Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session PR3: Gas Phase Plasma Chemistry |
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Chair: Timo Gans, University of York Room: Nassau Room |
Thursday, October 3, 2013 1:30PM - 1:45PM |
PR3.00001: Reaction kinetics of a kHz-driven atmospheric pressure plasma with humid air impurities T. Murakami, Q. Th. Algwari, K. Niemi, T. Gans, D. O'Connell, W.G. Graham Atmospheric-pressure plasma jets (APPJs) have been gaining attention because of their great potential in bio-plasma applications. It is important to know the complex chemical kinetics of the reactive multi-species plasma. This is a study starting to address this by using a 0D time-dependent global simulation (comprising 1050 elementary reactions among 59 specie [1]) of kHz-driven (20 kHz) APPJ with a helium-based oxygen-mixture (0.5{\%}) with ambient humid air impurity. The present model is initiated from time dependent measurements and estimates of the basic plasma properties [2]. The dominant neutral reactive species are reactive oxygen species and atomic hydrogen. The positive and negative oxygen ions and electrons are the most pronounced charged species. While most of the neutral reactive species are only weakly modulated at the driving frequency, the atomic oxygen metastables and atomic nitrogen metastables are strongly modulated. So are also the electrons and most of the positive and negative ions, but some are not, as will be discussed.\\[4pt] [1] T. Murakami et al Plasma Sources Sci. Technol.22 (2013) 015003.\\[0pt] [2] Q. Th. Algwari and D. O'Connell, Appl. Phys. Lett. 99 (2011) 121501. [Preview Abstract] |
Thursday, October 3, 2013 1:45PM - 2:00PM |
PR3.00002: Homogeneous and Heterogeneous Reaction Mechanisms in CH$_{3}$F-O$_{2}$ Inductively Coupled Plasmas Vincent M. Donnelly, Erdinc Karakas, Sanbir Kaler, Qiaowei Lou, Demetre J. Economou CH$_{3}$F/O$_{2}$ containing plasmas are used in selective Si$_{3}$N$_{4}$ etching over Si or SiO$_{2}$. Fundamental plasma studies in these gas mixtures are scarce. In this work, optical emission rare gas actinometry and a global chemistry model were employed to study inductively couple plasmas in CH$_{3}$F/O$_{2}$ gas mixtures. For constant CH$_{3}$F and O$_{2}$ flow rates, the absolute H, F and O atom densities increased linearly with power. The feedstock gas was highly dissociated and most of the fluorine and oxygen was contained in reaction products HF, CO, CO$_{2}$, H$_{2}$O and OH. Measured number densities as a function of O$_{2}$ addition to CH$_{3}$F/O$_{2}$ changed abruptly for H, O, and particularly F atoms (factor of 4) at 48{\%} O$_{2}$ A corresponding transition was also observed in electron density, electron temperature and gas temperature, as well as in C, CF and CH optical emission. These abrupt transitions were attributed to the reactor wall reactivity, changing from a polymer-coated surface to a polymer-free surface, and vice-versa, as the O$_{2}$ content in the feed gas crossed 48{\%}. Homogeneous chemistry dominates above 48{\%} O$_{2}$; a kinetic model with no adjustable parameters is in excellent agreement with the absolute F and H and relative HF number density dependence on power and pressure. [Preview Abstract] |
Thursday, October 3, 2013 2:00PM - 2:15PM |
PR3.00003: Plasma-assisted combustion in lean, high-pressure, preheated air-methane mixtures Timothy Sommerer, John Herbon, Seyed Saddoughi, Maxim Deminsky, Boris Potapkin We combine a simplified physical model with a detailed plasma-chemical reaction mechanism to analyze the use of plasmas to improve flame stability in a gas turbine used for electric power generation. For this application the combustion occurs in a lean mixture of air and methane at high pressure (18.6 atm) and at ``preheat'' temperature 700~K, and the flame zone is both recirculating and turbulent. The system is modeled as a sequence of reactors: a pulsed uniform plasma (Boltzmann), an afterglow region (plug-flow), a flame region (perfectly-stirred), and a downstream region (plug-flow). The plasma-chemical reaction mechanism includes electron-impact on the feedstock species, relaxation in the afterglow to neutral