Electrical Discharge in Deeply Subcritical Field of Microwave Beam in a High-Speed Air Stream and in Propane-Air Mixture

Abstract

Results are present of an investigation into the characteristics of an electric gas discharge generated in the deeply subcritical field of a quasi-optical microwave (MW) beam. The electrical gas breakdown is initiated by a tubular electromagnetic vibrator. The discharge is realized in a submerged high-speed stream of either air or a propane-air mixture. The stream flows from an internal hole in the aft end of the vibrator, which has sharpened points to serve as initiation sites. A short quartz tube covers the aft end of the vibrator to stabilize the stream. Experiments have been carried out for flow velocities in the range of several hundred meters per second. Photographs of the discharge area have been collected and measurements of the stagnation temperature in the wake of the discharge have been obtained. In this experimental configuration, the experiments show that a MW discharge is realized in the aft area of the vibrator attached to the sharpened ends of the vibrator. This discharge is shown to ignite and stabilize the combustion of a lean propane-air mixture. Complete propane combustion occurs for stream velocities smaller than some threshold value. At larger velocities in the experiments, we have observed effects of thermal choking and throttling of the stream.