Serge Larigaldie

Plasma assisted combustion: effect of a coaxial DBD on a methane diffusion flame

An experimental study of plasma assisted combustion has been initiated at ONERA in order to evaluate the potential application to supersonic combustion with various fuels. For this first step, we choose an easier and more versatile configuration where a coaxial dielectric barrier discharge is applied to a methane diffusion flame. The effects of this discharge on the flame structure and especially the reduction in its detachment height have been investigated. The role of the large scale motion of the flame on its anchoring by the plasma has then been revealed, along with the presence of a plasma channel linking the flame to the burner. Electrical and optical investigations demonstrated the pulsed nature of the light emission of the plasma and the spectroscopic study of OH, CH and exhibits a 10 mm overlap between the plasma and the flame.

Experimental Study of a Methane Diffusion Flame Under Dielectric Barrier Discharge Assistance

Plasma assistance is a promising method for improving combustion, especially for NOx reduction by burning hydrocarbons at lower fuel-air ratio or for flame stabilization under unfavorable conditions (supersonic combustion or small volume combustion where the chemical time is close to the fuel residence time). Thus, we conceived a combustion test bench where we could study the effect of a coaxial dielectric barrier discharge on a lifted nonpremixed methane flame. In this paper, we were especially interested in the effect of the discharge on the detachment height of the flame up to a blowout. There, we could achieve the anchoring of the flame (detachment height=5-10 mm as opposed to 50-60 mm without plasma) on a plasma channel leaving the burner exit. Electrical investigations demonstrated that only 1 W applied to the discharge at the nozzle of the burner was necessary for this anchoring. Coupling the electrical and optical measurements revealed the pulsed nature of the light emission of the plasma, while a spectroscopic study of OH, CH, and N2 * exhibits a 10-mm overlap between the plasma and the flame. Finally, the by-products of the discharge in methane were analyzed by gas chromatography

Study of the breakdown phase in a pseudospark switch. I. Basis experiments and crude model

A transparent and compact pseudospark prototype was built to analyze the physical processes of pseudospark breakdown. It allows accurate measurements of the current and gap voltage during the collapse of the switch impedance. This led to a surprising result-the pseudospark impedance follows the same time-evolution law as the high pressure spark-gaps. However, electronic collision processes are of a different nature. A crude theoretical model based on plasma relations is proposed to solve this contradiction. This model shows how the current is controlled by the azimuthal magnetic field it induces. However, discrepancies still remain. A more sophisticated distribution of the field and current lines is assumed and investigated in a companion paper. >