Some phenomena during electric discharge ignition in long tubes

Phenomena in slow nonlinear ionization waves are propagated under the action of changes in the electrode potential in discharge tubes. It is well known that the motion of such waves is accompanied by potential redistribution along the tube with a substantial role of charging its walls. The experimentally observed independence of the ionization wave velocity on the induction of the applied longitudinal magnetic field is discussed. In the case of the strong magnetization of electron motion, the radial current on walls is admittedly connected with the loss of axial symmetry in the ionization front. The cause of this may be the development of the ionization instability of discharges in crossed E, B fields. Evaluations of the average number of ionizations induced by one electron in the zone of the potential jump before its drift on the wall are given at the negative polarity of the ionization wave for helium in the pressure range of 33–840 Pa.     

Transverse electric discharges in supersonic air flows: microscopic characteristics of discharge

The spectroscopic and probe methods are used to measure the microscopic parameters of plasma of pulsed and stationary transverse discharges in a supersonic air jet flowing into a submerged space. The measurements are performed for the Mach number of flow M = 2, submerged space pressure p = 5 to 30 kPa, degree of the jet being off-design n 2, and discharge current I = 1 to 10 A. The discharge current dependences of the average values of gas temperature, charged particle concentration, and reduced electric field are measured for a discharge mode close to that of current generator. The measured values of gas temperature lie in the range of 1 to 3 kK, those of charged particles concentration — of 10¹³ to 10¹⁴ cm^-3 , and of reduced electric field — of 40 to 20 Td. The axial distribution of temperature is characterized by high values of temperature even at short distances from the electrodes and by a slow decrease along the flow.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 856–864.Original Russian Text Copyright © 2004 by A. P. Ershov, A. V. Kalinin, O. S. Surkont, I. B. Timofeev, V. M. Shibkov, and V. A. Chernikov.     

Effect of the electric discharge on nonstationary processes during supersonic air and methane jet flow over a flat obstacle

The features of supersonic air and methane jet flows over a flat obstacle, accompanied by an electric discharge, were studied. The flow under consideration is characterized by a number of unsteady effects appearing as oscillations of shock-wave fronts with various amplitudes and frequencies depending on the nozzle-obstacle system configuration and jet gas-dynamic parameters. The oscillation frequency of the bow shock wave increases as the obstacle becomes closer to the nozzle edge and the relative obstacle diameter and the supersonic jet stagnation pressure increase. Initiation of the energy release region at the supersonic jet edge causes a change in the oscillation frequency of the bow shock wave; under certain conditions, it causes a change in the entire shock-wave flow pattern.     

Glow discharge in a transverse supersonic gas flow at low pressures

A low-pressure glow discharge in a transverse supersonic gas flow was experimentally studied for the case where the flow only partially fills the interelectrode gap. It is shown that the space region with supersonic gas flow has a higher concentration of gas particles and, therefore, works as a charged particle generator. The near-electrode regions of glow discharge are concentrated specifically in this region. This structure of glow discharge is promising for plasma deposition of coatings under ultralow pressures.     

Ionization kinetics in a supersonic xenon plasma flow entering electric field

We have studied xenon plasma moving in a supersonic diffuser in external electric and magnetic fields. The main physical parameters of the plasma (electron temperature and density) were determined using specially developed methods based on the theory of continuous optical emission from inert gas atoms. These experimental data are compared to the results of theoretical calculations. Based on an analysis of the results of spectroscopic measurements, a mechanism of plasma ionization is established which is capable of maintaining a high degree of ionization in the supersonic xenon plasma flow.     

Initiation of combustion of supersonic propane-air flow by magnetoplasma compressor discharge

Results are given of investigations of the initiation of ignition and combustion of an air-propane flow in a supersonic wind channel with preheating by a pulsed discharge of a low-power magnetoplasma compressor of the erosion type. The mode of explosive ignition of mixture with formation of a combustion wave propagating towards the flow is revealed. The effect of initial conditions (fuel excess coefficient, preheating of air) on the spatial position and intensity of ignition is investigated.     

