Ilya Kosarev

Nanosecond-Pulsed Discharges for Plasma-Assisted Combustion and Aerodynamics

The efficiency of nanosecond discharges as an active-particle generator for plasma-assisted combustion and ignition has been shown. The kinetics of alkane oxidation have been investigated from methane to decane in stoichiometric and lean mixtures with oxygen and air at room temperature under the action of high-voltage nanosecond unform discharge. The study of nanosecond barrier discharge influence on a flame propagation and flame blowoff velocity has been carried out. A significant increase of the flame blowoff velocity has been demonstrated. A decrease of 2-3 orders of magnitude of the plasma-assisted ignition delay time in comparison with the autoignition has been registered. Detonation initiating by high-voltage gas discharge has been demonstrated. The energy deposition in the discharge ranging from 70 mJ to 12 J for propane-oxygen-nitrogen mixtures leads to the transition to detonation at a distance of less than one diameter of the detonation tube. The influence of pulsed surface dielectric discharge on the flow separation for airfoils at a high angle of attack has been investigated within the velocity range from 20 to 110 m/s for the power consumption less than 1 W/cm of the wing span. The conclusion has been made that the main mechanism of plasma impact is the boundary-layer turbulization rather than acceleration.

Kinetic mechanism of plasma-assisted ignition of hydrocarbons

Ignition of hydrocarbon-containing gaseous mixtures has been studied experimentally and numerically under the action of a high-voltage nanosecond discharge at elevated temperatures. Ignition delay times were measured behind a reflected shock wave in stoichiometric CnH2n+2 :O2 mixtures (10%) diluted with Ar (90%) for n = 1‐5. It was shown that the application of the gas discharge leads to more than an order of magnitude decrease in ignition delay time for all hydrocarbons under consideration. The measured values of ignition delay time agree well with the results of a numerical simulation of the ignition based on the calculation of atom and radical production during the discharge and in its afterglow. The analysis of simulation results showed that a non-equilibrium plasma favours the ignition mainly due to O atoms produced in the active phase of the discharge. (Some figures in this article are in colour only in the electronic version)

Plasma-assisted combustion

This paper presents an overview of experimental and numerical investigations of the nonequilibrium cold plasma generated under high overvoltage and further usage of this plasma for plasma-assisted combustion. Here, two different types of the discharge are considered: a streamer under high pressure and the so-called fast ionization wave (FIW) at low pressure. The comprehensive experimental investigation of the processes of alkane slow oxidation in mixtures with oxygen and air under nanosecond uniform discharge has been performed. The kinetics of alkane oxidation has been measured from methane to decane in stoichiometric and lean mixtures with oxygen and air at room temperature under the action of high-voltage nanosecond uniform discharge. The efficiency of nanosecond discharges as active particles generator for plasma-assisted combustion and ignition has been investigated. The study of nanosecond barrier discharge influence on a flame propagation and flame blow-off velocity has been carried out. With energy input negligible in comparison with the burners chemical power, a double flame blow-off velocity increase has been obtained. A signicant shift of the ignition delay time in comparison with the autoignition has been registered for all mixtures. Detonation initiating by high-voltage gas discharge has been demonstrated. The energy deposition in the discharge ranged from 70 mJ to 12 J. The ignition delay time, the velocity of the flame front propagation, and the electrical characteristics of the discharge have been measured during the experiments. Under the conditions of the experiment, three modes of the flame front propagation have been observed, i.e., deflagration, transient detonation, and Chapman-Jouguet detonation. The efficiency of the pulsed nanosecond discharge to deflagration-to-detonation transition (DDT) control has been shown to be very high.

Plasma decay in N2, CO2 and H2O excited by high-voltage nanosecond discharge

Plasma decay after a high-voltage nanosecond discharge was studied experimentally and numerically in room temperature N2, CO2 and H2O for pressures between 1 and 10 Torr. The time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range 8 × 1011–3 × 1012 cm−3 and the effective electron–ion recombination coefficient was determined. It was shown that this coefficient varies in time and depends on pressure. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. A good agreement was obtained between the calculated and the measured electron density histories. It was shown that the loss of electrons is governed by dissociative recombination with complex ions, their density being dependent on pressure. In N2 at low pressures, a hindered electron thermalization in collisions with molecules led to a delay in the plasma decay. This effect was observed both experimentally and theoretically.

Ignition with low-temperature plasma: Kinetic mechanism and experimental verification

The results of experiments and calculations performed at the Laboratory of Physics of Nonequilibrium Systems, Moscow Institute of Physics and Technology from 1996 to 2008 to demonstrate the efficiency of low-temperature plasma in initiation of combustion of gas mixtures over a wide range of initial conditions are surveyed. In the studies reviewed, a method for quantitative analysis of kinetic processes during ignition of combustible gas mixtures by nonequilibrium plasma was developed.

