Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session BT2: Plasma Aerodynamics and Propulsion I |
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Chair: A. Aanesland, LPTP, Ecole Polytechnique, France Room: Salon A-D |
Tuesday, October 14, 2008 8:00AM - 8:15AM |
BT2.00001: Laser Induced Fluorescence Studies of NO Kinetics in Short Pulse Air and Air-Fuel Nonequilibrium Discharges Walter Lempert, Mruthunjaya Uddi, Igor Adamovich Laser Induced Fluorescence is used to measure absolute NO concentrations in air, methane-air, and ethylene-air non-equilibrium plasmas, as a function of time after initiation of a single 25 nsec discharge pulse. Peak NO density in air at 60 torr is $\sim $8.10$^{12}$ cm$^{-3}$ occurring at $\sim $500 $\mu $s after the pulse, with decay time of $\sim $16.5 msec. Peak NO atom mole fraction in methane-air at $\phi $=0.5 is approximately equal to that in pure air with similar rise and decay rate. In $\phi $ = 0.5 ethylene-air, the rise and decay times are also comparable to air and methane--air, but peak NO concentration is a factor of $\sim $2.5 lower. Spontaneous emission measurements show that N$_{2}$(C) and NO (A) decay in $\sim $25ns and $\sim $2.5$\mu $s, respectively. Kinetic modeling calculations incorporating Boltzmann solver for EEDF, and electron impact and full air species kinetics, complemented with the GRI Mech 3.0 hydrocarbon oxidation mechanism, are compared with the experimental data using three different mechanisms. It is concluded that processes involving long lifetime ($\sim $100 $\mu $sec) meta-stable states, such as N$_{2}$ (X,v) and O$_{2}$(b$^{1}\Sigma )$, which are formed by quenching of the metastable N$_{2}$ (A) state by ground state O$_{2}$, play a dominant role in NO formation. [Preview Abstract] |
Tuesday, October 14, 2008 8:15AM - 8:30AM |
BT2.00002: Deflagration-to-detonation transition control by high voltage nanosecond discharges Andrei Starikovskii, Aleksandr Rakitin A smooth square detonation tube with a transverse size of 20 mm and a single-cell discharge chamber has been assembled to study DDT mechanisms under initiation by high-voltage nanosecond discharges. Stoichiometric propane-oxygen mixture was used at initial pressures of 0.3 and 1 bar. Two general mechanisms of DDT initiation have been observed and explained under the experimental conditions. When initiated by a spark, the mixture ignites simultaneously over the volume of the discharge channel, producing a shock wave with Mach number over 2 and a flame wave. The waves then form an accelerating complex, and, after it reaches a certain velocity, an adiabatic explosion occurs resulting in DDT. At 1 bar of initial pressure, the DDT length and time do not exceed 50 mm and 50 $\mu $s, respectively. Under streamer initiation, the mixture inside the discharge channel is excited non-uniformly. The mixture is first ignited at the hottest spot with the shortest ignition delay, which is at the high voltage electrode tip. Originating at this point, the ignition wave starts propagating along the channel and accelerates up to the CJ velocity value. The initiation energy is by an order of magnitude lower for the streamer-gradient mode when compared to the spark initiation. [Preview Abstract] |
Tuesday, October 14, 2008 8:30AM - 9:00AM |
BT2.00003: Jet Diffusion Flame Stabilization via Pulsed Plasma Forcing Invited Speaker: In this work we investigate the use of high repetition rate pulsed plasma sources as a means to enhance the stability of jet diffusion flames for application to practical combustion devices. Such plasma sources have recently become popular owing to their low power requirements and their proven abilities to ignite leaner mixtures and hold stable flames. They are known to create a radical pool which can enhance combustion chemistry and thus provide increased flame stability. By first investigating a fully premixed methane/air environment we show that the resulting radical species quickly decay but leave behind a set of stable chemical species. Thus, the plasma source appears to act as a fuel reformer leading to the formation of a ``cool flame'' -- a trailing zone of weak oxidation consisting of a slightly elevated temperature stream of products containing small amounts of hydrogen and carbon monoxide. These two key species are then directly responsible for the enhanced flame behaviors. Flame stability enhancements are shown for methane jets in co-flow and cross-flow in room temperature air, and in elevated temperature vitiated air environments. Elevated ambient temperatures deplete the hydrogen and carbon monoxide due to enhanced oxidation, so while there is an enhancement to flame stability, the beneficial effects diminish with increasing temperatures in a non-linear fashion, and ultimately, provide very limited benefits at $\sim $1000K ambient temperature for the present studies. The conclusions here are supported by simple plasma and chemical kinetic modeling and spectroscopic and chemiluminescence measurements. [Preview Abstract] |
Tuesday, October 14, 2008 9:00AM - 9:15AM |
BT2.00004: Simulations of Direct Current Glow Discharges in Supersonic Air Flow Shankar Mahadevan, Laxminarayan Raja In recent years, there have been a significant number of computational and experimental studies investigating the application of plasma discharges as actuators for high speed flow control. The relative importance of the actuation mechanisms: volumetric heating and electrostatic forcing can be established by developing self-consistent models of the plasma and bulk supersonic flow. To simulate the plasma discharge in a supersonic air stream, a fluid model of the glow discharge is coupled with a compressible Navier-Stokes solver in a self-consistent manner. Source terms for the momentum and energy equations are calculated from the plasma model and input into the Navier-Stokes solver. In turn, the pressure, gas temperature and velocity fields from the Navier-Stokes solution are fed back into the plasma model. The results include plasma species number density contour maps in the absence and presence of Mach 3 supersonic flow, and the corresponding effect of the glow discharge on gas dynamic properties such as the gas pressure and temperature. We also examine the effect of increasing the discharge voltage on the structure of the discharge and its corresponding effect on the supersonic flow. [Preview Abstract] |
Tuesday, October 14, 2008 9:15AM - 9:30AM |
BT2.00005: Pulse Discharge in Mixing Layer of Reacting Gases Sergey Leonov, Yuri Isaenkov, Michail Shneider A subject of consideration is the dynamic of filamentary pulse discharge generated along contact zone of two co-flown gases. Experimental facility consists of blow-down wind tunnel PWT-50, system of the high-voltage pulse-repetitive feeding, and diagnostic equipment (schlieren device; pressure, voltage, current, radiation sensors; spectroscopic system; etc.) Typical parameters: p=0.2-1Bar, velocity M=0-2, pulse duration $\tau $=0.1-1$\mu $s, power release W=20-100MW. Recently the effect of enormously fast turbulent expansion of the post-discharge channel was observed experimentally [S. Leonov, oth., AIAA Paper 2005-0159 and S. Leonov, oth. ``Physics of Plasmas'', v.15, 2007]. In this paper a result of parametrical study of the mixing efficiency due to instability development are discussed. The next announced item is that the discharge position and dynamics depend on the test parameters and physical properties of gases involved. The result of interaction can be controlled by the discharge's duration and current as well as by small additives to the gas. The effects found can be applied for high-speed combustion enhancement due to mixing acceleration in multi-components flow.. [Preview Abstract] |
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