Spectroscopic investigations of longitudinal discharge in supersonic flow of air with injection of propane into the discharge zone

Results are given of investigations of a longitudinal contracted electric discharge in a supersonic flow of air at Mach number M = 2, static pressure of 3.47 × 10⁴ Pa (260 torr), and discharge current of 1 A with injection of propane into the discharge zone via electrode located upstream. The special feature of the discharge is that only one, anode, branch is realized in this case. Emission spectroscopy is used to obtain data on the composition of radiating products arising in the process of conversion of fuel-and-air mixture in the discharge and on their space distribution. In particular, data are given on the distribution of intensity of radiation of C₂, OH, CN, and CH radicals, as well as of atomic hydrogen, oxygen, carbon, and nitrogen, in a number of discharge channel sections. It is found that the main reaction zone in such a channel is preceded by the induction zone, where the development of reactions is hampered in spite of the electron flow in this zone. The employed procedure makes it possible to determine the variation of the transverse dimensions along the discharge channel and the details of flow such as a gradual shift of the gasdynamic lines of current due to the pattern of flow past the electrodes. Analysis of distribution of radiation intensity in the spectrum of atomic oxygen in a discharge without injection of propane gives estimates of the electron temperature which turns out to be approximately 1.1–1.2 eV.     

The interaction between plasma jet of a capillary discharge and transverse supersonic air flow

An experimental investigation is performed of modes of outflow into stationary air and of supersonic flow of a plasma jet developed by a capillary plasma generator. A theoretical model is suggested, which explains the obtained experimental results and enables one to simulate the process of injection of plasma jet into a supersonic air flow. The possibility is demonstrated of using such jets for the ignition of supersonic flows of combustible mixture.     

Spinning front formation in fuel gas-air flame

The method of forming a spinning front of the flame in a propane-air mixture in a flat gap between two plates is proposed. It is shown that the spinning flame fronts (SFFs) are formed in gas mixtures with an excess fuel component and are due to the decay of an initial cylindrical front. It is established that the decay of a cylindrical front is related to the onset of a thermodiffusion instability, which is accompanied by the suppression of the majority of small perturbations on the flame surface and results in the development of only two of these perturbations. The subsequent evolution of the fields of temperatures, concentrations, and velocities in the vicinity of the leader points of developing perturbations results in the formation of an SFF, which resembles extended arc-shaped whiskers. Temporal variations in the angular and tangential velocities of SFF propagation are determined.     

Parametric excitation and stabilization of dust structures in glow discharge under the action of nanosecond electric pulses

The phenomena of (i) parametric excitation of the resonance oscillations of dust particles due to pulsed heating of plasma electrons in a glow discharge, (ii) spatial stabilization of these particles due to additional local ionization, and (iii) disordering of the dust structure as a result of the breakage of a plasma trap (caused by an increase in the residual ionization in discharge with increasing frequency of the external action) have been experimentally studied.     

Digital imaging-based three-dimensional characterization of flame front structures in a turbulent flame

This paper focuses on the application of a multicamera imaging system for three-dimensional (3-D) visualization and quantitative characterization of the flame front structures of a turbulent flame. The 2-D images of the flame front are captured simultaneously using identical monochromatic CCD cameras from three different directions around the flame. Dedicated computing algorithms have been developed to reconstruct the 3-D structures of the flame front using various image processing techniques such as edge detection, contour extraction, and mesh generation. A set of flame parameters, including ignition points, ignition volume, ignition surface area, and circularity, is determined from the models generated to characterize the flame front. Results obtained under a range of combustion conditions demonstrate the capability of the system for 3-D quantitative characterization of flame front structures.     

Experimental study of heat transfer in an electric arc gas heater with vortex stabilization of the discharge

The results of an experimental investigation into heat transfer in the discharge chamber of an electric-arc gas heater are presented. For the anode the resultant data are expressed in the form of generalized relationships q_an=f(I, d), St=f(l/d, Re, N/GH₀). The energy losses in the basic arc spot are estimated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 1, pp. 76–81, January, 1971.     

