Bulletin of the American Physical Society
63rd Annual Gaseous Electronics Conference and 7th International Conference on Reactive Plasmas
Volume 55, Number 7
Monday–Friday, October 4–8, 2010; Paris, France
Session UF1: Pulsed Discharges and Combustion |
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Chair: Christophe Laux, EM2C, Ecole Centrale Paris, France Room: Petit Amphitheatre |
Friday, October 8, 2010 2:00PM - 2:30PM |
UF1.00001: Physics and chemistry of nanosecond pulsed discharges Invited Speaker: Recent decades have seen particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition (PAI) and plasma-assisted combustion (PAC). Starting with a monitoring of the existence/absence of the flame in supersonic flows under plasma excitation, plasma applications arrived at advanced diagnostics, the use of quantitative experimental data and complex kinetic schemes to describe the effect of ignition delay time and ignition length decrease. A great amount of experimental data was accumulated during this period which, for a number of applications, gave rise to the use of low temperature plasma of nonequilibrium gas discharges under the conditions of high speed flows and those similar to automotive engines. The talk reviews the data obtained to date and discusses outstanding problems. The basic possibilities of low temperature plasmas to ignite gas mixtures will be evaluated, and historical references that highlight pioneering work in this field will be presented. Special attention will be given to physics and chemistry of pulsed nanosecond discharges, widely used for PAI/PAC applications.\\[4pt] In collaboration with Andrey Starikovskii, Drexel University, USA. [Preview Abstract] |
Friday, October 8, 2010 2:30PM - 2:45PM |
UF1.00002: ABSTRACT WITHDRAWN |
Friday, October 8, 2010 2:45PM - 3:00PM |
UF1.00003: Modeling of Streamer Discharges in Supersonic Flows for Combustion Applications Doug Breden, Laxminarayan Raja Experiments in recent years have shown that high voltage, nanosecond pulsed plasma discharges are capable of enhancing combustion in supersonic fuel-air mixtures. At pressures near one atmosphere the plasma forms as a highly non-equilibrium, filamentary streamer discharge. The plasma decreases ignition delay time by producing highly reactive radicals such as atomic oxygen and electronically excited metastable species such as singlet delta oxygen. Our objective is to model single high-voltage pulses over nanosecond timescales to determine the relative importance of thermal heating versus plasma chemical reactions in enhancing combustion. This work is a continuation of previous work utilizing an expanded oxygen-hydrogen chemistry and a high pressure argon chemistry. We investigate 10 ns pulses with applied voltages ranging from 4-8 kV in Mach 3 oxygen-hydrogen and argon flows. The resulting plasma is weakly ionized with ion densities on the order of 10$^{20}$ m$^{-3}$ and O radical densities on the order of 10$^{21}$ m$^{-3}$. The argon plasma streamers propagate over a larger distance compared to the oxygen-hydrogen streamers, with smaller streamers branching from the main streamers near the electrode. The oxygen-hydrogen streamers are highly electronegative with electrons present primarily in the streamer heads. Most gas heating taking place in the electrode near field region due to ion Joule heating. [Preview Abstract] |
Friday, October 8, 2010 3:00PM - 3:15PM |
UF1.00004: Spatiotemporal evolutions of gas density and gas temperature in spark-plug assisted atmospheric-pressure microwave discharges Mansour Elsabbagh, Shinichiro Kado, Masashi Kaneko, Yuji Ikeda, Koichi Sasaki The gas temperature ($T_{\rm g}$) and gas density ($n$) are important parameters in plasma-assisted combustion. The gas heating results in the concomitant reduction of the gas density. The reduction of the gas density affects the reduced electric field ($E/n$) in the plasma, and correspondingly all the plasma parameters which depend on $E/n$. In this work, a rotational Raman scattering technique was used for measuring spatiotemporal evolutions of $T_{\rm g}$ and the density ($n_{\rm N2}$) of molecular nitrogen in spark-plug assisted atmospheric-pressure microwave discharges generated in N$_2$-He mixture (${\rm N}_2/{\rm He} = 700/50$ Torr) with pulsed microwave power of 360 W. Measured values of $T_{\rm g}$ in the discharge phase suggests that the discharge is in a nonequilibrium state. Unexpected, significant depletion of $n_{\rm N2}$ (up to 95\%) was observed in the intermediate stage of the discharge phase and in the early afterglow at a distance of 4.5 mm from the discharge center. Although the most probable mechanism for the significant depletion of N$_2$ is dissociation, further investigation is necessary to confirm the huge degree of dissociation. [Preview Abstract] |
Friday, October 8, 2010 3:15PM - 3:30PM |
UF1.00005: Plasma assisted ignition below self-ignition threshold in hydrogen, hydrogen-CO and hydrocarbon-air mixtures Liang Wu, Jamie Lane, Nicholas Cernansky, David Miller, Alexander Fridman, Andrey Starikovskiy The paper presents measurements of the time evolution of hydroxyl (OH) radicals in premixed hydrocarbon-air flows in the afterglow of a nanosecond-pulsed discharge at atmospheric pressure. The temperature ranged from 300 to 800 K (below the self-ignition point). The fuels were hydrogen, hydrogen-CO, methane, ethane, propane and butane at an equivalence ratio of 0.1 from 400 to 800 K. The plasma was generated by 20-kV pulses of 10 ns duration and a $<$1 ns rise time at a repetition rate of 10 Hz. Laser-induced fluorescence was used to measure the concentration of OH radicals after the discharge. The energy of the excitation laser was adjusted to ensure that the measurements were made under saturation conditions for all experiments. The time evolution of OH radicals was tracked by adjusting the delay time between the high-voltage pulse and the concentration measurement. The [OH] profiles show that after generation by the plasma the [OH] persists at significant level for a long time that lengthens with increasing temperature (starting at 500 K), which is not predicted in current kinetic models. [Preview Abstract] |
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