Transient Plasma Induced Production of OH and its Effects on Ignition in Atmospheric CH4-AIR Quiescent Mixtures (Postprint)

Transient plasma from a 60 kV, 70 ns pulse induced OH production in air and CH4/air quiescent mixtures inside a cylindrical chamber is analyzed. The resulting OH from the plasma discharge, ignition, and subsequent combustion is analyzed using planar laser induced fluorescence. A high-framing-rate camera was also used to image ignition and flame propagation in the chamber, providing spatial and temporal resolution over the entire combustion event. Results indicate OH structures produced during the discharge in humid, ambient air are less branched, thicker, and last longer when compared to structures in CH4/dry-air. Transient plasma successfully ignited the CH4/air mixture, populating the discharge volume with radicals. Mean OH number densities produced by the discharge were found to decay within 100 s of the plasma. Ignition under these conditions was found to occur approximately 1 ms after the discharge along the anode, creating multiple ignition kernels whose proximity to the anode is consistent with the region of highest field and, thus, maximum radical density. Published in the Proceedings of the AIAA Aerospace Sciences Meeting and Exhibit, 46th, held in Reno, NV on 7-10 Jan 2008. Sponsored in part by ONR.