Andre Agneray

Tracking an individual streamer branch among others in a pulsed induced discharge

The electro-dynamical properties and the mutual influence of several simultaneously propagating streamers are investigated in a point-to-plane configuration in air at atmospheric pressure under impulse voltage. When a fast and short high voltage pulse is applied to the point, a bunch of streamer branches develops into the interval. Since no previous ionized path has been traced before in the gap, streamers spread in the whole gap, branching while propagating. This behaviour is quite different from streamers under DC voltage conditions, which successively extend on the point–plane axis. The aim of this work is an attempt to distinguish the properties of an individual streamer simultaneously propagating with the others, by means of fast techniques based on simultaneous streak and still photographs and space-time decoupled currents measurements. Especially, their mean velocity can be estimated. In most cases, an axial streamer is observed, propagating faster than the others. This result can be interpreted in terms of the electric field space distribution by means of a three-dimensional electrostatic solver. This analysis shows that a mutual electro-dynamical influence is exerted from one streamer on another.

Pressure effects on the development of an electric discharge in non-uniform fields

Discharges at several atmospheres are widely used for triggering combustion in cars. However, their properties are not well understood since the size and duration of the discharges become very small at high pressures, which makes the experimental approach more difficult. One possibility should be to infer the discharge properties at high pressures from those at atmospheric pressure, provided that the so-called discharge similarity rules work correctly. Thus, an attempt to check this validity is provided in this paper. Then, after establishing the exact conditions which preserve pressure similarity rules in non-uniform gaps, an example is given of two discharges under similar conditions. A departure from similarity is quite clearly observed. At several atmospheres, the streamer induced plasma channel, instead of developing the usual streamer filaments seen at atmospheric pressure, demonstrates a leader structure, i.e. the formation of a hot channel before the whole gap is bridged. Finally, reasons are given explaining that such a fast rise in temperature with pressure is indeed to be expected.

A physical model to explain electrostatic charging in an automotive environment; correlation with experiments

Electrostatic shock is a very common feature in an automotive environment. Such a phenomenon may be detrimental for the embarked electronic devices and/or the passengers. The work presented in the following deals with this latter aspect and consists of the research of physical solutions able to avoid the human body voltage rise up and its associated discharge. This paper is focused on the determination of the cause of its appearance and on the development of an appropriate model able to predict the charging values versus the different characteristics of the materials used inside the car. The paper presents a model of the occupant charging during the exit from a car and its correlation with the measured values, in a real situation. Getting a better understanding of the individuals static build up could allow us to find a reliable solution to avoid both static charge accumulation (and electrostatic voltage increase) on the human body and shock risk.

Plasma-to-flame transition at the AC driven filamentary discharge ignition

Non-equilibrium plasmas make a new effective way for plasma-assisted ignition. The mechanisms of transition toward a flame kernel are investigated for the case of ignition initiated by the ac-driven discharge thanks to fast optical techniques. The study is done under 1-10 bars pressure range for air-propane mixtures. At atmospheric pressure, filaments of the discharge present two regions with the hotter one near the electrode. Time-resolved imaging coupled with emission spectroscopy reveals that the inflammation takes place all along the hottest part of the filamentary structure. At higher pressure, the region of inflammation extends over the whole discharge because the more important heating of the gas inside. Thus, the plasma-to-flame transition indicates the energy and so the gas temperature distribution along the filaments. By scanning the spatial expansion of the kernel flame, it can be correlated with the chemical and thermal properties of the discharge. It results that thermal effect presents the governing mechanism of the ignition enhanced by the presences of reactive species created by the discharge. These species could play an important role during the spatial expansion of the kernel flame.

Micro-Injection System Using Ultrasonic Vibrations for Drop on Demand Ejection

This micro-injection system consists of a (50 mm long, 5mm wide, 570 μm thick) silicon beam comprising a micro-structure with a glass cover plate on one side and a piezoelectric plate bonded on the other side. The micro-structure is composed of a feeder canal transforming right across in several parallel channels which end individually at the extremity of the beam thus forming a multi-orifice line.