Nanosecond discharge ignition in acetylene-containing mixtures

We study experimentally and numerically the kinetics of ignition in lean and stoichiometric C2H2?:?O2?:?Ar mixtures after a high-voltage nanosecond discharge. The ignition delay time is measured behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to a decrease in ignition delay time. Discharge processes followed by chain chemical reactions with energy release are simulated during ignition in the C2H2?:?O2?:?Ar mixtures. The generation of atoms, radicals and excited and charged particles in the discharge phase is numerically simulated. The calculations are based on the measured time-resolved discharge current and electric field. The calculated densities of the active particles produced in the discharge on a nanosecond time scale are employed as input data to simulate plasma-assisted ignition on a microsecond scale. The calculated ignition delay times are compared with the experimental data. It is shown that the effect of the discharge plasma on ignition of the acetylene-containing mixtures is associated with active species production in the discharge phase rather than with gas heating during the discharge and in its afterglow. A sensitivity analysis is made to determine limiting reactions in acetylene autoignition and ignition after the discharge under the conditions studied.

Plasma decay in air and O2 after a high-voltage nanosecond discharge

This paper presents the results of experimental and theoretical studies of an afterglow in room temperature air and O2 excited by a high-voltage nanosecond discharge for pressures between 1 and 10?Torr. We measured time-resolved electron density by a microwave interferometer for initial electron densities in the range (2?3)???1012?cm?3. Discharge uniformity was investigated by optical methods. The balance equations for charged particles and electron temperature were numerically solved to describe the temporal evolution of the densities of electrons and ions in the discharge afterglow. It was shown that the loss of electrons is governed by dissociative and three-body electron recombination with ions under the conditions considered. Good agreement between the calculated and measured electron density histories could be obtained only when the rate of three-body recombination was increased by an order of magnitude and when the dependence of the recombination rate on electron temperature was changed. This could testify that the well-understood mechanism of three-body electron recombination with atomic ions could be noticeably modified in the case of molecular ions.

Plasma decay in air and N2 : O2 : CO2 mixtures at elevated gas temperatures

Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically behind incident and reflected shock waves in high temperature (600?2400?K) air and N2?:?O2?:?CO2 mixtures for pressures between 0.05 and 1.2?atm. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1?3) ? 1012?cm?3 and the effective electron?ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged and neutral particles under the conditions considered. It was shown that the loss of electrons in this case is determined by dissociative recombination with ions, whereas the effect of complex ions is negligible. Electron attachment to O2 to form negative ions is not important because of fast electron detachment in collisions with O atoms produced in the discharge. In the absence of O atoms the electron density could decay as if the loss of charged particles were governed by electron?ion recombination with the effective rate coefficient being much higher than the dissociative recombination coefficient.

Plasma decay in the afterglow of a high-voltage nanosecond discharge in air

The decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 1–10 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 1012 cm−3. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electron-ion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three-body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination.

Analysis of Ignition by Nonequilibrium Sources. Ignition of Homological Series of Hydrocarbons by Volume Nanosecond Discharge

Kinetics of an artificial ignition at injection a certain amount of radicals is analyzed numerically on example of H2:O stoichiometric mixture. Kinetic curves for gas temperature and production of radicals are analyzed and compared for cases of thermal and artificial ignition. Kinetic curve for gas temperature under dissociation similar to one realized in volume nanosecond discharge is given. Possible mechanisms of a shift of the ignition threshold by nonequilibrium plasma are analyzed. Experimental examples of the discharge ignition of H2:O2 mixture diluted with Ar under the kinetic explosive limit (II) are demonstrated. Examples of low–temperature oxidation and high–temperature ignition of different gas mixtures containing hydrocarbons are listed and analyzed. For low–temperature oxidation, we have investigated experimentally kinetics of alkanes (from methane to decane) with oxygen or air at different equivalence ratios, kinetics of C2H5OH, CH3COCH3 ,C 2H2 in their mixtures with oxygen and CO:O2 mixtures with small controlled additives of water vapor. For high–temperature ignition, a set of stoichiometric mixtures CxH2x+2 :O 2 (20%) diluted by Ar (80%) for hydrocarbons from CH4 to C4H10 and stoichiometric mixtures CxH2x+2 :O 2 (10%) diluted by Ar (90%) for hydrocarbons from CH4 to C5H12 have been analyzed experimentally. Typical energy values are given for all the experiments. Kinetic scheme for low–temperature oxidation is discussed. For a case of a high–temperature ignition, the shift of a temperature threshold in comparison with the autoignition is represented. The kinetic approach to the problem of artificial ignition is discussed on the basis of experiments where the autoignition, ignition by pulsed volume discharge and laser flash– photolysis at 193 nm. Values of the ignition delay in gas mixture O2:H2:N2O:Ar=3:30:10:50 are represented. The kinetic scheme has been proposed to describe autoignition and ignition by a flash–photolysis. The results of a numerical modelling are given.