Sergey Stepanyan

CentraleSupélec | ECP · Laboratory of Energetics and Combustion (E.M2.C, CNRS-UPR 288)

Non-equilibrium plasmas are known to improve ignition and extend flammability limits. In this study, NRP discharges of 2 mJ are applied at 20 kHz in the recirculation zone of a premixed methane-air bluff-body burner with a lean equivalence ratio of 0.8. The operating point is close to the lean blow out limit and NRP discharges efficiently enhance t...

The formation and decay of the thermal spark generated by a single nanosecond high-voltage pulse between pin electrodes are characterized in this study. The influence of air pressure in the range 50–1000 mbar is investigated at 300 K. By performing short-gate imaging and optical emission spectroscopy (OES), we find that the thermal sparks exhibit a...

In this paper, the mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied by numerical simulations. The plasma kinetics is solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The originality of the model is to consider not only the excited electronic states of...

The mechanisms controlling the hydrodynamic effects induced by nanosecond pulsed discharges applied between two pin electrodes in air at atmospheric conditions are investigated experimentally and numerically. A cylindrical plasma kernel is formed between the electrodes during the discharge. After the discharge, schlieren images show that the cylind...

This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ mm⁻¹) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm³) surrounding the initial plasma channel. This process infl...

The cycle to cycle combustion variability which is observed in spark-ignition engines is often caused by fluctuations of the early flame development. LES can be exploited for a better understanding and mastering of their origins. For that purpose appropriate models taking into account energy deposition, mixture ignition and transition to propagatio...

This work aims to provide a better understanding of the cumulative effect of successive nanosecond repet- itively pulsed (NRP) discharges on the ignition process. Fast chemiluminescence imaging of both the postdischarge and the following flame was used to analyze the ignition of a lean propane/air mixture ( f = 0.7) by a train of 82 NRP discharges...

This work presents experimental observations of strong expanding thermal jets following the application of nanosecond spark discharges. These jets propagate in a toroidal shape perpendicular to the interelectrode axis, with high velocities of up to 30 m s⁻¹ and over distances of the order of a cm. Their propagation length is much larger than the th...

Non-equilibrium plasmas have strong potential to enhance performance of combustion systems due to generation of large numbers of reactive species. Kinetic and dynamic fundamental studies using advanced spectroscopic diagnostics are presented.

Streamer-to-filament transition is a general feature of high pressure high voltage (HV) nanosecond surface dielectric barrier discharges. The transition was studied experimentally using time- and space-resolved optical emission in UV and visible parts of spectra. The discharge was initiated by HV pulses 20 ns in duration and 2 ns rise time, positiv...

The effects of pulse repetition frequency (PRF) and energy deposition was investigated using nanosecond repetitively pulsed discharges in a constant volume combustion chamber. Quiescent lean propane-air mixtures (equivalence ratio of 0.7) at 0.2 MPa were ignited using fixed total energy deposition and number of pulses across the range of PRF from 2...

This paper presents 3-D DNS and experimental schlieren results used to study a non-equilibrium plasma discharge in a lean methane-air mixture. A detailed combustion mechanism and a plasma model, developed in our previous work, are used in the 3-D computations in order to study the impact of gas flow recirculation on the temporal evolution of specie...

Nanosecond surface dielectric barrier discharge (nSDBD) is an efficient tool for a multi-point plasma-assisted ignition of combustible mixtures at elevated pressures. The discharge develops as a set of synchronously propagated from the high-voltage electrode charged channels (streamers), with a typical density up to a few streamers per millimetre o...

A novel experimental scheme to study the ignition of combustible mixtures at high pressures under the action of a high-voltage nanosecond discharge has been developed. The experiments were performed in the combustion chamber of a Rapid Compression Machine (RCM) with a specially designed system of electrodes. A nanosecond surface dielectric barrier...

The ratio of emission intensities of the second positive N2(C³Πu, v′ = 0) → N2(B³Πg, v = 0), 337.1 nm and first negative N2+ > (B2Σg+,v′=0) > → N2+ > (X2Σg+,v=0) >, 391.4 nm systems of nitrogen have been measured in a nanosecond surface dielectric barrier discharge (SDBD). The measurements were carried out in synthetic air for a pressure range 1–3...

The development of a nanosecond surface dielectric barrier discharge in air at pressures 1?6 bar is studied. At atmospheric pressure, the discharge develops as a set of streamers starting synchronously from the high-voltage electrode and propagating along the dielectric layer. Streamers cover the dielectric surface creating a 'quasi-uniform' plasma...

Surface nanosecond dielectric barrier discharge has been studied in air and at pressures ranging from 1 to 5 bar, with a coaxial geometry of the electrodes for positive and negative polarities of the high-voltage pulses. Pulses of a 24-55 kV amplitude on the electrode, positive or negative polarity, 20 ns duration, 0.5 ns rise time and 10 Hz repeti...

The integral energy balance is analysed for the fast-heated plasmas in tokamaks and stellarators. This is an approach to resolving the so-called 'missing power' problem (Andreev et al 2004 Plasma Phys. Control. Fusion 46 319). The analysis is based on ideal MHD and includes plasma interaction with the magnetic field, which is traditionally disregar...