Ablation Study in a Capillary Sustained Discharge

Abstract

Abstract-Electrothermal-chemical (ETC) ignitionsystems have been demonstrated in gun systems to provide desirable characteristics including reproducible shorter ignition delays. The optimum combination of capillary tube and fuse wire properties has not been identified yet. We present a combined theoretical and experimental study of the capillary discharge with an aim to develop a capillary plasma source with efficient energy conversion. The major emphasis in the present capillary discharge model is the ablation phenomenon. Consideration is given to different characteristic subregions near the ablated surface: namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer. A kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa in the case of a 0.6 kJ discharge. In parallel, a parametric experimental study of the capillary ablation process is conducted. The ablation rates are measured for capillary tubes made of polyethylene and Teflon. Both experimental measurements and simulations indicate that the ablated mass increases with the peak discharge current and that a smaller diameter capillary yields a larger ablated mass. It is found that model predictions agree well with experimental measurements. Report Documentation PageForm Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Modeling of Plasma-Induced Ignition and Combustion

“…To account for this the model includes a parameter ν, which is the fraction of the backflux that deposits on the surface, with ν = 1 being the most deposition, and ν = 0 neglecting deposition entirely. Previous simulations and experiments found good agreement with ν = 0.6 [4].…”

“…To date, models have been developed that address the capillary plasma source [3], [4], the plasma-air chemistry of the expanding capillary plasma jet into the combustion chamber [5], the plasmapropellant interaction via a coupled ablation and thermal model [6], and the convective heat flux to the propellant bed by means of a collisional plasma sheath model [7]. This effort represents the first attempt to create a model of the ETC phenomena, from the initial capillary firing through the plasma-propellant interaction leading up to propellant ignition.…”

“…Typically, the amount of material deposited back onto the ablating surface is calculated using a fitting parameter [4]. The ability to use a fitting parameter does not present itself [6], [15].…”

Study on the characteristics of a two gap capillary discharge

“…Under this condition, more polyethylene is ablated and better performance of the ejection is acquired. 15 During the main discharge, the major loop inductance exists in the saturated magnetic switch. However, the value of the remaining inductance of the saturated magnetic switch is proportional to the square of the winding amount.…”

Response of TEGDN Propellants to Plasma Ignition with the Same Magnitude of Ignition Energy as Conventional Igniters in an Interrupted Burning Simulator

“…Significant efforts have beena pplied to model the ablation-controlled discharge that is commonly used as ap lasma source for ETC [19].H owever,t here is little research on the ablation of propellants during the plasma ignition. Am ore detailed model should be developed to describe the ablationp rocess and rate of propellant exposed in the plasma flow.…”