Large-volume excitation of air, argon, nitrogen and combustible mixtures by thermal jets produced by nanosecond spark discharges

International audienceThis 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 and over distances of centimeter scale. Their propagation length is much larger than the thermal expansion region produced by the conventional millisecond sparks used in car engine ignition, thus greatly improving the volumetric excitation of gas mixtures. The shape and velocity of the jets is found to be fairly insensitive to the shape of the electrodes. In addition, their spatial extent is found to increase with the number of nanosecond sparks and with the discharge voltage, and to decrease slightly with the pressure between 1 and 7 atm at constant applied voltage. Finally, this thermal jet phenomenon is observed in experiments conducted with many types of gas mixtures, including air, nitrogen, argon, and combustible CH 4 /air mixtures. This makes Nanosecond Repetitively Pulsed (NRP) discharges particularly attractive for aerodynamic flow control or plasma-assisted combustion because of their ability to excite very large volumes of gas