molecules and radicals, and methane combustion chemistry (GRI-Mech 3.0), with extensions to properly describe low-temperature combustion 700--1000~K [M Deminsky et al, Chem Phys \textbf{32}, 1 (2013)]. We find that plasma treatment of the incoming air-fuel mixture can improve the stability of lean flames, expressed as a reduction in the adiabatic flame temperature at lean blow-out, but that the plasma also generates oxides of nitrogen at the preheat temperature through the reactions $e +$ N$_{2} \to $ N $+$ N and N $+$ O$_{2} \to $ NO $+$ O. We find that flame stability is improved with less undesirable NOx formation when the plasma reduced-electric-field $E$/$N$ is smaller. [Preview Abstract] |
Thursday, October 3, 2013 2:15PM - 2:30PM |
PR3.00004: NO Formation and Consumption Mechanisms in a Plasma Filament David Burnette, Ivan Shkurenkov, Igor Adamovich, Walter Lempert Laser-induced fluorescence measurements have been performed on nitric oxide, oxygen atoms, and nitrogen atoms in low temperature, diffuse plasma filaments of air and air/fuel mixtures. The results have been compared to a one-dimensional numerical model and show that NO is rapidly formed in air as a result of excited species within the plasma and is consumed quickly by the reverse Zel'dovich mechanism. The evolution of the nitric oxide concentration in hydrogen and ethylene fuels is presented and the possibility of additional NO formation channels is discussed. [Preview Abstract] |
Thursday, October 3, 2013 2:30PM - 2:45PM |
PR3.00005: A spectroscopic study of ethylene destruction and by-product generation using a three-stage atmospheric packed-bed plasma reactor Marko Huebner, Olivier Guaitella, Antoine Rousseau, Juergen Roepcke Using a three-stage dielectric packed-bed plasma reactor at p $=$ 1 bar the destruction of C$_{2}$H$_{4}$ and the generation of major by-products have been studied by FTIR spectroscopy. As test gas mixture air containing 0.12{\%} humidity with 0.1{\%} ethylene admixture was used. In addition to the fragmentation of the precursor gas, the evolution of the concentration of ten stable reaction products, CO, CO$_{2}$ O$_{3}$, NO$_{2}$, N$_{2}$O, HCN, H$_{2}$O, HNO$_{3}$, CH$_{2}$O and CH$_{2}$O$_{2}$ has been monitored. Applying three sequentially working discharge cells (f $=$ 4 kHz, U $=$ 9 - 12 kV) a nearly complete decomposition of C$_{2}$H$_{4}$ could be achieved. In maximum the specific energy deposition was about 900 Jl$^{-1}$. The value of the specific energy $\beta $, characterizing the energy efficiency of the ethylene destruction in the used reactor, was 330 Jl$^{-1}$. The carbon balance of the plasma chemical conversion of ethylene has been analyzed. As a main result of the study, the application of three reactor stages suppresses essentially the production of harmful by-products as formaldehyde, formic acid and NO$_{2}$ compared to the use of only one or two stages. [Preview Abstract] |
Thursday, October 3, 2013 2:45PM - 3:00PM |
PR3.00006: Physical-chemical characterization of nitrogen atmospheric pressure plasma jets Sylwia Ptasinska, Matej Klas Most of atmospheric pressure plasma jet (APPJ) sources operate with noble gases as the feed gas, which require lower breakdown voltage than typical molecular gases in order to ignite the plasma. However, a high consumption of expensive noble gases during long term plasma operation in many applications increases costs of usage. Therefore, the development of new sources working with less expensive gases such as nitrogen or air is needed. In this work we concentrated on electrical, optical and thermal characterization of two nitrogen plasma jet sources. Both APPJ sources have been constructed with the same materials and dimensions, the only difference is the shape of the electrodes: spiral and 4-strip. This distinction is responsible for different electrical, optical and thermal properties of plasma jets, which will be reported at the meeting. It has been also observed that by adding specific amount of oxygen to the N$_{2}$ flow the production of different species such as NO or ON$_{2}$ excimer can be controlled. [Preview Abstract] |
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