AbstractNon-thermal atmospheric pressure plasma jets are a promising new field of research which are beneficial to many associated technologies, such as material treatment and biomedical applications. The interest in this type of plasma lies in their ability to deliver significant densities of reactive species remote from the discharge area and the low gas temperature. In this study the electrically driven plasma source is a dielectric barrier discharge of a structure similar to that designed by Teschke et al in 2005, which has been studied recently by many research groups in different configurations. Here two helium APR Jets were developed to study the plasma dynamics using ICCD imaging and optical emission spectroscopy. They consist of a cylindrical quartz tube with two electrodes, the powered electrode driven by a pulsed or sinusoidal high voltage source in the kHz range. An intense streamer discharge is created inside the tube, and a relatively long plasma plume propagates into the surrounding air in the helium gas channel. It is well established that the plume is propagating ionization fronts consisting of “plasma bullets”.
The past few years have seen tremendous progress in the optical, electrical and chemical studies of such systems, while there is still a lack of experimental data on the plasma parameters including electron densities and electron temperatures. In this work we present the use of Thomson scattering to measure the spatially resolved properties of the electrons in a kHz-driven helium APPJet. Since the jet propagates into air, a key aspect of this approach is to distinguish the three types of laser scattering; Rayleigh, Thomson and Raman. The measurements were performed by using by a Nd:YAG laser operating at 532nm and 10Hz.
The investigation focused on revealing a “ring-like” radial distribution of both the electron density and temperature in the first five millimetres of the plasma plume. In the radial direction the measured electron densities and the electron temperatures are both found to increase towards the outer edge of the plume. Both these observations are consistent with our radial light emission measurements. It was found that along the central axis and in the direction away from the exit of the tube, the electron density decreases from 5x1013 cm'3 at 1.25 mm from the exit of the quartz tube to 3x1013 cm'3 at 4.5 mm, while at the same positions the electron temperature changes from 0.17 eV to 0.13 eV.
With the advent of increasing interest in catalyst technologies as a rapidly growing research area, the use of a atmospheric pressure helium nonthermal plasma jet to assist a SCR deNOx reaction over a silver-based catalyst at a low temperature using simulated diesel fuels was explored. A coupled IR-plasma reactor was developed allowing direct interaction of the plasma with the catalyst bed whilst accommodating a FTIR spectrometer and NOx analyzer. Two KHz-driven quartz tube jet configuration were developed to operate at low gas flows, one with a circular copper electrode but with a grounded electrode in the reaction area, and the other with a central powered electrode with the vessel as a ground. The catalyst was prepared by the impregnation of Y-AI2O3 with a silver nitrate solution. NOx and hydrocarbon conversions were studied with toluene and octane on an Ag-catalyst at two different temperatures. The results of the diagnostic have led to a better advantage of plasma- catalyst research.
|Date of Award||Jan 2014|