An axisymmetric electric discharge as a means for remote heating of gas and for ignition of combustible gas mixture

Experimental and theoretical investigations are performed of gasdynamic phenomena accompanying a ring electric discharge excited in air at atmospheric pressure. It is experimentally demonstrated that the discharge generates a toroidal (three-dimensional) shock wave which cumulatively converges toward the axis. A mathematical model is constructed, which describes the process of focusing of the toroidal shock wave. The results of measurements of shock-wave processes accompanying the discharge are in good agreement with the calculation results; this enables one to estimate the gas temperature which may be attained in the region of cumulative convergence at some distance from the ring center. Results are given of first experiments in the excitation of a ring shock wave in a combustible gas mixture (stoichiometric mixture of CH₄:O₂).     

Transverse electric discharges in supersonic air flows: Simulation of the effects influencing the heating of gas in discharge channel

The Navier-Stokes equations are used to numerically investigate the gasdynamic aspects of interaction between a transverse discharge and supersonic flow in a model of heat source. The effect made by the jet and by the gasdynamic interaction of discharge channels on temperature is analyzed for plane flows with a pair of identical heat sources. Axisymmetric flows are calculated for a uniform incident flow. A marked variation of the flow parameters in the discharge zone and in the wake is observed if the power of energy input corresponds to, or is higher than, the gas enthalpy flow incident via the characteristic cross section of heat source. The calculation results are compared with experimental data. Explanations are provided of the results of experiments in heating a supersonic flow by a transverse electric discharge.     

Drag of an object in a supersonic flow with an isobaric region of energy release in front of the object

The problem of interaction between a steady-state supersonic flow and a planar isobaric region of energy release is solved. The solution is used to investigate the drag of an object in the wake behind the region of energy release. Conditions are determined for which the drag of the object can be reduced appreciably. The energy efficiency of this method of reducing the drag is studied. Pis’ma Zh. Tekh. Fiz. 25, 68–74 (January 12, 1999)     

Drag and heat exchange of an object in a supersonic flow with a planar source of energy in front of the object

The problem of a steady-state wake behind an energy source in a supersonic gas flow is analyzed and solved. The energy source is a planar gasdynamic discontinuity supplying a given energy to the flow. The parameters behind the source correspond to the weak detonation regime (supersonic combustion). The solution obtained is used to investigate the drag and heat exchange of an object in the wake behind the source. It is shown that the drag and thermal loads of the object may be reduced appreciably when the Mach numbers of the incoming flow are fairly high. An investigation was made of the energy efficiency of this method of reducing the drag and thermal loads of an object. The conditions under which this method is energetically favorable are determined. Pis’ma Zh. Tekh. Fiz. 24, 76–82 (December 26, 1998)     

Experimental investigations into electric discharge grinding and ultrasonic vibration-assisted electric discharge grinding of Inconel 601

The paper presents experimental investigations into electric discharge grinding (EDG) and ultrasonic vibration-assisted electric discharge grinding (UVAEDG) of Inconel 601. The process parameters selected for both processes were duty cycle, discharge current, pulse on time, grinding wheel speed, work speed, and speed ratio to study their influence on responses like surface roughness (R_a) and material removal rate (MRR). It was found that duty cycle, wheel speed, work speed, discharge current, speed ratio, and pulse duration significantly influenced MRR and R_a. It was inferred that MRR increased with increase in duty cycle, wheel speed, current, work speed, and pulse duration in both EDG and UVAEDG processes. It was also inferred that R_a increased with rise in duty factor, pulse on time, and discharge current in EDG and UVAEDG processes.     

Optical pulsating discharge plasma dynamics in a supersonic jet: Experiment and an analytical model of the quasistationary flow development

An analytical method for determining the wave structure and quasistationary flow parameters of an optical pulsating discharge plasma expanding in a supersonic flow is developed. The method is based on a physical model of the optical gas breakdown, a theory of the point explosion, the results of numerical modeling of the breakdown plasma dynamics along a laser beam, experimental data, and numerical estimates.