results show that it is the chemically active species, instead of heat, ultraviolet radiation, intense electric field, and/or charged particles, that break the double chains of the plasmid DNA. The genetic effects depend on the plasma operating parameters, e.g., power input, helium flow rate, processing distance, time, etc.

Novel mutation breeding method for Streptomyces avermitilis using an atmospheric pressure glow discharge plasma

Aims:  Avermectins are major antiparasitic agents used commercially in animal health, agriculture and human infections. To improve the fermentation efficiency of avermectins, for the first time a plasma jet generated by a novel atmospheric pressure glow discharge (APGD) was employed to generate mutations in Streptomyces avermitilis.

Direct In Situ Quantification of HO2 from a Flow Reactor

The first direct in situ measurements of hydroperoxyl radical (HO2) at atmospheric pressure from the exit of a laminar flow reactor have been carried out using mid-infrared Faraday rotation spectroscopy. HO2 was generated by oxidation of dimethyl ether, a potential renewable biofuel with a simple molecular structure but rich low-temperature oxidation chemistry. On the basis of the results of nonlinear fitting of the experimental data to a theoretical spectroscopic model, the technique offers an estimated sensitivity of <1 ppmv over a reactor exit temperature range of 398-673 K. Accurate in situ measurement of this species will aid in quantitative modeling of low-temperature and high-pressure combustion kinetics.

Plasma Assisted Low Temperature Combustion

This paper presents recent kinetic and flame studies in plasma assisted low temperature combustion. First, the kinetic pathways of plasma chemistry to enhance low temperature fuel oxidation are discussed. The impacts of plasma chemistry on fuel oxidation pathways at low temperature conditions, substantially enhancing ignition and flame stabilization, are analyzed base on the ignition and extinction S-curve. Secondly, plasma assisted low temperature ignition, direct ignition to flame transition, diffusion cool flames, and premixed cool flames are demonstrated experimentally by using dimethyl ether and n-heptane as fuels. The results show that non-equilibrium plasma is an effective way to accelerate low temperature ignition and fuel oxidation, thus enabling the establishment of stable cool flames at atmospheric pressure. Finally, the experiments from both a non-equilibrium plasma reactor and a photolysis reactor are discussed, in which the direct measurements of intermediate species during the low temperature oxidations of methane/methanol and ethylene are performed, allowing the investigation of modified kinetic pathways by plasma-combustion chemistry interactions. Finally, the validity of kinetic mechanisms for plasma assisted low temperature combustion is investigated. Technical challenges for future research in plasma assisted low temperature combustion are then summarized.

Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen

In this letter, atmospheric-pressure glow discharges in γ mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the α-γ coexisting mode or γ mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable γ mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.

Nanosecond Pulsed Plasma Activated C2H4/O2/Ar Mixtures in a Flow Reactor

The present work combines numerical and experimental efforts to investigate the effect of nanosecond pulsed plasma discharges on the low-temperature oxidation of C2H4/O2/Ar mixtures under reduced pressure conditions. The nonequilibrium plasma discharge is modeled using a one-dimensional framework, employing separate electron and neutral gas temperatures, and using a detailed plasma and combustion chemical kinetic mechanism. Good agreement is seen between the numerical and experimental results, and both results show that plasma enables low-temperature C2H4 oxidation. Compared to zero-dimensional modeling, the one-dimensional modeling significantly improves predictions, probably because it produces a more complete physical description (including sheath formation and accurate reduced electric field). Furthermore, the one- and zero-dimensional models show very different reaction pathways, using the same chemical kinetic mechanism and thus suggest different interpretations of the experimental results. Two kine...

Parallel On-the-fly Adaptive Kinetics for Non-equilibrium Plasma Discharges of C2H4/O2/Ar Mixture

To enhance the computational efficiency for the simulation of plasma assisted combustion (PAC) models, three new techniques, on-the-fly adaptive kinetics (OAK), point-implicit stiff ODE solver (ODEPIM), and correlated transport (CoTran), are combined together to generate a new simulation framework. This framework is applied to non-equilibrium plasma assisted oxidation of C2H4/O2/Ar mixtures in a low-temperature flow reactor. The new framework has been extensively verified by both temporal evolution and spatial distribution of several key species and gas temperature. Simulation results show that it accelerates the total CPU time by 3.16 times, accelerates the calculation of kinetics by 80 times, and accelerates the calculation of transport properties by 836 times. The high accuracy and performance of the new framework indicates that it has great application potentials to many different areas in the modeling and simulation of plasma assisted combustion.

Discharge features of radio-frequency, atmospheric-pressure cold plasmas under an intensified local electric field

In this paper, stable atmospheric-pressure argon, nitrogen or air glow discharges driven by a radio-frequency power supply with water-cooled, bare copper electrodes are obtained by employing a newly-designed plasma generator. Due to the existence of the intensified local electric field by using an insulated tungsten wire between the two bare copper electrodes, which is also verified by the modelling results, the experimental measurements show that stable glow discharges of argon, nitrogen or air can be obtained following a local breakdown process in the vicinity of the tungsten wire under lower applied voltages between the electrodes.

The back-diffusion effect of air on the discharge characteristics of atmospheric-pressure radio-frequency glow discharges using bare metal electrodes

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform α mode discharge of the RF APGD plasmas are presented. The experiments are conducted by placing the home-made planar-type plasma generator in ambient and in a vacuum chamber, respectively, with helium as the primary plasma-forming gas. When the discharge processes occur in ambient, particularly for the lower plasma-working gas flow rates, the experimental measurements show that it is the back-diffusion effect of air in atmosphere, instead of the flow rate of the gas, that results in the obvious decrease in the breakdown voltage with increasing plasma-working gas flow rate. Further studies on the discharge characteristics, e.g. the luminous structures, the concentrations and distributions of chemically active species in plasmas, with different plasma-working gases or gas mixtures need to be conducted in future work.

Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol

Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure α-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.