Svetlana Starikovskaia

Plasma assisted ignition and combustion

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

The 2012 Plasma Roadmap

Low-temperature plasma physics and technology are diverse and interdisciplinary fields. The plasma parameters can span many orders of magnitude and applications are found in quite different areas of daily life and industrial production. As a consequence, the trends in research, science and technology are difficult to follow and it is not easy to identify the major challenges of the field and their many sub-fields. Even for experts the road to the future is sometimes lost in the mist. Journal of Physics D: Applied Physics is addressing this need for clarity and thus providing guidance to the field by this special Review article, The 2012 Plasma Roadmap.

Nanosecond gas discharge ignition of H2− and CH4− containing mixtures

Abstract An analysis of the ignition of H2− and CH4− containing mixtures at high temperatures under the action of a nanosecond high-voltage discharge has been performed both numerically and experimentally for a wide range of parameters. A comparison of the equilibrium and nonequilibrium excitation was performed. The preliminary numerical analysis of ignition efficiency helped to plan experimental investigations of the initiation of the ignition by nanosecond discharge at high temperatures. A novel experimental scheme for the investigation of ignition delay at high temperatures under the action of a high-voltage nanosecond discharge has been developed. Electrical parameters on a nanosecond time scale and the ignition processes on a microsecond time scale were investigated. Ignition delays for different mixtures, gas pressures and temperatures were obtained experimentally. The dependence of the ignition delay upon temperature, high voltage amplitude, and the energy release into the discharge was determined experimentally for H2-O2, H2-air and CH4-air mixtures diluted with argon or helium. Obtained data were compared with the results of numerical calculations.

Pulsed breakdown at high overvoltage: development, propagation and energy branching

This paper presents a review of investigations of detailed spatial and temporal structures of high-voltage pulsed nanosecond discharges in the form of fast ionization waves. The most distinctive features of this type of discharge are a high propagation velocity (109-1010 cm s-1), good reproducibility of the discharge parameters at a moderate (tens of hertz) repetition rate and spatial homogeneity over a large gas volume. The discharge was initiated by voltage pulses of negative polarity with an amplitude of 10-15 kV, a duration at half maximum of 25 ns and a rise time of the front of 3-5 ns. The behaviour of the electric field and electron and excited-state concentrations were analysed on the basis of experimental data within the frame of the unified kinetic approach. It was found that the longitudinal component of the electric field has a sharp (2-3 ns) maximum and that the electrons and excited particles are produced preferentially behind the front in relatively weak electric fields. The peak field value was close to or even stronger than the threshold for the generation of runaway electrons in a steady-state uniform electric field. An analysis based on absolute time-resolved measurements of the spectrum of two molecular bands showed that, behind the breakdown front, the EEDF should be substantially overpopulated with high-energy electrons. Energy branching in the discharge was analysed. Possibilities of application of the fast ionization wave as a source of a uniform pulsed plasma were suggested and justified.

Collisional deactivation of N2(C , v=0, 1, 2, 3) states by N2, O2, H2 and H2O molecules

Abstract The radiative lifetimes of four low vibration levels of the N 2 (C 3 Π u ) state are measured and rate constants of collisional deactivation of these states by N 2 , O 2 , H 2 and H 2 O molecules are determined with the help of emission spectroscopy. To excite levels under study a high-voltage nanosecond periodic discharge is used.

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.

Fast gas heating in nitrogen?oxygen discharge plasma: II. Energy exchange in the afterglow of a volume nanosecond discharge at moderate pressures

The process of fast gas heating in air in the near afterglow of a pulsed nanosecond spatially uniform discharge has been investigated experimentally and numerically at moderate (3?9?mbar) pressures and high (200?400?Td) reduced electric fields. The temporal behaviour of discharge current, deposited energy, electric field and temperature was measured. The role of processes with participation of excited and charged species was analysed. It was shown that under the considered conditions the main energy release takes place in reactions of nitrogen and oxygen dissociation by electron impact and quenching of electronically excited nitrogen molecules, such as N2( , B?3?g, C?3?u, ) by oxygen and quenching of excited O(1D) atoms by N2. It was shown that about 24% of the discharge energy goes to fast gas heating during the first tens of microseconds after the discharge.

Experimental and modeling analysis of fast ionization wave discharge propagation in a rectangular geometry

Fast ionization wave (FIW), nanosecond pulse discharge propagation in nitrogen and helium in a rectangular geometry channel/waveguide is studied experimentally using calibrated capacitive probe measurements. The repetitive nanosecond pulse discharge in the channel was generated using a custom designed pulsed plasma generator (peak voltage 10–40 kV, pulse duration 30–100 ns, and voltage rise time ∼1 kV/ns), generating a sequence of alternating polarity high-voltage pulses at a pulse repetition rate of 20 Hz. Both negative polarity and positive polarity ionization waves have been studied. Ionization wave speed, as well as time-resolved potential distributions and axial electric field distributions in the propagating discharge are inferred from the capacitive probe data. ICCD images show that at the present conditions the FIW discharge in helium is diffuse and volume-filling, while in nitrogen the discharge propagates along the walls of the channel. FIW discharge propagation has been analyzed numerically usi...

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)

Measurements of rate constants of the N2(C3Πu,v′=0) and N2+(B2Σ+u,v′=0) deactivation by N2, O2, H2, CO and H2O molecules in afterglow of the nanosecond discharge

Abstract The lifetimes of N 2 ( C 3 Π u , v′=0) and N 2 + ( B 2 Σ + u , v′=0) states and rates of their quenching by molecules of N2, O2, H2, CO and H2O have been determined by emission spectroscopy. To excite the states involved a nanosecond pulse repetitive high-voltage discharge was used.