*Preetom Borah1, T.P. Weihs1, M.J. Johnson2, D.R. Boris3, S.G. Walton3
1Johns Hopkins University, Baltimore, MD; 2Syntek Technologies, Fairfax, VA; 3U.S. Naval Research Laboratory, Washington, DC
This study aims to develop and optimize a plasma system to ignite metal powders as they are propelled into a cylindrical combustion chamber via a gas burst. The chamber will be used to characterize the combustion behavior of the powders, as well as the ability of the combustion products to neutralize chemical-agent simulants, such as Diisopropyl methyl-phosphonate (DIMP) and Triethyl-phosphate (TEP). In order to perform these tests, a plasma-based ignition system must be developed that can operate at or near atmospheric pressures and transfer sufficient energy to the powders to initiate their reaction within a short residence time. Current methods for the ignition of metal fuels for chamber-based studies include laser ablation and explosive launch. Laser ignition of many powders is difficult and explosive detonation requires extensive regulation and oversight, along with greatly increased pressure demands for the combustion chamber. Neither approaches are feasible in this work. While few studies have examined the use of plasmas to ignite metal powders, developing such a source will enable the simultaneous ignition of multiple powders suspended in a flowing gas with minimal pressure rises within the test chamber. Dielectric barrier discharges are robust sources for atmospheric pressure applications and will be developed in both cylindrical and parallel plate geometries. As a first step, plasmas will be generated in helium/air mixtures to determine requisite operating conditions needed to ignite stationary powders. The preferred plasma source will then be transitioned to a combustion chamber and modified to ignite flowing powders as they enter the chamber. Ignition thresholds as a function of applied power will be identified for various flow rates in both air and helium.